Noise and ultrasound protection. Noise control techniques

Date: 05.03.2020

Why are the cogwheels still rattling? The obvious answer is “because the curves”. Obvious, but not sufficient. A gear wheel is a rather complex part and its geometry is described by many parameters, and they all affect the transmission noise in different ways. Depending on the circumstances, in each specific case, some errors can affect the noise more, others less.

The basic concept in this question is - kinematic transmission error or a cogwheel. According to GOST 1643-81 (Appendix 1, clause 1).

The kinematic error of the transmission F i is the difference between the actual and nominal (calculated) angle of rotation of the driven gear wheel of the transmission.

Suppose the transmission consists of a gear z 1 = 20 and a wheel z 2 = 40, i.e. gear ratio u = 2. If the gears are made with perfect accuracy, then when the gear is turned by one angular step 360 ° / 20 = 18 °, the wheel will turn by an angle of 18 ° / 2 = 9 °. If the gear is rotated two angular steps of 36 °, the wheel will turn 18 °, and so on. These are the nominal (calculated) angles of rotation and for ideal gears they are related by the gear ratio. At any angle of rotation of the gear, the wheel will turn by an angle 2 times smaller.

angle of rotation of the wheel = angle of rotation of the gear / u

But in reality, nothing is perfect. All details have some kind of inaccuracies. Therefore, in fact, the driven wheel will turn at an angle different from the nominal (calculated) and the error can be expressed as follows:

Fi= angle of rotation of the wheel - angle of rotation of the gear / u

Those. in reality, the gear ratio is not constant, which means that the rotational speed of the driven wheel will fluctuate. And the spectrum of these vibrations can contain frequencies with a sufficiently high amplitude. These vibrations can cause noise.

Manufacturing of extremely precise gears. Turetskiy I.Yu., Lyubimkov L.N., Chernov B.V.

Why is there a kinematic error?

The reasons can be very different:

engagement geometry: interference or suboptimal overlap. These errors can occur both at the stage of gear design and during manufacture (for example, the use of an unsuitable tool).
Errors in the manufacture of wheels that distort the tooth profile (involute) and the uniformity of the teeth (pitch errors)
assembly errors and related parts (housing, shafts, bearings)
thermal deformations and deformations of the tooth under load distorting the tooth profile

vertical axis - kinematic error, taking into account the stiffness of the tooth at different loads.

horizontal axis - the angle of rotation of the wheel

The noise level measured by acoustic methods will depend on the entire structure as a whole - not only on the gear wheels, but also on the bearings, housing, gearbox housing mountings, the nature of the load, etc.

The physical essence of the phenomenon can be schematically expressed as follows:

geometric errors of wheels

kinematic transmission error

mass, moment of inertia, stiffness and damping

Vibrations in engagement

Forces acting on bearings

Mass, stiffness and damping of body parts

Body vibration

Fastening the gearbox housing

Oscillation of the whole machine as a whole

There is currently no single generally accepted calculation method that would take into account the effect of all errors on noise. The calculations are based either on empirical dependencies or on some models with assumptions.

Why does the spur gear make noise, but the helical gear does not make noise?

The principle is often found: "If the gear is noisy, then it needs to be replaced with a helical gear"... This is primarily due to the fact that overlap angle in helical gearing, more than in spur gear.

Overlap angle- the angle of rotation of the gear wheel from the position of the teeth entering the engagement until it leaves the engagement.

The overlap is estimated by the overlap ratio - the ratio of the overlap angle to the wheel pitch.

If the overlap ratio = 1, then each tooth disengages exactly the moment the next tooth engages.
If the overlap ratio< 1, то между выходом из зацепления одного зуба и входом в зацепления следующего зуба контакт между колёсам разрывается.
If the overlap ratio is> 1, then at each moment of time there are two or more teeth in mesh. The more teeth are simultaneously in engagement, the less stress in the engagement and less deformation of the teeth and the effect of profile errors is smoothed and averaged.

Replacing spur gears with helical gears is not a panacea. In real life, different options need to be evaluated. Taken together, reducing noise by improving the accuracy of spur gears or some other measure may be more effective than simply replacing with helical gears.

How to measure kinematic error?

As described in the beginning, measuring the kinematic error is a rather expensive business. This requires the ability to install angle sensors of appropriate accuracy on the gear and wheel. Or you need a special device and a reference gear. These methods are good for mass or high volume production. At the same time, the measurement of the kinematic error itself gives little information about its source. The kinematic error is a complex indicator and is made up of different errors arising from different operations.

With small series and one-off production, it is often advisable to carry out control according to several individual parameters, which together make it possible to assess the kinematic accuracy:

Radial runout F r
Oscillation of the length of the common normal F vw
step error fpt and accumulated step error F p
profile error f f

This article describes a simulation technology that aims to eliminate noise generated by power train gears. This is a rather unpleasant high-frequency dominated noise resulting from rotational deviations (transmission errors) due to tooth shape and manufacturing defects. To reduce transmission error, it is necessary to determine the appropriate tooth profile, taking into account the influence of several factors.

This gearbox simulation technology has been used in product design since 2012. The example shows the reduction of transmission error and gear noise by optimizing the tooth profile using the presented simulation technology.

1. Introduction

As a component manufacturer within the Yanmar group of companies, Kanzaki Kokyukoki Mfg. Co., Ltd. designs, manufactures and markets hydraulic equipment and various transmissions. The company has extensive experience and proprietary technologies in a wide variety of areas of design and manufacture, especially gears, which are the main components of kinematic systems. In addition, in recent years, the trend towards increased vehicle speed and comfort has made it imperative to reduce gear noise, which is very difficult to achieve with traditional technology. This article describes a simulation technology for gear noise reduction currently being developed by Kanzaki Kokyukoki Mfg.

2. Types of gear noise

Gear noise in transmissions is usually divided into 2 types: screeching and crackling (see table 1). Whistling is a subtle, high-frequency noise mainly caused by small errors in the profile of the gear teeth and in their rigidity. A crackling sound is the sound of contact between the flanks of the gear teeth, the main sources of which are fluctuations in the load acting on the gears and the clearances between the flanks of the teeth (side clearances). Kanzaki Kokyukoki Mfg. squealing is most often the main problem, so the company focuses on determining the appropriate tooth profile during the design, construction, and quality control of the gears produced.

3. The mechanism of screeching

Squealing is caused by vibration generated by small rotational deviations due to inaccuracies in the tooth profile or manufacturing defects, transmitted through the gear shaft bearings to the housing, resulting in vibration of the housing surface (see Fig. 1).

These deviations of rotation occur due to errors in the angle of rotation of the teeth when they mesh, which is called the transmission error.

The causes of transmission error, in turn, can be subdivided into geometric factors and tooth stiffness factors. If geometrical factors are present (see Fig. 2), deviation from ideal involute engagement occurs due to installation error or shaft displacement, which leads to a lag or lead in the angle of rotation of the driven gear. In addition, deviations in the angle of rotation occur due to the unevenness of the flank surfaces of the teeth.

In the presence of factors related to the stiffness of the teeth (see Fig. 3), the stiffness of the engagement changes depending on how many teeth are in contact at a given time, resulting in deviations in the angle of rotation of the driven gear.

In other words, geometrical factors and tooth stiffness factors work together to influence transmission error and thereby create an exciting force. Therefore, when designing a gear with a low noise level, these factors must be considered in order to select a suitable tooth profile.

4. How to reduce transmission error

As stated above, several factors need to be considered in order to reduce the transmission error in the gears.
In fig. 4 shows the relationship between torque and transmission error for a helical gear with an ideal involute profile (unmodified) and another gear with a specially modified tooth profile. Here, to change the profile of the teeth, a deviation from the ideal involute profile is specially introduced, as shown in Fig. 4 (right). An unchanged gear with a lower profile error has optimal performance against fluctuations in transmission error at a low load torque, while a modified gear works better when the load torque is above a certain value. This shows how you can minimize the fluctuation in transmission error by changing the tooth profile to match the load on the gear.

To predict the impact of various phenomena on the gear in the kinematic system and take it into account at the design stage, Kanzaki Kokyukoki Mfg. has developed a modeling technology that has been used by it in product design since 2012 (see Fig. 5). By using data on the profile of the teeth for different types of gears as input data, the technology can evaluate parameters such as load capacity and transmission error under real operating conditions by analyzing the deformation of the gear shaft and bearings.

5. An example of the application of technology in product design

The example below shows the reduction in transmission error in a utility vehicle gearbox. In this case, the goal is to reduce the transmission error by analyzing the possible change in the three-dimensional profile of the bevel gear teeth at the initial design stage, taking into account the deviations of the tooth profile as a result of deformation of the shaft, bearings and other components, as shown in Fig. 6.

To confirm the improved performance of the improved tooth profile, the tooth profiles, transmission error and meshing noise of the gear in production and the improved version were measured.
The results for the transmission error are shown in Fig. 7. The measurements are shown on the left, and the results of the analysis of these measurements with tracking the order of engagement are shown on the right. The results of the meshing order comparison show that the improved gear has less deviation in transmission error.
The meshing noise measurements shown in Fig. 8 show a significant reduction in noise in the improved gear at second and third order gearing frequencies.

6. Conclusion

This article describes the simulation technology developed by Kanzaki Kokyukoki Mfg, a group of companies. to reduce gear noise. This technology is used in new designs where it helps predict performance during the design phase. In the future, this simulation technology is expected to continue to help develop better solutions for customers by reducing size and increasing power output and product reliability.

In a number of industries, mechanical noise dominates due to vibrations of machine parts and their mutual movement. It is caused by the force effects of unbalanced rotating masses, impacts in the joints of parts, knocks in gaps, movement of materials in pipelines or in trays, vibrations of machine parts caused by forces of a non-mechanical nature, etc.

These vibrations cause both airborne and structure-borne noise. Since the excitation of mechanical noise is usually of a shock nature, and the structures and components emitting it are distributed systems with numerous resonant frequencies, the mechanical noise spectrum occupies a wide frequency range. It presents the components at the indicated resonant frequencies and at the frequency of the shocks and their harmonics.

The presence of high-frequency components in mechanical noise leads to the fact that it is usually very subjectively unpleasant. Vibrations of moving parts are transmitted to the body (frame, casing), which changes the spectrum of vibrations and radiated noise. The process of occurrence of mechanical noise is very complex, since the determining factors here are, in addition to the shape, size, speed, type of construction, mechanical properties of the material, the method of excitation of vibrations, also the state of the surfaces of interacting bodies, in particular rubbing surfaces, and their lubrication. Usually it is not possible to determine the emitted sound field by calculation. The application of the theory of dimensions to the calculation of mechanical noise does not give an unambiguous assessment of it.

Gear transmission

Gear noise is caused by vibrations of wheels and their associated structures. The reasons for these vibrations are mutual collision of the teeth when entering the engagement, variable deformation of the teeth caused by the inconstancy of the forces applied to them, kinematic errors of gear wheels, variable friction forces.

The noise spectrum occupies a wide frequency band, it is especially significant in the 2000-5000 Hz range. Against the background of the continuous spectrum, there are discrete components, the main of which are the frequencies caused by mutual collision of the teeth, the action of errors in the meshing and their harmonics. The components of vibration and noise from deformation of the teeth under load have a discrete nature with a fundamental frequency equal to the frequency of the teeth reconnection. The frequency of action of the accumulated oshnbcn of the gear wheel is a multiple of the rotation frequency. However, there are cases when the accumulated error of the circumferential pitch does not coincide with the rotational speed; in this case, there will be one more discrete frequency equal to the frequency of this error.

Oscillations are also excited with frequencies determined by the errors of the gear pair (axes misalignment, deviation from the center-to-center distance, etc.). The gearing is a system with distributed parameters and has a large number of natural vibration frequencies. This leads to the fact that in almost all modes of operation of the gearing is accompanied by the occurrence of oscillations at resonant frequencies. Reducing the noise level can be achieved by reducing the magnitude of the acting alternating forces, increasing the mechanical impedance at the places where the alternating forces are applied, reducing the transmission coefficient of sound vibrations from the places of origin to the places of radiation, reducing the oscillatory speeds by improving the design of the oscillating body, reducing the radiation surface by increasing the internal friction of the material. wheels.

For the manufacture of gears, carbon and alloy steels are mainly used. In those cases where it is necessary to ensure a less noisy operation of the transmission, non-metallic materials are used for the gears. Earlier, for this purpose, gears were made of wood and leather; currently they are made from textolite, wood plastics, polyamide plastics (including nylon).

Gear wheels made of plastics have a number of advantages over metal ones: wear resistance, noiseless operation, the ability to recover their shape after deformation (at low loads), a simpler manufacturing technology, etc. Along with this, they have significant disadvantages that limit their area application of relatively low strength of teeth, low thermal conductivity, high coefficient of linear thermal expansion. The most widely used for the manufacture of gears are thermosetting plastics based on phenol-formaldehyde resin. Durable products from them are obtained by introducing an organic filler into the material. As a filler, cotton fabric is used in the amount of 40-50% by weight of the finished plastic or wood in the amount of 75-80%, as well as fiberglass, asbestos, fibers.

Gear wheels made of polyamide materials cannot work for a long time at temperatures above 100 ° C and below 0 ° C, as they lose their mechanical strength. In order to increase the mechanical strength, plastic gears are reinforced by introducing special parts made of metal, fiberglass or other material with a strength higher than that of plastic. A reinforcing part is made from a sheet of 0.1-0.5 mm, which reproduces the shape of a gear wheel, but is much smaller in outer dimensions. The part is provided with holes and grooves for the passage of plastic and is installed in the mold so that it is completely covered with plastic. One or more of these parts are introduced depending on the thickness of the wheel. In a similar way, it is possible to reinforce not only spur gears, but also globoidal wheels, as well as worms and cams.

Comparative tests of gears with plastic wheels and steel wheels, carried out by TsNIITMASH, confirmed the effectiveness of the use of plastics for noise reduction. Thus, the sound pressure level of steel-nylon pairs decreased in comparison with the sound pressure level of steel gear pairs by 18 dB. The increased load on plastic gears causes less noise increase than steel gears. A comparative assessment of the noise of gear pairs of steel - nylon and nylon - kapron in all operating modes shows that to reduce the noise of gears, it is practically enough to replace one gear with a plastic one.

The efficiency of noise reduction due to the use of plastic wheels is higher at high frequencies than at low frequencies. The material that finds more and more new areas of application in modern technology is rubber. Strength, reliability, durability of rubber parts are determined by the correct choice of design, optimal dimensions, rubber grade, rational technology for manufacturing parts. Practice has shown the effectiveness of the use of elastic gear wheels, as well as wheels with internal vibration isolation. Flexible rubber hinges are used as elements of such products. The elasticity of the gear is achieved by reinforcing rubber inserts between the hub and the wheel rim. This helps to soften and reduce shock loads on the wheel tooth.

The technology of manufacturing gears, the principle of gearing, the type of cutting tool, machining allowances, the accuracy of machines not only determine the quality by deviations in individual gearing elements, but also predetermine the kinematic interaction of the gearing elements. The accumulated errors in the circumferential pitch of the gears and the combination of these errors, as a rule, cause low-frequency oscillations.

Local accumulated and single errors on the tooth profile, the location of which along the rotation of the wheel is random, also lead to low-frequency excitations of the systems. Defects in the operation of the worm gear of the gear cutting machine (inaccuracy of the step of the worm wheel, beating of the worm) causes the formation of elevations or transition areas (waves) on the surface of the teeth. The circumferential distance between the lines of irregularities corresponds to the pitch of the teeth of the indexing wheel of the machine, in connection with which the frequency of oscillations of this type depends on - the number of teeth of the indexing wheel of the gear cutting machine. Intense noise at high frequencies is caused by deviations from the involute, size, shape and pitch of the teeth. In these cases, the direction of action of the forces applied to the teeth; may differ from the direction of the theoretical action of the forces in ideal engagement. This gives rise to other modes of vibration. torsional, transverse with frequencies different from those considered.

In addition to the considered accumulation errors, which are of a cyclical nature, there are so-called run-in errors. One of the ways to reduce vibration and noise of gears is to improve the accuracy of their manufacture. Accuracy of manufacturing is ensured by the correct choice of the cutting process and finishing the crown (shaving, lapping, fine grinding and polishing).

As a result of applying these operations, the magnitude of cyclically acting errors decreases, and thereby significantly reduces noise generation (by 5-10 dB). Prolonged grinding of teeth is not recommended, as it leads to unacceptable distortion of their profile. The elimination and reduction of cyclic errors in the gearing elements of the gear wheels is achieved by increasing the accuracy of manufacturing the profile of the teeth and the accuracy of the main pitch. The main pitch error should be less than deformation under load or thermal deformation and therefore will not result in a noticeable additional dynamic load. In some cases, it is also possible to reduce the harmful effect of cyclic errors by fitting the points of contact during testing and increasing the oil supply. The noise level will decrease if the wheel teeth are made as elastic as possible due to high correction or if they are modified along the profile height. A significant factor in improving the quality of gears is an increase in the precise and kinematic chain of running in and the supply chain of gear hobbing machines, as well as ensuring a constant temperature during the gear cutting process.

The magnitude of these pulses and the intervals between them can be variable. At a constant rotational speed, a doubling of the transmitted torque leads to a doubling of the linear deformations and the vibration amplitude. The radiated sound power is proportional to the square of the load. Therefore, noise and vibration depend on the load in about the same way as on the speed. Reducing transmission noise can be achieved by reducing the speed of the gears. For example, through the use of two-stage gearboxes, decreasing the modulus, changing the number.

The increase in the noise level of gears is also significantly influenced by assembly and operational defects. Mounting defects include increased bearing clearances, axle misalignment, non-maintenance of center-to-center distances of paired gears, inaccurate centering of them, runout of couplings among the operational factors affecting the noise of gears include a change in the transmitted torque (in particular, its fluctuations), wear, and lubrication modes and amount of lubricant. The change in the transmitted torque gives rise to the impact character of the interaction of the teeth in the engagement.

Lack or insufficient lubrication of metal gears leads to increased friction and, as a consequence, an increase in sound pressure levels by 10-15 dB. Reducing the intensity of low-frequency noise components is achieved by improving the assembly quality and dynamic balancing of rotating parts, as well as the introduction of elastic couplings between the gearbox and the motor, the gearbox and the actuator. The introduction of elastic elements into the system reduces the dynamic loads on the teeth of the gear wheels. The arrangement of gears near the supports on double-bearing shafts, if possible, on a fixed fit without gaps in the supports also leads to noise reduction.

The use of special dampers both in the gears themselves and in the entire mechanism as a whole shifts the maximum of sound energy towards the middle frequencies. A decrease in the clearances between the teeth significantly reduces the amplitude of vibrations of the gear wheels caused by external causes, however, reducing the clearance to values less than the allowable norms will cause a noticeable deterioration in the operation of the transmission.

Timely and high-quality repair of gears, in which clearances in all joints are brought to the specified tolerances, is necessary to reduce noise and vibration. The housings are small in size and the internal air cavity of the gear systems belongs to the class of "small" acoustic volumes, the dimensions of which are smaller than the wavelength at low and medium frequencies. Fencing structures are rigidly connected to metal supporting structures, the general level of noise emitted by gearbox systems is determined by the level of noise emitted by thin-walled fencing covers, usually the dimensions of the radiating fences are commensurate with the distances to the areas in which the service personnel are located.

Cam mechanisms

Noise and vibration from cam gears are dominant in the printing, textile and food processing industries. The occurrence of noise from cam mechanisms is associated with the presence of variable forces in the contact zone of the cam-roller pair, which cause vibrations of the parts, leading to radiation. Disturbing forces in cam mechanisms are divided into forces caused by technological loads, friction forces, inertial and impact forces determined by the kinematics of the law of periodic motion (LPA) of the cam, dynamic forces caused by inaccuracy in the manufacture of the profile or parts of the cam mechanism.

The reasons that are determined by the applied LPD are deterministic. To reduce oscillations and noise of cam mechanisms, sinusoidal, parabolic and polynomial ZPD should be used. The laws of constant and equally decreasing accelerations, cosine and trapezoidal ones, lead to the occurrence of wider-band oscillations.

The manufacturing technology of the profile of the cam mechanisms also affects their vibroacoustic characteristics. Oscillations arising from irregularities in the cam profile depend on the technological modes of processing, the material of the roller and the modes of operation of the mechanisms. The most effective ways to reduce the vibrations of cam mechanisms are the optimal mode of machining the cam profiles and the introduction of additional operations that improve the quality of their surface (for example, smoothing); the use of materials for the manufacture of rollers and cams with damping properties, the use of roller bearings in cam mechanisms as rollers, the proper design of the cam profile in order to reduce uneven movement and impacts.

With static imbalance, the rotor axis of rotation and its main central axis of inertia are parallel. Bringing all unbalanced forces from imbalances to the center of mass of the rotor gives only the main vector of imbalances. The reasons for the static imbalance of the rotor, in addition to imbalances caused by the difference in the masses of structural elements located on opposite sides of the rotor, may be the inability of the rotor surface with the surfaces of the necks, the curvature of the rotor shaft, etc.

A rotor moment imbalance occurs when the rotor axis and its main central axis of inertia intersect at the rotor's center of mass. In this case, bringing all unbalanced forces to the center of mass of the rotating rotor gives only the main moment. When the rotor axis and its main central axis of inertia do not intersect at the center of mass or intersect, dynamic imbalance of the rotor occurs. It consists of static and momentary imbalances and is completely determined by the main vector and the main moment of the imbalances. A typical case of dynamic imbalance occurs when rolling bearings with differential-walled inner races are mounted on a balanced rotor.

For a flexible rotor, the concepts discussed above are retained, but here, in addition to the forces from imbalances, there are forces arising from the deflection of the rotor. Vibration caused by rotor imbalance has a frequency equal to the rotor speed. Vibration with the rotor speed can be caused, in addition to imbalances, by forces arising in the bearings due to misalignment of the connected machine rotors and the drive motor as a result of incorrect alignment. In this case, two positions are possible: angular displacement of the shafts to be connected and parallel displacement of the shafts. In the first case, axial vibration prevails, in the second - transverse.

However, even with ideal shaft alignment, forces arise in the coupling of uneven load on the fingers, which also cause vibration at a frequency. The uneven load on the pins is caused by inaccuracies in the pitch and shape of the bushings and pins of the coupling. As a result, a radial unbalanced force “rotating with the clutch” acts on each of the half-couplings. In the extreme case, the torque is transmitted by one finger. In this case, the unbalanced force acting on the shaft reaches the greatest value. The circumferential force acting on the pin is converted to a radial force and to a torque relative to the coupling axis. An oppositely directed radial force is applied to the second coupling half. These forces rotate together with the coupling and bend in opposite directions the ends of the shafts, which in any axial fixed plane cause antiphase vibration with the rotational speed. Since the circumferential force is proportional to the transmitted torque, the vibration amplitude is proportional to the transmitted power.

Studies of gear couplings, manufactured in accordance with GOST tolerances, showed that the circumferential force in the coupling is transmitted by the teeth, as a result of which the unbalanced force reaches the value (0.1- ^ -g-0.3) F, where F is the circumferential force, referenced to the starting circle of the teeth. Roughly the same thing takes place in resilient finger couplings.

In addition to the forces considered, the misalignment of the axes of the shafts causes friction forces in the elastic elements of the couplings, which create a moment periodically changing with frequency, bending the shafts in the plane of misalignment and displacement of their axes and causing vibration of the bearings, as well as periodically changing bending stresses in the shafts. High-frequency vibration is superimposed on vibration with frequency due to uneven finger operation.

Vibration and Noise Reduction Techniques

Methods for reducing noise and vibration from the imbalance of the rotating masses, as well as those arising in the joints of the shafts, are discussed below in application to pumping units (pumps) for which they are very important. Much of this applies to other machines as well.

Correct alignment of the shafts is a prerequisite for ensuring the required vibration levels at the rotational speed. When connecting half-couplings of pumping units, the requirements of OST 26-1347-77 "Pumps General technical conditions" must be observed. When centering the pump unit along the half couplings, the values of mutual misalignment and parallel displacement of the axes of the shafts and the motor must be limited.

To eliminate the imbalance of the pump rotor, it is necessary to balance the rotor, as well as its components, on special balancing machines. If, after balancing, the vibroactivity of the centrifugal pump (CP) at the rotational speed does not meet the requirements, it is possible to balance the CP during operation in the operating mode. Balancing the CN rotor includes the following operations; element-wise balancing of the rotor components (impellers, half-couplings, etc.), dynamic balancing of the complete rotor, balancing of the central pump on site (if necessary).

Balancing of the impeller and other elements of the central pump is carried out in accordance with the requirements specified in the working drawings and in the balancing card. All constructive and technological measures must be taken so that all seats are made from one installation, axial symmetry is not violated, there is no mandrel deformation, and the fit of the balanced part with the mandrel is carried out. It is advisable to balance the TsN rotor assembly in its own bearings. Particular attention should be paid to the choice of the type of fit of the assemblies on the pump shaft, the absence of runout of the seats and the observance of the concentricity of all rotor parts.

It is necessary to fix the mutual position of the rotor components during balancing, strictly preserving it during subsequent pump bulkheads. On-site balancing is recommended to be done on an insulated unit, while separating the rotors belonging to the drive motor and pump. Therefore, balancing in place should be performed on each pump if necessary. In this case, it is recommended to use the balancing unit of the drive motor and a special balancing unit on the pump shaft as correction planes, which, if possible, should be accessible during pump operation.

Bearings

Roller bearings are an intense source of mechanical vibration and noise in many machines. Internal forces causing vibration in rolling bearings are due to tolerances of bearing elements and mounting dimensions, which depend on the accuracy adopted in the manufacture of parts.

The forces arise from the difference in wall thickness of the bearing rings, ovality and different dimensions of the rolling elements, waviness on the raceways, radial and axial clearances between the rolling elements and rings, as well as the gap in the cage seats. However, even a perfectly manufactured rolling bearing is subject to a source of vibrations due to elastic deformations of parts, sliding of rolling elements in contact with rings, and turbulence of air entrained by the rolling system.

Oscillations of rolling bearings are manifested in a wide range from tens to tens of thousands of Hz, the most energy-intensive oscillations are concentrated in the range from the shaft rotation frequency to 3000 Hz. It should be noted that a precision-manufactured bearing can generate intense vibration and noise if the bearing is not properly installed. Another factor affecting bearing noise is the quality of its lubrication. Plain bearings are significantly less vibrational than rolling bearings, especially at high frequencies.

The main reason for the noise generated by sleeve bearings is the frictional forces between the bearing surfaces and the shaft journal, resulting from uneven and improper lubrication of the bearings. In improperly lubricated bearings, contact between the shaft and bearing surfaces occurs and a "creak" appears as a result of the abrupt movement of the shaft journal and the bearing surface. These oscillations occur at subharmonics of the rotational speed.

Another source of vibration and noise in radial sliding bearings is a process called vortex lubrication, which occurs in horizontal or vertical bearings with self-lubricating systems or forced lubrication systems under pressure under light loads. The presence of "vortex lubrication" is determined by the occurrence of vibration with a frequency approximately equal to half the rotational speed of the shaft. This vibration is the precession of the shaft in the bearing under the influence of the lubricant. The film of lubricant, which is in direct contact with the shaft in the boundary layer, rotates at the speed of the shaft, and the film on the fixed surface of the bearing is stationary.

The average speed of the lubricant, approximately equal to half the speed of the shaft, is the frequency of its precession in the bearing clearance. The combined action of this vibration with the vibration of the rotor speed will create the so-called resonant beats.

The problem of reducing noise from bearings includes three independent tasks: the use of rolling bearings with improved noise characteristics, vibration damping and vibration isolation of vibrations transmitted to the machine body; creation of the most favorable conditions for the operation of bearings in the machine.

Single row deep groove ball bearings are the best choice for noise reduction; other types of bearings generate higher noise and vibration levels. Thus, the vibration level of roller bearings is higher than that of ball bearings by 5 dB or more. The same amount is the excess of the vibration levels of the bearings in the heavy series compared to the bearings in the medium series.

The noise and vibration of rolling bearings are determined by the degree of deviation of the bearing elements from ideal geometric shapes, the magnitude of the radial clearance between the rings and rolling elements. This circumstance is important when choosing an accuracy class of bearings and a range of radial clearance. Dirt and other foreign bodies in the bearing and in the lubricant can press into the raceway and cause increased noise.

The correct choice of landings should ensure that the inner and outer rings are secured against turning and that the required radial clearances are maintained. It was found that the elimination of internal clearances in ball bearings using a spring axial tension in some cases leads to an improvement in the vibroacoustic characteristics of machines. When choosing the type of lubricant for low-noise machines, it is advisable not to use too thick lubricant, since it does not damp vibration of the rolling elements poorly, fill the oil chamber by 50%.

In addition, it should be borne in mind that the design of the bearing must allow the replacement of the lubricant with thorough flushing of the traces of the old used lubricant, the lubricant must ensure the stability of its properties during the conservation and storage of the machine until it is put into operation. Low-noise machines require careful handling during transportation and storage, in order to avoid brinelling of the raceways of rolling bearings and, as a result, deterioration of vibroacoustic characteristics.

A radical means of reducing the noise and vibration of bearings is to switch to plain bearings, which have noise levels 15-20 dB lower than those of rolling bearings, especially in the high frequency range. However, for a number of machines (for example, centrifugal pumps), the use of sleeve bearings is difficult for design and operational reasons.

Forging and pressing equipment

Most types of press-forging equipment refer to impact machines, during the operation of which impulse noise occurs, and its level at workplaces, as a rule, exceeds the permissible level.

Depending on the principle of operation, purpose and type of the main sources of noise generation, forging and pressing equipment can be divided into the following groups: mechanical presses, hydraulic presses, automatic forging and pressing machines, hammers; others (forging, bending and straightening machines, scissors, etc.).

The main source of noise emitted by a mechanical press is vibrations of its frame and flywheel as a result of blows in all movable joints of the press that occur at the moment of switching on and at the beginning of the movement of the crank-connecting rod or eccentric mechanism, when play is sampled in the joints of the connecting rod with the journal of the working shaft and a slide, as well as in the bearings of the working shaft. The process of interaction of the die with the workpiece is also of an impact character. During stamping, the sound levels of the presses increase noticeably - by 4-10 dB.

There is no noise when the press is switched on in the automatic mode of its operation. At the same time, the noise levels remain the same as in the single start mode. An increase in the background noise level in the room when the presses are switched to automatic operation can be largely eliminated by acoustic treatment of the enclosing surfaces of the room. Another way to reduce the switching noise of the press is to ensure smooth switching processes. It can be realized by replacing the mechanical (cam) clutches of the presses with friction, pneumatic ones. Such a replacement allows to reduce the switching noise in the near sweat of the coupling by 15 dB, and at the punch operator's workplace by 8-11 dB.

The punching noise can be reduced by the same method - by increasing the smoothness of the process by installing beveled dies on the presses instead of straight ones. This is usually done to reduce the required punching force of any part and can increase the life of the die. With a beveled die (the bevel of the die is equal to the thickness of the workpiece), the sound level at the punch operator's workplace decreases by 14 dB.

The use of beveled dies is most rational when cutting parts of a large perimeter, when significant efforts are required. The presses must be kept in good technical condition. The more the press is worn out, the greater the backlash in all links of its kinematic chain and the greater the noise of sampling these backlashes both when the press is turned on and during punching. The noise of presses of the same type, which are in different technical conditions, may differ by 6-8 dB.

To reduce the noise of the exhaust of the exhaust compressed air on presses with a pneumatic clutch for switching on and brakes, conventional silencers of pneumatic systems containing a porous sound-absorbing material cannot be used. This is due to the fact that when porous materials become clogged, the back pressure in the system increases, which can lead to accidents due to doubling of the press strokes.

To reduce noise during operation of a friction clutch and a press brake with a force of up to 10 MN, a special muffler has been developed and is widely used at the Gorky Automobile Plant. To create safe working conditions and increase its productivity on light presses, it is widely used to remove small stamped parts with a jet of compressed air using pneumatic nozzles that work constantly or are switched on synchronously with the stroke of the press slide. To reduce the level of intense high-frequency noise that occurs during the operation of air blowing systems, special silencers have been developed. To remove small parts stamped from sheet steel, it is advisable to use vacuum suction cups instead of blowing off. In the presence of transporting devices, one should strive to shorten the path of free movement of parts, replace metal slides with plastic ones or cover them with vibration-damping coatings, fasten slides to racks not connected to the press bed.

Replacing stamping by pressing significantly reduces noise, since this process is shock-free. Sound levels at the workplace of most hydraulic presses do not exceed 90-96 dB [for mechanical presses they are 100-110 dB]. Particularly noisy are single and double-acting hydraulic sheet metal presses up to 31.5 MN, with workplace sound levels reaching 106 dB. Most of the noise reduction measures for hydraulic presses are related to auxiliary equipment and operations - hydraulic system, feeding and removal of parts. The hydraulic pump should be installed in an insulated chamber or covered with a soundproof casing, pipelines should be covered with vibration-absorbing materials or soundproofed. Pressing equipment is widely used for cold heading of small parts, which is a highly productive and progressive process. However, sound levels near cold heading presses (automatic machines) are very high [up to 97-108 dB], and often even a small group of such equipment creates an unfavorable noise environment not only in the workshop or area where they are located, but also in adjacent rooms.

Reducing the noise of press-forging machines in the source is associated with significant difficulties, however, at present, designs of low-noise machines have already been developed. Thus, the use of the original kinematic diagram of the nailing machine made it possible to create a machine with a sound level at the workplace of 80 dB. The noise of the nailing machine is made up of noise from several independent sources, which are the upsetting, clamping, sharpening and feeding mechanisms. A feature of the work of the mechanisms of the automatic nailing machine is the shock nature of the interaction between the links in the joints and the tool with the workpiece. A change in the temporal characteristics of the collisions of the links leads to a change in the levels of noise generated, and a decrease in the speed of collisions of the links and an increase in the time between impacts leads to a decrease in the noise level. This is the basis of the low-noise design of each of the mechanisms of the nailing machine.

Reducing the radius of the crank of the upsetting mechanism allows to reduce the speed of impact of the tool with the workpiece by 2.5-3 times, which leads to a decrease in sound pressure levels by 7-9 dB in the frequency range, where there is the greatest excess over the permissible levels. Reducing the number of joints and clearances in them helps to reduce the noise of the crank feed mechanism. The main sources of noise generation in clamping and cutting mechanisms are gears. A decrease in the forces of impact in them is, in principle, possible due to an increase in the accuracy of the manufacture of wheels. However, the transition to the required 7th degree of accuracy of gears of nailing machines is unacceptable for technological reasons, therefore the only real way to reduce the noise of these mechanisms is to exclude gears from the kinematic diagram of the nailing machine.

In the conditions of existing production, to reduce noise in the cold heading sections, sound-insulating casings can be used, designed taking into account the convenience of maintenance and repair of machine tools and partially open from the wire feed side. When planning industrial premises, it is advisable to separate the cold heading sections from the rest of the workshop and auxiliary sections with a sound-insulating partition, and place the presses in groups of 4-6 pcs. in separate compartments formed by screens with a height of about 3 m with sound-absorbing lining.

The ceiling and walls of the room must also be lined with sound-absorbing structures. A radical way of protecting hardware workers from noise is to increase the degree of automation of production processes, in which machine tools are controlled and monitored remotely, and the operators spend most of their working time in soundproofed observation posts.

Steam-air and pneumatic hammers are the main source of particularly intense impulse noise in press-forging production. The noise is emitted at the moment the hammer head (punch) strikes the workpiece. According to the work data, various hammers of equal power, stamping products of the same nomenclature, have similar frequency characteristics of impulse noise. With an increase in the mass of the falling parts of the hammer, the maximum in the spectrum of sound pressure levels moves towards lower frequencies. Sound levels in the workplace with heavy forging and stamping hammers can be as high as 110-120 dB.

To reduce noise in forging shops, it is advisable, if technologically permissible, to replace hammers with hot stamping presses. Although the latter are also a source of intense noise, the noise of the press is 9-10 dB lower across the entire frequency spectrum than that of a hammer of approximately equal power. The noise associated with the operation of the presses has less effect on the physiological functions of the body than the noise of working hammers, and therefore is less dangerous for humans.

A chamber-type muffler can be used to reduce the noise of the exhaust superheated steam during the operation of steam-air hammers with a mass of falling parts up to 2000 kg. It is a steel cylinder, inside which there are three transverse partitions with tubes 42 mm in diameter and 250 mm in length. This design can also be used on hammers of greater productivity, for which it is necessary to increase the dimensions of the muffler, which are in direct proportion to the volume of the working cylinders, and the diameters of the hammer exhaust hole. Such mufflers are large enough, so it is advisable to install them outside the workshop, bringing exhaust pipes to them.

One of the significant negative factors in the use of hammers is the excitation of intense shock loads, which are transmitted through the base of the hammer to the structure of the building where it is installed (and in some cases to neighboring buildings), creating increased noise levels in them. To reduce them, it is necessary to provide vibration isolation of the hammers. Recommended methods of vibration isolation of foundations of heavy hammers are given in the work. During the operation of horizontal forging machines, broadband noise occurs with a maximum in the range of low and medium frequencies. As the die diameter decreases, the maximum in the spectrum shifts towards higher frequencies. The main sources of noise generation are periodic blows when the dies are closed and the exhaust of compressed air. Noise protections are similar to those used for mechanical presses. Shears, swaging machines and edging presses do not have colliding elements and therefore, unlike most types of press-forging equipment, are not sources of impulse.

Metal and woodworking machines

Metal cutting machines

Depending on the type of metal-cutting equipment, the power of its drives, the intensity and stability of the cutting process, the sound levels generated at a distance of 1 m from the enclosing surfaces are 60-110 dB. Under typical machine operating conditions, the upper limit of this range is 90 dB. The noise spectrum of machine tools usually has a maximum located in the frequency range 500-2000 Hz (most often in the frequency band 1000 Hz). Most metal-cutting machines, when properly manufactured, have noise characteristics that meet sanitary standards without the use of additional measures to reduce noise.

The main sources of noise of metal-cutting machines can be divided into five groups: 1) gears included in the drives of the main and auxiliary movements, this includes replaceable wheels and closed gearboxes, 2) hydraulic units; 3) electric motors, 4) guide tubes of automatic lathes, 5) cutting process. In addition, bearings, belt drives, cam gears, disc couplings are sources of noise, but these usually do not affect the overall noise level of the machine.

The noise of machine tools is reduced at the source of occurrence by reducing the transfer of vibrational energy from the source to the noise emitters (usually the outer walls of the machine tool), damping the emitters and construction-acoustic measures. Pumps and motors should be mounted on vibration dampers using measures to eliminate the transmission of vibration to oil reservoirs, which, having a large surface, emit intense noise. To connect the pipelines of hydraulic units, vibration isolating clamps should be used. To reduce the influence on the overall noise level, individual units installed on the machine are vibration-insulated from the elastic system of the machine, if there are no special requirements for the accuracy and rigidity of the installation. The same applies to control cabinets installed on the machine, which themselves are not sources of vibration, but, having a large surface area, emit intense noise.

Vibration isolation of motors can reduce the sound level of the machine by 6 dB or more. In workshops and in areas of automatic lathes, which are distinguished by high productivity and reliability, the noise during their operation slightly exceeds the permissible level. Its main source is the impact of the processed bar on the walls of the guide tubes.

Currently, a large number of designs of low-noise guide tubes have been developed, which, when properly operated and timely adjusted, provide noise levels within the acceptable limits. The stilling tube is widely used. Novocherkassk machine-tool plant, which is a metal tube with a spring of variable diameter inside it. Unlike other similar structures, the largest diameter of the springs in the free state is greater than the inner diameter of the pipe.

Before assembly, the spring is twisted, inserted into the pipe and released. The presence of a spring excludes direct impacts of the processed bar on the metal pipe. The decrease in the sound level of such a pipe in comparison with a conventional pipe is more than 20 dB. If the spring is worn and incorrectly adjusted, this effect can be greatly reduced. The disadvantages of this design include the difficulty of replacing the spring when it is worn out and the impossibility of processing multifaceted rods, whose edges are knocked off during rotation.

Reducing noise [up to 12 dB] in other designs of guide pipes is achieved by eliminating the impact of the bar on the metal pipe through the use of vibration isolators made of rubber or other polymer material. When designing low-noise structures, the main attention is paid to the sound insulation of the slot for the pusher flag and vibration isolation of the inner pipe from the outer one.

It is preferable to choose pipes that do not have a longitudinal slot, in which the rod moves axially by a piston under the action of compressed air. German Thraub, Germany, offers two progressive and fundamentally different guide tube designs. The bar moves between elastic rollers located along the circumference and along the length of the bar and with a certain force pressing it to the center of the guide system. The elasticity of the rollers and their suspension compensate for the non-circularity of the hexagonal and tetrahedral rods and their non-straightness.

To reduce vibrations caused by the eccentricity of the rotating rods, the rollers are installed at 90 °, 1 in the axial direction are spaced along the length, and only at the point of transition to the spindle the set of rollers is installed as tightly as possible.The diameter of the pusher exceeds the diameter of the bar, and when the pusher passes through the rollers, the latter open up. The pusher guide is made of vibration-damping plastic. With this bar feed system, noise is reduced and automatic cross-bar loading is ensured. However, the combination of the requirement for the elasticity of the rollers and the centering of the bar along the spindle axis is provided only within certain limits of the curvature of the bars and with a difference in the maximum and minimum diameters of the bars used. Due to the rotation of the bar between it and the inner wall of the guide tube, an oil wedge is created, eliminating contact between metal surfaces. Such a bar feeder makes it possible to process non-circular four-sided, rectangular, etc. profiles on automatic lathes without noise and vibration.

The disadvantages of this device include the lack of accurate centering of the bar along the spindle axis, the need to coordinate the pipe diameter. The Swiss company J1HC (LNS) manufactures a complex guide tube, in which the outer and inner tubes are separated by a space filled with oil. The noise of the machine with such a device depends little on the presence of a rod in the pipe, and the sound level is reduced by more than 30 dB. When cutting, the sound level increases by 2-3 dB due to an increase in the load on the drives of the main and auxiliary movements and an increase in the vibration levels of the elastic system of the machine due to its interaction with the working process (cutting process, friction process).

Noise levels during cutting are determined not only by cutting conditions, but also by the dynamic characteristics of the elastic system, which includes both the workpiece and the cutting tool. Particularly unpleasant is the tonal noise that often occurs when machining hollow or thin-walled parts, when mounting tools and when removing thin chips. The level of the tonal component of noise is especially high if the natural frequencies of the cutting tool and the workpiece are close to each other. This level can be reduced by increasing the rigidity of the tool, damping vibrations of the workpiece and the tool. The damping of the workpiece can be accomplished by pressing plates made of rubber or other damping material against the thin surfaces of the workpiece. The pressing method depends on the type of machine and the shape of the workpiece.

By damping the workpiece, the high frequency noise can be reduced by 10 dB. Damping the instrument can reduce the tonal components of the noise by 20 dB or more. Broadband noise is reduced by 2-5 dB at low frequencies and by 10-15 dB at high frequencies. To maintain the dimensional accuracy of the tool, spacers are inserted into the damping layer on the support surfaces of the holder to maintain the constant position of the holder under load. Dissipation of vibrational energy can be achieved due to friction in the joints when the steel plates are firmly pressed against the surface of the holder. The design of the boring tool dampers is similar to that described above for the cutters. A sleeve is put on the boring bar, the inner diameter of which is greater than the diameter of the boring bar. Coaxiality of the bushing and boring bar is ensured by rigid spacers. The rest of the space between the boring bar and the bushing is filled with damping material.

Similar designs can be applied to other types of rotating tools. When mounting the instrument, this can lead to intense self-oscillation and tonal noise at frequencies of 2000-4000 Hz. When installing the insert with an interference fit in the direction of the cutting speed, such self-oscillations are weakened by 10-20 dB or completely eliminated. When working on cutting machines with circular saws, there is often significant noise, especially when cutting light metals, where the cutting speed reaches 70 m / s. At the same time, as a result of vibrations of circular saws, the sound level reaches 115 dB.

Split saws generate less noise due to internal damping. The noise of solid saws is reduced by external dampers. When using oil dampers with a viscoelastic saw blade clamp, cooling oil is used as a damping medium, supplied to special pockets made in segments located with a gap of 0.2 mm near the plane of the blade. Fitting damping rings to the saw blade is an effective means of reducing noise.

The annular damper consists of two rings made of a composite material (steel sheet - plastic - steel sheet). Damping rings are riveted on both sides of the saw blade. In this case, energy dissipation occurs in the damping rings themselves during bending vibrations of the saws and at the junction of the rings with the saw blade. Modifications are possible in which the saw blade is made multi-layer instead of the rings to be fitted. With the help of such methods, it is possible to reduce the sound level during the cutting process by 8-10 dB.

Reducing noise is also achieved by reducing the speed during the return stroke after cutting the saw blade. By pre-straightening the saw blade and increasing the accuracy of its installation, it is possible to reduce the sound level by another 6 dB. By using covers that cover the saw blade, an additional reduction of the sound level by 6-10 dB can be achieved.

All the methods described above cannot completely eliminate the noise associated with metal cutting, which is due to the physics of the cutting process itself by spalling of chip elements, friction of the chip and the cutting surface against the tool surface, the presence of a moving high-gradient stress field on the workpiece, etc. this is the most effective method for reducing cutting noise. The occurrence of tonal noise when mounting a cutting tool and when removing thin chips is greatly influenced by the mechanism for attaching carbide inserts to the holder.

Usually, when mechanically the fastened plate is not tightly pressed in the direction of the cutting speed, the clamp during processing is the equipping of the machine with movable casings that tightly cover the cutting zone. Conventional covers, made of sheet iron, are only intended to protect the operator from emulsion and swarf ingress. Chip impacts on these housings and vibrations transmitted to them from the drives create additional noise. The soundproof enclosure for machine tools consists of two layers of sheet iron, between which there is a damping material. The movable part of the casing should seal the cutting zone hermetically, the points of contact with the stationary part should, if possible, be sealed with vibration-absorbing material. With such covers, the noise during cutting differs little from the noise during the idle of the machine.

Covers and guards on the machine, designed to eliminate accidental human contact with moving mechanisms, are made of thin sheet iron and rigidly attached to the elastic system of the machine. With a large surface area, they often contribute to an increase in noise. When fastening, such barriers must be vibration-insulated from the elastic system of the machine. The fastening parts (screws, bolts) must be vibration-insulated from the enclosure being installed. If the requirements for the rigidity and accuracy of fastening do not allow the use of vibration isolation, soundproof panels can be used, which are attached using vibration isolators to the outer surfaces of intense noise sources, for example, to the spindle head.

The use of such panels makes it possible to reduce the sound level emitted by the covered surfaces by 10 dB or more. Fences and enclosures should, if possible, be made tight, the walls should be multi-layer or have a damping coating.

Woodworking machinery

The highest noise levels are generated during the operation of circular saws and planers (planers, planers, four-sided planers). The sources of noise of thicknessing and planing machines are vortex processes in the zone of maximum convergence of the edges of the knives with the edges of the pressing jaws or with the edges of the table, mechanical noise of the drive and vibration of the processed material. Spiral shafts are the best way to reduce the noise of planers.

The reason for the occurrence of noise when planing with straight knives is intense vibrations of the workpiece to be machined and the bearing systems of the machine when the knife strikes along the entire length of the line of contact with the workpiece. When planing with a spiral knife, only one point works on its edge, the cutting force is directed at an angle to the wood grain. When working with spiral knives with a helix angle of 72 °, sound levels are reduced by 10-12 dB compared to using straight knives.

However, the use of such knives is complicated by the complexity of their manufacture, installation and regrinding. When using straight knives, measures should be taken to reduce noise. A cheap and practical way to reduce the aerodynamic component of the cutter shaft noise of planers is to insert the shaft grooves with a solid sound absorbing material such as Tecsound. By perforating the table jaws with an inclined slotted perforation, it is possible to reduce the sound level of jointing machines at idle speed by 10-15 dB.

Slotted perforation on the front and rear clamps of thicknesser machines can reduce the aerodynamic component of their noise. By reducing the rotational speed of the working body of woodworking machines, you can achieve a significant reduction in noise, but this leads to a decrease in their productivity. The balancing of the knife shafts when changing knives helps to reduce the noise of the planers.

During the operation of circular saws, noise occurs as a result of turbulence and pulsations of air in the area of the saw ring gear, vibrations of the saw blade itself, vibrations of the processed wood. Additional sources of noise are the machine drive, shaft bearings and the sawdust pneumatic suction system. As with metal cutting machines, the main method for reducing the noise of circular saws is to damp the saw blade, balance it, and reduce backlash and beating. For all models of woodworking machines, soundproofing and noise shielding casings are widely used.

The casing designs developed by the Ural Forestry Institute and intended for use on a wide variety of woodworking machines (circular saws, four-sided planers, thickness planers) have proven themselves well in industry. They allow to reduce the idling noise of machine tools and cutting noise by 10 dB, are easy to manufacture, and do not interfere with machine maintenance.

Vibrating machines

Characteristics of the noise of vibration and vibration impact machines

The noise of vibration machines used in construction and in industry for the processing or transportation of various materials is mainly of mechanical origin and is the result of bending or piston vibrations of the surfaces of the installation.

The direct source of vibration and noise, the spectrum of which covers a wide range of frequencies, is collisions in the drive of the machine, as well as in its individual parts. Shock processes occur in almost all types of mechanically driven machines. In particular, for some vibratory platforms for compacting concrete mixtures, the most intense shocks occur when the form is not properly fixed by the electromagnets of the platform. However, even when these parts of the installation are rigidly connected to each other, such sources of vibration and noise as the rolling bearing of cebalance vibrators, gear drives, and articulated joints of individual units remain.

In bearings, rolling elements collide with rings and a separator, in gear drives - blows of teeth, in pneumatic vibration exciters - when the runner rolls over the vibrator housing. Similar phenomena are observed in electromagnetic feeders, where the main source of broadband noise is collisions in an elastic system. In low-frequency impact machines for forming reinforced concrete products of the "shock-table" type and other machines of this type, for example, knock-out inertial grids, periodic impacts between individual parts are a source of intense mechanical noise.

The noise intensity of vibration and shock units depends on the design of the movable frame and the shape. The movable frame usually consists of elements of thin-walled rolled metal and metal sheets, which, under the influence of impacts, perform intense bending vibrations.

The shape in which the product is formed has a similar design. The bending vibrations of the pallet sheathing sheets and the sides of the concrete mold are, especially in low-frequency percussion installations, the source of the main technological effect on the concrete mixture. Since the concrete mix has high vibration damping properties, the noise of installations is largely determined by the ratio of the areas of radiation surfaces of metal sheets and elements of thin-walled rolled products in contact with the mix and vibrating in the air. At the technological frequencies of the vibrating platforms, the piston oscillations of the molds have a predominant influence on the noise emission. Their role is especially important for molds of small dimensions in plan and with a relatively rigid frame.

The sound power emitted by the form is determined from the expression. At low frequencies, when the sound wavelength in air is greater than the characteristic size of the radiator. The value increases when a screen is installed that prevents free air circulation around the emitter. So, when installing a vibrating platform with a fixed form in the pit and dividing the free space between the form and the pit with shields or an apron, the noise emission conditions become close to the noise emission by the piston in the screen, and the noise levels at the vibration frequency reach 115-120 dB.

Basic Design Principles of Low Noise Vibration Machines

Collisions in vibrating machines and high-frequency vibrations excited by them are the result of imperfect design of these machines and practically do not affect the efficiency of the working process. Therefore, if necessary, you should first of all change the design of the parts interacting with each other in order to avoid the impulsive nature of the transfer of force.

Such measures for machines with unbalanced vibrators include the use of special rolling bearings with smaller clearances and a fixed cage position, as well as the replacement of rolling bearings with plain bearings. The decrease in the sound pressure level is, on average, 10 dB. In electro-vibration feeders, collisions in the elastic system can be significantly reduced due to the use of a suspension in the nodes of the spring package and the correct choice of the angle of force transmission in the chute shock absorbers.

The decrease in the sound pressure level at high frequencies reaches 15 dB. Vibration and noise levels at medium and high frequencies are significantly reduced with decreasing rotational speed of the vibrators, which is associated with a change in the temporal characteristics of collisions in rolling bearings and gears. It follows from this that with a 2-fold decrease in the frequency of rotation of the vibrators, the octave sound power levels decrease by 9-11 dB.

Plants with a reduced vibration frequency (24 Hz) for compacting concrete mix are used in industry. They have a low noise level, but they also differ in a lower sealing ability, which is permissible with sufficiently mobile mixtures. Lowering the fundamental process frequency (vibration frequency) is a radical means of reducing noise at low frequencies, where a decrease in the ratio between the characteristic shape size and the wavelength at the vibration frequency leads to a decrease in emissivity.

So, for a vibrating platform with the dimensions of a vibrated structure in terms of 1.3X0.9 m, a decrease in the vibration frequency from 50 to 25 Hz reduces the sound pressure level at the vibration frequency by 13 dB, and a decrease in frequency from 100 to 50 Hz - by 8 dB. A change in the position of the vibrated structure relative to the workshop floor also leads to a decrease in noise at the vibration frequency. If the bottom of the mold is raised above the floor level (noise emission by a piston without a screen), then the radiated power at the vibration frequency decreases, and it is especially significant for small molds.

In particular, with a smaller form size of less than a quarter of the sound wavelength at the vibration frequency, the sound power level is reduced by 10 dB. The greatest reduction in noise is achieved when constructing a vibrating platform in such a way that the mold with the mixture is located at the level of the hearing organs of the workers (1.5 m from the floor), and the vibration exciters are removed from the zone of compensation for excessive pressures arising from vibrations of the mold. Low frequency noise is also reduced if the direction of vibration is perpendicular to the side of the mold with the smallest surface area.

To suppress the noise emitted by thin sheets of vibrated metal structures at medium and high frequencies, it is advisable to damp them with vibration, for example, with rubber. In all cases, the number of elements not in contact with the material being processed should be minimal, and their rigidity should be chosen so that the fundamental frequency of bending vibrations is outside the range where the most intense components of the disturbing force are concentrated.

In the ShS-10 percussion unit, a significant reduction in noise was achieved by replacing metal sheets in the structure of the upper frame with concrete slabs resting on a fixed foundation box, and installing beams on which a form of thick-walled rolled products is installed. The high-frequency vibrations and noise of impact machines can be reduced by increasing the duration of the impact between machine parts.

At the same time, the spectrum of intensely excited vibrations is compressed and most of the impact energy is concentrated in the low-frequency region.For example, in the vibration plate SMZH-460, rubber buffers are installed at the points of collisions between the movable frame and the fixed one, which contributes to a significant increase in the impact time and a decrease in the intensity of the force components at medium and high frequencies.

However, in some cases, for example, when compacting thin layers of concrete mix in a mold with a rigid base, compression of the impact force spectrum reduces the dynamic pressures in the mix. Increasing the duration of contacts during micro impacts significantly reduces medium and high frequency vibration and noise. For this, materials with a lower Young's modulus should be used or the radii of curvature of the colliding bodies should be reduced.

Plasterboard cladding of the working surfaces of the pneumatic vibration exciter reduces the sound power level at peak frequencies by 15 dB, and the installation of non-metallic gaskets (fan belt, rubber protected by a steel plate) between the loose mold and the vibration plate frame leads to a decrease in the noise level at frequencies above 500 Hz by 20 dB ...

To suppress the noise emitted by sheets of mold sheathing in contact with the concrete mixture, one should strive to reduce the fundamental vibration frequency of the mold sheathing with concrete mixture, which is achieved by reducing the thickness of the sheet or increasing the size of the cells).

For vibrating platforms with harmonic vibrations, this frequency should be 15-20% lower than the vibration frequency, and for shock installations - within 20-40 Hz. Vibrating machines should be designed in such a way that the vibrators do not come into contact with the mold at all, but only act on the concrete mixture. An example is the various surface concrete compactors. In addition, the vibrated metal structure should not have closed and semi-closed cavities in which sound amplification is possible. An effective measure is also the installation of rubber vibration isolators between the vibrators and the metal structure, especially in cases where a significant part of its elements vibrate in the air.

The stiffness of vibration isolators (preferably made of rubber) is selected based on the operation of the system at frequencies below the second natural frequency of the two-mass system. It is especially advisable to adjust to the anti-resonance mode, in which the vibration amplitude of the vibrators becomes minimal without reducing the vibrations of the vibrated metal structure. The vibration plates converted in this way reduced the noise level at medium and high frequencies by about 10 dB.

Material shredding machines

Mills

The noise of the mill drum is generated by the impact of the balls on the lining plates. As the oscillation frequency increases, the noise level increases, which is due to an increase in the emissivity of the mill body. Starting from 2000 - 3000 Hz, the noise level decreases due to local crushing of the surfaces of the body and balls during impacts.

Another source of mill noise is gearing. The most intense noise components of this source are observed in the frequency range 63-500 Hz. Reducing the noise level of mills to the required values ensures compliance with sanitary standards for noise in the workplace.

Octave levels of the required noise reduction in mills summarized from the results of field measurements. With low emissivity at frequencies below the cutoff. In mills with lining bolts, the shell is attached to the casing through steel cups and foam rubber washers. In the absence of lining bolts, the shell is connected to the body at the points of abutment of the cylindrical part of the drum to the ends through gaskets made of foam rubber with a thickness of 15-20 mm. The air gap between the shell and the body is filled with sound-absorbing material (flexible self-extinguishing polyurethane foam plastic PPU-ES, flexible polyurethane foam plastic PPU-ET, basalt sound-absorbing material BSTV, VTCHS nylon fiber in fiberglass covers, Texcool material, FonStarVuSuSVUZ).

The thickness of the layer of sound-absorbing material is assumed to be 25-50 mm. The choice of the design of the sound insulating shell for mills is made according to the data. It is advisable to install sound-insulating shells on dry grinding mills even if they do not provide noise reduction to the required level.

To reduce the noise of gears, helical and chevron gears are used instead of spur gears (when the crown is located on the trunnion, and not on the drum) cast gear bodies instead of thin-walled sheet steel elements, elastic couplings between the drive motor and the gears and, finally, the sound insulation of gears.

Discharge openings are closed with steel casings, which are lined with soft sheet rubber inside. Under the action of short-term forces during crushing of lumps of material inhomogeneous in size and physical properties, dynamic deformations occur in crushing parts, which are transmitted to the mating elements of the crusher body and support casing, causing their intense vibrations.

Vibrations, in addition, arise as a result of contact engagement of the teeth of the drive wheels, imbalance in the masses of crushing parts, impacts of pieces of material on the distribution plate and hopper. Sound emission as a result of vibration of the outer surfaces of the housing, support casing and hopper occurs at frequencies above 600 Hz. At lower frequencies, noise propagates directly from the crushing zone due to insufficient sound insulation by the structural elements of the loading area. The frequency characteristics of the noise of cone crushers of coarse crushing (CKD), medium crushing (KSD) and fine crushing (CMD) are given.

Noise levels depend on the hardness of the material being crushed, the size of the falling pieces and the uniformity of the load. During loading of the crusher, the noise level increases by 8-10 dB compared to the noise level at steady state operation under load. As a result of wear of the armor plates, the noise level increases by 5-6 dB. Reducing the noise of crushers is associated, first of all, with a decrease in the transmission of vibration from its main sources to the mating parts, from the surfaces of which noise is emitted. For this purpose, rubber gaskets must be installed. A soundproofed observation booth should be provided for the operator servicing the crusher.

Machines and equipment for the printing industry

Newspaper units

The noise of modern newspaper units, not equipped with noise protection devices, fluctuates depending on the speed parameters and the layout of the machines. The noise of printing machines can be divided into several characteristic groups: 1) noise caused by the operation of technological mechanisms (grippers, printing devices, cutting devices), 2) noise generated by gear and chain drive mechanisms, cam mechanisms, etc., 3) noise, generated by the processed materials (paper, foil, etc.), 4) the noise of auxiliary equipment.

In newspaper aggregates, the prevailing noises are noises of the 1st and 2nd groups, i.e. noises of mechanical origin. The noise of the processed material and auxiliary equipment is insignificant. The main sources of noise from the printing units are drive systems, sponge gears located on the bed of the printing units, inking unit mechanisms, and paper transfer system mechanisms.

The sound level of the printing unit, switched on autonomously, averages 101-105 dB. The noise is broadband in nature with a maximum in the frequency range 1000-2000 Hz. In the folding machine, in addition to the drive mechanisms that create a uniform broadband noise, which in their characteristics does not differ much from the noise of the printing units, the folding mechanisms (rollers, knives, supporting parts) create significant noise. The noise of these mechanisms is impulsive in nature. In terms of level, it does not exceed the noise of the driving mechanisms.

The development of methods for reducing the noise of newspaper units is in the following directions; application of polymeric materials with improved vibroacoustic properties in mechanisms; placement of newspaper units in separate rooms (houses) on vibration-insulated foundations controlled by telemetry equipment, creation of special zones for service personnel using cabins and screens. Products are discharged through soundproof booths. At the entrance and exit, the conveyors must be equipped with soundproof channels. The cabins are installed on a vibration-insulated foundation.

The walls of the cabin are made of lightweight sound-insulating materials, such as: Termozvukoizol, Texound, Fonstar, Zkozvukoizol, Zvukoizol, Rockwool, Basaltin, etc. The use of soundproof booths of this design is the best means of protecting operators from noise. At the same time, the traditional technology is retained, the level of automation is increased slightly and the design of the printing units and folding machines is preserved.

Web printing machines

The sound level from high-speed role-playing machines, not equipped with noise protection devices, reaches an average of 90-95 dB. The noise is broadband. Noises of mechanical origin predominate. As with newspaper machines, the main sources of noise are found in the folder and in the printing units. These are folding mechanisms, drive boxes for printing and ink devices.

The main electric motors in the area of their installation create noise, the level of which exceeds the general background radiation by 1-3 dB. The sound level of 88-90 dB is also created by paper rollers and cylinders. The permissible noise level during the operation of web-based printing machines can be achieved without fundamental changes in the schemes of machines and traditional methods of working on them by soundproofing the printing units and the folding machine.

The section on the service side of technological mechanisms should be hermetically closed by easily movable or removable covers. Places of exit and entry of paper should be equipped with noise protection devices. The drive housings are mounted on elastic spacers with a high loss factor. The design of the connecting elements and materials are fenced and selected in accordance with the recommendations set out in the specialist literature. Damped gear drives should be used in the drives of inking units. Passages between printing and folding units must have additional sealed doors. The folding machine must also be enclosed in a soundproofing casing.

Rotary sheet machines

Modern sheetfed rotary machines produce sound levels in the range of 82-89 dB. The noise is broadband in nature. The dominant source is the outfeed conveyor, so the focus should be on reducing chain drive noise. Unlike role-playing machines in these machines, it is first of all necessary to deal with noise at the sources of occurrence, that is, directly in the mechanisms, by installing vibration-isolating devices in gear and chain drives. In sheet-fed machines, increase the area of the fences at the reception and the covers of the printing units.

Flat printing machines

The sound level of most flatbed presses is between 86-87 dB at maximum speeds. At operating speeds, the noise of these machines does not exceed the permissible values. Vibroacoustic studies have shown the promise of using sprung gears in drive mechanisms. This not only reduces noise, but also improves the dynamic performance of mechanical systems.

Bookbinding machines

Most bookbinding machines have relatively slow speeds. Therefore, their sound level (except for large format folding machines and some others) is in the range of 80-90 dB. The specificity of binding and stitching machines requires the use of a large number of various lever-cam mechanisms (for example, about a hundred cam mechanisms are used in BTG machines). Therefore, in all machines with a sound level of up to 90 dB, damped gear and cam structures should be used. In high-speed modular finishing lines, sound levels in individual local areas reach 96-100 dB. At such sound levels, it is advisable to use structures that provide for the complete sealing of machines, and design sound-insulating barriers as separate modules.

Machines and equipment for the textile and light industry

Mechanical and aerodynamic noise occurs during the operation of machinery and equipment in the textile and light industry. Mechanical noise is emitted by vibrating surfaces of machinery and equipment. Aerodynamic noise is generated by flux-generating and cytoconducting devices (compressors, fans of built-in pneumatic systems of machines, aerodynamic nozzles, etc.) and rapidly rotating elements (spindles, drums of spinning machines, etc.). A feature of the equipment and machines under consideration is the widespread use of dedusting and humidifying systems both built into the equipment and existing autonomously, which are additional sources of vibration and noise.

Major sources of noise

In preparatory-spinning equipment (open-beater, belt, carding machines), the main source of noise is the parts of drive systems, gear, chain and other drives, and for combing equipment - also the comb mechanism, in carding machines - drums and couplings.

The ventilation system creates significant noise in the workshops. Intense noise occurs during the transportation of the ridges in the worm guides, both from the impact of the cams on them, and when the ridges fall on the comb strips. The noise spectrum of spinning and twisting industries contains significant high-frequency components. The main source of noise in tangentially driven twisting and spinning machines is the spindles and their drive (pulleys, idler pulleys with belt).

In twisting, spinning-twisting, stretching-stretching and spinning machines with a belt drive, sources of increased noise are drive parts, spindle bearings, spinning box spores, runners, where noise is generated during friction, for example, a steel runner on a steel ring. In spinning machines equipped with individual aerodynamic dedusting systems, the fans emit increased broadband noise.

The preparatory weaving production is one of the quiet ones. The highest values of sound pressure levels in the spectrum are found at low and medium frequencies. The main source of machine noise is parts of drive and actuating mechanisms. In the weaving industry, the most noisy are mechanical and automatic shuttle looms, in which the main source of noise is a mechanism that transports a massive shuttle with a bobbin at a speed of up to 20 m / s.

The main source of the increased noise is the impact of the drive on the shuttle and shuttle on the shuttle box. Less noisy are looms where this mechanism is structurally changed or completely excluded (shuttleless, pneumatic, pneumatic rapier and hydraulic looms). mechanisms, as well as pneumatic and hydraulic systems.

Sewing production is medium noise. The main sources of noise are the mechanisms of the needle bar, the thread take-up, the shuttle, the transport of the fabric, and in machines with copier eccentrics - and its mechanism. Noisy production of knitwear is similar to that of sewing. The main sources of machine noise are working bodies, drive parts and fans (automatic round-nozzles).

In light industry, leather and shoe industries are classified as high-noise. At the same time, in the leather industry, the most noisy are adjustable (roller and drum), shearing, flesh, grinding machines, beater drums and sole rollers. The most noisy are suspended drums (gear drives) and dryers (fans). A lot of noise is also generated in some auxiliary shops of leather and shoe production (nailing, woodworking, hardware).

The main sources of machine noise in the shoe and leather industries are shock technological operations performed by the working bodies of the machines. Sometimes significant noise is emitted by gear drives, grinders and fans. The reason for the emission of noise by adjustable machines (drum and roller) is the blows of the working organs (knives) on the stretched skin. With drum adjustable machines, noise also occurs when the drive belt slips when reversing the stroke. The same source of noise occurs during the operation of the plantar rollers, as well as during the movement of the rolling roller on the kneaded hard skin.

The main source of noise from planing and fleshing machines is the vibration of the knives during clipping. The emission of noise from the operation of tanning, fat and dyeing drums usually slightly exceeds the permissible levels. Its source is a gear drive. The noise of the running presses is the result of impacts on the cutter of the hammer mechanism. The main source of noise in branding machines is the mechanism of the branding drum striking the workpiece, and in nail, hairpin and tightening machines - mechanisms for making and driving nails, staples, and hairpins.

In milling, glazing, ruffling and pumice machines, noise is generated by friction between the tool and the workpiece. The sources of noise in screw machines are wire feeders and screwdrivers, as well as the transmission mechanism. High-frequency noise is emitted from the coils. Fur production is characterized by an average noise level. In the equipment of fur production, spur gears are widely used as gears, which emit noise during operation. The most noisy equipment are drums, centrifuges, wool shearing, shearing, breaking and sewing machines. The main sources of noise are drive parts (gear drives of drums, launches and flesh machines, friction transmission of centrifuges with cone rollers); working bodies (knife drum of dividing machines, knives of shearing machines), technological fans (exhaust and circulation, fans of dryers and pneumatic suction of wool and shearing machines).

Basic methods and means of noise reduction

Reducing noise and vibrations in sources of origin of devices, units, machine tools, machines, equipment. This requires constructive, technological and other solutions that imply the improvement of kinematic schemes and the development of modern machines based on new principles for obtaining textile and other products with higher productivity and less noise and vibration.

These include, for example, rotor-mechanical, aeromechanical and self-spinning machines, pneumatic rapier machines, sewing machines without threading, etc.

Design changes aimed at reducing noise at the source of occurrence include changes in the stiffness or masses of individual elements; the use of sound-absorbing and sound-insulating materials, vibration-damped parts, assemblies, shock dampers in the combed head of draw frames, vibration damping of heel frames and frame, vibration isolation of the compressor, bearings of the spinning chambers of rotor spinning machines, casings of the combed head and head frame from the frame of the belt mechanism, belt machine movement of weaving looms due to the reduction of moving links, the use of plastic dividers of heald mechanisms (shedding, batanny, etc.), etc.

A list of specific measures to reduce the noise of weaving machines, twisting, spinning, belt and other machinery and equipment in the textile and light industry. Additionally, in weaving equipment, vibration damping of heald frames and machine beds, frames with bitumen is used, the installation of rivets in the body of the frames reduces noise to 20 dB at frequencies above 3000 Hz. In pneumatic spinning, the sound insulation of the spinning box drive gives a noise reduction of up to 6 dB, of the combing drums - up to 4 dB at frequencies above 150 Hz, vibration isolation of the spinning box support gives a noise reduction of up to 10 dB at frequencies of 500-4000 Hz.

For ring spinning and twisting machines, the introduction of powder rings and plastic runners for ballless silk spinning machines, spinning machines for lia and cotton twisting machines results in a sound level reduction of up to 5 dB , twisting single-process machines leads to a decrease in the sound level up to 6 dB; balancing of the main drums and friction clutches of cards, cartridges, spools, spools, etc., reduces the sound level to 3 dB.

The noise spectrum occupies a wide frequency band, it is especially significant in the 2000-5000 Hz range. Against the background of the continuous spectrum, there are discrete components, the main of which are the frequencies caused by mutual collision of the teeth, the action of errors in the meshing and their harmonics. The components of vibration and noise from deformation of the teeth under load have a discrete nature with a fundamental frequency equal to the frequency of the teeth reconnection. The frequency of the accumulated gear error is a multiple of the rotational speed. However, there are cases when the accumulated circumferential pitch error does not coincide with the rotational speed; in this case, there will be one more discrete frequency equal to the frequency of this error.

Oscillations are also excited with frequencies determined by the errors of the gear pair (axes misalignment, deviation from the center-to-center distance, etc.). The gearing is a system with distributed parameters and has a large number of natural vibration frequencies. This leads to the fact that in almost all modes of operation of the gearing is accompanied by the occurrence of oscillations at resonant frequencies. Reducing the noise level can be achieved by reducing the magnitude of the acting alternating forces, increasing the mechanical impedance at the places where the alternating forces are applied, reducing the transmission coefficient of sound vibrations from the places of origin to the places of radiation, reducing the vibrational speeds by improving the design of the oscillating body, reducing the radiation surface by increasing the internal friction of the material. wheels. For the manufacture of gears, carbon and alloy steels are mainly used. In those cases where it is necessary to ensure a less noisy operation of the transmission, non-metallic materials are used for the gears. Earlier, for this purpose, gears were made of wood and leather; currently they are made from textolite, wood plastics, polyamide plastics (including nylon).

Gear wheels made of plastics have a number of advantages over metal ones: wear resistance, noiseless operation, the ability to restore shape after deformation (at low loads), a simpler manufacturing technology, etc. Along with this, they have significant disadvantages that limit the area their application, relatively low strength of teeth, low thermal conductivity, high coefficient of linear thermal expansion. The most widely used for the manufacture of gears are thermosetting plastics based on phenol-formaldehyde resin. Durable products from them are obtained by introducing an organic filler into the material. As a filler, cotton fabric is used in the amount of 40-50% to the mass of the finished plastic or wood in the amount of 75-80%, as well as fiberglass, asbestos, fibers.

Laminated plastics are made of two types of textolite and wood-laminated plastic (chipboard). Products from these plastics are obtained in most cases by mechanical processing. Of thermoplastic resins, polyamide resins are widely used. They combine good casting properties, sufficiently high mechanical strength and low coefficient of friction. Gear wheels are made entirely of polyamides or in combination with metal. The use of polyamides for wheel rims with metal hubs makes it possible to reduce the harmful effect of the high coefficient of linear thermal expansion of polyamide resins on the accuracy of the gear transmission. Gear wheels made of polyamide materials cannot work for a long time at temperatures above 100 ° C and below 0 ° C, as they lose their mechanical strength. In order to increase the mechanical strength, plastic gears are reinforced by introducing special parts made of metal, fiberglass or other material with a strength higher than that of plastic. A reinforcing part is made from a sheet of 0.1-0.5 mm, reproducing the shape of a gear wheel, but much smaller in outer dimensions. The part is provided with holes and grooves for the passage of plastic and is installed in the mold so that it is completely covered with plastic. One or more of these parts are introduced depending on the thickness of the wheel. In a similar way, it is possible to reinforce not only spur wheels, but also globoidal wheels, as well as worms and cams.

Comparative tests of gears with plastic wheels and steel wheels, carried out by TsNIITMASH, confirmed the effectiveness of the use of plastics for noise reduction. Thus, the sound pressure level of steel-nylon pairs decreased in comparison with the sound pressure level of steel gear pairs by 18 dB. The increased loading of plastic gears causes less noise increase than steel gears. A comparative assessment of the noise of gear pairs of steel - nylon and nylon - kapron in all operating modes shows that to reduce the noise of gears, it is practically enough to replace one gear with a plastic one.

Local accumulated and single errors on the tooth profile, the location of which along the rotation of the wheel is random, also lead to low-frequency excitations of the systems. Defects in the operation of the worm gear of the gear cutting machine (inaccuracy of the step of the worm wheel, beating of the worm) causes the formation of elevations or transition areas (waves) on the surface of the teeth. The circumferential distance between the lines of irregularities corresponds to the pitch of the teeth of the indexing wheel of the machine, in connection with which the frequency of oscillations of this type depends on - the number of teeth of the indexing wheel of the gear cutting machine. Intense noise at high frequencies is caused by deviations from the involute, size, shape and pitch of the teeth. In these cases, the direction of action of the forces applied to the teeth; may differ from the direction of the theoretical action of the forces in ideal engagement. This leads to other modes of vibration. torsional, transverse with frequencies different from those considered.

As a result of applying these operations, the magnitude of cyclically acting errors is reduced, and thus noise generation is significantly reduced (by 5-10 dB). Prolonged grinding of teeth is not recommended, as it leads to unacceptable distortion of their profile. The elimination and reduction of cyclic errors in the gearing elements of the gear wheels is achieved by increasing the accuracy of manufacturing the profile of the teeth and the accuracy of the main pitch. The main pitch error should be less than deformation under load or thermal deformation and therefore will not lead to noticeable additional dynamic load. In some cases, it is also possible to reduce the harmful effect of cyclic errors by fitting the points of contact during testing and increasing the oil supply. The noise level will decrease if the wheel teeth are made as elastic as possible due to high correction or if they are modified along the profile height. A significant factor in improving the quality of gears is an increase in the precise and kinematic chain of running in and the supply chain of gear hobbing machines, as well as ensuring a constant temperature during the gear cutting process.

The magnitude of the cyclic error on the cut wheel decreases rapidly with an increase in the number of teeth of the gear wheel of the machine. Therefore, machines with a large number of teeth of the pitch wheel are used. When the gear mechanism operates at low speeds without openings and shocks, the frequency spectrum of the noise corresponds to the spectrum of the kinematic error of the gear train. The amplitudes of the components of the spectrum are determined in this case by the values of the admitted errors and the conditions for the emission of sound waves into the environment. When the gearing is operating with opening, which takes place at high speeds and variable loads, short-term pulses with wide frequency spectra occur, which contribute to an increase in the noise level in some cases by 10-15 dB. The magnitude of these pulses and the intervals between them can be variable. At a constant rotational speed, a doubling of the transmitted torque leads to a doubling of the linear deformations and the vibration amplitude. The radiated sound power is proportional to the square of the load. Therefore, noise and vibration depend on the load in about the same way as on the speed. Reducing transmission noise can be achieved by reducing the speed of the gears. The increase in the noise level of gears is also significantly influenced by assembly and operational defects. Mounting defects include increased bearing clearances, axle misalignment, non-maintenance of center-to-center distances of paired gears, inaccurate centering of them, runout of couplings among the operational factors affecting the noise of gears include a change in the transmitted torque (in particular, its fluctuations), wear, and lubrication modes and amount of lubricant. The change in the transmitted torque gives rise to the impact character of the interaction of the teeth in the engagement.

Lykov A.V., Lakhin A.M.The paper deals with the issues of noise reduction in the operation of gears. The analysis of the causes of noise and vibration in the operation of gears is carried out, the main design and technological methods of its reduction are determined.

Keywords:

gear, noise, wear.

Introduction

One of the most important performance indicators of gear transmissions is the noise of their operation. To the greatest extent, the increased noise of gears is characteristic of high-speed and heavily loaded gears, and this indicator in most cases also characterizes the reliability and durability of a mechanism with gears.

Main content and results of work

The noise level of gears depends on many factors, the main of which are the accuracy of the gearing, as well as the inertial and stiffness parameters of the system. Meshing errors are the causative agents of forced vibrations, and the inertial and stiffness parameters determine the natural vibrations of the system.

Due to the difference in the actual steps of the driving and driven wheels, there are blows of the mating teeth at the moment of their engagement. This causes an oscillatory process. The force of impact is in direct proportion to the difference between the steps of the engagement and the peripheral speed. Therefore, with an increase in the speed of rotation of shafts with gear wheels, the intensity of noise also increases.

Another reason for vibration and noise of gears is an instantaneous change in the rigidity of the gearing during the transition from two-pair to single-pair gearing, as well as an instantaneous change in the friction force acting between the working profiles of the teeth in the gearing pole. This causes vibration to propagate from the gears to all parts of the gear train and to generate sound waves.

When considering various forms of the contact spot of the teeth, the following typical cases can be distinguished (Fig. 1).

Figure 1 - Forms of contact spots of pairs of teeth

With the shape of the contact patch shown in Fig. 1, a, the gear transmission emits a quiet rustle and a low hum, which practically increases with an increase in the peripheral speed. In this case, the load is distributed evenly over the teeth, and the gear is considered good. With the shape of the contact patch (Fig. 1, b), a rustling is heard without a load, and a howl code with a load, increasing with an increase in the peripheral speed. Transmissions with the contact patch shape shown in Fig. 1, c, when operating without load, they emit a small knock, which develops into a howl and a frequent intermittent knock. In the case (Fig. 1, d), the transmission emits a frequent intermittent knock, which grows into a howl.

As can be seen from the shapes of the contact patch, the occurrence of noise is also facilitated by errors in the processing of the base holes of the gear housing, which causes misalignments of the shafts and bearings during the installation of the gear. This produces results similar to circumferential pitch and tooth direction errors.

Based on the reasons for the occurrence of noise in the operation of gears, it is possible to determine the main ways to reduce it, among which we will single out constructive and technological methods.

The constructive methods include methods associated with improving the design of gears, which eliminate shocks and vibrations when the pairs of teeth mesh.

To improve the smooth operation of the gear transmission, it is advisable to use helical, chevron and curved-tooth wheels instead of straight-toothed ones. Such gearing allows each tooth to engage not immediately along the entire length, usually with a shock, but gradually, smoothly, causing elastic microdeformations of the tooth sections, which compensate for errors in the circumferential pitch and direction of the tooth. The transition from spur to helical or curved tooth shape can reduce the noise level by 10-12 dB.

If the design of the gear train, for any reason, does not allow the use of oblique or curved tooth shape, noise reduction can be achieved by modifying the tooth shape. Two methods can be distinguished here: longitudinal modification and modification of the shape of the tooth profile. Longitudinal modification consists in a smooth change in the dimensions of the section of the tooth along its length, and most often comes down to the use of barrel-shaped teeth. In such gears, the tooth width decreases from the middle to the edges of the ring gear. This makes it possible to reduce the influence of the skew of the teeth due to the non-parallelism of the axes of the shafts and errors in the direction of the tooth, while the noise of the gear transmission is reduced by 3-4 dB.

Modification of the shape of the involute tooth profile is most often reduced to flanking the head and root of the tooth - directed removal of a part of the tooth profile for a more even arrangement of the teeth on the wheel and reducing the errors of the main pitch. This makes it possible to simplify the mounting of the gears in the transmission and to reduce the effect of deformation of the teeth during operation under load. Flanking replaces the contact of the teeth outside the line of engagement with the theoretically correct contact along the line of engagement, resulting in an increase in the contact patch of the teeth and a decrease in the noise level of the gear train.

It is also known that one of the factors determining the ability of a gear train to damp vibrations is the material of the wheel. By replacing at least one gear of the transmission with a wheel made of plastic, it is possible to significantly reduce the noise level, which is most achieved for high-speed transmissions, at resonant modes of operation and also at increased loads. It is possible to significantly reduce the noise of non-power transmissions by using steels with low surface hardness, metal powders, etc. A good combination in the gear transmission is the use of a gear made of high hardness steel and ground teeth with a wheel made of softer steel and shaved teeth.

For a quieter and smoother operation of the gear train under constant loading conditions, the minimum gear module should be assigned. This increases the end and axial overlap ratios for smoother operation and less engagement vibrations. At the same time, due to a decrease in the cross-section of the base of the engaging tooth, the level of permissible loads on the tooth decreases. To compensate for this disadvantage, the pitch diameter, the width of the ring gear, the use of multi-pair gearing, etc. should be increased.

Transmission noise can also be reduced by providing an integer overlap ratio. Tests have shown that an overlap factor of 2.0 provides the quietest transmission performance.

The noise of the gear train is affected by the load on the teeth. With an increase in the load factor, the dynamic load in the engagement decreases. At the same time, elastic deformations in the engagement increase, compensating for the inevitable errors of the tooth pitch, the smoothness of the transmission increases and the noise level decreases.

In addition, the noise is influenced by the design and material of the gear housing, which should prevent the propagation of sound into the environment. In general, cast housings are better at damping vibrations than welded housings. The quality of the lubricant is also determined by their ability to damp vibrations. Greater viscosity lubricants provide quieter operation, however, reducing the efficiency of the gear train. The type of gear shaft bearings also affects the transmission noise. Rolling bearings, working with an oil film at high speeds, provide a quieter operation of the gear train, while having, however, significantly higher frictional losses compared to rolling bearings. Therefore, rolling bearings are recommended for use in high speed transmissions.

Among the technological methods for reducing noise in the operation of gears, we will consider the main technological operations of finishing the teeth. As discussed earlier, the accuracy and quality of the tooth surfaces are the main influences on gear noise. Reducing gear noise for non-hardened gears can be most effectively achieved by shaving. At the same time, the errors of the circumferential pitch, the direction of the tooth and the deviation of the tooth profile are significantly reduced. For hardened gears, gear honing is the most effective and efficient method of noise control, which reduces transmission noise by 2-4 dB. Gear grinding provides the highest accuracy of the girth gear parameters and the lowest transmission noise. However, this method is the least productive.

conclusions

In general, the study found that the main source of noise in the operation of the gear train is shocks and vibrations arising from inaccuracies of the gear train elements. Defined the main design and technological methods of noise reduction in the operation of the gear transmission.

List of used literature

1. Kudryavtsev VN Gear transmissions. - M .: Mashgis, 1957. - 263 p.
2. Kosarev OI Methods of reducing excitation and vibrations in spur gear. / OI Kosarev // Bulletin of mechanical engineering. - 2001. - No. 4. S. 8-14.
3. Rudnitskiy VN Influence of geometrical parameters of gears on noise in gears / VN Rudnitsky. Sat. Art. The contribution of scientists and specialists to the national economy / BGITA - Bryansk, 2001. - pp. 125-128.