JPH059582A - Multi-stage heating furnace and heating system for steel pipe - Google Patents

Abstract

PURPOSE:To provide the multi-stage heating device and system which execute efficient heating and a heat treatment without generating bends and twist along the longitudinal axis and work large-diameter steel pipes having uniform and stable quality in the continuous heat treatment system 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 heating furnace and heating system for the steel pipes consist in segmenting the heat treating furnace to plural sections in the longitudinal axis direction, alternately installing heating chambers and non-heating chambers in each one of these sections, thermally shutting off these chambers from each other, successively heating the materials to be treated while successively repeating heating and heat dissipation during the continuous transportation of these materials through the above-mentioned chambers, and finally subjecting the materials to a heat treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in a process of cold-plasticizing a thick steel plate to form a round steel pipe or a rectangular steel pipe, deterioration of local member quality of the steel plate and generation of residual stress due to bending work. On the other hand, a method for improving the material quality of a large-diameter round steel pipe or square steel pipe, in which the formed steel pipe material is heated to a uniform predetermined temperature for a certain period of time and tempered so as to restore the deterioration of the steel material due to cold working. Regarding

[0002]

2. Description of the Related Art The mass production method of a one-seam or two-seam large-diameter rectangular steel pipe, which is used as a column of a building and is formed by bending a thick steel plate, is roughly classified into practical use, regardless of the literature. The following construction methods are 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 a square steel pipe, both side edges of the steel sheet are butt-welded to form a one-seam large-diameter steel pipe with a square 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 after undergoing a sizing process, an electric resistance welded round steel pipe is manufactured once, and then the cross section of the round steel pipe is shaped into a square shape to have a large diameter of one seam. Form a square steel pipe. Also, a one-seam large-diameter round steel pipe is formed in the middle of the above-mentioned construction method. One seam large diameter round steel pipe forming method is
In addition to this, the UO press system and the like are used. Such construction methods are widely used in detail, even if there are slight differences. As described above, the conventional economical economical manufacturing method for a large-diameter round steel pipe or a square steel pipe is, in any case, cold plastic deformation of a thick steel plate, that is, a thick steel plate for forming a steel pipe. Cold-bending of, or approximately 90 ° cold-bending for corner steel plates for forming square steel pipes is included.

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

Conventionally, regarding the specifications of this kind of large-diameter round steel pipe or square steel pipe, the demand has been increased because the merit was recognized mainly in the shape / structural characteristics or the construction characteristics. Looking at the molding and processing conditions,
Large-diameter steel pipes tended to be distributed in the market without sufficient objective and technical analysis and examination of 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, and are also being used as columns for medium- and high-rise buildings.
There is an increasing interest or remorse from consumers and experts that the deterioration of the local member quality due to the cold bending during steel pipe forming may accelerate the brittleness change of the location.

[0006]

According to the method of the present invention, in response to a request from those users, etc., a corner portion of cold plastic deformation in a large diameter round steel pipe or a rectangular steel pipe formed by a conventionally known manufacturing method is provided. The present invention aims to provide a multi-stage heating furnace or a multi-stage heating system for steel pipes used for heat treatment, in order to recover the deterioration of the steel sheet material at the relevant location by annealing the steel material. That is, regardless of whether the round steel pipe is heat-treated by cold forming or the square steel pipe is annealed, it is necessary to accommodate a steel pipe of a standard length long in the axial direction that can be used for a column and simultaneously heat it over the entire length. Since it is difficult to control the temperature inside the furnace uniformly and uniformly by installing a long furnace that can be operated, it is unavoidable that a temperature difference will occur in the furnace depending on the location. The same applies to the heating temperature. And when a temperature difference occurs in the axial direction of a long steel pipe, thermal expansion strain occurs as a whole, the steel pipe bends,
The material is not stable due to twisting, etc., and after heat treatment, large equipment is required to correct the distortion. Further, in the above heat treatment method, a heating furnace for that purpose cannot be installed in-line in the molding apparatus.

[0007] Therefore, the applicant of the present invention, the inside of the heating furnace,
The material to be heat-treated was divided into a plurality of parts along the transport direction of the longitudinal axis, which were alternately divided into heating chambers and non-heating chambers, and they were arranged so as to be connected in series in a plurality of stages, and were placed in a heating furnace. While transporting the steel material (pipe) through the compartment,
Sequential heating from the tip portion, then, the heating temperature of the steel material part is made uniform in the part of the furnace that is not heated to release the distortion of the steel material based on the temperature difference, and further, in the second heating chamber of the furnace, By repeating the process of reheating the steel material part, the heating temperature of the steel material is gradually increased and the distortion of the steel material due to the heating is dispersed, and as the temperature rises, a large distortion is generated in the heat treated material as a whole. A multi-stage heating furnace or heating method with little or no occurrence was proposed (see Japanese Patent Application No. 2-219996, Heating furnace and method for square steel tube without strain).

By the way, in the method of sequentially heating the material to be heat-treated in the heating furnace in the longitudinal axis direction, it is possible to control the heating temperature of each heating chamber so that the heating temperature of each heating chamber is uniform. It was found that the heating efficiency was not good. That is, in the multi-stage heating furnace, the temperature of the heating chamber on the side where the material to be heat-treated is loaded is set higher, and a temperature gradient is applied to the heating chamber so as to sequentially lower the heating temperature in the processing material transport direction. However, it has been found that the heating energy can be used most efficiently and effectively in a short time to heat the steel pipe to a necessary temperature before it is carried out from the heating furnace.

In the multi-stage heating system, since the steel pipes at room temperature are successively carried into the first compartment heating chamber and the furnace portion close to the heating chamber, one after another, the temperature of the steel pipe is higher than that of the entire furnace.
It is understood that by controlling so as to maintain a higher temperature atmosphere in the furnace, it is possible to effectively heat the incoming steel material. Therefore, an object of the present invention is to develop a multi-stage heating furnace based on the above-mentioned novel knowledge, and to provide a multi-stage heat treatment method with good thermal efficiency that minimizes the occurrence of distortion or twisting of a steel pipe due to heat treatment.

[0010]

In order to achieve the above-mentioned object, the present invention has the respective constituent features as described below. (1) The inside of the heating furnace is divided into a plurality of sections along the conveyance direction of the material to be heat treated, and heating chambers and non-heating chambers for the material to be heat treated are alternately provided for each of the sections, and The multistage heating furnace for steel pipes is characterized in that the heating room temperature is higher in the carry-in side heating chamber of the material to be heat treated, and is relatively low as it goes to the carry-out side heating chamber side.

(2) The material to be heat treated which is long in the axial direction, while being conveyed in the furnace, is sequentially and evenly heated from its tip portion while passing through the higher temperature first compartment heating chamber, and then the second compartment. When passing through the non-heating chamber, the heating temperature of the steel pipe is made uniform without being heated, and then passes through the third-compartment heating chamber, which is next high in temperature, and is uniformly heated again, and then at the fourth temperature. Generation of strain of the heat-treated material due to heating by repeating the step of equalizing the temperature while passing through the compartment non-heating chamber and further sequentially heating in the fifth compartment heating chamber having a low temperature due to heating. This is a multi-stage heating method for steel pipes, characterized in that the entire heat-treated material is heat-treated at a uniform required temperature.

[0012]

The heat treatment material having a standard length is charged and conveyed through the divided heating furnaces that are thermally isolated from each other, and the first heating chamber (first division) of a higher temperature atmosphere is supplied from the tip portion thereof. ), While the heated portion is being carried into the next first non-heating (cooling) chamber (second compartment), it is exposed to or blows against the refrigerant gas in the same chamber. While the heating temperature of the heat treated material is dissipated to the outside air, the temperature of all materials is made uniform by the action of heat conduction and the thermal expansion strain caused by unequal heating is released and dispersed. When the part of the material to be heat treated is carried into the second heating chamber (third section) of the furnace, the part is set to a heating room temperature atmosphere that is slightly lower than the heating temperature of the first heating chamber. That portion of the is reheated at that heating temperature. When the same portion is further conveyed to the second non-heating chamber (fourth section), the same operation as the first non-heating chamber is performed, and the heating temperature of the heat-treated material is equalized and the thermal expansion strain is dispersed. Done.

The next heating temperature atmosphere of the third heating chamber (fifth section) is set to be slightly lower than that of the second heating chamber. The function of the third non-heating chamber (sixth section) is
The action in the first non-heating chamber described above may be understood to be substantially the same. By repeating these steps in sequence,
When the material to be heat treated within a certain time passes through the steel pipe unloading port of the heating furnace, all of the material to be treated is raised to the required heating temperature without any apparent distortion, and if necessary, then slowly. Further, the annealing of the steel pipe material is completed by uniformly lowering the heating temperature. The multi-stage heating furnace or heating method for annealing the heat-treated material as described above is suitable for large-diameter steel pipe forming equipment because of the tempering of steel materials such as thick-walled large-diameter square steel pipe corners, welded joints, and welding points. Not only can it be installed in-line, but it can also be used for heat treatment of round steel pipes, steel bars, shaped steels, etc. that are long in the axial direction.

Further, the material to be heat-treated such as a round steel pipe or a rectangular steel pipe can be carried in a single row or in a plurality of rows at intervals when being loaded into a multi-stage heating furnace, and can be heat treated collectively. In particular, for a rectangular steel pipe, if the rectangular cross-sectional phase is aligned in the shape of an abacus and loaded into a heating furnace, the efficiency and uniform heating of the steel pipe will be uniform. As the heating means equipped in the heating chamber, a gas burner, LPG, LN
Burners using G, light oil, kerosene, heavy oil, and the like as fuels, electric heating means such as electric heating, induction heating, and the like are known, and each can be used as necessary.

According to the present invention, (1) a material to be heat treated that is long in the axial direction is divided into apparently short portions along the longitudinal axis, and thermal expansion that appears in the direction perpendicular to the axis in order to gradually heat these. There is little distortion. (2) A material to be heat-treated which is long in the axial direction can be continuously heat-treated. (3) Since the steel material is passed through a relatively high temperature heating furnace from the beginning, it is easy to obtain a required heat treatment temperature without fear of roughening the skin. (4) Since the amount of bending and twisting of the material to be heat-treated caused by the heat treatment is small, it is possible to simplify the equipment for correcting the strain remaining in the steel material after the heat treatment. (5) The structure of the heat-treated material is made uniform, and the material is stable. (6) If necessary, the material to be heat treated can be uniformly and forcibly cooled after heating, and the material can be lightly quenched to strengthen it. (7) Brittleness and deterioration of the local material due to cold working of the material can be eliminated or repaired, and a high quality product can be provided.

[0016]

EXAMPLES The following is a description of the examples of the present invention and a multi-stage heating furnace for carrying out the same, with reference to the drawings. The details of the furnace are known to those skilled in the art at the time of this application. Within the range of, it can be modified appropriately,
Unless there is a special reason, the constituent features of the present invention should not be limitedly interpreted based on the specific structure of this embodiment.

(No. 1) FIG. 1 is a schematic side view of a multi-stage heating furnace for continuously refining a standard length steel pipe base material, showing the relationship between the temperature inside the furnace and the non-heating chamber 2 is shown in FIG.
[Fig. 3] is a front sectional view of one of heating chambers constituting the heating furnace. In FIG. 1, 1 is a heating furnace main body, and its axial length is
For example, 12m to 13m, 2 is a material to be heat-treated and has a standard length, for example, a round steel pipe with a length of 12m, and its size is 216φm in diameter.
m, plate thickness 10.7 mm. 3 ₁ , 3 ₂ , 3 ₃ ... are heating furnaces
1. The first, second, third ... heating chambers forming a part of each of the above-mentioned ones.
As shown in FIG. 5, gas burners 5 are provided at positions on the symmetrical side of the vertical center line of the conveyed round steel pipe group region and its ceiling position, and the fuel (flame) injection direction of the burner is:
It is arranged so as to flow substantially along the inner wall of the room so as to wrap around the peripheral wall surface of the steel pipe to be conveyed, and to heat the pipe wall as uniformly as possible. In order to achieve that purpose more effectively, a fan 6 that stirs and circulates the atmosphere inside the heating chamber is provided at an appropriate place on the indoor wall.

The width of the cross section of each heating chamber is set to a certain degree so that a plurality of round steel pipes 2 can pass through. However, the interval between the parallel adjacent steel pipes is, for example, 1/2 of the pipe diameter so that the heating gas is evenly contacted with the lateral side of the peripheral walls of the parallel pipes.
It is not preferable to set the width narrower than that. In the case of the present embodiment, the combustion gas generated in each heating chamber is sucked from the heating chamber by a special exhaust means, and they are finally exhausted together as one. Although a roller for supporting the material to be heat treated is shown in the figure, the roller is actually installed in the non-heating chamber. Further, when the combustion gas in the heating chamber flows out to the adjacent non-heating chamber side as it is, the temperature of the non-heating chamber further rises, which hinders this. In comparison, it is kept at a higher pressure.

Thus, the room temperature of the first heating chamber (first section) 3 ₁ is set to be maintained and controlled at approximately 1250 ° C., and the temperature of the next second heating chamber (third section) 3 ₂ is set. room temperature, approximately, is set to maintain a 1000 ° C., room temperature in the third heating chamber (fifth compartment) 3 _3, substantially, is controlled to maintain 800 ° C., in the figure, the steel out opening side indoor temperature of the fourth heating chamber (seventh compartment) 3 _4, substantially, is controlled to hold the 800 ° C.. Although it depends on the capacity of the material to be heat treated and the transport speed, the temperature of the unloading steel pipe is about 300 ℃ to 400 ℃.
The goal is to be heated to about ℃.

Reference numerals 4 ₁ , 4 ₂ , 4 _3, ... Are first, second, third ... Non-heating chambers that constitute another part of the heating furnace 1 .
Alternate to the heating chambers 3 ₁ , 3 _2, ... And one by one, they are arranged side by side in the longitudinal direction of the heating furnace and connected, and constitute one heating furnace 1 as a whole. A guide roller 7 for the steel pipe 2 is installed in the non-heating chamber. The means must be equipped with a cooling device to prevent heating due to conduction heat from the heated steel pipe and the like. Alternatively, the non-heating chamber may be opened to the outside air for that purpose. In order to secure the mutual space between the parallel steel pipes, a plurality of steel pipe holding grooves (guides) are provided at intervals on the circumferential surface of the steel pipe conveying roller along the circumferential direction. In case of square steel pipe,
Regarding the shape of the guide groove, one formed so that the square steel pipe cross section is held in the dice phase (see FIG. 3) and one formed so as to be held in the abacus phase (see FIG. 4) are
possible.

In the non-heating chamber, heat energy is accumulated and accumulated due to radiation, conduction action or combustion gas inflow from the steel pipe 2 or the adjacent heating chamber, and the chamber cannot maintain its respective predetermined temperature. In order to prevent this, the area for loading and unloading the steel pipe is set as narrow as possible (this is possible because there is no heat treatment distortion in the steel pipe), and pressurized air for cooling is supplied to the chamber to increase the pressure. The room temperature of the non-heating chamber can be controlled by maintaining the state and providing a jacket or a heat energy dissipation fin for circulating a heat medium for absorbing the heat energy on the peripheral wall of the non-heating chamber, if necessary. Further, the length of the non-heating chamber in the longitudinal axis direction is appropriately set in order to make the heating temperature of the peripheral wall of the round steel pipe during transportation uniform. Again in FIG. 1, the standard length steel pipe 2
Is sent to the heating furnace 1 at outside temperature of 15 ℃ (base material temperature), and the speed is 6
When charged at m / min, first the first heating chamber (first section)
While passing through 3 ₁ , it is heated by touching high temperature gas and the temperature of the peripheral wall of the pipe rises up to about 200 ℃, but while this part passes through the next 1st non-heating chamber (2nd section) 4 _1. The uneven heating temperature of the steel pipe is made uniform by conduction, and the radiant heat is lost, so that the temperature of the steel pipe part is lowered to about 150 ° C as a whole. Therefore, the strain of the material due to the thermal expansion of the portion is also uniform with respect to the central axis and does not appear in the form of external strain.

[0022] The steel pipe is carried into the second heating chamber (third compartment) 3 ₂ Subsequently, the tube wall temperature the location is heated again rises to about 400 ° C., the second unheated thereafter step when passing through the chamber (fourth compartment) 4 _2, the heating temperature is equalized, and a slight temperature drop occurs. As a result, even if uneven thermal expansion strain occurs in the steel pipe 2 heated in the second heating chamber 3 ₂ in the previous step, while the steel pipe is transported in the second non-heating chamber 4 ₂ next, The distortion becomes uniform and does not appear externally. As shown in FIG. 1, the temperature distribution in the furnace is characterized in that the temperature of the heating chamber is set lower as the temperature of the heating chamber becomes closer to the outlet of the material to be heat treated.

As described above, while repeating the steps shown in FIG. 1, a specific portion of the round steel pipe is sequentially heated while passing through the heating furnace 1 for about 4 minutes, so that the base material temperature of the material to be heat treated is increased. The temperature rises to a maximum of 300 ℃ ~ 400 ℃, and after being taken out of the furnace, by gently cooling it by air,
Annealing of steel is completed. Thus, the thick steel plate is plastically deformed by cold working, and the residual stress of the formed round steel pipe material or the brittleness and deterioration of the material near each corner of the square steel pipe formed by bending at approximately 90 ° are heat treated. Tempered by
With respect to the steel material at the location, the material has a large elongation with respect to an external force, and the ratio of tensile strength and yield point can be returned to an old one. Further, if necessary, the heat-treated steel pipe may be rapidly quenched uniformly and lightly quenched to strengthen the product material softened by the heat treatment.

In this embodiment, steel pipes of standard length are arranged side by side.
Although it is arranged that the main body is charged into the heating furnace at once, it goes without saying that the continuous round steel pipe or the rectangular steel pipe may be heat-treated. Further, the material to be heat treated is a round steel pipe or a rectangular steel pipe having a standard length, and the material to be heat treated is inserted into the heating furnace 1 intermittently. The degree of annealing was almost the same in the case of continuous filling, but there was no difference.

( No. 2) FIG. 4 shows a front sectional view of one of the non-heating chambers which constitute the heating furnace 1. The square steel pipe 2 to be heat-treated which is conveyed here (including the heating chamber) is shown in FIG. , The cross-sectional phase is maintained in a soroban shape so that the gas flow contacts the peripheral surface evenly. In the non-heating chamber shown in the figure, a plurality of standard length square steel pipes 2 are installed in parallel and charged and tempered at the same time.
On the lower side of the room, an elongated steel pipe transport roller 7 is arranged which is axially driven horizontally across the same room, and a plurality of grooves 8 are arranged on the roller circumferential surface at equal intervals along the circumferential direction. Provided,
One corner of the square steel pipe 2 is placed in the groove and is conveyed in the longitudinal axis direction.

The distance between the grooves 8 on the peripheral surface of the conveying roller 7 is set in advance so that the adjacent distance between the steel pipe peripheral walls when the steel pipe having the maximum handling diameter is placed on the roller 7 becomes a predetermined length. It is provided. Correspondingly, the transport roller member 7 is composed of a roller having a length that is a multiple of the steel pipe diameter in the axial direction. The roller 7 is equipped with the forced cooling means as described above. Reference numeral 9 denotes an opening through which the plurality of heat-treated materials are loaded and unloaded, and the opening cross-sectional area is as narrow as possible in view of thermal efficiency. For other configurations and operations of this embodiment, refer to the description of the embodiment (part 1).

[0027]

The multi-stage heating furnace and heating system of the present invention are as described above. (1) The material to be heat treated which is long in the axial direction is apparently divided into short portions in the longitudinal direction, and these are divided. Since heating is performed at a high temperature by gradually and sequentially heating and cooling, the thermal expansion strain in the direction perpendicular to the axis is unlikely to occur. (2) Since the temperature of the heating chamber on the side of the material to be heat treated is set and controlled to be higher, the desired heat treatment is performed in the shortest possible time, and the cost increase factor due to the above treatment is reduced. it can. (3) Since the material to be heat treated is less likely to bend and twist, the cross-sectional volume of the heating chamber can be reduced when steel pipes are loaded in parallel. (4) Therefore, the guide of the material to be heat-treated provided in the furnace can be simplified. (5) Since the strain generated in the heat-treated material after heat treatment is small,
Post-process strain correction equipment is simple and good. (6) To provide uniform and high-quality products by recovering deterioration and brittleness of materials due to cold plastic working. (7) It is also possible to continuously heat-treat a material to be heat-treated.

[0028] And so on, a special action and effect which cannot be expected by the conventionally known steel heat treatment means are exhibited. Further, continuous material processing, annealing of standard length material, single material, or simultaneous plural material processing is possible.

[Brief description of drawings]

FIG. 1 is a schematic side view of an embodiment of a multi-stage heating furnace that carries out the heating system of the present invention.

FIG. 2 is a front sectional view of one of heating chambers constituting the multi-stage heating furnace.

FIG. 3 is a front sectional view of another embodiment of the non-heating chamber constituting the heating furnace of the present invention.

FIG. 4 is a front sectional view of another embodiment of the non-heating chamber constituting the heating furnace of the present invention.

[Explanation of symbols]

1 Multi-stage heating furnace 2 Heat treated material (steel pipe) 3 heating chambers 4 Non-heating room 5 heating burner 6 stirring fan 7 Conveyor rollers 8 Steel pipe support groove 9 openings

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C21D 11/00 101 8928-4K F27B 9/02 7308-4K F27D 19/00 A 8825-4K

Claims (2)

[Claims] 1. The heating furnace is divided into a plurality of sections along the conveyance direction of the material to be heat-treated, and heating chambers and non-heating chambers for the material to be heat-treated are alternately provided in every other section with respect to the section. The heating room temperature is such that the temperature of the heating chamber on the loading side of the material to be heat treated is higher, and the temperature is controlled to be relatively low as it goes to the heating chamber on the unloading side. Furnace. 2. The material to be heat treated which is long in the axial direction, while being conveyed through the furnace, while passing through the first compartment heating chamber having a higher temperature,
It is heated evenly from its tip part in order, and then, when passing through the second section non-heating chamber, the heating temperature of the steel pipe is made uniform without being heated, and the third section heating chamber, which is next high temperature, is heated. Passing, again heated uniformly, then while passing through the fourth compartment non-heating chamber, the temperature is made uniform, and further, the step of heating in the fifth compartment heating chamber having a lower temperature, a plurality of times, A multi-stage heating method for a steel pipe, characterized in that the occurrence of strain in the material to be heat-treated due to heating is suppressed by repeating, and the entire material to be heat-treated is heat-treated at a uniform required temperature.