(1) If it is determined that the problem is caused by the seal, remove the old seal, clean the seal groove with diesel or gasoline, and completely clamp the new seal into the seal groove. It should be noted that there is a joint after the sealing strip is annular, and both sides of the joint need to be glued together with double tube universal glue (such as acrylate glue).
(2) If the lubricating grease deteriorates due to the leakage of the swing motor, the swing motor must be repaired to fundamentally solve the problem, and then replace the lubricating grease of the whole swing gear ring.
(3) If the leakage is caused by improper selection of grease, replace all the grease of the rotary gear ring. At the same time, it should be noted that the same brand of grease should also be used in the bearing cavity. Lithium molybdenum based grease shall be used, which will not reduce its viscosity at high temperature.
(4) Correctly control the maintenance cycle of the slewing bearing, that is, the lubricating grease must be filled every 150 ~ 250h. The oil filling can be completed in several times, that is, the excavator can be filled every 90 ° rotation. The filling amount is limited to the overflow of grease from the outer oil seal.
(5) If the slewing bearing is damaged, the whole slewing bearing must be replaced. Due to the particularity of its structure and the diversity of on-site conditions, the slewing bearing of Caterpillar excavator is prone to damage to the slewing bearing, slewing ring gear or slewing motor due to oil leakage. Therefore, the leakage should be prevented and handled in time. This paper will introduce some maintenance methods summarized from practice.
1. Structure and lubrication principle of rotary bearing
In fact, the grease lubrication of the rotary part of Caterpillar excavator is divided into two cavities: the rotary bearing lubrication cavity and the rotary ring gear lubrication cavity.
The lubrication of the rotary bearing is completed by filling the lubricating grease through the lubricating nozzle located on the outer ring of the rotary bearing, and the lubrication of the rotary gear ring is completed by the pre added grease. The slewing bearing has two inner and outer (or upper and lower) rubber strips as oil seals. The outer oil seal is fixed on the inner ring (fixed plate) of the slewing bearing of the lower frame to prevent external dust and sundries from entering the slewing bearing. The inner oil seal is located on the outer ring (moving plate) of the bearing The grease in the rotary gear ring is prevented from entering the bearing. The rotary gear ring and the rotary bearing use the same brand of grease. See Fig. 1 for its structure and Fig. 2 for the cross-sectional structure of the oil seal. The rotary oil seal gradually thins from thickness and finally forms a sharp angle. Only the elasticity of the rubber itself compresses the end face of the rotary bearing by the deformation of the rubber (Figure 2 shows the shape of the sealing strip before deformation) . this kind of seal has a slight effect on preventing grease leakage, but the pressure is not high. Once the pressure increases due to excessive oil filling or the increase of working temperature, the grease will still leak through the oil seal. Under normal circumstances, the leakage amount is related to many factors, such as the filling amount, the working speed and frequency of the rotating part, as well as the on-site temperature. Therefore, there is a risk to the normal operation Fuzziness related to abnormal leakage.
2. Inspection method for leakage of slewing bearing
Generally, it is normal for a small amount of oil leakage from the outer oil seal under working conditions. The so-called normal means that the amount of grease leaked through the outer seal of the slewing bearing is roughly equal to the amount of grease filled into the slewing bearing. However, when a large amount of grease leakage occurs on the excavator, it must be checked. Due to the particularity of the lubrication structure of the slewing part, it needs to be separated Analyze whether there is leakage and determine the problem. The specific inspection steps and methods are as follows:
(1) Whether the maintenance is correct. The grease filling cycle of the rotary bearing cavity should be between 150 ~ 250h (the maintenance cycle recommended by the manufacturer is 250h, but it can be appropriately shortened according to the working intensity and frequency of the rotary part in actual work). If the filling is too frequent, a large amount of grease will leak out.
(2) Whether the hydraulic oil or gear oil of the slewing motor has channeled into the cavity of the slewing gear ring. If such leakage occurs, after opening the inspection cover of the lubricating oil of the slewing gear ring, it will be found that the lubricating oil has become thinner. This thinning is the characteristic of mixing hydraulic oil or gear oil.
（3） Whether the grease originally filled in the equipment is selected correctly. Because the grease filled in the original equipment may be incorrect, the grease will become thinner as soon as the temperature of the rotary bearing or rotary gear ring increases slightly. If the thinner grease is pushed to the upper end face of the inner gear ring by the driving gear of the rotary motor during meshing, it will flow into the bearing cavity through the inner oil seal, and finally the grease drips from the outer oil seal Flowing out.
(4) Check the outer oil seal carefully along the rotary oil seal to determine whether it is local, section leakage or uniform peripheral leakage. Check whether the whole rotary oil seal is missing.
（5） Whether the outer oil seal is fixed. The outer oil seal should be relatively fixed with the sealing groove of the lower frame. The key to the inspection is: observe when the excavator rotates. If the oil seal also rotates at the same time when the equipment rotates, it indicates that the existing oil seal has been loosened in the sealing groove and the outer oil seal must be replaced. This method is dangerous, so pay attention to safety, but this is to check the rotating oil Sealing is one of the important methods for sealing.
(6) Whether there is obvious damage to the inner oil seal, open the lubricating grease inspection cover of the rotary gear ring, and check whether there is a large reduction of grease in the oil chamber of the gear ring and whether there are broken fragments of the oil seal. If there is a large reduction of grease, it indicates that the grease has been leaked.
(7) Determine whether the leakage is the grease in the bearing cavity or the grease in the rotating gear ring cavity. Add the grease of different colors into the bearing cavity for a period of time After use (for example, about 150h), after the oil in the bearing cavity has been basically replaced with the filled grease, determine whether it is the grease of the rotary gear ring or the grease in the bearing cavity according to the color of the grease leaked around. This is one of the methods to preliminarily judge whether the internal seal is invalid from the outside.
(8) Observe whether the rotation of the equipment is abnormal. If the equipment makes abnormal noise or is unstable during the rotation movement, the bearing clearance may be too large and uneven, resulting in the extrusion of oil from the outer oil seal during the rotation of the bearing.
（9） Check the inner oil seal. After the above checks have been completed and the existing problems have been eliminated, the problems can be concentrated on the inner oil seal of the bearing. Take out the peripheral bolts of the rotating part, remove the oil pipe of the traveling part, and lift the upper frame part with a crane. Because this method requires a crane and the workload of the whole process is relatively large, this is the last step to check and solve the problems. Therefore It is recommended to use this method after all the above steps have been completed and other possibilities are excluded.
