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Importance of Cleanliness on Gear Box

Categories: Latest NewsRelease time: 2017-09-15 09:06:00
Source: ZHAOWEIEditor: ZHAOWEI Author: ZHAOWEI

 The function of gear box is to reduce the speed and increase the torque between drive motor and driven device. The quality of gear box will affect the normal operation of the whole transmission system. Therefore, the performances of gear box will play a significant role to keep the drive system in the good working condition.

 Nowadays there still have differences in performance for the machinery products from China and the other developed countries. Those differences are mainly in the basic components, such as hydraulic parts with big volume, low performance and serious oil leakage. On the contrary, the imported mechanical products still keep the excellent performance with the stable quality and low oil leakage after a long-term operation. The main problem is to ignore the importance of cleanliness during the assembly process, which will cause the bad quality and problems like low running rate, short lifetime, etc.

 Since the cleanliness is not concerned seriously during the assembly in China, it results in the performance difference between the domestic products and imported one. Although the processing technology is imported from the oversea countries with the same standard and requirements, the final performance is still much lower than the imported one. The problem of poor cleanliness is mainly from the iron scraps, impurities in lubricant and the other foreign matters.

 It seems that the cleanliness is a simple issue. But it will bring a lot of problems or faults which will lead to serious influence on the performance of gear box. Here with the explanations for the causes, effects and improvements on the bad cleanliness as follows:

 1. Possible causes on the poor cleanliness.

 1.1 Bad purity of gear oil. This is the direct reason causing the bad cleanliness. The oil will move to meshing and bearing areas when gear box starts working. Consequently, the impurities will also get to those areas with movement of the gear oil, which will shorten the lifetime of the gearbox. Hence we propose to use the special filter to remove the foreign substances before applying the lubricant.

 1.2 The iron scraps are not removed completely during the machining process. The operator carelessly forgets to clean the scrap on the parts when moving to next process on the one hand, which will cause the defects like pitting, scratch, etc. On the other hand, it is not easy to clean the iron scrap in the dead areas like internal hole, which will also bring the scarp into the working areas to harm the parts.

 1.3 Some areas in the oil channels are welded after acid pickling. It is not allowable to weld those areas generally. Otherwise, the welding residues will enter into the gearbox with movement of gear oil.

 1.4 The finished products are post-processed again with the same cause and problem as above.

 1.5 The parts are not stored in good orders and conditions after cleaning. This also allows the foreign matters like dust to get into the important part surface which will affect the mating dimensions accordingly.

 1.6 Poor sealing. To improve the performance of sealing, we can consider the 2 ways in the following. First, we could add V-shape seal ring on the input and output shafts in the design. Second, we could improve the surface roughness during the machining process.

 1.7 The painting can not withstand the high temperature. The coating inside the case can not bear that hot condition and will peel off into the lubricant when the gear box works in the high temperature. The peeling outside the case will also affect the appearance.

 1.8 Sealing glue falls into the housing. The glue will be squeezed into the box and move into the gear oil if there is too much glue in the joints.

 2. Effects of cleanliness on the gear box

 2.1 Effect on the lubricant and pipeline fittings. The diameter of oil hole will be small generally which is to increase the capacity of the oil injection. However, this small hole is easy to be blocked by the iron wraps and impurities which will stop the lubricant moving to the working areas for their normal function. The bad cleanliness will also have influence on the valve body. The foreign substance will also damage the surface of valve core to affect its sensitivity and reduce the working life.

 2.2 Effect on gear and meshing. The lubricant will brings the impurities into the meshing surfaces to destroy the roughness of gear surface which will reduce the mechanical performance and affect the smoothness of transmission to easily cause the failures like pitting, scoring, abrasion to shorten the lifespan of gears.

 2.3 Effect on the bearings. There will be an oil film on the bearing surfaces under the normal lubricating condition which will bring no direct contact between the bearings. This coating will reduce the friction and abrasion between the bearings to improve the performance and prolong the lifetime accordingly. However, the impurities will move to bearing surfaces between roller and inner/outer rings to increase the friction to cause the rotary defect if there are the foreign matters in the gear oil. Especially on the condition of heavy load and high speed, this will generate the pitting or other failure modes to affect the service life.

 2.4 Effect on the thread bolts. It will affect the tightening torque of the bolts if the foreign matters like the sealing glues or iron scrap enter into the thread hole. This will result in the two unexpected effects. One is that the tightening force is too large to damage the threads. The other is that the force is not enough to tighten up the bolts to give rise to the oil leakage. 

 3. Methods of improving the cleanliness on gear box.

 3.1 Use the special cleaning equipments like the ultrasonic cleaning machine.

 3.2 Strictly control the cleaning process and its post processes. We should design the reasonable cleaning procedures for the different products based on the real production conditions. The parts should be stored in the clean and good condition with the correct method after cleaning.

 3.3 The parts can not be further processed after cleaning or assembly, such as polishing.

 3.4 The parts should be cleaned twice. For the whole gear box, all parts should be cleaned before test. They should be cleaned again after test. The purpose is to get rid of all kinds of foreign matters like the iron scraps from both the machining process before test and gear meshing during the test. For the single parts, they should be cleaned respectively before storage and before assembly.

 3.5 We could add a magnet to attract the iron scrap in the proper place for a periodic cleaning when those scraps from the gear meshing can not be removed during the real operation.

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