A double-layer explosion-proof electric heating tube and its manufacturing method

Abstract

This invention provides a double-layer explosion-proof electric heating tube and its manufacturing method, comprising: a double-layer tube body, the double-layer tube body including an inner tube body and an outer tube body arranged coaxially, a first chamber formed within the inner tube body, and a second chamber formed by a gap between the inner tube body and the outer tube body; a heating wire disposed within the first chamber; end caps fixed at both ends of the double-layer tube body, forming a sealed cavity between the first chamber and the second chamber; a cooling needle disposed on the end caps and electrically connected to the heating wire; and filler made of an insulating and thermally conductive material, filling the first chamber and the second chamber. This double-layer explosion-proof electric heating tube significantly improves the safety, reliability, and service life of the heating tube through structural redundancy, making it particularly suitable for applications with high requirements for explosion protection and insulation.

Description

Technical Field

[0001] This invention relates to an electric heating element, and more particularly to a double-layer explosion-proof electric heating element and its preparation method. Background Technology

[0002] Existing electric heating elements are typically single-layered tubes containing heating elements such as resistance wires. When the heating element is powered on, the resistance wire generates heat as current flows through it. Under normal circumstances, the internal pressure of the heating element is maintained within a normal range. However, in actual use, problems may arise, such as moisture or impurities accumulating at the cold and hot ends, causing them to migrate at high temperatures; or contamination or defects in the raw materials leading to high-current spark breakdown. Alternatively, external moisture may seep into the tube, causing high-pressure gas to build up inside that cannot be released in time. When the pressure accumulates to a certain level, exceeding the mechanical strength of the tube shell at that temperature, the tube may burst due to excessive internal pressure, posing a safety hazard to the user. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a double-layer explosion-proof electric heating tube with a compact structure, high safety and long service life, and a method for its preparation.

[0004] This invention provides a double-layer explosion-proof electric heating tube, comprising: A double-layered tube body 1, comprising an inner tube body 11 and an outer tube body 12 arranged coaxially, wherein a first chamber 13 is formed inside the inner tube body 11, and a second chamber 14 is formed between the inner tube body 11 and the outer tube body 12 by a gap. Heating wire 2 is disposed in the first chamber 13; End caps 3 are fixed to both ends of the double-layer tube 1, and make the first chamber 13 and the second chamber 14 form a sealed cavity; The cold needle 4 is disposed on the end cap 3 and is electrically connected to the heating wire 2; The filler, made of an insulating and thermally conductive material, is filled in the first chamber 13 and the second chamber 14.

[0005] Furthermore, the end of the inner tube 11 protrudes or is flush with the end of the outer tube 12.

[0006] Furthermore, the distance between the inner wall of the inner tube 11 and the heating wire 2 is greater than or equal to 1.2 mm.

[0007] Furthermore, the distance between the outer wall of the inner tube 11 and the inner wall of the outer tube 12 is greater than or equal to 1.5 mm.

[0008] Furthermore, the packing density of the filler is greater than or equal to 2.3 g / cm³.3 .

[0009] Furthermore, the distance between the outer wall of the inner tube 11 and the inner wall of the outer tube 12 is greater than the distance between the inner wall of the inner tube 11 and the heating wire 2.

[0010] Furthermore, the inner tube 11 and the outer tube 12 have the same wall thickness.

[0011] Furthermore, the end cap 3 is provided with a coaxial first annular protrusion 31 and a second annular protrusion 32 at its end. The inner wall of the first annular protrusion 31 is attached to the inner wall of the outer tube 12. There is a gap between the inner wall of the first annular protrusion 31 and the outer wall of the second annular protrusion 32, forming a mounting groove 320. The wall thickness of the inner tube 11 is the same as the width of the mounting groove 320 and is embedded in the mounting groove 320.

[0012] Furthermore, the filler is magnesium oxide powder.

[0013] Furthermore, both the inner tube 11 and the outer tube 12 are made of stainless steel.

[0014] Meanwhile, the present invention also provides a method for manufacturing a double-layer explosion-proof electric heating tube, which includes the following steps: S1. Threading the wire: Place the lower rubber plug onto the cold needle at the lower end of the heating wire, and pass the heating wire through the inner tube that is vertically fixed on the powder filling machine. Fix the cold needles at both ends to ensure that the heating wire is coaxial with the inner tube. Fix the lower rubber plug to the lower end of the inner tube. S2. First filling: Magnesium oxide powder is filled into the tube. Vibration is used to make the magnesium oxide powder fill the first chamber evenly and densely, and the heating wire is fixed in the center position. A rubber stopper is installed at the upper end of the inner tube. S3. First tube shrinking: The inner tube body after filling is shrunk by a tube shrinking machine to compact the density of the magnesium oxide powder inside and expel air. S4. Sleeve: Remove the rubber plugs at both ends of the inner tube, pass the inner tube through the outer tube that is vertically fixed on the powder filling machine, and fix the cold needles at the upper and lower ends, and ensure that the inner tube and the outer tube are coaxial. S5. Secondary filling: Install a rubber plug at the lower end of the outer tube and fill the second chamber with magnesium oxide powder. Vibration is used to make the magnesium oxide powder fill the second chamber evenly and densely, and to fix the inner tube in the center position. S6. Secondary tube shrinkage: A rubber plug is installed at the upper end of the outer tube to shrink the diameter of the double-layer tube, so as to compact the magnesium oxide powder in the second chamber and expel the air. S7. Solution treatment: Remove the rubber stoppers at both ends of the outer tube. Under the protection of a protective gas, heat and solidify the double-layer tube to create a protective layer on the outer surface of the double-layer tube or achieve reduction, while simultaneously venting air. S8. Cooling: Cool the solution-solidified double-layer tube to room temperature in a dry environment. S9. Sealing: In a dry environment, inject sealing material into both ends of the double-layer tube and install end caps to complete the sealing. S10, Forming: Bending the double-layer tube into the desired shape; S11, Hydraulic pressure: Apply hydraulic pressure to the formed double-layer tube to further densify the magnesium oxide powder at the bends of the double-layer tube, eliminating voids and delamination defects. S12. Quality Inspection: Conduct quality inspection on the finished product.

[0015] Furthermore, in step S7, the heating temperature is 950℃-1050℃.

[0016] Furthermore, in steps S3 and S6, the density of magnesium oxide powder in the first chamber 13 and the second chamber 14 is (2.3~2.6) ±0.05 g / cm³.

[0017] Furthermore, in step S11, radial pressure is applied to the double-layered tube by hydraulic pressure, and the radial pressure is 15–20 MPa, with a holding time of 3–5 seconds.

[0018] Furthermore, in step S12, the quality inspection includes one or more of the following: insulation resistance test, withstand voltage test, leakage current test, and airtightness test.

[0019] Furthermore, step S11 includes the following steps: S111, Mold installation: Place the bent heating tube into the pressing mold, ensuring that the bent part is accurately aligned with the compaction area; S112. Pressing: Start the hydraulic press to provide clamping force to the mold and maintain pressure, so that the double-layer tube in the mold is evenly subjected to radial pressure, eliminating the micropores and interlayer interface defects of magnesium oxide powder at the bend.

[0020] This invention relates to a double-layer explosion-proof electric heating tube, which adopts a double-layer tube structure with double-chamber filling. Compared with existing heating tube structures, the inner and outer tubes simultaneously provide an explosion-proof barrier, providing double physical protection. The two independent filling chambers provide insulation redundancy, forming double electrical insulation performance. Even if the inner tube fails, the outer tube can still maintain basic safety, possessing failure tolerance capability. This double-layer explosion-proof electric heating tube significantly improves the safety, reliability, and service life of the electric heating tube through structural redundancy, and is especially suitable for application scenarios with high requirements for explosion protection and insulation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the double-layer explosion-proof electric heating tube of the present invention; Figure 2 This is a partially enlarged view of the double-layer explosion-proof electric heating tube of the present invention; Figure 3 This is a cross-sectional view of the double-layer explosion-proof electric heating tube of the present invention; Figure 4 This is a schematic diagram of the exploded structure of the double-layer explosion-proof electric heating tube of the present invention; Figure 5 This is a schematic diagram of the end cap structure of the double-layer explosion-proof electric heating tube of the present invention; Detailed Implementation The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] See Figures 1-5 The present invention provides a double-layer explosion-proof electric heating tube, which includes a double-layer tube body 1, an electric heating wire 2, an end cap 3 and a cooling needle 4.

[0023] The double-layered tube 1 serves as the main structure, comprising an inner tube 11 and an outer tube 12. The inner tube 11 is located inside the outer tube 12 and the two are coaxial. A first chamber 13 is formed inside the inner tube 11, and a gap is formed between the inner tube 11 and the outer tube 12 to form a second chamber 14.

[0024] The heating wire 2 serves as the heating element of the heating tube and is disposed in the first chamber 13. The heating wire 2 is spiral in shape and is located at the center of the first chamber 13.

[0025] The end cap 3 is made of ceramic and is fixed to both ends of the double-layer tube 1, so that the first chamber 13 and the second chamber 14 form a sealed cavity.

[0026] The cold needle 4 is set on the end caps 3 at both ends, and it is electrically connected to the heating wire 2, serving as the power input terminal of the heating tube.

[0027] The first chamber 13 and the second chamber 14 are filled with filler made of an insulating and thermally conductive material to achieve both insulation and thermal conductivity.

[0028] This application adopts a double-tube design, with the inner tube 11 and the outer tube 12 forming a double-layer physical barrier. When the inner tube ruptures due to extreme working conditions, such as local overheating of the heating wire or corrosion perforation, the outer tube can still remain intact, effectively preventing high-temperature media or molten material from splashing directly into the external environment and eliminating the safety accidents caused by the bursting of traditional single-layer tubes.

[0029] Meanwhile, both the first chamber 13 and the second chamber 14 are filled with insulating filler to form two independent insulation barriers, thus forming double electrical isolation. Even if the insulation layer of the inner tube ages and breaks down due to long-term use, the filler in the second chamber can still provide complete insulation protection, significantly reducing the risk of leakage. Furthermore, the filler layers of the two chambers share the function of heat conduction, resulting in a larger heat conduction area and better heat conduction efficiency compared to a single-layer tube.

[0030] This invention relates to a double-layer explosion-proof electric heating tube, which adopts a double-layer tube structure with double-chamber filling. Compared with existing heating tube structures, the inner and outer tubes simultaneously provide an explosion-proof barrier, providing double physical protection. The two independent filling chambers provide insulation redundancy, forming double electrical insulation performance. Even if the inner tube fails, the outer tube can still maintain basic safety, possessing failure tolerance capability. This double-layer explosion-proof electric heating tube significantly improves the safety, reliability, and service life of the electric heating tube through structural redundancy, and is especially suitable for application scenarios with high requirements for explosion protection and insulation.

[0031] In this application, the end of the inner tube 11 protrudes or is flush with the end of the outer tube 12. Preferably, it protrudes. The protruding part of the inner tube spatially separates the end seal of the first chamber 13 from the end seal of the second chamber 14, forming two relatively independent sealing interfaces. Even if a small leak occurs at the end seal of the outer tube, due to the protrusion of the inner tube, the leaking medium needs to overcome the resistance between the outer wall of the inner tube and the end of the outer tube to enter the second chamber, which prolongs the leakage path and improves the reliability of the overall seal.

[0032] Meanwhile, the inner tube protrusion increases the creepage distance between the cold needle 4 and the double-layer tube, reducing the risk of surface flashover in high humidity or polluted environments; the fillers of the two chambers are physically separated at the ends by the inner tube wall, avoiding the mutual influence of insulation performance that may be caused by the two insulation layers contacting each other at the ends, thus improving the overall electrical safety.

[0033] Furthermore, the prominent structure keeps the end sealing area away from the heat-generating core area, resulting in a relatively low end operating temperature, which helps extend the service life of the ceramic end cap 3 and the sealing material.

[0034] In this embodiment, the distance between the inner wall of the inner tube 11 and the heating wire 2 is greater than or equal to 1.2 mm. The thickness of the insulation layer between the heating wire and the inner tube wall directly affects the withstand voltage performance. When the distance is ≥1.2 mm, it can withstand higher AC withstand voltage tests, thereby reducing the risk of breakdown due to local thinning of the insulation layer. Under long-term high-temperature operating conditions, the insulation performance of the insulating filler will slowly decrease. A larger initial gap provides greater safety redundancy, ensuring that the insulation resistance remains above the safety standard throughout the entire service life, thus enhancing the anti-aging ability.

[0035] When the heating wire is too close to the tube wall, if there are tiny air bubbles or impurities in the filler, they may form material contamination (i.e., some metal raw materials precipitate out when the heating wire is working at high temperature, contaminating the insulation layer) or carbonization channels under long-term thermal cycling. In this embodiment, a gap of ≥1.2mm effectively increases the difficulty of material contamination and carbonization channel formation, reducing the probability of leakage. Even if the end seal shows slight water seepage due to long-term use, a larger gap means that water needs to penetrate a thicker filler layer to reach the heating wire, thus slowing down the rate of insulation degradation.

[0036] In this application, the distance between the outer wall of the inner tube 11 and the inner wall of the outer tube 12 is greater than or equal to 1.5 mm; the second chamber 14 serves as the second insulating barrier, and the thickness of the insulating filler is ≥1.5 mm. When the insulation layer of the first chamber 13 fails due to long-term high-temperature aging, local breakdown, or corrosion perforation of the inner tube, this independent insulation layer can still provide reliable electrical isolation to ensure that the outer tube 12 is not energized; the inner and outer insulation layers jointly undertake the withstand voltage task, and the thickness of the second chamber ≥1.5 mm makes the overall withstand voltage capacity far exceed that of a single-layer tube structure, and it can withstand higher surge voltage and transient overvoltage impacts.

[0037] Even if the inner tube has tiny perforations due to corrosion or mechanical damage, there is still an insulation layer thickness of ≥1.5mm between the live parts and the outer tube accessible to the human body, effectively preventing leakage current from being conducted to the outer surface. During long-term use, the insulating filler may become contaminated and carbonized due to local overheating. The thicker insulation layer can block the penetration of material contamination and carbonization channels, avoiding the formation of permanent conductive paths.

[0038] In this application, the filler is magnesium oxide powder, and the filler density is greater than or equal to 2.3 g / cm³. 3 Preferably, it is (2.3~2.6) ± 0.05 g / cm³. 3 When the density is ≥2.3g / cm³ 3 At this time, the contact points between magnesium oxide particles increase significantly, forming a continuous and dense heat-conducting network, which enables the heat generated by the heating wire 2 to be efficiently conducted to the inner tube 11, then to the outer tube 12 through the second chamber 14, and finally to the heated medium; the high-density filling reduces the air layer in the gaps between particles, effectively reducing the overall thermal resistance, so that the surface temperature of the heating tube is higher and the heating is faster under the same input power.

[0039] High-density filler eliminates large-sized pores inside the filler, significantly improving the dielectric strength of the insulation layer. The magnesium oxide powder layer with a density ≥2.3g / cm³ can withstand higher AC withstand voltage tests, ensuring electrical safety during long-term use. At the same time, high-density filler has a lower water absorption rate, maintaining a high insulation resistance even in humid environments, reducing the risk of leakage.

[0040] Finally, it can significantly reduce the volume fraction of micropores inside the filler, reduce the initiation points of corona discharge, and improve the long-term stability of the heating tube under high voltage conditions.

[0041] Preferably, the distance between the outer wall of the inner tube 11 and the inner wall of the outer tube 12 is greater than the distance between the inner wall of the inner tube 11 and the heating wire 2. The heating wire 2 serves as a heat source, with the highest surface heat flux density. The first chamber 13 is adjacent to the heat source, ensuring that heat can be quickly transferred from the heating wire to the inner tube 11, thus avoiding local overheating of the heating wire. After the heat is evenly distributed by the inner tube 11, it is initially dispersed when it reaches the second chamber 14. The thicker second chamber further reduces the heat flux density, allowing the heat to be conducted more evenly to the surface of the outer tube 12.

[0042] In this embodiment, the inner tube 11 and the outer tube 12 are made of the same type of material, preferably various austenitic stainless steels.

[0043] In this application, the end cap 3 is made of ceramic and has a cylindrical structure. Its outer wall is flush with the outer wall of the outer tube. At the end of the end cap 3, there are coaxial first annular protrusion 31 and second annular protrusion 32. The inner wall of the first annular protrusion 31 is attached to the inner wall of the outer tube 12. There is a gap between the inner wall of the first annular protrusion 31 and the outer wall of the second annular protrusion 32, forming a mounting groove 320. The wall thickness of the inner tube 11 is the same as the width of the mounting groove 320 and is embedded in the mounting groove 320. The width of the mounting groove is the same as the wall thickness of the inner tube, and the end of the inner tube is tightly embedded in it, fixing the position of the inner tube from the end. Since the first annular protrusion is attached to the inner wall of the outer tube and the mounting groove is embedded in the end of the inner tube, the relative position between the inner and outer tubes is precisely locked by the end cap, ensuring the concentricity of the entire tube.

[0044] Meanwhile, with the above structural design, the main contact surface between the inner and outer tubes and the end cap is the radial surface, that is, the contact between the inner wall and the outer wall, rather than the end face contact. During assembly, the tubes are bonded, fixed and sealed with glue, which greatly increases the contact area, significantly improves the reliability of the end seal and the connection strength, and enhances the stability and service life.

[0045] Meanwhile, the present invention also provides a method for manufacturing a double-layer explosion-proof electric heating tube, which includes the following steps: S1. Threading: Place the lower rubber plug onto the cold needle at the lower end of the heating wire, and pass the heating wire through the inner tube that is vertically fixed on the powder filling machine. Fix the cold needles at both ends. At the same time, fix the lower rubber plug to the lower end of the inner tube and ensure that the heating wire is coaxial with the inner tube.

[0046] Before threading the wire, cold needles are installed at both ends of the heating wire. Specifically, the cold needles are fitted into both ends of the spiral heating wire, and the connection is achieved under the action of the spiral elastic force. Then the resistance is measured. When the resistance meets the design requirements, the cold needles are welded and fixed to both ends of the heating wire to form an integral structure. In this embodiment, the cold needles are connected to the heating wire by resistance welding, and a rubber plug is inserted into the cold needle at the lower end of the heating wire assembly.

[0047] When threading the wire, first fix the inner tube vertically on the fixed bracket of the powder filling machine. Then, pass the connecting steel wire through the inner tube from top to bottom and connect it with the upper cold needle of the heating wire. Then, the connecting steel wire pulls the heating wire upward to the designated position. This achieves the positioning between the heating wire and the inner tube, making the heating wire and the inner tube coaxial.

[0048] S2. After the heating wire is installed, the inner tube forms a structure with an open top and a closed bottom. Magnesium oxide powder is filled into the tube. Vibration is used to make the magnesium oxide powder evenly and densely fill the first chamber 13 and fix the heating wire 2 in the center position. Specifically, the center of the lower rubber stopper allows the cold needle at the lower end of the heating wire to pass through, thereby radially limiting the lower end of the heating wire and achieving coaxiality; ultimately, the inner tube 11 forms a structure with a sealed lower end and an open upper end, which facilitates the filling of magnesium oxide powder. S3. After the inner tube is filled, a rubber stopper is installed at the upper end of the inner tube 11. The diameter of the inner tube 11 after filling is reduced by the tube shrinking machine to compact the magnesium oxide powder inside and expel the air. After the tube shrinking, the rubber stoppers at both ends of the inner tube are removed. Specifically, the single compression amount is controlled at 5%-10%, and the total compression ratio (cross-sectional area reduction rate) is usually 15%-25%, so that the filling density of the magnesium oxide powder after tube shrinkage is (2.3~2.6) ±0.05 g / cm³.

[0049] S4. Sleeve: Insert the inner tube 11 into the outer tube 12 and make them coaxial. Specifically, the outer tube is first vertically fixed on the fixed bracket of the powder filling machine. A connecting steel wire passes through the outer tube from top to bottom and connects to the upper end of the heating wire on the inner tube. Then the connecting steel wire pulls the inner tube upward to the designated position, thereby achieving the positioning between the outer tube and the inner tube and making the inner tube and the outer tube coaxial.

[0050] S5. Secondary filling: Install a rubber plug at the lower end of the outer tube and fill the second chamber 14 with magnesium oxide powder. Vibration is used to make the magnesium oxide powder evenly and densely fill the second chamber 14 and fix the inner tube 11 in the center position. Similarly, during filling, a rubber plug is set at the lower end of the outer tube. The rubber plug is circular and can allow the inner tube to pass through, thereby achieving radial restriction between the inner and outer tubes and ultimately making the outer tube form a structure with the lower end sealed and the upper end open. S6. Secondary tube shrinkage: After filling, install a rubber stopper at the upper end of the outer tube to shrink the diameter of the double-layer tube, so as to compact the magnesium oxide powder in the second chamber 14 and expel the air. Since the inner tube has already undergone one shrinkage, the impact on the inner tube during the second shrinkage is relatively small. The main purpose is to compact the magnesium oxide powder in the outer tube and the second chamber.

[0051] S7. Solution treatment: Remove the rubber stoppers at both ends of the outer tube. Under the protection of a protective gas, heat the double-layer tube to solidify at a temperature of 950℃-1050℃, and generate a protective layer on the surface of the double-layer tube or achieve reduction. At the same time, the air in the gap is discharged. The protective gas can be hydrogen or nitrogen. At high temperatures, it can reduce the outer surface of the tube, thereby removing defects such as rust and restoring the surface material of the tube.

[0052] It can also contain hydrogen, nitrogen and carbon dioxide at the same time. At high temperature, a reduction reaction will occur, thereby removing defects such as rust on the surface of the outer tube and restoring the surface material of the tube. Then an oxidation reaction will occur to form an oxide layer on the ideal outer surface of the tube, forming an ideal protective layer.

[0053] Different types of protective gases can be selected according to different application scenarios.

[0054] S8. Cooling: Cool the solution-solidified double-layer tube to room temperature in a dry environment. S9. Sealing: In a dry environment, sealant is injected into both ends of the double-layer tube. The sealant can be high-temperature resistant epoxy resin, glue, or low-melting-point sealing glass to prevent the magnesium oxide powder inside the tube from contacting the air and achieve a seal. Then, glue is applied to cover the entire end, and end cap 3 is installed to complete the final seal. The end cap is a cylindrical structure made of insulating ceramic material. Before sealing, cool to room temperature in a dry environment to avoid moisture absorption during the cooling process.

[0055] Because of the annular protrusion structure on the end cap, the contact surface between the end cap and the inner and outer tubes is radial, resulting in a large contact area, high connection strength, and good sealing performance.

[0056] S10. Forming: Bending the double-layer tube into the desired shape, usually a U-shape; S11, Hydraulic pressure: Apply hydraulic pressure to the formed double-layer tube to further densify the magnesium oxide powder at the bends of the double-layer tube, eliminating voids and delamination defects. During the bending process, the outer wall of the bent section is thinned by tension and thickened by pressure. This geometric deformation causes the magnesium oxide powder layer filling the space between the inner and outer pipes to shift violently, making the outer side loose and less dense, while the inner side is over-compacted, resulting in excessively high density and even obvious delamination. This application utilizes the powerful pressure of a hydraulic press to extrude the bent section in multiple directions using a special mold, forcing the loose magnesium oxide powder to rearrange and compact, eliminating the delamination interface, and restoring the powder density at the bent section to a level comparable to that of the straight pipe section.

[0057] In severe cases, the powder on the outside of the bend cannot migrate synchronously with the stretching of the pipe wall, forming microscopic or even macroscopic voids. These voids are poor conductors of heat and weak points for electrical breakdown. By applying pressure to cause slight deformation of the pipe wall, the void space is compressed, forcing the surrounding powder to flow in and fill the void, ensuring that there are no insulation and thermal breaks along the entire bending path.

[0058] After eliminating voids and low-density areas, the dielectric strength of the insulation layer is significantly improved; moreover, the high-density, defect-free powder layer has lower hygroscopicity, and after long-term placement or use in a humid environment, the decay rate of its insulation resistance is greatly reduced, thus improving electrical safety performance.

[0059] After hydraulic pressure, the thermal conductivity of the bend is basically the same as that of the straight section, and the heat can be conducted away quickly and evenly, fundamentally eliminating hot spots caused by loose powder; improving the uniformity of heat conduction, avoiding the risk of local overheating at the bend, and ensuring the thermal stability and lifespan consistency of the electric heating tube under high-power continuous operation.

[0060] Specifically, radial pressure is applied to the double-layered tube body via hydraulic pressure, with a radial pressure of 15–20 MPa and a holding time of 3–5 seconds.

[0061] It includes the following steps: S111, Mold installation: Place the bent heating tube into the pressing mold, ensuring that the bent part is accurately aligned with the compaction area; the pressing mold includes an upper mold and a lower mold, which together form a cavity that matches the curvature of the U-shaped tube. S112. Pressing: Start the hydraulic press to provide clamping force to the mold and maintain pressure, so that the double-layer tube in the mold is evenly subjected to radial pressure, eliminating the micropores and interlayer interface defects of magnesium oxide powder at the bend.

[0062] S12. Quality Inspection: Conduct quality inspection on finished products. Specifically, quality inspection includes one or more of the following: insulation resistance test, withstand voltage test, leakage current test, and airtightness test.

[0063] The double-layer explosion-proof electric heating element of this application has electrical performance that is at least 1.5 times that of existing electric heating elements.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A double-layer explosion-proof electric heating tube, characterized in that, include: A double-layered tube body, comprising an inner tube body and an outer tube body arranged coaxially, wherein a first chamber is formed within the inner tube body, and a second chamber is formed between the inner tube body and the outer tube body by a gap; The heating wire is disposed in the first chamber; End caps are fixed to both ends of the double-layered tube, and the first chamber and the second chamber form a sealed cavity. A cold needle is disposed on the end cap and electrically connected to the heating wire; The filler, made of an insulating and thermally conductive material, is filled in the first chamber and the second chamber.

2. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The end of the inner tube protrudes or is flush with the end of the outer tube.

3. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The distance between the inner wall of the inner tube and the heating wire is greater than or equal to 1.2 mm.

4. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The distance between the outer wall of the inner tube and the inner wall of the outer tube is greater than or equal to 1.5 mm.

5. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The packing density of the filler is greater than or equal to 2.3 g / cm³. 3 .

6. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The end cap has a coaxial first annular protrusion and a second annular protrusion. The inner wall of the first annular protrusion is attached to the inner wall of the outer tube. There is a gap between the inner wall of the first annular protrusion and the outer wall of the second annular protrusion to form a mounting groove. The wall thickness of the inner tube is the same as the width of the mounting groove and is embedded in the mounting groove.

7. The double-layer explosion-proof electric heating tube as described in claim 1, characterized in that: The filler is magnesium oxide powder, and the inner tube and outer tube are made of stainless steel.

8. A method for manufacturing a double-layer explosion-proof electric heating tube, characterized in that, Includes the following steps: S1. Threading the wire: Place the lower rubber plug onto the cold needle at the lower end of the heating wire, thread the heating wire through the inner tube that is vertically fixed on the powder filling machine, fix the cold needles at both ends, fix the lower rubber plug to the lower end of the inner tube, and ensure that the heating wire is coaxial with the inner tube. S2. First filling: Magnesium oxide powder is filled into the tube. Vibration is used to make the magnesium oxide powder fill the first chamber evenly and densely, and the heating wire is fixed in the center position. A rubber stopper is installed at the upper end of the inner tube. S3. First tube shrinking: The inner tube body after filling is shrunk by a tube shrinking machine to compact the density of the magnesium oxide powder inside and expel air. S4. Sleeve: Remove the rubber plugs at both ends of the inner tube, pass the inner tube through the outer tube that is vertically fixed on the powder filling machine, and fix the cold needles at the upper and lower ends, and ensure that the inner tube and the outer tube are coaxial. S5. Secondary filling: Install a rubber plug at the lower end of the outer tube and fill the second chamber with magnesium oxide powder. Vibration is used to make the magnesium oxide powder fill the second chamber evenly and densely, and to fix the inner tube in the center position. S6. Secondary tube shrinkage: A rubber plug is installed at the upper end of the outer tube to shrink the diameter of the double-layer tube, so as to compact the magnesium oxide powder in the second chamber and expel the air. S7. Solution treatment: Remove the rubber stoppers at both ends of the outer tube. Under the protection of a protective gas, heat and solidify the double-layer tube to create a protective layer on the outer surface of the double-layer tube or achieve reduction, and then expel the air. S8. Cooling: Cool the solution-solidified double-layer tube to room temperature in a dry environment. S9. Sealing: In a dry environment, inject sealing material into both ends of the double-layer tube and install end caps to complete the sealing. S10, Forming: Bending the double-layer tube into the desired shape; S11, Hydraulic pressure: Apply hydraulic pressure to the formed double-layer tube to further densify the magnesium oxide powder at the bends of the double-layer tube, eliminating voids and delamination defects. S12. Quality Inspection: Conduct quality inspection on the finished product.

9. The manufacturing method of the double-layer explosion-proof electric heating tube as described in claim 8, characterized in that: In step S7, the solution temperature is 950℃-1050℃.

10. The manufacturing method of the double-layer explosion-proof electric heating tube as described in claim 8, characterized in that: In steps S3 and S6, the density of magnesium oxide powder in the first chamber and the second chamber is (2.3~2.6) ±0.05 g / cm³.

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