JP2900819B2 - Expansion dies for steel pipe expansion machines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe expanding die used for a steel pipe expanding machine for expanding a raw pipe for a large diameter steel pipe.

[0002]

2. Description of the Related Art A steel pipe expander has a function of removing residual stress of a UO tube at the time of pressing or welding and shaping the tube to a final size. The steel pipe expander is provided with a pipe expanding die that can be expanded and contracted in the radial direction, is inserted from one end of the pipe, and is sequentially moved to the other end of the pipe while expanding.

[0003] Conventional pipe expanding dies consist of a plurality of circumferentially divided die segments, all of which are made of tool steel. But,
The pipe expanding dies made of this tool steel have the following problems.

[0004] 1. Production costs are very high.

[0005] 2. The production period is long.

[0006] 3. Since the die becomes heavy, a crane is required, and it takes a long time to change the die.

[0007] 4. Die breakage, chipping, etc. occur.

[0008] 5. When expanding the tube, the inner surface of the tube is scratched by pushing foreign matter or pushing up the weld bead.

[0009] In addition, there is a problem that a die mark (squaring) is generated when a conventional pipe expanding die made of tool steel is used. Gaps are created between adjacent die segments when the die is expanded. There is no support for the inner surface of the tube between the gaps, and the tube is deformed linearly. As a result, the inner surface of the tube after the tube expansion has a polygonal shape when viewed microscopically. Further, since the side edge of the die segment is rigid, a distinct step is formed on the inner surface of the pipe between a portion in contact with the die segment and a portion not in contact with the die segment. In particular, this tendency becomes remarkable as the die surface pressure increases. In this way, a dice mark is generated.

In order to prevent the occurrence of such a die mark, Japanese Patent Application Laid-Open No. 57-41836 discloses a method in which an uneven pattern is formed on the surface of a die and the frictional force between the surface of the die and the inner surface of the pipe is adjusted. It is proposed to make the slip during the expansion of the pipe uniform. However, in this die, there is a problem that an uneven pattern is transferred to the surface of the base tube, and problems of roundness and a die mark still remain.

Japanese Patent Laying-Open No. 4-71737 proposes an optimum ratio between a die diameter and a tube inner diameter in order to reduce a die mark. However, dice must be prepared for each pipe diameter, and dice marks cannot be completely removed.

Japanese Patent Application Laid-Open No. Sho 62-244529 proposes that when a straight pipe is bent, a resin core material is inserted into the bent portion to prevent elliptical deformation of the bent portion. However, this resin core material cannot be applied to a die that receives a high compressive force.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to change the material of an expanding die from a conventional tool steel to a synthetic resin and to make each die segment elastic so as to prevent generation of a die mark. I have to.

[0014]

According to the present invention, there is provided an expanding die for a steel pipe expander, wherein the expanding pipe die is formed in a steel pipe expanding machine for expanding and shaping a large-diameter steel pipe blank with an expandable die. The above-mentioned problem is solved by molding each die segment with a crystalline thermoplastic resin.

[0015] The die segment may be formed of a crystalline thermoplastic resin on a surface side portion in contact with the inner surface of the base tube, and a support portion side portion of the die segment may be formed of a steel material on a cone of the steel pipe expanding machine. .

[0016] The die segment may be formed of a phenolic resin at a surface side portion in contact with the inner surface of the raw pipe, and a support portion side portion of a die contacting with a cone of the steel pipe expander may be formed of a polyamide resin.

The outer diameter D1 of the expansion die and the inner diameter D of the expanded tube
It is preferable to set the ratio (D1 / D2) to 2 to 1.00 or more.

[0018]

In the tube expanding die of the present invention, since each die segment has elasticity, the side edges are smoothly deformed and no abrupt steps are formed on the inner surface of the tube. As a result, the degree of cornering is also reduced.

In the present invention, a crystalline thermoplastic resin is used. This resin has elasticity and high compressive strength. Conventionally, there was no such resin, but it has recently been developed and commercially available.

The following advantages are obtained by making the die segment made of resin.

1. High compressibility A large compressive force is exerted on the die segments by plastically deforming the tube when expanding. The die segments withstand this compressive force.

2. When there are small protrusions such as foreign matter and weld beads on the inner surface of the highly elastic pipe, the compressive force concentrates on them. Even in such a case, the die segments are elastically deformed and the segments do not crack. Further, the die marks are not generated as described above due to the elastic deformation of the side edges.

3. Ease of repair If the die is used repeatedly, the surface of the die segment will have flaws and wear will progress. In such a case, the die needs to be repaired or replaced. The resin is
Although flaws are easily formed, processing is easy. Defective portions of the die segments can be easily repaired by cutting or overlaying.

4. Low specific gravity In general, the specific gravity of steel is 7.8 and the specific gravity of resin is 1.2, and steel has a specific gravity of about 6.5 times that of resin. When changing the dies, the resin dies are lightweight, and the work is performed safely and quickly.

[5] Roundness Since the die segment has elasticity, the side edge of the die segment is first brought into contact with the inner surface of the base tube, and then the pressure is applied while the side edge is elastically deformed. By doing so, the die segment is brought into close contact with the inner surface of the raw tube, and maintains an arc close to a perfect circle. For this purpose, the ratio (D1) between the inner diameter D2 of the expanded pipe and the outer diameter D1 of the die is determined.
/ D2) is preferably 1 or more.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pipe expanding die for a steel pipe expanding machine according to the present invention will be described with reference to FIGS.

First, a steel pipe expanding machine using the expanding die of the present invention will be described with reference to FIGS. The steel pipe expanding machine 1 is a pipe expanding die 3 for expanding a large-diameter steel pipe blank 2.
Spread out and shape. The steel pipe expander 1 includes a drawbar 11, a cone 12, a retaining ring 13, and an expansion die 3.
Made of

A cone 12 is fitted on the outer circumference of the draw bar 11, a pipe expanding die 3 is slidably mounted on the outer circumference of the cone 12, and holding rings 13 are mounted on both ends in the axial direction. A table key 14 is provided inside the holding ring 13 for keeping the expansion and contraction movement of the expansion die 3 constant.

As shown in FIG. 2, the expansion die 3 is made up of a plurality of die segments 31 divided in the circumferential direction.

By pulling the draw bar 11 in the direction of the arrow 15 in FIG. 1 (to the left), the tapered cone 12 moves to the left together with the draw bar 11, and
The diameter of the segment 31 is increased in the direction of arrow 32 shown in FIGS. Thus, the large diameter steel pipe blank 2 is expanded. In this way, the expander 1 removes the residual stress generated during the pressing or welding process of the raw tube 2 made of UO and shapes it to the final dimensions.

As shown in FIG. 3, the expanding die 3 of the present invention may be configured such that each die segment 31 is formed of a crystalline thermoplastic resin (A) or the surface side portion 3 in contact with the inner surface of the raw tube 2.
11 is formed of a crystalline thermoplastic resin, and the support portion side portion 312 in contact with the cone 13 of the steel pipe expander 1 is formed of a steel material (B), or the surface side portion is formed of a phenolic resin, and The support side portion 312 may be formed of a polyamide resin (C) or any of these.

Crystalline thermoplastic resin (polyamide resin,
Phenolic resin) has elasticity and high compressive strength. This property is suitable for the die segment 31 of the present invention.

The supporting portion 312 of the die segment 31 which comes into contact with the cone 12 is preferably made of steel from the viewpoint of lubricity, wear coefficient, durability and the like.

It is preferable that the resin is made into multiple layers in consideration of the abrasion of the die segment 31, and the outermost layer is coated with a high-strength resin. For example, as shown in FIG.
The body is made of polyamide resin and the thickness is about 3mm on it
Phenolic resin.

The outer diameter D1 of the expansion die and the inner diameter D of the expanded tube
It is preferable to set the ratio (D1 / D2) to 2 to 1.00 or more.

Next, specific examples of the present invention will be described.

The die segment 31 was made of a polyamide resin and D1 / D2 = 1.15. Raw pipe 2
Has an outer diameter of 760 mm (30 in), a thickness of 6.35 mm,
The material STPY400 (JISG3457) was expanded.
The maximum peak-to-peak distance (peak-to-peak) was 0.6 mm. Conventional dies had a diameter of 0.8-2.0 mm. No flaws were generated on the inner surface of the raw tube, and the surface quality was extremely good.

Further, a phenol resin was covered on the die segment 31 made of a polyamide resin with a thickness of 3 mm. Both the surface flaws and the wear amount of the die segment after use were reduced by about half as compared with the die segment made of polyamide resin. As a result, the die life is approximately doubled.

In the die segment made of a polyamide resin, both side edges were worn during use, but D1 / D2 =
Even at 0.95, processing was possible without particularly large eccentricity. It has been found that wear dies can also be used depending on the product requirements.

For comparison, a conventional tool steel (SKD-1) was used.
The results of tube expansion using a 1) die and a polyamide resin die of the present invention are shown below.

First, the mechanical properties of the dies used are shown in Table 1.

[0042]

[Table 1] With the SKD-11 die, the die mark is left on the inner surface of the raw tube because it is very hard to be distorted. The result is a polygonal shape. According to the polyamide resin die of the present invention, it was possible to expand the pipe almost smoothly without leaving any die marks.

FIG. 4 shows the squareness of the inner surface of the raw tube after expansion.
(A) shows the case where the conventional dice is used, and (B) shows the case where the dice of the present invention is used.

When expanding a tube using a conventional die,
To correct the squaring, the squaring was reduced by rotating the tube circumferentially by half the width of the die segment and performing two expansions. This requires twice the normal tube expansion time and reduces production efficiency.

FIG. 5 shows a comparison result of the die setup change time. Since the weight of the die of the present invention is reduced to about 6.5 times that of the conventional die, the use of a crane is unnecessary, and the working time is shortened.

[0046]

According to the present invention, since the die segment is formed of resin, the die segment has elasticity, does not generate a die mark and polygonalization on the inner surface of the base tube, and has a light weight. Dice can be changed in a short time, and D
1 / D2 can be used in a large range, and the number of dice possessed can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a steel pipe expanding machine.

FIG. 2 is a cross-sectional view of the steel pipe expanding machine of FIG.

FIG. 3 is a cross-sectional view of a die segment showing various structures.

FIG. 4 is a graph showing the squareness of the inner surface of a steel pipe.

FIG. 5 is a graph showing a die setup time of a steel pipe expanding machine.

[Explanation of symbols]

 1: steel pipe expander 2: pipe blank 3: pipe expansion die 11: draw bar 12: cone 14: table key 31: die segment 311: surface side portion 312: support portion side portion

Claims (4)

(57) [Claims] 1. A steel pipe expanding machine for expanding and shaping a large-diameter steel pipe blank by an expanding die capable of expanding the diameter, wherein each die segment constituting the expanding die is formed of a crystalline thermoplastic resin. Expanding dies for steel pipe expanding machines. 2. The die segment is molded from a crystalline thermoplastic resin on a surface side portion in contact with an inner surface of a base tube,
2. The expansion die for a steel pipe expander according to claim 1, wherein a support portion side portion of the steel pipe expander in contact with a cone is formed of a steel material. 3. A support portion side portion of the die segment, the surface side portion of which is in contact with the inner surface of the base tube is formed of a phenolic resin which is a kind of crystalline thermoplastic resin, and the die segment is in contact with a cone of the steel pipe expander. 2. The expansion die for a steel pipe expansion machine according to claim 1, wherein said expansion die is formed of a polyamide resin which is a kind of crystalline thermoplastic resin. 4. The method according to claim 1, wherein the ratio (D1 / D2) of the outer diameter D1 of the expansion die to the inner diameter D2 of the expanded die is set to 1.00 or more. A pipe expanding die for a steel pipe expanding machine according to the above item.