Preparation method of high-voltage heating element

Abstract

The invention belongs to the technical field of heating elements, and relates to a preparation method of a high-voltage heating element. The preparation method comprises the following steps: (1) penetrating a heating material into a shell of the high-voltage heating element, and then filling an insulating material between the heating material and the shell; and (2) integrally firing the high-voltage heating element, and cooling the high-voltage heating element, wherein the high voltage is 13.6-50 kV. According to the preparation method of the high-voltage heating element, the heating material, the insulating material and the shell of the high-voltage heating element can be integrally formed, so that the prepared high-voltage heating element has higher voltage resistance grade, electrical performance, heat-conducting performance, compressive strength, thermal shock resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of heating element technology and relates to a method for preparing a high-voltage heating element. Background Technology

[0002] Driven by the "dual carbon" environment, the demand for efficient electrothermal technology is continuously rising in wind and solar power generation, thermal energy storage, coal-fired power plant flexibility upgrades, and high-energy-consuming process industries. Fluctuating renewable energy sources require fast-response electro-thermal conversion devices to promptly absorb surplus power during periods of surplus and supply energy during power shortages. Thermal storage systems rely on high-power electric heating to achieve high-temperature heat storage, matching the intermittent output of green electricity. Coal-fired units achieve deep peak shaving through electric supplementary heating, realizing heat-electric decoupling and improving operational flexibility. Meanwhile, high-energy-consuming sectors such as metallurgy, chemicals, and building materials urgently require ultra-high-power electrothermal elements capable of stable operation under extreme temperatures and rapid heating conditions to reduce energy consumption and lower operating costs.

[0003] However, current mainstream low-voltage heating solutions have revealed many drawbacks in high-power applications: the current increases linearly with the power, the cable cross-sectional area increases dramatically, which not only increases the amount of raw materials used, but also brings significant heat loss; new energy and industrial busbars are generally thousands to tens of thousands of volts, and low-voltage components need to be stepped down in multiple stages before they can be used, which brings additional energy loss and system complexity; in addition, steelmaking, chemical and other processes require "high voltage direct connection and rapid heating", and low-voltage designs are difficult to connect directly, which limits their promotion in high-temperature industrial scenarios.

[0004] In contrast, high-voltage heating elements that can be directly connected to the power grid bus can systematically solve the above-mentioned pain points. With the help of high voltage, the current is greatly reduced for the same power, the line loss is reduced accordingly, and the overall energy efficiency is significantly improved; the higher power density allows it to cover megawatt-level industrial heat loads and can be directly connected to new energy sources or high-voltage power grids, eliminating or reducing voltage reduction links, reducing electrical investment, and improving system integration; in addition, the microsecond-level response capability allows for precise temperature control, further optimizing production line efficiency and energy utilization.

[0005] In high-voltage heating elements, electrical insulation and thermal conductivity are achieved by filling the space between the heating wire and the metal casing with insulating material. Existing high-voltage heating elements generally achieve insulation and thermal conductivity by filling with powder materials or pre-formed materials.

[0006] Filling the space between the heating wire and the metal casing with powder material creates numerous air gaps between the powder particles. The insulation strength and thermal conductivity of these air gaps are significantly lower than those of pure solid particles, making high-voltage heating elements prone to insulation failure at high temperatures. Filling the space between the heating wire and the metal casing with pre-formed material is also problematic. Due to limitations in industrial processing and material properties, it's difficult to fabricate materials with large aspect ratios. Therefore, short pieces of material are typically used for splicing. While special shapes or multiple solid insulation combinations can be implemented with these short pieces, interfaces inevitably exist between the insulating materials. These interfaces are weak points in electrical insulation, making them susceptible to insulation failure under high voltage. Furthermore, pre-formed materials often involve complex processes requiring high temperatures and long firing times, significantly increasing industrial energy consumption and manufacturing costs for the heating elements.

[0007] The aforementioned problems in the design and manufacturing processes of high-voltage heating elements result in low yield, high cost, and poor performance stability, making it difficult to rapidly promote high-voltage heating elements in the market. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a high-voltage heating element, which enables the heating material, insulating material and shell of the high-voltage heating element to be integrally formed, thereby giving the high-voltage heating element higher voltage resistance, electrical performance, thermal conductivity, compressive strength and thermal shock resistance.

[0009] To achieve this objective, in a basic implementation, the present invention provides a method for preparing a high-voltage heating element, the method comprising the following steps:

[0010] (1) Insert the heating material into the outer shell of the high-voltage heating element, and then fill the space between the heating material and the outer shell with insulating material;

[0011] (2) The high-voltage heating element is fired and cooled as a whole.

[0012] The high voltage mentioned therein is a voltage of 13.6-50kV.

[0013] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), the heating material is an electric heating wire, and / or the outer shell is a metal shell. The electric heating wire and the metal shell are preferably made of a nickel-chromium alloy.

[0014] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), the raw materials for preparing the insulating material contain 75-85 parts of magnesium oxide, 8-12 parts of titanium dioxide, 3-7 parts of copper oxide, 3-7 parts of bismuth oxide, and 2-8 parts of boron nitride as additives by weight ratio.

[0015] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), the insulating material is mixed and / or dried before filling.

[0016] The mixing can be achieved by methods such as ball milling, airflow mixing, fluidized bed mixing, and ultrasonic mixing.

[0017] Preferably, the raw materials used to make the insulating material are micron-sized powder raw materials.

[0018] Preferably, the raw materials constituting the insulating material are further subjected to particle size distribution before mixing, so that the flow rate of the powder raw material with a particle size in the range of 40-325 mesh is ≤45s / 100g (determined according to the method specified in JB / T 8508-1996), so as to ensure the flowability of the insulating material powder after mixing.

[0019] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), the insulating material is compacted after filling. The filling can be achieved by the traditional powder filling process of the heating element, and the compaction can be achieved by tube shrinking and extrusion to improve the density of the insulating material powder.

[0020] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), the high-voltage heating element is a straight rod-shaped high-voltage heating element or a U-shaped high-voltage heating element.

[0021] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), after the insulating material fills the space between the heating material and the outer shell, the high-voltage heating element is further subjected to partial or overall annealing.

[0022] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein the temperature of the partial or overall annealing is 700-1200℃ and the time is 0-2h, wherein overall annealing is to heat the entire straight rod-shaped high-voltage heating element to eliminate stress; and partial annealing is to heat the bent part of the U-shaped high-voltage heating element to eliminate stress.

[0023] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (1), after the insulating material fills and compacts the space between the heating material and the outer shell, the loose insulating material filling the end of the high-voltage heating element is removed.

[0024] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (2), the overall firing is to heat the element to 830-870°C at a heating rate of 5-10°C / min and hold it at that temperature for 3-5 hours, and then heat the element to 1000-1100°C at a heating rate of 5-10°C / min and hold it at that temperature for 5-7 hours.

[0025] In a preferred embodiment, the present invention provides a method for preparing a high-voltage heating element, wherein in step (2), after the high-voltage heating element is integrally fired and cooled, insulating sealant is filled at the end of the high-voltage heating element, and / or a sealing insulator is installed at the end of the high-voltage heating element.

[0026] The beneficial effect of the present invention is that, by using the preparation method of the high-voltage heating element of the present invention, the heating material, insulating material and shell of the high-voltage heating element can be integrally formed, thereby making the high-voltage heating element with higher voltage resistance, electrical performance, thermal conductivity, compressive strength and thermal shock resistance.

[0027] This invention integrates low-melting-point multi-component oxides into the raw materials of insulating materials, enabling the metal shell, heating wire, and insulating material to be integrally sintered at low temperatures. This process densifies and vitrifies the material, thereby improving its voltage withstand rating. Low-temperature sintering does not damage the properties of the metal material; integral molding reduces electrical insulation weaknesses and simplifies industrial manufacturing; and optimizing the sintering temperature profile reduces energy consumption during industrial processing. The design method and manufacturing process of this invention combine low-temperature co-firing technology for ceramics with the processing technology of electric heating elements, maximizing the use of existing equipment and processes for producing electric heating elements, and rapidly promoting industrial upgrading. Attached Figure Description

[0028] Figure 1 The cross-sectional view of the structure of the U-shaped high-voltage heating element prepared in the embodiments and comparative examples of the present invention includes: an electric heating wire lead-out rod 1, a sealing insulator 2, an insulating sealant 3, an insulating material 4, a metal shell 5, an electric heating wire 6, and a gap filling layer 7. Detailed Implementation

[0029] The following examples and comparative examples further illustrate specific embodiments of the present invention. The structural composition of the U-shaped high-voltage heating elements prepared in each example and comparative example is as follows: Figure 1 As shown.

[0030] Example 1: Fabrication of a U-shaped high-voltage heating element (Part 1)

[0031] The preparation method of the U-shaped high-voltage heating element in this embodiment (processing using low-temperature co-firing technology) includes the following steps:

[0032] (1) Weigh magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride in a mass ratio of 80:10:5:5:5. The particle size of magnesium oxide is 40-325 mesh, the particle size of titanium dioxide, copper oxide and bismuth oxide is 100 mesh, and the particle size of boron nitride is 100 mesh. Mix them evenly with a ball mill and dry them at 100-150℃ for 3 hours to obtain insulating powder material.

[0033] (2) Winding a spiral-shaped nickel-chromium alloy material Ni 80 Cr 20 The electric heating wire 6 (0.5 mm in diameter) is welded to the electric heating wire lead rod 1 and then inserted into the metal shell 5 (20 mm in diameter and 1000 mm in length) made of the same material.

[0034] (3) Using a powder filling machine, the dried insulating powder material is filled between the electric heating wire 6 and the metal shell 5 of the high voltage heating element through the traditional powder filling process of the heating element. After filling, the insulating powder material is compacted by the tube shrinking machine. Finally, the loose insulating powder material filled at the end of the high voltage heating element is removed.

[0035] (4) The high-voltage heating element is placed into the kiln for firing. First, the temperature is raised to 850℃ at a heating rate of 8℃ / min and held for 4 hours. Then, the temperature is raised to 1050℃ at a heating rate of 8℃ / min and held for 6 hours. After completion, it is cooled with the furnace to form a dense insulating material 4 (thickness of 4mm).

[0036] (5) The insulation material 4 is highly densified and its volume shrinks, resulting in a gap between the insulation material 4 and the metal shell 5. The insulation powder material is then filled between the insulation material 4 and the metal shell 5 using a powder filling machine, that is, the gap filling layer 7 is added to compensate for the thermal conductivity defects caused by the air gap.

[0037] (6) Fill the end of the U-shaped high-voltage heating element with insulating sealant 3, and install a sealing insulator 2 on the outside of the insulating sealant 3.

[0038] Example 2: Preparation of a U-shaped high-voltage heating element (Part 2)

[0039] The preparation method of the U-shaped high-voltage heating element in this embodiment is basically the same as that in Embodiment 1, except that the raw material mass ratio in step (1) is changed to 75:12:7:3:2 for magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride, and the firing in step (4) is changed to first heating to 830°C at a heating rate of 5°C / min and holding for 5h, and then heating to 1100°C at a heating rate of 5°C / min and holding for 5h.

[0040] Example 3: Preparation of a U-shaped high-voltage heating element (Part 3)

[0041] The preparation method of the U-shaped high-voltage heating element in this embodiment is basically the same as that in Embodiment 1, except that the raw material mass ratio in step (1) is changed to 85:8:3:7:8 for magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride, and the firing in step (4) is changed to first heating to 870°C at a heating rate of 10°C / min and holding for 3 hours, and then heating to 1000°C at a heating rate of 10°C / min and holding for 7 hours.

[0042] Example 4: Preparation of a U-shaped high-voltage heating element (Part 4)

[0043] The preparation method of the U-shaped high-voltage heating element in this embodiment is basically the same as that in embodiment 1. However, in step (3), after removing the loose insulating powder material filled at the end of the high-voltage heating element, the high-voltage heating element is also locally annealed. The part of the local annealing is the bent part of the U-shaped high-voltage heating element, the temperature is 800℃, and the time is 0.5h.

[0044] Comparative Example 1: Preparation of a U-shaped high-voltage heating element (Part 5)

[0045] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the raw material mass ratio in step (1) is changed to 96:4:5 for magnesium oxide, calcium fluoride and boron nitride.

[0046] Comparative Example 2: Preparation of a U-shaped high-voltage heating element (VI)

[0047] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the raw material mass ratio in step (1) is changed to 90:5:2.5:2.5:5 for magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride.

[0048] Comparative Example 3: Preparation of a U-shaped high-voltage heating element (VII)

[0049] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the raw material mass ratio in step (1) is changed to 70:15:9:9:5 for magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride.

[0050] Comparative Example 4: Preparation of a U-shaped high-voltage heating element (Part 8)

[0051] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the raw material mass ratio in step (1) is changed to 80:10:5:5:10 for magnesium oxide, titanium dioxide, copper oxide, bismuth oxide and boron nitride.

[0052] Comparative Example 5: Preparation of a U-shaped high-voltage heating element (IX)

[0053] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the firing in step (4) is changed to heating to 850°C for 4 hours at a heating rate of 8°C / min.

[0054] Comparative Example 6: Preparation of a U-shaped high-voltage heating element (X)

[0055] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the firing in step (4) is changed to heating at a rate of 8℃ / min to 1050℃ for 6 hours.

[0056] Comparative Example 7: Preparation of a U-shaped high-voltage heating element (XI)

[0057] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the firing in step (4) is changed to heating to 950°C at a heating rate of 8°C / min for 7 hours.

[0058] Comparative Example 8: Preparation of a U-shaped high-voltage heating element (XII)

[0059] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the firing in step (4) is changed to first heating to 800°C at a heating rate of 8°C / min and holding for 4 hours, and then heating to 1150°C at a heating rate of 8°C / min and holding for 6 hours.

[0060] Comparative Example 9: Preparation of a U-shaped high-voltage heating element (XIII)

[0061] The preparation method of the U-shaped high-voltage heating element in this comparative example is basically the same as that in Example 1, except that the firing in step (4) is changed to first heating to 900°C at a heating rate of 8°C / min and holding for 4 hours, and then heating to 950°C at a heating rate of 8°C / min and holding for 6 hours.

[0062] Example 5: Performance Testing of High-Voltage Heating Element

[0063] The U-shaped high-voltage heating elements prepared in Examples 1-4 and Comparative Examples 1-9 were tested using the following methods and procedures.

[0064] During the withstand voltage test, the heating wire 6 is connected to a high voltage, 13.6-50kV, the metal casing 5 is grounded, the voltage rise rate is 0.5kV / s, and the voltage holding time is 60s.

[0065] Electrical performance testing shall be conducted in accordance with the insulation resistance measurement method specified in JB / T 2379-2016.

[0066] Thermal conductivity testing shall be conducted in accordance with the thermal conductivity test method specified in JB / T 8508-1996.

[0067] The compressive strength test shall be conducted in accordance with the method specified in GB / T 8489-2006.

[0068] Thermal shock resistance performance was tested according to the method specified in GB / T 8411.2-2008.

[0069] The results of each test are summarized in Table 1 below.

[0070] Table 1 Performance test results of high-voltage heating elements

[0071]

[0072] The test results in Table 1 above indicate that:

[0073] (1) The results of Examples 1-4 show that the preparation method of the present invention can be used to prepare high voltage heating elements with a voltage rating of 21-22kV. The ratio of insulating material raw materials and the firing process significantly affect the performance of the high voltage heating elements.

[0074] (2) Compared with Comparative Examples 5-9, Example 1 shows that using a staged firing method and holding the mixed oxide of titanium dioxide, copper oxide and bismuth oxide at a temperature near the melting point for a certain period of time can promote the growth of insulating material grains, thereby improving the voltage withstand rating and insulation resistance of the high-voltage heating element made from the insulating material.

[0075] (3) Compared with Comparative Example 1, Example 1 shows that adding titanium dioxide, copper oxide and bismuth oxide to magnesium oxide can produce a higher voltage rating and insulation resistance than adding calcium fluoride.

[0076] (4) Compared with Comparative Examples 2-3, Example 1 shows that if the total content of titanium dioxide, copper oxide and bismuth oxide is too high or too low, it will lead to abnormal or insufficient growth of insulating material grains, which will result in a decrease in the voltage withstand rating and insulation resistance of the high-voltage heating element made of the insulating material.

[0077] (5) Compared with Comparative Example 4, Example 1 shows that although adding excessive boron nitride can improve thermal conductivity, the boron nitride powder is prone to agglomeration, which makes it difficult to mix the raw materials evenly. As a result, the voltage resistance and insulation resistance of the high-voltage heating element obtained after firing decrease.

[0078] (6) Compared with Comparative Examples 2, 5, 7 and 9, Example 1 shows that if the total content of titanium dioxide, copper oxide and bismuth oxide is too low or the firing temperature is too low, the grain growth of the insulating material will be insufficient, which will lead to a decrease in the voltage withstand rating and insulation resistance of the high-voltage heating element made of the insulating material.

[0079] (7) Compared with Example 4, Example 1 shows that local annealing can improve the mechanical properties of high voltage heating elements, such as compressive strength and thermal shock resistance.

[0080] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention is also intended to include these modifications and variations. The above embodiments or implementations are merely illustrative examples of this invention, and it can also be implemented in other specific ways or forms without departing from its gist or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of this invention should be defined by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of this invention.

Claims

1. A method of making a high voltage heating element, characterized by, The preparation method includes the following steps: (1) Insert the heating material into the outer shell of the high-voltage heating element, and then fill the space between the heating material and the outer shell with insulating material; (2) The high-voltage heating element is fired and cooled as a whole. The high voltage mentioned therein is a voltage of 13.6-50kV.

2. The method of claim 1, wherein: In step (1), the heating material is an electric heating wire, and / or the outer shell is a metal shell.

3. The method of claim 1, wherein: In step (1), the raw materials for preparing the insulating material contain 75-85 parts magnesium oxide, 8-12 parts titanium dioxide, 3-7 parts copper oxide, 3-7 parts bismuth oxide, and 2-8 parts boron nitride as additives by weight ratio.

4. The method of claim 1, wherein: In step (1), the insulating material is mixed and / or dried before filling.

5. The method of claim 1, wherein: In step (1), the high-voltage heating element is a straight rod-shaped high-voltage heating element or a U-shaped high-voltage heating element.

6. The method of claim 5, wherein: In step (1), after the insulating material fills the space between the heating material and the outer shell, the high-voltage heating element is partially or entirely annealed.

7. The method of claim 6, wherein: The temperature for partial or overall annealing is 700-1200℃, and the time is 0-2h. Overall annealing involves heating the entire straight rod-shaped high-voltage heating element to eliminate stress. Partial annealing involves heating the bent portion of the U-shaped high-voltage heating element to eliminate stress.

8. The method of claim 1, wherein: In step (1), after the insulating material fills and compacts the space between the heating material and the outer shell, the loose insulating material filling the end of the high-voltage heating element is removed.

9. The method of claim 1, wherein: In step (2), the overall firing process involves heating the temperature to 830-870℃ at a heating rate of 5-10℃ / min and holding it at that temperature for 3-5 hours, and then heating the temperature to 1000-1100℃ at a heating rate of 5-10℃ / min and holding it at that temperature for 5-7 hours.

10. The method of claim 1, wherein: In step (2), after the high-voltage heating element is fired and cooled as a whole, insulating sealant is filled at the end of the high-voltage heating element, and / or a sealing insulator is installed at the end of the high-voltage heating element.

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