JPH08243659A - Tube expanding die for steel tube expanding machine - Google Patents

Abstract

PURPOSE: To prevent the development of die mark by forming each die segment constituting a tube expanding die with a crystalline thermoplastic resin to hold the elasticity to each die segment. CONSTITUTION: The tube expanding die is selected from any one by forming each die segment 31 with the crystalline thermoplastic resin (A) or the surface side position 311 contacting with the inner surface of the tube stock and the supporting side position 312 contacting with the cone of a steel tube expanding machine with a steel (B) or the surface side position 311 with phenolic resin and the supporting side position 312 with polyamide resin (C). These crystalline thermoplastic resins, i.e., polyamide resin, phenolic resin, etc., have the elasticity and high compressive resistant strength. Therefore, the die mark and polygonal- formation are not developed in the inner surface of the tube stock and the change fo the die for lightening can be executed in a short time.

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 for use in a steel pipe expanding machine for expanding the diameter of a large diameter steel pipe.

[0002]

2. Description of the Related Art A steel pipe expander functions to remove the residual stress of a UO-made tube during pressing or welding and shape it to its final size. The steel pipe expanding machine is equipped with a pipe expanding die which can be expanded and contracted in the radial direction, and inserts it from one end of the base pipe and sequentially moves it to the other end of the base pipe while expanding the pipe.

A conventional expanding die is composed of a plurality of circumferentially divided die segments, and all these die segments are made of tool steel. But,
The tube expanding die made of this tool steel has the following problems.

1. The production cost is very high.

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 setup.

4. Dies may be broken or missing.

5. When expanding the pipe, scratches are formed on the inner surface of the raw pipe by pushing in foreign substances, pushing up the welding beads, etc.

Further, there is also a problem that when a pipe expanding die made of a conventional tool steel is used, a die mark (squareness) is generated. When expanding the die, a gap is created between adjacent die segments. There is nothing to support the inner surface of the blank tube between the gaps, and it is deformed linearly. As a result, the inner surface of the tube after expansion becomes polygonal when viewed microscopically. Further, since the side edges of the die segment are rigid, a clear step is formed on the inner surface of the pipe between the portion in contact with the die segment and the portion not in contact with the die segment. In particular, this tendency becomes more prominent as the die surface pressure increases. In this way, the dice mark is generated.

In order to prevent the occurrence of such die marks, in JP-A-57-41836, an uneven pattern is formed on the surface of the die, and the frictional force between the surface of the die and the inner surface of the blank is adjusted. It has been proposed to make the slip during pipe expansion uniform. However, this die has a problem that an uneven pattern is transferred to the surface of the tube, and the problems of roundness and dice marks still remain.

Japanese Unexamined Patent Publication (Kokai) No. 4-71737 proposes an optimum ratio of the diameter of the die to the inner diameter of the raw pipe in order to reduce the die marks. However, a die must be prepared for each pipe diameter, and the die mark cannot be completely removed.

Japanese Unexamined Patent Publication (Kokai) No. 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-made core material cannot be applied to a die that receives a high compression force.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the generation of die marks by changing the material of the tube expanding die from conventional tool steel to synthetic resin and making each die segment elastic. I have to.

[0014]

A pipe expanding die for a steel pipe expander according to the present invention comprises a pipe expanding die for a steel pipe expander for expanding and shaping a large-diameter steel pipe raw pipe with a diameter-expanding expandable die. The above problems are solved by molding each die segment with a crystalline thermoplastic resin.

In the die segment, the surface side portion in contact with the inner surface of the raw pipe may be formed of the crystalline thermoplastic resin, and the support portion side portion in contact with the cone of the steel pipe expander may be formed of steel material. .

In the die segment, the surface side portion in contact with the inner surface of the raw pipe may be formed of phenol resin, and the support portion portion in contact with the cone of the steel pipe expanding machine may be formed of polyamide resin.

Outer diameter D1 of the tube expanding die and tube inner diameter D after tube expanding
It is preferable to set the ratio (D1 / D2) of 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 not deformed smoothly and a sharp step is not formed on the inner surface of the raw tube. As a result, the degree of squaring is also reduced.

In the present invention, a crystalline thermoplastic resin is used. This resin has elasticity and high compression strength. There has been no such resin in the past, but it has been developed and marketed in recent years.

By making the die segment of resin, the following advantages can be obtained.

1. High compressibility A large compressive force acts on the die segment by plastically deforming the base pipe during expansion. The die segment withstands this compressive force.

2. High elasticity If there are small protrusions such as foreign matter or weld beads on the inner surface of the tube, the compressive force concentrates there. Even in such a case, the die segment is elastically deformed and the segment is not cracked. Further, due to the elastic deformation of the side edge portion, the die mark does not occur as described above.

3. Ease of repair If the die is repeatedly used, the surface of the die segment will be flawed and wear will progress. In such a case, the die needs to be repaired or replaced. The resin is
Although it is easily scratched, it is easy to process. The defective part of the die segment can be easily repaired by cutting or padding.

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

5. Circularity 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 pipe, and then the side edge is elastically deformed and pressed. By doing so, the die segment is brought into close contact with the inner surface of the blank tube and holds an arc close to a perfect circle. For that purpose, the ratio (D1 of the inner diameter D2 of the raw pipe after the pipe expansion to the outer diameter D1 of the die)
/ D2) is preferably 1 or more.

[0026]

EXAMPLE An example of the pipe expanding die for a steel pipe expanding machine of the present invention will be described with reference to FIGS.

First, with reference to FIGS. 1 and 2, a steel pipe expanding machine using the pipe expanding die of the present invention will be described. The steel pipe expanding machine 1 is a pipe expanding die 3 for expanding the diameter of a raw pipe 2 for large diameter steel pipe.
Spread and shape by. The steel pipe expanding machine 1 includes a draw bar 11, a cone 12, a retaining ring 13, and a pipe expanding die 3.
Made of

A cone 12 is fitted on the outer periphery of the draw bar 11, a pipe expanding die 3 is slidably mounted on the outer periphery 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 tube expansion die 3 constant.

As shown in FIG. 2, the pipe expanding die 3 is made up of a plurality of die segments 31 which are circumferentially divided.

By pulling the draw bar 11 in the direction of the arrow 15 (leftward direction) in FIG. 1, 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 the arrow 32 shown in FIGS. As a result, the large diameter steel pipe blank 2 is spread. In this way, the expander 1 removes the residual stress generated during the pressing or welding process of the UO pipe tube 2 and shapes it into the final size.

As shown in FIG. 3, in the tube expanding die 3 of the present invention, 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 is used.
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 steel (B), or the surface side portion is formed of a phenolic resin, and The support side portion 312 may be molded with a polyamide resin (C) or any of these may be used.

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

The supporting portion side 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 multi-layered in consideration of the wear of the die segment 31 and the outermost layer is coated with the high-strength resin. For example, as shown in FIG.
Main body is polyamide resin, and the thickness is about 3mm.
It can also be covered with a phenolic resin.

Outer diameter D1 of the tube expanding die and tube inner diameter D after tube expanding
It is preferable to set the ratio (D1 / D2) of 2 to 1.00 or more.

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

The die segment 31 was made of polyamide resin and set to D1 / D2 = 1.15. Tube 2
Outer diameter of 760 mm (30 in), wall thickness 6.35 mm,
The material STPY400 (JISG3457) was expanded.
The maximum ridge-valley distance (peak-to-peak) was 0.6 mm. It was 0.8-2.0 mm in the conventional die. No flaws were found on the inner surface of the blank, and the surface properties were extremely good.

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

In the polyamide resin die segment, both edges were worn during use, but D1 / D2 =
Even with 0.95, it was possible to process without particularly large eccentricity. We have found that it can also be used in wear dies depending on product requirements.

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

First, Table 1 shows the mechanical properties of the die used.

[0042]

[Table 1] Since the SKD-11 die is very unlikely to be distorted, the die mark remains on the inner surface of the blank tube. The result is a polygonal shape. According to the polyamide resin die of the present invention, the pipe could be expanded almost smoothly without leaving any die mark.

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

When expanding with a conventional die,
In order to correct the squeezing, the squeezing was reduced by rotating the raw pipe in the circumferential direction by half the width of the die segment and expanding the pipe twice. This takes twice as long as the normal tube expansion time and reduces the production efficiency.

FIG. 5 shows a comparison result of die change times. The die of the present invention is about 6.5 times lighter than the conventional die, so that the use of a crane is unnecessary and the working time is shortened.

[0046]

EFFECTS OF THE INVENTION According to the present invention, since the die segment is formed of resin, it has elasticity, does not produce die marks and polygonal shapes on the inner surface of the raw pipe, and is lightweight. Dies can be changed within a short time, and D
1 / D2 can be used in a large range, and the number of dice held can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a steel pipe expanding machine.

2 is a cross-sectional view of the steel pipe expander 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 changeover time of the steel pipe expanding machine.

[Explanation of symbols]

 1: Steel pipe expander 2: Element pipe 3: Pipe expanding die 11: Draw bar 12: Cone 14: Table key 31: Die segment 311: Surface side part 312: Support part side part

Claims (4)

[Claims] 1. A steel pipe expander for expanding and shaping a large-diameter steel pipe by a pipe expander capable of expanding its diameter. In a steel pipe expander, each die segment constituting the pipe expand die is formed of a crystalline thermoplastic resin. Expanding dies for steel tube expanders. 2. The die segment is molded with the crystalline thermoplastic resin at the surface side portion in contact with the inner surface of the raw pipe,
The pipe expanding die for a steel pipe expander according to claim 1, wherein a portion of the supporting portion side of the steel pipe expander that contacts the cone is formed of steel. 3. The die segment has a surface side portion in contact with the inner surface of the raw pipe molded with a phenolic resin, and
The pipe expanding die for a steel pipe expander according to claim 1, wherein a portion of the steel pipe expander that is in contact with a cone is formed of a polyamide resin. 4. The ratio (D1 / D2) between the outer diameter D1 of the tube expanding die and the tube inner diameter D2 after tube expanding is set to 1.00 or more. A pipe expanding die for a steel pipe expanding machine according to the item.