The cold assembly process

Cold assembly  is a kind of assembly method that uses cooling medium to cool the parts which need to be installed in the base hole first, so as to shrink their dimensions and generate assembly clearance between the assembly surfaces, so as to facilitate the assembly of parts.

Characteristics of cold charging process

(1)It is simple, convenient, economical and practical. In operation, it is only necessary to carry out a simple verification of the reference dimension, and after cooling, it is not necessary to measure the dimension, and it can be assembled directly;

(2) More secure and reliable. In the past, in the case of being unable to load, it was often necessary for workers to use sledgehammer or crane to lift heavy objects for impact in order to complete the assembly. This kind of operation has a certain degree of danger. Some workers broke their fingers in the impact. However, with cold assembly, the parts can be easily put into the base hole because of the large shrinkage when they are cooled below – 120 ℃ in the industrial refrigerator, and the small size parts can be assembled by only one person;

(3) The repair quality is improved and the assembly requirements are ensured. In the past, when it was impossible to install in the hot assembly, the use of hammer and impact often made the sleeve and shaft outer edge to the inner surface of the base hole, resulting in extrusion and scraping effects, resulting in the surface finish and fit interference of the inner surface of the base hole are affected, and the base hole will be worn due to the lack of tension between the sleeve and the hole in the future operation. After cold assembly, the assembly gap increases, which completely avoids the above problems and ensures the quality and accuracy of parts assembly. In addition, in the process of hot assembly, the base hole parts need to be heated and heated, and then cooled in the air, which is equivalent to a low-temperature annealing treatment of parts, reducing the hardness and strength of parts. Cold assembly is equivalent to a deep cold treatment of parts (deep cold treatment, also known as ultra-low temperature treatment, refers to a method of material treatment below – 130 ℃, which changes the retained austenite in the steel structure into Martian loose iron process). After cryogenic treatment, the parts can obtain the following advantages:

A. reduction of austenite, which can make the products not deformed for a long time;

B. increase of hardness and its average;

C. improvement of mechanical properties;

D. dimensional stability;

E. increase of magnetism;

F. increase of wear resistance.

(4) It improves the efficiency and reduces the labor intensity of workers. In the past, the hot assembly of all sets, bearings, shafts and other parts in the overhaul of an electric shovel required 2-3 fitters with strong technical ability. With the cooperation of lifting, gas welding and other types of work, it would take 3-4 days to complete. Now we use cold assembly, only need 2 ordinary fitters, one day to complete. The pure assembly time is less than 4 hours, and in the assembly process, it does not need to use sledgehammer and heavy objects for impact, and it also avoids the repeated measurement of part size under high temperature, thus reducing the labor intensity of workers.

The cold assembly process is easy to operate and has a wide range of applications. In the maintenance of mining shovel, rotary drilling machine and other equipment, the cold assembling method is used to assemble the transition and interference fit parts of some copper sleeve, steel sleeve, bearing, shaft and gear in the equipment, which has changed the traditional assembly process and repair method for decades and achieved good results.

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