JP3021285B2 - Method for manufacturing tapered square tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tapered rectangular tube having a truncated quadrangular pyramid shape suitable for use as a connecting portion of rectangular steel tube columns having different diameters.

[0002]

2. Description of the Related Art Large electric resistance welded square steel pipes are often used as pillars in steel-framed buildings. In this case, when a rectangular steel tube column having a smaller diameter is used toward the upper floor, a truncated quadrangular pyramid-shaped short tapered square tube 1 as shown in FIG. Used. When manufacturing this kind of tapered square tube 1 from an ERW square steel tube, a long ERW square steel tube is cut to obtain a short material square tube, and the short material square tube is divided into a male mold and a female mold. Draw forming is performed using a press machine.

[0002]

SUMMARY OF THE INVENTION
The size of the material square tube used is, for example, 12 mm thick x 2 vertical
Since it is a large size of 50 mm x 250 mm in width, the drawing process is a severe process, and the mechanical properties such as tensile strength, yield point and elongation of the material are adversely affected by work hardening, etc.
In some cases, the material is not preferable as a steel frame material.
In this case, it is conceivable to improve the mechanical properties by annealing the tapered square pipe after drawing, but if the entire tapered square pipe after drawing is simply annealed, it softens more than necessary, especially the yield point. And other mechanical properties are not always appropriate.

The present invention has been made in view of the above circumstances, and provides a method of manufacturing a tapered rectangular tube capable of obtaining a tapered rectangular tube having good mechanical properties such as tensile strength, yield point, and elongation as a steel frame material. The purpose is to provide.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to form a tapered square tube by drawing a short material square tube, which is an electric resistance welded square steel tube, with a male die and a female die. And a heat treatment step in which the tapered square tube is heated by a high-frequency induction heating method at a temperature gradient such that the small-diameter end is high temperature and the large-diameter end is low temperature, and then naturally cooled.

The temperature gradient in the region from the position closer to the large diameter end to the large diameter end is steeper than the temperature gradient in the region from the small diameter end to the position closer to the large diameter end. It is characterized in that it is set so that

A third aspect of the present invention is to heat the tapered square tube by covering the induction coil with the tapered square tube so as not to cover the vicinity of the large diameter end of the tapered square tube but to cover only a certain area on the small diameter end side. Features.

[0007]

In the above-mentioned heat treatment step, the temperature of the large-diameter end side naturally rises. However, in a certain region on the large-diameter end side, the temperature is kept at a temperature at which the annealing action does not occur. In order to realize such a heat treatment, a high-frequency induction heating method using an induction coil is appropriate. Although the tapered square pipe drawn and formed in the tapered square pipe forming step is work hardened, its mechanical properties are improved by a heat treatment step of selectively annealing only a certain area on the small diameter end side. In this case, the large-diameter end side with less work hardening is not annealed, rather than simply annealing the entire tapered square tube uniformly, so that the material at the large-diameter end side does not soften unnecessarily. In addition, the work hardening of the tapered rectangular tube is large at the small diameter end and small at the large diameter end. Therefore, appropriate annealing can be performed on each part of the tapered rectangular tube by annealing at a temperature gradient where the small diameter end becomes high temperature. Will be

According to the second aspect, it is easy to realize a temperature distribution such that the large-diameter end side is not annealed.

According to the third aspect, it is easy to heat the tapered square tube with a temperature gradient. Further, as described above, it is easy to realize a temperature distribution such that the large-diameter end side is not annealed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the method of manufacturing a tapered square tube according to the present invention, a long material square tube manufactured by an electric resistance welded steel pipe manufacturing facility is cut at a predetermined interval to obtain a short material square tube. As shown in FIG. 3, a taper square tube 1 having a truncated quadrangular pyramid shape as shown in FIG. FIG. 2 shows a state before pressing, and FIG. 3 shows a drawn state. In both figures, 1a is a material square tube, 2 is a male mold, and 3 is a female mold. Male mold 2 is a tapered square tube 1 to be drawn.
The female mold 3 has a truncated quadrangular pyramid-shaped inner surface 3a that matches the outer surface shape of the tapered square tube 1. Reference numeral 4 denotes a cradle of the press machine, and 5 denotes a ram of the press machine. As shown in FIG.
Then, as shown in FIG. 3, the female mold 3 is lowered and pressurized to perform drawing, thereby obtaining the tapered square tube 1. The above process is a tapered square tube forming process. In the drawing, in order to reduce the pressing load, it is preferable that the forming is performed by a plurality of pressing operations if necessary, and that the lubricating oil is applied to the surface of the material before the pressing operation.

Next, the tapered square tube 1 is heated by a high-frequency induction heating method with a temperature gradient such that the small-diameter end (upper end in FIG. 1) has a high temperature and the large-diameter end (lower end in FIG. 1) has a low temperature. Heat treatment for cooling is performed. FIG. 4 shows this heat treatment method, in which an induction coil 10 is put on the tapered square tube 1, and after the induction coil 10 is energized for a certain period of time, the energization is turned off and natural cooling (air cooling) is performed.

A concrete example of the heat treatment will be described below. The size of the material square tube 1a is 12 mm in thickness x 250 mm in height x 250 mm in width x 265 mm in height. This is drawn and formed, and the large diameter end is 250 mm in length x 250 m in width.
m, a tapered square tube 1 having a small diameter end of 200 mm long × 200 mm wide. This tapered square tube 1 was heat-treated under the following heat treatment conditions. (A) Heating method: high-frequency induction heating method (b) Induction coil: 9 turns of a brass tube having a thickness of 1.5 mm and an outer diameter of 19 mmφ.
Coil inner diameter 262mmφ, coil height 250mm. Pour cooling water inside. (C) Positional relationship between the induction coil and the tapered rectangular tube: The induction coil 10 is shifted over the tapered rectangular tube 1 as shown in FIG. The large-diameter end side dimension S of the tapered rectangular tube 1 not covered by the induction coil 10 is approximately 20% of the height of the tapered rectangular tube 1 (in this case, approximately 53 mm). Therefore, it covers about 212 mm of the small diameter end side region of the tapered square tube 1. The induction coil 10 extends about 53 mm further above the small diameter end of the tapered square tube 1. (D) Input: 50 KW (e) Frequency: 1.8 KHz (f) Heating time: 2-3 minutes. In the experimental example, the energization time is 1 minute 5 minutes
Two types: 7 seconds (energization time T ₁ ) and 2 minutes 54 seconds (energization time T ₂ ).

At the time of the above heat treatment, the temperature of the tapered rectangular tube 1 was measured. FIG. The measurement points are the center positions of the sides of the outer surface indicated by numerals 1 to 5, the corner positions of the outer surface indicated by numerals 6 to 8, the position indicated by numeral 9 (the inner surface position corresponding to numeral 1), and the position indicated by numeral 10 (numeric 6 (Inner surface position corresponding to). It indicated by the numeral in ○ in the case of energization time T _{1 (1} ~10), indicated by the numbers in the case of the energization time T ₂ □ (1 ~10). The heating curve of the tapered square tube 1 during heating in the above heat treatment is shown in FIG.
It is shown in (b). Figure 5 (b) in the case of the energization time T _1, FIG. 5
(B) shows a case of the energization time T _2. As shown in both figures, after the start of energization, the temperature rises almost linearly until it reaches the maximum temperature (heating temperature). Then, it was gradually cooled by natural cooling. The starting point of the temperature rise curve for each measurement point in FIG. 5 is the origin (point 0), but is shifted for ease of understanding. FIG. 6 shows the heating temperature distribution on the tapered square tube 1 in which the highest temperature in the heating curves of FIGS. 5A and 5B is represented as the heating temperature. In this graph, the heating temperature of the inner surface of the tapered rectangular tube 1 was excluded. The temperature distribution is about 710-760 ° C at the small diameter end, 660-740 ° C at the center of the pipe length, and about 460-5 at the large diameter end.
30 ° C. As shown in the graph, from the temperature gradient of the region (L ₁ ) from the small diameter end to the position near the large diameter end from the center, the region (L ₂ ) from the position near the large diameter end to the large diameter end
Has a steep temperature gradient. In this graph, the heating temperature of the inner surface of the tapered rectangular tube 1 is omitted as described above, but the inner surface is lower by about 40 ° C. than the outer surface.

The mechanical properties of the tapered rectangular tube 1 subjected to the above-mentioned heat treatment have been improved as can be clearly seen from FIGS. FIG. 8 shows the measurement results of the tensile strength and the 0.2% proof stress, which are the measurement results of a hot coil, a square tube made of a material, an azroll drawn product, and a heat treated product of the present invention. The hot coil is a hot-rolled steel sheet which is a material used for manufacturing an electric resistance welded square steel pipe. The as-roll drawn product refers to a non-heat-treated tapered square pipe as drawn.
The heat-treated product of the present invention refers to a tapered rectangular tube that has been subjected to the heat treatment of the above-described experimental example. In addition, 0.2% proof stress is a value of 0.
The yield strength (corresponding to the yield point) is the stress when 2% elongation occurs. As can be clearly seen from the graph of FIG. 8, in the heat-treated product of the present invention (tapered square tube according to the method of the present invention), the difference in tensile strength and proof stress between the large-diameter end side and the small-diameter end side is small. For as-rolled products, there is a large difference in tensile strength and proof stress between the large-diameter end and the small-diameter end.
As for the tensile strength and proof stress on the small diameter end side, the tensile strength and proof stress of the as-rolled product are higher than those of the heat-treated product of the present invention. As for the tensile strength and proof stress on the large diameter end side, there is little work hardening from the beginning, so there is little difference between the two. Further, the tensile strength and proof stress of the heat-treated product of the present invention are little different from those of the square steel pipe, and it can be seen that the selective annealing method of the present invention can almost eliminate the influence of drawing on mechanical properties.

FIG. 9 shows the results of an elongation test. In addition, the elongation value has shown the elongation value by a JIS No. 5 tensile test piece. As is clear from Fig. 9, in the as-roll drawn product, the elongation at the large-diameter end is a square steel pipe (that is, before drawing).
Approximately the same as above, but greatly reduced on the small diameter end side. On the other hand, in the heat-treated product of the present invention, the elongation at the large-diameter end is slightly reduced, and the difference between the elongation at the large-diameter end and the elongation at the small-diameter end is extremely small.

The tapered square tube 1 of the embodiment is a four-sided throttle tube in which all four surfaces are tapered, but three surfaces are tapered.
Naturally, the present invention can also be applied to a three-sided restrictor having a vertical surface (perpendicular to the bottom surface) or a two-sided restrictor having two tapered surfaces and two vertical surfaces.

[0017]

According to the present invention, the large-diameter end with less work hardening is not annealed, and only a certain area on the small-diameter end is not simply annealed uniformly to the entire drawn tapered square tube. Since the material is selectively annealed, the material at the large-diameter end does not soften unnecessarily. In addition, the work hardening of the tapered rectangular tube is large at the small diameter end and small at the large diameter end. Therefore, appropriate annealing can be performed on each part of the tapered rectangular tube by annealing at a temperature gradient where the small diameter end becomes high temperature. Will be By the above, mechanical properties such as tensile strength, yield point, elongation and the like of the tapered rectangular tube are improved to be appropriate as a whole, and a tapered rectangular tube excellent as a steel frame material can be obtained. Further, since the entire tapered square tube is not uniformly annealed, power consumption can be reduced.

According to the second aspect, it is easy to realize a temperature distribution such that the large diameter end side is not annealed.

According to the third aspect, it is easy to heat the tapered square tube with a temperature gradient. Further, as described above, it is easy to realize a temperature distribution such that the large-diameter end side is not annealed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a tapered square tube to be manufactured by the method of the present invention.

FIG. 2 is a view showing a stage before pressing in a tapered square tube forming step in the method for manufacturing a tapered square tube according to one embodiment of the present invention.

FIG. 3 is a diagram showing a pressed state in a tapered square tube forming step in the method for manufacturing a tapered square tube according to one embodiment of the present invention.

FIG. 4 is a view showing a heat treatment step in the method for manufacturing a tapered rectangular tube according to one embodiment of the present invention, and is a diagram showing a state where an induction coil for high-frequency induction heating is put on the tapered rectangular tube.

FIG. 5 is a graph showing a specific experimental example of the heat treatment step and showing a temperature rising curve at the time of heating the tapered square tube.

FIG. 6 is a graph showing a distribution of a heating temperature of a tapered square tube in the experimental example.

FIG. 7 is a diagram showing a temperature measurement point on a tapered square tube in the experimental example.

FIG. 8 is a graph showing the measurement results of tensile strength and proof stress of the tapered rectangular tube obtained in the experimental example.

FIG. 9 is a graph showing a measurement result of elongation of a tapered square tube obtained in the above experimental example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Taper square tube 1a Material square tube 2 Male type 3 Female type 10 Induction coil of high frequency induction heating

Continuation of the front page (72) Inventor Masanori Arakawa 7-8-41 Ichinomiya, Samukawa-cho, Koza-gun, Kanagawa Prefecture Inside the Samukawa Plant of High-Frequency Thermal Refining Co., Ltd. (56) References JP-A-63-295027 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B21C 37/15-37/18 B21D 22/20 B21D 22/26

Claims (3)

(57) [Claims] 1. A tapered square tube forming step of forming a tapered rectangular tube by drawing a short material square tube which is an ERW square steel tube with a male die and a female die, and forming the tapered square tube by a high-frequency induction heating method. A heating step of heating at a temperature gradient such that the small-diameter end side is at a high temperature and the large-diameter end side at a low temperature, and then allowing it to cool naturally. 2. The temperature gradient in the region from the large-diameter end to the large-diameter end is steeper than the temperature gradient in the region from the small-diameter end to the position near the large-diameter end from the small-diameter end. 2. The method for manufacturing a tapered rectangular tube according to claim 1, wherein 3. The tapered square tube is heated by covering the induction coil over the tapered square tube so as not to cover the vicinity of the large diameter end of the tapered square tube but to cover only a certain area on the small diameter end side. A method for manufacturing a tapered rectangular tube according to claim 1.