Severe Wear on Gear Teeth Surfaces: One of the common failure phenomena of couplings is the severe wear on the gear teeth surfaces. This wear can significantly affect the meshing and transmission performance of the coupling. When the gear teeth surfaces are worn, the smooth engagement between the gears is disrupted, leading to potential issues such as increased vibration, noise during operation, and a decrease in the efficiency of power transmission.
Large Axial Displacement of the Internal Gear Ring: Another observed failure is that the internal gear ring of the coupling may experience a relatively large axial displacement. In some cases, this displacement can be so significant that the gears may even fail to mesh properly. Such a situation can cause an immediate interruption in the power transmission process, as the correct meshing of the gears is crucial for the smooth operation of the connected machinery.
Tooth Breakage: The occurrence of tooth breakage is also a serious failure phenomenon in couplings. Broken teeth can not only disrupt the normal meshing of the gears but also may lead to more severe consequences such as the scattering of broken gear fragments, which could potentially damage other components within the machinery system. This can pose a significant threat to the safety and continuous operation of the entire equipment.
Fracture of the Coupling’s Butt Bolts: The fracture of the butt bolts used to connect the two halves of the coupling is yet another failure that can occur. When these bolts break, the structural integrity of the coupling is compromised, and it may no longer be able to maintain the proper connection and alignment between the shafts it is coupling. This can result in misalignment of the shafts and subsequent problems in power transmission.
A. Insufficient Lubrication or Improper Grease Usage
The first major cause of the above-mentioned coupling failures is related to lubrication issues. Specifically, there may be insufficient lubricating oil in the coupling or even a complete lack of it. Additionally, improper use of grease can also lead to problems. For example, if the grease used is not of the appropriate type or if it is not applied correctly, it can cause the grease to calcify over time.
When there is insufficient lubrication or the grease has calcified, the gear teeth surfaces within the coupling cannot be effectively lubricated. As a result, the friction between the teeth increases significantly during the operation of the coupling. This excessive friction is the primary reason for the severe wear on the gear teeth surfaces. In such cases, to avoid this type of failure, it is necessary to replace the old lubricating grease with new, high-quality grease. Regular injection of qualified lubricating grease should also be ensured, and measures should be taken to prevent oil leakage to maintain an adequate amount of lubricant within the coupling.
B. Excessive Errors in the Horizontal and Coaxial Alignment of the Two Shafts
The second significant cause of coupling failures lies in the misalignment of the two shafts being coupled. If the horizontal and coaxial alignment errors between the two shafts are too large, exceeding the compensation range of the coupling itself, several problems can arise.
Firstly, the shaft teeth and the internal gear may not mesh correctly. Instead of a uniform and full meshing, there will be only local contact between the gears. This local contact generates an additional torque, which can be decomposed into an axial force acting on the internal gear ring. The magnitude of this force is directly proportional to the size of the alignment deviation. That is, the larger the deviation, the greater the force exerted on the internal gear ring.
As a result of this axial force, the internal gear ring of the coupling will experience axial displacement. If the displacement amount becomes too large, it can lead to severe gear wear, and in extreme cases, even tooth breakage. Moreover, the misalignment can cause the internal and external gears to be unable to mesh properly, eventually resulting in the inability to transmit power.
This type of failure is relatively difficult to handle and often requires shutting down the production process for repair. The typical repair method involves realigning the shafts. This may involve re-aligning the reducer side or the drum side, depending on where the misalignment is more significant. To do this, it is necessary to first identify the part with the larger offset error. This requires measuring the horizontal and coaxial alignment of the main shaft as well as that of the reducer’s main shaft to determine in which direction the coupling is offset. Then, by re-leveling and realigning according to the quality standards, the failure can be eliminated.
For example, in a practical case on a construction site, a JK-2.5/11.5 single-rope winding hoist was encountered with such a problem. At that time, the concentricity deviation of the coupling was measured to be 2n, with the reducer side being lower. This misalignment caused the coupling of the hoist’s accessories to fail to work properly. The axial displacement of the internal gear ring exceeded the gear width. After surveying and calculating, the reducer was realigned according to the quality standards. After the adjustment, the hoist operated normally, and the failure was resolved.
In addition, large errors in the horizontal and coaxial alignment of the two shafts can also cause the coupling to “bind” during rotation. This is similar to the cause of gear wear in the coupling mentioned above. In this situation, the connecting bolts are not only subjected to the normal forces but also to an additional bending moment, which can cause them to break. This is a common occurrence, especially when there is a significant difference in the horizontal level of the reducer’s main shaft. Moreover, if the diameter of the bolts is too small, their strength may not be sufficient, or if the bolt material is of poor quality, it can also lead to bolt fracture.
In conclusion, understanding the various failure phenomena and their corresponding causes in couplings is crucial for maintaining the normal operation of machinery systems that rely on couplings for power transmission. By carefully analyzing these issues and taking appropriate preventive and corrective measures, such as ensuring proper lubrication and accurate shaft alignment, the reliability and service life of couplings can be significantly improved, thereby reducing the occurrence of failures and the associated downtime and maintenance costs.
