Hydraulic excavators generally utilize single-row four-point contact ball-type internal gear slewing bearings. These bearings handle complex loads, including axial force, radial force, and tipping moments during operation. Proper maintenance of these bearings is essential to ensure their longevity and efficiency. This comprehensive guide will delve into the detailed aspects of maintaining an excavator’s slewing bearing, including lubrication and cleaning of the raceway and the inner gear ring, maintenance of the inner and outer oil seals, and the upkeep of the fastening bolts.
Slewing bearing rolling elements and raceways endure significant stress, making them highly susceptible to damage and failure. Regular lubrication is crucial to mitigate this stress. Proper lubrication reduces friction and wear among the rolling elements, raceway, and spacers. Given the small space in the raceway cavity and the high resistance to grease filling, manual filling using a grease gun is necessary. Lubrication points are typically distributed around the outer wall of the slewing bearing.
A commonly used lubricant is 2# lithium-based grease, which is recommended to be applied every 100 hours of operation. However, under harsh conditions such as high dust environments, high temperatures, or continuous operation, the interval should be shortened accordingly. During the lubrication process, it is important to rotate the slewing bearing and add grease every 15° to 25°. Monitor the outer sealing ring closely and stop adding grease once it starts seeping out.
Improper filling methods like “refueling in a static state” or “single-point oiling” should be avoided. These methods can lead to local oil leakage and potentially permanent damage to the slewing bearing oil seal, resulting in grease loss, impurity intrusion, and accelerated wear. It is also crucial not to mix different types of grease, as this can cause premature failure. When replacing deteriorated grease, rotate the slewing bearing slowly and uniformly to ensure even distribution. This process should be gradual to allow proper grease metabolism.
Many operators make the mistake of either under-lubricating or over-lubricating the bearings. Over-lubrication can cause the grease to overflow and allow impurities to enter the bearing, accelerating wear. Conversely, under-lubrication can lead to increased friction and wear. Following the recommended lubrication intervals and techniques is crucial to maintaining the health of the slewing bearing.
Maintaining the gear meshing area is vital for the longevity and efficiency of the slewing bearing. Start by removing the metal cover on the base of the slewing platform to observe the lubrication and wear of the ring gear and the pinion of the slewing motor reducer. The metal cover should be secured with bolts and a rubber pad to prevent water from seeping into the lubricating cavity, which can degrade the grease and increase gear wear.
To replace the grease in the ring gear lubricating cavity, support the excavator with its working device and open the metal cover. Lower the excavator to the ground, start it, and perform a rotating action for about ten laps to expel the old grease. The lubricating cavity is typically filled with 2# lithium-based grease, with a replacement cycle of about 2000 hours. The exact amount of grease needed will depend on the model of the excavator.
Water ingress can severely damage the gear meshing area by causing the grease to degrade and increasing the wear on gears. Ensure that the rubber gasket under the metal cover is intact and that the bolts are securely fastened. Regularly check for any signs of water ingress and address them promptly to prevent long-term damage.
Regularly inspect the gears for signs of wear and tear. Any unusual noises or changes in performance may indicate that the gears are wearing unevenly or excessively. Addressing these issues promptly can prevent more severe damage and ensure the smooth operation of the slewing bearing.
The internal and external oil seals of the slewing bearing play a crucial role in preventing contaminants from entering the raceway and ensuring proper lubrication. These seals are made of rubber and are less pressurized. The outer oil seal, located on the lower surface of the inner ring gear, prevents foreign objects from entering the raceway, while the inner oil seal, on the upper surface of the slewing bearing’s outer ring, keeps the grease within the gear ring’s lubricating cavity from seeping into the raceway.
Regular inspection of these seals is essential. If they are damaged, repair or replace them promptly. Damage to the sealing ring of the rotary motor reducer can cause gear oil to leak into the lubricating cavity, thinning the grease and potentially leading to it seeping into the raceway through the inner oil seal. This can accelerate damage to the rolling elements, raceway, and outer oil seal.
It is a common misconception that slewing bearings should be lubricated as frequently as the boom and stick bearings. However, over-lubrication can lead to excessive grease in the raceway, causing it to overflow and allowing impurities to enter the bearing, accelerating wear. Therefore, it is important to follow the recommended lubrication intervals.
Ensuring the integrity of the oil seals is crucial for the overall health of the slewing bearing. Regularly check for any signs of wear or damage to the seals and replace them as needed. Proper maintenance of the seals can significantly extend the lifespan of the slewing bearing.
The fastening bolts of the slewing bearing are critical for ensuring its stability and performance. There is a misconception that the bolts should be tightened with as much force as possible. However, over-tightening can exceed the tensile strength of the bolts, preventing proper pre-tightening force. It is essential to follow the specified pre-tightening torque for each type of bolt. For bolts with a strength grade of 10.9, use flat washers made from 45# steel that are quenched and tempered to a hardness of HRC39. Spring washers should be avoided.
If 10% of the slewing bearing bolts become loose, the remaining bolts will be subjected to increased stress, leading to further loosening and potential bolt breakage or even machine failure. Therefore, after the first 100 hours and 504 hours of operation, check the pre-tightening torque of the bolts. Subsequently, check the pre-tightening torque every 1000 hours to ensure they remain securely fastened.
Reusing bolts can reduce their tensile strength, so even if the torque meets the specified value, the pre-tightening force may still be insufficient. Therefore, when retightening, increase the torque by 30 to 50 N·m above the specified value. Tighten the bolts in a 180° symmetrical pattern multiple times to ensure even pre-tightening force.
Regularly inspect the fastening bolts for signs of wear or damage. Replacing worn or damaged bolts promptly can prevent more severe issues and ensure the stability and performance of the slewing bearing.
Adjusting the gear clearance between the ring gear of the slewing bearing and the output gear of the slewing motor reducer is essential for smooth operation. This adjustment should be made at the highest point of the radial runout of the slewing bearing’s pitch circle. The gear meshing backlash should be selected according to the gear module, with larger modules requiring greater backlash. At the maximum radial runout, the backlash between the gears should be ≥0.03m, where m is the gear module.
During adjustment, ensure the connecting bolts between the rotary motor reducer and the rotary platform are not loose. If the gear meshing gap is too large, it can cause significant impact forces during operation, leading to abnormal noise. Conversely, if the gap is too small, it can cause the gears to jam and potentially lead to broken teeth.
Additionally, check whether the positioning pin between the slewing motor and the rotary platform is secure. The positioning pin, which should be an interference fit, enhances the fastening strength of the rotary motor reducer bolts and reduces the likelihood of loosening.
Regularly adjust and inspect the gear clearance to ensure smooth operation and prevent abnormal wear and tear. Proper maintenance of the gear clearance can significantly extend the lifespan of the slewing bearing and improve the overall performance of the excavator.
The slewing bearing block is crucial for the disassembly and assembly of the rolling elements. It is fixed in place by a conical positioning pin, which prevents movement of the block. The block is located at the non-load bearing position of the slewing bearing, on both sides of the main load plane.
If the positioning pin becomes loose, it can cause the block to shift, leading to changes in the raceway at the blockage position. This can result in collisions between the rolling elements and the block, causing abnormal noises. Operators should regularly clean any soil covering the block and check for any displacement.
Regularly inspect the positioning pin and the block to ensure they are secure. Any signs of wear or damage should be addressed promptly to prevent more severe issues. Proper maintenance of the block can significantly improve the performance
Maintaining the hydraulic excavator slewing bearing is a multifaceted task that demands regular attention to lubrication, gear meshing, oil seals, fastening bolts, gear clearance, and clog maintenance. Each of these components plays a critical role in ensuring the efficient and long-lasting operation of the excavator’s slewing bearing. Regular and thorough maintenance helps prevent premature wear and failure, extending the lifespan of the equipment and ensuring safe and reliable operation. Adhering to the recommended maintenance practices and intervals, promptly addressing any signs of wear or damage, and ensuring proper lubrication and seal integrity are essential steps in achieving optimal performance and longevity of the slewing bearing. By prioritizing these maintenance tasks, operators can significantly reduce downtime and repair costs, enhancing the overall productivity and efficiency of their hydraulic excavators.
Answer: The primary functions of a hydraulic excavator’s slewing bearing include enabling the rotation of the excavator’s upper structure relative to its undercarriage, facilitating smooth and precise movement, and supporting axial, radial, and moment loads. This rotation capability allows the excavator to perform digging, lifting, and material handling tasks efficiently by positioning the boom and bucket at the required angle.
Answer: The single-row four-point contact ball-type slewing bearing is designed to accommodate high radial, axial, and moment loads simultaneously. This design benefits excavators by providing a compact and robust bearing solution that can handle the complex load demands encountered during excavation operations. The four-point contact ensures stability and precision, contributing to the efficient and reliable performance of the excavator.
Answer: Common signs of wear or damage in a slewing bearing include unusual noises during operation (such as grinding or knocking sounds), increased play or movement between the upper and lower parts of the excavator, visible damage or deformation of the bearing components, and leakage of lubricant from the bearing seals. Operators should also look for signs of uneven rotation or difficulty in rotating the upper structure, which may indicate internal bearing issues.
Answer: Environmental factors such as dust, moisture, extreme temperatures, and corrosive substances can significantly impact the performance and longevity of a slewing bearing. Dust and debris can enter the bearing, causing increased wear and potential damage to the rolling elements and raceways. Moisture can lead to corrosion and lubricant degradation, while extreme temperatures can affect the viscosity and effectiveness of the lubricant. Corrosive substances can damage the bearing materials and seals, leading to premature failure.
Answer: Replacing a damaged slewing bearing involves several key steps:
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