JPH0513004B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention is a method of manufacturing a square steel pipe by reducing the diameter of a round pipe manufactured by an electric resistance welded pipe, a forge welded pipe, a seamless pipe, or other methods using a die or a die and a plug. Regarding. (Prior Art) In general, methods for manufacturing square steel pipes can be broadly classified into two types. One is to form a steel strip of a predetermined width into a tube by roll forming using several stages of stands, and then weld it into a round tube. This method then uses several stages of drawing stands to continuously manufacture square tubes from round tubes. This method is generally widely used and has the advantage of being highly efficient and low-cost manufacturing, but it is disadvantageous for manufacturing many sizes in small quantities because it uses several stages of stands that match the shape. be. For this reason, another method is to manufacture a square tube by reducing the diameter of a round tube manufactured by an electric resistance welded tube, a forge welded tube, a seamless tube, or other methods using a die or a die and a plug. This method has the advantage that rectangular tubes of various shapes can be efficiently manufactured even in small quantities as long as dies and plugs are available. However, if the reduction is too large, the die and plug will seize and the quality of the cylinder will deteriorate significantly.
For this reason, depending on the shape of the square tube, it may be necessary to pull it twice. That is, a round tube is once shrunk into a predetermined shape and then shrunk again to produce a predetermined square tube. This is inefficient and extremely costly. Therefore, even if the conventional cost is high,
The reduction is reduced to the point where burn-in no longer occurs. However, in the latter case, the dimensional accuracy deteriorates, making it impossible to manufacture products with high dimensional accuracy. (Problems to be Solved by the Invention) As mentioned above, it is possible to reduce the diameter of a round tube manufactured by an electric resistance welded tube, a forge welded tube, a seamless tube, or other methods using a die or a die or a plug. In the method of manufacturing square tubes, if the reduction is large, seizure occurs locally, which greatly impedes efficiency and dimensional accuracy. In other words, it was necessary to perform two pulls with reduction that does not cause burn-in, or to lower the reduction at the expense of dimensional accuracy. The present invention is a method of manufacturing a rectangular tube by reducing the diameter of a round tube manufactured by such an electric resistance welding tube, a forge welding tube, a seamless tube, or other methods using a die or a die or a plug, and is relatively cost-effective. The purpose is to provide a manufacturing method that does not cause burn-in even in reduction. (Means for Solving the Problems) The present invention provides a method for manufacturing a square steel pipe by a diameter reduction method using a die from a round pipe or a die and a plug. )×1.00〜
1.20], the main tube wall thickness is reduced [1-(square tube cross-sectional area / main tube cross-sectional area)] to 20 to 35%, and manufactured so that [main tube wall thickness ≧ square tube wall thickness] This is a method of manufacturing square steel pipes by reducing the diameter of round pipes. The present invention will be explained in detail below. FIG. 1 is a diagram showing a method of reducing the diameter from a round tube to a square tube. A main tube (round tube) 1 is drawn through a die 2 and a plug 3 while reducing its diameter to form a square tube. In this method of reducing the diameter from a round tube to a square tube, the degree of processing differs in each part in the circumferential direction. For this reason, there will be parts where the degree of machining is very high and parts where it is very low. If the degree of processing is high, the surface pressure applied to the die and plug will be high and seizure will occur, and if the work hardening of the material is also high, cracks will occur during drawing or the pipe will break. On the other hand, if the processing degree is low, the shape
Dimensional accuracy deteriorates. In particular, the smoothness of the sides of the rectangular tube and the accuracy of the radius of the corner portion deteriorate, making it difficult to manufacture products with strict dimensional accuracy specifications. The present invention solves these problems by using a main tube (round tube).
It is intended to be manufactured in a limited size. In other words, the diameter of the main pipe is [(length of diagonal of square pipe) ×
1.00~1.20]. As long as the diameter reduction method is used, from the viewpoint of dimensional accuracy, the diameter of the main tube needs to be at least 1.00 times the length of the diagonal of the square tube, but if it is 1.20 times or more, seizure will occur. Next, for the main tube wall thickness, reduce [1-(square tube cross-sectional area / main tube cross-sectional area)] to 20 to 35%, and [main tube wall thickness ≧ square tube wall thickness]
Decide to be. That is, 0.20≦1−4t ₂ (L−t ₂ )/πt ₁ (D−t ₁ )≦0.35 and t ₁ ≧t ₂ where D: mother pipe diameter (mm) t ₁ : mother pipe wall thickness (mm) Determine the main tube wall thickness t ₁ so that t ₂ ; Square tube wall thickness (mm) L: Square tube side length (mm). The diameter D of the main tube can be determined by the method described above, and since the wall thickness t ₂ of the square tube and the length L of the side of the square tube are known, the wall thickness t ₁ of the main tube can be determined. The reason why the reduction is set to 20% to 35% is because if it exceeds 35%, seizing or pipe cutting will occur, and if it is less than 20%, it will result in poor shape and dimensional accuracy. This method can be effectively applied not only to steel but also to other metals such as stainless steel, aluminum, copper, etc. (Example) In Table 1 and Figure 2, component C: 0.13 to 0.18%,
Si; 0.15-0.35%, Mn; 0.60-0.85% and P,
When manufacturing square steel pipes of size □22mm x t3.0mm made of steel containing small amounts of S, Cr, Mo, etc., when the present invention is used (Figure 2a) and when it is not (Figure 2b) This is a comparison. Without the present invention, burn-in may occur,
Although the dimensional accuracy is poor, according to the present invention, there is no burn-in and the dimensional accuracy is good.

[Table] (Effects of the invention) As detailed above, according to the present invention, when manufacturing square steel pipes by the diameter reduction method using a round pipe as the mother pipe, there is no seizure of dies, plugs, etc. It is possible to stably and efficiently manufacture square steel pipes with high precision.

[Brief explanation of the drawing]

Figure 1 a shows a method for manufacturing square steel pipes by the tube shrinking method using dies and plugs, and Figure 1 b
1A is a cross-sectional view taken along line A-A' in FIG. 1A, FIG. This is a comparison diagram. 1: round tube, 2: die, 3: plug, 4: square tube, 5: drawing direction.

Claims (1)

[Scope of Claims] 1. A method of manufacturing a square steel pipe by a diameter reduction method using a die or a die and a plug from a round pipe, in which the mother pipe diameter is set to [(diagonal length of the square pipe) x 1.00 to 1.20]. The main pipe wall thickness should be reduced so that [1-(square pipe cross-sectional area/main pipe cross-sectional area)] is 20 to 35%, and [main pipe wall thickness ≧ square pipe wall thickness]. A method for manufacturing square steel pipes by reducing the diameter of round pipes.