Scrap Standard and Service Life of Tower Crane Slewing Bearing
All machines will suffer loss and failure after a long period of use. When the parts exceed the service life or are damaged beyond repair, they should be scrapped and replaced. The tower crane slewing bearing is prone to failure and damage when subjected to harsh outdoor environments and high-load operation for a long time. So to what extent can it meet the scrap standard of the tower crane slewing bearing?
The scrap standard of tower crane slewing bearing
1. The slewing ring and rolling elements are worn out and scrapped
The wear of raceway ring and rolling element is one of the common forms of slewing bearing scrap. When the raceway pitting corrosion occurs on the surface of the slewing bearing, the surface metal is peeled off and the overall wear is worn, the tower crane will experience abnormal noise, rolling element jamming and excessive clearance between the raceway rings during operation; vibration and local impact will be caused. With the development of the state, the turning resistance will continue to increase and the turning function will be lost.
2. The slewing ring cage is damaged and scrapped
In order to avoid friction between the rolling elements of the tower crane slewing support, an isolator cage is usually added between the rolling elements. The material of the cage is generally copper, plastic, powder metallurgy or mild steel. The cage does not transmit load during the bearing, but it moves with the rolling elements. When the cage is damaged or broken, there will be a sharp and piercing noise. As the broken body of the cage is pushed and crushed by the rotating rolling elements, it will cause serious damage to the raceway ring and rolling elements. At this time, the slewing bearing meets the scrap standard and can be replaced.
3. The slewing ring teeth are damaged and scrapped
The gear meshing mode of the tower crane slewing support has two kinds of external gear meshing and internal gear meshing. When the surface of the gear teeth is excessively worn, cracks and broken teeth appear. The tooth side clearance of the gear teeth of the tower crane slewing bearing is enlarged, and the slewing bearing will immediately lose its function when the tooth is broken and cannot be repaired. At this time, it reaches the scrap standard of the tower crane slewing bearing.
4. The slewing ring connecting bolts are damaged and scrapped
Although the connecting bolt of the slewing ring is not the bearing body, the failure of the bolt will also cause the slewing ring to fail to work. The damage of connecting bolts in tower crane work is also a common phenomenon. When a slewing bearing connecting bolt is loosened or broken, it will often cause a chain reaction to cause the loosening and fracture of other bolts. At this time, the slewing bearing also needs to be replaced.
5. The slewing bearing is damaged and scrapped due to corrosion and burns
Due to the complex working environment of the tower crane slewing bearing, the situation that the bearing may encounter is also unpredictable. If it is corroded by corrosive substances such as acid and alkali during operation, the internal components of the bearing will be damaged and the bearing will be scrapped.
The service life of the tower crane slewing bearing
Under a certain load, the number of revolutions or hours that the bearing experiences before pitting corrosion is called the bearing life. The service life of the tower crane slewing bearing is affected by the speed, radial load, basic rated load, equivalent conformity, speed coefficient, and fatigue life coefficient.
1. Calculation formula of bearing life
L10-When the bearing load is P, the basic rating life (106 revolutions)
C–Basic dynamic load rating N
ε–index
Ball bearing: ε=3
Roller bearing: ε=10/3
P–Equivalent dynamic load (N)
The load on the bearing under actual conditions: A, R, transformed into the load under experimental conditions is called equivalent dynamic load. For bearing components, this load is variable. In the experimental study, the bearing life is changed to 106 The unit is more convenient (counter), but in actual production, the life is generally expressed in hours. For this reason, it must be converted L10×106=Lh×60n
2. Calculation method of tower crane slewing bearing life
(1) Knowing the bearing model, load and shaft speed, calculate Lh;
(2) Knowing the load, speed and expected life, calculate C and select the bearing model.
Usually take the middle repair or overhaul limit of the machine as the design life of the bearing, generally Lh’=5000, and the temperature coefficient ft should be introduced for the bearing working at high temperature
Ct=ftC
t ≤120 125 150 200 300
ft 1 0.95 0.90 0.80 0.60
The above is about the relevant content of the scrap standard of the tower crane slewing bearing. The tower crane’s service life may be affected due to its complicated use environment. At the same time, good maintenance and repair can also extend the service life of the tower crane slewing bearing.
