How to repair hydraulic excavator slewing bearing?

Hydraulic excavators generally use single-row four-point contact ball internal tooth slewing bearings. When the excavator is working, the slewing bearing bears complex loads such as axial force, radial force, and overturning moment, and its reasonable maintenance is very important. The maintenance of the slewing ring mainly includes the lubrication and cleaning of the raceway and the inner ring gear, the maintenance of the inner and outer oil seals, and the maintenance of the fastening bolts. It is mainly divided into the following five aspects:

1. Raceway lubrication

The rolling elements and raceways of the slewing ring are easy to damage and fail, and the failure rate is high. During the use of the excavator, adding grease to the raceway can reduce the friction and wear between the rolling elements, the raceway and the gasket. The space of the raceway cavity is narrow, and the ability to resist grease filling is strong, so a manual grease gun is required for manual oiling. When filling the raceway cavity with grease, avoid bad filling methods such as “static oiling” and “single point oiling”. This is because the above-mentioned poor oil filling method will cause partial oil leakage of the slewing bearing, or even a permanent oil seal of the slewing bearing. Sexual damage, resulting in grease loss, foreign matter intrusion, and accelerated raceway wear. Be careful not to mix different types of grease as this can cause premature failure. When replacing the seriously deteriorated grease in the raceway of the slewing bearing, the slewing bearing should be rotated slowly and evenly so that the grease can be evenly filled in the raceway.

2. Maintenance of gear meshing area

Open the metal cover on the base of the slewing platform to observe the lubrication and wear of the slewing bearing gear and the pinion of the slewing motor reducer. Rubber pads should be placed under the metal cover and secured with bolts. If the bolts are loose or the rubber pads fail, water will seep from the metal cover into the lubricating chamber (catch pan) of the rotating ring gear, causing premature grease failure, reduced lubrication, and increased gear wear and corrosion.

3. Overhaul of inner and outer oil seals

During the use of the excavator, check whether the inner and outer oil seals of the slewing bearing are intact. If it is damaged, it should be repaired or replaced in time. Damage to the sealing ring of the rotary motor reducer will cause the gear oil in the reducer to leak into the lubricating chamber of the ring gear. During the meshing process of the slewing bearing ring gear and the pinion gear of the slewing motor reducer, the grease is mixed with the gear oil, the temperature rises, the grease becomes thinner, and the diluted grease will be pushed to the upper surface of the ring gear, and penetrates through the inner oil seal The raceway will cause oil leakage and dripping from the outer oil seal, resulting in accelerated damage to the rolling elements, raceways and outer oil seal.

4. Maintenance of fastening bolts

If 10% of the bolts of the slewing ring are loose, the rest of the bolts will be under greater force under the action of tension and compression loads. Loose bolts will generate axial impact loads, which will cause the bolts to loosen more and loosen more, causing the bolts to break. Therefore, after the first 100h and 504h of the slewing ring, the bolt pre-tightening torque should be checked. After that, the pre-tightening torque should be checked every 1000 hours of work to ensure that the bolts have sufficient pre-tightening force.

After the bolt is used repeatedly, its tensile strength will decrease. Although the torque when reinstalling reaches the specified value, the pre-tightening force of the bolt will also decrease after tightening. Therefore, when retightening the bolts, the torque should be 30-50 N·m larger than the specified value. The tightening sequence of the slewing support bolts should be tightened multiple times in a 180° symmetrical direction. All bolts should have the same preload when tightened the last time.

5. Adjustment of gear clearance

When adjusting the gear gap, pay attention to observe whether the connecting bolts between the reducer of the rotary motor and the rotary platform are loose.