RADIANT TUBE HEATER AND HEAT TREATMENT FURNACE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2024-160033 filed on Sep. 17, 2024, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

[0002]The present invention relates to a radiant tube heater used as a heating unit for heating an object to be treated, such as a steel material, and a heat treatment furnace provided with this radiant tube heater.

BACKGROUND ART

[0003]In a heat treatment furnace for performing a heat treatment on an object to be treated, such as a steel material, a radiant tube heater is used as a heating unit (see, for example, Patent Literature 1 below). Such a radiant tube heater accommodates an electric resistance heating element inside a straight protective pipe (tube). The radiant tube heater configured in this way is particularly suitable for use in an atmosphere heating furnace that performs a heat treatment under various atmospheres, because an inside of the protective pipe accommodating the electric resistance heating element is isolated from the atmosphere in the furnace.

[0004]However, the radiant tube heater configured in this way does not have a cooling function, and although the radiant tube heater can be used in heating processes such as soaking and increasing a temperature of the object to be treated, a separate cooling device is required for a temperature decreasing (cooling) process.

[0005]Patent Literature 1: JP2003-42664A

SUMMARY OF INVENTION

[0006]The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radiant tube heater that can be used not only in a heating process but also in a cooling process if necessary, and a heat treatment furnace using the same.

[0014]According to the radiant tube heater according to the first aspect defined in this way, in the state where the radiant tube heater is disposed in the heat treatment furnace, not only can the electric resistance heating element generate heat by supplying electric power to the electric resistance heating element to heat an object to be treated in the furnace, but also, if necessary, furnace cooling gas can be introduced into the tube through the gas inlet and circulated in the tube to cool the object to be treated in the furnace.

[0015]The tube may include a curved portion, and the openings at both ends may be open in the same direction (second aspect).

[0016]A U-shaped or W-shaped tube used in a radiant tube burner in the related art can be used as the tube in the radiant tube heater of the present invention.

[0017]The gas inlet may be provided in the first cover body that closes one opening of the tube, and the gas outlet may be provided in the second cover body that closes the other opening of the tube (third aspect).

[0018]In this way, the tube of the radiant tube burner in the related art can be reused, and a gas inlet and a gas outlet can be easily added in an external attachment manner.

[0019]The support member may include a protruding portion that faces an inner wall surface of the tube while being disposed in the tube, and the protruding portion may include, on an outer circumferential portion thereof, a plurality of convex portions spaced apart in a circumferential direction and a concave portion that constitutes a part of a flow passage of the furnace cooling gas flowing through the tube (fourth aspect).

[0020]According to the radiant tube heater according to the fourth aspect defined in this way, the furnace cooling gas can flow to come into contact with the inner wall surface of the tube while a position of the electric resistance heating element in the tube is regulated, and a furnace cooling capacity can be improved.

[0021]The support member may include a first electric resistance heating element provided at a first end side portion of the tube; and a second electric resistance heating element provided at a second end side portion of the tube (fifth aspect).

[0022]According to the radiant tube heater according to the fifth aspect defined in this way, a furnace heating capacity can be improved.

[0023]A heat treatment furnace according to a sixth aspect of the present invention is a heat treatment furnace configured to perform a heat treatment on an object to be treated, in which the radiant tube heater according to any one of the above-mentioned aspects is provided as a heating unit for heating the object to be treated in the furnace.

[0024]According to the heat treatment furnace according to the sixth aspect defined in this way, the same effect obtained in the corresponding aspect can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

[0025]FIG. 1 is a diagram illustrating a schematic overall configuration of a radiant tube heater according to an embodiment of the present invention.

[0026]FIG. 2A is a diagram illustrating a front view of a support member of FIG. 1, and FIG. 2B is a cross-sectional view taken along a line B-B in FIG. 2A.

[0027]FIG. 3 is a diagram illustrating a schematic overall configuration of an atmosphere heat treatment furnace using the radiant tube heater in FIG. 1.

[0028]FIG. 4 is a schematic diagram illustrating elements related to a furnace temperature control in the atmosphere heat treatment furnace in FIG. 3.

DESCRIPTION OF EMBODIMENTS

[0029]Next, embodiments of the present invention will be described in detail with reference to the drawings.

[0030]FIG. 1 illustrates a radiant tube heater 20 according to an embodiment of the present invention, more specifically, a state in which the radiant tube heater 20 is attached to a furnace wall 1a of a heat treatment furnace 1.

[0031]The radiant tube heater 20 includes a cylindrical tube 22 that penetrates from the inside to the outside of the furnace wall 1a, an electric resistance heating element 30 provided in the tube 22, a support member 35 that supports the electric resistance heating element 30, and a first cover body 45A and a second cover body 45B that close openings 24 and 25 at both ends of the tube 22.

[0032]The tube 22 is a one-piece metal pipe made of a heat-resistant alloy such as stainless steel with a circular cross-section, and in the present embodiment, the entire of the tube 22 is U-shaped. The tube 22 includes a first end side portion 22a and a second end side portion 22b that penetrate through the furnace wall 1a in parallel to each other along an inner-outer direction of the furnace, a curved portion 22c that protrudes in a semicircular shape toward a heat treatment chamber 3 side (toward the inside of the furnace), and a hollow portion 23 that continuously communicates with the insides of the first end side portion 22a, the second end side portion 22b, and the curved portion 22c. The shape of the tube 22 may be a W shape or the like other than a U shape if necessary. The tube 22 is not limited to being made of metal, and may be made of non-oxide ceramics that have excellent heat resistance, such as SiC, in some cases.

[0033]The electric resistance heating element 30 generates heat at a predetermined temperature (for example, 800° C.) when a current passes through the electric resistance heating element 30.

[0034]The electric resistance heating element 30 may use a metal heating element or a non-metal heating element. The electric resistance heating element 30 according to the present embodiment is supported by a plurality of support members 35 connected in an axial direction, and is accommodated in the hollow portion 23 of the tube 22 (more specifically, a linearly extending portion of the hollow portion 23) while being folded back at a predetermined length.

[0035]Electrode rods 32, 32 connected to both ends of the electric resistance heating element 30 penetrate through heat insulation materials 52 and lid portions 50 disposed near the openings 24 and 25 of the tube 22 to protrude to the outside (left side in the drawing), and are connected to a power source (not illustrated).

[0036]In the radiant tube heater 20 according to the present embodiment, the electric resistance heating element 30 includes a first electric resistance heating element 30A provided at the first end side portion 22a of the tube 22, and a second electric resistance heating element 30B provided at the second end side portion 22b of the tube 22.

[0037]The heat insulation materials 52 are respectively disposed between the first electric resistance heating element 30A and the opening 24 of the tube 22, and between the second electric resistance heating element 30B and the opening 25 of the tube 22. Each of the heat insulation materials 52 is a material formed by laminating graphite fiber or ceramic fiber, and prevents heat from the electric resistance heating element 30 from escaping to the outside. In the present embodiment, a through hole 53 is formed in the center of the heat insulation material 52 to allow furnace cooling gas to flow.

[0038]FIGS. 2A and 2B illustrate the support member 35 disposed in the tube 22. The support member 35 is made of a non-conductive and fire-resistant ceramic, and is a member formed integrally with a shaft-shaped portion 36 extending in an axial direction (longitudinal direction) of the tube 22, and a protruding portion 38 extending from one end of the shaft-shaped portion 36 in a direction perpendicular to the axial direction as illustrated in FIG. 2B.

[0039]The protruding portion 38 is a disk-shaped portion having a predetermined thickness. As illustrated in FIG. 2A, the protruding portion 38 has, on an outer circumferential portion facing an inner wall surface 26 of the tube 22, a plurality of convex portions 39, which are spaced apart at 90° intervals in a circumferential direction and are in contact with or close to the inner wall surface 26 of the tube 22, and a plurality of concave portions 40 formed between the adjacent convex portions 39, 39. Such concave portions 40 constitute a part of a flow passage of the furnace cooling gas flowing in the tube 22. In FIG. 2B, a flow of the furnace cooling gas at the first end side portion 22a of the tube 22 is indicated by arrows. As illustrated in FIG. 2B, the furnace cooling gas can flow in the tube 22 by passing through the concave portions 40 so as to come into contact with the inner wall surface 26 of the tube 22.

[0040]A plurality of through holes 43 through which the electric resistance heating element 30 is inserted are formed at equal intervals in the circumferential direction at a position of the protruding portion 38 more radially inward than the concave portions 40.

[0041]As illustrated in FIG. 2B, an engagement recess 42 that is configured to engage with a tip end 36a of the shaft-shaped portion 36 of the adjacent support member 35 is formed in the center of a side surface 38a, opposite to the shaft-shaped portion 36, of the protruding portion 38. Accordingly, the plurality of support members 35 can be connected at equal intervals along the longitudinal direction of the tube 22.

[0042]Next, the cover bodies will be described. The first cover body 45A illustrated in FIG. 1 is a member that closes the opening 24 of the tube 22, and includes a cylindrical portion 46 and the lid portion 50.

[0043]The cylindrical portion 46 has a hollow portion with approximately the same diameter as the tube 22. The cylindrical portion 46 is attached to an end of the tube 22 on a side where the opening 24 is formed, so as to communicate with the hollow portion 23 of the tube 22. The lid portion 50 is attached to an end of the cylindrical portion 46 on a left side in the drawing via an insulation packing 49. In the present embodiment, a gas inlet 47A is provided in the cylindrical portion 46, and the furnace cooling gas can be introduced into the tube 22 through the gas inlet 47A.

[0044]The second cover body 45B is a member that closes the opening 25 of the tube 22, and includes a cylindrical portion 46 and the lid portion 50, similar to the first cover body 45A. A gas outlet 47B is provided in the cylindrical portion 46 of the second cover body 45B, and the furnace cooling gas introduced into the tube 22 can be discharged through the gas outlet 47B. The components of the second cover body 45B are substantially the same as those of the first cover body 45A, and the components common to those of the first cover body 45A are indicated by the same reference numerals, and descriptions thereof are omitted here.

[0045]In the radiant tube heater 20 according to the present embodiment configured in this way, the furnace cooling gas introduced into the tube 22 through the gas inlet 47A flows in the tube 22 to pass through the first end side portion 22a, the curved portion 22c, and the second end side portion 22b while coming into contact with the inner wall surface 26 of the tube 22, and the inside of the furnace can be cooled by a heat exchange that occurs during the flowing.

[0046]Next, an atmosphere heat treatment furnace 1 using the radiant tube heater 20 will be described. FIG. 3 is a diagram illustrating a schematic overall configuration of the atmosphere heat treatment furnace 1. The atmosphere heat treatment furnace 1 illustrated in FIG. 3 is a batch-type atmosphere heat treatment furnace used for heating wire coils, steel bars, or the like, in which a heat treatment chamber 3 is formed inside a box-shaped furnace body 2. An inlet/outlet 4 is formed at one end in a longitudinal direction of the furnace body 2, and a workpiece as an object to be treated is to be introduced into the furnace (heat treatment chamber 3) through the inlet/outlet 4 by a roller group 5. Note that the inlet/outlet 4 can be opened and closed by a door 7 connected to a driving device 6.

[0047]A plurality of radiant tube heaters 20 and ceiling fans 10 are provided in the heat treatment chamber 3 along a transport direction (longitudinal direction), and a gas introduction pipe 11 for introducing various kinds of gas is connected to the heat treatment chamber 3.

[0048]FIG. 4 is a schematic diagram illustrating elements related to a furnace temperature control in the atmosphere heat treatment furnace 1.

[0049]As illustrated in FIG. 4, the atmosphere heat treatment furnace 1 includes a temperature detector 60, the plurality of radiant tube heaters 20 as a heating unit, and a temperature controller 61.

[0050]The temperature detector 60 detects a temperature in the furnace and transmits temperature information to the temperature controller 61.

[0051]The type of the temperature detector 60 is not particularly limited, and a known thermocouple, radiation thermometer, or the like can be used in consideration of a measurable range, responsiveness, and the like.

[0052]The radiant tube heater 20 is configured such that electric power is supplied from a commercial power source (not illustrated) to the electric resistance heating element 30 via a thyristor 63 as a current controller.

[0053]A cooling gas supply pipe 64 is connected to the gas inlet 47A of the radiant tube heater 20, and the furnace cooling gas (for example, air) sent by a blower 65 can be introduced into the tube 22 through the cooling gas supply pipe 64 and the gas inlet 47A. A flow rate adjustment valve 66 is provided on an upstream side in the cooling gas supply pipe 64.

[0054]The temperature controller 61 adjusts a control output to the thyristor 63 or the flow rate adjustment valve 66 such that a detected temperature received from the temperature detector 60 approaches a preset heat pattern (target temperature) during an operation. Such a temperature controller 61 can be implemented by, for example, a programmable logic controller (PLC) including a data processing unit, a storage unit, and a communication I/F unit, or by a temperature adjuster.

[0055]In the atmosphere heat treatment furnace 1 configured in this way, in a heating process, a control signal from the temperature controller 61 is sent to the thyristor 63, and the amount of electric power supplied to the radiant tube heater 20 (specifically, the electric resistance heating element 30) is adjusted. Accordingly, a heat treatment can be performed under desired heating conditions.

[0056]In a cooling process, the supply of the electric power to the electric resistance heating element 30 is stopped, and the control signal from the temperature controller 61 is sent to the flow rate adjustment valve 66, and the amount of the furnace cooling gas introduced into the radiant tube heater 20 (specifically, the tube 22) is adjusted. Accordingly, a cooling treatment can be performed under desired cooling conditions.

[0057]As described above, according to the radiant tube heater 20 according to the present embodiment, in the state where the radiant tube heater 20 is disposed in the heat treatment furnace 1, not only can the electric resistance heating element 30 generate heat by supplying electric power to the electric resistance heating element 30 to heat an object to be treated in the furnace, but also, if necessary, the furnace cooling gas can be introduced into the tube 22 through the gas inlet 47A and circulated in the tube 22 to cool the object to be treated in the furnace.

[0058]The radiant tube heater 20 according to the present embodiment uses the tube 22 having the curved portion 22c and the openings 24, 25 that are open in the same direction at both ends, and thus, a U-shaped or W-shaped tube that has been used in a radiant tube burner in the related art can be used.

[0059]The radiant tube heater 20 according to the present embodiment is configured such that the gas inlet 47A is provided in the first cover body 45A that closes the opening 24 on one end of the tube 22 and the gas outlet 47B is provided in the second cover body 45B that closes the opening 25 on the other end of the tube 22, so that a gas inlet and a gas outlet can be easily added as an external attachment manner while the tube of the radiant tube burner in the related art is reused.

[0060]In the radiant tube heater 20 according to the present embodiment, the plurality of convex portions 39 and the concave portions 40 that constitute a part of the flow passage of the furnace cooling gas flowing in the tube 22 are formed on the protruding portion 38 of the support member 35 supporting the electric resistance heating element 30, so that the furnace cooling gas can flow to come into contact with the inner wall surface 26 of the tube 22 while a position of the electric resistance heating element 30 in the tube 22 is regulated, and a furnace cooling capacity can be improved.

[0061]The radiant tube heater 20 according to the present embodiment includes the first electric resistance heating element 30A provided at the first end side portion 22a of the tube 22 and the second electric resistance heating element 30B provided at the second end side portion 22b of the tube 22, so that a furnace heating capacity can be improved.

[0062]Although the embodiment of the present invention has been described in detail above, the embodiment is merely an example. For example, in the above embodiment, each of the cover bodies attached to the ends of the tube includes the cylindrical portion and the lid portion, and the gas inlet (or gas outlet) is provided in the cylindrical portion, but the gas inlet (or gas outlet) may be provided in the lid portion constituting the cover body, and in some cases, the gas inlet (or gas outlet) may be directly provided in the tube. The above embodiment is an example in which the radiant tube heater according to the present invention is used in an atmosphere heat treatment furnace, but the present invention can be embodied in various modified forms without departing from the scope of the invention, for example, the radiant tube heater according to the present invention may also be used in an air heat treatment furnace and a vacuum heat treatment furnace.