All machines will experience wear and tear 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 in the long-term outdoor harsh environment and high-load operation, so to what extent does it meet the scrapping standard of the tower crane slewing bearing?

Scrap standard of tower crane slewing bearing

1. Slewing bearing raceway ring and rolling element wear and scrap

The wear of raceway rings and rolling elements is one of the common forms of scrapped slewing bearings. When there is raceway pitting on the surface of the slewing bearing, surface metal peeling and overall wear, abnormal noise, rolling element jamming and excessive clearance between the raceway rings will occur in the tower crane during operation, resulting in vibration and local impact. With the development of the state, the slewing resistance will continue to increase and the slewing function will be lost.

2. The slewing bearing cage is damaged and scrapped

In order to avoid mutual friction between the rolling elements, the tower crane slewing bearing usually adds a spacer cage between the rolling elements. The material of the cage is generally copper, plastic, powder metallurgy or mild steel. During the working process of the bearing, the cage does not transmit the load, but it moves with the rolling elements. When the cage is damaged or broken, there will be a sharp and ear-piercing abnormal sound. As the broken body of the cage is pushed and rolled by the rotating rolling body, it will cause serious damage to the raceway ring and the rolling body. At this time, the slewing bearing meets the scrap standard and can be replaced.

3. The slewing bearing gear teeth are damaged and scrapped

The gear meshing methods of tower crane slewing bearing include external tooth meshing and internal tooth meshing. When the surface of the gear teeth is excessively worn, cracks and broken teeth occur. The tooth side clearance of the tower crane slewing bearing gear teeth increases, causing the slewing bearing to lose its function immediately when the tooth is broken, and it cannot be repaired. At this time, the scrapping standard of the tower crane slewing bearing is reached.

4. The connecting bolts of the slewing bearing are damaged and scrapped

Although the connecting bolt of the slewing bearing is not the bearing body, the failure of the bolt will also cause the slewing bearing to fail to work. The damage of connecting bolts in tower crane work is also a common phenomenon. When a slewing bearing connecting bolt loosens or breaks, it often brings about a chain reaction of loosening and breaking of other bolts. At this time, the slewing bearing also needs to be replaced.

5. The slewing bearing is scrapped due to corrosion and burn damage

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, it will damage the internal components of the bearing and cause the bearing to be scrapped.

Service life of tower crane slewing bearing

Under a certain load, the number of revolutions or hours that a bearing experiences before pitting occurs is called bearing life. The service life of tower crane slewing bearing is affected by rotational speed, radial load, basic rated load, equivalent compliance, 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, converted into the load under the experimental conditions is called the equivalent dynamic load. For the bearing components, this load is variable. During the experimental study, the bearing life is 106 turns to The unit is more convenient (counter), but in actual production, the general life is expressed in hours, so it is necessary to convert L10×106=Lh×60n.

2. Calculation method of tower crane slewing bearing life

(1) Knowing the bearing type, load and shaft speed, calculate Lh;

(2) Knowing the load, speed and life expectancy, calculate C, and select the bearing model.

Usually, the medium repair or overhaul limit of the machine is taken 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 the relevant content about the scrapping standard of the tower crane slewing bearing. The tower crane may affect its service life due to its complex use environment. At the same time, good maintenance and repair can also prolong the service life of the tower crane slewing bearing.

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