1、 Factors causing spindle failure

Due to long-term operation, the centerless grinder experiences wear on the five tiles and spindle, resulting in a decrease in surface roughness and geometric accuracy, as well as a decrease in oil film rigidity. This causes the spindle to experience radial runout under stress, resulting in the formation of vibration patterns in the processed workpiece. Due to the decrease in the viscosity of the lubricating oil, the bearing is in a boundary lubrication state. The larger bearing load causes abrasive particles to scratch the lubricating oil film on the working surface of the friction pair, resulting in high stress solid-phase contact and strong deformation. The contact area has a high temperature rise and local solid-phase welding occurs. Then, the soft surface and low strength bearing alloy is locally torn off, and the torn off part of the bearing alloy adheres to the shaft neck, causing adhesive damage, commonly known as "shaft hugging".

2、 How to repair the spindle and bearing shell?

1. Repair of the spindle

For the worn spindle, when the wear amount is small and does not exceed the thickness of the ammoniated layer, the working surface can be directly ground to restore the spindle accuracy and surface roughness. In addition, when the wear is large, the chrome plating process can be used to restore the original size. After precision grinding and calendering treatment, the dimensional accuracy and surface roughness can be ensured. The trimming of the center hole at the shaft end is often overlooked, and grinding the center holes at both ends of the spindle is an important process related to repairing the spindle accuracy. When repairing the center hole of the spindle on the grinder, one hand should pinch the spindle and the other hand should gently adjust the tailstock handwheel. The hand-held spindle should be loose and tight to achieve uniform grinding of the center hole. After the grinding of one end of the center hole is completed, the other end is ground again. After multiple repeated corrections such as grinding, measurement, and re grinding, the spindle's working surfaces meet the required technical standards.

2. Repair of bearing shells

During the scraping and grinding process of the coarse scraping bearing, a shallow scraping process is used, with a very light blade. Firstly, the main shaft is used as the reference to roughen it, and the contact points are first smoothed out evenly, with a point size of 25mm2 between 14 and 16 points. Scratching the knife marks should be done in a cross pattern, so that the dots are evenly distributed.

3、 Scraping and adjustment of bearing shell (using centering process kit)

After even spots appear on the bearing shell, it needs to be finely scraped again. It can play a role in centering and aligning in each matching research, thereby shortening the adjustment time and overcoming the problem of side deviation caused by scraping the bearing shell. During scraping and scraping, install the pre sweetened 89 bearing bush and the elegant bearing screw into the box hole according to the design requirements, pay attention to the mutual position and rotation direction, then adjust the gap to make it tight and loose in the same direction, and rotate the main shaft according to the rotation direction of the grinding wheel. After lapping, remove all the surface blocks for fine scraping, and then repeatedly grind and scrape until the requirements are met. During fine scraping, shallow scraping is necessary, rather than deep scraping, and the points should not be too fine. The bearing bush should be scraped lower at the big end of the oil wedge to form an oil wedge. Although deep scraping can store oil, it can cause irritation and prevent the formation of the maximum dynamic pressure lubricating oil film.

4、 Assembly and adjustment of grinding wheel holder spindle

In order to ensure the accuracy of grinding processing, the clearance between the spindle bearing shell at the front end (the end where the grinding wheel is installed) should be slightly smaller than that at the rear end, and the spindle should be flexible and unobstructed during rotation

5、 Conclusion

Centerless Grinding machines