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Jul 05 2023
How to Improve the Lifespan and Feasibility of Double Row Ball Slewing Bearings?
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Slewing bearing is important connecting component of excavators, playing a supporting role. During use, due to installation accuracy errors, improper use and maintenance, and other factors, some faults and hidden dangers may arise in the slewing bearing, which can seriously affect the normal operation of excavators and even cause major safety accidents, resulting in unnecessary losses. Therefore, it is particularly important to effectively carry out the reasonable design, selection, installation, use, and maintenance of slewing bearing, and to prevent failures. SWBTEC recommends doing the prevention work well from the following aspects to ensure the normal operation of the host to the greatest extent.
The internal structure of the excavator slewing bearing is relatively precise, and the slewing bearing of excavators must withstand the effects of large axial loads, radial loads, and overturning moments at the same time. At present, the most commonly used slewing bearings are four types, including single-row and double-row ball-shaped, single-row cross-roller, and three-row cylindrical roller. The bearing capacity of different types of slewing bearing is different. The bearing capacity of the bearing is given by the bearing load curve. When calculating the selection, the allowable torque should be greater than twice the calculated torque of the excavator to ensure that it has sufficient margin.
The turntable bearing is a relatively weak part of the whole machine structure. If there is not enough connection stiffness up and down, it is extremely easy to cause deformation, produce abnormal release of strain energy, and finally cause fatigue cracking of the connecting components or too large periodic elastic deformation, which will also cause additional impact loads on the raceway.
In theory, the axial assembly clearance of the slewing bearing should be strictly controlled between the rolling elements and the rolling groove to values smaller than 0.3-0.5mm. However, due to factors such as manufacturing processes, it is often unable to meet the control requirements. This results in a significantly greater dynamic load during rotation, and in the process of the boom being retracted and extended, the turntable bearing has a large transverse motion at the variable amplitude balance point, damaging the raceway. In addition, improper control of manufacturing tolerances of the rolling elements can also result in too small installation clearances. During the process of transferring the axial load to the rolling elements, it causes extrusion between the rolling elements, increases the local operating resistance, increases the sliding friction force between the rolling elements and the raceway, increases wear between the moving pairs, and reduces the service life.
As a heavy-duty, high-precision product, the excavator slewing bearing have detailed installation technical requirements, and several points must be highly valued:
For welded cylinders, heat treatment should be performed to eliminate internal stress, and the installation base surface should be mechanically machined or ground to maintain flatness.
When the turntable bearing is manufactured, there will be a quenched soft belt on the raceway. This soft belt should be placed in the non-load area or non-frequent load area. For excavators, it can be installed in the direction parallel to the track.
The gear tooth jump of the slewing bearing ring gear and gear often has the largest value in three teeth. Turntable bearing manufacturers mostly make obvious markings at this point, which is the best position to adjust the tooth side clearance of the drive small gear. If the clearance adjustment between the large and small gears is not good, it will bring destructive wear to the large gear and also bring additional loads such as impact or resistance to the rotation drive and its connecting components, affecting the service life of the rotation drive motor and reducer.
The installation of excavator slewing bearing should use high-strength bolts of appropriate strength grade, and use quenched washers instead of spring washers. The installation bolts should use a torque wrench to ensure sufficient preload force.
