The traditional two main factors to measure the transmission performance of gears are load capacity and fatigue life, and transmission noise and transmission accuracy are often ignored. With the promulgation of ISO14000 and ISO18000 standards, the importance of controlling gear transmission noise is becoming more and more obvious. The requirements of industrial development and demand on transmission error of high-precision equipment are becoming more and more strict (gear transmission backlash). At present, the known formation factors of gear noise can be analyzed from the aspects of design, manufacturing, installation, use and maintenance.
Design reasons and Countermeasures
1. Gear accuracy grade
In the design of gear transmission system, designers usually consider the economic factors and determine the gear accuracy grade as economically as possible, but they don't know that the accuracy grade is the mark of gear noise level and backlash. Through a lot of gear research, American Gear Manufacturing Association has determined that the noise generated by high-precision gear is much lower than that of low-precision gear. Therefore, if conditions permit, the accuracy level of gear should be improved as much as possible to reduce gear noise and transmission error.
2. Gear width
When the gear transmission system allows, increasing the tooth width can reduce the unit load under constant torque. It can reduce the deflection of gear teeth and noise excitation, so as to reduce the transmission noise. The results of the research by H. oppaz in Germany show that the noise curve gradient of small tooth width is higher than that of large tooth width when the torque is constant. At the same time, increasing the tooth width can increase the bearing capacity of the gear.
3. Pitch and pressure angle
Small pitch can ensure that more teeth contact at the same time, increase gear overlap, reduce single gear deflection, reduce transmission noise and improve transmission accuracy. Because the contact angle and lateral overlap ratio of gears are relatively large, the small pressure angle has low noise and high precision.
4. Running speed
According to the experimental research of hopatz in Germany, the noise level increases with the increase of gear speed.
5. Gearbox structure
The experimental results show that the cylindrical box is beneficial to the vibration reduction. Under the same other conditions, the noise level of the ordinary gear box is 6 dB higher than that of the cylindrical box. The vibration and noise can be reduced obviously by testing the resonance of the gear box, finding out the resonance position and adding appropriate ribs (plates). In multi-stage gear transmission, the change of instantaneous transmission ratio should be as small as possible to ensure stable transmission, small impact and vibration, and low noise.
6. Analysis of gear acoustic radiation characteristics
When choosing gears with different structures, the acoustic radiation model is established for the specific structure, and the dynamic analysis is carried out, and the noise of gear transmission system is evaluated in advance. In order to meet the different requirements of users (the place of use, whether it is unmanned, whether it is in the urban area, whether there are specific requirements for ground and underground buildings, whether there is noise protection, or there are no other specific requirements).
Manufacturing reasons and Countermeasures
1. Error influence
In manufacturing process, tooth profile error, pitch error and tooth alignment error are the main errors that cause transmission noise. It is also a problem that the accuracy of gear transmission is difficult to guarantee.
Under the same test conditions, the noise of gears with small profile error and small tooth surface roughness is 10 dB lower than that of ordinary gears. Under the same test conditions, the noise level of gears with small pitch error is 6-12db lower than that of ordinary gears. But if there is pitch error, the influence of load on gear noise will be reduced.
The tooth alignment error will lead to the transmission power is not transmitted through the whole tooth width. The contact area turns to this or that end face of the tooth, and the tooth deflection increases due to the local force, resulting in the increase of the noise level. However, under high load, the tooth deformation can partially compensate for the tooth alignment error.
The generation of gear noise is directly related to transmission accuracy.
2. Assembly concentricity and dynamic balance
The misalignment of the assembly will lead to the unbalance of the shafting operation, and the noise will be aggravated due to the loose half of the meshing and the tight half of the gear theory. The unbalance of high precision gear transmission assembly will seriously affect the accuracy of transmission system.
3. Tooth surface hardness
With the development of gear hard tooth surface technology, its large bearing capacity, small size, light weight, high transmission accuracy characteristics make its application field more and more widely. However, in order to obtain the hard tooth surface, the carburizing and hardening method makes the gear deform, which leads to the increase of gear transmission noise and the shortening of its service life. In order to reduce the noise, it is necessary to finish the tooth surface. At present, in addition to the traditional gear grinding method, a hard tooth surface scraping method is developed. By modifying the tooth top and root, or reducing the tooth profile of the driving and driving gears, the impact of gear engagement and meshing out is reduced, so as to reduce the gear transmission noise.
4. System index verification
Before assembly, the machining accuracy of parts and the selection method of parts (complete exchange, group selection, single piece selection, etc.) will affect the accuracy level of the system after assembly, and its noise level is also within the influence range. Therefore, it is very important to verify (or calibrate) various indicators of the system after assembly to control the system noise.
Installation reasons and Countermeasures
1. Damping and blocking measures
When installing the gear transmission system, the resonance between the fuselage and the foundation support and the connecting parts should be avoided as far as possible, which may cause noise. The resonance of one or several gears often occurs in gear transmission system in some speed range. In addition to the design reason, the resonance position is found out without empty test during installation. It is directly related to take corresponding measures of vibration reduction or blocking. For some gear transmission systems (such as testing instruments) which require low transmission noise and vibration, high toughness and high damping base materials (such as epoxy resin mortar foundation materials developed by Metallurgical Design and Research Institute) should be selected to reduce noise and vibration.
2. Geometric accuracy adjustment
Because the geometric accuracy of the installation does not meet the requirements of the standard, the transmission system resonance, resulting in noise, which should be in the improvement of the installation process, increase tooling, to ensure the overall quality of the assembly personnel has a direct relationship.
3. Parts are loose
During installation, due to the looseness of individual parts (such as bearing preloading mechanism, shafting positioning mechanism, shifting fork limiting mechanism, etc.), the system positioning is not accurate, abnormal position meshing, shafting moving, resulting in vibration and noise. This series should start from the design structure, try to ensure the stability of the connection of each mechanism, and adopt a variety of connection methods.
4. The transmission parts are damaged
During installation, the transmission parts are damaged due to improper operation, which leads to inaccurate or unstable movement of the system; high-speed moving parts cause oil film vibration due to damage; dynamic imbalance of moving parts caused by human; all of these produce vibration and noise. These reasons must be paid attention to and avoided as far as possible in the installation process. The damaged parts that cannot be repaired must be replaced to ensure the stable noise level of the system.
Use and maintenance reasons and Countermeasures
The correct use and maintenance of gear transmission system can not reduce the noise level of the system and ensure the transmission accuracy, but it can prevent the deterioration of its index and increase the service life.
1. Internal cleaning of transmission system
The internal cleaning of the transmission system is the basic condition to ensure the normal operation of the gear. Any impurities and dirt will affect and damage the gear transmission system, eventually leading to the generation of noise and damage to the transmission system.
2. Working temperature of the system
Ensure the normal working temperature of the transmission system, prevent the deformation of the system due to excessive temperature rise, resulting in abnormal meshing, and prevent the increase of noise.
3. Timely lubrication and correct use of oil
Careless lubrication and incorrect use of lubricating grease will cause immeasurable damage to the system. To ensure that the system is lubricated timely and correctly, the system can be kept in a certain range of noise level and the deterioration trend can be delayed. High speed gear, tooth surface friction will produce a lot of heat energy, improper lubrication, will lead to tooth damage, affect accuracy, noise will also increase. In the design, the gear pair should have proper clearance (the clearance between the non working surfaces of meshing teeth to compensate for thermal deformation and storage of lubricating grease). The correct use and selection of lubricating grease can ensure the safe and effective operation of the system and stabilize the noise level.
4. Correct use of gear motion system
Using it according to the normal operation sequence of the system can avoid the damage and damage of the system to the maximum extent, and ensure the stable noise level. Use the system in the normal load range of the system, because the transmission noise of the gear transmission system increases with the increase of the load.
5. Regular maintenance
Regular maintenance (oil change, replacement of worn parts, fastener loose parts, removal of impurities in the system, adjustment of the clearance of each part to the standard value, verification of geometric accuracy, etc.) It can improve the ability to resist the degradation of noise level and maintain the stability of the system.