Correction of the Reverse Rotation Support of a Hydraulic Excavator

Source: China Bearing Network | Time: 2014-03-29

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A Sumitomo S2800FJ hydraulic excavator, with an operating time of 8,664 hours, was involved in an accident where a dump truck collided with its counterweight. After the incident, it was discovered that several sealing components of the reverse support had failed, and there was unusual movement inside the unit. When reversing, the machine made a creaking noise when turning forward and to the left. By lifting the bucket off the ground and extending the boom, it was found that both axial and radial clearances in the reverse bearing were significantly increased. Upon further inspection, the reverse motor and speed reducer were confirmed to be functioning properly. This led to the initial conclusion that the steel balls and cage within the reverse support were damaged, resulting in excessive clearance and compromised sealing. The reverse bearing was removed by first disconnecting all oil lines from the reverse motor and sealing their ends with plastic film. Using a crane, the upper part of the excavator was lifted, and the bolts securing the outer ring of the reverse support were loosened and removed. The upper and lower parts of the machine were then separated. As shown in Figure 1, the taper pin was driven out, followed by the removal of the plug using a Screw. The steel balls and cage were extracted using a wire. Only two intact cages were found, while the rest were crushed. Over 30 steel balls showed severe pitting and deformation, with others exhibiting varying degrees of damage. The inner and outer raceways were cleaned, and visible pitting was observed under daylight. The impact caused by the collision subjected the reverse bearing to significant radial force, leading to damage in some of the nylon-based cage components. If the machine continued to operate, this damage would worsen, increasing the gap between the races and allowing grease to escape. This would lead to further wear on the raceway, cage, and steel balls, resulting in abnormal noises and sticking during reversal. ### Repair and Replacement of the Reverse Support Replacing the entire reverse bearing is expensive, costing around 100,000 yuan, and the delivery time is long. Given that the excavator is an older model, replacing the bearing was not considered necessary. Instead, the original reverse support was repaired. After inspection, the inner and outer raceways showed minor deformation and pitting but remained functional. The repair involved replacing the steel balls and cage. However, the original steel balls had a diameter of 28.48 mm, while available domestic alternatives measured 28.60 mm, which is 0.12 mm larger. This difference affected the total length of the raceway, requiring adjustments to the thickness of the cage by 0.12 mm to ensure proper fit. The replacement steel balls needed to have a diameter less than 0.002 mm smaller than the original to maintain compatibility. Some cages also required trimming to match the original number of components and ensure full coverage of the raceway. ### Installation and Final Steps Once the components were replaced, the inner and outer races, along with the raceway, steel balls, cage, and sealing devices, were thoroughly cleaned. The outer race was placed on the inner one, ensuring the raceways were aligned as closely as possible. The steel balls and cages were inserted through the radial holes, following the correct order until fully filled. The plug was reinstalled, and the taper pin was secured. A sealant was applied to the sealing device and groove to ensure a tight seal. The outer raceâ€™s grease ring was refilled, and the raceway was packed with grease. The reverse pinion and large oil tank were also refilled with grease. Using a crane, the upper part of the excavator was lifted, and the lower end of the reverse housing was aligned with the outer seat of the reverse support. Bolts were inserted and positioned using round steel bars matching the Bolt hole diameters. The bolts were installed symmetrically in a triangular pattern, tightened gradually with a torque wrench to 650 NÂ·m. After installation, the engine was started, and various checks were performed until normal operation was restored. --- **Related Bearing Knowledge:** - Rolling Bearing Basic Knowledge Summary - Double Outer (Inner) Ring, Double Row Angular Contact Ball Bearing [Contact Angle 40Â°] - How to Properly Seal Rolling Bearings - Bearing Installation (Positioning) - Bearing Steel Metallurgical Skills This article is linked to http:// Please cite the Bearing Network: http:// Previous: "TIMKEN Imported Bearings Smooth Protection" Next: What is an Air Bearing?

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