Why the end of electric tubular heating elements should not be sealed completely?
In order to prevent both ends of electric tubular heating elements from being damaged by moisture and moisture absorption, both ends of tubular heating elements orifice are generally sealed, also referred to as "sealing". However, the end of electric tubular heating elements should not be sealed completely because there is a "breathing" process in the working process of the electric tubular heating elements.
In the manufacturing process of electric heating pipe, when the electric melting crystal magnesium oxide or other fillers are filled between the pipe and the electric heating wire, it can not fill all the space. For example, the bulk density of the electric melting crystal magnesium oxide is 3.32g/cm3, but the filling density can only reach 2.5g/cm3. In other words, there is residual air. Although some of the residual air can be eliminated in the following processes, such as shrinkage, annealing and bending, it can not be completely eliminated. When the tubular electric heating element is powered on and heated, the residual air in the heating pipe expands and forms a large air pressure in the tube. The pressure depends on the amount of residual air, moisture, crystal water and temperature in the tube. Sometimes it is as high as 200 kgf / cm3. Depending on this strong pressure, a part of the gas inside the electric heating tube will be released through the end of the tube to form "exhalation". When the electric heating tube stops heating or cooling, the residual air in the tube shrinks due to cooling, resulting in negative pressure or local vacuum. Depending on the negative pressure, a part of air will be inhaled from the outside through the tube end, which is called "suction". The existence of the breathing process of the tubular electric heating element puts forward special requirements on the performance of the sealing material, that is, it needs to be sealed and can not be sealed, unless the residual air, moisture and crystal water content in the electric heating tube are sufficient, and the maximum pressure is formed inside after heating When the metal shell in the working state has enough strength, will not burst, otherwise, there will be a huge danger.
People need to breathe. In fact, for electric heating elements, they also need to breathe. Therefore, the end of electric tubular heating elements should not be sealed completely.