How big is the role of magnesium oxide powder in electric heating tubes?

Since a Chinese electric heating pipe factory produced electric heating elements in 1958, the application of electric heating pipe products has become more and more extensive. With the development of society and the national economy, the application of electric heating pipes in the market has become more and more extensive and popular, and has entered thousands of households. As one of the most critical materials for electric heating pipes, magnesium oxide powder is in greater and greater demand, because it has a great influence on the performance of electric heating pipes, so we need to fully understand it.

Introduction to material properties of magnesium oxide

1. At present, the main filling materials of electric heating pipes are: quartz sand, alumina, and electrical grade magnesium oxide. Why choose magnesium oxide as a filling material? Mainly because it is an electrical insulator and thermal conductor. It has high stability. And the price is cheap. Easy to buy. Therefore, it has been widely used in electric heating pipes for a long time.

2. Magnesium oxide manufacturing method After magnesium oxide is refined, it needs 28000℃ when it is electro-melted to make its crystallization completely stable, and then cooled into blocks. Due to the influence of cohesion, the purity of the middle part is higher (ratio 3.58-3.6). This piece is broken by a hammer, and then the iron filings are removed, and then mixed into the currently used filler material magnesium oxide powder. The mesh specification is 40-325 mesh.

3. Magnesium oxide related data Molecular formula: MgO Molecular weight: 40.3 Specific gravity: 3.58 Melting point: 2800℃ Hardness: 5. Specific heat: 0.25Kcal/kg℃ Seawater magnesium oxide crystals are square, and magnesite magnesium oxide crystals are spherical, so magnesite magnesium oxide has a better filling density. In terms of electrical properties, seawater magnesium oxide is better because it contains many impurities, but the performance after processing is better because the content of magnesite magnesium oxide B2O3 is less.

Other impurities in magnesium oxide can improve thermal conductivity, but reduce insulation.

4. Heat treatment of magnesium oxide After heat treatment, the thicker the color of magnesium oxide, the more impurities are precipitated in the crystal. The particle diameter is 1. mm. Fe is not easy to precipitate after heat treatment. The particle diameter reaches 0.5mm. After heat treatment, Fe precipitates and combines with oxygen Fe2O3.

5. The mesh number of magnesium oxide has too much influence on the electric heating tube: the particles are small, the surface is fish scale, the unit weight area is large, it is easy to absorb moisture, which affects the service life of the electric heating tube and causes serious pollution to the on-site filling environment. The mesh number is too small: the larger the particles, the surface of the electric heating wire affects the service life of the electric heating tube, and the filling is easy to cause eccentricity of the fine wire, messy wire, heating wire core voids and other undesirable phenomena.

6. Magnesium oxide hygroscopic characteristics Magnesium oxide produces chemical hygroscopicity when stored for more than one year. It must be dried at 500℃ for 4 hours before use. If stored in a short term, it should be dried at 150℃ for 1 hour before use.

7. The relationship between the thermal conductivity of magnesium oxide and temperature When the filling density of the electric heating tube is 2.9/cm3, the thermal conductivity coefficient of the linear electric heating tube is 15mm. When the bending radius of the electric heating tube is 1/2 times that of the straight line, high temperature will cause wire breakage. The remedy is to process the oil pressure of the bent part.

8. Magnesium oxide sintering ℃ After heat treatment, the bond between MgO particles is cement, and this phenomenon is called sintering. The main reason for this phenomenon is the B2O3 or Fe2O3 contained in magnesium oxide.

9. Magnesium oxide impurity capacity The continuous use of Fe2O3 contained in MgO will gradually reduce the insulation resistance of the electric heating tube, which is due to the partial pressure of O2 in Fe2O3.

Definition of electrical grade magnesium oxide

The fused crystal magnesium oxide block is broken and mixed with different particle sizes (mesh size) in a certain proportion, and used directly or after modification as a high-temperature thermal conductive insulating medium.

Classification of electrical grade magnesium oxide

Magnesium oxide is divided into four categories according to production methods and main uses:

1. Ordinary magnesium oxide classification code P

2. Low temperature moisture-proof magnesium oxide classification code D

3. Medium temperature moisture-proof magnesium oxide classification code Z

4. High temperature magnesium oxide classification code G

Main advantages and disadvantages of electrical magnesium oxide

I. Advantages

1. Good insulation performance and good electrical strength

2. Good thermal conductivity, can transfer the heat emitted by the heating wire to the metal tube

3. Good heat resistance and vibration resistance

II. Disadvantages

It is easy to absorb carbon dioxide and water in the air, and slightly soluble in pure water, but after absorbing carbon dioxide, the solubility increases rapidly, and reacts with water to produce magnesium hydroxide, which rapidly reduces the insulation resistance. Therefore, the electrical insulation performance of the electric heating tube filled with magnesium oxide raw materials is reduced during storage and use, resulting in electrical breakdown and damage. This is the fundamental reason for the short service life of the electric heating tube filled with magnesium oxide raw materials.

In order to overcome the water absorption of magnesium oxide raw materials, magnesium powder manufacturers have tried many methods, one of which is to modify fused magnesium oxide with silicon.

Precautions and problems that magnesium oxide powder should be used in the production and use process

1. Since magnesium oxide is one of the most critical materials in electric heating tubes, relevant performance tests need to be carried out on magnesium powder before adding it to prevent it from being in a budding state. In particular, the leakage current test is more important.

2. At present, many companies often reduce grade requirements in order to save costs, and choose low-priced magnesium powder instead of high-priced magnesium powder or medium-temperature powder instead of high-temperature powder, resulting in frequent explosions of electric heating tubes. Magnesium powder carbonization blackening. Insulation resistance decreases. Poor pressure resistance or poor thermal performance. Therefore, be cautious when choosing magnesium powder. Do not unilaterally ignore quality for the sake of cost, which will cause serious consequences.

3. The storage and placement of magnesium powder should be ventilated, dry, without sunlight, and prevent dust pollution.

Reasons for the blackening of magnesium oxide powder

1. The precipitation of ions in stainless steel causes the magnesium powder to turn black.

2. Due to the low oxygen pressure in the electric heating tube, the magnesium powder turns black.