Among the gold cutting equipment used in our factory, there is a M1083A centerless cylindrical grinder manufactured by Haining Machine Tool Plant. This machine is known for its high rigidity, excellent production efficiency, and reliable performance, making it suitable for mass production. The grinding wheel and the front and rear bearings of the guide wheel are equipped with membrane feedback hydrostatic bearings, which feature a symmetrical structure with four oil chambers. Recently, the machine experienced issues with the main shaft bearing of the grinding wheel spindle, but we successfully repaired it. Below is a detailed summary of the failure causes identified during the repair process and the subsequent steps taken to fix the hydrostatic bearings.
**1. Analysis of Failure Causes**
The primary cause of the grinding wheel spindle (spindle) failure was mainly due to two factors: blockage in the lubricant pump's oil circuit and blockage in the main oil circuit of the bearing chamber. These issues directly led to insufficient lubricating oil entering the bearing chamber or low oil pressure, resulting in the bearing failing to decelerate properly when the spindle started.
The blockage in the oil delivery circuit was primarily caused by the oil filter. The M1083A model has three oil filters on the delivery line, with the fine filter being particularly prone to clogging or even melting, which reduced the delivery pressure and caused inadequate oil flow and low pressure. In addition, the electrical interlock system of the spindle starter failed, leading to a loss of static pressure in the bearing.
The blockage in the oil path into the bearing chamber mainly occurred at the diaphragm feedback throttle gap. When this clearance became severely blocked, the oil flow into the chamber dropped significantly, causing very low oil pressure. As a result, the spindle could not float properly within the bearing, making it difficult or impossible to move when the grinding wheel was engaged. This condition also caused the hydrostatic bearing pair to fail.
Here is a diagram of the M1083A spindle:
1.2-Ø105mm clearance with the bearing 0.055 ~ 0.060mm
2.2-Ø105mm ellipticity, taper tolerance 0.002mm
M1083A spindle frame spindle diagram
The parts of the M1083A wheel frame spindle are shown on the right.
**2. Repair Process**
After removing the grinding wheel spindle, we found that the main issue was in the front bearing, while the rear bearing showed no signs of damage. First, we used a micrometer to accurately measure the front spindle journal. The actual size was Ø105-0.008-0.007mm. Using an inner diameter dial gauge, we measured the inner diameter of the bearing as Ø105+0.048+0.051mm. This resulted in a fitting gap of 0.055~0.059mm. According to the static clearance requirement of 0.006D (where D is the nominal size of the spindle journal), the technical requirement for the M1083A spindle journal (D = 105mm) is 0.063mm. The design specification requires a clearance of 0.055–0.060mm. After measurement, the clearance met the requirements. The roundness error of the spindle journal was 0.001mm, which is within the 0.002mm tolerance specified on the drawing, ensuring the precision and rigidity of the spindle components.
From the removed spindle, there were no visible scratches on the surface. We then performed surface polishing on the spindle journal using a C630-1 lathe to achieve an Ra0.8μm finish. After polishing, the dimensions were measured again as Ø105-0.010-0.008mm. If there were any noticeable flaws on the spindle journal, it would have been ground to ensure proper surface roughness. If after grinding, the clearance between the spindle and the bearing was not met, the spindle journal would have been electroplated and repaired to meet the required clearance, otherwise it would have seriously affected the rigidity and normal operation of the equipment.
We checked the bearing bore and found signs of friction on the front bearing hole. However, the accuracy of the spindle journal was within the acceptable range, eliminating the possibility of spindle misalignment. At the same time, we inspected the lubrication oil path and found it to be severely blocked.
Once the spindle journal reached the required surface roughness, the repair of the bearing bore became more complex and challenging, with less certainty in achieving the desired accuracy. To address this, we designed a test spindle with a diameter of Ø105+0.038+0.040mm based on the spindle journal’s size of Ø105-0.010-0.008mm and the required clearance of 0.063mm between the spindle and the bearing. The taper and roundness tolerances were set to 0.002mm, serving as a final inspection tool. We also designed and manufactured a mandrel of Ø105+0.038+0.040mm, which could be smoothly inserted into the bearing bore. Once the mandrel made uniform contact with the inner bore, the repair of the bearing bore was essentially complete.
Finally, we used an inner diameter dial indicator to accurately verify the inner diameter of the bearing bore. Using a mandrel to test the inner hole offers several advantages. It is smaller and easier to handle during the grinding process, allowing for real-time measurements. Unlike the larger and heavier spindle, which is difficult to move, the mandrel helps avoid unnecessary damage to the spindle. During the grinding of the bearing inner bore, careful attention was given to measurements, repeated studies, and precise checks until all requirements were satisfied.
It should be noted that during the repair of dead bearing holes, the inner bore must not be scraped with a spatula, as this can easily lead to excessive coaxiality and roughness, and may result in damage to the spindle when the equipment is reassembled. After the repair of the spindle journal and bearing holes was completed, all hydraulic components and oil pools in the lubrication system had to be thoroughly cleaned. In particular, the membrane feedback throttle valve needed to be disassembled and cleaned repeatedly with clean kerosene.
Under the conditions of maintaining the original gap G0=0.07mm and the lubrication system supply pressure P=1MPa, the four outlet pressures should be equal. If there is no blockage, the spindle should be able to turn smoothly by hand to start the grinding wheel spindle. Otherwise, the film feedback system must be re-disassembled and cleaned.
After starting the grinding wheel spindle, it should not be rushed into operation. Instead, it should run idle for at least 4 hours continuously without any abnormalities before being put into production. At this point, the hydrostatic bearing failure has been successfully resolved.
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