JPH059581A - Multi-stage cooling system - Google Patents

Abstract

PURPOSE:To provide the multi-stage cooling device and system which form large-diameter steel pipes having uniform and stable quality by executing such a cooling stage which does not generate bends and twists along the axis in the longitudinal direction in the uniform cooling system for high-temp. materials in a continuous heat treatment for improving the toughness of round or square steel pipes by restoring the work hardening of the material in the peripheral walls of these pipes and for removing the residual stresses particularly in the corner parts to a permissible stress or below. CONSTITUTION:This multistage cooling system consists in segmenting the cooling device to plural sections in the longitudinal axis direction, alternately installing cooling chambers and non-cooling chambers in each one of these sections, thermally shutting off these chambers from each other, successively cooling the materials to be treated while successively repeating cooling and heat dissipation during the continuous transportation of these materials through the above-mentioned chambers, and finally allowing the materials to cool down to ordinary temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a process for forming a large diameter round steel pipe or a rectangular steel pipe by cold plastic working of a thick steel plate, and in the process of bending, deterioration of local member quality of the steel plate and generation of residual stress. In contrast, after heating and refining the steel pipe material to a predetermined temperature for a certain period of time, it is left to cool and heat-treated to repair the deterioration of the steel material due to cold working. The present invention relates to an improved construction method, particularly a multi-stage cooling method after heating a steel pipe material.

[0002]

2. Description of the Related Art Used as a building column,
One seam or two made by bending and forming thick steel plate
Conventionally, mass production methods for large-diameter seam rectangular steel pipes have been roughly classified practically, regardless of the literature, and the following construction methods have been adopted. The single plate steel plate is parallel to the longitudinal axis direction, and overlaps along the width direction, and the corner-corresponding parts are bent at four positions,
After forming the cross-section into a shape similar to that of a rectangular steel pipe, both side edges of the steel sheet are butt-welded to form a one-seam rectangular steel pipe with a rectangular cross-section. A pair of steel plates with a square cross-section are formed by bending a single plate steel plate parallel to the longitudinal axis direction and bending it in two places along the width direction to form a U-shaped cross section. The two parts are butt-welded to produce a large diameter square steel pipe with two seams.

While conveying the strip steel plate in the longitudinal direction,
This is passed through a round steel pipe forming roll stand to be formed into a round cross section, and once manufactured into an electric resistance welded round steel pipe, then the cross section of the round steel pipe is shaped into a square shape, and a one-seam large-diameter square steel pipe is formed. To form. In detail, even if there are some differences, the construction methods described above or are widely practiced. A one-seam large-diameter round steel pipe is formed in the middle of the above method. In addition, it is known that there is a UO pressing method and the like as a method for forming a large-diameter round steel pipe. As described above, the economical method for producing a large-diameter round steel pipe or square steel pipe that has been conventionally performed is cold plastic deformation of a thick steel plate in any case, that is, a thick steel plate for forming a steel pipe. Includes cold bending, or approximately 90 ° cold bending for corner steels to form square steel tubes.

By the way, when a flat thick steel plate is bent at approximately 90 ° in the cold, even if a required R is given to the bent part of the steel plate, its corner portion In the steel cross section, the tensile force is exerted on the outer material of the neutral surface and the compressive force is exerted strongly on the inner side, and as a result plastic deformation occurs, the material at the relevant point deteriorates, the local material quality is low, the tensile strength and material The ratio to the yield point is extremely small, and brittle fracture may occur if repeated stress is applied to the deformed part. Further, even after removing the external force, residual stress due to cold plastic deformation exceeding the limit occurs.

However, conventionally, regarding the specifications of this type of large-diameter round steel pipe or square steel pipe, there has been an increase in demand due mainly to its merit in its shape / structural characteristics or construction characteristics. Looking back from the above processing state,
There has been a tendency that the large-diameter steel pipe is distributed in the market without sufficient objective and technical analysis / examination of the material weaknesses or unstable parts inherent in the steel pipe material. However, recently, large-diameter steel pipes formed by cold bending have been widely used as columns for buildings.
Consumers' concern that deterioration of local member quality due to cold bending at the time of steel pipe forming may promote brittleness change of the relevant part, as it is about to be used as a column of high-rise buildings. Or, reflection is increasing.

[0006] In response to the requests from those users and the like, the deterioration of the steel plate material at the relevant location is recovered by annealing the cold plastically deformed steel material in the large diameter round steel tube or the square steel tube formed by the conventionally known manufacturing method. It is considered to apply a heat treatment. The Applicant has previously divided the heating furnace into a plurality of sections along the conveyance direction of the material to be treated, and alternately equipping them into a heating chamber and a non-heating chamber, and connecting them in multiple stages in series. The steel material (tube) charged into the heating furnace is conveyed through the compartment, and is heated from the tip part in order, and then the heating temperature of the steel material is changed in the part of the chamber that is not heated. By homogenizing and repeating the process of releasing the strain of the steel material based on the temperature difference, the heating temperature of the steel material is gradually increased uniformly, and a large strain does not occur in the steel pipe with the heat treatment, or , A multi-stage heating furnace or a heating method for a steel pipe (see Japanese Patent Application No. Hei 2-219996, a heating furnace for a rectangular steel pipe without strain and a construction method).

However, when cooling a large-diameter steel having a high temperature in the axial direction and carried out from the heating furnace, the large-diameter steel is cooled uniformly along the circumferential direction and / or the longitudinal axis direction at a uniform speed. Otherwise, the steel pipe after returning to room temperature may be bent or twisted. Whether you heat-treat a round steel pipe or anneal a square steel pipe, the space required to cool the heated steel pipe with a long axial standard length that can be used for the column and return it to room temperature is a large space. In addition, if the cooling rate and temperature of the steel pipe become uneven depending on the location, or if there is a temperature difference in the axial direction, distortion due to thermal expansion occurs as a whole, bending, twisting, etc. occur and the material is stable. However, after heat treatment, large equipment is required to correct the distortion of the steel pipe. Even if a large-diameter steel pipe with a standard length after heat treatment is naturally cooled, a large space and equipment are required to evenly cool it slowly.

[0008]

Therefore, the method of the present invention is
It is an object of the present invention to provide a multi-stage cooling system in which the deformation such as bending and twisting of the steel pipe does not occur in the cooling process of the heated steel pipe as much as possible. Moreover, it aims at developing the multistage cooling device which sets the space required for heating steel pipe cooling as space-saving as possible. Further, the present invention provides a multi-stage cooling means capable of continuously and uniformly cooling.

[0009]

In order to achieve the above-mentioned object, the present invention has the respective constituent features as described below. (1) The inside of the cooling device is divided into a plurality of sections along the conveyance direction of the material to be treated, and for each of the compartments, a forced cooling chamber for the material to be treated and a non-cooling chamber for the material to be treated are alternately provided. A multi-stage cooling device for steel pipes characterized by the above.

(2) The material to be treated which is long in the axial direction is conveyed through the cooling device and while passing through the first compartment cooling chamber,
From the tip portion, the refrigerant gas is sequentially and evenly contacted with the refrigerant gas to be forcibly cooled, and then, when passing through the second compartment non-cooling chamber, the heat of the forcibly cooled steel pipe is naturally dissipated and is evenly distributed. When heat is conducted to the third section cooling chamber, it is again contacted with the refrigerant gas and forcedly cooled evenly when it passes through the third compartment cooling chamber. The temperature is gradually reduced by repeating the process of spontaneously dissipating in the non-cooling chamber, conducting heat evenly, and forcibly cooling evenly in the fifth compartment cooling chamber several times, thereby gradually lowering the temperature. A multi-stage cooling system for a steel pipe, characterized in that distortion of the material to be treated is suppressed and the whole is uniformly heat-treated.

[0011]

[Operation] A long heating steel pipe in the axial direction is continuously charged and conveyed through a thermally partitioned cooling chamber and a non-cooling chamber (which does not have a forced cooling facility), and cooling is performed from its tip. In the first cooling chamber (first compartment) where the fluid circulates, the refrigerant gas is touched or blown and cooled from the peripheral wall, and the same heated portion passes through the next first non-cooling chamber (second compartment). During this period, the steel pipe material that has been rapidly cooled through the first cooling chamber touches the room atmosphere or is blown in the same room, and is naturally cooled, while the cooling speed of the steel pipe temperature is moderated Conduction etc. acts to raise the temperature to some extent, thermal uniformity is obtained throughout, and the thermal expansion strain of the steel pipe caused by forced cooling is released / dispersed. However, the heating temperature of the steel pipe portion is considerably lower than the initial temperature. When the relevant portion of the heated steel pipe is carried into the second cooling chamber (third compartment) of the device, the same portion is again subjected to the same action as the forced cooling action in the first cooling chamber and is exposed to the refrigerant gas. And is forced to cool.

When the steel pipe portion is further conveyed to the second non-cooling chamber (fourth section), the same operation as in the first non-cooling chamber is performed therein, and the cooling speed of the heated steel pipe temperature is moderated. On the other hand, the temperature slightly rises due to conduction heat or the like and becomes uniform, and the thermal expansion strain generated by the forced cooling or the like is released and dispersed. As a result, the temperature of the heated steel pipe is considerably lower than the temperature in the first non-cooling chamber.
The next behavior of the cooling gas in the third cooling chamber (fifth section) on the heated steel pipe is the same as that in the first cooling chamber.
Further, the action of the third non-cooling chamber (sixth section) may be understood to be substantially the same as that of the action in the first non-cooling chamber described above. By repeating such steps in sequence, the heating temperature of the steel pipe is gradually lowered, and eventually the material temperature is approximately room temperature or a temperature close to room temperature by the time it passes through the processing material carry-out port of the cooling device. And complete the annealing of the entire length of the material to be treated without any apparent distortion.

The multi-stage cooling method for annealing the material to be treated as described above is based on a thick-walled large-diameter rectangular steel pipe corner portion, a welded joint,
In order to perform the material cooling process after heat treatment for refining the steel material at the welded place, etc., it can be installed in-line in the steel pipe forming machine, and of course it is intended for round steel pipes, bar steel, shaped steel, etc. that are long in the axial direction It can also be used in the cooling step after the heat treatment. Further, when a material to be treated such as a round steel pipe or a square steel pipe is charged into a multi-stage cooling device, it can be treated in a single row or in a plurality of rows with an interval. In particular,
Regarding the rectangular steel pipe, if the rectangular cross-sections are aligned in the shape of an abacus and loaded into a cooling device, the cooling can be performed efficiently, and the cooling condition of the entire peripheral wall of the steel pipe can be made as uniform as possible.

As a device equipped in the cooling chamber, generally, a nozzle for injecting a refrigerant fluid such as room temperature or low temperature air (refrigerant gas), spray, water, indoor atmosphere circulation / agitation fan, heated air exhaust duct, exhaust fan, etc. But you will need it. By appropriately selecting the degree of low temperature of the refrigerant gas, the supply amount, the order of the cooling chambers to be supplied, the position, etc.,
It is not impossible to lightly quench and strengthen the treated steel pipe material. Even in the case of the non-cooling room, equipment that does not prevent uniform radiation of heat and radiation of the heated steel pipe is required, and it is desirable to install a circulation fan for the indoor atmosphere. In addition, a supporting / conveying means for the heated steel pipe can be installed here. In order to prevent the gas warmed in the cooling chamber from flowing into the non-cooling chamber, it is preferable to adjust the gas pressure inside the cooling chamber slightly higher than the pressure inside the cooling chamber. If necessary, an exhaust device or a known cooling, exhausting heat or heat radiating means is installed so that the thermal energy radiated from the heated steel pipe does not stay in the non-cooling chamber and the temperature inside the chamber does not rise.

According to the present invention, (1) a material to be treated which is long in the axial direction is apparently divided into short portions along the longitudinal axis, and heat treatment strains appearing in the direction perpendicular to the axis for gradually cooling them. Less is. (2) A material to be treated which is long in the axial direction can be continuously cooled. (3) Since the bending and twisting distortion of the material to be processed caused by cooling in the longitudinal axis direction are small, the capacity of the cooling device can be reduced accordingly. (4) Since the material to be processed has little bending and twisting distortion, the guide inside the cooling device can be simplified. (5) Since the bending and twisting distortion of the material to be treated is small, the equipment for correcting the distortion of the steel material remaining after the cooling process becomes simple. (6) Since the distortion due to the cooling step is small, the final product can be obtained with a little straightening work, and the quality is improved. (7) If necessary, the heat-treated steel material may be uniformly and forcibly cooled, and the material after the treatment may be lightly quenched and strengthened. (8) It is possible to eliminate or repair brittleness and deterioration of the local member quality due to cold working of the material, make the material of the material to be treated uniform, and provide a high quality product.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A schematic embodiment of a system of the present invention and a multi-stage cooling device for carrying out the system will be described below with reference to the drawings. Details of the device are known to those skilled in the art at the time of the application of the present invention. Within the range of (4), it is possible and appropriate to modify, so unless there is a special reason, the constituent features of the present invention should not be limitedly interpreted based on only the specific structure of this embodiment.

(Part 1) FIG. 1 is a schematic side view of a multi-stage cooling device for continuously and forcibly cooling a steel pipe base material having a unit length.
FIG. 2 shows the relationship between each of the partitioned cooling chambers and a non-cooling chamber (which has no facility for forced cooling means). FIG. 2 shows a peripheral wall of a heated steel pipe conveyed through the multi-stage cooling device and corresponding to each chamber. An example of changes in temperature is shown. In FIG. 1, 1 is a cooling device body,
Its axial length is, for example, 15 m, 2 is a standard length heated steel pipe, for example, a 15 m long round steel pipe, and its size is 21 mm in diameter.
The size is 6 mm and the plate thickness is 10.7 mm.

Reference numerals 3 ₁ , 3 ₂ , 3 ₃ ... Constituting a part of the cooling device 1 , first, second, third ... Cooling chambers. As shown in FIG. 3, cold air jetting or atomizing nozzles 5 are provided at the symmetrical side surface position of the vertical center line of the conveyed round steel pipe group region and its ceiling or / and bottom surface position, respectively, and fluid injection of the nozzles is performed. The direction is set so as to wrap around the entire surface of the heated steel pipe wall being conveyed substantially along the interior wall, and to cool the pipe wall face as uniformly as possible. Its purpose,
In order to achieve this more effectively, a fan 6 that stirs and circulates the atmosphere in the cooling chamber is provided in a suitable place on the inner wall, if necessary. The cross-sectional width of each cooling chamber is large enough to allow a plurality of round steel pipes 2 to pass therethrough.

In the case of the present embodiment, as shown in FIG. 3, a total of three cold air jet nozzles 5 are provided for one cooling chamber cross section, and in order to uniformly cool the peripheral surface of the steel pipe, the jetting is performed. The flow is
Substantially oriented to flow along the furnace wall. The used heating gas and fluid generated in each cooling chamber are sucked from the cooling chamber by a special exhaust means, and they are finally combined into one and exhausted. Although there is a description that a steel pipe supporting / conveying roller is installed on the lower side in the drawing, the roller is generally installed in a non-cooling chamber described below.

Reference numerals 4 ₁ , 4 ₂ ... Comprise another part of the cooling device 1 , first, second ... Non-cooling chambers, which alternate with the cooling chambers 3 ₁ , 3 ₂ ,. One cooling device 1 is arranged as a whole in the longitudinal axis direction and connected, and constitutes one cooling device 1 as a whole. The length of the non-cooling chamber in the longitudinal axis direction is set to an appropriate length in order to make the temperature of the peripheral wall of the round steel pipe during transportation uniform. In addition, when the used gas in the adjacent cooling chamber flows into the non-heating chamber as it is, or when thermal energy is accumulated and accumulated due to radiation from the steel pipe 2 or the adjacent cooling chamber, conduction action, etc., Since the temperature in the room rises further, it is not preferable from the purpose of setting the non-cooling room. In order to prevent this, the inlet / outlet area of the treated steel pipe is made as narrow as possible (the distortion in the longitudinal axis of the steel pipe and the amount of twist are extremely small), or pressure air for cooling is supplied to the room to increase the room pressure. Measures such as maintaining a higher pressure or installing a stirring fan to make the temperature of the atmosphere in the non-cooling room uniform are taken. If necessary, a jacket or a heat energy dissipating fin for circulating a coolant for absorbing heat energy is provided on the peripheral wall of the non-cooling chamber to control the temperature inside the non-cooling chamber.

A guide / support for the steel pipe 2 is provided in the non-cooling chamber.
The transport roller 6 is installed. The same means, to prevent heating due to heat conduction from the cooled steel pipe, etc.,
Install a cooling device. Further, for the purpose of ensuring a mutual interval between a plurality of parallel steel pipes that are loaded and conveyed, a plurality of steel pipe holding grooves (guides) are provided at intervals along the circumferential direction on the circumferential surface of the steel pipe conveying roller. In the case of a square steel pipe, the shape of the guide groove is formed so that the cross section of the square steel pipe is held in a dice-shaped phase (see FIG. 4) and that formed in a soroban-shaped phase (see FIG. 4). 5)). In any case, the distance between the adjacent steel pipes should be such that the refrigerant gas evenly touches the side walls of the steel pipes in parallel conveyance.
For example, it is not preferable to set the diameter smaller than about 1/2 of the pipe diameter.

[0022] In FIG. 2, is heat treated at about 650 ° C., heating the steel pipe which has been carried into the cooling device, thus, is forced evenly cooled while passing through the first chamber of the cooling chamber 3 _1, the peripheral wall temperature Falls to about 450 ° C. This portion, while passing through the indoor first uncooled chamber 4 of _the following, while the steel pipe temperature being forced cooling is generally equalized by thermal conduction, radiation, slightly temperature rises 500 It becomes about ℃. Therefore, the strain of the material due to the forced cooling of the portion is also uniform with respect to the central axis of the steel pipe, and does not appear in the form of external strain. When the steel pipe portion is carried into the second cooling chamber 3 ₂ Subsequently, the location is in the first cooling chamber similar process, the same steel peripheral surface because it is forcibly cooled again substantially, 300
Although the steel pipe is cooled to ℃, when the steel pipe is transferred to the second non-cooling chamber 4 ₂ in the subsequent step, the same action as in the case of the first non-cooling chamber 4 ₁ is performed and the steel pipe is forcibly forced. The temperature of the cooled peripheral wall of the steel pipe is made uniform by heat conduction and heat radiation, and the temperature rises slightly to about 350 ° C.

Therefore, even if a non-uniform thermal expansion strain occurs in the steel pipe 2 forcibly cooled in the second cooling chamber 3 ₂ in the previous step, the steel pipe conveys in the next second non-cooling chamber 4 ₂ . During this, the strain is uniformized and does not appear externally. The homogenized steel pipe temperature is forcibly cooled again in the third cooling chamber 3 ₃ as it passes through the third cooling chamber 33, as in the first cooling chamber, so the circumferential wall surface is approximately 150 ° C. Is cooled down. In the figure, cooling the steel pipe wall temperature from the third cooling chamber 3 ₃ steel-out port side is carried out in ambient air, such as for the size of the heat capacity, slightly raised, rising to about 200 ° C., then, Nature It is left to cool and is slowly cooled to room temperature. As described above, while repeating the process as shown in FIG. 2, a specific portion of the round steel pipe is sequentially cooled while passing through the inside of the cooling device 1 and cooled to a temperature of about 200 ° C., and thereafter, outside the device. Then, the steel is annealed. Although it depends on the capacity of the material to be treated and the transport speed, as mentioned above, the goal is to cool the temperature of the discharged steel pipe to at least about 200 ° C.

Thus, the thick steel plate is plastically deformed by cold working and the residual stress of the formed round steel pipe material, or approximately,
Brittleness and deterioration of the material near each corner of a square steel pipe bent by 90 ° are tempered by heat treatment, and the steel material at that location has a large material elongation against external force, and the tensile strength and yield point The ratio can be returned to the old one. Further, if necessary, by lightly quenching the steel material by uniformly quenching it, the product material softened by the heat treatment can be strengthened. In this embodiment, the material to be treated is a round steel pipe or a rectangular steel pipe having a standard length, and the material to be treated is intermittently charged into the multi-stage cooling device. There is almost no difference in the annealed state of the material in the vicinity even in the case where the material to be treated is continuously inserted.

(No. 2) FIG. 4 shows a front sectional view of another embodiment of one of the non-cooling chambers constituting the multi-stage cooling device. The heat-treated steel pipe 2 conveyed therein has a peripheral surface. The refrigerant gas is held in a dice-shaped cross section on the transport roller so that the refrigerant gas uniformly contacts (including the cooling chamber). In the figure, grooves 8 equidistantly spaced from each other are provided in the circumferential direction on the peripheral surface of the elongated conveying roller 7 which is horizontally supported and driven, and square steel pipes 2 which are conveyed in parallel in the cooling chamber are provided at the same place. A peripheral portion of the steel pipe is placed and guided, and the steel pipe peripheral walls are secured to each other and conveyed in the longitudinal axis direction. In the present embodiment, four standard length steel pipes are arranged and placed in the cooling device at one time, but it goes without saying that a continuous round steel pipe or a square steel pipe may be used.

Correspondingly, the conveying roller member 7 for the material to be treated is constituted by a roller member having an axial length which is a multiple of the steel pipe diameter. It is provided in advance so that the adjacent distance when the steel pipe is placed on the roller becomes a predetermined length. In addition,
The arrangement of the grooves does not need to be roughly set because the amount of distortion and twist of the steel material due to cooling is small. Also,
The transport roller is provided with a cooling means in order to prevent it from being heated by heat conduction from a steel pipe or the like. Reference numeral 9 is an opening through which the plurality of heat-treated materials are loaded and unloaded,
The opening cross-sectional area is as narrow as possible in view of thermal efficiency. In the case of this embodiment, since the amount of bending and twisting in the longitudinal direction of the steel pipe due to the progress of the cooling process is extremely small, the opening area can be made as narrow as possible.

(No. 3) FIG. 5 shows a front sectional view of another embodiment of a non-cooling chamber, which is a component of a multi-stage cooling device for inserting and refining a plurality of steel pipes at the same time. The heat-treated steel pipe 2 is held on the conveying roller in a soroban-shaped cross section so that the refrigerant gas uniformly contacts the peripheral surface (including the cooling chamber). In the figure, an elongated conveying roller 7 which is horizontally supported and driven is provided below the non-cooling chamber and is provided with grooves 8 equidistant from each other in the circumferential direction on the roller peripheral surface. One corner portion of the square steel pipe 2 to be transported into the cooling chamber is placed at the same position to secure a space between the adjacent steel pipes, while transporting the steel pipe in the longitudinal axis direction. Therefore, the mutual intervals of the grooves on the roller peripheral surface are provided in advance so that the adjacent distance when the steel pipe having the maximum handling diameter is placed on the roller has a predetermined length.

[0029]

Since the multi-stage cooling system of the present invention is as described above, (1) a material to be treated which is long in the axial direction is divided into apparently short portions in the longitudinal direction, and these are gradually In addition, since the cooling is performed forcibly in sequence, and the non-cooling is repeated to cool the whole, thermal expansion strain in the direction perpendicular to the axis due to cooling hardly occurs. (2) Since the material to be treated is hardly distorted by cooling or is extremely small, the cross-sectional areas of the cooling chamber and the non-cooling chamber can be reduced when the steel pipes are loaded in parallel. (3) Therefore, the guide of the material to be processed provided in the apparatus is also simplified. (4) In addition, the opening area that separates the cooling chamber and the non-cooling chamber can be set as narrow as possible, and efficient operation of heat energy is possible. (5) Since the amount of strain and twist generated in the material to be treated is small, the strain correction equipment after the cooling process is simple and good.

(6) Deterioration of material due to cold plastic working,
Recover brittleness and provide high quality products. (7) A continuous cooling process of the material to be processed is also possible. And so on, there are special actions and effects that cannot be expected by the conventionally known steel heat treatment means. In the multi-stage cooling system of the present invention, as a material to be treated, it is also possible to prepare a material such as a steel bar or a shaped steel. Further, heat treatment of a continuous material, annealing of a standard length material, single material, or simultaneous formation of a plurality of materials is possible.

[Brief description of drawings]

FIG. 1 is a schematic side view of an embodiment of a multi-stage cooling device that implements a cooling system of the present invention.

FIG. 2 is a heat and temperature distribution diagram of the steel pipe peripheral wall in the longitudinal axis (conveyance) direction of the material to be treated in the multi-stage cooling system.

FIG. 3 is a front sectional view of an example of a cooling chamber of a multi-stage cooling device that implements the cooling system of the present invention.

FIG. 4 is a front cross-sectional view of another embodiment of the non-cooling chamber that constitutes the multi-stage cooling device that implements the cooling system of the present invention.

FIG. 5 is a front sectional view of another embodiment of a non-cooling chamber that constitutes a multi-stage cooling device that implements the cooling system of the present invention.

[Explanation of Codes] 1 multi-stage cooling device 2 material to be heat treated (steel pipe) 3 ₁ cooling chamber 4 ₁ non-cooling chamber 5 refrigerant injection nozzle 6 stirring fan 7 conveying roller 8 steel pipe supporting groove 9 opening.

Claims (2)

[Claims] 1. A cooling device is divided into a plurality of compartments along a conveyance direction of a material to be treated, and a forced cooling chamber for the material to be treated and a non-cooling chamber for the material to be treated are alternately arranged with respect to each of the compartments. A multi-stage cooling device for steel pipes characterized by being provided. 2. The material to be treated which is long in the axial direction is forcibly cooled by being brought into contact with the refrigerant gas evenly from the tip portion thereof while passing through the first compartment cooling chamber while being conveyed in the cooling device. Then, when passing through the second compartment non-cooling chamber, the heat retained in the forcibly cooled steel pipe is naturally and uniformly dissipated, and heat conduction is performed, and then the third compartment cooling chamber is passed. Then, it again comes into contact with the refrigerant gas and is forcibly and evenly cooled, whereby the slightly lowered steel pipe temperature is then naturally dissipated uniformly in the fourth compartment non-cooling chamber, and heat conduction is performed. The temperature is gradually lowered by repeating the step of forcibly and uniformly cooling in the fifth compartment cooling chamber a plurality of times to suppress the generation of strain of the material to be treated due to the cooling and to make the whole uniform. A multi-stage cooling system for steel pipes, characterized by heat treatment to.