The three main factors traditionally used to measure the performance of a reducer are: load capacity, fatigue life and operating accuracy, and transmission noise is often ignored.With the successive promulgation of the ISO14000 and ISO18000 standards, the importance of controlling the transmission noise of the reducer is becoming more and more obvious. Industrial development and demand have stricter requirements on the transmission error of the reducer, and the requirements for noise control are also increasing. high.
At present, the noise forming factors of the reducer can be roughly analyzed from the design, manufacture, installation, use and maintenance of internal and external gears.
Design reasons and countermeasures
1 Accuracy grade of internal gear of reducer
When designing a reducer, the designer often considers economic factors to determine the gear accuracy grade as economically as possible, ignoring that the accuracy grade is a mark of gear noise and backlash.The American Gear Manufacturers Association has conducted a lot of gear research and determined that high-precision gears produce much less noise than low-precision gears.Therefore, when conditions permit, the accuracy level of the gear should be increased as much as possible, which can reduce transmission errors and noise.
2 Internal gear width of reducer
When the transmission space of the reducer allows, increasing the gear width can reduce the unit load under constant torque.Reduce gear tooth deflection, reduce noise excitation, thereby reducing transmission noise.The research of German H Opaz shows that when the torque is constant, the noise curve gradient of small tooth width is higher than that of large tooth width.At the same time, increasing the width of the gear can also increase the bearing capacity of the gear and increase the bearing torque of the reducer.
3 Tooth pitch and pressure angle of the internal gear of the reducer
The small tooth pitch can ensure that there are more gear teeth in contact at the same time, the gear overlap increases, the deflection of a single gear is reduced, the transmission noise is reduced, and the transmission accuracy is improved.The smaller pressure angle is because the gear contact angle and lateral overlap ratio are relatively large, so the running noise is small and the accuracy is high.
4 Selection of internal gear modification coefficient of reducer
Correct and reasonable selection of the modification coefficient can not only make do with the center distance, avoid gear undercutting, ensure that the concentric condition is met, improve the transmission performance of the gear, increase its load-bearing capacity and increase the service life of the gear, but also effectively control the backlash, temperature rise and noise.In the closed gear transmission, for gears with hard tooth surfaces (hardness: 350HBS), the main failure mode is tooth root fatigue fracture. This gear transmission design is generally carried out according to the bending fatigue strength, and the modification coefficient is selected. It should be ensured that the meshing gear teeth have equal bending strength.For gears with soft tooth surfaces (hardness #lt; 350HBS), the main failure mode is fatigue pitting. The design of this gear transmission is generally carried out according to the contact fatigue strength. When selecting the modification coefficient, ensure that the Possibly large contact fatigue strength and fatigue life.
The restrictive conditions for a reasonable choice of displacement coefficient are:
①Ensure that the cut gear does not undercut;
② To ensure the smoothness of gear transmission, the coincidence degree must be greater than 1, and the general requirement is greater than 1.2;
③Ensure that the tooth top has a certain thickness;
④When a pair of gears are engaged in transmission, if the involute of the tooth tip of one gear is in contact with the transition curve of the tooth root of the other gear, since the transition curve is not an involute, the common normal of the two tooth profiles at the contact point cannot pass through a fixed Nodal points, which cause changes in the transmission ratio, and may also make the two wheels stuck. This kind of "transition curve interference" must be avoided when selecting the displacement coefficient.
5 The internal gear tooth profile trimming (trimming and root trimming) and tooth top chamfering of the reducer
Cut the tooth profile of the tooth tip into a slightly convex shape than the correct involute curve.When the gear tooth surface is deformed by an external force, interference with the gear meshing with it can be avoided, noise can be reduced, and the gear life can be prolonged.It should be noted that excessive trimming is not allowed. Excessive trimming is equivalent to increasing the tooth profile error, which will adversely affect the meshing.
6 Gear acoustic radiation characteristics analysis
When selecting gears with different structures, a sound radiation model is established for the specific structure, dynamic analysis is performed, and the gear transmission system noise is pre-evaluated.In order to meet the different requirements of users (the place of use, whether unmanned operation, whether it is in the urban area, whether there are specific requirements for ground and underground buildings, whether there is noise protection, or no other specific requirements).
7 Speed of power source of reducer
According to the test of the reducer under different speed conditions, the noise will increase as the input speed of the reducer increases.
8 Reduced case body structure
Experimental research shows that the use of cylindrical boxes is beneficial to shock absorption. Under the same other conditions, the noise level of cylindrical boxes is 5dB lower than other types of boxes on average.Carry out resonance test on the gear box body to find out the resonance position and add appropriate ribs (plates) to improve the rigidity of the box body, reduce the vibration of the box body, and achieve noise reduction.In multi-stage transmission, the change of the instantaneous transmission ratio is required to be as small as possible to ensure smooth transmission, low impact and vibration, and low noise.
Manufacturing reasons and countermeasures
1 Influence of internal gear error of reducer
The tooth profile error, base pitch error, tooth direction error and ring gear radial runout error in the gear manufacturing process are the main errors that cause the transmission noise of the planetary reducer.It is also a problem in controlling the transmission efficiency of the planetary reducer.The tooth profile error and tooth direction error are briefly explained.
For gears with small tooth profile errors and small tooth surface roughness, under the same test conditions, their noise is 10dB lower than that of ordinary gears.Gears with small pitch error, under the same test conditions, the noise level is 6-12dB lower than ordinary gears.But if there is a pitch error, the influence of the load on gear noise will be reduced.
Tooth direction error will cause transmission power not to be transmitted in the full tooth width. This or that end surface of the steering tooth in the contact area will increase the deflection of the tooth due to the local force, resulting in an increase in the noise level.But under high load, tooth deformation can partly compensate for tooth direction error.
2 Assembly concentricity and dynamic balance
The misalignment of the assembly will result in unbalanced shafting operation, and due to the loose and tight half of the tooth meshing, the noise will increase.The unbalance during assembly of high-precision gear transmission will seriously affect the accuracy of the transmission system.
3 Hardness of the internal tooth surface of the reducer
With the development of gear hard tooth surface technology, its large load-bearing capacity, small size, light weight, and high transmission accuracy make its application fields increasingly extensive.However, the carburizing and hardening used to obtain the hard tooth surface deforms the gear, resulting in increased gear transmission noise and shortened service life.In order to reduce noise, the tooth surface needs to be finished.At present, in addition to the traditional grinding method, a hard tooth surface scraping method has been developed to reduce the impact of gear meshing and meshing by correcting the tooth tip and tooth root, or reducing the tooth profile of the active and passive wheels. , Thereby reducing gear transmission noise.
4 Verification of reducer system index
The machining accuracy of the parts before assembly and the selection method of the parts (complete interchange, group selection, single-part selection, etc.) will affect the accuracy level of the system after assembly, and the noise level is also in the affected range Therefore, the verification (or calibration) of the various indicators of the system after assembly is critical to the control of system noise.
Installation reasons and countermeasures
1 Vibration reduction and blocking measures
When the reducer is installed, try to avoid resonance between the body, the foundation support and the connecting parts, resulting in noise.In the reducer, one or several gears often resonate in a certain speed range. In addition to design reasons, the resonance position has not been found out during installation without empty test.And it is directly related to taking corresponding damping or blocking measures.For some reducers that require low transmission noise and vibration, base materials with high toughness and high damping should be selected to reduce the occurrence of noise and vibration.
2 Adjust the geometric accuracy of parts
Because the geometric accuracy of the installation does not meet the requirements of the standard, the reducer components resonate and generate noise. This should be directly related to improving the installation process, increasing the tooling, and ensuring the overall quality of the assembly personnel.
3 loose parts
During installation, due to the loosening of individual parts (such as bearing pre-tensioning mechanism, shafting positioning mechanism, etc.), the system is not positioned correctly, the abnormal position is engaged, the shafting moves, and vibration and noise are generated.This series needs to start from the design structure, try to ensure the stability of the connection of each organization, and adopt a variety of connection methods.
4 The transmission parts are damaged
During installation, improper operation damages the transmission parts, resulting in inaccurate or unstable motion of the system; high-speed moving parts cause oil film vibration due to damage; artificial imbalance of moving parts; vibration and noise are caused.These reasons must be noted and avoided as much as possible during the installation process.Damaged parts that cannot be repaired must be replaced to ensure that the system obtains a stable noise level.
Reasons for use and maintenance and countermeasures
Although the correct use and maintenance of the reducer can not reduce the system noise level and ensure the transmission accuracy, it can prevent the deterioration of its indicators and increase the service life.
1 Internal cleaning
The cleanliness of the internal parts of the reducer is the basic condition to ensure its normal operation. Any entry of impurities and dirt will affect and damage the transmission system and cause noise.
2 working temperature
Ensure the normal working temperature of the reducer, avoid the deformation of parts due to excessive temperature rise, and ensure the normal meshing of the gears, thereby preventing the increase of noise.
3Timely lubrication and correct use of oil
Unreasonable lubrication and incorrect use of lubricating grease will cause immeasurable damage to the reducer.At high speeds, gear tooth surface friction will generate a lot of heat, improper lubrication will cause damage to the gear teeth, affect accuracy, and increase noise.The design requires the gear pair to have an appropriate clearance (the clearance between the non-working surfaces of the meshing gear teeth to compensate for thermal deformation and store lubricating grease).The correct use and selection of lubricating grease can ensure the safe and effective operation of the system, delay the deterioration trend, and stabilize the noise level.
4 Correct use of reducer
The correct use of the reducer can avoid damage and damage to the parts to the greatest extent and ensure a stable noise level.The noise of the reducer will increase with the increase of the load, so it should be used within the normal load range.
4Regular maintenance and maintenance
Regular maintenance (oil change, replacement of worn parts, loose parts of fasteners, removal of internal debris, adjustment of the gap of each part to the standard specified value, verification of various geometric accuracy, etc.) can improve the reducer's resistance to noise level degradation Ability to maintain a stable state of use.
Reducer transmission noise control is a system engineering, which involves the whole process of transmission system (gear, box, coupling, bearing, etc.) design, manufacturing, installation, use and maintenance until update. It is not only for designers, manufacturers , Also put forward many requirements for the installation, use and maintenance personnel, any of the above links are not effectively controlled, and the gear transmission noise control will be invalidated.