In the electric heating tube structure, the spiral heating wire and the metal tube outer casing are filled with a dense powdery filler. The filler has good thermal insulation properties in the case of dry compaction. However, they all have different degrees of hygroscopicity, and the fillers exposed at both ends of the heating tube are greatly reduced in electrical insulation properties once moisture is absorbed. When the end of the heating pipe is not sealed, the influence of the moisture absorption of the packing on the insulation performance of the electric heating pipe is great.
On the other hand, when magnesium oxide is moisture-absorbing, a part of magnesium oxide (especially a portion having a poor or incomplete crystalline state) will undergo hydration. The hydrated magnesium oxide will thicken its molecular size and agglomerate. For the electric heating tube, the nozzle has the most moisture absorption, so the agglomeration is also serious. Once the nozzle is agglomerated, the moisture absorbed by the deeper filling of the nozzle is more difficult to discharge, so that the electric heating tube can not restore the insulation when the electric heating is self-heating, and even the water in the heating tube is heated and vaporized and expanded. The false heating tube wall is convex and bursting.
When the humidity is wet, the insulation decreases, and the molecular size increase after hydration affects the recovery of the insulation resistance of the heating tube. For these two points, the electric heating tube needs to be sealed by the port.
Therefore, electric heating pipe port sealing is a very important production process.
