Lubrication constitutes the core guarantee for stable operation of Universal Joint Coupling. Precision components including cross shafts, needle roller bearings and sliding mating surfaces rely entirely on lubricant films to isolate metal contact and reduce friction losses. When the coupling suffers insufficient lubrication, dried grease or inadequate refilling, the overall operating condition gradually deteriorates from stable, efficient operation to frequent malfunctions. All operating parameters and component performance degrade noticeably, and the whole degradation process is gradual and irreversible.
At the initial stage of insufficient lubrication, surging friction resistance and emerging abnormal noise become the most obvious symptoms. Under adequate lubrication, oil films buffer metal collisions and suppress friction noise. Once lubrication fails, metal components make direct hard contact. Continuous metallic scraping and squeaking occur during high-speed operation, and abnormal noise turns sharper under increased loads. Meanwhile, operational resistance rises, motor load increases, accompanied by higher power consumption and unstable power output. Minor coupling jitter can be observed under light loads, and transmission smoothness begins to decline.
In the medium-term phase of lubricant shortage, component wear accelerates exponentially and operating clearances exceed standard limits. Uniform wear develops on cross shaft surfaces, needle roller outer walls and shaft sleeve inner surfaces. Widened mating gaps significantly reduce the coupling' s transmission accuracy. Power transmission generates obvious hysteresis and offset; coaxial deviation worsens, vibration amplitude rises sharply, and strong impact loads occur during startup and shutdown. Massive heat from friction cannot be dissipated by lubricant, resulting in persistent component overheating. High temperature carbonizes residual grease, further clogging lubrication channels and forming a vicious cycle.
Long-term insufficient lubrication leads to catastrophic failures and completely ruins the coupling' s operating state. Continuous dry friction at high temperatures causes metal surface ablation, galling and scratching. Needle rollers deform, jam or fall off, while cross shafts develop uneven wear and cracks. Excessively large transmission clearances trigger eccentric rotation and violent shaking. The coupling loses capacity for accurate power transfer and imposes impact damage on connected motors, reducers and main shafts. Ultimately, critical failures including bearing seizure, cross shaft breakage and coupling lockup occur, directly halting production, raising maintenance costs and increasing equipment failure risks. During daily operation, special lubricating grease should be replenished regularly, and carbonized sludge cleared to maintain consistent oil film protection for friction surfaces.
