JP7528959B2 - Tool and method for cutting oil well pipe joints, and method for manufacturing oil well pipes - Google Patents

Description

The present invention relates to a cutting tool for cutting pins of oil well pipe joints, as well as a cutting method for oil well pipe joints using this cutting tool and a manufacturing method for oil well pipes.

The pins of oil well pipe joints usually have a nose at the tip of the male thread to form a seal and shoulder. When cutting the male thread, the thread portion is cut with a tool that has the same shape as the multiple threads. On the other hand, cutting the nose to form the seal and shoulder requires strict machining accuracy on the level of a few microns. In addition, it is necessary for the cutting to achieve high machining efficiency and ensure the smoothness of the cut surface (low surface roughness), as well as to improve the discharge of cutting chips and the tool life.

Regarding cutting technology for oil well pipe joints, Patent Document 1 discloses a cutting tool having three or more cutting blade faces with different radii of curvature adjacent to each other at the tip, and claims that this cutting tool is capable of cutting with fine surface roughness even when cutting at a constant high feed rate.
Furthermore, Patent Document 2 discloses a cutting tool having two cutting blade surfaces (cutting edges) with different radii of curvature provided in succession and a connecting portion between the two cutting blade surfaces formed at a specific position, and claims that by performing finish cutting with a cutting tool of this shape, it is possible to improve surface roughness.

Japanese Patent Application Publication No. 10-6108 Japanese Utility Model Application Publication No. 5-85505

According to the above-mentioned Patent Documents 1 and 2, by using a cutting tool having a cutting edge surface defined in each of them, it is possible to cut faster and with a smoother surface roughness than conventional cutting tools.
However, according to the inventor's investigation, it is difficult to perform finish cutting at high speed while ensuring a predetermined surface roughness on the seal portion and shoulder portion of the pin of the oil well pipe joint with a cutting tool having a cutting blade surface as shown in Patent Documents 1 and 2. This results in low productivity (long cutting time) and a problem that the desired surface roughness cannot be obtained.
Furthermore, these techniques inevitably result in large cutting resistance (thrust force), which makes chipping more likely to occur and also leads to problems such as chatter vibration, making it difficult to obtain a sufficient tool life.

Therefore, an object of the present invention is to solve the problems of the conventional technology as described above, and to provide a cutting tool which, in cutting pins for oil well pipe joints, can smoothly cut seal portions, shoulder portions, etc., and finish them to a prescribed surface roughness, can perform cutting at high speed while suppressing the occurrence of chatter vibration, and has an excellent tool life.
Another object of the present invention is to provide a cutting method and a manufacturing method of oil country tubular goods, which are capable of appropriately cutting pins of oil country tubular goods joints using such a cutting tool.

The inventors have studied the problems of conventional cutting tools (e.g., Patent Document 1) in which the cutting blade (cutting edge) is composed of only arcs and the means for solving them. Figures 4(a) and (b) show the axial cross-sectional profile of the cutting surface after processing with the cutting tool, and of these, Figure 4(a) is the axial cross-sectional profile of the cutting surface processed with a cutting tool (conventional cutting tool) in which the cutting blade 10 is composed of only arc portions C as shown in Figure 13 and the radius of curvature R of the arc portions C is 1.2 mm. In the case of this cutting tool, if the tool feed amount per rotation is 0.9 mm, the height of the unevenness of the cutting surface is h1. In this way, if the cutting blade is composed of only arc portions, even if the radius of curvature of the arc portions is increased, unevenness of the height of h1 will remain, so in principle, if the tool feed amount per rotation is increased, an increase in surface roughness is unavoidable.

In order to solve such problems, the inventors of the present invention have conducted extensive research based on the idea of reducing the height of the unevenness of the cutting surface by using a cutting blade that combines a circular arc portion and a straight line portion. As a result, they have found that by configuring (shaping) the cutting blade to have a first circular arc portion C1 that constitutes the tip of the tool, a straight line portion S that is connected to this circular arc portion C1, and a second circular arc portion C2 that is connected to this straight line portion S, and more preferably by optimizing the radii of curvature of the circular arc portions C1 and C2 and the configuration of the straight line portion S, the height of the unevenness of the cutting surface can be made very small, and cutting at high speeds (high feed rates) while suppressing the occurrence of chatter vibrations is possible. Figure 4 (a) shows an example of a cross-sectional profile in the pipe axis direction of the cutting surface using such a cutting tool (radius of curvature of the circular arc portion C1: 1.2 mm, radius of curvature of the circular arc portion C2: 0.4 mm). Even with the same tool feed amount (0.9 mm per rotation) as in Figure 4 (a), the height of the unevenness of the cutting surface becomes very small at h2, making it possible to cut smoothly.

The present invention has been made based on the above findings, and has the following gist.
[1] A cutting tool for oil well pipe joints, characterized in that a cutting blade has a first arcuate portion (C1) constituting a tip of the tool, and at one end side of the arcuate portion (C1), has a straight portion (S) continuing to the arcuate portion (C1), and a second arcuate portion (C2) continuing to the straight portion (S).
[2] The cutting tool for an oil well pipe joint according to the above-mentioned [1], further characterized in that the cutting blade has a straight portion (S) connected to the arc portion (C1) on the other end side of the arc portion (C1).
[3] The cutting tool according to [1] above, further comprising a cutting blade having, at the other end side of the arc portion (C1), a straight portion (S) continuing to the arc portion (C1) and a second arc portion (C2) continuing to the straight portion (S);
A cutting tool for oil well pipe joints, characterized in that the straight line portion (S) and the arc portion (C2) on one end side of the arc portion (C1) and the straight line portion (S) and the arc portion (C2) on the other end side are configured symmetrically with respect to the arc portion (C1).

[4] The cutting tool for an oil well pipe joint according to any one of the above [1] to [3], wherein the length L of the straight portion (S) is 0.8 mm or more and 1.2 mm or less.
[5] The cutting tool for an oil well pipe joint according to any one of the above [1] to [4], wherein the radius of curvature R1 of the arc portion (C1) is 0.4 mm or more and 1.5 mm or less, and the radius of curvature R2 of the arc portion (C2) is 0.4 mm or more and 1.2 mm or less.
[6] A cutting tool for an oil well pipe joint according to any one of the above [1] to [5], characterized in that the angle θ ₁ between a straight line parallel to the pipe axis of the pipe to be cut and a straight line portion (S) during cutting of the outer circumferential surface of the nose portion of the pipe to be cut is 1.0° or more and 2.0° or less.
[7] A cutting tool for an oil well pipe joint according to any one of the above [1] to [6], characterized in that the central angle α of the arc of the arc portion (C1) is 111°±1.25°.

[8] A method for cutting an oil well pipe joint, comprising cutting at least an outer circumferential surface of a nose of a pin constituting the oil well pipe joint using a cutting tool according to any one of the above [1] to [7].
[9] A method for cutting an oil well pipe joint according to the above item [8], characterized in that the cutting tool according to the above item [2] or [3] is used to continuously cut from the outer peripheral surface of the nose portion to the shoulder portion.
[10] The cutting method for an oil well pipe joint according to [8] above, characterized in that, when cutting the outer peripheral surface of the nose portion using the cutting tool according to [6] above, the feed amount in the axial direction of the cutting tool per rotation of the pipe to be cut is equal to or less than the product [L × cosθ ₁ ] of the length L of the straight portion (S) and cosθ ₁ .
[11] A method for cutting an oil well pipe joint portion according to any one of the above-mentioned [8] to [10], characterized in that the cutting tool is held by a fixture so that the angle _θ2 between the center line of the cutting tool and a perpendicular line passing through the axis of the pipe to be cut is 7° or more and 11° or less.

[12] A method for manufacturing oil well tubular goods, comprising cutting at least an outer peripheral surface of a nose portion of a pin constituting an oil well tubular goods joint portion using a cutting tool according to any one of the above [1] to [7].
[13] A method for producing oil country tubular goods, characterized in that in the manufacturing method described above in [12], the cutting tool described above in [2] or [3] is used to continuously cut from the outer circumferential surface of the nose portion to the shoulder portion.
[14] The method for producing oil well tubular goods according to the above [12], characterized in that when cutting the outer peripheral surface of the nose portion using the cutting tool according to the above [6], the feed amount of the cutting tool in the axial direction of the pipe to be cut per one rotation of the pipe to be cut is equal to or less than the product [L × cos θ ₁ ] of the length L of the straight portion (S) and cos θ ₁ .
[15] In any one of the manufacturing methods according to [12] to [14] above, the cutting tool is held by the fixture so that the angle _θ2 between the center line of the tool and a perpendicular line passing through the axis of the pipe to be cut is 7° or more and 11° or less.

The cutting tool for oil well pipe joints according to the present invention can smoothly cut the seal and shoulder parts of the nose part and finish them to a predetermined surface roughness when cutting pins for oil well pipe joints, and can perform cutting at high speed while suppressing the occurrence of chatter vibration. In addition, the tool has a long tool life, which reduces manufacturing costs.
Furthermore, according to the method for cutting an oil country pipe joint and the method for manufacturing an oil country pipe of the present invention, it is possible to appropriately and efficiently cut a seal portion, a shoulder portion, and the like using the cutting tool as described above, and it is possible to manufacture an oil country pipe having a high-quality joint with high productivity.

FIG. 2 is an enlarged front view of a cutting blade in one embodiment of the cutting tool of the present invention. FIG. 2 is a front view showing a cutting blade when the outer circumferential surface of the nose portion of a pipe to be cut is cut by the cutting tool of the embodiment of FIG. FIG. 2 is a front view showing a cutting blade when cutting a pipe end arc portion, which is a boundary between an outer peripheral surface of a nose portion and a shoulder portion of a pipe to be cut, by the cutting tool of the embodiment of FIG. 1. FIG. 2 is a front view showing a cutting blade when cutting a shoulder portion with the cutting tool of the embodiment of FIG. 1; FIG. 2 is a front view showing the entire cutting tool (tip) according to the embodiment of FIG. 1; FIG. 1 is an explanatory diagram showing the profiles of cut surfaces in the axial direction of a pipe made by a cutting tool of the present invention and a conventional cutting tool; FIG. 4 is a side view showing a state in which the cutting tool of the embodiment shown in FIG. 3 is attached to a fixture. FIG. 4 is a perspective view showing a state in which the cutting tool of the embodiment shown in FIG. 3 is attached to a fixture; FIG. 7 is an explanatory diagram showing a feed direction during cutting of the cutting tool shown in FIGS. 5 and 6 attached to a fixture. FIG. 2 is an explanatory diagram showing a schematic view of the mounting angle θ ₂ of the cutting tool of the present invention relative to the mounting fixture. A graph showing the relationship between the angle _θ1 of the cutting tool of the present invention and the surface roughness Ra of the cutting surface A graph showing the relationship between the mounting angle _θ2 of the cutting tool of the present invention and the surface roughness Ra of the cutting surface. Graph showing surface roughness Ra of the cutting surface by the cutting tool of the present invention and a conventional cutting tool at different tool feed speeds Vertical cross section of oil well pipe joint FIG. 4(A) is an explanatory diagram showing the cutting state by a conventional cutting tool, showing the profile of the cut surface in the pipe axial cross section.

12 is a vertical cross-sectional view of an oil well pipe joint, with a pin 1 and a box 2. In the pin 1, 3 is a male thread, 4 is a nose portion (flat tip pipe portion) provided at the tip portion of the male thread 3 and having a seal portion formed on part of the outer circumferential surface 8, 5 is a shoulder portion formed on the tip surface of the nose portion 4, 6 is a pipe end arc portion formed at the outer circumferential tip of the nose portion 4 (boundary portion between the outer circumferential surface 8 of the nose portion 4 and the shoulder portion 5), and 7 is a chamfer surface (thread cutting start chamfer surface) which is the starting end of the male thread 3.
The cutting tool of the present invention is applicable to cutting at least the outer peripheral surface 8 of the nose portion 4, and is preferably applicable to continuous cutting from the outer peripheral surface 8 of the nose portion 4 to the shoulder portion 5 (continuous cutting of the outer peripheral surface 8 of the nose portion 4 → pipe end arc portion 6 → shoulder portion 5).

Figure 1 is an enlarged front view of a cutting blade in one embodiment of the cutting tool of the present invention. Also, Figure 2 (Figures 2-1 to 2-3) shows the situation when the cutting tool of Figure 1 is used to cut the outer circumferential surface 8 of the nose portion 4 of the pipe to be cut, the pipe end arc portion 6, and the shoulder portion 5 in succession, with Figure 2-1 being a front view of the cutting blade when cutting the outer circumferential surface 8 of the nose portion 4, Figure 2-2 being a front view of the cutting blade when cutting the pipe end arc portion 6, and Figure 2-3 being a front view of the cutting blade when cutting the shoulder portion 5.

As shown in Figures 1 and 2, the cutting tool of the present invention has a cutting blade (cutting edge) having a pointed planar shape with an arc-shaped tip, and such a planar cutting blade has a first arc portion C1 that constitutes the tip of the tool, and at one end side of this arc portion C1, has a straight portion S (Sa in the figures) continuing to the arc portion C1, and a second arc portion C2 (C2a in the figures) continuing to the straight portion S.
Furthermore, in this embodiment, the cutting blade has, at the other end side of the arc portion C1, a straight line portion S (Sb in the figure) connected to the arc portion C1, and a second arc portion C2 (C2b in the figure) connected to this straight line portion S, and the straight line portion Sa and arc portion C2a on one end side of the arc portion C1 and the straight line portion Sb and arc portion C2b on the other end side are configured symmetrically (with a symmetrical shape) around the arc portion C1.

When cutting the outer peripheral surface 8 of the nose portion 4 of the pipe to be cut with the cutting tool of the present invention as shown in Figure 2-1, cutting is performed by "arc portion C2a + straight portion Sa + one end portion of arc portion C1" with arc portion C2a as the main component (i.e., arc portion C2a is the main component of the cutting action). Therefore, as long as cutting the outer peripheral surface 8 of the nose portion 4 of the pipe to be cut, it is sufficient for the cutting tool to have arc portion C1 and the straight portion Sa and arc portion C2a on one end side of the arc portion C1.
On the other hand, when the cutting tool of the present invention cuts the outer peripheral surface 8 of the nose portion 4 of the pipe to be cut, the pipe end arc portion 6, and the shoulder portion 5 in sequence, the outer peripheral surface 8 of the nose portion 4 of the pipe to be cut is first cut as described above (FIG. 2-1), and then the pipe end arc portion 6 is cut by the arc portion C1 as shown in FIG. 2-2. Furthermore, the shoulder portion 5 is cut by the "other end portion of the arc portion C1 + straight portion Sb" with the other end portion of the arc portion C1 as the main part (i.e., the other end portion of the arc portion C1 is the main part of the cutting action) as shown in FIG. 2-3. Therefore, in order to cut the outer peripheral surface 8 of the nose portion 4 of the pipe to be cut, the pipe end arc portion 6, and the shoulder portion 5 in sequence, the cutting tool only needs to have the arc portion C1, the straight portion Sa and the arc portion C2a on one end side, and the straight portion Sb on the other end side. In other words, the arc portion C2b on the other end side may not be present.

Here, the cutting tool of this embodiment has a straight line portion Sa and an arc portion C2a at one end of the arc portion C1 and a straight line portion Sb and an arc portion C2b at the other end, and they are configured symmetrically (with a symmetrical shape) around the arc portion C1 so that when the cutting blade life of the straight line portion Sa and the arc portion C2a at one end of the arc portion C1 has expired, the tool can be flipped over to use the straight line portion Sb and the arc portion C2b at the other end.
3 is a front view showing the cutting tool (tip) of this embodiment, in which arcuate portions C1 are provided at both ends of the diamond-shaped tip, and linear portions Sa and C2a and linear portions Sb and C2b are provided symmetrically (symmetrically) on both sides of each arcuate portion C1. This allows cutting to be performed with a total of four cutting edges, ensuring a long tool life.

As explained above based on Figures 4(A) and (B), when the tool feed amount per rotation is the same, the cutting surface cut by a conventional cutting tool whose cutting blade (cutting edge) is composed only of arc portion C has a height of unevenness h1 as shown in Figure 4(A), whereas the cutting surface cut by the cutting tool of the present invention has a height of unevenness h2, which is very small as shown in Figure 4(B), making it possible to perform smooth cutting.
In the cutting tool of the present invention, there are no particular limitations on the configuration of the arc portions C1, C2 and the straight portion S. However, from the viewpoints of ensuring the tool life, ensuring the smoothness of the cut surface, high-speed cutting performance and productivity, and suppressing chatter vibration, it is preferable to have the following configuration.

First, it is preferable that the length L of the straight line portion S (the length of the straight line portion S between the arcuate portions C1 and C2) be 0.8 mm or more and 1.2 mm or less.
If the length L of the straight portion S is less than 0.8 mm, it is difficult to obtain the effect of combining the arc portions C1, C2 and the straight portion S, which is a feature of the present invention. Also, if the length L of the straight portion S is too small, the cutting heat is not dispersed and continues to accumulate, and the tool base material is softened by the influence of the heat, and the tool life is likely to be reduced. However, by making the length L of the straight portion S 0.8 mm or more, the cutting heat can be dispersed, and the tool life can be improved. Generally, the tool feed speed in finish cutting is about 0.1 mm/revolution, but in the case of the cutting tool of the present invention, chatter vibration is suppressed, so high-speed cutting is possible, and the tool feed speed is targeted to be 0.3 mm/revolution or more, which makes it possible to shorten the cutting time. Here, for example, when cutting is performed at a tool feed rate of 0.35 mm/revolution using the cutting tool of the present invention, the outer peripheral surface 8 of the nose portion 4 is cut mainly by the arc portion C2 (the straight portion S and the end of the arc portion C1 also participate in the cutting as an auxiliary), and the shoulder portion 5 is cut mainly by the arc portion C1 (the straight portion S also participates in the cutting as an auxiliary), but even if the cutting blades of the arc portions C1 and C2 reach the end of their life, the cutting blade of the straight portion S located behind them is still in good condition, so the life of the tool itself can be improved. If the length L of the straight portion S in the cutting tool of the present invention is 0.9 mm, the theoretical tool life can be increased to 2.57 times (=0.9 mm÷0.35 mm/revolution) that of a conventional cutting tool (general-purpose tip). In addition, when an L80 oil well pipe having an outer diameter of 139.7 mm was cut at a tool feed rate of 0.35 mm/revolution and a life survey was carried out, the conventional cutting tool (general-purpose tip): end 45, the cutting tool of the present invention: end 142, and the tool life was 3.16 times longer. For this reason, the length L of the straight portion S is preferably 0.8 mm or more.

On the other hand, if the length L of the straight section S is too large, the contact area with the pipe to be cut will be large, increasing the cutting resistance, which will make chatter vibrations more likely to occur. If chatter vibrations occur, the tool life will be significantly reduced. This makes it impossible to increase the tool feed speed, resulting in reduced productivity. Although the cutting resistance can be reduced by reducing the amount of cut, multiple cuts will be required, which will increase the cutting time and reduce productivity. For this reason, it is preferable that the length L of the straight section S be 1.2 mm or less.

The arcuate portion C1 preferably has a radius of curvature R1 of 0.4 mm or more and 1.5 mm or less.
If the radius of curvature R1 of the arc portion C1 is too small, chipping is likely to occur. Also, if the radius of curvature R1 is relatively large, cutting heat is easily dispersed and the tool base material is less likely to soften, which is advantageous for improving the tool life. On the other hand, if the radius of curvature R1 is too large, the R portion dimension between the outer circumferential surface 8 of the nose portion 4 and the chamfer surface 7 becomes too large, which may cause interference when the oil well pipe joint is tightened. For this reason, the radius of curvature R1 of the arc portion C1 is preferably 0.4 mm or more and 1.5 mm or less.

The arcuate portion C2 preferably has a radius of curvature R2 of 0.4 mm or more and 1.2 mm or less.
Similarly to the radius of curvature R1 of the arc portion C1, if the radius of curvature R2 of the arc portion C2 is too small, chipping is likely to occur. In addition, if the radius of curvature R2 is relatively large, cutting heat is easily dispersed and the tool base material is less likely to soften, which is advantageous for improving the tool life. On the other hand, if the radius of curvature R2 is too large, the cutting resistance increases, and a force pushing up the cutting tool acts on the opposite side of the cutting edge performing cutting, which is a concern for the impact on the parts around the cutting tool. For example, the parts that clamp the cutting tool may wear out due to the effect of a large force being applied to them, the clamping force may be weakened, or the parts themselves may be damaged. In addition, if the cutting resistance increases, there are problems such as (i) chatter vibration is likely to occur, which makes the surface roughness of the cutting surface easily deteriorate, and (ii) cutting heat is abnormally generated, which makes the arc portion C2 soften due to the temperature rise, which makes the tool life easily shorten. For this reason, the radius of curvature R2 of the arc portion C2 is preferably 0.4 mm or more and 1.2 mm or less.

The angle _θ1 between a straight line (straight line x in FIG. 1) parallel to the axis of the pipe to be cut and a straight line portion S during cutting of the outer circumferential surface (outer circumferential surface 8) of the nose portion of the pipe to be cut is preferably 1.0° or more and 2.0° or less.
If the angle _θ1 is too small, the straight line portion S and the arc portion C2 may bite into the cutting surface due to the backlash caused when the cutting tool is attached to the fixture, and if such bite occurs, the discharge of chips becomes poor and the cutting resistance (thrust force) increases. As a result, chatter vibration occurs and the surface roughness becomes large. In principle, the smaller the angle _θ1 is, the greater the effect of smoothing the surface roughness, but if chatter vibration occurs as described above, the effect of smoothing the surface roughness is canceled. On the other hand, if the angle _θ1 is too large, the height of the uneven parts of the cutting surface becomes high, so the surface roughness becomes large, and it becomes difficult to obtain a good surface roughness, especially when cutting is performed at a high tool feed rate. Fig. 9 shows the results of a cutting test performed at a tool feed rate of 0.1 mm _/ revolution using a cutting tool of the present invention (length L of straight portion S: 1.0 mm, radius of curvature R1 of arc portion C1: 1.2 mm, radius of curvature R2 of arc portion C2: 0.4 mm, mounting angle θ ₂ : 9°) with angles θ 1 changed in the range of 0° to 3.0°, and investigating the surface roughness Ra of the cut surface. In the present invention, the tentative target for the surface roughness Ra of the cut surface is set to 1.6 μm or less, but Fig. 9 shows that the surface roughness of the cut surface is smallest and high smoothness is obtained when the angle θ ₁ is in the range of 1.0 to 2.0°. Among them, an angle of about 1.5° (about 1.5°±0.25°) is preferable because it is the smoothest.

In addition, the central angle α (tip angle) of the arc of the arc portion C1 is important in accurately cutting the shape of each portion when cutting the outer peripheral surface 8 of the nose portion 4 → the pipe end arc portion 6 → the shoulder portion 5 in succession, and it is preferable that the central angle α (tip angle) be 111°±1.25°.
The material of the cutting tool of the present invention must have the same hardness as the conventional general-purpose tip, and may be made of cemented carbide, diamond, or the like.

Next, a method for cutting a pipe to be cut and a method for manufacturing an oil country tubular good using the cutting tool of the present invention will be described with reference to Figures 2-1 to 2-3. Figures 2-1 to 2-3 show the positional relationship between the pipe to be cut and the cutting tool when the cutting tool of the embodiment of Figure 1 is used to cut the outer circumferential surface 8 of the nose portion 4, the pipe end arc portion 6, and the shoulder portion 5 in a general special thread in succession.
First, the chamfer surface 7 is cut by "arc portion C1 + straight portion Sa" mainly consisting of the arc portion C1 (i.e., the arc portion C1 is the main cutting action), and then, the outer peripheral surface 8 of the nose portion 4 is cut by "arc portion C2a + straight portion Sa + one end portion of the arc portion C1" mainly consisting of the arc portion C2a (i.e., the arc portion C2a is the main cutting action) as shown in FIG. 2-1. Next, the pipe end arc portion 6 is cut by the arc portion C1 as shown in FIG. 2-2, and further, the shoulder portion 5 is cut by "the other end portion of the arc portion C1 + straight portion Sb" mainly consisting of the other end portion of the arc portion C1 (i.e., the other end portion of the arc portion C1 is the main cutting action) as shown in FIG. 2-3. At this time, since the angle θ ₁ of the straight portion Sb is 1.0° or more, the straight portion Sb is cut without biting into the cutting surface of the shoulder portion 5.

In this way, by using the cutting tool of the present invention to cut the outer peripheral surface 8 of the nose portion 4, the pipe end arc portion 6, and the shoulder portion 5 in succession, the surface roughness can be improved not only of the outer peripheral surface 8 of the nose portion 4 where the seal portion is formed, but also of the shoulder portion 5. Therefore, by continuous cutting using one cutting tool, it is possible to cut the entire pin tip at high speed and high efficiency while ensuring surface roughness. In addition, as mentioned above, the cutting tool of the present invention has a long tool life. This makes it possible to manufacture high-quality oil well pipe joints (oil well pipes) with high productivity and low cost.

Next, preferred conditions for using the cutting tool of the present invention will be described.
Fig. 5 and Fig. 6 show the cutting tool of the embodiment shown in Fig. 3 held by a fixture of a cutting device (lathe), Fig. 5 is a side view and Fig. 6 is a perspective view. Fig. 7 is an explanatory diagram showing the feed direction of the cutting tool attached to the fixture during cutting. In the figure, A is the cutting tool, B is the fixture, and P is the pipe to be cut.

Here, as a mounting form of the cutting tool A of the present invention to the cutting device (lathe), it is preferable to hold it on the mounting fixture B so that the angle θ ₂ (mounting angle) that the tool center line f or a straight line f' parallel to it makes with the perpendicular line g passing through the pipe axis of the workpiece P is 7° or more and 11° or less. FIG. 8 is an explanatory diagram showing the mounting angle θ ₂ of the cutting tool A to the mounting fixture B. If this mounting angle θ ₂ is too small, the gap between the tip flank face and the workpiece pipe becomes small, and the tip itself is likely to experience abnormal temperature rise and wear, so the smoothness (surface roughness) of the cutting surface is likely to deteriorate, and in extreme cases, there is a risk that the tool body may come into contact with the workpiece pipe. On the other hand, if the mounting angle θ ₂ is too large, the sharpness of the cutting blade decreases. 10 shows the results of a cutting test conducted at a feed rate of 0.1 mm/revolution with the mounting angle _θ2 of a cutting tool of the present invention (length L of straight portion S: 1.0 mm, radius of curvature R1 of arc portion C1: 1.2 mm, radius of curvature R2 of arc portion C2: 0.4 mm, angle _θ1 : 1.5°) changed from 0° to 12°, and the surface roughness of the cut surface was examined. This shows that the best surface roughness can be obtained by setting the mounting angle _θ2 to 7 to 11°. Among these angles, an angle of around 9° (approximately 9°±1°) is the optimal angle.

In cutting using the cutting tool of the present invention, cutting can be performed at high speed to a predetermined surface roughness while suppressing the occurrence of chatter vibration, and cutting can be performed at a tool feed speed about 3.5 times faster than when using a conventional cutting tool. Figure 11 shows the results of investigating the relationship between the tool feed speed and the surface roughness Ra of the cut surface when cutting using the cutting tool of the present invention (length L of straight portion S: 1.0 mm, radius of curvature R1 of arc portion C1: 1.2 mm, radius of curvature R2 of arc portion C2: 0.4 mm, angle _θ1 : 1.5°, mounting angle _θ2 : 9°) and a conventional cutting tool (Figure 13). According to this, in cutting using the conventional cutting tool, the surface roughness Ra of the cut surface is about 1.3 μm at a feed speed of 0.10 mm/revolution, and about 1.8 μm at a feed speed of 0.15 mm/revolution, which does not satisfy the target surface roughness Ra of 1.6 μm or less. In contrast, when cutting using the cutting tool of the present invention, the surface roughness Ra of the cut surface is about 0.8 to 0.9 μm even at a feed rate of 0.35 mm/revolution, which shows that significantly smoother cutting is possible even at high speed cutting.
When the cutting time for a pin of an L80 oil well pipe joint having an outer diameter of 244.5 mm was compared with that of a conventional cutting tool (general-purpose tip), the following results were obtained, and by using the cutting tool of the present invention, the cutting time was reduced to about half.
Conventional cutting tool: Feed rate 0.10 mm/revolution, cutting time 185 seconds Cutting tool of the present invention: Feed rate 0.35 mm/revolution, cutting time 92 seconds Cutting time reduction effect of the present invention: 93 seconds (50.3% productivity improvement)

When cutting the outer peripheral surface 8 of the nose portion 4 with the cutting tool of the present invention, it is preferable to set the tool feed rate (feed rate in the axial direction) per revolution of the pipe to be cut to less than the product [L× _cosθ1 ] of the length L of the straight portion S and _cosθ1 . If the tool feed rate per revolution of the pipe to be cut is not less than the product [L× _cosθ1 ], the cutting allowance will extend beyond the straight portion S, making normal cutting impossible. For example, when the length L of the straight portion is 1.0 mm and the angle _θ1 is 1.5°, it is preferable to set the feed rate to 1.0 mm/revolution or less.
In addition, when cutting using the cutting tool of the present invention, cutting may be started from the shoulder portion 5 side, and cutting may be performed successively from the shoulder portion 5 to the pipe end arc portion 6 to the outer peripheral surface 8 of the nose portion 4 in that order.

REFERENCE SIGNS LIST 1 Pin 2 Box 3 Male thread 4 Nose 5 Shoulder 6 Pipe end arcuate portion 7 Chamfer surface 8 Nose outer peripheral surface A Cutting tool B Fixture P Pipe to be cut C1 Arcuate portion C2, C2a, C2b Arcuate portions S, Sa, Sb Straight portions

Claims (14)

A cutting tool for cutting oil well pipe joints, characterized in that the cutting blade has a first arc portion (C1) constituting the tip of the tool, and at one end side of the arc portion (C1), has a straight portion (S) continuing to the arc portion (C1), and a second arc portion (C2) continuing to the straight portion (S) (however, cutting tools having a step portion between the arc portions (C1) and (C2) are excluded) . The cutting tool for oil well pipe joints according to claim 1, further characterized in that the cutting blade has a straight portion (S) connected to the arc portion (C1) at the other end side of the arc portion (C1). Further, the cutting blade has, at the other end side of the arc portion (C1), a straight portion (S) continuing to the arc portion (C1) and a second arc portion (C2) continuing to the straight portion (S),
2. The cutting tool for an oil well pipe joint according to claim 1, characterized in that the straight portion (S) and the arc portion (C2) on one end side of the arc portion (C1) and the straight portion (S) and the arc portion (C2) on the other end side are configured symmetrically with respect to the arc portion (C1). A cutting tool for oil well pipe joints according to any one of claims 1 to 3, characterized in that the length L of the straight section (S) is 0.8 mm or more and 1.2 mm or less. A cutting tool for oil well pipe joints according to any one of claims 1 to 4, characterized in that the radius of curvature R1 of the arc portion (C1) is 0.4 mm or more and 1.5 mm or less, and the radius of curvature R2 of the arc portion (C2) is 0.4 mm or more and 1.2 mm or less. 6. The cutting tool for an oil well pipe joint according to claim 1 , wherein the central angle α of the arc of the arc portion (C1) is 111°±1.25°. A cutting method for an oil well pipe joint, comprising cutting at least an outer circumferential surface of a nose of a pin constituting the oil well pipe joint by using the cutting tool according to any one of claims 1 to 6 . 8. A method for cutting an oil well pipe joint according to claim 7 , characterized in that the cutting tool according to claim 2 or 3 is used to continuously cut from an outer circumferential surface of the nose portion to a shoulder portion. The method for cutting an oil well pipe joint according to claim 7, characterized in that, when cutting the outer peripheral surface of the nose portion , the angle _θ1 between a straight line parallel to the pipe axis of the pipe to be cut and the straight line portion (S) of the cutting tool is set to 1.0° or more and 2.0° or less, and the feed amount in the pipe axial direction of the cutting tool per _one rotation of the pipe to be cut is set to be equal to or less than the product [L x cos _θ1 ] of the length L of the straight line portion (S) and cos θ1. The cutting method for an oil well pipe joint according to any one of claims 7 to 9, characterized in that the cutting tool is held by the fixture so that the angle _θ2 between the center line of the tool and a perpendicular line passing through the pipe axis of the pipe to be cut is 7° or more and 11 ° or less. A method for manufacturing an oil well tubular good, comprising cutting at least an outer circumferential surface of a nose portion of a pin constituting an oil well tubular good joint portion, using the cutting tool according to any one of claims 1 to 6 . 12. The method for producing an oil country tubular good according to claim 11 , wherein cutting is performed continuously from the outer peripheral surface of the nose portion to the shoulder portion by using the cutting tool according to claim 2 or 3. 12. A method for manufacturing an oil well tubular good according to claim 11, characterized in that, when cutting the outer peripheral surface of the nose portion , an angle _θ1 between a straight line parallel to the pipe axis of the pipe to be cut and a straight line portion (S) of the cutting tool is set to 1.0° or more and 2.0° or less, and a feed amount in the pipe axial direction of the cutting tool per _one rotation of the pipe to be cut is set to be equal to or less than the product [L × cos _θ1 ] of the length L of the straight line portion (S) and cos θ1 . The method for manufacturing an oil well tubular good according to any one of claims 11 to 13, characterized in that the cutting tool is held by the fixture so that the angle _θ2 between the center line of the tool and a perpendicular line passing through the axis of the pipe to be cut is 7° or more and 11 ° or less.

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