JPH04103721A - Heating furnace and working method for unstrained angular steel tube - Google Patents

Abstract

PURPOSE:To provide the heating furnace by dividing the inside of the heating furnace into plural sections in the traveling direction of a material to be treated and setting a material heater in every other section to form a heating chamber. CONSTITUTION:First to third heating chambers 31-33 each provided with four heating burners 5 symmetrical to the center axis of a conveyed continuous round steel tube 2 are provided to a heating furnace 1 in its longitudinal direction. First to third unheated chambers 41-43 are furnished alternately between the heating chambers. The tube 2 to be refined at the atmospheric temp. of 15 deg.C is introduced into the furnace 1 and heated in the heating chamber 31, and its peripheral wall is heated to about 200 deg.C. The part is soaked in the unheated chamber 41 by conduction, the radiant heat is lost, and the part is adjusted to about 150 deg.C. Consequently, the strain of the base material due to the thermal expansion of the part concerned is uniformized with respect to the center axis, and the external strain is not caused. The steel tube is further heated in the heating chamber 32 and unheated chamber 42, the process is repeated, and the specified part of the steel tube is heated to a requisite temp. in the furnace 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for forming large-diameter square steel pipes, in which a corner portion of a square steel pipe is formed by cold plastic working of a thick steel plate. In order to deal with local material deterioration and residual stress in steel sheets due to bending, the parts corresponding to the steel pipes are heated to a specified temperature for a certain period of time to improve the quality, thereby repairing the deterioration of the steel sheet material due to cold working. , relates to a material improvement method for a part of a corner of a large-diameter square steel pipe where the seam line is located on a side other than the corner.

[Conventional technology]

The mass production method of one-seam or two-seam large-diameter rectangular steel pipes, which are used as columns in buildings by bending and forming thick steel plates, has traditionally been broadly divided into two types: A steel plate is bent at four corners parallel to the longitudinal axis and overlapping in the width direction, the cross section is formed into a shape similar to a square steel pipe, and the edges on both sides of the steel plate are butt welded. Then, a one-seam steel pipe with a square cross section is formed.

■- A steel plate is bent in two places along the width direction to form a U-shaped cross section, and a pair of steel plates with a rectangular cross section is formed by facing each other, and the edges of both legs are butt welded to form a tool. - Manufacture seam square steel pipes.

■The steel strip is conveyed in the longitudinal direction and passed through a round steel tube forming roll stand to produce a jointed round steel tube, and then the cross section of the round steel tube is shaped into a square shape to create a one-seam size. Form a square diameter steel pipe.

Although there are slight differences in the details of the construction methods, they are widely used.

As mentioned above, conventionally implemented economical manufacturing methods for large-diameter square steel pipes include cold plastic deformation of thick steel plates, that is, rough deformation of steel plates to form corners. Includes 90° cold bending.

By the way, when cold is applied to a flat thick steel plate, the angle is approximately 90°.
When the bending process is performed, even if the required R (outer radius) is given to the bent part of the steel plate, in the cross section of the corner steel material, the tensile force is applied to the material outside the neutral plane. Since there is no compressive force acting on the inside, cold plastic deformation takes place, and as a result, the material at that location has little elongation and the ratio between tensile strength and yield point of the material becomes extremely small, causing material deterioration and deformation at the deformed location. There is no risk of brittle fracture occurring if repeated stress is applied.

Further, even after the external force is removed, residual stress is still generated due to cold plastic working.

However, conventionally, the specifications of this type of large-diameter rectangular steel pipe have mainly focused on its shape and structural characteristics, namely: (1) The cross section per unit weight is 2. It has a large moment of order and section modulus, and is resistant to external bending and torsion forces.

(2) It has a large secondary radius of cross section and is strong against buckling.

(3) Good balance of cross-sectional characteristics in the X=Y direction.

(4) The cross-sectional area of the column can be made relatively small;
It is possible to increase the usable area ratio for the same building floor area.

(5) Since the cross section is box-shaped, the material can be used exposed without damaging its aesthetic appearance.

(6) Fireproof coating, painting, and other decorations and construction around the column are easy and economical.

Demand was growing due to the recognition of the advantages of construction features such as these, but looking back at the processing conditions described above, it is necessary to conduct an objective and technical analysis of the material weaknesses or unstable parts inherent in square steel pipes. There is a tendency for the large diameter rectangular steel pipes to be distributed on the market without sufficient consideration.

However, in recent years, large-diameter square steel pipes formed by cold bending have been frequently used as columns in buildings, and
As the steel pipe is intended to be used as a column for high-rise buildings, the problem arises that the deterioration of the material due to the cold bending process during steel pipe forming may accelerate brittle changes at the relevant location. , consumers' interest or remorse is increasing.

[Problem to be solved by the invention]

The construction method of the present invention has been developed in response to requests from users, etc.
The present invention provides a heating furnace or a method for heating a steel plate for annealing a steel material near a corner of cold plastic deformation in a large-diameter square steel pipe formed based on a conventionally known manufacturing method to repair deterioration of the steel plate material at that location. That is.

That is, whether heat treating a round steel pipe by cold-open forming or annealing a square steel pipe material, a heating furnace is required to heat the steel material at a required temperature for a predetermined period of time.

Even if the steel pipes are charged and heated in a long furnace that can simultaneously heat the entire length of axially long round steel pipes or square steel pipes that can be used for columns, the steel pipes will be heated uniformly over their entire length. It is almost impossible to do so, and it is inevitable that temperature differences will occur depending on the location.

A heating furnace 10 shown in FIG. 7 is a conventionally known furnace and treatment method for refining standard rectangular steel pipes having corners formed by a plurality of cold plastic workings as shown in FIG. 8. This shows that.

The heating furnace 10 is equipped with a charging port 11 on one side, has an internal volume long enough to accommodate a regular rectangular steel pipe, and has a plurality of heating burners arranged at required parts of the furnace wall. ,
In front of the charging port 11 are hung doors 12 whose weights are balanced by weights 13 and 13, respectively. In addition, 14 is
This is a pulley that pulls the wire connecting the door 12 and the weight 13.

After raising the door J2 and opening the charging port 11 of the furnace 10,
A standard long, large diameter rectangular steel pipe 8, which is a material to be treated, is charged into the furnace through the same port 11.

At this time, since the axially long steel pipe 8 is heated at the same time, it is impossible to uniformly heat the entire pipe, and temperature differences occur depending on the location, resulting in large thermal expansion strain in the steel pipe 8.

When a temperature difference occurs in a long steel pipe in the axial direction, a large strain occurs as a whole, making uniform heating of the steel pipe difficult and requiring large-scale strain straightening equipment for subsequent processing.

Therefore, the present invention divides the inside of the heating furnace into a heated part and a non-heated part along its longitudinal axis, and constructs a plurality of these parts in series so that the steel material charged into the heating furnace is (pipe) from its tip, then equalize the heating temperature of the steel material in the part of the furnace that is not heated to equalize the distortion of the steel material due to temperature difference, and then heat the part of the furnace that is heated again. By repeating the process of reheating the steel material, the heating temperature of the steel material is gradually raised, and the strain caused by heating is dissipated, and as the temperature rises, large distortions occur in the material to be treated as a whole. The purpose is to develop a heating furnace or heating method that rarely or does not occur.

[Means to solve the problem]

In order to achieve the above object, the present invention includes the following constituent elements.

(1) The interior of the heating furnace is divided into a plurality of sections along the conveyance direction of the material to be treated, and every other section is a heating chamber in which a heating device for the material to be treated is installed. A heating furnace made of rectangular steel pipes that produces no distortion.

(2) While the axially long workpiece is being conveyed through the furnace, it is heated sequentially from its tip while passing through the first section, and then is not heated when passing through the second section. By sequentially repeating the steps of equalizing the heating temperature, passing through the third section, being heated again to a higher temperature, and then equalizing the temperature in the fourth section, the heating-based A distortion-free heating method for square steel pipes that suppresses the occurrence of distortion in the material to be treated and heats the entire material to the required temperature.

[For production]

A long material to be treated in the axial direction is transported and charged into a thermally partitioned heating furnace, and is heated from the tip surface part in the first heating chamber of the furnace, and the heated part is heated in the first non-heating chamber of the furnace. While being carried into the chamber, the heating temperature of the relevant part is made uniform throughout the material by effects such as thermal conduction, and the thermal expansion strain caused by uneven heating is dispersed.

When the part of the material to be treated is carried into the second heating chamber of the furnace,
The same portion is reheated to a temperature slightly higher than the heating temperature of the first heating chamber.

When the same portion is further conveyed to the second non-heating chamber, the heating temperature of the material to be processed is equalized and the thermal expansion strain is dispersed, as described above.

By repeating these steps one after another, the entire material to be treated can be heated to the required heating temperature within a certain amount of time without any apparent distortion, and if necessary, the same temperature can be maintained for the required time. Complete the annealing of the material.

The heating furnace or heating method for annealing the material to be treated as described above is useful not only for refining steel parts such as corners of large-diameter square steel pipes, welded joints, and welded parts, but also for annealing long round steel pipes and steel bars in the axial direction. It can also be used for heat treatment for etc.

Moreover, when the materials to be treated, such as round steel pipes or square steel pipes, are charged into a heating furnace, they can be arranged in a single row or in double rows and treated all at once.

The heating means installed in the heating chamber include a gas bar,
Burners for LPG, LNG, light oil, kerosene, heavy oil, etc., electric heating,
Electrical heating means such as induction heating are known and can be used.

According to the present invention, (I) Since the axially long workpiece is divided into short parts along the longitudinal axis and gradually heated, thermal expansion strain appearing in the direction perpendicular to the axis is small.

(2) The elongated material to be treated can be heated continuously.

In short, it is also possible to incorporate the heat treatment means into a production line for steel pipes and the like.

(3) Since the material to be treated is less distorted by heating, the heating furnace can be made smaller.

(4) Since the material to be treated is less distorted, the structure of the guide in the furnace for the same material can be simplified.

(5) Since less strain occurs in the treated material, the strain correction equipment for the steel material remaining after treatment can be simplified.

(6) Local embrittlement and deterioration of the material due to cold working of the material can be eliminated or repaired, and high-quality products can be provided.

〔Example〕

Examples of the method of the present invention and a heating furnace for carrying out the method will be described below with reference to the drawings, but the details of the opening will be described as appropriate within the technical level known in the industry at the time of this application. Since modifications are possible, the constituent features of the present invention should not be interpreted in a limited manner based only on the specific structure of this embodiment unless there is a particular reason.

(Part 1) Fig. 1(a) is a schematic side view of a heating furnace for refining the base material of continuous round steel pipes, and Fig. 1(b) shows the round steel pipe base material being conveyed in the heating furnace. The figure shows the heating temperature and the corresponding furnace temperature. And Figure 2 is like Figure 1(a)
FIG.

In FIG. 1(a), 1 is a heating furnace main body, the axial length of which is, for example, 23 m, and 2 is a round steel pipe that is the material to be treated and is continuous in the axial direction, and its size is 216φI , the plate thickness is 10.7mm. 3□, 3□, 33... are first, second, third... heating chambers constituting a part of the heating furnace 1; A gas burner 5 is installed at a symmetrical position with respect to the center axis of the round steel pipe, and the fuel injection direction of the burner rotates approximately along the wall surface of the steel pipe being transported within the chamber, heating the wall surface as uniformly as possible. It is arranged so that

In the case of this embodiment, one heating chamber is equipped with a total of four heating burners (see Figure 2), and the injection is applied to the peripheral wall of the round steel pipe inside the chamber through burner injection holes drilled in the furnace wall. It is oriented so that the flame can reach it. The temperature in the heating chamber is maintained at approximately 1070°C to 1100°C.

Preferably, the combustion gases in the heating chamber are evacuated from the heating chamber by special exhaust means and are finally discharged together.

The cross-sectional volume of the furnace chamber is large enough to allow one round steel pipe 2 to pass through.

4□, 4□, 43... are first, second, third... non-heating chambers constituting other parts of the heating furnace 1, and the same chambers are arranged alternately with the heating chamber, and They are connected one by one in parallel in the longitudinal axis direction, and constitute one heating furnace 1 as a whole.

A guide/conveying means 6 for the round steel pipe 2 is installed in the non-heating chamber. Further, the length of the non-heating chamber in the longitudinal axis direction is set appropriately in order to equalize the heating temperature of the peripheral wall of the round steel pipe during transportation.

In addition, measures are taken as necessary to prevent thermal energy from accumulating and staying in the non-heating chambers due to radiation or conduction from the steel pipe 2 or each heating chamber, making it impossible for the non-heating chambers to maintain their respective predetermined temperatures. The indoor temperature of the non-heating chamber can be controlled by providing thermal energy dissipation fins or a jacket through which a heat medium flows for absorbing thermal energy on the peripheral wall of the non-heating chamber.

In FIG. 1(b), the continuous round steel pipe 2 is exposed to the outside air 15
℃ (base material temperature) into the heating furnace 1 at a speed of 6 m/min.
When the tube is charged, it is first heated while passing through the first heating chamber 3□, and the temperature of the peripheral wall of the tube rises to approximately 200°, but that portion passes through the next first non-heating chamber 4□. During this time, the uneven heating temperature of the steel pipe becomes uniform due to conduction, and radiant heat is lost, causing the overall temperature to drop to about 150°C.

For this reason, the strain in the material due to thermal expansion of the relevant portion becomes uniform with respect to the central axis, and does not appear in the form of external strain.

The steel pipe is then carried into the second heating chamber 3□, where the relevant portion is heated again and the tube wall temperature rises to approximately 400°C, but when passing through the second non-heating chamber 4□ in the subsequent process, Second, the heating temperature is equalized and a slight temperature drop occurs. Therefore, even if uneven thermal expansion strain occurs in the steel pipe 2 heated in the second heating chamber 3□ in the previous step, while the steel pipe is transported in the next second non-heating chamber 4□, The distortion becomes uniform and does not appear externally.

By repeating the process shown in FIG. 1(b), the specific part of the round steel pipe is heated to about 950°C while passing through the heating furnace 1 for about 4 minutes. The steel is transported outside, where it is air cooled to complete the annealing of the steel.

Regarding the heating state of the peripheral wall of the steel pipe in the heating furnace 1 and other effects, please also refer to the explanation in the above-mentioned [Function] section.

(Part 2) Figure 3 (a) is a schematic side view of a heating furnace for refining a large-diameter rectangular steel pipe base material of standard length, and Figure 3 (b) is a schematic side view of a square steel pipe base metal transported in the heating furnace. The location of the material, its heating state, and the corresponding temperature in the furnace are shown.

FIG. 4 is a front view of the above-mentioned heating furnace, in which the material to be treated is a large-diameter steel pipe 7 with a rectangular cross section, and the structure of the steel pipe conveying/guiding device 8 is slightly different due to the warping. Other than that, the general structure of the heating furnace is not much different from that explained in the embodiment (part 1).

In Fig. 3(b), the heating (chamber) temperature of the furnace is approximately 1070° to 100°C, and a large diameter rectangular steel pipe 7 of standard length is installed in the furnace at room temperature of 15°C. When the parts are loaded and transported, they are heated one after another as they pass through the heating chamber as shown in the figure, and when the relevant part is in a non-heating chamber, the temperature is equalized by radiation and conduction, and thermal expansion strain occurs axially symmetrically. As the process is repeated, the entire product is heated to a high temperature.

In this way, the embrittlement and deterioration of the material near each corner of the square steel pipe due to plastic deformation of the thick steel plate by cold working and bending approximately 90 degrees is tempered by heat treatment, and the steel material at that location is The elongation of the material is large in response to external forces, and the ratio of tensile strength to yield point can be returned to close to the old one.

In this example, the material to be treated is a rectangular steel pipe of standard length, and the material to be treated is not continuous with respect to the heating furnace.

Although the charging was done intermittently, the annealing state of the material near the corner of the steel pipe was almost the same as in the example (above).

(Part 3) Figure 5 (a) shows how multiple round steel pipes of standard length are simultaneously charged and
A schematic side view of the heating furnace for refining is shown, and (b) of the same figure shows the position of the round steel pipe base material transported in the heating furnace, its heating temperature, and the corresponding temperature in the furnace. .

FIG. 6 is a front view of the heating furnace, and since the materials to be treated are a plurality of round steel pipes, the width of the cross-sectional area thereof is wide.

Accordingly, the material conveyance/guide member 9 includes a horizontal roller having a length multiple times the diameter of the steel pipe, and vertical rollers rotatably supported at both ends of the horizontal roller. , they are placed in an unheated chamber.

The total length of the heating furnace is approximately 23 m, the diameter of the individual round steel pipes to be treated is 216 φ, and the steel wall thickness is 10.7 m.
mm, the length was 12 m, and the feed speed of the material to be processed by the guide roller 9 was 6 m/min.

As shown in FIG. 1(b), the temperature inside the furnace may be set slightly lower as the heating chamber temperature approaches the outlet for the material to be processed.

The base material temperature of the material to be treated is heated to a maximum of about 650° to 700° C. while passing through the heating furnace, and after being carried out of the furnace, annealing is performed by air cooling.

In this embodiment, six standard-length round steel pipes are placed side by side and charged into the heating furnace at a time, but it goes without saying that square steel pipes may also be used.

〔Effect of the invention〕

As described above, the present invention has the following advantages: (1) The material to be treated which is long in the axial direction is divided into short parts in the longitudinal direction, and the parts are heated gradually and sequentially. Thermal expansion strain in the right angle direction is less likely to occur.

(2) Continuous heat treatment of treated materials is possible.

(3) Since the material to be treated is less likely to be distorted, the cross-sectional volume of the furnace can be reduced.

(4) Therefore, it is possible to easily guide the material to be treated inside the furnace.

(5) Since less distortion occurs in the material to be processed after processing, the distortion correction equipment is simple and good.

(6) Prevent or recover material deterioration and embrittlement caused by cold plastic working, and provide high-quality products.

(7) Apply heat treatment in the shortest possible time and at low cost,
Reduce cost increase factors.

These and other special functions and effects cannot be expected with conventionally known steel heat treatment means.

The apparatus and method of the present invention are capable of refining not only rectangular steel pipes but also round steel pipes, steel bars, and other materials to be treated.

In addition, it is possible to process continuous materials, annealing standard length materials, amniotic fluid, or multiple materials at the same time.

[Brief explanation of drawings]

FIGS. 1(a), 3(a), and 5(a) are a schematic side view, FIG. 1(b), and FIG. ) and FIG. 5(b) are
Each shows the position and heating temperature of the steel pipe base material transported in the heating furnace, and the temperature within the furnace corresponding to the distance. 2, 4, and 6 are respectively front views of the heating furnace of the present invention, FIG. 7 is a perspective view of a conventionally known Calothermal furnace, and FIG. 8 is a large-diameter rectangular shape of the material to be treated. It is a perspective view of a steel pipe row. 1.10... Heating furnace, 3... Heating chamber, 5... Heating burner 7... Square steel pipe of standard length, 12... Door, 14... Pulley. 2... Continuous round steel pipe, 4... Non-heating chamber, 6.8.9... Guide roller, 11... Charging port, ]3... Weight,

Claims (2)

[Claims] (1) The interior of the heating furnace is divided into a plurality of sections along the conveyance direction of the material to be treated, and every other section is a heating chamber in which a heating device for the material to be treated is installed. A heating furnace made of square steel pipes that does not produce distortion. (2) While the axially long workpiece is being conveyed through the furnace, it is heated sequentially from its tip while passing through the first section, and then is not heated when passing through the second section. By sequentially repeating the steps of equalizing the heating temperature, passing through the third section, being heated again to a higher temperature, and then equalizing the temperature in the fourth section, the heating-based A distortion-free heating method for square steel pipes that suppresses the occurrence of distortion in the material to be treated and heats the entire material to the required temperature.