There are two main reasons for the early failure of slewing bearings used in excavators: one is broken teeth; the other is raceway damage. Among them, broken teeth are the main reason, accounting for more than 90%, and most of them occur within six months after the excavator leaves the factory. This not only seriously troubles the product quality reputation of the slewing bearing manufacturer, but also has an adverse impact on the product market of the main engine factory. Therefore, it is the common goal and responsibility of the slewing bearing manufacturer and the main engine factory to seriously solve this problem, and it is also the further cooperation between the two parties. The fundamental guarantee for common development.
What is the root cause of the early failure of the slewing bearing due to broken teeth? Design issues; manufacturing issues, material issues; assembly issues or use issues. It is not difficult to find the essence of the problem through the following phenomena:
①In the past 12 years, Ma'anshan Slewing Bearing Factory has provided more than 20,000 sets of slewing bearings for various main engines. Except for the excavator industry, there is only one record of slewing bearing broken teeth, and it happened in the late period. Of course, the working condition of the excavator is worse than that of the main engine in most other industries that use slewing bearings such as tower cranes and automobile cranes. This is also an indisputable fact. Therefore, the modulus of the slewing bearing for excavators is one grade larger than that of the slewing bearings for main engines in other industries with the same raceway diameter, and it is a hard tooth surface (generally choose different hardness segments between 47HRC and 58HRC), which basically meets the requirements Excavator requirements for slewing gears. Although statistics show that the probability of early broken teeth of slewing bearings used by excavators is greater than that of other main engines, it is only limited to two or three types of excavators, and most models rarely have early broken teeth accidents of slewing bearings.
②According to the analysis of the data we have, the modulus of the slewing bearing gear used by most of the 20-22 ton excavators at home and abroad is 10mm (or diameter pitch = 2.5), the heat treatment and precision level are basically the same, and the domestic excavators are generally Adopt standard tooth height and standard pressure angle. Permissible circumferential force P of slewing ring gear can be calculated as follows:
P=Kz*m*b/78 (tons) where Kz=(z/150)^(±0.09) + for external teeth; -z for internal teeth - number of teeth m - modulus mmb - tooth width mm If the tooth is set Width b=80; number of teeth z=90~110; and it is internal meshing, then the allowable circumferential force of the gear is:
p=(90～110/150)^(-0.09)*10*80/78=10.74～10.55 (tons)
It can be seen that the circumferential allowable force of the gear can meet the load requirements of the tonnage excavator on the slewing ring gear, but the early tooth breakage rate of the slewing ring of some models in this level is as high as 2%, and most other models have no This phenomenon occurs.
③Through the analysis and study of many early broken teeth, it is found that most of the broken teeth occurred in the upper half along the tooth width direction, and more than half of the broken surfaces intersected with the upper end surface of the teeth, and formed an angle of about 45°-60° Even if all the teeth fall off, the cracks are caused by the expansion from top to bottom. The plastic deformation caused by the extrusion of the gear is also quite obvious, and the upper part is much more serious than the lower part. The width of the tooth space of the whole ring varies to varying degrees, and the width of the tooth space increases from bottom to top and from root to top.