Created on:2021-04-22 09:13

High noise fault and diagnosis of zcbg3350 gear pump

High noise fault and diagnosis of zcbg3350 gear pump

① Function and fault phenomenon zcbg3350 gear pump is a low pressure and large displacement gear pump produced by a hydraulic component factory for users, which is mainly used for lubrication and cooling of marine gear box. During the installation test, it was found that the noise of the pump was high (about 91 dB), which affected the performance and service life of the system. At the same time, it was not conducive to the working and living environment of the ship. Other performances were basically normal, and the user said that it could not be used with the main engine.

② Cause analysis: firstly, the pitch error and profile error of the gear are too large, which may cause the gear meshing unsteadiness and high mechanical noise. Therefore, the gear grinding technology is adopted to adjust the gear meshing backlash and improve the gear machining accuracy, but after the test, the noise does not decrease significantly. Secondly, the axial and radial clearance of the assembled pump should be appropriately increased to reduce the pressure loss of the suction port of the user system (to prevent cavitation noise), but the effect is still not ideal. After many times of analysis and comparison tests, it is concluded that the flow area of the round unloading hole on the side plate (high pressure side) of the pump is too small, which leads to the poor unloading of trapped oil in the high pressure area, resulting in great periodic hydraulic impact and high noise. The most common way to solve the problem of trapped oil is to open the unloading groove on the side plate (or shaft sleeve) of the gear meshing part. When the closed volume becomes smaller, the unloading groove is connected with the oil discharge chamber to avoid the sharp rise of pressure. When the volume increases, the low-pressure unloading groove is connected with the oil suction chamber to avoid the formation of vacuum. Zcbg3350 gear pump is improved from cbg3200 middle and high pressure gear pump. The main change is that the tooth width is increased by 75% compared with cbg3200, so the trapped oil volume is increased by 75%, while the structural dimension of the unloading hole remains unchanged (Fig. C). When the meshing points (A and B) of the driving and driven gears are symmetrical relative to the meshing node, the tooth side clearance is the smallest, while the unloading hole and the trapped oil cavity on the high pressure side are the same Because of the small flow area, the unloading of trapped oil will not be smooth and complete, resulting in vibration and noise.

C1.jpg

③ Improvement scheme and effect According to the above analysis, two improvement measures have been taken for the structure of zcbg3350 pump: one is to change the side plate into a floating shaft sleeve, and Du bearing is installed in the shaft sleeve, which can better ensure the assembly coaxiality. Because the floating shaft sleeve is much thicker than the side plate, the matching surface with the inner hole of the pump is long, and the vibration caused by the impact is relatively small. At the same time, the depth of the unloading groove can not be limited by the thickness (because the thickness of the side plate is only 7mm, In order to ensure a certain strength, the unloading groove should not be too deep; second, the circular unloading hole should be changed into an asymmetric rectangular unloading groove with high and low pressure cavities (Fig. d), and the depth increased from 2.5mm to 6mm; the flow capacity of the unloading groove on the high pressure side was greatly improved, and the volume of the low pressure side increased, so the oil could be replenished from the low pressure unloading groove in time to avoid the formation of vacuum when the volume increased.

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After adopting the above improvement scheme, the noise value is reduced to about 82db by simulating the user's working conditions and multiple measurements at different positions, which can meet the user's requirements of the host. It is proved that changing the shape of the unloading groove and increasing the unloading flow area are correct to reduce the noise caused by the hydraulic impact of the gear pump.

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