A laser printer ceramic heating bar with thermal protection

Abstract

The present application relates to a kind of laser printer ceramic heating strip with thermal protection, including ceramic substrate, electrode, heating wire, glass glaze, fuse point is arranged on heating wire;Fuse point is gradually narrowed section or directly narrowed section;The length of the fuse point is between 0.1-5mm, the width of the fuse point is less than or equal to 70% of the width of non-fuse point;Local narrow design is made to heating wire, so that ceramic heating strip is self-fused when heated to a certain temperature, can effectively avoid the fire phenomenon caused by temperature too high or other conditions;Temperature measuring point can be welded on the back of fuse point design, since temperature measuring point will take away local heat, can effectively balance the temperature too high problem at fuse point design, avoid the printing color difference phenomenon caused by local overheating in printing process;Fuse point design can adopt gradually narrowed form in drawing, or directly narrowed form, and the shape of temperature measuring point can also be changed according to the shape design of self-fuse point.

Description

Technical Field

[0001] This invention relates to the field of ceramic heating strips for laser printers with thermal protection, and in particular to a ceramic heating strip for laser printers with thermal protection. Background Technology

[0002] Laser printing, as the name suggests, refers to documents printed by a laser printer. Under computer control, the laser printer processes a series of characters, graphics, and other data through the coordination of various mechanical components, ultimately outputting the document onto paper or other media. Compared to inkjet printers or other types of printers, laser printers have three main advantages: 1. Better print quality; 2. Faster printing speed; 3. Lower printing costs. The design and manufacturing complexity of the internal scanning and printing components of a laser printer far exceeds that of its external mechanical operation; these internal components are crucial for the long-term, reliable operation of a laser printer.

[0003] The internal structure of a laser printer mainly consists of: a scanning unit, a printing unit, a developing unit, a fusing unit, and a transport unit. Among them, the "fusing unit" is the main component for long-term preservation of printed documents. Its working principle is as follows: when toner is adsorbed onto the printing medium, it is attracted to the surface of the printing medium by opposite charges. If you want the printed document to be preserved for a longer period of time, the fusing unit uses pressure and heat to melt the toner and embed it into the surface of the printing medium, forming a fixed printed document.

[0004] Currently, there are two main types of heating components in fixing devices: tungsten filament lamp heating and ceramic heating strips.

[0005] In traditional laser printers, the fuser heating device is a lamp heater, which generates heat by using the principle of tungsten filament heating when energized. However, ceramic heating strips have superior characteristics compared to tungsten filament heating, such as faster heating speed, more uniform heat distribution, shorter first-page printing time, and longer service life, and have gradually become the preferred material for heating components in laser printers.

[0006] The ceramic heating strip consists of four parts: a ceramic substrate, electrodes, heating wire, and glass glaze. It also uses the principle of heating the heating wire through electricity to provide a heat source. However, compared with lamp tubes, the ceramic substrate has good thermal conductivity, high thermal conductivity, and high temperature resistance, which can make the entire heating device dissipate heat more quickly.

[0007] Although ceramic heating strips have many excellent properties, there are still technical challenges in ensuring their safety and reliability during use. Based on the fact that ceramic heating strips use ceramic as a substrate and that ceramic materials are resistant to high temperatures, the heating element encapsulated on the surface of the ceramic heating strip for laser printers is a metal heating wire.

[0008] The typical operating temperature of the heating strip is between 180℃ and 220℃. The melting point of the heating wire in the ceramic heating strip is above 400℃. When abnormal problems such as excessive current occur, the excessively high temperature of the heating wire will be transmitted and diffused through the ceramic substrate to other organic components of the fixing device, thereby causing a fire and damaging the equipment.

[0009] After being powered on, the heating wire typically melts at temperatures above 400°C. The ceramic substrate, due to its excellent high-temperature resistance and high thermal conductivity, rapidly transfers the temperature to other media. The excessively high temperature of the heating wire can be transferred and diffused through the ceramic substrate to other organic components of the fusing unit. Since the components of the fusing unit are made of a lot of organic materials with low ignition points, they are extremely prone to combustion at high temperatures of 400°C and above, which can cause fires and damage the equipment, potentially destroying the entire printer.

[0010] Therefore, for the metal heating wire of the heating element encapsulated on the surface of the ceramic heating strip in a laser printer, there is no protection mechanism for the heating wire to melt after power is applied. According to the temperature control mechanism of the laser printer, it relies on the temperature adjustment module. After the temperature exceeds the limit, a fault shutdown will occur. The fault temperature is generally between 500-800°C, which triggers the shutdown and stops heating. This fault temperature protection has such a problem for metal heating wires, which is highly random. After the ceramic heating strip exceeds the temperature required for operation, there is a risk of high temperature and fire. Summary of the Invention

[0011] The purpose of this invention is to provide a ceramic heating strip for laser printers with thermal protection, which is safe, simple in structure, easy to modify and implement, and has reliable melting.

[0012] To address the aforementioned problems, this invention provides a ceramic heating strip for laser printers with thermal protection, comprising a ceramic substrate, electrodes, a heating wire, and a glass glaze, wherein a melting point is provided on the heating wire; the melting point is a gradually narrowing section or a directly narrowing section;

[0013] The length of the melting point is between 0.1 and 5 mm, and the width of the melting point is less than or equal to 70% of the width of the non-melting point.

[0014] The technical solution provided by this invention also has the following technical features:

[0015] Furthermore, the shape of the melting point is a constricted arc.

[0016] Furthermore, the length of the melting point is 3mm.

[0017] Furthermore, the width of the melting point is half the width of the non-melting point.

[0018] Furthermore, the melting point is located at the end of the heating wire of the printer strip, and the length of the end section is less than or equal to 4 / 5 of the entire heating wire, with the electrode end as the starting point.

[0019] Furthermore, a temperature balancing module is provided on the back of the upper end of the melting point, which is used to absorb heat from the melting point.

[0020] Furthermore, the temperature balancing module is a temperature measuring point.

[0021] The material composition formulation technology solution for designing the melting point provided by this invention also has the following technical features:

[0022] A melting point of a ceramic heating strip for a laser printer with thermal protection comprises the following components: 30-60% silver, 5-10% tin, 5-10% lead, 3-5% palladium, 3-5% titanium dioxide, 2-3% boron oxide, 10-20% glass chemical components, 5-10% methylcellulose, 5-10% octadecanoic acid, and 3-5% tin fluoride.

[0023] The present invention provides a process method for designing the width of the melting point, which also has the following technical features:

[0024] A process design method for the melting point width and thickness of a ceramic heating strip for a laser printer with thermal protection:

[0025] The cross-sectional area of ​​the melting point is S, S = ah, where a is the width of the cross-section and h is the height of the cross-section or its thickness. The length of the melting point is L, the current through the melting point is I, the surface temperature of the melting point is θ, the ambient temperature is θ0, the resistivity of the material at the melting point is ρ0, and the temperature coefficient of resistance is α.

[0026] Material heat formula: Where ρ=ρ0(1+αθ);

[0027] According to the heat dissipation formula for materials: P = K t Aτ;

[0028] P is the heat dissipation power; Kt is the comprehensive heat dissipation coefficient, which is a comprehensive parameter of heat conduction, heat convection and heat radiation; A is the heat dissipation area; τ is the temperature rise, which is the difference between the material surface temperature θ and the ambient temperature θ0, i.e. τ=θ-θ0;

[0029] Therefore, the heat dissipated at the melting point is:

[0030] Q2 = K t Aτt=K t MLτt;

[0031] Where A does not include the unfolded area of ​​the melting point on both end faces, and M is the perimeter of the melting point cross section, i.e., A = ML;

[0032] When the fuse is working normally, the heat generated at the fuse is equal to the heat dissipated by the fuse, Q1, i.e., Q1 = Q2.

[0033]

[0034] Simplifying the formula, we get:

[0035]

[0036] Further details:

[0037]

[0038] Further clarification: Substituting into M = 2(a + h)

[0039] Simplifying the formula, we get:

[0040]

[0041] In the formula: a is the width of the cross-sectional area of ​​the melting point of the heating wire, and h is the thickness of the melting point. Substituting the known h, we get a.

[0042] The present invention has the following beneficial effects:

[0043] 1. This invention addresses the risk of high temperature and fire posed by ceramic heating strips continuing to heat beyond the required operating temperature after overheating. It employs a temperature control design on the ceramic heating strip, enabling it to automatically melt and break when the set operating temperature is exceeded, thus preventing fire due to excessive heat. Typically, the operating temperature of a heating strip is between 180℃ and 220℃, while the melting point of the heating wire encapsulated in the ceramic heating strip is above 400℃. In the event of abnormal problems such as excessive current, the excessively high temperature of the heating wire can be transmitted through the ceramic substrate to other organic components of the fixing device, potentially causing a fire and damaging the equipment.

[0044] Based on the above problems, a narrow design scheme is proposed for the printing of heating wires in the ceramic heating plate. During power-on use, if strong current fluctuations occur, under the same resistivity, the heating wire unit volume is smaller in the narrower part, and more heat is generated. The temperature rises faster than in other parts, so it will melt and break earlier. This self-melting point design can effectively prevent the printer from catching fire and being damaged due to the overall temperature of the ceramic heating plate being too high.

[0045] This type of melting point printing design results in a higher temperature for the ceramic heating wire during normal operation compared to other parts, which can affect the printing effect. Therefore, by setting a temperature balancing module at the melting point, the excess heat generated during normal operation is absorbed, balancing the temperature with the surrounding environment to avoid affecting the printing effect and maintain normal printing.

[0046] 2. The present invention addresses the issue that ceramic heating strips require temperature measurement points during use. These measurement points often draw away some heat, resulting in lower temperatures. Therefore, a temperature balancing module is integrated into the temperature sensor on the back of the ceramic heating wire's melting point. This minimizes the cost of the modification and balances the excessively high temperature at the melting point, preventing poor printing results caused by excessively high melting point temperatures.

[0047] To improve the safety of ceramic heating strips, the design can adopt a gradually narrowing form or a direct narrowing form (both are based on the same principle). At the same time, the shape of the temperature measuring point can also be changed according to the design of the self-melting point. For example, if the self-melting point is designed to be a direct narrowing form, the temperature measuring point can be designed as a square.

[0048] 3. The advantage of the melting point design created in this invention is that it can effectively prevent the ceramic heating plate from catching fire due to excessive temperature caused by abnormal current, effectively improve the safety of the ceramic heating element, and the back of the design can be welded with a temperature measuring point, which effectively solves the problem of temperature difference in the ceramic substrate heater caused by excessive local temperature at the melting point, and ensures the uniformity of the temperature of the entire ceramic heater.

[0049] 4. The present invention adopts a local narrowing design of the heating wire, so that the ceramic heating strip melts and breaks when heated to a certain temperature. The narrowing amount can be controlled by the material resistance, resistivity and melting point, which can effectively avoid fire or other situations caused by excessive temperature.

[0050] A temperature balancing module can be soldered to the back of the fuse point design to serve as a temperature measuring point. Since the temperature measuring point will carry away local heat, it can effectively balance the problem of excessive temperature at the fuse point design and avoid the printing color difference caused by local overheating during the printing process.

[0051] The melting point design can adopt a gradually narrowing form as shown in the figure, or a direct narrowing form. At the same time, the shape of the temperature measuring point can also be changed according to the shape design of the melting point. For example, if the melting point is designed to be a direct narrowing form, the temperature measuring point can be designed as a square. Attached Figure Description

[0052] Figure 1 This is a front view of a ceramic heating strip for a laser printer with thermal protection, according to an embodiment of the present invention.

[0053] Figure 2 This is a rear view of a ceramic heating strip for a laser printer with thermal protection, according to an embodiment of the present invention.

[0054] Figure 3 A front view of a ceramic heating strip for a laser printer using existing technology;

[0055] Figure 4This is a front view of the mesh plate 1 of the ceramic heating wire according to an embodiment of the present invention;

[0056] Figure 5 This is a front view of the mesh plate 3 of the ceramic heating wire according to an embodiment of the present invention;

[0057] Figure 6 This is a front view of a ceramic heating strip for a laser printer with thermal protection, according to an embodiment of the present invention.

[0058] Figure 7 This is a rear view of a ceramic heating strip for a laser printer with thermal protection, according to an embodiment of the present invention.

[0059] In the diagram: 1. Electrode; 2. Heating wire; 3. Glass glaze; 4. Ceramic substrate; 5. Melting point; 6. Temperature balance module; 8. Low-temperature slurry heating wire. Detailed Implementation

[0060] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0061] like Figure 1 , 2 A ceramic heating strip for a laser printer with thermal protection, shown in figures 4, 5, 6, and 7, includes a ceramic substrate 4, an electrode 1, a heating wire 2, and a glass glaze 3. A melting point 5 is provided on the heating wire 2. The melting point 5 is a gradually narrowing section or a directly narrowing section.

[0062] The length of the melting point 5 is between 0.1 and 5 mm, and the width of the melting point 5 is less than or equal to 70% of the width of the non-melting point.

[0063] The technical solution provided by this invention also has the following technical features:

[0064] In one embodiment of the present invention, the shape of the melting point 5 is a constricted arc.

[0065] In one embodiment of the present invention, the length of the melting point 5 is 3 mm.

[0066] In one embodiment of the present invention, the width of the melting point is half the width of the non-melting point.

[0067] In one embodiment of the present invention, the melting point is located at the end of the heating wire of the printer strip, and the length of the end section is less than or equal to 4 / 5 of the entire heating wire, with the electrode end as the starting end.

[0068] In one embodiment of the present invention, a temperature balancing module is provided on the back side of the upper end of the melting point, and the temperature balancing module is used to absorb the heat of the melting point.

[0069] In one embodiment of the present invention, the temperature balancing module is a temperature measuring point.

[0070] In one embodiment of the present invention, the melting point of a ceramic heating strip for a laser printer with thermal protection comprises the following components: 30-60% silver, 5-10% tin, 5-10% lead, 3-5% palladium, 3-5% titanium dioxide, 2-3% boron oxide, 10-20% glass chemical components, 5-10% methylcellulose, 5-10% octadecanoic acid, and 3-5% tin fluoride; the resistance wire paste applied to the melting point is a low-melting-point paste, and the melting point is between 270°C and 320°C.

[0071] In one embodiment of the present invention, a process method for designing the thickness and width of the melting point further has the following technical features: a process design method for the width of the melting point of a ceramic heating strip for a laser printer with thermal protection: the cross-sectional area of ​​the melting point is S, S = ah, a is the width of the cross-section, h is the height of the cross-section or the thickness, the length of the melting point is L, the current through the melting point is I, the surface temperature of the melting point is θ, the ambient temperature is θ0, the resistivity of the material at the melting point is ρ0, and the temperature coefficient of resistance is α;

[0072] Material heat formula:

[0073] Where ρ=ρ0(1+αθ);

[0074] According to the heat dissipation formula for materials: P = K t Aτ;

[0075] P is the heat dissipation power; Kt is the comprehensive heat dissipation coefficient, which is a comprehensive parameter of heat conduction, heat convection and heat radiation; A is the heat dissipation area; τ is the temperature rise, which is the difference between the material surface temperature θ and the ambient temperature θ0, i.e. τ=θ-θ0;

[0076] Therefore, the heat dissipated at the melting point is:

[0077] Q2 = K t Aτt=K t MLτt;

[0078] Where A does not include the unfolded area of ​​the melting point on both end faces, and M is the perimeter of the melting point cross section, i.e., A = ML;

[0079] When the fuse is working normally, the heat generated at the fuse is equal to the heat dissipated by the fuse, Q1, i.e., Q1 = Q2.

[0080]

[0081] Simplifying the formula, we get:

[0082]

[0083] Further details:

[0084]

[0085] Further clarification: Substituting into M = 2(a + h)

[0086] Simplifying the formula, we get:

[0087]

[0088] In the formula: a is the width of the cross-sectional area of ​​the melting point of the heating wire, and h is the thickness of the melting point. Substituting the known h, we get a. The cross-sectional dimensions can be adjusted according to the current and the selected heating wire material. The normal operating temperature of this design is 180℃-220℃, and the melting temperature range is 350℃-400℃.

[0089] The key points of implementation for this invention are as follows:

[0090] 1. In existing technologies, ceramic heating strips, such as Figure 3 The device mainly consists of four parts: a ceramic substrate, electrodes, a heating wire, and a glass glaze. It also utilizes the principle of heating the wire through electricity to provide a heat source. However, compared to lamps, the ceramic substrate has excellent thermal conductivity, high thermal conductivity, and high temperature resistance, allowing for faster heat dissipation from the entire heating device. However, ceramic heating strips still suffer from extreme temperature runaway issues. Typically, the operating temperature of the heating strip is between 180℃ and 220℃, while the melting point of the heating wire encapsulated in the ceramic heating strip is above 400℃. In the event of abnormal problems such as excessive current, the excessively high temperature of the heating wire can be transferred and diffused through the ceramic substrate to other organic components of the fixing device, potentially causing a fire and damaging the equipment.

[0091] Based on the above problems, a design scheme is proposed to narrow the printed area of ​​the heating wire in the ceramic heating plate, such as... Figure 1 As shown; during power-on use, if strong current fluctuations occur, under the same resistivity, the heating wire unit volume is smaller in the narrower part, and more heat is generated. The temperature rises faster than in other parts, so it will melt prematurely. This self-melting point design can effectively prevent the printer from catching fire and being damaged due to excessive temperature of the ceramic heating plate.

[0092] This type of printing design for the melting point occurs when the temperature of the ceramic heating wire is higher than other parts during normal operation, which affects the printing effect. The back of the melting point design can be soldered with a temperature balancing module as a temperature sensing point. However, the temperature sensing point typically carries away some localized heat, resulting in a lower temperature at that point. Therefore, a heat absorption point is set on the back of the ceramic heating wire's melting point, or in other words, the temperature balancing module is integrated into the temperature sensor. Figure 2As shown, this is used to balance the excessively high temperature at the melting point, avoiding poor printing results caused by excessively high melting point temperature.

[0093] Designs that improve the safety of ceramic heating strips can be adopted. Figure 1 Gradually narrowing form, or directly narrowing form (both operate on the same principle, with simultaneous temperature measurement points) Figure 2 The shape can also be changed according to the design of the self-melting point. For example, if the self-melting point is designed to be a directly narrowed form, the temperature measuring point can be designed as a square.

[0094] In one embodiment of the present invention, the specific technical requirements, dimensions, proportions, and shape requirements for the gradually narrowing melting point form are as follows:

[0095] The shape of the melting point is a constricted arc. With the printing thickness remaining constant, the length is generally 3mm and the width is half that of the non-melting point.

[0096] In one embodiment of the present invention, the technical requirements for the location of the melting point and the corresponding different technical effects, and the relative distance or position ratio, are required as follows:

[0097] The fuse point should be aligned with the temperature sensor point (the temperature sensor point is on the back of the fuse point). The temperature sensor point is determined by the printer's structural design. Generally, the fuse point is located at three-twentieth of the way along the printer strip (with the electrode end as the starting point). The fuse point will be placed as close as possible to the edge of the heating element on the printer strip (within one-tenth of the range). Special note: The fuse point setting has no substantial impact on the printer's heating element and its position can be adjusted arbitrarily according to the printer's mechanism.

[0098] In one embodiment of the present invention, the technical requirements for existing heating wire materials are as described in the above embodiment. If other applicable materials are used, the corresponding adjustments are as follows: if other heating wire materials are used, the preparation process is consistent with the process described in this column; according to the formula in this application, based on the properties of the heating wire material and the printer model used, the design width and length of the melting point can be calculated, and the design method is consistent with the present invention.

[0099] In one embodiment of the present invention, the following is adopted: Figure 6The design method shown (gradually narrowing form or direct narrowing form, both of which are based on the same principle) is used to design the shape of the melting point. The above-mentioned bidirectional printing process is also used for coating. First, the ceramic heating screen plate 1 is used for the first printing (printing direction from left to right) to form the prototype of two heating wires. Then, the ceramic substrate and screen plate 1, which have been printed with resistance wire paste and melting point resistance wire paste, are reversed 180° and the ceramic heating screen plate 1 is used again (printing direction from left to right) for the second printing. Finally, the screen plate 3 is used to coat the empty defect positions to form the narrowed I-shaped melting point. Low temperature paste heating wire 8 is set on the screen plate 3.

[0100] Except at the melting point, the two heating wires are printed in reverse order twice to ensure that they have the same thickness and print volume. This effectively avoids temperature differences caused by uneven printing due to the long substrate. Because the melting point is printed in a single pass, it is relatively thinner and narrower. In actual use, the heating wire at this point is relatively small in size and has higher resistance, resulting in a higher temperature compared to other locations. When the current is high, this point will reach the melting point before other locations, thus preventing the entire ceramic heating substrate from overheating and catching fire. This melting point printing design means that the temperature of the ceramic heating wire is higher than other parts during normal operation, which may affect the printing effect. However, the ceramic heating strip requires a temperature measuring point during use. The temperature measuring point is located on the ceramic substrate surface behind the melting point (e.g., ...). Figure 7 As shown), the temperature measuring point usually carries away some heat to balance the excessively high temperature at the fuse point, resulting in a lower temperature at the measuring point and avoiding poor printing quality caused by excessively high fuse point temperature; the temperature measuring point ( Figure 7 The shape can be changed according to the design of the self-fusing point. For example, if the self-fusing point is designed to be a narrow, H-shaped structure, then the temperature measuring point can be designed as a square. The fuse point must be set on the back of the temperature measuring point. The temperature measuring point is designed according to the internal structure of the printer equipment. Generally, the fuse point is located at the rear end of four-fifths of the printer strip length or at the connection between the electrode and the heating wire (with the electrode end as the starting point).

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ceramic heating strip for a laser printer with thermal protection, comprising a ceramic substrate, electrodes, a heating wire, and a glass glaze, characterized in that: A fusing point is provided on the heating wire; the fusing point is a gradually narrowing section or a directly narrowing section; the length of the fusing point is between 0.1-5mm, and the width of the fusing point is less than or equal to 70% of the width of the non-fusing point; The melting point is located at the end of the heating wire of the printing strip. The length of the end section is less than or equal to 4 / 5 of the total length of the heating wire. The starting point is the electrode end. A temperature balancing module is provided on the back of the upper end of the melting point. The temperature balancing module is used to absorb the heat of the melting point. The temperature balancing module is a temperature measuring point. The shape of the temperature measuring point is matched with the shape of the melting point. The melting point comprises the following components: 30-60% silver, 5-10% tin, 5-10% lead, 3-5% palladium, 3-5% titanium dioxide, 2-3% boron oxide, 10-20% glass chemical components, 5-10% methylcellulose, 5-10% octadecanoic acid, and 3-5% tin fluoride.

2. A ceramic heating strip for laser printers with thermal protection according to claim 1, characterized in that: The shape of the melting point is a constricted arc.

3. A ceramic heating strip for laser printers with thermal protection according to claim 1, characterized in that: The width of the melting point is half the width of the non-melting point.

4. The process design method for determining the melting point width of a ceramic heating strip for a laser printer with thermal protection as described in claim 1, characterized in that: The cross-sectional area of ​​the melting point is S, S = ah, where a is the width of the cross-section and h is the height of the cross-section or its thickness. The length of the melting point is L, the current through the melting point is I, the surface temperature of the melting point is θ, the ambient temperature is θ0, the resistivity of the material at the melting point is ρ0, and the temperature coefficient of resistance is α. Material heat formula Where ρ=ρ0(1+αθ); According to the heat dissipation formula for materials: P = K t Aτ; P is the heat dissipation power; Kt is the comprehensive heat dissipation coefficient, which is a comprehensive parameter of heat conduction, heat convection and heat radiation; A is the heat dissipation area; τ is the temperature rise, which is the difference between the material surface temperature θ and the ambient temperature θ0, i.e. τ=θ-θ0; Therefore, the heat dissipated at the melting point is: Q2=K t Aτt=K t MLτt; Where A does not include the unfolded area of ​​the melting point on both end faces, and M is the perimeter of the melting point cross section, i.e., A = ML; When the fuse is working normally, the heat generated at the fuse is equal to the heat dissipated by the fuse, Q1, i.e., Q1 = Q2. Simplifying the formula, we get: Further details: Further clarification: Substituting into M = 2(a + h) Simplifying the formula, we get: In the formula: a is the width of the cross-sectional area of ​​the melting point of the heating wire, and h is the thickness of the melting point. Substituting the known h, we get a.

Images