Keywords: radial spherical plain bearing; self-lubricating bearing; structure; improvement
1 Existing problems
2ZU5/8KMF self-lubricating radial spherical plain bearing is a support bearing on a certain type of helicopter automatic tilter. Its self-lubricating layer is made of DU material. It is pasted on the inner diameter surface of the bearing outer ring with adhesive and squeezed between the working surfaces of the inner and outer rings of the bearing by pressure. When the bearing is working, the DU material lubricating layer plays a lubricating role between the inner and outer rings, and no lubricant needs to be replenished. In actual work, due to the normal wear of the bearing self-lubricating layer, the bearing clearance increases. When the temperature, load and other conditions change suddenly, the self-lubricating layer falls off from the pasted surface and slides out of the outer diameter end face. If the lubricating layer slides out completely, the bearing will lose its self-lubricating function, the inner and outer rings will be severely worn and overheated, causing the bearing to fail prematurely, endangering flight safety.
2 Improvement measures
(1) Add anti-slip ribs at both ends of the inner surface of the outer ring (see Figure 1). The lubricating layer material is 0.5mm thick, while normal wear of the lubricating layer over the bearing's lifespan is 0.008-0.01mm. Therefore, ribs 0.3mm high and 0.6mm wide were added to both ends of the inner surface of the outer ring of the 2ZU5/8KMF bearing. The lubricating layer width was reduced by twice the rib width, while the remaining structure remained unchanged. This way, after cladding, the self-lubricating layer material is confined by the ribs on the inner surface of the bearing outer ring and its thickness exceeds the ribs by 0.2mm. Even if its thickness decreases due to normal wear during operation, it will not fall below the ribs and slide out to the sides.
(2) Improve the interface method at both ends of the self-lubricating layer. The original simple bevel joint method at both ends of the lubricating layer was changed to a "dovetail" joint method (see Figure 2), which also effectively avoided the relative sliding phenomenon of the lubricating layer at the interface.
3. Conclusion
The two improved bearings were subjected to one million swing tests on an E06-12 swing tester according to the original test guidelines. A comprehensive inspection of the bearings after testing revealed normal wear of the self-lubricating layer and excellent condition. No slippage was observed; all bearing parameters and appearance met requirements. The improved bearings have been in field use for over a year and have performed well, with no slippage of the lubricating layer. This design improvement offers guidance for addressing the issue of lubricating layer slippage in other types of self-lubricating spherical plain bearings.
