JPH0976011A - Method for heat treatment for thickening work of metallic tube and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deformation generated n the cross section of thick part formed at the time of executing local thickening work and heat treatment to a metallic tube such as a square tube. SOLUTION: By preliminarily setting a die 10 for heat treatment in the square tube 1 to be thickened, forming a heated part 5 by locally heating the square tube with a heating device 4 under the state where compressive force is added to the square tube 1 with a compressing device 3 and moving the heated part 5 in the longitudinal direction to the square tube, thick part 1A thickened is continuously formed, the heated part 26 for heat treatment is formed by heating the thick part 1A with an auxiliary heating device 9 and heat treatment of the whole thick part is executed by moving the heated part 26 for heat treatment in the longitudinal direction of the thick part. At the time of these thickening work and heat treatment, deformation on the verge of generating in the thick part 1A is prevented with the die 10 for heat treatment which is set inside the square tube 1 and the thick part 1A having a good cross-sectional shape is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an increase in a metal pipe such as a square steel pipe or a round steel pipe, in which a desired section in the longitudinal direction is thickened to form a thick portion, and the thick portion is heat-treated. The present invention relates to a meat processing heat treatment method and a metal pipe thickening processing heat treatment apparatus used for carrying out the method.

[0002]

2. Description of the Related Art Conventionally, a small region in the longitudinal direction of a metal pipe such as a steel pipe is locally heated to a constant width to form a heating unit, and the position of the heating unit is relatively moved in the longitudinal direction of the pipe. While applying a compressive force in the axial direction of the pipe to increase the thickness, and cooling and solidifying the rear end portion of the heating portion, the metal pipe is gradually increased in thickness along the longitudinal direction. The free thickening method) is known (see, for example, Japanese Patent Publication No. 52-470). Therefore, by using this thickening method,
It is possible to increase the thickness of a desired region of the metal pipe to form a thick reinforcing portion, that is, a thick portion integrated with the metal pipe, and to use the metal pipe having such a thick portion as a building material. By using the metal pipe integrally having this thick wall portion as a building material, the thick wall portion can be used for beam joining, etc., and it is possible to omit troublesome reinforcement work such as welding of the diaphragm which has been conventionally performed. It brings great benefits.

[0003]

However, the thick-walled portion formed by the above-described thickening processing method, after being heated to a high temperature,
Since it is rapidly cooled, it becomes a quenched state, and there is a problem that mechanical properties such as elongation deteriorate. Therefore, it is conceivable to heat the thick-walled part again to heat-treat it to improve the mechanical properties.However, when heat-treating the thick-walled part by heating or cooling, the thick-walled part may be changed due to residual stress during thickening. Distortion occurred and was found to be a problem. For example, when the above-mentioned thickening and heat treatment are performed on a circular pipe, the circularity of the cross section of the thick wall portion is distorted from a circular shape, and the roundness is reduced. It was found that a phenomenon in which a flat tube surface is lowered due to an inward depression on a smooth tube wall. Such distortion is particularly noticeable in a prismatic tube, which is a serious problem.

The present invention has been made in view of the above problems, and a desired region in the longitudinal direction of a metal pipe is subjected to thickening processing and heat treatment while preventing undesired distortion in the cross section, and thus the cross-sectional shape is improved. An object of the present invention is to provide a method of heat treatment for increasing the thickness of a metal tube capable of forming a good thick portion and an apparatus used for the method.

[0005]

SUMMARY OF THE INVENTION A metal pipe thickening heat treatment method of the present invention, which has been made to achieve the above object, provides a metal pipe to be thickened in a thick portion formed by the thickening process. To be located inside, insert a heat treatment die having a length equal to or greater than the length of the thick portion in advance,
In this state, a small area in the longitudinal direction of the metal tube is locally heated by a heating device to form a heating section in a red heat state, and the heating section is heated while moving the heating section relatively in the longitudinal direction of the metal tube. By applying compressive force in the longitudinal direction of the metal pipe to the portion to successively increase the thickness, and by cooling the rear end portion of the heating unit immediately after the thickness increase, the metal pipe is continuously increased in thickness and the heat treatment is performed. A thick part is formed on the outside of the die for heat treatment, and then the thick part is heat-treated while the heat treatment die is positioned inside the thick part.

Here, in order to heat-treat the thick-walled portion, the entire thick-walled portion may be simultaneously heated to a desired temperature to be heat-treated, but like the thickening process, a small region of the thick-walled portion is required. Is heated to a desired heat treatment temperature by an auxiliary heating device to form a heat treatment heating part, and the heat treatment heating part is relatively moved in the longitudinal direction of the thick part to heat the entire thick part. It is preferable to adopt a method of heat treatment. In this method, the thick portion can be heated to a desired temperature by a relatively small auxiliary heating device. In addition, it is preferable to perform the heat treatment operation in parallel with the thickness increasing process because the productivity is improved.

In the method of the present invention having the above-mentioned structure, since the thick portion is formed on the outside of the heat treatment die by the thickening process and the thick portion is heat treated in that state, heating and cooling during the heat treatment are performed. Even if the cross-section of the thick-walled portion is distorted, the heat-treating die restrains the inner surface of the thick-walled portion to prevent undesired distortion. Therefore, the heat-treated thick-walled portion having a predetermined cross-sectional shape is formed. it can. Further, since distortion during heat treatment can be forcibly prevented by the heat treatment die, there is no need to adjust the heating rate, cooling rate, etc. during heat treatment to prevent distortion, in other words, heating rate, cooling rate, etc. Can be set so that the necessary heat treatment can be performed.

Further, since the heat treatment die is inserted before the metal pipe is subjected to the thickening process, an appropriate gap is formed between the heat treatment die and the metal pipe, and therefore the die is easily inserted at a predetermined position. It is possible. Moreover, the heat treatment die has an effect of preventing the cross-sectional shape from being distorted during the thickening process, and also from this point, it is possible to form a thick wall portion having a good cross-sectional shape. Further, the heat treatment die has an action of preventing unstable deformation (for example, a bellows-like deformation) which is likely to occur in the portion where the thickness increase occurs, and stabilizing the thickness increase process. It is possible to increase the range of thickening conditions (for example, temperature of heating part, compression force, cooling speed, thickening processing speed, etc.) that enables various thickening processing, and increase the thickening processing speed to improve productivity. There are effects such as energy saving and the like, by improving, by setting a large thickness increase rate, and by setting a low temperature for thickening processing.

Here, the outer dimension of the heat treatment die may be any as long as it can restrain the inner surface of the thick portion formed by the thickening process so as not to cause excessive distortion during the heat treatment. The outer surface of the die for heat treatment may strongly contact the inner surface of the thick portion to support the thick portion, or the outer surface of the heat treatment die may substantially contact the inner surface of the thick portion. It may be in a state where they are lightly contacted with each other or a minute gap (for example, about 0.5 mm) is formed between them. It should be noted that the latter dimension has an advantage that the operation of pulling out the heat treatment die after the heat treatment becomes easy.

In order to bring the heat treatment die into almost contact with the inner surface of the thick portion, the gap g between the heat treatment die and the metal pipe before being thickened is set before the thickness increase. With respect to the wall thickness t of the tube wall and the thickness increase ratio β (= thickness increased by the thickness increase / thickness before the thickness increase) to be generated in the metal pipe, g≈0.5tβ may be set. Generally, when the thickness increase is performed by the above-mentioned free thickness increase method without using a die, the thickness increase occurs almost at the inner and outer surfaces of the pipe wall. As a result, the portion that bulges toward the inner surface almost fills the gap g, and the inner surface of the thick portion is in almost contact with the outer surface of the heat treatment die, that is, in the state where it is lightly contacted or there is a minute gap between the two. Become. That is, the heat treatment die acts as a shaping die that limits the position of the inner surface of the pipe wall during the thickening process to the position where the free thickening is preferably performed (the depression as shown in FIG. 4 does not occur). The inner surface of the thick portion formed by increasing the thickness is regulated to a regular shape.

In order to bring the heat treatment die into strong contact with the inner surface of the thick portion to support the thick portion, a gap g between the heat treatment die and the thickened portion is inserted into the metal pipe before the thickening process. Should be set as 0 <g <0.5tβ. Here, the gap g is made larger than 0 in order to facilitate the operation of inserting the heat treatment die into the metal tube. When set in this range, the tube wall portion that bulges inward due to the increased wall thickness fills the gap g and is pressed against the outer surface of the heat treatment die, and thereafter the outer surface is regulated by the heat treatment die at the inner surface position. This will cause thickening on the side. In other words, the heat treatment die acts as an inner surface forming die that restricts the position of the inner surface of the pipe wall by shifting the position of the inner surface of the pipe wall toward the outer surface of the pipe as compared with the case of free thickening, and is formed by the thickening. The inner surface of the thick portion is formed into a predetermined shape. In this way, when the heat treatment die is made to act as a molding die for the inner surface at the time of thickening, the inner surface of the thick portion can be made smooth and can be molded to a desired size.

When the heat treatment die is used as a molding die for the inner surface during thickening, the thick portion formed is in a state of being strongly pressed against the outer surface of the heat treatment die. After the heat treatment, it may be difficult to pull out the heat treatment die. Therefore, in order to facilitate the drawing operation, it is preferable that the heat treatment die has a structure capable of being reduced. As an example of a structure that can be reduced, a screw mechanism can be used to reduce the outer dimensions of the heat treatment die, or a metal tube is used as the heat treatment die, and hydraulic pressure is supplied to the inside to expand it slightly. It is possible to cite a configuration in which it is used in a closed state and is reduced by releasing the hydraulic pressure at the time of withdrawal.

When the metal pipe to be thickened and heat treated is a rectangular pipe, the heat treatment die to be inserted therein has a structure capable of restraining the inner surface of the thick portion of the rectangular pipe over the entire circumference. Not limited to this, the intended purpose can be achieved even with a configuration in which only a flat tube wall is constrained so as not to cause a recess. With this structure, it is possible to obtain an advantage that the heat treatment die can be easily manufactured and that the heat treatment die can be easily extracted from the rectangular tube.

As described above, when the heat treatment die is used as a molding die for the inner surface at the time of thickening processing, at the start of the thickening processing, the thickening rate is set at a constant ratio according to the longitudinal position of the metal pipe. After the time when the inner surface of the metal pipe comes into contact with the heat treatment die, the increase rate of the thickness increase rate is reduced to about half, and after reaching the predetermined rate, the thickness increase rate is kept constant and the thickness increase rate is increased. It is preferable to adopt a method of performing processing. By adopting this method, it is possible to form a slope with a constant gradient from the non-thickened portion to the thick portion of a predetermined thickness at the thickening start side end portion of the thick portion formed by the thickening process. As a result, it is possible to form a thickened portion where stress concentration is less likely to occur.

Further, at the end of the thickness increasing process, the rate of increase in thickness is reduced at a constant rate according to the longitudinal position of the metal tube, and after the time when the inner surface of the metal tube is not in contact with the heat treatment die, the rate of increase in thickness is increased. It is preferable to adopt a method in which the reduction ratio of is reduced to about double. If this method is adopted, it is possible to form a slope with a constant gradient from the thick portion having a predetermined thickness to the non-thickened portion at the end portion of the thick portion formed by the thickening processing on the thickening end side. As a result, it is possible to form a thickened portion where stress concentration is less likely to occur.

When thickening the metal tube,
It is also possible to dispose an outer surface forming die on the outside of the heating portion formed in the metal tube, and to control the outer surface position of the tube wall that is deformed outward by increasing the thickness by the outer surface forming die. If this configuration is adopted, the outer surface of the wall of the increased wall can be molded and made smooth. In addition, it is possible to suppress a part of the thickness increase on the outer surface side of the pipe wall with this outer surface forming die and increase the inner surface side by that amount, and increase the outer surface side thickness increase as necessary. Can be less than.

The present invention also provides an apparatus suitable for carrying out the method described above. That is, the thickening heat treatment apparatus for a metal pipe of the present invention is inserted into a metal pipe to be thickened so as to be located inside a thick portion formed by the thickening work, and the length of the thick portion is increased. A die for heat treatment having a length equal to or more than a length, a compression device for exerting a compressive force in the longitudinal direction on the metal tube, and heating for heating a small region in the longitudinal direction of the metal tube to form a heating part in a red heat state A device, a cooling device for cooling one end of a heating part thereof, a moving device for moving the heating device and the cooling device relative to a rectangular tube, and a moving device behind the heating device together with the heating device. And a supplementary heating device for heating the small region of the thick portion formed by the thickness increasing process to a temperature at which the heat treatment is performed to form the heat treatment heating portion. In the apparatus having this configuration, the heating device locally heats the metal pipe to cause the thickness increase, and moves relatively to the metal pipe to form the thick portion in parallel with the thickness increasing operation. , An auxiliary heating device heats a small area of the thick part to form a heat treatment heating part,
In addition, the auxiliary heating device moves relative to the metal pipe to move the heat treatment heating portion relatively in the longitudinal direction of the thick portion, and heat treatment of the entire thick portion can be performed, resulting in work efficiency. Is good. Further, the heating device for thickening and the auxiliary heating device for heat treatment can be moved relatively to the metal pipe by a single moving device, and the device configuration can be simplified.

[0018]

1 is a schematic sectional view showing a preferred example of a thickening heat treatment apparatus used for carrying out the method of the present invention, FIG.
(A), (b) is an arrow AA sectional view of FIG. 1, an arrow BB sectional view, respectively, and FIG. 3 is an enlarged sectional view of the thickened portion in FIG. Reference numeral 1 is a metal pipe to be thickened, and a rectangular steel pipe is used here. Hereafter, this metal tube 1
Is called a square tube. 2, the rectangular tube 1 has four flat tube walls (hereinafter referred to as side walls) 1a and four corner-shaped arc-shaped tube walls (hereinafter referred to as corner walls) 1b. . In this embodiment, with respect to the rectangular tube 1, a thick wall portion 1A is formed in a region indicated by a length L in FIG.
A case of forming (a part is shown by a chain double-dashed line) is shown. For the sake of convenience of explanation, in the region in the longitudinal direction of the rectangular tube 1, the portions which are not thickened and are left as the original thickness are the non-thickened portions 1B and 1C, and the thickening is still performed. The non-thickened portion is referred to as a non-thickened portion 1D.

Reference numeral 2 is a fixing device for fixing and holding one end of the rectangular tube 1 in a fixed position, 3 is a compression device such as a hydraulic cylinder for pressing the opposite end of the rectangular tube 1 to apply a compressive force to the rectangular tube, 4
Is an annular heating device capable of locally heating a small region in the longitudinal direction of the rectangular tube 1 to form a heating part 5 in a red hot state, and a high frequency heating coil is used here. The heating device 4 sprays a cooling medium 7 such as cooling water on a rear end portion in the moving direction of the heating part 5 when the heating device 4 moves in the direction of the arrow C along the rectangular tube 1 (see FIG. 3). Is equipped with. A moving device 8 moves the heating device 4 and the cooling device 6 along the rectangular tube 1 at a desired speed. The moving device 8a holds the heating device 4 and the cooling device 6 and moves, and the moving device 8a. Moving feed screw 8b
And a motor 8c for rotating the feed screw 8b. The moving device 8 is not limited to the one using the motor and the feed screw shown in the illustrated embodiment, but may be appropriately changed to one using a motor and a feed chain, one using a digital cylinder, or the like.

Reference numeral 9 denotes an auxiliary heating device for heat treatment, which is arranged behind the heating device 4 at an appropriate distance so as not to interfere with each other and is held on a moving table 8a so as to move together with the heating device 4. This is for forming the heat treatment heating portion 26 by heating the small region of the thick portion 1A formed by the thickness increasing process annularly and to a desired heat treatment temperature. A high frequency heating coil is also used as the auxiliary heating device 9. The auxiliary heating device 9 may be provided with a cooling device that cools the rear end of the heat treatment heating unit 26 by water injection or the like, if necessary. In addition, in front of the auxiliary heating device 9, the rectangular tube 1
Drainer 24 to eliminate the influence of the cooling medium 7 sprayed on
Is arranged.

Reference numeral 10 denotes a heat treatment die arranged inside the rectangular tube 1 for preventing the occurrence of distortion by regulating the inner surface position of the thick portion 1A during the heat treatment of the thick portion 1A. In this embodiment, as the heat treatment die 10, as shown in FIG. 2, a rectangular tube having an outer surface similar to the inner surface of the rectangular tube 1 is used, and a flat sidewall die facing the inner surface of the sidewall 1a of the rectangular tube 1. Surface 10a and corner wall 1b of rectangular tube 1
It has an arc-shaped corner die surface 10b opposed to. Further, a reinforcing material 10c is arranged inside for maintaining a constant distance between the facing wall surfaces. This reinforcement 10
c may be provided as needed, and its structure is also arbitrary. For example, a rigid steel material may be fixed by welding or the like, or a turnbuckle in which bolts and nuts are combined is used, The heat treatment die 10 may have an adjustable wall surface interval. When the reinforcing material 10c having a wall surface interval to which it is attached is adjustable, the outer dimension (distance between the side wall die surfaces 10a and 10a located on opposite sides) can be changed, and thus the thickness increase When the heat treatment die 10 is drawn out from the rectangular tube 1 after the processing and heat treatment are completed, it is possible to obtain an advantage that the drawing can be facilitated by reducing the outer dimension of the heat treatment die. The heat treatment die 10 may be heated or cooled as necessary.

This heat treatment die 10 has a length longer than the length L of the thick wall portion 1A formed in the rectangular tube 1,
And, so that it is located in the region where the thick portion 1A is formed,
It is fixedly provided on the fixing device 2.

The outer dimensions of the heat treatment die 10 are determined so as to prevent the occurrence of distortion by restricting the inner surface position of the thick portion when heat treating the thick portion 1A formed by the thickening process. Specifically, the heat treatment die 10
The outer peripheral surface of is thickly contacted with the inner surface of the thick portion 1A so as to support the thick portion 1A, or is so dimensioned as to be substantially in contact therewith. Furthermore, specifically, in order to easily insert the heat treatment die 10 into the rectangular tube 1 before thickening,
A gap g larger than 0 between the side wall die surface 10a of the heat treatment die 10 and the inner surface of the side wall 1a of the rectangular tube 1 before thickening.
Is present, and the gap g is determined such that when the rectangular tube 1 is thickened, it is completely or almost completely filled with the thickening. In general, when the rectangular tube 1 is compressed to increase the thickness, if the inner and outer surfaces are not constrained, the thickness increase is usually the inner side,
It occurs almost equally on the outside. Therefore, if the thickness increase ratio β is defined as “thickness Δt increased by thickness increase (= thickness T after thickness increase−thickness t before thickness increase) / thickness t before thickness increase”, the thickness increase When the thickness is increased by the rate β, the inner surface of the side wall 1a of the rectangular tube 1 is bulged inward by 0.5 × t × β due to the increased thickness.
Therefore, if the gap g is set to be substantially equal to 0.5tβ or smaller than 0.5tβ, the gap g is almost or completely filled by the bulging of the side wall 1a during the thickening process. Therefore, the inner surface of the thick portion 1A formed by increasing the thickness is the side wall die surface 10a.
The state in which the thick portion 1A is almost in contact with the thick portion 1A (a slight gap even if it is not lightly contacted) or a state in which the thick portion 1A is strongly contacted can prevent the thick portion 1A from being distorted during the heat treatment.

In this embodiment, this gap g is set to be approximately equal to 0.5tβ. The gap between the corner wall 1b and the corner die surface 10b is also defined in the same manner as the gap g described above. The above-mentioned gap g is theoretical,
In the actual design, it is preferable to make an appropriate correction in consideration of the thermal expansion of the heat treatment die 10.

Next, the operation of the above-structured thickness increasing apparatus during heat treatment for increasing thickness will be described. In FIG. 1, a state in which one end of the rectangular pipe 1 to be thickened is fixed and held by a fixing device 2 and the opposite end is pressed by a compression device 3 such as a hydraulic cylinder to apply a compressive force to the rectangular pipe 1. Then, a small area in the longitudinal direction of the rectangular tube 1 is heated by the heating device 4 to form a heating part 5 in a red hot state that is easily plastically deformed. 4 is moved in the direction of arrow C along the rectangular tube 1, and at the same time, the cooling medium 7 is sprayed from the cooling means 6 to the rear end portion of the heating portion 5 to cool and solidify the portion immediately after the thickness increase. As a result, the rectangular tube 1 is continuously thickened in the longitudinal direction, and the thick portion 1A is formed.

During this thickening operation, the auxiliary heating device 9 is also moved by the movement of the moving table 8a, and when the auxiliary heating device 9 reaches the end of the thick portion 1A, the auxiliary heating device 9 starts heating. While the small area of the thick portion 1A is heated to a desired heat treatment temperature to form the heat treatment heating portion 26, it moves in the direction of arrow C and the rear end of the heat treatment heating portion 26 is forcibly cooled or left to cool. Thereby, the thick portion 1A is continuously heat-treated. Thus, the thickening process in the heating unit 5 and the heat treatment in the heat treatment heating unit 26 are performed in parallel to form the thick portion 1A having the desired length L, and the heat treatment heating unit 26 reaches the end of the thick portion 1. The operation ends when is moved. As a result, the thick portion 1A having the predetermined length L is formed and the whole is heat-treated, so that the mechanical characteristics are improved.

By the way, when the thickening is performed without restraining the inner and outer surfaces of the rectangular tube 1, the cross-sectional shape of the thick portion 1A obtained by compressive deformation and contractive deformation by cooling is shown in FIG. ), The side wall 1Aa, which should be flat, is recessed inward and recessed at that position 12
(Depression amount e) occurs and flatness decreases, and in order to prevent this, it is necessary to set the heating temperature, the thickening processing speed, the cooling speed, etc. within a narrow condition range in which depression is less likely to occur. It was Further, the phenomenon of dents on the side wall 1Aa also occurs when the thick portion 1A is heat-treated, and the dent amount e tends to increase particularly during the heat treatment. On the other hand, in the present embodiment, since the heat treatment die 10 is present inside during the thickness increasing process, even if the heating portion 5 increases the thickness due to the compressive force and the depression 12 tends to occur at that time, The inner surface of the thickened portion contacts the flat die surface 10a of the heat treatment die 10 and is regulated, and in that state, it is cooled and solidified. Thus, the recess 12 hardly occurs in the formed thick portion 1A. Next, the thick portion 1A is heated for heat treatment, and the recess 12 is likely to occur in the flat side wall 1Aa at that time as well, but the inner surface thereof is restricted by the flat die surface 10a of the heat treatment die 10, It is heat-treated while being kept flat. Thus, as shown in FIG. 4 (a), the formation of depressions on the side wall 1Aa is suppressed, and the formation of depressions on the side wall is prevented while substantially increasing the inner and outer surfaces of the pipe wall of the rectangular tube 1 substantially. In the state, the thickening process and the heat treatment are performed to form the thick portion 1A including the side wall 1Aa having good flatness.

The above-described embodiment also has the following advantages. That is, since it is possible to suppress the occurrence of depressions on the side wall 1Aa by the heat treatment die 10, it is not necessary to keep the thickness increase processing speed low in order to suppress the occurrence of depressions. Therefore, the thickness increase processing speed is increased to improve productivity. It is possible to raise. Further, since the heat treatment die 10 supports the inner surface of the portion where the thickness increasing process is performed, the bellows-like deformation (see FIG. 13) that is apt to occur during the thickness increasing process is unlikely to occur, and thus the thickness increasing process condition (for example, , The temperature of the heating part,
Even if the compression force, the cooling speed, the thickening processing speed, etc.) fluctuates to some extent, good thickening processing is possible and the operability is improved. Further, it is possible to perform a thickness increasing process in a state where the temperature of the heating part is lowered, and it is possible to suppress hardening due to heating and cooling during the thickness increasing process, and to suppress deterioration of mechanical properties of the thickness increasing part. Further, by regulating the inner surface of the entire thick portion 1A with the heat treatment die 10, the inner surface of the thick portion 1A can be made smooth, and the straightness of the thick portion 1A can be increased. The quality of the part 1A can be improved.

In this embodiment, the corner die surface 10b is located on the inner surface of the corner wall 1b of the rectangular tube 1 to regulate the inner wall of the thickened corner wall. However,
Since an abnormality such as a dent is unlikely to occur in the corner wall 1b during thickening or heat treatment, the inner surface of the corner wall 1b does not necessarily have to be regulated. Therefore, as shown in FIG. The inner surface of the inner die and the corner die surface 10b facing the inner surface of the inner die are enlarged so that the two remain in non-contact with each other even if the thickness is increased, or as shown in FIG. It is also possible to change the corner portions of the adjacent flat die surfaces 10a, 10a such that the corner portions are notched or the corner die surface is not formed.

In the above embodiment, the wall thickness is increased so that the inner and outer surfaces of the rectangular tube 1 have substantially the same thickness. However, the inner and outer surfaces may have different amounts of wall thickness increase. FIG. 6 shows an embodiment in which the amount of thickness increase on the outer surface side is increased. In this embodiment, the size of the heat treatment die 10 set inside the rectangular tube 1 is larger than that shown in FIG. The gap g between the square tube 1 and the inner surface of the tube wall before thickening is made small. That is, g <0.5tβ. However, in order to facilitate insertion of the heat treatment die 10 into the metal tube 1, the gap g is set to be larger than zero. Other configurations are similar to those of the embodiment shown in FIGS.

In the embodiment of FIG. 6, when the thickness of the heating portion 5 is increased, the amount of inward deformation tends to be larger than the gap g, so that the inner surface thereof is strongly pressed against the outer surface of the heat treatment die 10, Molded into the shape of the heat treatment die 10,
Therefore, the amount of deformation inward is limited, and the amount of thickness increase on the outer surface side is correspondingly increased. At this time, since the flat side wall die surface 10a of the heat treatment die 10 is flatly restraining the inner surface of the thickened portion, the recess 12 as shown in FIG. 4B does not occur. Further, the thick portion 1A formed by the thickening process is the heat treatment die 1
Auxiliary heating device 9 while being strongly pressed to 0
Is heated and heat-treated. Therefore, even during the heat treatment, the flat side wall 1Aa of the thick portion 1A is kept flatly restrained by the flat side wall die surface 10a, and the recess 12 as shown in FIG. It never happens.

The thickness increase rate β when performing the above-mentioned thickness increase processing is
It is determined by the moving speed of the heating part 5 and the speed of the non-thickened portion 1D of the rectangular tube 1 pushed toward the heating part 5. Now, in FIG. 1, the moving speed of the heating part 5 with respect to the thick part 1A of the rectangular tube 1 located behind the heating part 5 or the non-thickened part 1B behind it is W, and the unthickened part in front of the heating part 5 is W. When the moving speed of the portion 1D is V, the thickness increase rate β is represented by β = V / W 2. Here, in this embodiment, the thick portion 1A or the non-thickened portion 1B behind the thick portion 1A is configured so as not to move by the fixing device 2. Therefore, the moving speed W of the heating unit 5 is set to the heating device 4 as described above. Equal to the moving speed of
The moving speed V of the non-thickened portion 1D is equal to the speed at which the compression device 3 pushes the end of the rectangular tube 1. Therefore, the moving speed W of the heating device 4 and the pushing speed V of the compression device 3
By maintaining a constant ratio, for example, the moving speed W of the heating device 4 is kept constant and the pushing speed V by the compression device 3 is kept constant, thickening is performed at a constant thickening rate. Here, in order to keep the pushing speed by the compression device 3 constant, the compression force by the compression device 3 is kept constant and the temperature of the heating part 5 is kept constant (therefore, the heating part 5).
Method for maintaining constant average deformation resistance), a compression device 3 having a controllable pressing speed (for example, a device having a digital cylinder, a digital servo mechanism, etc.) is used, and a constant pressing speed is controlled by the control of the compression device 3. And the like can be used.

By the way, when the thickening process is started for the rectangular tube 1 having a constant thickness, the thickening process is simply started from the beginning so as to obtain a predetermined thickening rate β, as shown in FIG. 7 (a). Thus, the step portion 14 is formed between the thick portion 1A and the non-thickened portion 1B at the starting point. Such a step 14 is not preferable because it causes stress concentration, and therefore, FIG.
It is preferable to form the inclined surface 15 as shown in (b). When the thickness of the thick portion formed by the thickness increasing process is T, there is a relationship of T = (1 + β) t between the thickness T and the thickness increasing ratio β. Therefore, by changing the thickness increase ratio β,
It is possible to change the wall thickness T, and in FIG. 7 (b), change the wall thickness increase ratio β from the wall thickness increase start point D so as to increase at a constant ratio according to the position in the longitudinal direction of the rectangular tube 1. Thus, it is possible to form the inclined surface 15 at the start position of the thick portion 1A, and keep the thickness increase rate β constant after the thickness increase rate β reaches a predetermined value (after reaching the point E). By performing the thickening process by using the thickening process, it is possible to form the thick portion 1A having a constant thickness and having the inclined surface 15 at the thickening starting portion.

As described above, since the thickness increase rate β is equal to V / W, the heating device 4 is moved along the rectangular tube 1 and the heating part 5 is moved so that the position where the thickness increase occurs is the longitudinal direction of the rectangular tube 1. When moving in the direction, one or both of the moving speed W of the heating device 4 and the pushing speed V of the compression device 3 are controlled so that V / W (= β) increases at a constant ratio according to the position. Thereby, the inclined surface 15 can be formed at the thickening start portion, and the inclination of the inclined surface 15 can be appropriately set by appropriately setting the increasing ratio at that time. Similarly, at the end of the thick portion 1A, V / W (= β) is reduced at a constant rate depending on the position where the increase in thickness moves in the longitudinal direction of the rectangular tube 1. One or both of the moving speed W of the heating device 4 and the pushing speed V of the compression device 3 are controlled. This makes it possible to form an inclined surface whose thickness is gradually reduced.

The formation of the above-mentioned inclined surfaces 15 at both ends of the thick portion 1A formed by the thickening process can be applied to both the embodiment shown in FIGS. 1 to 3 and the embodiment shown in FIG. Is. However, as in the embodiment shown in FIG. 6, when it is applied to the case where the thickened portion is extruded to the outer surface side by the heat treatment die 10, a slight problem occurs. That is, as shown in FIG. 8A, when increasing the thickness increase rate β so as to form the inclined surface 15 with a constant slope at the thickness increase start portion, as shown in FIG. The wall thickness increasing position moves in the longitudinal direction of the rectangular tube 1 while increasing the wall thickness ratio, and after the portion having the wall thickness increasing on the inner surface side has passed the position P where it contacts the heat treatment die 10, it is attempted to increase the wall thickness on the inner surface side. Since the portion (portion indicated by hatching a) is limited by the heat treatment die 10, the thickness is increased on the outer surface side by that amount, and the portion indicated by hatching b is added to the outer surface side. Therefore, the inclined surface 15 bends at the position P, and the inclined surface 15A has a steep slope. Such bending is not preferable because it causes stress concentration.

In one embodiment of the present invention, it is possible to prevent such bending of the inclined surface. That is, in one embodiment, as shown in FIGS. 9A and 9B, when the thickening start point D is passed, the thickening ratio β (= W / V) is first set to the longitudinal position of the rectangular tube 1. Accordingly, the inclined surface 15 having a constant slope is formed at a constant rate, and after the portion P having the increased thickness on the inner surface side passes the position P at which the heat treatment die 10 is contacted, the increasing rate of the increase rate is increased. Reduce to about half. As a result, as shown in FIG. 9A, the heat treatment die 10 is formed.
If it is assumed that there is no gradient, a sloped surface 15B having a slope that is about half the slope of the sloped surface 15 that was formed earlier is formed next to the position P. )
Since the heat treatment die 10 is provided as shown in FIG. 3, the portion (portion indicated by hatching a) where the thickness is to be increased on the inner surface side is limited by the heat treatment die 10 and the thickness is increased to the outer surface side by that amount. Is added with a portion indicated by hatching b to form an inclined surface 15C. The slope of the inclined surface 15C is substantially equal to that of the inclined surface 15. Thus, the inclined surfaces 15 and 15C having almost no bending are formed on the outer surface side, and as shown in FIG. 9C, the thick portion 1A having no portion where stress concentration is likely to occur can be formed.

Similarly at the end portion of the thick portion 1A, however, an inclined surface with almost no bending can be formed on the outer surface side by changing the thickness increasing rate in the opposite direction to the thickening starting portion. That is, as shown in FIG. 10, from the time when the starting point F of the end of the wall thickness increase is exceeded, the wall thickness increase rate β (= W / V) is reduced at a constant rate according to the longitudinal position of the rectangular tube 1. Thereby forming an inclined surface 16 having a constant gradient (at this time, if it is assumed that the heat treatment die 10 is not present, an inclined surface 16A indicated by a chain double-dashed line is formed), and the thickened portion on the inner surface side After passing the position Q away from the heat treatment die 10, the decrease rate of the increase rate is increased to about double. As a result, after the position Q, the inclined surface 1 is formed on the inner and outer surfaces.
6B is formed, and the inclined surface 16 on the outer surface side is formed.
B has the same slope as the inclined surface 16 formed previously. Thus, an inclined surface with almost no bending can be formed on the outer surface side even at the end portion of the thick portion 1A.

11 and 12 show still another embodiment of the present invention. In this embodiment, a molding die 20 for the outer surface is arranged behind the heating device 4 so as to move together with the heating device 4. This external forming die 20
Has a die surface 20a that regulates the outer surface position of the pipe wall that is deformed outward due to the increase in thickness, and is configured to cool the inside with a cooling medium. It is possible to cool the pipe wall that is in contact with the die surface 20a. is there. Therefore, in this embodiment, the outer surface forming die 20 constitutes cooling means for cooling the rear end of the heating portion 5 of the rectangular tube 1. A cooling means for injecting a cooling medium into the rectangular tube to cool it may be disposed behind the outer surface molding die 20.

Heat treatment die 10 and outer surface molding die 2
The interval with 0 is set to be equal to the thickness of the thick portion 1A formed by the thickness increasing process. The gap g'between the outer surface forming die 20 and the outer surface of the rectangular tube 1 is usually smaller than the amount by which the tube wall is thickened to the outer surface side by thickening, that is, g '<0.5tβ. . Therefore, the gap g between the heat treatment die 10 arranged inside and the inner surface of the rectangular tube 1 is g> 0.5tβ. Other configurations are the same as those in the above embodiment.

In the embodiment shown in FIGS. 11 and 12, the heating device 4 locally heats the rectangular tube 1 to form the heating portion 5 while the rectangular tube 1 is subjected to a compressive force, and Tube 1
Move along. As a result, the heating portion 5 moves in the longitudinal direction of the rectangular tube 1 while increasing the thickness of the heating portion 5 and cooling and solidifying the rear end of the heating portion 5 by the outer surface forming die 20.
The meat is continuously thickened. At this time, the pipe wall of the heating unit 5 which tends to increase in thickness to the outer surface side due to the increase in thickness is suppressed by the outer surface forming die 20, and accordingly, the thickness increases on the inner surface side.
Further, the heat treatment die 10 suppresses the recesses that are likely to occur on the side wall of the rectangular tube. Thus, it is possible to form the thick-walled portion 1A having the side wall without a recess while controlling the outer surface side dimension with the outer surface molding die 20. The thick portion 1A thus obtained is extremely smooth because both the inner and outer surfaces are regulated by the die surface. The thick portion 1A formed by the thickening process is then immediately heated by the auxiliary heating device 9 to be heat-treated. Even in this case, the thick portion 1
Since the inner surface of A is regulated by the heat treatment die 10, a dent does not occur, and a thick portion without distortion can be formed.

Note that, also in the embodiments shown in FIGS. 11 and 12, the thickness increase rate is changed as described with reference to FIGS. 8 to 10 at the position where the thickness increase starts and / or the position where the thickness increase ends. Thus, by forming an inclined surface, and at that time, by changing the change rate of the thickness increase rate at the time when the outer surface of the thickness increasing portion comes into contact with or separates from the outer surface forming die 20,
It is possible to form a slope with a constant slope.

Further, in the embodiment shown in FIGS. 11 and 12,
A gap g ′ between the outer surface forming die 20 and the outer surface of the rectangular tube 1.
Is set to g '<0.5tβ, and the thickness is regulated so that the increase in the thickness increases on the inner surface side of the rectangular tube. However, the present invention is not necessarily limited to this configuration, and the gap g between the heat treatment die 10 and the inner surface of the rectangular tube 1 is set so as to satisfy 0 <g ≦ 0.5tβ, and the thickness increase is made uniform on the inner and outer surfaces. It may occur or may occur more frequently on the outer surface side. In this case, a gap g ′ between the outer surface forming die 20 and the outer surface of the rectangular pipe.
Is g ′ ≧ 0.5tβ. Also in this case, a smooth outer surface can be obtained by molding the portion of the heating unit 5 immediately after the thickness increase with the outer surface molding die 20.

In all of the above embodiments, the auxiliary heating device 9 for heat treatment is provided after the heating device 4 for thickening so as to move together with the heating device 4, but the present invention is not necessarily required. Not limited to this configuration, the auxiliary heating device 9 may be replaced by the heating device 4
It may be configured to move independently of. Further, in the above-mentioned embodiment, the structure is configured such that the thickness increasing process and the heat treatment are performed in parallel, but the heat treatment does not necessarily have to be performed in parallel with the thickness increasing process, and only the heat treatment is performed after the thickness increasing process is completed. May be. When the heat treatment alone is performed, it is not necessary to apply the compression force of the compression device 3 to the metal tube 1. In that case, the moving direction of the auxiliary heating device 9 for heat treatment is not limited to the arrow C direction in FIG. 1, but may be the opposite direction. Furthermore, it is not necessary to provide the auxiliary heating device 9 for heat treatment separately from the heating device 4 for thickening, and the heating device 4 may be used for heat treatment. Further, in order to perform the heat treatment of the thick portion 1A, a heating device for heat treatment capable of simultaneously heating the entire thick portion 1A is used, and the entire region is heated at the same time, and the heat treatment is performed by cooling or forced cooling. You may.

The case where the thickening process and the heat treatment are performed on the rectangular tube 1 has been described above, but the present invention is not limited to the rectangular tube 1 and can be applied to a round tube, for example. Needless to say.

[0045]

The following is an example of a specific example of a thickening process. [Example 1] Used device A thickening heat treatment device having the configuration shown in Fig. 1. The specifications of each part are as follows. Compressor 3: Hydraulic cylinder Heating device 4: High frequency heating coil (width 20 mm) Cooling device 6: Water injection cooling method Heating width (distance from tip of heating device 4 to water spraying position): 65 mm Auxiliary heating device 9: High frequency heating Coil (width 50 mm) Cooling system for heat treatment heating unit 26: water injection cooling system Distance between heating device 4 and auxiliary heating device 9: 300 mm Heat treatment die 10: external shape 264 x 264 mm, length 3
00 mm

Thickening processing and heat treatment conditions Test square tube: 300 × 300 mm × 12 mmt square steel tube Thickening rate β: 1.0 (thickness increased from 12 mm to 24 mm) Maximum temperature of heating part 5: 1150 ± 50 ° C moving speed W of heating device 4: 0.45 mm / s compression force P: 53,600 kg by the compression device 3 (as a result, pushing speed V = 0.45 by the compression means 3)
mm / s) Thickness increase processing speed (W + V): 0.9 mm / s Maximum temperature of heat treatment heating section 26: 950 ± 50 ° C

Thickening and Heat Treatment Results Under the above conditions, the thickening and heat treatment were performed to form a thick portion 1A having a length of about 250 mm. The thickness of the obtained thick portion 1A was about 24 mm (thickness increase ratio β = 1.0), which was almost the expected value. The external dimensions are 311.8.
The thickness was × 311.5 mm, and the inner and outer surfaces were almost equally thickened. The inner and outer surfaces of the thick portion 1A were both smooth, and had a good appearance without bellows or fine wrinkles.
Depression amount e on the four flat surfaces of the obtained thick portion [Fig.
[See (b)], it was in the range of 0.2 to 0.7 mm, which was extremely small. Further, when the mechanical properties of the obtained thick portion 1A were measured, the surface hardness was Hv 200 or less and the elongation was 20% or more.

Comparative Example 1 When an attempt was made to increase the thickness and heat treat the same rectangular tube under the same conditions as in Example 1 except that the heat treatment die was removed, as shown in FIG. On the other hand, a bellows-like deformation 30 was generated, and good thickness increase could not be achieved.

[Comparative Example 2] The maximum temperature of the heating section 5 was set to 130.
0 ± 50 ° C., the compression force P by the compression device 3 is 34,
Thickening processing and heat treatment were performed under the same conditions as in Comparative Example 1 except that the weight was 500 kg to form a thick portion 1A having a length of about 250 mm. The thickness of the obtained thick portion 1A was about 24 mm (thickness increase ratio β = 1.0), which was almost the expected value. The inner and outer surfaces of the thick portion 1A were both smooth, and had a good appearance without bellows or fine wrinkles. However,
When the amount of depression e on the four flat surfaces of the obtained thick portion was measured, it was 1.2 to 2.8 mm, which was considerably large.

[Comparative Example 3] Under the same conditions as in Comparative Example 2 except that the auxiliary heating device 9 was not operated, only thickening processing was performed.
A thick portion 1A having a length of about 250 mm was formed. The thickness of the obtained thick portion 1A was about 24 mm (thickness increase ratio β = 1.0), which was almost the expected value. The inner and outer surfaces of the thick portion 1A were both smooth, and had a good appearance without bellows or fine wrinkles. When the amount of depression e in the four flat surfaces of the obtained thick portion 1A was measured, it was 0.5 to 1.5 mm.
Although smaller than Comparative Example 2, it was considerably larger than that of Example 1. Furthermore, when the mechanical properties of the obtained thick portion 1A were measured, the surface hardness was Hv350 ±
50, the elongation was 10 ± 5%, and since no heat treatment was performed, there was an effect of hardening due to the thickening process.

[Example 2] Equipment used Same as in Example 1 Conditions for increasing wall thickness Test square tube: Square steel tube of 300 x 300 mm x 12 mmt Thickness increase rate β: 1.0 (12 mm thickness was increased to 24 mm) Heating Part maximum temperature: 1300 ± 50 ° C. Moving speed W of heating means 4: 0.9 mm / s Compression force P by compression means 3: 38,000 kg (as a result, pushing speed V = 0.9 m by compression means 3)
m / s) Thickness increase processing speed (= W + V): 1.8 mm / s Maximum temperature of heat treatment heating part 26: 1000 ° C

Thickening processing result Under the above-mentioned conditions, the thickening processing and the heat treatment were performed to form the thick portion 1A having a length of about 250 mm. The thickness of the obtained thick portion 1A was about 24 mm (thickness increase ratio β = 1.0), which was almost the expected value. The external dimensions are 312.5.
The thickness was × 311.6 mm, and the inner and outer surfaces were almost equally thickened. The inner and outer surfaces of the thick portion 1A were both smooth, and had a good appearance without bellows or fine wrinkles.
The amount of depression e on the four flat surfaces of the obtained thick portion is
It was in the range of 0.2 to 0.7 mm, which was extremely small. As described above, in Example 2, the thickening processing rate and the heat treatment rate were doubled as compared with Example 1, but the thick portion 1A having an outer shape substantially equal to that of Example 1 could be formed. When the mechanical properties of the obtained thick portion 1A were measured, the surface hardness was Hv 200 or less and the elongation was 20% or more, and the mechanical properties were sufficiently improved by heat treatment.

[0053]

As described above, according to the method of the present invention, the heat treatment die is inserted into the metal pipe to be thickened, and the metal pipe is thickened to the outside of the heat treatment die. Since the thick part is formed and the thick part is heat-treated in that state, it is likely that the cross-section of the thick part will be distorted by heating and cooling during thickening and heating and cooling during heat treatment. In addition, the heat treatment die can restrain the inner surface of the thick portion to prevent undesired distortion. Therefore, the thick portion having a predetermined cross-sectional shape and subjected to the desired heat treatment can be formed. Further, since the distortion during the heat treatment can be forcibly prevented by the heat treatment die, it is not necessary to adjust the heating rate, the cooling rate, etc. during the heat treatment to prevent the distortion. The heating rate, cooling rate, etc. of
It is also possible to obtain an effect that a thick portion that has been subjected to favorable heat treatment can be manufactured with high productivity.

Further, the heat treatment die not only prevents the cross-section from being distorted in the portion where the metal pipe is thickened, but also causes an unstable deformation during the thickening process, for example, a bellows shape which tends to occur in the longitudinal direction. The present invention also has the effect of preventing the deformation of the steel sheet, and therefore the present invention provides the thickening processing conditions (for example, the temperature of the heating portion, the compressive force, the cooling speed, the thickening processing speed) that enable the favorable thickening processing. It is possible to widen the range of (1), etc., and it is possible to obtain the effects of increasing the thickness increase processing speed to improve productivity, and setting a large thickness increase rate.

Here, as a method of heat-treating the thick-walled portion, a small area of the thick-walled portion is heated to a desired heat-treatment temperature by an auxiliary heating device to form a heat-treated heated portion, and the heat-treated heated portion is thickened. If a method of relatively moving in the longitudinal direction of the portion is adopted, it is possible to heat the thick portion to a desired temperature by a relatively small auxiliary heating device and perform heat treatment, and it is possible to reduce the facility cost. . Further, the heat treatment operation can be performed in parallel with the thickness increasing process, and if the thickness increasing process and the heat treatment are performed in parallel, the effect of improving productivity can be obtained.

Here, the gap g between the heat treatment die and the inner surface of the rectangular pipe before the metal thickening is set in the state where the heat treatment die is set in the metal pipe to be thickened, and g≈0.5tβ If set, the thickness increase due to the thickness increase process will occur almost equally on the inner and outer surfaces of the pipe wall, and the inner surface of the thick part formed by the thickness increase will lightly contact the outer surface of the heat treatment die or there will be a small amount between them. A large gap remains, and after the heat treatment in this state, it is possible to easily remove the heat treatment die from the thick portion.

Further, if the gap g is set to 0 <g <0.5tβ, the heat treatment die acts as an inner surface forming die at the time of thickening, so that the inner surface of the pipe wall can be formed into a predetermined shape. In addition to preventing distortion in the cross section, the inner surface can be smoothed.

In carrying out the above-described thickening process, at the start of the thickening process, the thickness increasing rate is increased at a constant rate according to the longitudinal position of the metal pipe, and after the time when the inner surface of the metal pipe contacts the heat treatment die. The increase rate of the thickness increase rate is reduced to about half, and after reaching a predetermined thickness increase rate, the thickness increase rate can be kept constant and the thickness increase processing can be performed.
At the thickening start side end of the thick portion formed by the thickening process, a slope with a constant gradient can be formed from the non-thickened portion to the thick portion having a predetermined thickness, and stress concentration is less likely to occur. The effect that the thickened portion can be formed is obtained.

Further, at the end of the thickness increasing process, the thickness increasing rate is reduced at a constant rate according to the longitudinal position of the metal tube, and after the time when the inner surface of the metal tube is not in contact with the heat treatment die, the thickness increasing rate is It is also possible to reduce the reduction ratio of
In that case, a slope having a constant gradient from the thick portion having a predetermined thickness to the non-thickened portion can be formed at the end portion on the thickening end side of the thick portion formed by the thickening process, It is possible to obtain an effect that it is possible to form a thickened portion that is unlikely to occur in stress concentration.

Further, when the outer surface forming die is arranged outside the heating portion formed on the metal tube, the outer surface of the thickened tube wall can be formed to be smooth, and the outer surface forming die can be formed. It is possible to suppress a part of the wall thickness increase on the outer surface side of the pipe wall with the molding die, and to increase the inner surface side portion by that amount, and to reduce the wall thickness increase on the outer surface side as compared to the inner surface side as necessary. The effect of being able to do is obtained.

The device of the present invention is inserted into a metal pipe to be thickened so as to be located inside a thick portion formed by the thickening, and has a length equal to or longer than the length of the thick portion. A die for heat treatment, a compression device that applies a compressive force in the longitudinal direction to the metal pipe, a heating device that heats a small region in the longitudinal direction of the metal pipe to form a heating part in a red heat state, and a heating part of the heating part. A cooling device for cooling one end, a moving device for moving the heating device and the cooling device relative to the rectangular tube, and a heating device provided behind the heating device so as to move together with the heating device. The heating device locally heats the metal pipe by having a configuration in which a small region of the thick portion formed by meat processing is heated to a temperature for heat treatment to form a heat treatment heating portion. To increase the thickness of the metal pipe Auxiliary heating device heats a small area of the thick portion to form a heat treatment heating portion in parallel with the thickening operation of moving relatively to form the thick portion, and the auxiliary heating device. Is relatively moved with respect to the metal pipe to relatively move the heat treatment heating part in the longitudinal direction of the thick part,
It is possible to perform heat treatment on the entire thick-walled portion, and since those thickening processing and heat treatment are performed in the state where the heat treatment die exists in the metal pipe, there is no distortion in the cross-sectional shape, It has an effect of being able to efficiently manufacture a thick portion which is good and has improved mechanical properties by heat treatment. Further, the heating device for increasing the thickness and the auxiliary heating device for the heat treatment can be relatively moved to the metal tube by a single moving device, which also has the effect of simplifying the device configuration.

When the metal tube to which the present invention is applied is a rectangular tube, it is possible to prevent the occurrence of dents that tend to occur on the flat side wall during thickening and heat treatment, and to form a thick wall portion with good flatness. Is obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a preferred example of a thickening heat treatment apparatus used for carrying out the method of the present invention.

2A and 2B are cross-sectional views taken along arrows AA and BB of FIG. 1, respectively.

FIG. 3 is an enlarged cross-sectional view of a thickened portion in the embodiment of FIG.

FIG. 4A is a thick portion 1A formed in the embodiment of the present invention.
A cross-sectional view (b) is a thick portion 1 formed without using a heat treatment die.
Sectional view of A

5 (a) and 5 (b) are sectional views of the same portion as FIG. 2 (a) showing a modified example of the heat treatment die.

FIG. 6 is an enlarged cross-sectional view of a thickened portion in another embodiment of the present invention.

FIG. 7 (a) is a schematic cross-sectional view showing a thickness-increasing start portion in a case where normal thickness-increasing processing is performed, and FIG. 7 (b) is a schematic cross-sectional view showing a thickness increase starting portion having a preferable inclined surface.

FIG. 8 (a) is a schematic cross-sectional view showing a portion where the thickness increase starts at a constant rate assuming that there is no heat treatment die, and FIG. 8 (b) shows an increase with the heat treatment die. Schematic cross-sectional view showing the portion where the meat increase starts when the meat ratio is increased at a constant ratio

9A and 9B are views for explaining an embodiment of the present invention, in which (a) is a case where the thickness increase rate is increased at a constant rate on the assumption that there is no heat treatment die and the rate is changed from the position P. FIG. (B) is a schematic cross-sectional view showing the thickness increase starting portion in the case where the heat treatment die is provided, the thickness increasing rate is increased at a constant ratio, and the thickness increasing start portion is changed from the position P. FIG. 6C is a schematic cross-sectional view showing the thickening start portion of the thick portion obtained in this example.

FIG. 10 shows another embodiment of the present invention, showing a portion where the thickness increase ends when the rate of increase in thickness is reduced at a constant ratio with the heat treatment die and the ratio is changed from the position Q. Schematic cross section

FIG. 11 is a schematic cross-sectional view showing another example of the thickening heat treatment apparatus used for carrying out the method of the present invention.

FIG. 12 is an enlarged cross-sectional view of a thickened portion in another embodiment shown in FIG.

FIG. 13 is a schematic cross-sectional view showing a square tube having a wall thickness increased in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rectangular tube 1a Side wall (flat tube wall) 1b Corner wall 1A Thick part 2 Fixing device 3 Compressor 4 Heating device 5 Heating part 6 Cooling device 7 Cooling medium 8 Moving device 9 Auxiliary heating device 10 Heat treatment die 10a Side wall die Surface 10b Corner die surface 12 Recess

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tsuguo Minagawa, 2-17-8, Tonomachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Daiichi Kogyo Kogyo Co., Ltd. (72) Inventor, Akira Fukuda, 1-chome, Awaza, Nishi-ku, Osaka-shi, Osaka No. 5-16 Daiwa House Industry Co., Ltd.

Claims (10)

[Claims] 1. A heat treatment die having a length equal to or greater than the length of the thick portion is previously provided in the metal pipe to be thickened so as to be located inside the thick portion formed by the thickening process. In this state, a small area in the longitudinal direction of the metal tube is locally heated by a heating device in this state to form a heating section in a red heat state, and the heating section is relatively moved in the longitudinal direction of the metal tube. The metal tube is continuously thickened by applying a compressive force in the longitudinal direction of the metal tube to the heating part while moving to sequentially increase the thickness and cooling the rear end portion of the heating part immediately after the thickness increase. To form a thick portion on the outside of the heat treatment die,
After that, the thick-walled portion is heat-treated while the heat-treating die is positioned inside the thick-walled portion. 2. A small area of the thick portion is heated to a desired heat treatment temperature by an auxiliary heating device to form a heat treatment heating portion, and the heat treatment heating portion is relatively moved in the longitudinal direction of the thick portion. The heat treatment method for increasing the thickness of a metal pipe according to claim 1, wherein the heat treatment is performed on the thick portion. 3. The thickening process for a metal pipe according to claim 2, wherein the thickening process operation for the metal pipe and the heat treatment process for the thick portion formed by the thickening process are performed in parallel. Processing heat treatment method. 4. The gap g between the heat treatment die and the inner surface of the metal pipe before the thickness increase is set in the state where the heat treatment die is set in the metal pipe to be thickened, and 4. The thickness t and the thickness increase rate β generated in the metal pipe are set so that g≈0.5tβ.
The method for thickening and heat treating a metal tube according to any one of 1. 5. The gap g between the heat treatment die and the inner surface of the metal pipe before the thickness increase in a state where the heat treatment die is set in the metal pipe to be subjected to the thickness increase processing, The thickness t and the thickness increase ratio β generated in the metal pipe are set so that 0 <g <0.5tβ.
The method for thickening and heat treating a metal tube according to any one of 1. 6. The method of heat treatment for increasing the thickness of a metal pipe according to claim 5, wherein at the start of the thickness increasing process, the increase ratio of the thickness is increased at a constant rate according to the longitudinal position of the metal pipe, After the point of contact with the heat treatment die, the increase rate of the thickness increase rate is reduced to about half, and after reaching the predetermined thickness increase rate, the thickness increase rate is kept constant and the thickness increase processing is performed. Metal tube thickening heat treatment method. 7. The metal pipe thickening heat treatment method according to claim 5 or 6, wherein at the end of the metal thickening process, the metal thickening rate is reduced at a constant rate according to the longitudinal position of the metal pipe. A heat treatment method for increasing the thickness of a metal tube, characterized in that after the surface is not in contact with the heat treatment die, the reduction rate of the increase rate is reduced by about twice. 8. An outer surface forming die is arranged outside a heating part formed for increasing the thickness of the metal pipe, and the outer surface position of the pipe wall which is deformed outward by increasing the thickness is determined by the outer surface forming die. It is restricted, It is characterized by the above-mentioned.
The method for thickening and heat treating a metal tube according to any one of 1. 9. The method of heat treatment for increasing the thickness of a metal tube according to claim 1, wherein the metal tube is a rectangular tube. 10. A heat treatment die which is inserted into a metal pipe to be thickened so as to be located inside a thick portion formed by the thickening and has a length equal to or greater than the length of the thick portion. A compression device that applies a compressive force in the longitudinal direction to the metal pipe, a heating device that heats a small region in the longitudinal direction of the metal pipe to form a heating portion in a red heat state, and one end of the heating portion is cooled. Cooling device, a moving device for moving the heating device and the cooling device relative to the rectangular tube, and a moving device provided behind the heating device so as to move together with the heating device. An apparatus for thickening and heat treating a metal tube, comprising: an auxiliary heating device that heats a small region of the formed thick portion to a temperature for heat treatment to form a heat treatment heating portion.