Among the factors that affect the quality of electric heating pipes, the quality of materials accounts for important reasons. Reasonable selection of raw materials for electric heating pipes is a prerequisite for ensuring the quality of electric heating pipes.
1. Selection principle of pipe: temperature and corrosion resistance.
For low temperature pipes, BUNDY, aluminum pipes and copper pipes are generally used, and high temperature pipes are generally made of stainless steel pipes and Ingle pipes. Ingrid 800 electric heating tube can be used under the condition of poor water quality. Ingle 840 electric heating tube can have good anti-oxidation performance under high temperature working condition and has good corrosion resistance.
2. Selection of resistance wire
Commonly used electric resistance wire materials in electric heating pipes are Fe-Cr-Al and Cr20Ni80 electric resistance wires. The iron chrome wire selected by KAWAI is 0Cr25Al5 grade, which has higher melting point than ordinary iron chrome wire and has better service life. The main difference between the two types of resistance wires is that the melting point of 0Cr25Al5 is higher than that of Cr20Ni80, but at higher temperatures, 0Cr25Al5 is more susceptible to oxidation, while Cr20Ni80 can maintain stable performance at high temperatures. Therefore, the resistance wire used in a high temperature state generally uses Cr20Ni80.
3. Selection of magnesium oxide powder
Magnesium oxide powder is located between the resistance wire and the tube wall for insulation between the resistance wire and the tube wall. At the same time, the magnesium oxide powder has good thermal conductivity. However, magnesium oxide powder has a strong hygroscopic property, so it must be subjected to moisture-proof treatment (magnesium oxide powder modification or electric heating tube sealing treatment).
Magnesium oxide powder can be divided into low temperature powder and high temperature powder according to the temperature range used. The low temperature powder can only be used below 400 ° C, generally modified magnesium oxide powder.
The magnesium oxide powder is granulated, and the magnesium oxide powder used for the electric heating tube is configured by arranging magnesium oxide powder particles of different thicknesses according to a certain ratio (mesh ratio).
4. Selection of sealing materials
The function of the sealing material is to prevent the moisture in the atmosphere from entering the magnesium oxide powder from the nozzle, so that the magnesium oxide powder is damp, the insulation performance is lowered, and the electric heating tube is leaked and fails. The modified magnesium oxide powder may not be sealed.
The materials used for the sealing of electric heating pipes (moisture proof) are mainly glass, epoxy resin, silicone oil and the like. In the electric heating tube sealed with silicone oil, after heating, the silicone oil in the nozzle portion is volatilized by heat, and the insulation of the electric heating tube is lowered. The temperature resistance of the epoxy resin material is not high, and it cannot be used in a high-temperature electric heating tube such as a grill or a microwave oven having a high nozzle temperature. Glass has a higher temperature resistance, but the price is higher, and more is used for the sealing of high temperature pipes.
In addition, there are silicone tube, silicone sleeve, porcelain beads, plastic insulators and other components in the nozzle part, mainly to increase the electrical clearance and creepage distance between the lead rod and the metal wall of the nozzle. Silicone rubber acts as a filler and bond.
