Application Note of Low Temperature Refrigerator for Cold Shrink Assembly of Automobile Engine Parts
Engine assembly is carried out in a low-temperature environment below minus 30°C in a low-temperature refrigerator. The mainstream automobile engine manufacturers have their own low-temperature assembly workshops. Engines assembled in a low-temperature environment have good sealing properties and are not prone to oil leakage. Only in this way can they be produced. Produce high-quality engines.
There are three typical fits of hole and shaft, namely clearance fit, transition fit and interference fit In simple terms, clearance fit means that the diameter of the hole is larger than the shaft diameter, which can be assembled at room temperature. The shaft diameter of the interference fit is larger than the aperture, and the interference fit is a tighter and firmer fit. But the problem is that it is impossible for us to fit the large-diameter shaft into the small-diameter hole at room temperature. This requires the help of very hand-breaking, using the principle of thermal expansion and contraction to let the shaft shrink and expand, and then match the shaft hole. Return to normal temperature and achieve a tight interference fit.
The principle is like this. This is why the overall performance of the engine is severely reduced after the overhaul of the engine, because the room temperature fit cannot meet the technical requirements of the interference fit, so there will be poor sealing, and perhaps no oil leakage, but During high-temperature and high-speed operation, there will be slight air leakage, so the power will also drop, and fuel consumption will naturally increase. In order for the two parts to achieve an interference fit to transmit torque, the hole must be heated to expand, and the shaft must be cooled and contracted. In this way, under different temperature differences, the hole and the shaft in the original interference state become a clearance fit, which can be assembled smoothly. When the hole and the shaft return to the same temperature, the hole and the shaft are in an interference state and can withstand The predetermined torque and axial force.
The low-temperature refrigerator for cold-shrinkable assembly of automobile engine parts must be different in temperature between the shaft part and the hole part. If the temperature is the same, the same expansion or the same contraction of the shaft and the hole, it is impossible to complete the interference fit. Therefore, the low-temperature assembly in the so-called low-temperature workshop is not true. The hole needs to be heated to a higher temperature, and the shaft needs to be frozen to a low temperature in the low-temperature assembly box. At this time, the fit will change the nature of the fit, from an interference to a clearance fit.
to sum up The assembly process of cold shrink assembly of automobile engine parts is as follows: Take out the workpiece cooled to low temperature from the low temperature assembly equipment, the workpiece will not return to room temperature immediately. At this time, the heated mating part will be assembled with it, and then returned to room temperature to complete the process. The interference fit.
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