JPH07178619A - Method of cutting theread on steel pipe - Google Patents

Abstract

PURPOSE:To enable the cutting reaction force of a thread cutter to be uniform by using a working machine in which the x-axis and z-axis can be independently controlled before a thread cutting step, so as to add a step of previously forming a tapered cone. CONSTITUTION:With the use of a working tip 11 on rotation, a seal part and the inner surface of one end part of a fixed steel pipe is rough-cut so as to form a tapered cone. In a working machine for rotating the working tip 11, the x-axis and x-axis are independently controlled. Next, with the use of a thread cutter incorporating an NC servo-mechanism, a working chip 12 such as a form cutting tool is rotated while a chamfering process for the inner surface and a sealing process are carried out, and thereafter, a thread cutting tool 13 such as a chaser is rotated so as to cut a thread through only one path. Thereby it is possible to enhance the accuracy of thread cutting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread cutting method for steel pipes.

[0002]

2. Description of the Related Art Conventionally, the screws of oil country tubular goods used for drilling oil have generally been manufactured by the American Petroleum Institute (AP).
The screws specified in I) are used. But,
In recent years, oil country tubular goods have been required to have screws that do not leak gas even under various conditions such as tension and compression bending. Therefore, a special joint having a seal portion between metal surfaces at the joint portion has been developed.

The special screw of the oil well pipe having the special seal portion is called a premium joint. For example, as shown in FIG. 3, the inner surface 2 and the outer surface of the seal portion provided from the end face 1a of the pipe end 1 to the inner face 1b are provided. The outer surface 3 of the seal portion provided on the outer peripheral surface 1c and the screw portion 4 provided on the outer surface 1c are formed by cutting. Conventionally, the so-called lathe method has been used for cutting such a screw, in which a steel pipe is rotated along its axis to sequentially select a cutting tool set on a turret for cutting.

On the other hand, in recent years, for example, as disclosed in Japanese Patent Laid-Open No. 3-270818 already proposed by the present applicant, a steel pipe is fixed and a plurality of tools are arranged on a rotating die head. , A threading machine having an NC servo mechanism independent of the x-axis and z-axis has been developed, and a method of cutting a special screw of the same kind in less than half the time of the conventional method has been developed and put into practical use.

The contents of the above-mentioned Japanese Patent Laid-Open No. 3-270818 are as follows: As shown in FIG. 4, the side blade portion 5a for cutting the inner and outer surfaces 2 and 3 of the seal portion at the pipe end and the taper outer diameter portion of the screw lower portion are cut. This tool holder 7 is rotated by using a tool holder 7 in which a forming tool 5 provided with a lower blade portion 5b to be processed and a screw cutting tool 6 such as a checker for cutting the screw portion 4 are integrated. However, the inner surface 2 of the seal portion → the outer surface 3 of the seal portion
Part and the end surface → the outer surface 3 of the seal portion and the taper outer diameter portion of the screw lower portion → the screw portion 4 are sequentially cut in four steps.

[0006]

However, when a taper screw is machined with less than half the number of passes as in the conventional case using the pipe fixing type threading machine equipped with the NC servo mechanism as described above, it is close to the pipe end. At the part on the entry side and the part on the back side close to the finish of the screw, the cutting reaction force applied to the cutting tool and the elastic deformation amount of the material to be cut change due to the difference in the cutting area, so the tapered shape cut Tends to be small on the entry side and large on the back side, which is a problem in screw cutting accuracy.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a threading method for a steel pipe capable of thread cutting with high accuracy.

[0008]

According to the present invention, when a special screw is cut on a pipe end of a steel pipe fixed by using a threading machine equipped with an NC servo mechanism, before the step of cutting the special screw. , A x-axis and a z-axis can be independently adjusted, and a step of cutting in a taper cone shape is added in advance using a processing machine.

[0009]

[Operation] The inventors of the present invention have conducted various research and experiments on the above problems, and as a result, the above-mentioned taper variation is N
It is possible to correct up to the level that is the setting of C,
It has been found that it is difficult to completely correct due to the influence of various factors such as the strength variation or dimensional variation of the material to be cut, the bending of the pipe end, and the present invention has been completed based on this finding. is there.

That is, according to the present invention, a processing machine capable of independently controlling the x-axis and the z-axis is used before the thread cutting process using the pipe fixing type threading machine equipped with the NC servo mechanism. Since a step of cutting into a tapered cone shape has been added in advance, when cutting special screws with a thread cutting machine, the cutting load applied to the cutting tool is made constant and its backlash and elastic deformation of the material to be cut are made constant. It becomes possible.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a process chart showing the method of the present invention. First, as shown in FIG. 1 (a), rough cutting is performed on the seal portion and the inner surface of the pipe end 1 of the steel pipe 10 fixed by using a rotating machining tip 11, and a taper cone as shown in FIG. 1 (b). Process into a shape. At this time, the processing machine for rotating the processing chip 11 is not shown, but the x-axis and the z-axis can be controlled independently.

Next, using a threading machine equipped with an NC servo mechanism (not shown), the inner chamfering process and the sealing process are performed while rotating with a sealing chip 12 such as a forming tool shown in FIG. 1 (c). After that, the thread cutting tool 13 such as a checker as shown in FIG. 1 (d) is rotated to perform thread cutting in one pass. The sealing tip 12 and the thread cutting tool 13 used at this time are described in the above-mentioned Japanese Patent Laid-Open No.
If the tool holder 7 described in No. 270818 is used, it is possible to perform continuous cutting without requiring cutting interruption for exchanging the tool in the transition from the internal chamfering processing step to the thread cutting processing step. You can

The method of the present invention was applied to the cutting of an external thread having a special seal portion on an oil well pipe having a standard of API L80 and a pipe diameter of 244.5 mmφ × wall thickness of 11.99 mmt. That is, using the machined tip 11, the screw crest diameter +0.2 to 0.5 mm
After performing the taper cone-shaped screw-down processing, the thread was cut with the sealing tip 12 and the thread cutting tool 13. The result of the thread cutting accuracy at this time is shown by a circle in FIG. For comparison, the case of the conventional example is shown by a triangle mark in the figure.
As shown in this figure, when the API standard buttress tolerance is applied to the cutting accuracy, the target tolerance is 0.0625 in / in.
The upper limit is + 0.0045in / in, and the lower limit is -0.0025in / i.
Whereas n is 0.0620 to 0.0630 in / in
Also, the conventional example is 0.0610 to 0.0640 in / in, and both are within the tolerance, but the accuracy of the present invention example is 1/2 or less compared to the conventional example, You can see that it is excellent.

[0014]

As described above, according to the present invention,
Before the process of thread cutting using a pipe-fixing type threading machine equipped with an NC servo mechanism, a process of cutting into a tapered cone shape was added in advance using a processing machine that can control the x-axis and z-axis independently. Since the cutting reaction force of the thread cutting machine is made constant, the thread cutting accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a process chart showing a method of the present invention.

FIG. 2 is a characteristic diagram showing screw cutting accuracy.

FIG. 3 is a partial cross-sectional view showing a special screw shape of a conventional oil country tubular good.

FIG. 4 is a side view showing an example of a conventional tool holder.

[Explanation of symbols]

 1 Pipe end 2 Inner surface seal part 3 Outer surface seal part 4 Thread part 5 Form tool 6 Screw cutting tool 7 Tool holder 10 Steel pipe 11 Machining tip 12 Sealing tip 13 Screw cutting tool

Claims (1)

[Claims] 1. When cutting a special screw on a pipe end of a steel pipe fixed by using a threading machine equipped with an NC servo mechanism, before the step of cutting the special screw, an x-axis and a z-axis are formed.
A method for threading a steel pipe, characterized in that a step of cutting into a tapered cone shape is added in advance by using a processing machine capable of independently adjusting the axis.