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Treatment Of Leakage Of Caterpillar Excavator Rotary Bearing Aug 05, 2018

Because of the particularity of the structure of the Carter excavator and the diversity of the field conditions, it is easy to occur the failure of the rotating bearing, rotary gear ring or rotary motor because of oil leakage. Therefore, the leakage should be prevented and treated in time. This paper will introduce some maintenance methods summarized from practice.


The structure and lubrication principle of 1. rotary bearing


In fact, grease lubrication at the rotary part of the excavator is divided into two chambers: the rotary bearing lubrication cavity and the rotary ring gear lubrication cavity.


The lubrication of the rotary bearing is accomplished by adding lubricating oil to the lubricating oil nozzle in the outer ring of the rotary bearing, and the lubrication of the rotary gear ring is completed by the pre added oil. The rotary bearing has two rubber strips as oil seal, and the outer seal is fixed on the inner ring of the rotating bearing of the lower frame. It is used to prevent the outside dust from entering the rotary bearing. The inner oil seal is located on the outer ring of the bearing (moving disc) to prevent grease in the rotary gear ring from entering the bearing. Rotary gear ring and rotary bearing use the same brand of grease. Its structure is shown in Figure 1, and the section structure of the oil seal is shown in Figure 2. The oil seal is thinned by the thickness. Finally, a sharp angle is formed, and the rubber itself is only elastic by the protruding part of the rubber to press the end face of the rotary bearing by rubber. (Figure 2 is shown as the shape before the deformation of the seal). This seal has a little effect on preventing oil leakage, but the pressure is not high. Once the internal pressure increases due to overrefueling or the increase of working temperature, the oil will still be leaked through the oil seal. Under normal circumstances, the leakage is related to many factors, such as the injection rate, the working speed and frequency of the rotating part, and the site temperature. Therefore, there exists ambiguity between normal and abnormal leakage.


Inspection mode of leakage of 2. rotary bearing


Usually, a small amount of oil leakage occurs outside the oil seal under normal working conditions. The so-called normal, it means through the axis of revolution


The amount of grease leaked from the external seal is approximately equal to that of the grease injected into the rotary bearing. However, when a large number of grease leakage occurs on the excavator, it must be inspected. Because of the particularity of the lubrication structure of the rotating part, it is necessary to analyze whether there is leakage and determine the problem in order to solve the problem. The detailed procedures and methods are as follows:


(1) whether the maintenance is correct or not


The grease filling cycle of the rotary bearing chamber should be between 150~250h (the recommended maintenance period recommended by the manufacturer is 250h, but in practice)


The work can be shortened according to the working intensity and frequency of the revolving part. If the injection is too frequent, it will lead to a lot of grease leakage.


(2) does the hydraulic oil or gear oil of the rotary motor run into the cavity of the rotary gear ring?


If there is a leakage of this situation, open the check cover of the rotary gear ring grease.


Thinning. This dilute is mixed with hydraulic oil or gear oil.


(3) the proper selection of the original oil and grease for the equipment


Since the oil injected into the original equipment may not be correct, the grease will become thinner as the temperature of the rotary bearing or gear ring rises slightly. If the dilute oil is pushed to the upper end of the inner gear by the drive gear of the rotary motor, it will flow into the bearing cavity through the inner oil seal, and the oil drops out from the outer oil seal.


(4) whether the external oil seal is lacking


Check the rotary oil seal carefully to determine whether partial or partial leakage or uniform peripheral leakage. Check whether the whole rotary oil seal is missing.


(5) whether the external oil seal is fixed or not


The outer oil seal shall be relatively fixed with the sealing groove of the lower frame. The key to the inspection is to observe the excavator when turning. If the oil seal is also rotating at the same time when the equipment is rotating, it means that the existing oil seal has been loosened in the sealing groove, and the external oil seal must be replaced. It is dangerous to adopt this method, so we should pay attention to safety, but this is one of the important methods to check whether the rotary oil seal really plays a sealing role.


(6) whether there is obvious damage to the inner oil seal


Open the rotary gear rim grease inspection cover, check the gear rim oil cavity whether there is a large reduction in grease, whether there is fragmentation of oil seal. If the oil is reduced a lot, it indicates that the grease has been left out.


(7) it is determined whether the grease leaked from the bearing cavity or the grease in the rotary gear ring is leaking out.


After a period of time (such as 150h), oil of different colors is added into the bearing chamber. After the oil has been replaced in the bearing cavity, the oil of the leaked oil or oil of the bearing cavity is determined by the oil color of the surrounding leaked oil. This is one of the ways to judge whether the internal seal is invalid from the outside.


(8) whether the rotation of the equipment is not normal


If the equipment has abnormal or unstable phenomena in the rotary motion, it may be that the bearing gap is too large and uneven, thus causing the bearing to squeeze out of the oil seal in the process of rotation.


(9) check the internal oil seal


After the above inspections have been completed and the problem is eliminated, the problem can be concentrated on the oil seal inside the bearing.  The peripheral bolts of the rotary part are removed and the oil pipes of the walking part are removed, and the upper frame part is lifted by a crane. This is the last step in checking and solving the problem, because the crane is needed and the workload of the whole process is large. Therefore, it is suggested that all the steps mentioned above have been completed, and other possibilities are excluded before using this method.


3. processing methods

(1) if it is determined that the seal is caused by the seal, the old seal should be removed and the seal groove is cleaned with diesel or gasoline, and the new seal is completely stuck into the sealing groove. It should be noted that there is a joint after the sealing strip is annular, and the two sides of the joint need to be bonded together with a double tube universal adhesive (such as acrylic adhesive).


(2) if the lubricating oil is deteriorated due to the leakage of the rotary motor, it is necessary to repair the rotary motor, solve the problem fundamentally, and then replace the grease of the whole rotary gear ring.


(3) if the oil leakage is caused by improper selection of grease, it is necessary to replace all the grease of the rotary gear ring. At the same time, attention should be paid to the same type of grease in the bearing cavity. Lithium molybdenum based grease should be used. The viscosity of the grease will not decrease at high temperature.


(4) correctly control the maintenance period of the slewing bearing, that is to say, every work 150~250h must be lubricated once. It can be completed several times during oil injection, that is, the excavator has 90 degrees of rotation per time. The amount of injection is limited by the overflow of oil from the outer oil seal.


(5) if the slewing bearing is damaged, the whole slewing bearing must be replaced. Because of the particularity of the structure of the Carter excavator and the diversity of the field conditions, it is easy to occur the failure of the rotating bearing, rotary gear ring or rotary motor because of oil leakage. Therefore, the leakage should be prevented and treated in time. This paper will introduce some maintenance methods summarized from practice.


The structure and lubrication principle of 1. rotary bearing


In fact, grease lubrication at the rotary part of the excavator is divided into two chambers: the rotary bearing lubrication cavity and the rotary ring gear lubrication cavity.


The lubrication of the rotary bearing is accomplished by adding lubricating oil to the lubricating oil nozzle in the outer ring of the rotary bearing, and the lubrication of the rotary gear ring is completed by the pre added oil. The rotary bearing has two rubber strips as oil seal, and the outer seal is fixed on the inner ring of the rotating bearing of the lower frame. It is used to prevent the outside dust from entering the rotary bearing. The inner oil seal is located on the outer ring of the bearing (moving disc) to prevent grease in the rotary gear ring from entering the bearing. Rotary gear ring and rotary bearing use the same brand of grease. Its structure is shown in Figure 1, and the section structure of the oil seal is shown in Figure 2. The oil seal is thinned by the thickness. Finally, a sharp angle is formed, and the rubber itself is only elastic by the protruding part of the rubber to press the end face of the rotary bearing by rubber. (Figure 2 is shown as the shape before the deformation of the seal). This seal has a little effect on preventing oil leakage, but the pressure is not high. Once the internal pressure increases due to overrefueling or the increase of working temperature, the oil will still be leaked through the oil seal.  Under normal circumstances, the leakage is related to many factors, such as the injection rate, the working speed and frequency of the rotating part, and the site temperature. Therefore, there exists ambiguity between normal and abnormal leakage.


Inspection mode of leakage of 2. rotary bearing


Usually, a small amount of oil leakage occurs outside the oil seal under normal working conditions. The so-called normal, it means through the axis of revolution


The amount of grease leaked from the external seal is approximately equal to that of the grease injected into the rotary bearing. However, when a large number of grease leakage occurs on the excavator, it must be inspected.  Because of the particularity of the lubrication structure of the rotating part, it is necessary to analyze whether there is leakage and determine the problem in order to solve the problem. The detailed procedures and methods are as follows:


(1) whether the maintenance is correct or not


The grease filling cycle of the rotary bearing chamber should be between 150~250h (the recommended maintenance period recommended by the manufacturer is 250h, but in practice)


The work can be shortened according to the working intensity and frequency of the revolving part. If the injection is too frequent, it will lead to a lot of grease leakage.


(2) does the hydraulic oil or gear oil of the rotary motor run into the cavity of the rotary gear ring?


If there is a leakage of this situation, open the check cover of the rotary gear ring grease.


Thinning. This dilute is mixed with hydraulic oil or gear oil.


(3) the proper selection of the original oil and grease for the equipment


Since the oil injected into the original equipment may not be correct, the grease will become thinner as the temperature of the rotary bearing or gear ring rises slightly. If the dilute oil is pushed to the upper end of the inner gear by the drive gear of the rotary motor, it will flow into the bearing cavity through the inner oil seal, and the oil drops out from the outer oil seal.


(4) whether the external oil seal is lacking


Check the rotary oil seal carefully to determine whether partial or partial leakage or uniform peripheral leakage. Check whether the whole rotary oil seal is missing.


(5) whether the external oil seal is fixed or not


The outer oil seal shall be relatively fixed with the sealing groove of the lower frame. The key to the inspection is to observe the excavator when turning. If the oil seal is also rotating at the same time when the equipment is rotating, it means that the existing oil seal has been loosened in the sealing groove, and the external oil seal must be replaced. It is dangerous to adopt this method, so we should pay attention to safety, but this is one of the important methods to check whether the rotary oil seal really plays a sealing role.


(6) whether there is obvious damage to the inner oil seal


Open the rotary gear rim grease inspection cover, check the gear rim oil cavity whether there is a large reduction in grease, whether there is fragmentation of oil seal. If the oil is reduced a lot, it indicates that the grease has been left out.


(7) it is determined whether the grease leaked from the bearing cavity or the grease in the rotary gear ring is leaking out.

After a period of time (such as 150h), oil of different colors is added into the bearing chamber. After the oil has been replaced in the bearing cavity, the oil of the leaked oil or oil of the bearing cavity is determined by the oil color of the surrounding leaked oil. This is one of the ways to judge whether the internal seal is invalid from the outside.


(8) whether the rotation of the equipment is not normal


If the equipment has abnormal or unstable phenomena in the rotary motion, it may be that the bearing gap is too large and uneven, thus causing the bearing to squeeze out of the oil seal in the process of rotation.


(9) check the internal oil seal


After the above inspections have been completed and the problem is eliminated, the problem can be concentrated on the oil seal inside the bearing. The peripheral bolts of the rotary part are removed and the oil pipes of the walking part are removed, and the upper frame part is lifted by a crane. This is the last step in checking and solving the problem, because the crane is needed and the workload of the whole process is large. Therefore, it is suggested that all the steps mentioned above have been completed, and other possibilities are excluded before using this method.


3. processing methods


(1) if it is determined that the seal is caused by the seal, the old seal should be removed and the seal groove is cleaned with diesel or gasoline, and the new seal is completely stuck into the sealing groove. It should be noted that there is a joint after the sealing strip is annular, and the two sides of the joint need to be bonded together with a double tube universal adhesive (such as acrylic adhesive).


(2) if the lubricating oil is deteriorated due to the leakage of the rotary motor, it is necessary to repair the rotary motor, solve the problem fundamentally, and then replace the grease of the whole rotary gear ring.


(3) if the oil leakage is caused by improper selection of grease, it is necessary to replace all the grease of the rotary gear ring. At the same time, attention should be paid to the same type of grease in the bearing cavity.  Lithium molybdenum based grease should be used. The viscosity of the grease will not decrease at high temperature.


(4) correctly control the maintenance period of the slewing bearing, that is to say, every work 150~250h must be lubricated once. It can be completed several times during oil injection, that is, the excavator has 90 degrees of rotation per time. The amount of injection is limited by the overflow of oil from the outer oil seal.


(5) if the slewing bearing is damaged, the whole slewing bearing must be replaced.


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