Cold assembly method of bushing parts

The cold assembly of bushing parts used in construction machinery is based on the principle of heat expansion and cold contraction of materials, that is, the bushing is frozen first It is the dimension shrinkage of the bushing (changing the interference fit into clearance fit), and then in the process of assembly, the cold assembly scheme can reduce the labor intensity of the assembly workers, reduce the risk in the assembly process, improve the labor efficiency and assembly quality, and avoid the damage of the base metal and the bushing.

1.Liquid nitrogen refrigerant is used for cold assembly. The disadvantage is that the refrigerant is easy to overflow, which may cause frostbite, and the waste of refrigerant will increase the assembly cost. Therefore, industrial freezer is recommended.
The industrial freezer can adjust the refrigeration temperature according to the needs, the temperature control range is – 150 ~ – 10 ℃, the temperature control accuracy is generally ± 0.1 ℃, the cooling speed is 1 ~ 30 ℃ / min, and it is continuously controllable.
Compared with the purchase cost, operation cost, maintenance cost and cooling speed, it is more appropriate to choose industrial freezer.

2.Determine the technical parameters of cold assembly
The technical parameters that need to be determined for cold assembly include the minimum clearance, cold shrinkage, freezing temperature and freezing time.
In order to ensure that all the bushings meet the required cold shrinkage, the freezing time is selected; when the frozen parts are the same bushing, the calculated freezing temperature and freezing time can be used directly; when the frozen bushing is of different specifications, the calculated minimum temperature and the calculated maximum time are taken as the freezing temperature.

3.Precautions for cold assembly
In order to ensure assembly safety, antifreeze gloves should be worn during operation. In order to ensure the assembly quality, the following points should be paid attention to: first, the surface of the bushing should be wiped clean before freezing; second, if the bushing of various specifications and materials is frozen at the same time, the bushing should be labeled; third, the bushing should be arranged orderly in the industrial freezer, and the freezing speed should not be set too fast, so as to avoid the internal injury of the bushing caused by the sharp drop of temperature; fourth, the bushing should be contained before assembly The burr of the parts shall be cleaned, the inner wall of the hole shall be wiped clean, and then the containing parts shall be arranged in order; fifthly, the assembly shall be carried out quickly. If the assembly is not smooth, the copper bar shall be used with the aid of tooling to tap gently. Sixth, when the bushing surface is condensed with thick frost, it shall not be assembled, and the bushing surface shall be wiped clean and then frozen again.

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