Application of cold shrink assembly process
(1) Product limited by structure
The reducer for excavator is an integral main steel structure, with irregular shape and high processing accuracy. If hot mounting is adopted, it is easy to produce deformation, and if press mounting is adopted, it is easy to affect the assembly accuracy, so it can only be assembled by the method of cold shrink idler shaft.
(2) Strictly guarantee the quality of products
Due to the limitation of the box structure, the matching of sleeve and gear must be carried out in the box, and the assembly and correction are not easy, and there is enough assembly space, so it is not suitable to use press mounting. If the hot mounting is adopted, the gear must be heated to more than 350 ℃ according to the juice calculation to meet the requirements in view of the high accuracy and hardness of the gear surface. However, if the heating temperature is 200 ℃ higher than the tempering temperature of the gear, the hardness and service life of the gear will be reduced, and the accuracy will also be affected. Therefore, the cold shrinkage method can be considered for assembly, so that the heating temperature of the containing part (gear) is not higher than the tempering temperature for assembly. In order to ensure the fit quality, it is also necessary to use the cold shrinkage method to assemble and form the assembly clearance.
(3) Product is limited by heating equipment
For some parts with large structure size, the weight can reach several tons, and its complex structure will lead to uneven thickness of the wall. If the hole on the part is locally heated, the whole part will deform greatly. If the whole huge parts are heated, there is no corresponding heating equipment. At this time, it is more economical and feasible to use the method of cold shrink shaft to assemble. Therefore, for the assembly of thin-walled sleeve parts and frame or shell, the interference connection of large package parts and small shaft or pin shaft is particularly suitable for cold shrink assembly.
Determination of cold shrinkage of interference joint
(1) How to obtain low temperature
The methods of obtaining low temperature are compared among industrial low temperature box, deep low temperature box, dry ice condensation, liquid oxygen condensation and liquid nitrogen condensation. Among them, the industrial low temperature box is most suitable for the needs of processing parts, and the cost of deep low temperature box is more economic, which can be used for precise temperature control. The source and storage of dry ice are difficult, while the method of liquid oxygen is not safe because of the active oxygen. The liquid nitrogen cold shrinkage is not suitable for use because of its uncontrollable temperature and accuracy.
(2) Calculation of material shrinkage at low temperature
The shrinkage of different materials at low temperature is different, and the shrinkage of the same material at different low temperature is also different, and the calculation of the shrinkage of materials also needs to consider the technological requirements, mainly to design the appropriate minimum assembly clearance to ensure the smooth assembly.
Advantages of shrink fit interference joint of industrial refrigerator
Through the assembly of interference joint and comparing with other assembly methods of interference joint, it can be seen that the cold shrink assembly of industrial refrigerator has the following advantages:
(I) the shrink fit method of industrial refrigerator basically keeps the interference of connection and meets the design requirements. However, the press fitting mainly by axial force is easy to gnaw the part of the interference, which affects the connection strength;
(2) Considering the influence of the surface roughness of the parts on the connection, the cold shrink assembly increases the firmness of the connection;
(3) after the material with retained austenite is cooled, part of retained austenite can be eliminated, dimensional stability of parts can be improved, and surface hardness can be improved;
(4) the industrial refrigerator cold shrinkage method can save energy, and the cold shrinkage time is short, the assembly time is short, the labor productivity is improved, and the economic benefit is good.