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Maintenance of hydraulic excavator slewing bearing

07-07, 2022 / in Bearing Knowledge / by LDB

Hydraulic excavators generally use single-row four-point contact ball-type internal gear slewing bearings. During the excavator operation, the excavator 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 excavator slewing bearing 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 from these seven aspects will be described in detail.

1. Lubrication of raceways

Slewing bearing rolling elements and raceways are easy to damage and fail, and their failure rate is high. During the use of the excavator, adding grease to the raceway can reduce the friction and wear among the rolling elements, the raceway and the spacer. The space of the raceway cavity is small, and the resistance to filling grease is large, so manual filling with a manual grease gun is required. The lubricating oil nozzles of the slewing bearing raceway are generally distributed at the position of the outer wall of the slewing bearing.

The raceway cavity is generally lubricated with 2# file-based grease, and the grease filling cycle is generally 100h. Under special working conditions such as high dust, high temperature, and continuous operation, the filling cycle should be appropriately shortened. When adding grease, it is necessary to rotate the slewing bearing, and add it about once every 15°~25°. When filling, pay attention to observe the outer sealing ring of the slewing bearing. When you see grease seeping out from the outer sealing ring, stop filling.

When the raceway cavity is filled with grease, bad filling methods such as "refueling in static state" and "single-point oiling" should be avoided, because the above-mentioned bad filling methods will cause local oil leakage of the slewing bearing, and even cause the oil seal of the slewing bearing to become permanent. Damaged, resulting in grease loss, impurity intrusion, and accelerated raceway wear. Be careful not to mix different types of grease to avoid premature failure.

When replacing the seriously deteriorated grease in the raceway of the slewing bearing, the slewing bearing should be rotated slowly and uniformly while filling, so that the grease can be filled evenly in the raceway. This process can not be rushed, it needs to be done step by step to complete the metabolism of grease.

excavator slewing bearing

2. Maintenance of the gear meshing area

Open the metal cover on the base of the slewing platform to observe the lubrication and wear of the ring gear of the slewing bearing 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 lubricating cavity (oil collecting pan) of the rotating inner gear ring, causing premature failure of the grease, reduced lubrication effect, and increased gear wear and corrosion.

The method of replacing the grease in the lubricating cavity of the ring gear is as follows: first, use the working device to support the excavator, and the operator goes under the crawler frame of the excavator and opens the metal cover; secondly, drop the excavator to the ground and start the excavator Do the rotating action for about 10 laps, and the failed grease can be exhausted. The lubricating cavity of the ring gear of the slewing bearing is also filled with 2# file base grease. The replacement cycle is generally 2000h, and the filling amount should be determined according to the model of the excavator.

3. Maintenance of internal and external oil seals

The inner and outer oil seals of the slewing bearing are of rubber sealing strip structure, which bear less pressure. The outer oil seal is located on the lower surface of the inner ring gear of the slewing bearing, which is used to prevent foreign objects such as sand outside the slewing bearing from entering the raceway, causing wear of the rolling elements and the raceway; the inner oil seal is located on the upper surface of the outer circle of the slewing bearing to prevent the lubrication of the inner gear ring The grease in the cavity enters the raceway cavity.excavator slewing bearing

During the use of the excavator, you should always check whether the inner and outer oil seals of the slewing bearing are in good condition. If they are damaged, they should be repaired or replaced in time. If the sealing ring of the rotary motor reducer is damaged, the gear oil in the reducer will leak into the lubricating cavity of the ring gear. After rising, the grease will be thinned, and the thinned grease will be pushed to the upper end face of the inner gear ring, and penetrate into the raceway through the inner oil seal, causing the outer oil seal to seep and drip oil, resulting in rolling elements, raceways and outer Accelerated damage to the oil seal.

Some operators think that the lubricating cycle of the slewing bearing is the same as that of the boom and stick, and it is necessary to add grease every day. In fact, this is wrong. This is because adding grease too frequently will cause too much grease in the raceway, which will lead to the overflow of grease at the inner and outer oil seals. At the same time, impurities will enter the inside of the slewing bearing raceway, accelerating the wear of the rolling elements and the raceway.

4. Maintenance of fastening bolts

Some operators think that the greater the force when the slewing bearing bolts are tightened, the better. In fact, when the tensile force on the bolt exceeds the tensile strength of the bolt itself, the pre-tightening force will not be formed. In order to ensure the reliability of the bolt work, it should be tightened according to the provisions of the pre-tightening torque of the type of bolt. For bolts with a strength of 10.9, a flat washer with a material of 45# steel, quenched and tempered at medium temperature, and a hardness of HRC39 should be used. Spring washers are prohibited.

If 10% of the bolts of the slewing bearing are loose, the remaining bolts will be more stressed under the action of tensile and compressive loads. Loose bolts will generate axial impact loads, resulting in increased loosening and more bolt loosening, resulting in bolt breakage and even machine crashes. Therefore, after the first 100h and 504h of the slewing bearing operation, the bolt pre-tightening torque should be checked. After that, the pre-tightening torque should be checked once every 1000h of work to ensure that the bolts have sufficient pre-tightening force.

After repeated use of the bolt, its tensile strength will be reduced, although the torque when it is reinstalled meets the specified value, but the bolt pre-tightening force after tightening will also be reduced. Therefore, when retightening the bolts, the torque should be 30 to 50 N•m larger 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 pass, all bolts should have the same pre-tightening force.

5. Adjustment of gear clearance

When the ring gear of the slewing bearing is assembled with the output gear of the slewing motor reducer, the backlash of the gear teeth should be adjusted at the highest point of the radial runout of the pitch circle of the slewing bearing. The meshing backlash is selected according to the size of the gear module. Under normal circumstances, the meshing backlash of the gear increases correspondingly with the increase of the gear teeth. At the maximum point of radial runout of the inner pitch circle of the excavator slewing bearing, the backlash Sh value between the gear of the slewing motor reducer and the gear of the slewing motor is ≥0.03m (m is the gear module).

When adjusting the gear gap, pay attention to observe whether the connecting bolts between the rotary motor reducer and the rotary platform are loose, so as to avoid the gear meshing gap being too large or too small. This is because if the gap is too large, it will cause a large impact force on the gear when the excavator starts and stops, and it is prone to abnormal noise; if the gap is too small, it will cause the slewing bearing and the slewing motor reducer pinion to get stuck, even lead to broken teeth.

When adjusting, you should also pay attention to observe whether the positioning pin between the slewing motor and the slewing platform is loose. The positioning pin and the pin hole belong to an interference fit. The positioning pin not only plays a positioning role, but also increases the fastening strength of the rotary motor reducer bolts and reduces the possibility of the rotary motor reducer loosening.

6. Clogged maintenance

The slewing bearing is blocked for the disassembly and assembly of the rolling elements. The positioning pin is of conical structure, which is used to fix the blockage and prevent the blockage from moving. The blockage is located at the non-load bearing position of the slewing bearing, on both sides of the main load plane.

Once the positioning pin that fixes the blockage is loose, it will cause the blockage displacement, causing the raceway to change at the blockage position. When the rolling element moves, it will collide with the blockage and make abnormal noises. When the operator uses the excavator, he should pay attention to cleaning up the soil covered by the blockage, and pay attention to observe whether the blockage is displaced.

7. It is forbidden to wash the slewing bearing with water

It is forbidden to flush the slewing bearing with water, so as to prevent the flushing water, impurities and dust from entering the slewing bearing raceway, causing the raceway to corrode and rust, resulting in the dilution of the grease, the destruction of the lubrication state, and the deterioration of the grease; avoid any solvent from contacting the slewing bearing oil seal , so as not to cause oil seal corrosion.

In short, after the excavator has been used for a period of time, its slewing bearing is prone to noise, impact and other faults. The operator should pay attention to observation and timely inspection in order to eliminate the fault. Only correct and reasonable maintenance of the slewing bearing can ensure its normal operation, give full play to its performance and prolong its service life.

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