High-insulation, anti-adhesion electric heating tube and its manufacturing process

This invention discloses a high-insulation, anti-adhesion, and corrosion-resistant electric heating tube and its manufacturing process. Its shape is scissor-like. The main feature is that the insulation filling inside the sleeve is composite magnesium oxide powder. The inner cavity of the tube end at the riveting point with the connecting base is sealed with inorganic sealant. The outer surface of the sleeve is sprayed with an anti-adhesion coating. This electric heating tube has high heat transfer efficiency, is corrosion-resistant, and anti-adhesive, making it suitable for heating various hydraulic media.

High-Insulation, Anti-Adhesion Electric Heating Tube and Manufacturing Process Instruction Manual

This invention relates to an electric heating tube for immersion heating that is scale-free and corrosion-resistant, and its manufacturing method.

Existing electric heating tubes use magnesium oxide powder as the insulating filling material. Magnesium oxide powder is hygroscopic, has poor insulation performance, and is prone to leakage. Both ends of the electric heating tube are sealed with resin glue, which is not heat-resistant and softens at around 95°C, resulting in poor sealing. Furthermore, due to the influence of the electric field and water quality, the outer wall of the electric heating tube is prone to scale formation, leading to poor heat transfer performance. These factors cause unstable quality and short service life of existing electric heating tubes.

The purpose of this invention is to provide society with a novel electric heating tube and its manufacturing process, characterized by high insulation, high sealing performance, resistance to scaling, and corrosion resistance.

This invention can be achieved as follows: The electric heating tube comprises a sheath, a heating wire, insulating filler, terminals, a base, and a base cover. The heating tube has a scissor-shaped shape. Its distinguishing feature is that the insulating filler inside the sheath is composite magnesium oxide powder, both ends of the sheath are sealed with inorganic sealant, and the outer surface of the heating tube shell is coated with an anti-adhesion coating.

The composite magnesium oxide powder composition and content are as follows: 78-80% magnesium oxide powder, 11-13% boron carbide, 5-7% boron dioxide, and 2-4% calcium oxide. The above-mentioned magnesium oxide powder is passed through a 60-120 mesh sieve to remove iron, dried to remove moisture, and then a mixture of boron carbide, boron dioxide, and calcium oxide is added and stirred evenly.

The inorganic sealant comprises titanium dioxide, silicon carbide, nickel dioxide, quartz sand, and water glass, wherein titanium dioxide accounts for 15-18%, silicon carbide for 26-30%, nickel dioxide for 6-8%, quartz sand for 13-15%, and water glass for 32-36%. After mixing according to the above formula, the mixture is ball-milled at 200#, stirred evenly, and then water glass is added and stirred again.

The anti-adhesion coating comprises the following components and contents: F-4 dispersion 48.5-49.5%, F-46 dispersion 11-12%, zinc oxide 6-7%, titanium dioxide 2.5-3.5%, mica powder 2.2-2.6%, O-P solvent 1.2-1.5%, tributyl phosphate 0.9-1.1%, white clay 0.6-0.7%, carbon black 0.08-0.11%, and distilled water 24.5-25.5%. The above raw materials are ball-milled and then placed in a container.

The composition and content of the magnesium oxide powder are as follows: 95-96% magnesium oxide, 1.3-3% silicon dioxide, 1-2% aluminum oxide, 0.3-0.4% iron oxide, and 0.8-1.5% calcium oxide.

The positive effects of this invention are: the outer surface of the tube is coated with an anti-adhesion coating, preventing scaling and corrosion; high thermal efficiency; under the same heating conditions, the heating tube of this invention can save 15% more electricity than ordinary heating tubes; good insulation; the national standard specifies an insulation resistance of 2MΩ and a withstand voltage of 1500V/min, while the heating tube of this invention has an insulation resistance of 50MΩ and a withstand voltage of 1600V/min, ensuring safe and reliable use; the composite magnesium oxide powder has a cold insulation resistance of 80MΩ and a hot and humid insulation resistance of 5MΩ. Under conditions of 95% humidity and 45℃, after 48 hours of placement, the water absorption rate is only 0.1%, demonstrating extremely strong moisture resistance. The inorganic sealant has an insulation resistance of up to 2500MΩ, strong adhesion, and high sealing strength (over 200-250 N/cm²), is airtight, watertight, and can withstand temperatures up to 120℃ without softening. The anti-stick coating has good corrosion resistance; after immersion in acid, alkali, salt, and oil solutions at 170-250℃ for 2 hours, it does not soften, peel off, or bubble, making it suitable for heating liquid media.

Figure 1 is a cross-sectional view of the heating element;

Figure 2 is a top view of Figure 1.

The invention and its manufacturing process are further described below with reference to the accompanying drawings: The high-insulation, anti-adhesion heating element comprises a sleeve 1, a heating wire 2, a composite magnesium oxide powder filler 3, a terminal block 4, a connecting base 6, and a base cover 7. The connecting base 6 and base cover 7 are made of aluminum or plastic. A plastic core 11 is installed inside the connecting base 6. The sleeve 1 is made of 10 or L2 aluminum tubing, or T4 or 10 steel. The heating wire 2 is made of iron-chromium-aluminum alloy (OCr13Al1MO2), with a maximum operating temperature of 1250℃ and a tensile strength of 700–850 Nc㎡. The two ends of the heating element are connected to the connecting base 6. The sleeve 1, inserted into the base, is filled with inorganic sealant 5. The outer surface of sleeve 1 is sprayed with an anti-adhesion coating. In this embodiment, the composite magnesium oxide powder composition is as follows: 79% magnesium oxide, 12% boron carbide, 6% boron dioxide, and 3% calcium oxide. The magnesium oxide powder is then sieved through a 60-120 mesh sieve to remove iron, dried, and then mixed with chemical reagents (boron carbide, boron dioxide, and calcium oxide) until homogeneous. This results in composite magnesium oxide powder with the following composition and content: 95% magnesium oxide, 2% silicon dioxide, 1.5% aluminum oxide, 0.4% iron oxide, and 1.1% calcium oxide.

The inorganic sealant 5 comprises 16.3% titanium dioxide, 28% silicon carbide, 7% nickel dioxide, 14% quartz sand, and 34.7% water glass. The mixture (excluding water glass) is ball-milled at 200# after mixing according to the above composition and content, and then water glass is added and mixed thoroughly.

The composition and content of the anti-adhesion coating are as follows: F-4 dispersion 49.1%, F-46 dispersion 11.4%, zinc oxide 6.55%, titanium dioxide 3.3%, mica powder 2.4%, O-P solvent 1.33%, tributyl phosphate 0.1%, white clay 0.66%, carbon black 0.09%, and distilled water 25.1%. During preparation, the 50% solids content of the F-46 dispersion is poured into a flat container and placed in an oven at a temperature not exceeding 120℃. A fan is used to accelerate moisture evaporation. The dried F-46 is then ground into powder in a ball mill and passed through a 120-mesh sieve. According to the formula, F-46, pigments, and dispersions are added to the ball mill cylinder, and water is added to form a slightly flowing viscous substance. Magnetic balls are then added, and the mixture is ground for 36 hours. The F-46 dispersion is then added to the ground slurry according to the formula, and the mixture is stirred until homogeneous to obtain the anti-adhesion coating.

In this embodiment, tubes 10 and 12 are used as the casing for the heating element. The process involves cutting and deburring, straightening, spraying, cleaning, winding the heating wire, riveting, applying composite magnesium oxide powder, filling with powder, shrinking the tube, forming, and sealing. After the two ends of the heating element are riveted to the connecting base 6, inorganic sealant is injected into the cavities at both ends of the tube for sealing. The first step in the anti-adhesion coating spraying process is to clean the oil stains on the outer surface of the casing; the second step is sandblasting, followed by sand removal; the third step... The first step is to spray an anti-adhesion coating onto the outer surface of the sleeve using a spray gun at a pressure of 20-40 N/cm². Then, immediately place the sprayed sleeve into an oven at 60-80°C to dry it. The fourth step is to place the dried sleeve into a high-temperature oven at 360-380°C for sintering for 15 minutes to allow the anti-adhesion coating to slightly melt and form a film. The fifth step is to remove the sleeve from the high-temperature oven, quickly immerse it in water to cool it, and then slightly polish the surface to increase the smoothness of the outer surface.