JP6624148B2 - Radiant tube and heat treatment furnace - Google Patents

Description

  The present invention relates to a radiant tube arranged in a furnace of an industrial heating furnace such as a heat treatment furnace, and more particularly to an improvement in durability of a radiant tube.

  The radiant tube is a radiant heat transfer tube which is installed in a furnace such as a heat treatment furnace and serves as a heat source of a heat treatment furnace using an atmospheric gas. The radiant tube is used as a heat source of an indirect heating system in which a heated high-temperature gas is supplied into the tube and the inside of the furnace is heated by radiant heat from the outer periphery of the radiant tube. According to the heating using the radiant tube, the inside of the furnace due to the combustion gas can be prevented. The radiant tube has a straight type consisting only of a straight pipe, a U type having a curved pipe part provided at one place by bending a part of the pipe, a W type having three bent pipe parts, or three straight pipe parts. There is a special type consisting of four curved pipes. As a method of installing these radiant tubes in a furnace, there are a vertical installation method, a horizontal installation method, and the like.

  When the W-shaped radiant tube is installed in a vertical manner, for example, in the technique described in Patent Document 1, as shown in FIG. 4, the open ends of the straight tubes 1a and 1d are aligned in the vertical direction, and the furnace wall is arranged. Each support 3a, 3b, 3c fixed to 5a and welded to the curved pipes 2a, 2b, 2c is supported by metal fittings 4a, 4b, 4c provided to protrude from the furnace walls 5a, 5b. In the case of a U-shaped radiant tube or a case where the radiant tube is installed in a horizontal manner, similarly, the radiant tube is often structured to be supported by a support and a receiving object.

  The radiant tube is made of heat-resistant steel or heat-resistant alloy, but it is exposed for a long time in a furnace such as a heat treatment furnace, which is a high temperature environment, so a large heat load is applied. Creep stress or the like due to its own weight acts on the radiant tube, often causing deformation such as bending or cracking.

  Further, the thermal expansion and thermal shrinkage of the radiant tube are restricted by the fixation of the support and the receiving object and the deformation of the support, and a crack is often generated in the curved tube. When cracks occur, furnace atmosphere gas flows into the radiant tube, increasing the furnace atmosphere gas usage, lowering heating efficiency, lowering furnace pressure, and contaminating the furnace atmosphere with combustion gas. This causes various quality problems.

  In order to solve such a problem, for example, Patent Document 1 discloses a diagram in which a support 3 provided at an end of a bent tube of a radiant tube and a receiving member 4 projecting from a furnace wall and supporting the support 3 are provided. As shown in FIG. 5, there is described a radiant tube support device in which rotating members such as rollers 6 and a shaft 7 which roll between the members are arranged. According to the technique described in Patent Document 1, the mutual movement between the support of the radiant tube and the receiver becomes smooth and easy due to the presence of the rotating members such as the rollers and rollers, and the radiant tube undergoes thermal expansion and thermal contraction. However, the support can easily move on the receiving object, absorb thermal expansion and thermal contraction, and suppress deformation and cracking of the radiant tube. In the technique described in Patent Document 1, an example of the support 3 having a U-shaped cross section is shown.

  Patent Literature 2 describes a radiant tube support structure. In the support structure of the radiant tube described in Patent Document 2, at least near the apex of the U-shaped bent portion of the radiant tube which is arranged so as to be at least approximately symmetric in the vertical direction in a widthwise direction of the heating furnace and arranged. A protruding portion 3 protruding and fixed in the furnace width direction and a supporting portion 4 fixed to the furnace wall 5 for mounting and supporting the protruding portion are provided. As shown in FIG. It is characterized in that it has a round bar material 6 that is in contact with the upper surface of the support part 4 and has a vertically symmetrical shape. According to the technique described in Patent Literature 2, the bent radiant tube can be installed upside down, and the life of the radiant tube can be extended to about the same as the life due to oxidation thinning. In the technique of the radiant tube described in Patent Document 2, as shown in FIG. 6, it is exemplified that the projecting portion 3 has a vertical cross-sectional shape having a trapezoidal shape in which a square portion is chamfered.

JP-A-10-237539 JP 11-257612 A

  However, in the technology described in Patent Literature 1, an example of the support 3 having a U-shaped cross section is shown. However, when the support 3 is used in a high-temperature environment for a long time, the support 3 and the metal fitting are rotated. In many cases, sticking or deformation occurred in the member. In such a case, the thermal expansion or thermal contraction of the radiant tube cannot be absorbed, and the support may be deformed due to insufficient rigidity of the support, and further, the radiant tube body may be deformed or cracked.

  Further, in the technique described in Patent Literature 2, it is necessary to re-install the radiant tube upside down every time the radiant tube is used for a predetermined period in order to suppress drooping, which requires a complicated maintenance and inspection process. Further, in the round bar material disposed on the protruding portion, deformation and adhesion occur, smooth movement is hindered, thermal expansion and thermal contraction of the radiant tube cannot be absorbed, and the rigidity of the support is insufficient. Therefore, there is a problem that the support may be deformed, and furthermore, the radiant tube body may be deformed or cracked, which may shorten the service life.

  Thus, the present invention provides a radiant tube that solves the problems of the conventional technology, suppresses deformation of the support, deformation and cracking of the radiant tube main body, particularly a curved tube portion, and can achieve an increase in the life of the radiant tube. The purpose is to do.

  In order to achieve the above-described object, the present inventors have intensively studied various factors that affect the deformation of the support, the radiant tube main body, particularly the deformation of the curved tube portion and the occurrence of cracks in the curved tube portion. As a result, they came to the conclusion that it is important to ensure a delicate balance between the rigidity (strength) of the support and the strength of the radiant tube. This is because, for example, when a rotating member as used in the prior art is fixed, smooth movement between the support and the receiving object is hindered, and therefore a large load is applied to the support. If the rigidity of the support is high, the support does not deform, but the load concentrates on the curved tube portion of the radiant tube, and the support bites into the curved tube portion, causing deformation or cracking of the curved tube portion. On the other hand, when the rigidity (strength) of the support is low, the support is deformed and cannot play a role of supporting the radiant tube.

  Therefore, further studies were conducted to increase the rigidity (strength) of the support to the extent that the support was not deformed, and to suppress deformation and cracking of the radiant tube, avoid stress concentration on the curved pipe. I thought that it would be important to adjust the shape of the support attached to the curved tube so that it could be done. It has been found that such a shape is such that the cross-sectional area on the connection side with the radiant tube curved tube portion is larger than the cross-sectional area on the distal end side.

The present invention has been completed based on such findings and further studied. That is, the gist of the present invention is as follows.
(1) A radiant tube main body comprising a straight pipe portion and a curved pipe portion connected to each other to form one combustion gas flow path, and protruding in the furnace width direction near a vertex of the curved pipe portion of the radiant tube main body. A radiant tube having a support comprising: the projecting support comprises a contact plate, a base portion, and a distal end portion, and is joined to the curved tube portion via the contact plate, and at least A radiant tube, wherein the base has a cross section perpendicular to the longitudinal direction and has a shape in which a cross-sectional area gradually decreases toward a tip.
(2) The radiant tube according to (1), wherein the distal end has a cross section perpendicular to the longitudinal direction and a shape having a constant cross-sectional area.
(3) The radiant tube according to (1) or (2), wherein the base has a hollow truncated cone shape, and the tip has a cylindrical shape.
(4) The radiant tube according to (1) or (2), wherein the base has a truncated hollow pyramid shape, and the tip has a hollow prism shape.
(5) A heat treatment furnace having a radiant tube arranged in a furnace, wherein the radiant tube is the radiant tube according to any one of (1) to (4), and the furnace corresponds to the support of the radiant tube. A heat treatment furnace characterized in that a receiving object is arranged at a position of a wall.

  According to the present invention, without using a rotating member or the like, or in the case of using a rotating member, even if the rotating member does not function, deformation of the support is suppressed, and stress concentration on the radiant tube curved tube portion is reduced. Thus, deformation and cracking of the radiant tube can be suppressed or prevented, so that the life of the radiant tube can be significantly increased or a risk caused by deformation of the radiant tube can be avoided. Further, according to the present invention, a combination of a radiant tube main body having a curved shape and a support having a smooth shape using a large number of curves is provided, and the radiant tube as a whole has an effect of satisfying an aesthetic appearance (aesthetic feeling).

It is (a) front view and side view which show an example of a structure of the radiant tube of this invention, (b) It is a top view. It is the front view and side view which show an example of the preferable structure of the support provided in the radiant tube of this invention. It is a front view showing an example of the composition of the radiant tube of the present invention. It is sectional drawing which shows an example of a structure of the conventional W type radiant tube. It is a front view which shows an example of the support structure of the conventional radiant tube. 1 shows an example of a conventional radiant tube support structure. (A) is a front view, (b) is a side view.

  The radiant tube according to the present invention has a main body 10 and a support 3. The main body 10 of the radiant tube is composed of a straight pipe section and a curved pipe section which are joined together to form one combustion gas flow path. For example, it is composed of at least two straight pipe portions 1 and 1 and at least one bent pipe portion 2 in which two straight pipes 1 and 1 having open ends are connected by at least one bent pipe 2. You. As shown in FIG. 3, the radiant tube main body connects two straight pipes having open ends with one curved pipe by welding or the like, and connects the two straight pipes 1a, 1b and one curved pipe 2a. As shown in FIG. 1, or as shown in FIG. 1, three straight pipes having an open end, two straight pipes, and three bent pieces that connect adjacent straight pipes by welding or the like. It may be a W-type formed of four straight pipes 1a, 1b, 1c and 1d and three curved pipes 2a, 2b and 2c. Alternatively, any conventional radiant tube main body such as a special type including three straight pipes and four curved pipes can be applied.

  Moreover, since the radiant tube main body 10 is exposed to high temperatures, it is preferable that the radiant tube main body 10 be made of heat-resistant steel or a heat-resistant alloy. Examples of the heat-resistant alloy include Ni-based alloys such as Inconel and Hastelloy. Needless to say, a burner is provided at one or both of the open ends of the radiant tube body 10. Further, the arrangement of the radiant tube body 10 in the furnace may be either a vertical type or a horizontal type.

  In the radiant tube according to the present invention, for example, as shown in FIG. 1, a support 3 is protruded in the furnace width direction near the vertex of the curved tube portion 2 of the radiant tube main body 10. In the present invention, the support 3 protruding in the vicinity of the vertex of the curved pipe portion 2 is configured by the contact plate 30, the base 31, and the tip 32 in this order. The support 3 is joined to the surface of the curved tube portion 2 of the radiant tube main body by welding or the like via the contact plate 30, and is provided in a protruding manner. It is preferable to join the support 3 with the support plate 30 interposed between the curved tube portion 2 and the support 3 in order to further distribute the load from the support 3 to the radiant tube main body curved tube portion 2. In addition, it is preferable that the thickness of the contact plate 30 be about 1 to 2 times as large as the thickness of the curved tube portion 2 and that the thickness is equal to or larger than the area of the bottom surface of the base portion 31 from the viewpoint of load distribution. . In addition, it is preferable that the surface of the contact plate 30 to be joined to the curved tube portion has a shape adapted to the shape of the curved tube portion.

  It should be noted that there is no problem whether the base portion 31 and the distal end portion 32 are integrally formed from one material, or formed separately and joined by welding or the like. . It suffices if it is manufactured smoothly without any step at the boundary between the outer surface and the inner surface.

  The base 31 has a cross section perpendicular to the longitudinal direction of the support 3 and has a shape in which the cross-sectional area gradually decreases toward the tip. That is, the shape of the support 3 is such that, as the base portion is closer to the side connected to the radiant tube curved tube portion 2, the cross-sectional area is larger than the cross-sectional area at the distal end side. The cross-sectional area of the base connected to the curved tube portion 2 is preferably 1.2 times or more, more preferably 1.5 times or more, the cross-sectional area of the smallest distal end.

  By setting the shape of the support 3 to such a shape, the deformation of the support 3 is suppressed, and the deformation and crack generation of the radiant tube curved tube portion provided with the support 3 are suppressed and further prevented. . It is considered that this is because the bending stiffness of the support 3 is increased and the load from the support 3 to the radiant tube curved tube portion 2 can be dispersed. If the base of the support 3 has a constant cross-sectional area, for example, a round bar shape, the rigidity of the support becomes too high, and there is a high possibility that the bent portion of the radiant tube is greatly deformed.

  The base 31 of the support 3 is preferably solid or hollow. However, from the viewpoint of the rigidity balance between the radiant tube and the support, the base 31 is preferably hollow, and in particular, has a shape of a hollow truncated cone. Is preferred. Further, there is no problem even if the base portion 31 has a shape of a truncated hollow pyramid such as a square or a hexagon.

  The distal end 32 of the support 3 is disposed (fixed) at the upper end of the base 31 in the same axial direction as the base 31. The tip portion 32 preferably has a cross section perpendicular to the longitudinal direction of the support 3 and a shape having a constant cross-sectional area. The tip portion 32 is preferably solid or hollow, like the base portion 31. However, from the viewpoint of increasing the weight of the member, the tip portion 32 is preferably hollow like the base portion 31. It is preferable to adopt a shape having a cylindrical shape. Further, there is no problem even if the distal end portion 32 is formed in a hollow prismatic shape (square tubular shape).

  When the radiant tube is installed in the heat treatment furnace, the distal end portion 32 of the support 3 is disposed so as to be in contact with the upper surface of the metal receiving member 4 extending from the furnace wall 5 of the heat treatment furnace at a part of the distal end side. Supports its own weight, such as a radiant tube. For this purpose, in a heat treatment furnace in which radiant tubes are installed, a predetermined number of receivers 4 are arranged on a furnace wall 5 according to the support 3. Therefore, it is necessary to secure a sufficient contact length at the distal end portion 32 to support the weight of the radiant tube or the like. In addition, the support 3 does not need to be installed in all the radiant tube curved tube portions. Needless to say, the number may be sufficient to support the weight of the radiant tube.

  Further, as the temperature inside the furnace rises due to the operation of the heat treatment furnace, the support 3 moves to the furnace wall side while sliding on the upper surface of the receiver 4 due to the thermal expansion of the radiant tube body 10. When the operation of the heat treatment furnace is completed and cooled, the support 3 moves away from the furnace wall side while sliding on the upper surface of the receiving object 4. At this time, in order to prevent the base portion 31 of the support 3 from interfering with the metal receiving object 4, it is necessary to maintain an appropriate length at the distal end portion 32 as a thermal expansion allowance. Note that the thermal expansion allowance is affected by the length of the radiant tube, the material of the radiant tube, the temperature in the furnace, and the like, and it is needless to say that it is necessary to appropriately set the heat expansion allowance.

  Since the rigidity balance between the radiant tube body and the support changes according to the diameter, wall thickness, material, etc. of the radiant tube, it is necessary to select the cross-sectional area and material of the support according to the usage conditions. Become. Needless to say, the support 3 may be provided with a rotating member in order to smooth the sliding with the upper surface of the receiving object 4.

  The radiant tube having the above-described configuration is disposed at an appropriate position in the furnace of the heat treatment furnace, and indirectly heats a material to be heated such as a steel plate. In the heat treatment furnace, a metal receiving object 4 extending from the furnace wall 5 is provided at a position corresponding to the support 3. The support 4 is arranged so that the metal receiving object 4 may contact the upper surface, and supports the weight of a radiant tube or the like.

  In a radiant tube installed in a furnace, use of the radiant tube in a high-temperature environment usually causes deformation of the support itself and biting deformation of the support into the radiant tube curved tube due to its own weight or thermal expansion. Hanging deformation of the main body occurs. If the sag exceeds a predetermined amount, the radiant tube must be replaced. According to the radiant tube according to the present invention, the durability of the radiant tube is improved, the deformation of the support itself and the deformation of the bent portion of the radiant tube are small, and therefore, the amount of sag of the radiant tube is small, and the frequency of radiant tube replacement is reduced. Is reduced.

  Hereinafter, the present invention will be described based on examples.

  A W-shaped radiant tube (made of a heat-resistant alloy) was installed in a zone where the load was highest in an annealing furnace (heat treatment furnace) for heating a steel sheet by indirect heating using a radiant tube. The installed W-shaped radiant tube was a radiant tube having a support protruding near the top of the curved tube of the main body at a position as shown in FIG. In the radiant tube of the example of the present invention, a support consisting of a base portion and a distal end portion was welded to the curved tube portion via a plate (thickness: twice the thickness of the radiant tube curved tube portion). The base of the support has a cross section perpendicular to the longitudinal direction, and has a shape in which the cross-sectional area gradually decreases toward the distal end, and has a shape of a truncated cone ((outer diameter on the curved tube side) / (outer diameter on the distal end side) ): 1.5), a cylindrical shape (outer diameter, thickness: the same as the outer diameter and thickness at the tip side of the hollow truncated cone) whose tip is a section perpendicular to the longitudinal direction and the cross-sectional area is constant The length of the support including this plate was 200 mm. At the tip, the contact length with the receiving object can be secured to 80 mm or more. On the other hand, in the radiant tube of the comparative example, the curved tube portion has a cylindrical shape (outer diameter, wall thickness: the tip portion of the present invention example) via a plate (thickness: the same as the thickness of the radiant tube curved tube portion). A support (comparative example) exhibiting the same outer diameter and wall thickness) was welded. Each support was made of the same material (heat-resistant alloy) as the radiant tube.

  Two years after the installation of the radiant tube, the installed radiant tube was removed, and the deformation state was investigated. As a result, in the radiant tube of the comparative example, sag deformation of 331 mm was confirmed. Therefore, it was replaced. In the radiant tube of the comparative example, the support was bent upward while being bitten into the curved portion of the radiant tube. On the other hand, in the radiant tube of the example of the present invention, the hanging deformation was 35 mm. In the radiant tube of the example of the present invention, no deformation of the support and the bent portion of the radiant tube was observed. For this reason, it was used continuously.

1, 1a, 1c, 1d Straight pipe 2, 2a, 2b, 2c Curved pipe 3, 3a, 3b, 3c Support (projection part)
4, 4a, 4b, 4c Receiving object (support part)
5, 5a, 5b Furnace wall 6 Roller (round bar)
7 Shaft 10 Radiant tube main body 30 This plate 31 Base 32 Tip

Claims (4)

A radiant tube main body comprising a straight pipe portion and a curved pipe portion joined together to form one combustion gas flow path; and a support protruding in the furnace width direction near an apex of the curved pipe portion of the radiant tube main body. A radiant tube having a support, wherein the projecting support is composed of an abutment plate, a base portion, and a distal end portion, is joined to the curved tube portion via the abutment plate, and at least the base portion is in a cross section perpendicular to the longitudinal direction, characterized in that the cross-sectional area have a shape formed by gradually decreasing toward the tip, the tip in cross section perpendicular to the longitudinal direction, the cross-sectional area to have a shape that is constant And radiant tube. The radiant tube according to claim 1, wherein the base has a hollow truncated cone shape, and the tip has a cylindrical shape. The radiant tube according to claim 1, wherein the base has a truncated hollow pyramid shape, and the tip has a hollow prism shape. A heat treatment furnace comprising a radiant tube disposed in a furnace, wherein the radiant tube is the radiant tube according to any one of claims 1 to 3 , and the radiant tube is received at a position of a furnace wall corresponding to the support of the radiant tube. A heat treatment furnace characterized by disposing hardware.

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