JP2002235875A - Steel tube with high dimensional accuracy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel tube with high dimensional accuracy (for example steel tube for cylinder) which is excellent in manufacturing yield, hardly flawed, excellent in fatigue characteristic, inexpensive in manufacturing costs, and large in degree of freedom in dimension. SOLUTION: An electric resistance welded tube or a seamless steel tube is cut to have an original tube. A liquid pressure is exerted to an inner surface and an outer surface of the original tube so that the diameter is enlarged or contracted to be a given diameter, thereby providing the steel tube with high dimensional accuracy (for example not greater than ±0.1 mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a high-precision steel pipe,
For example, the present invention relates to a steel pipe for a cylinder constituting various hydraulic cylinders used for automobiles and industrial machines.

[0002]

2. Description of the Related Art A steel pipe for a cylinder is required to have high dimensional accuracy in the radial direction and high dimensional accuracy in wall thickness. For this reason, these demands have been met by improving the dimensional accuracy by drawing an electric resistance welded steel pipe (electric resistance welded pipe) or a seamless steel pipe conventionally produced in a normal steel pipe production line to improve the dimensional accuracy. However, in the drawing process, the end of the original tube is chucked and pulled out, so that the chucked end cannot be used as a product. For this reason, especially in the case of small-volume production, there are many discarded parts, and there is a problem that the processing yield is poor.

[0003] In the process of manufacturing an electric resistance welded steel pipe, it is usual to adjust the dimensions by pressing the outer surface of a raw pipe with a number of rolls. In this case, when a roll mark is formed on the outer surface of the product over its entire length. There is. For this reason, there is a problem that the appearance quality is reduced.

If there is a flaw on the outer surface of the original pipe, the flaw is stretched in the axial direction of the cylinder steel pipe in the drawing process as shown in FIG. Since the steel pipe for a cylinder repeatedly receives a high internal pressure in a used state, a circumferential hoop stress acts so as to push up the stretched flaw in a direction indicated by an arrow. For this reason, there was a problem that the flaws of the original pipe deteriorated the fatigue characteristics.

Therefore, in order to avoid the problems of the steel pipe for a cylinder manufactured by the above-described drawing, the ERW steel pipe has recently been used as it is (As-Roll) as a steel pipe for a cylinder. However, As-Roll cylinder pipes for cylinders have extremely poor dimensional accuracy compared to drawn pipes.
It is necessary to improve the dimensional accuracy by cutting the inner surface by about 0.5 to 2.0 mm, and there is a problem that the manufacturing cost is increased.

Further, the outer diameter, inner diameter, wall thickness, etc. of a steel pipe for a cylinder are finely determined by a cylinder maker.
Many types are defined in mm increments. In contrast, the types of outer diameters of steel pipes manufactured by steel pipe manufacturers are usually much smaller. For this reason, if the ERW steel pipe is used as it is for the cylinder steel pipe, there are problems such as the cost of installing new facilities for the steel pipe manufacturer and the need to reduce the number of types of cylinder steel pipe. Was constrained.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, has a good production yield, is hardly flawed on the outer surface, has excellent fatigue characteristics, has a low production cost, and has a high degree of dimensional freedom. The purpose of the present invention is to provide a high dimensional accuracy steel pipe such as a steel pipe for a large cylinder.

[0008]

SUMMARY OF THE INVENTION A high dimensional accuracy steel pipe of the present invention made to solve the above-mentioned problem is expanded or reduced to a predetermined diameter by applying hydraulic pressure to an inner surface or an outer surface of a raw tube. The feature is that the diameter is reduced and high dimensional accuracy is provided. The original tube may be an electric resistance welded steel tube or a seamless steel tube, but it is preferable to use an electric resistance welded steel tube in terms of cost. A high dimensional accuracy steel pipe (for example, ± 0.1 mm or less) can be obtained, and tensile stress in the circumferential direction of the pipe can be reduced by hydraulic processing, and fatigue characteristics can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a manufacturing process of a steel pipe for a cylinder which is a high-precision steel pipe of the present invention. An ERW steel pipe or a seamless steel pipe is cut into a predetermined length to obtain a raw pipe, which is stored in a mold. To apply hydraulic pressure. In general, ERW steel pipes are less expensive to manufacture than seamless steel pipes, and thus it is preferable to use ERW steel pipes as original pipes.

[0010] The original tube is expanded or contracted in the mold. FIGS. 2 and 3 are cross-sectional views when the diameter is enlarged. The original tube 1 is held at both ends by jigs 2 and set at the center of the inside of a split mold 3. A cavity 4 having a circular cross section is formed inside the mold 3, and the inner diameter of the cavity 4 is larger than the outer diameter of the original tube 1. The jig 2 is provided with a hydraulic pressure supply hole 5 for applying a high hydraulic pressure to the inner surface of the original tube 1. As a result, the diameter of the original pipe 1 is expanded until it is plastically deformed and closely adheres to the inner surface of the mold 3 to be a steel pipe for a cylinder.

When such a diameter expansion process is performed by hydraulic pressure, the original tube 1 is expanded to a predetermined diameter determined by the mold 3. Moreover, even if the dimensional accuracy of the original tube 1 is somewhat poor, the dimensional accuracy after the diameter expansion can be an excellent value of ± 0.1 mm or less. In addition, as long as the diameter can be expanded,
A plurality of types of steel pipes for cylinders having different outer diameters can be manufactured from the original pipes 1 having the same diameter, and the degree of freedom of the diameter is increased.

FIGS. 4 and 5 are cross-sectional views when the diameter is reduced. A core 6 is set at the center of the inside of a split mold 3, and the original tube 1 having a larger diameter is formed on the outer periphery. Is inserted into. The mold 3 has a hydraulic pressure supply hole 7 formed therein.
High hydraulic pressure is applied to the outer surface of. As a result, the original tube 1 is compressed from the outer surface and reduced in diameter until it comes into close contact with the outer peripheral surface of the cored bar 6, resulting in a cylinder steel tube having a high dimensional accuracy of the inner diameter.

If such diameter reduction by hydraulic pressure is performed, the inner diameter of the original tube 1 becomes a predetermined diameter determined by the cored bar 6, and its dimensional accuracy is ± 0.1 mm or less. In addition, a plurality of types of cylinder steel pipes having different inner diameters can be manufactured from the original pipes 1 having the same diameter, and the degree of freedom of the diameter is increased, and the wall thickness is increased by reducing the diameter. Can be manufactured. Further, the roundness can be improved by hydraulic processing.

In either case of the above-mentioned diameter enlargement and diameter reduction, a useless waste part is not generated unlike the case of the expansion tube, and a high yield can be obtained. In addition, temporarily
Even if there is a flaw on the outer surface of the tube, it is not stretched in the longitudinal direction as in the case of a drawn tube, and in the case of expanding the diameter, the flaw is only slightly enlarged in the circumferential direction, and The case is reduced. Therefore, the obtained steel pipe for cylinder is
Fatigue properties are improved as compared with those obtained by drawing. Further, unlike ERW steel pipes, the degree of freedom in adjusting the final outer diameter is increased, so that roll marks can be reduced and dimensional accuracy can be improved, so that there is no need to modify the surface.

[0015]

Examples of the present invention will be described below. Tensile strength 50k
g / mm ² SAE1026 material, outer diameter 139.8mm, wall thickness 1
A 0.5 mm original tube was set in the apparatus shown in FIG. 2 and expanded by using hydraulic pressure to obtain an outer diameter of 145.0 mm and a wall thickness of 15.0 mm.
A 0.5 mm cylinder steel pipe was obtained. Further, the same original tube was set in the apparatus shown in FIG. 4, and a hydraulic pressure was applied to the outer surface to reduce the diameter, thereby obtaining a cylinder steel tube having an outer diameter of 138.0 mm and a wall thickness of 10.5 mm.

The outer diameter tolerance of the pipe is about ± 0.5 mm in the case of a general electric resistance welded steel pipe, about ± 1.1 mm in the case of a seamless steel pipe, and about ± 0.09 mm in the case of a drawn pipe. The outer diameter tolerance of the steel pipe was ± 0.08 mm, which was about the same value as the drawn pipe. The wall thickness tolerance is ± 4.0% for general ERW steel pipes, ± 8.5% for seamless steel pipes and ± 2.0% for drawn pipes, but ± 3.0% for cylinder steel pipes in the examples. The value was almost the same as that of the drawn tube product. The processing yield is about 80-90% in the case of the drawn tube because the chucked end is discarded, but it is 98% because there is almost no discarded part in the product of the present invention. was gotten.

Further, a fatigue test was performed by repeatedly applying an internal pressure to the steel pipe for a cylinder of the present invention. The result was as shown in FIG. As shown in the figure, the product of the present invention showed clearly superior fatigue properties as compared with the conventional product obtained by drawing.
The reason is considered as follows.

That is, when the pipe is expanded, a contraction force acts in the pipe circumferential direction. For this reason, the circumferential residual tensile stress generated in the original pipe is reduced, or a compressive residual stress is generated. In the case of internal pressure fatigue of a steel pipe for a cylinder, a tensile hoop stress in the circumferential direction is applied. Therefore, by reducing the tensile residual stress in the circumferential direction as described above, the fatigue characteristics can be improved. Furthermore, in the product of the present invention, the flaws on the outer surface do not extend in the longitudinal direction, and this is also considered to contribute to the improvement of the fatigue characteristics.

[0019]

The effects of the present invention described above are summarized as follows. (1) High dimensional accuracy can be obtained even if the dimensional accuracy of the original tube is low. (2) The degree of freedom in diameter is large and steel pipes for cylinders of various diameters can be manufactured from a small number of original pipes. (3) The number of surface flaws is reduced, and the rate of repair can be reduced. (4) Fewer parts are discarded compared to the extruded products, and the yield is high. (5) Tensile residual stress in the circumferential direction of the tube can be reduced, and fatigue characteristics can be improved. (6) Since the equipment is simplified and the process can be omitted as compared with the drawing tube, the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a manufacturing process of a steel pipe for a cylinder.

FIG. 2 is a cross-sectional view in the longitudinal direction when expanding the diameter.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a cross-sectional view in the longitudinal direction when diameter reduction is performed.

FIG. 5 is a sectional view taken along line BB of FIG. 4;

FIG. 6 is a graph showing fatigue characteristics in Examples.

FIG. 7 is a perspective view showing a conventional product.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 original pipe 2 jig 3 mold 4 cavity with circular cross section 5 hydraulic pressure supply hole of jig 6 core metal 7 hydraulic pressure supply hole of mold

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuo Tamura 5-3 Tokai-cho, Tokai-shi, Aichi F-term in Nippon Steel Corporation Nagoya Works (reference) 3H111 AA01 BA03 CB02 CB14 DA26 DB19 EA09

Claims (3)

[Claims] Claims: 1. Applying a hydraulic pressure to an inner surface or an outer surface of a raw tube to increase or decrease the diameter to a predetermined diameter,
High dimensional accuracy steel pipe characterized by high dimensional accuracy. 2. The high dimensional accuracy steel pipe according to claim 1, wherein the original pipe is an electric resistance welded steel pipe or a seamless steel pipe. 3. The high dimensional accuracy steel pipe according to claim 1, wherein the tensile stress in the pipe circumferential direction is reduced by hydraulic working.