JPS6123505A - Method for working end of seamless steel pipe - Google Patents

Abstract

PURPOSE:To work easily the end of a seamless steel pipe to a prescribed wall thickness and outside diameter by inserting a specifically designed plug into the end of the seamless steel pipe which is thick-walled at the end and emerges from a stretch reducer and drawing out said pipe. CONSTITUTION:The end of the seamless steel pipe which is finally reduced in the outside diameter to the target outside diameter and wall thickness by the stretch reducer is walled more thickly than the specified thickness and is heretofore discarded. Such end 4 is restrained by dies 5 and the plug 1 supported by a supporting bar 2 is inserted into the pipe end. The plug is circumferentially quadrisected and is made movable in the axial direction of the bar 2 by tapered parts 3. The plug 1 is retreated by the tapers 3 and enters the end 4 in the state of a small diameter in the stage of inserting the plug into the pipe end. The bar 2 is then drawn out of the pipe end then the plug 1 moves toward the left along the tapers 3 by the friction with the inside surface of the pipe and increases the diameter, thereby decreasing the wall thickness at the pipe end between the same and the dies 5 and shaping the pipe end to the prescribed wall thickness and outside diamter. The yield as the seamless steel pipe product is improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is used in the manufacturing process of seamless steel pipes (herein, it eliminates the change in the longitudinal dimension of the material after stretch reduction and reduces the amount of cut-off as a clog). Regarding the rolling method.

(Prior art) The production of seamless steel 4-pipe is carried out, for example, by using a punching machine that makes a hollow tube by pushing a square piece of steel into a hollow tube with a circular hole shape.
An inclined roll rolling machine that further reduces the wall thickness of this hollow tube,
Furthermore, a mandrel mill inserts a mandrel into this tube to continuously reduce the wall thickness.After heating this tube again,
This is done using a stretch reducer or the like that reduces the outer diameter.

For example, the stretch reducer is
Publication No. 458 (as disclosed in this publication, a plurality of stands consisting of 1 to 2 CI-ru or 30-ru are arranged in succession, the number of roll rotations is adjusted, and rolling is carried out while applying general tension. , a rolling mill that obtains a predetermined outer diameter and wall thickness.

(Problem to be Solved by the Invention) However, as a characteristic of rolling that applies tension, there are inevitably areas where tension is not completely applied at the tip and rear ends of the material, and generally at the end of the tube. The wall thickness becomes thicker than the central part, and this part is finally cut off as a rib.

In the present invention, after finishing rolling in a stretch reducer, another processing method is added to reduce the thickness of only the thick end of the tube, making it the same as the center part, and converting this part into a product. We are trying to provide relief.

(Means for Solving the Problems) A feature of the present invention is that after the stretch reducer, only the ends of the material having different wall thicknesses in the longitudinal direction t are removed using a plug and a die. The flesh part is finished by drawing the outer diameter and wall thickness to a predetermined dimension G in the longitudinal direction, or if necessary, after the above-mentioned processing, the vagina-processed part is finished with one or more 20
The method is to carry out sizing and finishing rolling in a 30- or 30-mill rolling mill.

(Example) The present invention will now be described in detail with reference to Examples.

FIG. 1 shows an example of the structure of a plug used in the present invention and a bar supporting it. The plug l is divided into four parts in the circumferential direction, and a tapered part 3 is provided at the tip of the bar 2, so that the plug is movable in the axial direction.

Therefore, when the plug is closest to the right in the drawing, the outer diameter is the smallest, and when it is closest to the left, it is the largest outer diameter, and the inner diameter ζ is the desired value of the material described later. They are almost equal.

FIG. 2 shows the procedure of the present invention. The end portion of the material 4 has a wall thickness that increases toward the inner diameter side, and this portion is first inserted into the die 5 (thus, the circumferential direction of the tube is restrained, and the plug 2 supported by the support bar 2 enters the tube ( (b) Figure).

At this time, the plug retreats due to the frictional force with the inner surface, and the diameter of the plug becomes smaller than the inner diameter of the tube end. After reaching the internal steady thickness part, the support bar retreats, and the plug 1 also moves due to the frictional force with the material, and the outer diameter of the plug increases, and the wall thickness begins to decrease between the plug 1 and the die 5. ((d) Figure 9゜Next, the plug reaches the outside of the tube, and the end of the material has a predetermined thickness ((e) Figure).At this time, since the die is divided into four parts, the mating surface of the die There will be some parts where the wall thickness does not decrease, but by performing the drawing operation twice with different mating surfaces, the entire pipe circumferential surface will have a uniform thickness.Also, two 1 plugs can be attached to the same bar. Depending on the attachment, it is also possible to mix them all at once.

In addition, if necessary, to prevent the temperature of the material from decreasing,
A die made of a material with poor thermal conductivity, such as ceramic, is used, and a lubricant is used to increase the durability of the plug.

FIG. 3 is an example of a layout when the present invention is applied. The side of the cooling bed 7 at the rear of the stretch reducer 6 (this
A device 8 for processing the leading end and a device 9 for processing the rear end shown in FIG. 2 are arranged.

The material 10 leaving the stretch reducer 6 advances to the cooling bed 7, where the leading end is first processed by the leading end side device 8, and then retreated and the rear end is rolled down by the device 9. In addition, if the outer diameter accuracy is insufficient, it may be necessary to install a 20mm
In some cases, an outer diameter finishing mill consisting of a 1- or 30-ru diameter mill is installed.

In addition, the temperature of the material is basically determined by using the temperature after rolling, but if the temperature decreases too much, it may be supplemented by, for example, induction heating.

Furthermore, as an applied example, the processing does not necessarily have to be carried out near the cooling bed, and the material may be heated only at the tube end once it has reached room temperature, and then the processing may be carried out. The plug shown in FIG. 1 is an example.

It should be added that the diameter of the plug may be changed using hydraulic pressure or the like, and that these are also included in the present invention.

(Effects of the invention) Figure 4 (This is a comparison of the longitudinal wall thickness of the material when the present invention was implemented and when it was not. According to the method of the present invention, the yield can be improved and the wall thickness can be made uniform in the longitudinal direction, so that its industrial and practical value is extremely large.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are vertical and transverse cross-sectional views showing an example of the plug structure used in the present invention, FIGS. 2(a) to (e) are examples of the present invention and its procedures, and FIG. 3 is the present invention. FIG. 4, an example of a layout in which the invention is implemented, shows a plug in which the dimensions (wall thickness) according to the invention are compared with those of a conventional plug. DESCRIPTION OF SYMBOLS 1... Plug divided into 4 parts, 2... Plug support bar, 3... Tapered part, 4... Material, 5... Dice, 6... Trench reducer, 7... cooling bed, 8
, 9... Edge processing device, 10... Material.

Claims (1)

[Claims] After the steel pipe is reduced and rolled by a stretch reducer, a plug whose diameter can be freely expanded and contracted is inserted into the hollow part of the end of the material having parts with different wall thicknesses in the longitudinal direction, and the plug is inserted into the hollow part. Depending on the dice,
A seamless steel pipe characterized in that the outer diameter and wall thickness are finished to predetermined dimensions in the longitudinal direction by performing a drawing process to reduce the thickness of the extra thick part while axially displacing the plug in the direction of expanding the diameter of the plug. pipe end processing method.