A double-zone heating detection device for studying the fire spread critical criterion of a flame-retardant cable

Abstract

The present application relates to a kind of double-zone heating detection device for studying the critical criterion of flame spread of flame-retardant cable, belong to the field of flame-retardant cable ignition and fire spread characteristic detection.It includes base installed with vertical rod, four horizontal crossbars, first and second heating mechanism;Four horizontal crossbars are sequentially set on vertical rod from top to bottom by through hole, and are fixed or adjusted position by moving up and down through locking bolt, first heating mechanism is fixedly arranged on first horizontal crossbar, and second heating mechanism is fixedly arranged on second horizontal crossbar.When cable is detected, the upper part of the cable to be measured is fixed on the cantilever end of first horizontal crossbar, passes through first electric heating coil, second electric heating coil and base, and the end of the cable to be measured below base is tightly loaded with weight, so that the cable to be measured maintains vertical state during testing.The present application realizes the detection of critical criterion of self-sustaining fire spread of each flame-retardant cable formula by the comprehensive regulation and control of double-zone heat flow of first and second heating mechanism, and promotes the fine design of flame-retardant cable formula.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant cable ignition and fire spread characteristic detection, specifically involving a dual-zone heating detection device for studying the critical criteria for fire spread of flame-retardant cables. Background Technology

[0002] With the continuous improvement of electrification and intelligentization levels in various countries, wire and cable systems, as the "arteries and nerves" of the national economy for power transmission and signal transmission, have become increasingly important, with their usage scope and quantity constantly expanding. Fire safety requirements in public places and residential buildings are constantly increasing, leading to the rapid promotion and application of flame-retardant cables. However, since fires are ultimately sporadic events, the addition of flame retardants often causes a decline in the mechanical and electrical properties of cables. Therefore, how to scientifically and rapidly develop cables that meet customers' mechanical, electrical, and weathering requirements while also possessing qualified flame-retardant and fire-resistant properties is not only a crucial indicator of the current competitiveness of flame-retardant cable R&D but also a cutting-edge direction and challenge in the research of fire dynamics for flame-retardant cables. Among these challenges, the ability to quickly and accurately detect the microscopic flame-retardant and fire-resistant characteristics of cables with various formulations is key to the design of flame-retardant cable formulations and the research of fire dynamics evolution models in densely cabled locations such as shafts.

[0003] For testing the ignition and fire spread characteristics of flame-retardant cables, the most commonly used testing devices and methods are based on the testing standards for single or bundled cables in various countries, such as my country's standard "Cables and Optical Cables Combustion Tests under Flame Conditions Part 12: Vertical Flame Spread Test of Single Insulated Wires and Cables (1kW Premixed Flame Test Method) (GB / T18380.12-2022)". This standard specifies using a 1kW propane torch flame to test a single vertical cable. After the torch flame stops, the final char length formed after the cable's self-spreading combustion is used to determine whether it can be applied in actual engineering. However, existing methods for testing the ignition and fire spread characteristics of flame-retardant cables can only provide a final conclusion on the fire resistance performance of the flame-retardant cable under this standard: pass or fail. This method cannot determine the "flame-retardant safety margin of cables that pass the standard test" or the "flame-retardant deficiency of cables that do not pass the standard test". Summary of the Invention

[0004] To achieve quantitative detection and characterization of the flame-retardant and fire-resistant properties of cables, this invention provides a dual-zone heating detection device for studying the critical criteria for fire spread in flame-retardant cables.

[0005] A dual-zone heating detection device for studying the critical criteria for fire spread of flame-retardant cables includes a base 1, a vertical rod 2, a first horizontal bar 3, a second horizontal bar 4, a third horizontal bar 5, a fourth horizontal bar 6, a first heating mechanism, and a second heating mechanism; the vertical rod 2 is upright and fixed on one side of the base 1;

[0006] The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4 and the fourth horizontal bar 6 are respectively provided with through holes at the same end. The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4 and the fourth horizontal bar 6 are respectively sleeved on the vertical bar 2 from top to bottom through the through holes, and are fixed by locking bolts or adjusted by moving up and down. The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4 and the fourth horizontal bar 6 are parallel cantilevered.

[0007] The first heating mechanism includes a first power supply 7 and a first electric heating coil 8. The first power supply 7 is fixedly mounted on the first horizontal bar 3. The two terminals of the first power supply 7 are respectively fixedly mounted on the other end of the first horizontal bar 3 through wires, and the two ends of the first electric heating coil 8 are connected to the two terminals of the first power supply 7.

[0008] The second heating mechanism includes a second power supply 9 and a second electric heating coil 10. The second power supply 9 is fixedly mounted on the second horizontal bar 4. The two terminals of the second power supply 9 are respectively fixedly mounted on the other end of the second horizontal bar 4 through wires, and the two ends of the second electric heating coil 10 are connected to the two terminals of the second power supply 9.

[0009] A first fixing ring 11 is fixedly provided on the other end of the third horizontal crossbar 5, and a locking bolt is provided on the first fixing ring 11.

[0010] A second fixing ring 12 is fixedly provided on the other end of the fourth horizontal crossbar 6. The second fixing ring 12 is a hollow cylinder and is not provided with locking bolts.

[0011] A through hole 13 is provided on the other side of the base 1;

[0012] The first fixing ring 11, the second fixing ring 12, and the through hole 13 are coaxially aligned vertically.

[0013] When used for cable testing, the cable to be tested 14 is passed through the first fixing ring 11, the first electric heating coil 8, the second electric heating coil 10, the second fixing ring 12, and the through hole 13 on the base 1. The cable to be tested 14 is centered in the first electric heating coil 8 and the second electric heating coil 10. The end of the cable to be tested 14 below the base 1 is tightened with a weight 16 through the connector 15, so that the cable to be tested 14 remains vertical during the test.

[0014] By comprehensively controlling the dual-zone heating of the first and second heating mechanisms, the quantitative detection and characterization of the flame-retardant and fire-resistant properties of cables can be achieved.

[0015] When performing upward fire spread critical criterion detection on the cable 14 under test, the heating area of ​​the second electric heating coil 10 in the second heating mechanism is set as the direct ignition area, and the heating area of ​​the first electric heating coil 8 in the first heating mechanism is set as the critical fire spread area.

[0016] When performing downward fire spread critical criterion detection on the cable 14 under test, the heating area of ​​the first electric heating coil 8 in the first heating mechanism is set as the direct ignition area, and the heating area of ​​the second electric heating coil 10 in the second heating mechanism is set as the critical fire spread area.

[0017] The further defined technical solution is as follows:

[0018] Both the first power supply 7 and the second power supply 9 are DC or AC power supplies with control modules.

[0019] The first horizontal bar 3 and the second horizontal bar 4 are both made of insulating materials; the third horizontal bar 5, the fourth horizontal bar 6, the vertical bar 2, and the base 1 are all made of metal materials.

[0020] Both the first electric heating coil 8 and the second electric heating coil 10 are heating wire coils. The operating current and operating temperature of the first electric heating coil 8 and the second electric heating coil 10 are determined according to the type and thickness of the heating wire, wherein the maximum operating temperature is 1200℃.

[0021] The first heating mechanism heats the critical fire spread zone during the upward fire spread test and the direct ignition zone during the downward fire spread test; the second heating mechanism heats the direct ignition zone during the upward fire spread test and the critical fire spread zone during the downward fire spread test.

[0022] The beneficial technical effects of this invention are reflected in the following aspects:

[0023] (1) The dual-zone heating detection device of the present invention realizes the detection of the critical criteria for self-sustaining fire spread of each flame-retardant formula cable by comprehensively controlling the dual-zone heating of the first heating mechanism and the second heating mechanism. By adjusting the heating power of the first electric heating coil of the first heating mechanism or the heating power of the second electric heating coil of the second heating mechanism, the critical heating power for ignition of the direct ignition zone of the cable under test is measured; at the same time, by adjusting the preheating power of the critical fire spread zone of the cable under test, the critical criteria for the formation of self-sustaining fire spread of each flame-retardant cable under test are accurately detected.

[0024] (2) The minimum preheating power required for ignition of the critical fire spread zone of flame-retardant cables, i.e., the critical fire spread preheating intensity I scrThis study enables the quantitative detection and characterization of the flame-retardant and fire-resistant properties of cables, facilitates the accurate measurement of the safety margin or self-sustaining fire spread hazard of cables with different formulations, and provides detailed data support for the optimization of flame-retardant cable formulations and the improvement of overall performance.

[0025] (3) Applying a strong current to the first heating mechanism and a weak current to the second heating mechanism to form a detection method of "direct ignition of the upper heat flow + preheating and spread of the lower heat flow" can realize the quantitative measurement of the critical criterion for downward self-sustaining fire spread of flame-retardant cables; in addition, applying a weak current to the first heating mechanism and a strong current to the second heating mechanism to form a detection method of "direct ignition of the lower heat flow + preheating and spread of the upper heat flow" can realize the quantitative measurement of the critical criterion for upward self-sustaining fire spread of flame-retardant cables; it can be seen that the present invention realizes the comprehensive measurement of the critical criteria for "upward downstream fire spread" and "downward countercurrent fire spread" of flame-retardant cables. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the device structure of the present invention.

[0027] Figure 2 for Figure 1 A sectional view.

[0028] The numbers in the diagram above are: 1. Base; 2. Vertical rod; 3. First horizontal bar; 4. Second horizontal bar; 5. Third horizontal bar; 6. Fourth horizontal bar; 7. First power supply; 8. First electric heating coil; 9. Second power supply; 10. Second electric heating coil; 11. First fixing ring; 12. Second fixing ring; 13. Through hole; 14. Cable to be tested; 15. Connector; 16. Weight. Specific implementation methods

[0029] The present invention will now be described in a clearer and more complete manner with reference to the accompanying drawings.

[0030] Example 1

[0031] See Figure 1 and Figure 2 A dual-zone heating detection device for studying the critical criteria for fire spread in flame-retardant cables includes a base 1, a vertical rod 2, a first horizontal bar 3, a second horizontal bar 4, a third horizontal bar 5, a fourth horizontal bar 6, a first heating mechanism, and a second heating mechanism. The vertical rod 2 is upright and fixedly installed on one side of the base 1.

[0032] The base 1 is a cuboid with a length of 0.600 meters, a width of 0.200 meters, and a height of 0.050 meters, and the vertical rod 2 is a cuboid with a length of 0.030 meters, a width of 0.050 meters, and a height of 1.030 meters. Both are made of stainless steel.

[0033] The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4, and the fourth horizontal bar 6 each have through holes at the same end. The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4, and the fourth horizontal bar 6 are respectively installed on the vertical bar 2 from top to bottom through the through holes and are fixed by locking bolts. The position of each horizontal bar on the vertical bar 2 is adjusted by the locking bolts. The third horizontal bar 5, the first horizontal bar 3, the second horizontal bar 4, and the fourth horizontal bar 6 are parallel cantilevered.

[0034] The first horizontal bar 3 and the second horizontal bar 4 are both made of insulating bakelite board, and are both cuboids with a length of 0.325 meters, a width of 0.075 meters, and a height of 0.050 meters; the distance between the lower edge of the second horizontal bar 4 and the upper surface of the base 1 is 0.120 meters; the distance between the first horizontal bar 3 and the second horizontal bar 4 is the carbonization height L measured only under the heating action of the second heating mechanism.

[0035] The third horizontal bar 5 and the fourth horizontal bar 6 are both made of stainless steel and are both cuboids with a length of 0.35 meters, a width of 0.075 meters, and a height of 0.030 meters. The lower edge of the third horizontal bar 5 is 0.85 meters from the upper surface of the base 1, and the lower edge of the fourth horizontal bar 6 is 0.040 meters from the upper surface of the base 1.

[0036] The first heating mechanism includes a first power supply 7 and a first electric heating coil 8. The first power supply 7 is fixedly installed on the first horizontal crossbar 3, and the two terminals of the first power supply 7 are respectively fixedly installed on the other end of the first horizontal crossbar 3 through wires, and the two ends of the first electric heating coil 8 are connected to the two terminals of the first power supply 7.

[0037] The second heating mechanism includes a second power supply 9 and a second electric heating coil 10. The second power supply 9 is fixedly installed on the second horizontal bar 4, and the two terminals of the second power supply 9 are respectively fixedly installed on the other end of the second horizontal bar 4 through wires, and the two ends of the second electric heating coil 10 are connected to the two terminals of the second power supply 9.

[0038] Both the first power supply 7 and the second power supply 9 are adjustable DC power supplies with a maximum voltage of 30V and a maximum current of 30A, equipped with a control module.

[0039] Both the first electric heating coil 8 and the second electric heating coil 10 are nickel-chromium alloy wire coils (Ni20Cr80 alloy), with a wire diameter of 0.001m, a coil diameter of 0.014m, 12 turns, and a thread pitch of 0.004m. The operating current of the first electric heating coil 8 and the second electric heating coil 10 is (0, 25]A, and the operating temperature is (25, 1200]℃.

[0040] A first fixing ring 11 is fixedly installed on the other end of the third horizontal crossbar 5, and a locking bolt is fitted on the first fixing ring 11; a second fixing ring 12 is fixedly installed on the other end of the fourth horizontal crossbar 6.

[0041] The first fixing ring 11 and the second fixing ring 12 have the same dimensions: an outer diameter of 0.024 meters, an inner diameter of 0.014 meters, and a height of 0.030 meters. Both are made of stainless steel.

[0042] A through hole 13 is provided on the other side of the base 1. The diameter of the through hole 13 is 0.014 meters and the height is 0.050 meters.

[0043] The first fixing ring 11, the second fixing ring 12, and the through hole 13 are coaxially corresponding vertically.

[0044] When used for cable testing, the cable to be tested 14 is passed from top to bottom through the first fixing ring 11 fixed to the third horizontal bar 5, the first electric heating coil 8, the second electric heating coil 10, the second fixing ring 12 fixed to the fourth horizontal bar 6, and the through hole 13 on the base 1. The upper part of the cable to be tested 14 is fixed in the first fixing ring 11 by a locking screw, and the cable to be tested 14 is centered in the first electric heating coil 8 and the second electric heating coil 10.

[0045] The cable under test, 14, is a single-core flame-retardant cable. The outer side is made of flame-retardant polymer material, which consists of polyethylene (13wt%), ethylene vinyl acetate copolymer (25wt%), aluminum hydroxide (55wt%), and melamine salt (7%). The inner side is made of copper core, with a copper core diameter of 0.0028m and a total cable outer diameter of 0.0044m.

[0046] A weight 16 is fastened to the end of the cable under test 14 below the base 1 via a connector 15. The weight 16 weighs 200g, so that the cable under test 14 remains vertical during the test.

[0047] The operating procedure for performing the upward fire propagation critical criterion test on the cable under test 14 is as follows:

[0048] S1: According to the above requirements, first install the base 1, vertical rod 2, first horizontal bar 3, second horizontal bar 4, third horizontal bar 5, and fourth horizontal bar 6, and then install the second heating mechanism and the cable to be tested 14.

[0049] S2: By adjusting the operating current of the second power supply 9 controlling the second electric heating coil 10 in the second heating mechanism, the heating area of ​​the second electric heating coil 10 is the direct ignition area. A series of heating intensities are set for the heating wire heating coil in the direct ignition area, with the series heating intensities controlled by the current I. iThis indicates that the initial value I0 = 0A, at which point the heating wire operating temperature is 25℃. The current is increased by ΔI = 1A for each test, gradually increasing until the flame-retardant cable can be ignited. The minimum heating intensity I required to ignite the flame-retardant cable is recorded. i Critical ignition heating intensity I icr =12A, at which point the operating temperature of the heating wire is 643℃.

[0050] S3: Measure the critical ignition heating intensity I icr Under the action of 12A, the carbonization length of the flame-retardant cable is L=0.080 meters.

[0051] S4: Adjust the distance between the lower edge of the first horizontal bar 3 and the upper edge of the second horizontal bar 4 to L=0.080 meters, and then install the first heating mechanism.

[0052] S5: By adjusting the operating current of the first power supply 7 controlling the first electric heating coil 8 in the first heating mechanism, the heating area of ​​the first electric heating coil 8 is the critical fire spread zone. A series of heating intensities are set for the heating wire heating coil in the critical fire spread zone, and these series of heating intensities are controlled by the current I. j This indicates that the initial value I0 = 0A, at which point the heating wire operating temperature is 25℃. The current is increased by ΔI = 0.5A for each test, gradually increasing from small to large. The preheating time is 240s. The minimum heating intensity I required to ignite the critical fire spread zone of the flame-retardant cable is recorded. j Critical fire spread preheating intensity I scr =6A, at which point the operating temperature of the heating wire is 319℃.

[0053] S6: Using the heating coil specified in this embodiment, the critical ignition heating intensity I... icr =12A and critical fire spread preheating intensity I scr =6A is the critical criterion for upward fire spread of the flame-retardant cable 14 under test in this embodiment.

[0054] Example 2

[0055] The device structure of Example 2 is the same as that of Example 1.

[0056] The test cable 14 in Example 2 is a single-core flame-retardant cable. The outer side is a flame-retardant polymer material, which consists of polyethylene (9wt%), ethylene vinyl acetate copolymer (18wt%) and aluminum hydroxide (73wt%). The inner side is a copper core with a diameter of 0.0018m and a total outer diameter of 0.0034m.

[0057] The different dimensions are explained as follows: the distance between the lower edge of the first horizontal bar 3 and the upper surface of the base 1 is 0.70 meters.

[0058] The operating procedure for performing downward fire propagation critical criterion testing on the cable under test 14 is as follows:

[0059] S1: According to the above requirements, first install the base 1, vertical rod 2, first horizontal bar 3, second horizontal bar 4, third horizontal bar 5, and fourth horizontal bar 6, and then install the first heating mechanism and the cable to be tested 14.

[0060] S2: By adjusting the operating current of the first power supply 7 controlling the first electric heating coil 8 in the first heating mechanism, the heating area of ​​the first electric heating coil 8 is the direct ignition area. A series of heating intensities are set for the heating wire heating coil in the direct ignition area, and the series of heating intensities are controlled by the current I. i This indicates that the initial value I0 = 0A, at which point the heating wire operating temperature is 25℃. The current is increased by ΔI = 1A for each test, gradually increasing until the flame-retardant cable can be ignited. The minimum heating intensity I required to ignite the flame-retardant cable is recorded. i Critical ignition heating intensity I icr =14A, at which point the operating temperature of the heating wire is 727℃.

[0061] S3: Measure the critical ignition heating intensity I icr The carbonized length of the flame-retardant cable with an ampere rating of 14A is L = 0.030 meters.

[0062] S4: Adjust the distance between the upper edge of the second horizontal bar 4 and the lower edge of the first horizontal bar 3 to L=0.030 meters, and then install the second heating mechanism.

[0063] S5: By adjusting the operating current of the second power supply 9 controlling the second electric heating coil 10 in the second heating mechanism, the heating area of ​​the second electric heating coil 10 is set to the critical fire spread zone. A series of heating intensities are set for the heating wire coil in the critical fire spread zone, and these series of heating intensities are controlled by the current I. j This indicates that the initial value I0 = 0A, at which point the heating wire operating temperature is 25℃. The current is increased by ΔI = 0.5A for each test, gradually increasing from small to large. The preheating time is 240s. The minimum heating intensity I required to ignite the critical fire spread zone of the flame-retardant cable is recorded. j Critical fire spread preheating intensity I scr =8A, at which point the heating wire operates at a temperature of 440℃.

[0064] S6: Using the heating coil specified in this embodiment, the critical ignition heating intensity I... icr =14A and critical fire spread preheating intensity I scr =8A is the critical criterion for downward fire spread of the flame-retardant cable 14 under test in this embodiment.

[0065] Those skilled in the art will readily understand that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A two-zone heating detection apparatus for investigating the fire propagation threshold criterion of a flame-retardant cable, characterized in that: It comprises a base (1), a vertical rod (2), a first horizontal crossbar (3), a second horizontal crossbar (4), a third horizontal crossbar (5), a fourth horizontal crossbar (6), a first heating mechanism and a second heating mechanism; The vertical rod (2) is vertically fixed on one side of the base (1); The same end of the third horizontal crossbar (5), the first horizontal crossbar (3), the second horizontal crossbar (4) and the fourth horizontal crossbar (6) is provided with a through hole, and the third horizontal crossbar (5), the first horizontal crossbar (3), the second horizontal crossbar (4) and the fourth horizontal crossbar (6) are sequentially sleeved on the vertical rod (2) from top to bottom through the through holes, and are fixed or moved up and down to adjust the position through locking bolts, and the third horizontal crossbar (5), the first horizontal crossbar (3), the second horizontal crossbar (4) and the fourth horizontal crossbar (6) are in parallel and in the form of cantilever; The first heating mechanism comprises a first power supply (7) and a first electric heating coil (8), the first power supply (7) is fixed on the first horizontal crossbar (3), and the two wire ends of the first power supply (7) are fixed on the other end of the first horizontal crossbar (3) through wires, and the two ends of the first electric heating coil (8) are connected with the two wire ends of the first power supply (7); The second heating mechanism comprises a second power supply (9) and a second electric heating coil (10), the second power supply (9) is fixed on the second horizontal crossbar (4), and the two wire ends of the second power supply (9) are fixed on the other end of the second horizontal crossbar (4) through wires, and the two ends of the second electric heating coil (10) are connected with the two wire ends of the second power supply (9); The other end of the third horizontal crossbar (5) is fixed with a first fixed ring (11), and the first fixed ring (11) is matched with a locking bolt; The other end of the fourth horizontal crossbar (6) is fixed with a second fixed ring (12); The other side of the base (1) is provided with a through hole (13); The first fixed ring (11), the second fixed ring (12) and the through hole (13) are coaxial and corresponding; When detecting the cable, the cable (14) to be detected is passed through the first fixed ring (11), the first electric heating coil (8), the second electric heating coil (10), the second fixed ring (12) and the through hole (13) on the base (1), the cable (14) to be detected is located in the first electric heating coil (8) and the second electric heating coil (10), the cable (14) to be detected and the first fixed ring (11) are fixed through the locking bolt, and the end of the cable (14) to be detected at the lower part of the base (1) is tightly connected with a weight (16) through a connecting piece (15), so that the cable (14) to be detected remains vertical during the test; Through the comprehensive regulation and control of the double-zone heating of the first heating mechanism and the second heating mechanism, the quantitative detection and characterization of the cable flame-retardant and fire-resistant performance are realized; When detecting the upward fire spread critical criterion of the cable (14) to be detected, the heating area of the second electric heating coil (10) in the second heating mechanism is set as the direct ignition area, and the heating area of the first electric heating coil (8) in the first heating mechanism is set as the critical fire spread area. The weak current is applied to the first heating mechanism, and the strong current is applied to the second heating mechanism to form a detection mode of "direct ignition of lower heat flow + preheating of upper heat flow", and quantitative measurement of the upward self-sustaining fire spread critical criterion of the flame-retardant cable is realized. When the downward fire spread critical criterion detection of the cable (14) is performed, the heating area of the first electric heating coil (8) in the first heating mechanism is a direct ignition area, and the heating area of the second electric heating coil (10) in the second heating mechanism is a critical fire spread area. The strong current is applied to the first heating mechanism, and the weak current is applied to the second heating mechanism to form a detection mode of "direct ignition of upper heat flow + preheating of lower heat flow", and quantitative measurement of the downward self-sustaining fire spread critical criterion of the flame-retardant cable is realized.

2. A two-zone heating detection apparatus for studying the criticality of fire propagation in a flame-retardant cable according to claim 1, characterized in that: The first power supply (7) and the second power supply (9) are direct current or alternating current power supplies with control modules.

3. The dual-zone heating detection apparatus for studying the fire propagation threshold criterion of a fire-retardant cable according to claim 1, characterized in that: The materials of the first horizontal crossbar (3) and the second horizontal crossbar (4) are insulating materials; the materials of the third horizontal crossbar (5), the fourth horizontal crossbar (6), the vertical rod (2) and the base (1) are metal materials.

4. The dual-zone heating detection apparatus for studying the fire propagation threshold criterion of a fire resistant cable of claim 1, wherein: The first electric heating coil (8) and the second electric heating coil (10) are electric heating wire coils, and the maximum working temperature of the first electric heating coil (8) and the second electric heating coil (10) is 1200℃.

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