JPS63220908A - Rolling method for hollow blank pipe by elongator - Google Patents

Abstract

PURPOSE:To prevent the biting of a scale between a plug and blank pipe and to improve the quality by rolling with extension the roll and plug having the outer peripheral face part in parallel to a pass line with moving in the same direction as the progressing direction of a hollow blank pipe. CONSTITUTION:A plug 2 is moved to the progressing direction of a hollow blank pipe P from the position advancing it so that at least one part of the parallel face part 2a of the plug 2 may be superposed on the parallel part 1a of a roll 1. By this method, the gap between the roll 1 and plug 2 is not varied, so the biting of scales is prevented and the inner face quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for rolling a hollow shell pipe without producing an inner bottom due to scale in the second drilling step and the like in the manufacturing process of seamless steel pipes.

(Prior art) In order to manufacture seamless steel pipes, normally, a round billet heated to a high temperature is first perforated using a piercer (the first perforation step), and then the resulting hollow tube is expanded using an elongator. This is further stretched using a plug mill or the like, and then finished to a predetermined size using a reeler, sizer, reducer, or the like.

Of the above manufacturing steps, the second perforation step will now be described in some detail. As shown in FIG. 5, the main parts of the elongator F used here are two rolls 11° 11 arranged so that their axes are inclined to each other, and a plugper 13.
Rolled plug 1 held between rolls 11.11 by
It consists of 2. In the figure, 14 is a thrust block, and 16 is a thrust block table.

The hollow tube P obtained by the first punching process has a bushing (
(not shown) or the like into the gap between the rolls 11 and 11. Since the rolls 11.11 are rotating in the same direction at a constant speed and the roll axes are inclined, the hollow shell P caught in the rolls 11.11 moves forward while rotating. When the plug 12 is moved slightly forward from the biting position S (see Fig. 6), the plug 12 is inserted into the hollow shell P, and is rolled between the plug 12 and the rolls 11 and 11 to expand the diameter, thicken it, and Stretching is performed.

[Problem that the invention seeks to solve]

By the way, in the above-described second drilling step, the inner surface of the hollow shell P is descaled by injecting high-pressure water immediately before rolling. However, the scale could not be removed sufficiently by spraying high-pressure water alone. For this reason, as shown in FIG.
The hollow tube P is caught in the roll kl, 11.
to the position t where it contacts the plug 12), the remaining scale peels off from the inner surface 20 of the raw tube and stays just before the part where the plug 12 and the inner surface 20 of the raw tube contact.

This retained scale 30 accumulates as the hollow tube P progresses, and eventually grows into a lump. When the lumpy scale is caught between the inner surface 20 of the raw tube and the plug 12, it is printed on the inner surface 20 of the raw tube, causing flaws, and worsening the condition of the inner surface flaw. Furthermore, since the amount of scale retained increases as the process progresses, the degree of internal flaws worsens from the tip (top) to the rear end (bottom) of the hollow tube P. Furthermore,
The surface of the plug 12 may be scratched by lumpy scales, and when the plug 12 with scratches is used, there is a problem in that secondary inner surface scratches are generated.

[Means for solving problems]

The present invention aims to prevent inner surface flaws from occurring in a hollow raw tube by eliminating or minimizing scale encroachment in a method of rolling a hollow raw tube using an elongator. A feature of the rolling method is that a roll and a plug having an outer peripheral surface portion parallel to the pass line are used, and rolling is performed while moving the plug in the same direction as the traveling direction of the hollow blank tube.

[Effect]

As described above, the scale peeled off from the inner surface of the hollow tube remains just before the portion where the plug and the inner surface of the tube come into contact, and is accumulated as the rolling process progresses. Therefore, if the plug is moved in the same direction as the traveling direction of the hollow shell tube at the same time as rolling, the relative speed between the plug and the hollow shell tube will be reduced, and the amount of scale retained will be minimized. Therefore, it is completely eliminated or minimized that scale gets caught between the plug and the inner surface of the raw tube, and the occurrence of inner surface flaws is prevented. Even if scale were to be caught between the plug and the inner surface of the raw tube, the amount of accumulated scale would be so small that only a small number of very small pieces of scale would be caught. Therefore, even if an inner surface flaw occurs, it is fully possible to correct it in the subsequent process, and in some cases, it can be ignored. Furthermore, since there is no need to reduce the traveling speed of the hollow tube, the time required for one bus is the same as in the conventional method.

Note that the greater the moving speed of the plug, the greater the effect of preventing scale enmeshment.

In addition, by using rolls and plugs with outer circumferential surfaces parallel to the pass line, the minimum gap between the roll and the plug does not change while the plug is being moved. Therefore, the rolling load can be reduced. Since there is no fluctuation, there is no uneven thickness or eccentricity in the hollow tube. In addition, the longer the length of the parallel surface portion provided on the outer circumferential surface of the roll and plug, the greater the distance the plug can move. can.

Therefore, it is possible to adopt a higher plug moving speed, and the effect of preventing inner surface flaws can be further improved.

〔Example〕

The details of the present invention will be explained below based on examples.

The Elongator E used in the method of the present invention has a roll l, as shown schematically in plan view in FIG.

1, a plug moving device i! 5 is provided. The plug moving device 5 is, for example, a mechanism that is mounted on the thrust block 4 and supports the rear end 3a of the plugper 3 with a hydraulic cylinder (or hydraulic cylinder), or a mechanism that moves the plugper with a motor driving force combined with a gear box. A mechanism for moving 3 forward and backward is conceivable. Note that 6 is a thrust block table.

On the outer circumference of each of the roller 1.1 and the plug 2, a second
As is clear from the enlarged cross-sectional view in the figure, surface portions 1a and 2a parallel to the pass line 1 are provided. The length dimensions of the parallel surface portions 1a and 2a depend on the rolling speed, the dimensions of the hollow shell P to be rolled, and the roll 1. It is determined according to the shape of the plug 2, etc.

In order to roll the hollow shell P by the method of the present invention, first, the plug 2 is placed in a more advanced position than before so that at least a portion of the parallel surface portion 2a of the plug 2 overlaps the parallel surface portion 1a of the roll 1. 0 held in [2(α)] then,
The hollow shell P is inserted between the rolls 1 and 1 and advanced. Once the plug 2 is inserted into the hollow shell P, the plug 2 is moved in the advancing direction of the hollow shell P along the pass line l (2(β)), and this movement is parallel to the roll 1. The rolling process is performed in the range where the surface portion 1a and the parallel surface portion 2a of the plug 2 overlap.Therefore, since the minimum gap between the roll 1 and the plug 2 does not change during the rolling process, no variation in rolling load occurs either. , and the moving speed V of the plug 2
is determined by the distance to which the plug 2 is moved and the time required for the hollow tube P to be sent out from the rolls 1, 1.

Next, the hollow tube was rolled based on the method of the present invention, and the surface roughness of the inner surface was measured. The results are shown in Figures 3 and 4.
The surface roughness, which is expressed as a graph in the figure, is the maximum height Rm specified in JIS BO601.
ax). The rolling was carried out under the conditions listed in Table 1 below.

<Table 1> Fig. 3 shows the inner surface of the hollow shell when the roll and plug according to the present invention shown in Table 1 above are used and the plug is moved at a speed of 5 m/sec for rolling. It is a graph which shows the result of measuring Rmax). The vertical axis shows the surface roughness (Rmax), and the horizontal axis shows the distance from the tube end to the measurement position. As an example for comparison, the results of rolling under the conditions listed in Table 2 below using conventional rolls and plugs that do not have flat parts and without moving the plugs, that is, by stopping them. .

Table 2 As is clear from the figure, the surface roughness of the inner surface of the hollow tube rolled by the method of the present invention is almost uniform from the top to the bottom of the tube, and has a small value. On the other hand, in hollow tubes rolled by the conventional method, the surface roughness value of the inner surface increases from the top to the bottom of the tube. This means that the inner skin deteriorates. The cause of this deterioration of the inner surface is that the amount of scale that remains increases as the hollow tube progresses, and the amount that is caught between the plug and the inner surface of the tube increases. If you look back,
It can be seen that in rolling according to the method of the present invention, almost no scale encroachment occurs.

Figure 4 shows the results of rolling a hollow blank tube of the dimensions shown in Table 1 using the rolls and plugs according to the present invention listed in Table 1 and varying the moving speed V of the plugs. It is a graph showing surface roughness. The surface roughness is 100 to 200 m from the rolling rear end (bottom) of the hollow tube after rolling.
The measurements were taken at the inner surface area of The vertical axis is the surface roughness (Rmax), and the horizontal axis is the plug speed (v).

When the moving speed V was Qu+/sec, that is, when rolling was performed with the plug stopped, the surface roughness of the inner surface of the hollow shell was approximately 85 mm. By moving the plug by only 5 mm/sec, the surface roughness value is reduced to approximately 63 mm. The surface roughness value decreases as the plug's moving speed V increases, and V = 40m/sec
At V-50 mm/sec, it is reduced by half to about 30 Peng, and at V-50 mm/sec it is reduced to about 25 Peng.

〔Effect of the invention〕

As is clear from the above description, according to the method for rolling a hollow shell tube according to the present invention, it is completely or minimally possible that scale is caught between the plug and the inner surface of the shell tube.
The occurrence of inner surface flaws is prevented, and the surface roughness of the inner surface of the raw tube is kept uniform. In addition, since rolling is performed using rolls and plugs that have outer circumferential surfaces parallel to the pass line, there is no need to move the plugs. The rolling load does not fluctuate, and uneven thickness and eccentricity do not occur.

Moreover, since the time required for one rolling pass is the same as in the conventional method, manufacturing efficiency is excellent.

In short, the present invention makes it possible to efficiently manufacture steel pipes with extremely good inner surface conditions, and brings about a significant improvement in yield.

[Brief explanation of the drawing]

1 to 4 are related to the present invention, and FIG. 1 is a plan view schematically showing the elongator according to the present invention, and FIG.
The figure is an enlarged sectional view of the main parts same as above. FIG. 3 is a graph showing the change in surface roughness on the inner surface of the hollow mother tube after rolling over the entire length of the mother tube, and FIG. 4 is a graph showing the change in surface roughness when the moving speed of the plug is changed. FIG. 5 and FIG. 6 are related to the conventional example,
FIG. 5 is a plan view schematically showing the Elongator, and FIG. 6 is an enlarged sectional view of the main part of the improvement.

Claims (1)

[Claims] 1. In a method of inserting a plug into a hollow raw tube caught in the rolls of an elongator and expanding and rolling the hollow raw tube, a roll and a plug having an outer peripheral surface portion parallel to the pass line are used, and the plug is A method for rolling a hollow shell using an elongator, which is characterized in that rolling is carried out while moving the hollow shell in the same direction as the traveling direction of the hollow shell.