JP2011255401A - Method of manufacturing steel pipe for cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of cracks as much as possible.SOLUTION: There is provided a steel pipe for a cylinder which constitutes an outer cylinder of a cylinder actuator where a piston is slidably fitted to the inside. In the steel pipe, a drawing process 2 is applied after a grinding process 1 is applied to an entire area of a surface layer of an outer peripheral face in a pipe stock 10 and further press correction 4 is performed after stress relief heat treatment 3 is performed.

Description

  The present invention relates to a method of manufacturing a steel pipe for a cylinder in which an outer cylinder is formed in a cylinder actuator such as a hydraulic cylinder and a piston is slidably fitted therein.

  As the cylinder steel pipe constituting the outer cylinder of the cylinder actuator, it is common to apply a steel pipe that has been subjected to stress relief heat treatment after being drawn. Stress relief heat treatment is intended to improve fatigue characteristics against internal pressure during operation by removing residual stress of cylinder steel pipe, especially tensile stress in the direction of circumferential expansion in the outer surface layer of cylinder steel pipe. (For example, see Patent Document 1).

Japanese Patent Laid-Open No. 4-183820

  Factors that deteriorate the fatigue characteristics of the cylinder steel pipe include surface layer defects existing in the raw pipe in addition to the above-described residual stress. A surface layer defect is a defect of the surface layer part including the defect produced in the case of steelmaking, hot rolling, and hot pipe making. The surface layer defect includes, for example, fine and acute scratches generated on the surface layer of about 0.1 mm below the surface, fine non-metallic inclusions existing on the surface layer, or subdermal defects inside the surface layer not exposed on the surface. When surface layer defects exist on the outer peripheral side of the cylinder steel pipe, stress may concentrate and grow due to internal pressure during operation, which may cause cracks in the cylinder steel pipe.

  For this reason, conventionally, after carrying out the stress relief heat treatment, the surface is inspected, and when scratches or non-metallic inclusions are confirmed, a grinding tool such as a hand grinder is applied to perform grinding work to remove it. Has been done.

  However, even when the stress-relieving heat treatment and the work for removing surface layer defects are performed as described above, the situation where cracks occur in the cylinder steel pipe is still occurring, although the absolute number decreases. It is. Therefore, it is very important to improve the quality of the cylinder actuator how to determine the cause of cracks in the cylinder steel pipe and how to prevent this.

  An object of this invention is to provide the manufacturing method of the steel pipe for cylinders which can prevent the situation where a crack generate | occur | produces as much as possible in view of the said situation.

  As a result of intensive studies to achieve the above object, the present inventors have found that the grinding work performed to remove surface layer defects contributes to cracks in the steel pipe for cylinders. I found out. In other words, the grinding work that was carried out to prevent cracks in the cylinder steel pipe actually caused a residual tensile stress in the circumferential direction on the outer surface of the cylinder steel pipe. As a result, the steel pipe for cylinder was cracked. The present invention was created based on these findings and has the following characteristics.

  That is, the method for manufacturing a cylinder steel pipe according to the present invention includes a cylinder steel pipe that constitutes an outer cylinder of a cylinder actuator and in which a piston is slidably fitted. After carrying out the grinding process and the drawing process, a stress relief heat treatment is performed.

  Further, the present invention is characterized in that, in the above-described method of manufacturing a steel pipe for cylinder, after the stress relief heat treatment is performed, the base pipe is subjected to press correction.

  As a straightening process performed after the stress removal heat treatment, roll straightening is generally performed. However, this roll straightening also generates tensile residual stress in the circumferential direction on the outer surface layer of the cylinder steel pipe from the viewpoint of residual stress. In other words, the roll correction, which has been an essential operation for bending the raw pipe after the stress relief heat treatment, can contribute to cracking in the cylinder steel pipe from the viewpoint of residual stress. This is considered to be a cause of generating a tensile residual stress in the circumferential direction because an extra external force is inevitably applied by the roll even to a portion where correction is not originally required due to the roll straightening structure. Therefore, after the stress relief heat treatment is performed, press correction without applying external force to unnecessary portions is performed.

  Any of the drawing process and the grinding process may be performed first as long as the stress removing heat treatment is performed. However, when the influence on workability by work hardening is taken into consideration, it is preferable to perform grinding before carrying out the drawing process.

  According to the present invention, since the grinding process is performed before the stress removing heat treatment is performed, the residual stress caused by the grinding process is removed by the subsequent stress removing heat treatment. Accordingly, it is possible to prevent the cylinder steel pipe from being cracked due to the tensile residual stress in the circumferential direction. Moreover, since the grinding process is performed over the entire surface layer with respect to the outer peripheral surface of the raw pipe, there is no possibility of causing a situation in which a crack occurs in the cylinder steel pipe due to a surface layer defect.

FIG. 1 is a process diagram for explaining a method of manufacturing a cylinder steel pipe according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing a specific example of grinding performed in the manufacturing method shown in FIG. FIG. 3 is a conceptual diagram showing a specific example of a drawing process performed in the manufacturing method shown in FIG. FIG. 4 is a conceptual diagram showing a specific example of press correction performed in the manufacturing method shown in FIG.

  Hereinafter, preferred embodiments of a method for manufacturing a cylinder steel pipe according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a method for manufacturing a cylinder steel pipe according to an embodiment of the present invention. Here, the steel pipe for cylinders that exemplifies the manufacturing method constitutes, in particular, a cylinder tube (outer cylinder) of a relatively large hydraulic cylinder mounted on a construction machine. A steel cylinder having a cylindrical shape of 0.0 mm, an inner diameter of 140.0 mm, and a wall thickness of 11.0 mm.

  In this manufacturing method, first, the grinding process 1 is performed with respect to the raw | natural pipe | tube of the steel pipe for cylinders carried in. This grinding process 1 is for removing fine scratches and fine non-metallic inclusions, which are surface layer defects, by uniformly grinding the entire surface layer with respect to the outer peripheral surface of the raw tube. When the grinding process 1 is performed on the raw pipe, a centerless grinding machine can be applied as illustrated in FIG. In the centerless grinding machine, if the base tube 10 is disposed between two grinding wheels A and B that rotate about parallel axes, and the grinding wheels A and B are rotated from this state, the base tube 10 The grinding process 1 is performed so that grinding marks appear along the circumferential direction on the outer peripheral surface of the steel sheet. The grinding depth is a dimension capable of removing surface layer defects, for example, 0.1 mm. As a result, it is possible to prevent as much as possible a situation in which a crack occurs in the raw tube 10 due to a surface layer defect. Note that the grinding marks produced by the grinding process 1 do not cause cracks in the cylinder steel pipe even if they remain. This is because the surface layer defect shape generated during the manufacturing of the pipe is very sharp and formed along the axial direction of the pipe, whereas the grinding marks generated by the grinding machine are This is because the angle is only along the circumferential direction and the angle is gentle, and stress is not concentrated by internal pressure during operation, and cracks do not occur.

  Next, as shown in FIG. 1, a drawing process (drawing) 2 is performed on the raw tube 10 subjected to the grinding process 1. Specifically, as illustrated in FIG. 3, by pulling out the raw tube 10 at room temperature from the hole E of the die D with the plug C mounted inside the raw tube 10, the outer dimensions of the raw tube 10 are substantially reduced. It processes so that it may become the completion dimension of the steel pipe for cylinders mentioned above.

  As shown in FIG. 1, the stress relief heat treatment 3 is applied to the raw tube 10 after the grinding process 1 and the drawing process 2 described above. In this embodiment mode, a process of heating to about 600 to 650 ° C. is performed. Thus, even if a tensile residual stress is generated in the circumferential direction in the circumferential direction 1 in the previous grinding process 1, this is removed by the stress removal heat treatment 3.

  Next, press straightening 4 is performed on the raw tube 10 on which the stress relief heat treatment 3 has been performed, and the shape is corrected. For example, as illustrated in FIG. 4, the press correction 4 performs correction such as bending by applying a pressing force to the element tube 10 supported at two points. The reason why the press correction 4 is performed during the correction processing is as follows. That is, as a straightening process performed after the stress removal heat treatment 3, roll straightening is generally performed, but from the viewpoint of residual stress, the roll straightening is performed on the outer surface layer of the base tube 10 in the circumferential direction. A tensile residual stress is generated. Therefore, in the present embodiment, after the stress relief heat treatment 3 is performed, the press correction 4 that does not apply an external force to unnecessary portions is performed.

  By carrying out the above steps, it becomes possible to manufacture a steel tube for a cylinder from which residual tensile stress is removed in the circumferential direction as much as possible and surface layer defects are removed. Thereafter, the cylinder steel pipe is configured as a cylinder tube of a hydraulic cylinder by performing burnishing on the inner peripheral surface on which the piston slides, and further cutting and painting as appropriate.

  As described above, according to the manufacturing method of the present embodiment, since the grinding process 1 is performed before the stress removal heat treatment 3 is performed, the residual stress caused by the grinding process 1 is the subsequent stress relief. It is removed by the heat treatment 3. Accordingly, it is possible to prevent a situation in which a crack is caused in the raw tube 10 due to a residual tensile stress in the circumferential direction. Moreover, since the grinding process 1 is performed over the entire surface layer with respect to the outer peripheral surface of the raw tube 10, it is possible to completely remove subsurface subcutaneous defects that are not exposed to the outside, and the surface layer defects are the starting point. There is no possibility of incurring a crack in the raw tube 10.

  In addition, specific numerical values, such as the completion dimension of the steel pipe for cylinders described in embodiment, are for the purpose of illustration only, and do not limit the present invention at all. For example, the grinding depth at 1 o'clock grinding need not be 0.1 mm, and may be 0.1 mm or less as long as surface layer defects can be removed. Regarding the stress relief heat treatment 3, the temperature is not limited to 600 to 650 ° C, and may be less than 600 ° C or 650 ° C or more as long as the residual stress can be removed.

  In the above-described embodiment, the grinding process 1 is performed before the drawing process 2 is performed. Therefore, the workability after the drawing process 2 is not affected by work hardening, but the drawing process is performed. As long as 2 and the grinding process 1 are performed before the stress removal heat treatment 3 is performed, any of them may be performed first. In particular, when the residual stress of compression can be generated in the circumferential direction on the outer peripheral surface of the base tube 10 by performing the drawing process 2, the grinding process 1 is performed so that the residual stress is not removed by the grinding process 1. It is preferable to perform the process 1 first.

  10 Elementary tube

Claims (3)

In a method of manufacturing a cylinder steel pipe in which an outer cylinder of a cylinder actuator is configured and a piston is slidably fitted therein,
A method of manufacturing a steel tube for a cylinder, comprising subjecting the base tube to grinding and drawing to the entire surface layer of the outer peripheral surface and then performing stress relief heat treatment.   The method of manufacturing a steel pipe for a cylinder according to claim 1, wherein after the stress relief heat treatment is performed, the base pipe is subjected to press correction.   2. The method of manufacturing a steel pipe for a cylinder according to claim 1, wherein the surface layer on the outer peripheral surface is ground before the drawing process.

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