JPH0520162B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method of manufacturing a steel pipe with different thickness sections having different wall thicknesses in the cross section. (Prior Art) Steel pipes are often used as strength members, and for example, steel pipes are increasingly used as strength members in automobile parts to save fuel consumption. Some steel pipe members for automobiles are subjected to stress in only one direction, and in such members, only the part on the circumference of the steel pipe that corresponds to the stress direction has a predetermined wall thickness, and the other parts have a thinner wall thickness. Often good. That is, as shown in FIG. 1, if the wall thickness of unnecessary portions in the tube cross section can be made thinner and the inner surface shape of the tube can be made oval, the weight of the members can be reduced and fuel consumption can be reduced. However, conventionally, there has been no production means for supplying steel pipes with different thickness cross-sections as industrial products. For this reason, although they were aware that this was disadvantageous in terms of the performance of the automobile, they used an ordinary steel pipe whose entire circumference had the necessary wall thickness in the stress direction, that is, a uniformly thick wall. (Problems to be Solved by the Invention) On the other hand, there is a method in which a heated base steel pipe is reduced and rolled using a stretch reducer to produce a steel pipe of a predetermined size. For example, ``Journal of the Japan Society of Mechanical Engineers, Vol. 83,
740”. Naturally, when internal angularity occurs, dimensional accuracy deteriorates, and when reduced rolling is performed using a two-roll type stretch reducer, the finished steel pipe does not have a uniform wall thickness in cross section, and as shown in Fig. 3, the dimensional accuracy deteriorates. The surface shape may be close to a square (hereinafter referred to as a square). Therefore, in order to obtain the tube shape as shown in FIG. 1, it is necessary to use a two-roll type stretch reducer and control the wall thickness distribution in the tube circumferential direction so that the tube inner surface shape forms an ellipse. (Objective of the Invention) An object of the present invention is to provide a means for inexpensively manufacturing steel pipes with different wall thicknesses using a stretch reducer. (Means for solving the problem) The gist of the present invention is as follows. (1) When the heated base steel pipe is reduced and rolled using a stretch reducer, the ellipticity is 1.03 to 1.30 and the outer diameter reduction ratio is 3 to 10%, and the ellipticity is 0.99.
1. A method for manufacturing a steel pipe with different thickness cross sections, characterized by using a stretch reducer in which roll hole type drawing rolls with an outer diameter reduction ratio of 0 to 1% are alternately arranged. The method of the present invention will be explained in detail below with reference to the plan view of the stretch reducer shown in FIG. A base steel pipe 2 heated to a predetermined temperature in a heating furnace 1 is supplied to a two-roll type stretch reducer 3 by conveyor rolls (not shown), and is reduced and rolled into a finished steel pipe 4. The stretch reducer 3 consists of a pair of squeezing rolls 3 ₁ , 3 each having a roll hole shape expressed by the ellipticity α=W/2H shown in FIG.
It is composed of ₂ , 3 ₃ , ..., 3 _o . Also, the squeezing roll 3 _i of the stretch reducer 3 (i is 1 to
n (an integer representing the roll number) is given an outer diameter reduction ratio R expressed by equation (1) in order to reduce and roll the base steel pipe 2. R=d _i-1 −d _i /d _i-1 ×100 (%) ...(1) d _i : Average hole diameter of the i-th squeeze roll In the present invention, deformation resistance is reduced and deformability is improved. The base steel pipe 2 is heated in a heating furnace 1 in order to make the steel tube 2. The material is alternately rolled with squeeze rolls, that is, squeeze rolls that have a small ellipticity and a small outer diameter reduction ratio. In odd-numbered drawing rolls, the tube wall thickness increases according to the outer diameter drawing ratio, but the wall thickness increase rate is greatest at the flange portion where stress is concentrated, and the tube wall thickness increase is extremely small at the groove bottom. On the other hand, in the case of even-numbered drawing rolls, the outer diameter drawing ratio is extremely small, so that almost no increase in thickness occurs. Therefore, the thickness increases only at the flange portions of the odd-numbered drawing rolls, resulting in a difference in wall thickness in the circumferential direction, resulting in a steel pipe with different thickness cross-sections having an elliptical inner surface shape. That is, the method of the present invention is a method in which the hole shapes of the odd-numbered rolls and the even-numbered rolls are arranged approximately alternately in the form of an ellipse and a circle. In this reduction rolling, the ellipticity of the roll hole shape is in the range of 1.03 to 1.30 for the odd numbered drawing rolls, and 0.99 to 1.01 for the even numbered drawing rolls, and the outer diameter reduction ratio is 3 for the odd numbered drawing rolls. ~10%, and even-numbered squeeze rolls take a value of 0-1%. This is because the lower limit values of the ellipticity and outer diameter reduction ratio of the odd-numbered drawing rolls are less effective below these values.
The upper limit of the ellipticity is set because if it exceeds this, it may be twisted when entering the next squeeze roll, and the upper limit of the outer diameter drawing ratio is in balance with the upper limit of the ellipticity. This is because defects occur in finished steel pipes. Note that the outer diameter reduction ratio of the even-numbered drawing rolls serving as the final drawing rolls may take a value of about 1% in order to improve the accuracy of the outer diameter shape of the finished steel pipe. Next, if a large tension of 0.5 times or more than the deformation resistance of the pipe is applied to the odd-numbered drawing rolls, the pipe wall thickness will decrease even if a relatively large outer diameter drawing ratio is applied, but the thinning rate at the bottom of the groove will especially decrease. It is the largest and smaller at the flange. On the other hand, since there is almost no change in the wall thickness in the even-numbered drawing rolls, thinning progresses at the groove bottom of the odd-numbered drawing rolls, resulting in a difference in wall thickness in the circumferential direction, resulting in a steel pipe of different thickness with an elliptical inner shape. is obtained. In this reduction rolling, a tension of 0.6 times the deformation resistance of the pipe was applied to the odd-numbered reduction rolls, but the applied tension may be arbitrarily selected according to the manufacturing conditions of the reduction rolled product steel pipe. In other words, in this reduction rolling, a finished steel pipe of a predetermined shape can be easily obtained by selecting the dimensions of the base steel pipe, the roll hole shape of the odd-numbered drawing rolls, the ellipticity, the outer diameter reduction ratio, and more preferably the tension. be. Note that the heating temperature of the base steel pipe may be appropriately selected in consideration of the rigidity of the stretch reducer, the amount of scale generated, etc. (Example) In this example, the outer diameter was 76.3 by reduction rolling.
In order to obtain a finished steel pipe with a wall thickness of 6 mm in the thick part and 4 mm in the thin part, a base steel pipe with an outer diameter of 114.3 mm and a wall thickness of 3.7 mm was heated to 900°C and drawn into the roll hole type shown in Table 1. Reduction rolling was performed using a roll stretch reducer.

[Table] The thickness of the obtained finished steel pipe was increased in the odd-numbered rolls mainly at the part that contacts the flange part of the drawing roll (the part marked _3f in Fig. 4) to reach the required wall thickness of 6 mm. The part in contact with the groove bottom (part _3b in Figure 4) was slightly thickened to 4 mm, and had the required size and shape. Similarly, a base steel pipe with an outer diameter of 114.3 mm and a wall thickness of 6.5 mm was used.
Heating it to 900℃, using the stretch reducer of the roll-hole type squeeze rolls shown in Table 1, the even-numbered squeeze rolls apply almost no tension, and the odd-numbered squeeze rolls reduce the deformation resistance by 0.6 times the deformation resistance of the tube. By applying tension and reducing rolling to apply tension stress,
The wall thickness decreases to 4mm mainly in the part that contacts the groove bottom of the odd numbered rolls, and there is almost no change in wall thickness in the part that contacts the flange part of the odd numbered rolls, making it possible to obtain a finished steel pipe with the required dimensions and shape. Obtained. (Effects of the Invention) According to the present invention, steel pipes with different thickness cross-sections having different wall thicknesses in the circumferential direction can be manufactured by a reduction rolling method, so that they can be manufactured with high efficiency and at low cost. Although the present invention has described a method for producing steel pipes of different thicknesses with an elliptical inner shape, it is also possible to produce steel pipes of different thicknesses with a triangular inner shape by using a three-roll type stretch reducer in exactly the same way. It is.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the steel pipe of the present invention, FIG. 2 is a simple plan view of a stretch reducer explaining the present invention, and FIG. 3 is a sectional view of a conventional stretch reducer product shown in a square manner. FIG. 4 is a diagram illustrating the hole shape of the squeeze roll. DESCRIPTION OF SYMBOLS 1... Heating furnace, 2... Mother steel pipe, 3... Stretch reducer, 3 _i ... i-th drawing roll, 4
...Finished steel pipe.

Claims (1)

[Scope of Claims] 1. When reducing and rolling a heated base steel pipe with a stretch reducer, a roll hole type drawing roll with an ellipticity of 1.03 to 1.30 and an outer diameter reduction of 3 to 10% and an ellipticity of 0.99 to 1.30 are used. 1. A method for producing steel pipes with different thickness cross sections, characterized by using a stretch reducer in which roll hole type drawing rolls with an outer diameter reduction ratio of 0 to 1% are arranged alternately.