JPS60106606A - Manufacture of seamless steel pipe - Google Patents

Abstract

PURPOSE:To prevent the lowering of material yield caused by the wall-thickness increase of a pipe end, precisely in dimensions with a simple method by ironing the inner surface of the end of blank pipe into a set wall-thickness gradient with the aids of a punch and a die. CONSTITUTION:The end of a blank pipe 6 is flared by inserting a punch 11, by prescribed length, into the pipe 6 fixed by a die 12. The punch 11 is fixed thereafter to perform ironing while keeping the lubricating condition between the die 12 and the pipe 6 in well state. Thus a desired wall-thickness reduction is precisely achieved by a simple method.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing seamless steel pipes.

The manufacturing process for seamless steel pipes consists of a drilling process in which holes are made in the round mesh material, a stretching process in which the perforated hollow shell tube is stretched to reduce its thickness, and the stretched hollow shell tube is stretched to a predetermined outer diameter. Squeezing] Consists of three steps: two rolling steps.

That is, in a typical manufacturing process of seamless steel pipe using a mandrel mill, for example, as shown in FIG. Thereafter, the material is pierced and rolled by a piercer mill 3 as a pierce-rolling machine, and then elongated by a mandrel mill 5 as an elongation-rolling machine on a Y island with a mandrel bar 4 inserted therein. The hollow tube 6 which has been stretched to double or quadruple the length by the mandrel mill 5 is reheated in a reheating furnace 7 if necessary, and then reduced and rolled by a trench reducer 8 serving as a reduction rolling mill. , A]' double bond becomes 9.

By the way, in "2 Stretch Retire User 8",
A large number of rows of roll stands with oval hole shapes allow
A hollow element v6 without a mandrel bar inserted therein is reduced and rolled to form a key pipe 9 with a predetermined outer diameter and wall thickness. Here, the diameter of each roll hole shape in the continuous roll stand rows of the wrench retoucher 8 is set so that the diameter becomes smaller toward the later stage, and the roll hole shape of the final roll stand is set outside the predetermined finished tube 9. The size corresponds to the diameter, and this allows the outer surface of the finished tube 9 to be finished molded. Here, the wall thickness of the hollow shell 6 formed in the strain reducer 8 becomes thicker as its outer diameter is reduced to a smaller diameter by the roll hole shape of each roll stand, and as it passes through the oval hole shape. There is an inconvenience that the deformation of the tube at each circumferential direction becomes non-uniform, resulting in non-uniform wall thickness, making it impossible to obtain a finished pipe 9 of good quality.

In order to eliminate the above-mentioned disadvantages, in the conventional seamless steel pipe manufacturing process, a stretch reducer 8 is used to
When rolling, while applying a tensile force in the axial direction of the hollow blank v6 between each roll stand, the unevenness in wall thickness in the cross section of the hollow blank tube 6 is reduced, and at the same time, the tensile force is applied by the roll rotation speed of each roll stand. This makes it possible to control the thickness of the pipe, suppress the increase in thickness or reduce the thickness, and obtain a finished tube 9 with a predetermined wall thickness.

However, even with the conventional seamless manufacturing method described above, the tensile force between the roll stands is sufficient at both ends of the hollow shell 6 from when it passes through one roll until it is bitten by the next roll. cannot be granted to In other words, it becomes impossible to remove the uneven thickness due to the increased thickness at both ends of the hollow tube 6, and it becomes necessary to discard nine thickened portions that occur at both ends of the finished tube 9. Finished pipe 9
The amount of the thickened portion at both ends of the tube varies greatly depending on the outside diameter reduction ratio in the trench reducer 8 or the degree of control of the roll rotation speed in each roll stand, etc. The average percentage is about 5%.

Therefore, in order to prevent a decrease in yield due to the phenomenon of tube end thickening in the reduction rolling process as described above, various methods as shown below have been proposed.

That is, (1) Japanese Patent Application Laid-open No. 3752/1983 states that:
A hydraulic rolling mechanism that does not change the pass line is installed on a specific stand of the elongation rolling mill in the pre-process of the reducing rolling mill, and the upper and lower hole rolls are made symmetrical with respect to the pass line at both the time of tube biting and the time of ash removal. A method is shown in which the tube ends can be rolled down and opened, and the tube ends can be thinned to compensate for the phenomenon of tube end thickening in reducing mills.

(2) Japanese Patent Application Laid-Open No. 57-134204 discloses that in the tube drawing/f-drawing process, a roll having a hole shape that changes in the circumferential direction and whose downstream amount changes with rotation as the hole shape changes. A method is shown in which the above object is achieved by providing a roll and thinning the end portion of the tube.

(3) Japanese Patent Application Laid-Open No. 58-74804 discloses a core bar inserted into the inner circumference of the end of a hollow shell tube that has been perforated and drawn and rolled, and a hollow shell tube into which the core bar is inserted. It has a rolling roll that revolves and rotates in contact with the outer circumference of the end and rolls down the end of the hollow shell, and is applied to the end of the hollow shell by the reduction rolling that follows the elongation rolling. A method is shown in which the thickness of the thickened portion can be reduced in advance.

(4) Japanese Patent Application Laid-Open No. 56-138208 discloses a metal core having a tapered shape and a metal core rotatably held by guide gauges arranged at equal angular intervals along the longitudinal direction of the outer surface of the metal core. A method is shown in which the inner surface of the end of an elongated and rolled hollow tube is subjected to internal processing using a rotatable and reciprocatable mandrel equipped with three to four elongated rollers.

However, in each of the above methods, the mechanism is complicated and requires a large amount of equipment investment in order to thin the pipe end portion, and it is not possible to obtain a uniform wall thickness in the circumferential direction of the pipe material after thinning. However, there are problems such as the control force method for thinning the wall is complicated and difficult to put into practical use.

An object of the present invention is to perform pipe end wall thinning processing with good dimensional accuracy using a simple method, thereby preventing a decrease in yield due to thickening of the pipe end caused by reduction rolling.

In order to achieve the above objects, the present invention provides a seamless method in which a heated steel billet is hot-pierced and stretched, and the stretched and rolled blank tube is reduced and rolled into a tube with a predetermined outer diameter and wall thickness. In the method for manufacturing a steel pipe, in an intermediate step between the elongation rolling and the reduction rolling, the thickness of the thickened portion added to the end of the material pipe by the subsequent reduction rolling is reduced in advance. The inner surface of the end portion is ironed over a predetermined length range to a preset wall thickness gradient using a punch and a die.

Embodiments of the present invention will be described below with reference to the drawings.

The present invention provides an intermediate step between elongation rolling by the mandrel mill 5 and reduction rolling by the stretch reducer 8, such as re-rolling, by performing an intermediate step between elongation rolling by the mandrel mill 5 and reduction rolling by the stretch reducer 8. On the table before inserting into the heating furnace 7, the wall thickness of the thickened portion to be added to both ends of the blank tube 6 in the subsequent reduction rolling is determined in advance by the bow Z die 11 and the die 12 of the tube end thinning forming machine IO. After tapering the inner surfaces of both ends of the raw pipe 6 corresponding to the parts where the thickened part is discarded to reduce the thickness to a preset wall thickness gradient, it is inserted into a reheating furnace 7 and heated and soaked. Thereafter, the stretch reducer 8 is used to form the tube 9, which has an extremely small amount of thickened portions cut off at both ends, as a molding mouth I function.

FIGS. 2(A) to 2(D) show that the pipe end thinning machine 10
FIG. 6 is a process diagram showing a state in which the inner surface of the end portion of the raw pipe 6 is tapered. That is, FIG. 2(A) shows a state in which the raw tube 6 after elongation and rolling is fixed with a split die 12 and a clamp 13. The inner diameter of the die 12 is approximately equal to the outer diameter of the blank tube 6. The tip 14 of the punch 11 has a shape that allows the thickened portion added to the end of the finished tube 9 to be reduced in advance by reduction rolling, and the outer diameter of the tip 14 is adjusted to the inner diameter of the raw tube 6. They are set almost equal. The profile of the tip 14 of the punch 11 is given by the following equation (1), where X is the position from the most extreme surface as shown in FIG. 3, and y is the position in the radial direction with respect to the central axis.

y = f (ts, tt, Os, Dt, e4),,,
, 41) However, in the above equation (1), tS: wall thickness of the raw tube 6, 11: wall thickness of the tube 9, DS = thickness of the raw tube 6
Dt: outer diameter of tube 9, e: distance between roll stands of stretch reducer 8. Figure 2 (B
) shows the state in which the punch 11 is inserted a predetermined length into the blank tube 6 fixed with the die 12, and the tube end becomes flared. Thereafter, as shown in FIG. 2(C), the punch 11 is fixed, and ironing is performed while maintaining a good lubricating state between the die 12 and the raw pipe 6.
As shown in Figure CD), the desired pipe end thinning can be achieved with high precision using a simple method. Note that a lubricant is supplied between the raw tube 6 and the die 12.

Hereinafter, the implementation results of the present invention will be explained in comparison with the conventional method.

For example, when a raw tube 6 with an outer diameter of 90 mm and a wall thickness of 8 mm is reduced and rolled into a tube with an outer diameter of 34 mm and a wall thickness of 7.8 mm by the conventional method, the thickness of the tube 9 is as shown in FIG. Therefore, the cut-off length of the thickened part at the end 9A of the tube 9 is about 1.7 m, and when the total length of the tube 9 is 50 m, the weight ratio of the cut-off part is about 6.8%. Become.

On the other hand, according to the inventor's experiments, the length of the thickened portion at the end 9A of the tube 9 after reduction rolling of the raw tube 6 processed by the method of the present invention is as follows: As shown in FIG. 5, it is about 0.2 m, and the weight ratio of the cut-off portion of the thickened portion at both ends of the tube 9 under the same conditions as in the conventional method shown in FIG. 4 is about 0. 8% and 5
A dramatic improvement in walking distance was observed. In addition, the thickness unevenness rate at the tip and rear end of the tube is also very good, which was about 8.0% by the conventional method, but it was reduced to about 2.5% by applying the method of the present invention, which has a good improvement effect on Ml. was recognized.

In addition, the maximum human flesh "j" in any 16 arbitrary cross sections is tmax
, the minimum wall thickness tmin, and the average wall thickness Lm, the thickness unevenness rate is expressed by the following equation.

Thickness unevenness rate 2tmax 2j-=Lx=-x 100 (%)
Lm Therefore, as described above, a good thickness unevenness ratio at the front and rear ends of the tube means that there is little variation in wall thickness in the circumferential direction at each portion at the front and rear ends.

As described above, the present invention involves hot drilling a heated steel piece,
In a method for producing seamless steel scrap, which involves elongation rolling and reducing the elongated raw pipe into a tube with a predetermined outer diameter and wall thickness, the subsequent reducing rolling is performed in an intermediate step between the elongating rolling and the reducing rolling. The inner surface of the end of the raw pipe is punched at a preset wall thickness gradient over a predetermined length range so that the wall thickness added to the end of the raw pipe is reduced in advance by the thickness increase added to the end of the raw pipe. And it is designed to be cut with a die. Therefore, by carrying out end area wall processing with good dimensional accuracy using a simple method, it is possible to reliably prevent a decrease in yield due to the thickening of the pipe end caused by reduction rolling.

[Brief explanation of drawings]

Figure 1 is a process diagram showing the manufacturing process of seamless steel pipes, Figure 2 (
A) to (D) are process diagrams showing one embodiment of the present invention, FIG. 3 is a diagram showing the profile of the punch tip used in the present invention, and FIG. 4 is a pipe end manufactured by the conventional method. FIG. 5 is a line diagram showing the wall thickness distribution of the tube end manufactured by the present invention. DESCRIPTION OF SYMBOLS 1... Steel billet, 2... Heating furnace, 3... Piercer mill, 5... Mandrel mill, 6... Hollow JT, 8...
...Stroke 1z' inch reducer, 9... Finished pipe, 10... Tube end thinning forming machine, 11... Punch, 12
···dice. Agent Patent Attorney Osamu Shiokawa Figure 4 Figure 5

Claims (1)

[Claims] (1) In a method for producing a seamless steel pipe, in which a heated steel billet is hot-pierced and stretched, and the stretched and rolled blank pipe is drawn and rolled into a tube with a predetermined outer diameter and wall thickness, the stretching and drawing In an intermediate step between rolling and rolling, the inner surface of the end of the raw pipe is cut into a predetermined length range so as to reduce the wall thickness in advance by the increase in thickness that will be added to the end of the raw pipe by the subsequent reduction rolling. A method for producing a seamless copper pipe, which comprises ironing the pipe to a preset wall thickness gradient using a punch and a die.