Electric heating device for a strip steel heat treatment furnace

Abstract

The application provides an electric heating device for a strip steel heat treatment furnace, which comprises an electric heating radiation tube mechanism and an atmosphere protection cover mechanism, the electric heating radiation tube mechanism is horizontally suspended in the strip steel heat treatment furnace, one end of the electric heating radiation tube mechanism is fixed on a side wall of the strip steel heat treatment furnace, the end of the electric heating radiation tube mechanism is exposed to the strip steel heat treatment furnace, and the other end of the electric heating radiation tube mechanism extends into the strip steel heat treatment furnace, and the atmosphere protection cover mechanism covers the end of the electric heating radiation tube mechanism connected with the strip steel heat treatment furnace and is fixed on the wall of the strip steel heat treatment furnace, the electric heating device has the advantages of low cost, high temperature control precision, good energy-saving effect, long service life and low maintenance cost.

Description

Technical Field

[0001] This invention belongs to the technical field of strip steel heat treatment furnaces, and particularly relates to an electric heating device for strip steel heat treatment furnaces. Background Technology

[0002] In current applications of strip heating or heat equalization, the commonly used heating elements are resistance strips and radiant heating tubes. The heating elements of resistance strips and radiant heating tubes are typically made of iron-chromium-aluminum or nickel-chromium alloys. These heating elements are relatively mature in application and therefore widely used; however, they also have several problems:

[0003] (1) The temperature resistance range of iron-chromium-aluminum and nickel-chromium alloys is 1100~1400℃, the radiation power intensity is 1.7~3.5W / cm3, the thermal expansion coefficient is large at high temperature, and the creep resistance is poor.

[0004] (2) When using a resistance strip structure, it is generally necessary to place it at the bottom or side of the furnace because its own shielding coefficient is large and its effective radiation coefficient is low. In addition, after the resistance strip is used at high temperature for a long time, the internal crystal phase changes, which leads to frequent breakage and interruption of furnace heating, which has an adverse effect on the heating process and heating uniformity.

[0005] (3) Therefore, the structure of an electric heating radiant tube with a sleeve and built-in heating wire is relatively common and easy to maintain. However, it also has some shortcomings:

[0006] 1) Large material consumption. A set of heating elements weighs 50-70 kg, resulting in high material consumption and cost.

[0007] 2) High maintenance costs. This type of electric heating radiant tube with a sheath and built-in heating wire structure heats up first through the internal resistance wire, which then conducts the heat to the external high-alloy tube, and finally dissipates the heat into the furnace. Under certain conditions, to achieve the process heating target, the resistance wire inside the high-alloy tube must radiate heat at a higher temperature. Prolonged use at high temperatures shortens the lifespan of the resistance wire, eventually leading to short-circuit failure and requiring necessary maintenance, thus increasing the customer's maintenance costs.

[0008] 3) Relatively low temperature control accuracy. Electric heating radiant tubes using a sheath and built-in heating wire have a relatively large temperature control range due to the temperature gradient between the internal heating wire, the thick-walled high-alloy tube, and the ambient temperature caused by thermal inertia. For example, if the required furnace temperature is 900℃, the heating wire needs to reach 950-1000℃ during gradual heating to achieve this temperature, and the furnace temperature will gradually rise above 900℃. When the furnace temperature is too high, the heating wire temperature needs to be lowered, but due to thermal inertia, the temperature reduction is always gradual; conversely, the same applies when the furnace temperature decreases and the heating wire temperature needs to be increased. Therefore, it is difficult to maintain a stable furnace temperature around 900℃. The greater the thickness and material quality of the heating tube, the greater the influence of thermal inertia, and the lower the temperature control accuracy (the temperature control range is relatively large, generally ±30℃).

[0009] In summary, the resistance strips and sheathed electric heating radiant tubes with built-in heating elements that are currently widely used in the field of strip heat treatment have significant shortcomings and are inconsistent with the national concept of green industrial production. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide an electric heating device for a strip heat treatment furnace, which can replace the electric heating element made of electric heating alloy material, thereby reducing the cost of electric heating equipment.

[0011] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: an electric heating device for a strip steel heat treatment furnace, characterized in that: it includes an electric heating radiant tube mechanism and an atmosphere protection hood mechanism. The electric heating radiant tube mechanism is horizontally suspended inside the strip steel heat treatment furnace, with one end fixed to a furnace wall that passes through the strip steel heat treatment furnace and the other end exposed outside the strip steel heat treatment furnace. The atmosphere protection hood mechanism covers the end of the electric heating radiant tube mechanism that is connected to the strip steel heat treatment furnace and is connected and fixed to the furnace wall of the strip steel heat treatment furnace.

[0012] According to the above scheme, the electric heating radiant tube mechanism includes a positive electrode graphite radiant tube, a negative electrode graphite radiant tube, and a graphite connecting rod. One end of the positive and negative electrode graphite radiant tubes is connected and fixed by an insulating block, and the other end is connected by the graphite connecting rod. One end of the positive electrode graphite radiant tube is connected to the positive terminal by a bolt, and one end of the negative electrode graphite radiant tube is connected to the negative terminal by a bolt. Both the positive and negative electrode graphite radiant tubes are provided with protective atmosphere venting holes.

[0013] According to the above scheme, the atmosphere protection hood mechanism includes a protective hood body, which is provided with a protective atmosphere inlet hole and a residual oxygen detection hole.

[0014] According to the above scheme, the positive electrode graphite electric radiation tube and the negative electrode graphite electric radiation tube are respectively provided with connecting screw holes, and the two ends of the graphite connecting rod are provided with external threads, which are configured and screwed into the connecting screw holes.

[0015] According to the above scheme, the insulating block is made of aluminum oxide.

[0016] According to the above scheme, the protective atmosphere is nitrogen with a purity of 99.999% and a dew point below -40°C.

[0017] According to the above scheme, the outer diameter of the positive electrode graphite electric radiation tube and the negative electrode graphite electric radiation tube is 50-200mm, the wall thickness is 3-15mm, the voltage is 20-55V, and the power is 10-90kW.

[0018] According to the above scheme, the insulating block is fitted with a connecting sleeve, the outer end of the connecting sleeve is welded to the strip steel heat treatment furnace, and the inner end is provided with a retaining ring, which stops the insulating block.

[0019] The beneficial effects of this invention are as follows: It provides an electric heating device for a strip steel heat treatment furnace. The electric heating radiant tube is directly made of graphite radiant tube. The resistivity of graphite at high temperatures is 5 to 7 times that of radiant heating alloys, the radiation intensity per unit area is 8 to 20 times that of radiant heating alloys, and the density is only about 25% of that of radiant heating alloys. Therefore, under the same heating power, the weight of the material is generally only 15% of that of the traditional electric heating radiant tube structure with a sleeve and built-in heating wire, which greatly reduces the investment cost in the field of electric heating. The graphite radiant tube is a hollow tube made of graphite that is directly heated by electricity, eliminating an intermediate heat transfer link. It has a fast power adjustment response, high temperature control accuracy, and good energy-saving effect. The maximum temperature resistance of graphite material is up to 3100℃, and the coefficient of expansion at high temperatures is only about 20% of that of radiant heating alloys. At the same time, its compressive strength and flexural strength increase with the increase of temperature. Therefore, the graphite radiant tube will not experience creep or burn-off under high-temperature reducing atmosphere, which greatly extends the service life of the radiant tube and reduces the cost of heat treatment and maintenance of heating elements. Attached Figure Description

[0020] Figure 1 This is a front view of an embodiment of the present invention;

[0021] Figure 2 This is a top view of an embodiment of the present invention. Detailed Implementation

[0022] To better understand the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that in the description of this invention, the terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] like Figure 1 , Figure 2 As shown, the electric heating device for the strip heat treatment furnace includes an electric heating radiant tube mechanism and an atmosphere protection hood mechanism. The electric heating radiant tube mechanism is horizontally suspended inside the strip heat treatment furnace 1. One end is fixed to a furnace wall that passes through the strip heat treatment furnace and the end protrudes out of the furnace. The other end extends into the furnace. The atmosphere protection hood mechanism covers the end of the electric heating radiant tube mechanism that is connected to the strip heat treatment furnace and is fixed to the furnace wall.

[0025] The electric heating radiant tube mechanism includes a positive electrode graphite radiant tube 2, a negative electrode graphite radiant tube 3, and a graphite connecting rod 4. One end of the positive and negative electrode graphite radiant tubes is connected and fixed by an insulating block 5, and the other end is connected by a graphite connecting rod. One end of the positive electrode graphite radiant tube is connected to the positive terminal 6 by a bolt, and one end of the negative electrode graphite radiant tube is connected to the negative terminal 7 by a bolt. Both the positive and negative electrode graphite radiant tubes are provided with protective atmosphere venting holes 8.

[0026] The insulating block is made of alumina. The roots of the positive and negative graphite electric radiation tubes are insulated with alumina insulating blocks, which also serve as supports. A connecting sleeve 9 is fitted over the insulating block. The outer end of the connecting sleeve is welded to the strip steel heat treatment furnace, and the inner end is provided with a retaining ring 10 to stop the insulating block and prevent it from shifting or falling off.

[0027] Both the positive and negative graphite radiant tubes are provided with connecting screw holes. The two ends of the graphite connecting rod are provided with external threads, which are threaded into the connecting screw holes. The ends of the positive and negative graphite radiant tubes are effectively connected by the graphite connecting rod in a threaded manner, forming a conductive circuit.

[0028] The atmosphere protection shield mechanism includes a protective shield body 11, on which a protective atmosphere inlet 12 and a residual oxygen detection port 13 are provided.

[0029] After the protective atmosphere enters the protective enclosure, it maintains a positive pressure state to prevent outside air from intruding into the graphite material under high-temperature operating conditions. Furthermore, an online residual oxygen analyzer is used to control the oxygen content below 200 ppm to prevent oxidation of the graphite radiant tube at high temperatures and ensure the safe operation of the heat treatment furnace. Finally, the protective atmosphere introduced from the protective enclosure is discharged through protective atmosphere venting holes on the surface of the graphite radiant tube. In the field of strip steel heat treatment, the introduced protective atmosphere is generally 99.999% pure nitrogen with a dew point below -40℃.

[0030] The positive and negative graphite radiant tubes are connected to the positive and negative terminals of the electrical cabinet, respectively, and their power is adjustable. The outer diameter of the positive and negative graphite radiant tubes is 50–200 mm, the wall thickness is 3–15 mm, the voltage is 20–55 V, and the power is 10–90 kW. The main circuit of multiple graphite radiant tubes in the strip steel heat treatment furnace can be connected in star or delta configurations, and the branch circuits can be connected in parallel or series to achieve effective energization of the graphite radiant tubes.

[0031] Graphite radiant tubes can withstand temperatures up to 3100℃ in a reducing atmosphere, and their coefficient of thermal expansion at high temperatures is only about 20% of that of electrothermal alloys. Furthermore, their compressive and flexural strengths increase with temperature, preventing creep and burn-off in high-temperature reducing atmospheres. When the heat treatment furnace heats up to above 350℃, the graphite radiant tubes need to operate in a reducing protective atmosphere to prevent oxidation. When the heat treatment furnace cools down to below 350℃, rapid cooling can be achieved by directly introducing cold air, a simple and effective method.

[0032] The above description is only for the purpose of helping to understand the method and core idea of ​​the present invention, and is not intended to limit the present invention. At the same time, it will be understood by those skilled in the art that there may be changes in the specific implementation and application scope based on the ideas of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. An electric heating device for a strip steel heat treatment furnace, characterized in that: The system includes an electric heating radiant tube mechanism and an atmosphere protection hood mechanism. The electric heating radiant tube mechanism is horizontally suspended inside the strip steel heat treatment furnace. One end is fixed to a side wall of the furnace, with the end exposed outside the furnace, and the other end extends into the furnace. The atmosphere protection hood mechanism covers the end of the electric heating radiant tube mechanism connected to the furnace and is fixedly connected to the furnace wall. The electric heating radiant tube mechanism includes a positive graphite electric radiant tube, a negative graphite electric radiant tube, and a graphite connecting rod. One end of the positive and negative graphite electric radiant tubes is connected and fixed by an insulating block, and the other end is connected by the graphite connecting rod. One end of the positive graphite electric radiant tube is bolted to a positive terminal, and one end of the negative graphite electric radiant tube is bolted to a negative terminal. Both the positive and negative graphite electric radiant tubes are provided with protective atmosphere venting holes. The atmosphere protection hood mechanism includes a protective hood body, which is provided with a protective atmosphere inlet hole and a residual oxygen detection hole.

2. The electric heating device for a strip steel heat treatment furnace according to claim 1, characterized in that, The positive and negative graphite electric radiation tubes are respectively provided with connecting screw holes, and the two ends of the graphite connecting rod are provided with external threads, which are screwed into the connecting screw holes.

3. The electric heating device for a strip steel heat treatment furnace according to claim 2, characterized in that, The insulating block is made of aluminum oxide.

4. The electric heating device for a strip steel heat treatment furnace according to claim 3, characterized in that, The protective atmosphere is 99.999% pure nitrogen with a dew point below -40°C.

5. The electric heating device for a strip steel heat treatment furnace according to claim 3, characterized in that, The outer diameter of the positive and negative graphite electric radiation tubes is 50–200 mm, the wall thickness is 3–15 mm, the voltage is 20–55 V, and the power is 10–90 kW.

6. The electric heating device for a strip steel heat treatment furnace according to claim 5, characterized in that, The insulating block is fitted with a connecting sleeve. The outer end of the connecting sleeve is welded to the strip heat treatment furnace, and the inner end is provided with a retaining ring, which stops the insulating block.

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