Hydraulic excavators generally use single-row 4-point contact ball internal tooth slewing bearings. When excavator is working, the slewing bearing bears complex loads such as axial force, radial force, and tipping 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 gear ring, the maintenance of the inner and outer oil seals, and the maintenance of the fastening bolts. Now I will elaborate on seven aspects.
1. Lubrication of raceway
The rolling elements and raceways of the slewing ring are easily damaged and fail, and the failure rate is relatively high. During the use of the excavator, adding grease to the raceway can reduce the friction and wear among the rolling elements, raceway, and spacer. The raceway cavity has a narrow space and high resistance to grease filling, so manual grease guns are required for manual filling.
When filling the raceway cavity with grease, avoid bad filling methods such as “static state refueling” and “single point refueling”. This is because the above-mentioned poor filling methods will cause partial oil leakage of the slewing ring and even permanent slewing ring oil seals. Sexual damage, resulting in loss of grease, intrusion of impurities, and accelerated wear of raceways. Be careful not to mix different types of grease to avoid premature failure.
When replacing the severely deteriorated grease in the raceway of the slewing ring, the slewing ring should be slowly and uniformly rotated while filling, so that the grease is evenly filled in the raceway. This process cannot be rushed, it needs to be done step by step to complete the metabolism of grease.
 
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 ring gear and the pinion of the slewing motor reducer. A rubber pad should be placed under the metal cover and fastened with bolts. If the bolts are loose or the rubber gasket fails, water will seep from the metal cover into the lubrication cavity (oil collecting pan) of the rotating ring gear, causing premature grease failure and reduced lubrication effect, resulting in increased gear wear and corrosion.
 

Maintenance of internal and external oil seals
During the use of the excavator, check whether the inner and outer oil seals of the slewing ring are intact. If they are damaged, they should be repaired or replaced in time. If the sealing ring of the slewing motor reducer is damaged, it will cause the internal gear oil of the reducer to leak into the lubrication cavity of the ring gear. During the meshing process of the slewing ring ring gear and the pinion gear of the slewing motor reducer, the grease and gear oil will mix and the temperature When it rises, the grease will become thinner, and the thinned grease will be pushed to the upper end surface of the inner gear ring and penetrate into the raceway through the inner oil seal, causing oil leakage and dripping from the outer oil seal, resulting in rolling elements, raceways and outer The oil seal accelerates damage.
Some operators think that the lubrication cycle of the slewing ring is the same as that of the boom and stick, and it is necessary to add grease every day. In fact, it is wrong to do so. This is because too frequent refilling of grease will cause too much grease in the raceway, which will cause grease to overflow at the inner and outer oil seals. At the same time, impurities will enter the slewing ring raceway, accelerating the wear of the rolling elements and raceway.
4. Maintenance of fastening bolts
If 10% of the bolts of the slewing ring are loose, the rest of the bolts will receive greater force under the action of tensile and compressive loads. Loose bolts will generate axial impact loads, resulting in increased looseness and more loose bolts, resulting in bolt fractures, and even crashes and deaths. Therefore, after the first 100h and 504h of the slewing ring, the bolt pre-tightening torque should be checked. Thereafter, the pre-tightening torque should be checked every 1000h of work to ensure that the bolts have sufficient pre-tightening force.
After the bolt is used repeatedly, its tensile strength will be reduced. Although the torque during reinstallation meets the specified value, the pre-tightening force of the bolt after tightening will also be reduced. Therefore, when re-tightening the bolts, the torque should be 30-50 N·m greater than the specified value. The tightening sequence of the slewing bearing bolts should be tightened multiple times in a 180° symmetrical direction. When tightening the last time, all bolts should have the same pretightening force.
 
5. Adjustment of gear clearance
When adjusting the gear gap, pay attention to observe whether the connecting bolts of the slewing motor reducer and the slewing platform are loose, so as to avoid the gear meshing gap being too large or too small. This is because if the clearance is too large, it will cause greater impact on the gears when the excavator starts and stops, and it is prone to abnormal noise; if the clearance is too small, it will cause the slewing ring and the slewing motor reducer pinion to jam, or even Cause broken teeth.
When adjusting, pay attention to whether the positioning pin between the swing motor and the swing platform is loose. The positioning pin and the pin hole belong to an interference fit. The positioning pin not only plays a role in positioning, but also increases the bolt tightening strength of the rotary motor reducer and reduces the possibility of loosening of the rotary motor reducer.
Clogged maintenance
Once the positioning pin of the fixed blockage is loose, it will cause blockage displacement, causing the raceway to change in the blockage part. When the rolling element moves, it will collide with the blockage and make abnormal noise. When using the excavator, the operator should pay attention to cleaning up the mud covered by the blockage and observe whether the blockage is displaced.
Forbid to wash the slewing bearing with water
It is forbidden to flush the slewing bearing with water to avoid the scouring water, impurities, and dust from entering the slewing ring raceway, causing corrosion and rusting of the raceway, resulting in the dilution of the grease, destroying the lubrication state, and deterioration of the grease; avoid any solvent contacting the slewing ring oil seal , So as not to cause oil seal corrosion.
 
In short, after the excavator is used for a period of time, its slewing bearing is prone to malfunctions such as noise and impact. The operator should pay attention to observe and check in time to eliminate the malfunction. Only correct and reasonable maintenance of the slewing ring can ensure its normal operation, give full play to its performance, and extend its service life.