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Radiant heating tube is a device that encloses the electric heating element inside a protective sleeve and energizes it to generate heat. The sleeve indirectly radiates heat to the furnace lining and the workpieces being treated. It is widely used in various heating furnaces in the heat treatment industry.
Radiant Heating Tube The electric heating alloy material used should have high electrical resistivity and high electrothermal conversion efficiency. Since the radiant tube is placed inside a sleeve, the heat transfer process differs from that of open-type electric heating elements. It has greater thermal shielding, and the element temperature must be controlled during the heating process to prevent overheating. When the radiant tube is heated in a closed manner, the surface temperature of the electric heating element is about 100°C-150°C higher than the furnace temperature. Therefore, when selecting materials, it is necessary to analyze the furnace temperature and the atmosphere inside the furnace to choose the correct heating material.
Radiant Heating Tube The electric heating alloy material used should have high electrical resistivity and high electrothermal conversion efficiency. Since the radiant tube is placed inside a sleeve, the heat transfer process differs from that of open-type electric heating elements. It has greater thermal shielding, and the element temperature must be controlled during the heating process to prevent overheating. When the radiant tube is heated in a closed manner, the surface temperature of the electric heating element is about 100°C-150°C higher than the furnace temperature. Therefore, when selecting materials, it is necessary to analyze the furnace temperature and the atmosphere inside the furnace to choose the correct heating material.
Currently, the Radiant Tube Heating Tube series includes squirrel-cage type, vertical strip type, and spiral type. The heating elements use imported or domestic resistance wire, nickel-chromium wire (or strip), iron-chromium-aluminum (wire or strip). The protective tube is made of imported high-temperature alloy plate, heat-resistant steel plate rolled and welded, or centrifugally cast. It features high-temperature oxidation resistance, good carburization resistance, and long service life.
Main technical and performance parameters:
1. Cold state resistance error of electric heating wire ≤3%
2. Insulation resistance between the outer protective tube and the heating wire is greater than 2MΩ
3. Outer diameter of the heating tube: from φ60mm to φ300mm in various specifications
4. Heating power: from 2KW/piece to 24KW/piece in various specifications
5. Length of the heating tube outer tube: from 800mm to 2800mm in various specifications
6. Wall thickness of the radiant tube outer tube: from 1.5mm to 16mm in various specifications.
Radiant Heating Tube often uses materials such as Cr20Ni80 (nickel-chromium series), Cr25A15, Cr21A16Nb, Cr27A17Mo2 (iron-chromium-aluminum series). The chemical composition of each material is shown in the table below:
Cr20Ni80 is used at 500°C-800°C. Due to its stable, single, and uniform solid solution structure, it has good room temperature and high-temperature mechanical properties, uniform electrical and physical properties, and good processing properties. It differs from iron-chromium-aluminum series electric heating alloy materials in terms of low operating temperature, long service life, and resistance to damage.
Cr25A15, Cr21A16Nb, Cr27A17Mo2 are used at 800°C-1200°C, with the operating temperature increasing in that order. Low plasticity and high brittleness are the biggest disadvantages of iron-chromium-aluminum series electric heating alloy materials. Especially in the temperature range of 400°C-800°C, prolonged use can cause the precipitation of "CrFe" type metal compounds within the material, leading to a sharp decrease in alloy plasticity and severe embrittlement. Therefore, iron-chromium-aluminum series electric heating alloy materials should avoid forming and using in this temperature range. The earliest radiant tube furnace was invented and used in Germany in the 1930s. Its structure was a single-layer straight tube type, placed horizontally or vertically through the furnace chamber. It was not until the early 1950s that U-shaped radiant tubes were developed, and on this basis, W-shaped, as well as P-shaped and O-shaped with exhaust gas recirculation, were developed. Because U-shaped and W-shaped tubes have advantages such as large effective heating area, high fuel utilization, and relatively easy control and operation, they are most widely used in large continuous annealing furnaces for strip steel.
Note: The above information and technical parameters are compiled and released by Yangzhou Dare Electric Co., Ltd.
