The heat shrinkable sleeve is made of high pressure polyethylene with additives, extruded, treated with high energy radiation, and then expanded and shaped in proportion. When heated to a certain temperature, it has the ability of natural recovery to the shape and size before expansion, and has the characteristics of high mechanical strength, good wear resistance, chemical resistance, corrosion resistance and aging resistance. Therefore, it has been widely used in communication, electric power, petroleum, chemical industry and home appliance industry. In the past two years, in the refrigerator industry, heat shrinkable sleeve is applied to the fastening of copper aluminum joint, isolation of copper aluminum pipeline, parallel connection of low-pressure return pipe and capillary.
In the history of refrigerators at home and abroad, the combination of capillary tube and low-pressure return tube as heat exchanger adopts penetration method or welding method to absorb the heat of the liquid in the capillary tube through the steam in the return tube, so as to overheat the steam and supercooling the liquid in the capillary tube.
The penetration method has good heat exchange effect. The capillary is less exposed to the outside and is not easy to be worn and bruised, but the process is relatively complex. Two holes shall be drilled on the low-pressure pipe. After the pipe is cleaned, the capillary shall be penetrated, and then the two holes shall be firmly welded with silver electrode, and then leakage detection shall be carried out. This process not only wastes silver electrode, but also increases the chance of leakage for the refrigeration system, which leads to the decline of product quality. With this process, 1.2g silver electrode is used for two welded junctions, such as 200000 sets per year, 240 kg silver electrode, worth 108000 yuan. The leakage rate of this structure is about 5%. The maintenance cost of each set is 60 yuan, which is about 6000 yuan more per year.
The heat exchange effect of solder paste method is worse than that of penetration method, but the process is simpler. If mass production, special equipment is needed, and the cost of solder consumption is higher. In addition, due to the dry heating in the welding process, the walls of the low-pressure pipe and the capillary pipe should have a different degree of oxide layer, which makes it difficult to clean the pipe and easy to cause the dirty blockage of the throttling mechanism in the system, so this method reduces the life of the refrigerator to different degrees.
In order to improve the quality of products, we began to find new process methods. In 1985, inspired by the imported single door evaporator copper aluminum joint using heat shrinkable sleeve to protect the copper aluminum solder joint, the capillary tube and low-pressure tube were combined with heat shrinkable sleeve for test. It was found that this method is better than the penetration method and the welding method, which not only has the disadvantages of high cost, complex process, special tooling and equipment, but also plays a protective role It also avoids the corrosion caused by the contact of capillary tube and low pressure return pipe with the external medium. Especially in the refrigerator with aluminum tube sheet integrated evaporator, where the aluminum tube and copper tube are combined or contacted, they are respectively protected by heat shrinkable sleeve, which avoids the electrochemical corrosion caused by copper and aluminum, and relatively prolongs the life of the refrigerator. By using this process, the low flame temperature of gas welding gun can meet the requirements of the process. It is easy to operate, fast and suitable for large-scale production. The work efficiency is 5-6 times higher than that of penetration and welding.
The application of heat shrinkable sleeve in other refrigeration devices, such as freezer, large refrigerator, air conditioner and air conditioner, will also produce good results.