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Short cylindrical roller bearings are known for their high rotational precision, accurate fit, and ability to handle primary radial loads. They are widely used in large precision machine tools and finishing equipment. In recent years, this type of bearing has become one of the key products produced by Luo Axis Group’s large-scale bearing business unit, contributing significantly to its revenue—accounting for about one-third of the unit’s output value. However, the production process still relies on outdated methods, resulting in a low matching qualification rate (only 60%), which leads to excessive data processing, wasted working hours, and ultimately affects the economic benefits of the business unit.
The selection of short cylindrical roller bearings typically includes single-row, double-row, and four-row types. Despite these classifications, they share common layout features such as straight raceways and welded retainers. The challenges involved are also quite similar, meaning that the optimization process for one type can be applied to others. To explore this, the “32672†model, which has the highest annual output, was chosen as the subject for process layout optimization. This approach aims to achieve broader economic benefits across different bearing types.
However, several issues have been identified in the current production process:
1. The inner and outer rings of the “32672†bearing are made from Gcr15simn steel, with a large size range. The heat treatment quenching process is difficult to control, leading to deformation and ovality after quenching, leaving no grinding allowance and causing over-grinding of the raceway.
2. Due to the uneven composition and residual stress caused by quenching-induced ovality, the raceway surface becomes unstable during grinding, making it hard to maintain within the required tolerance limits.
3. The aging of the machine tools results in low spindle precision, leading to poor surface finish after rough grinding, which causes significant deviations after final grinding.
4. The skill level of the workers does not match the operational requirements, resulting in over-grinding of the raceway, affecting the installation clearance and causing instability in the bearing's operation.
These issues have led to a matching qualification rate of only 60%, increasing unnecessary repair work, processing time, material waste, and overall costs.
To address these problems, the original processing technology for the “32672†bearing has been optimized and improved through the following methods:
1. Collaborating closely with the heat treatment plant to control deformation and adjust the raceway retention based on the shortening data provided. This ensures sufficient grinding allowance after heat treatment.
2. Adding an additional tempering process to eliminate residual stresses and stabilize the raceway scale.
3. Upgrading the machine tool equipment to improve spindle rotation accuracy and control feed rates, enhancing the surface finish of the raceway and preventing over-grinding.
4. Adjusting the process layout to focus on the inner ring raceway, which is most affected by deformation. When over-grinding occurs, a method involving undercutting the housing and adjusting the middle diameter of the retainer hole is used to ensure proper matching.
5. Tightening the raceway finishing process to unify the scale within a small range, reducing variation between batches and further improving the matching qualification rate.
By implementing these improvements, the matching qualification rate of the “32672†short cylindrical roller bearing increased from 60% to over 96%. This significantly reduced the repair rate, saved man-hours and resources, and lowered overall production costs.
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Method to Improve the Matching Qualification Rate of Short Cylindrical Roller Bearings
Source: China Bearing Network | Time: 2014-04-24
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