Application of heating technology in Heat Shrinkable Tube of ultra long cable

Heat Shrinkable Tube is a common protection material in cable processing, which is divided into single wall Heat Shrinkable Tube (inner wall without glue) and double wall Heat Shrinkable Tube (inner wall with glue). Double-wall Heat Shrinkable Tube is mainly used to protect cable connectors, while single-wall Heat Shrinkable Tube is mainly used to protect the whole cable.

In the electronic installation and connection of the system, the number of cables larger than 20m is very large. The longest fully-protected cable is 60m long. After the whole cable is put through the heat shrink sleeve, the traditional heat shrink processing method is to use the heat gun to gradually shrink, which has the following disadvantages: 

(1) the heat capacity of the heat gun is small, and the temperature of the casing is slow; 

(2) local dispersion heating, heating needs to rotate the cable, the efficiency is very low; 

(3) the casing heating is not uniform, which is difficult to ensure the quality; 

(4) The tool cost is high, and the hot air gun is easy to be damaged in long-term use.

With the development of electronic system, hot air gun can no longer meet the demand of mass production. It is urgent to seek a new tool and a new process method to improve its production efficiency, shorten the processing cycle and improve product quality.

The heat shrinkable tube heating box has the advantages of fast heating, large heat capacity, centralized heating, simple structure and convenient use. The new heating box consists of two groups of heaters, thermocouple, temperature display controller, relay, fan and box, etc.

The heating box is a rectangular box, made of stainless steel plate, the wall of the box has a heat insulation sandwich, which plays the role of heat preservation and prevents the temperature of the outer wall of the box from burning the operator. The upper layer is heated by two 2kw electric furnaces, and a partition is installed in the electric furnace and cable heating area to ensure the safety of the cable and the operator. A WRN-191/K thermocouple is installed above the partition for temperature measurement in the cable heating area. The upper layer has a space of about 0.8m3. When heating the cable or the heat shrinkable tube, enough heat will be stored so that the temperature will not drop significantly due to the cable passing through, which ensures the continuity of cable processing. The lower part is installed with temperature controller, relay, fan and other parts, forming a complete heating and temperature measurement control circuit. The core part of the circuit is Omron E5CZ digital temperature controller.

When the heating box is working, the temperature controller compares the measured temperature provided by the thermocouple with the set upper and lower limits. When the measured temperature is less than the upper limit, the relay is turned on to connect the heater power for heating. When the measured temperature is greater than the lower limit, the relay is turned off to cut off the heater power to cool down. The heating box is equipped with two axial fans, which will start to work when the power is switched on, so that the air in the box can keep flowing, to achieve the purpose of heat balance and uniformity in the box.

In the previous processing with the hot air gun, the temperature of the hot air gun is set at 380℃, but the actual temperature is only about 260℃. The Heat Shrinkable Tube needs to be heated to 120℃~140℃, and it is an open disperse heating, which is really slow. The heating box adopts closed centralized heating, and the length of the heated cable is up to 0.7m(the heat gun is only 0.02m). Depending on the thickness of the cable, more than a dozen cables can be processed at a time.