JPS58184005A - Endless rolling method in stretch reducer - Google Patents

Abstract

PURPOSE:To prevent the thickness increase phenomenon at the forward and rear ends of a pipe by beforehand reducing the outside diameter at the pipe end in front of a reheating furnace, welding both base pipes between the reheating furnace and a stretch reducer, and cooling the coupled part to a specific temp. just prior to rolling. CONSTITUTION:The outside diameter of a pipe end is reduced to the diameter smaller than the caliber diameter of the final stand of a stretch reducer in the stage of reducing the metallic base pipe with the stretch reducer. The pipe end is reduced to about 1/3 the diameter of the pipe at the largest. Thereafter, the reduced end parts of the base pipe are butted and joined by welding between a reheating furnace and the stretch reducer. The coupled part is cooled to the temp. lower by >=50 deg.C than the temp. of the base pipes just prior to the rolling. The thickness increase phenomenon at the forward and rear ends of the product is thus prevented in the stage of producing a circular pipe of small diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing the phenomenon of thickening at the tip and diameter end of a product when manufacturing a small-diameter circular tube using a drawing and rolling method. The present invention will be described in detail below based on a stretch reducer rolling mill.

For example, when rolling a seamless steel pipe, a stretch reducer is installed as the final step after a plug mill, mandrel mill, or semi-floating mandrel mill, and then through a reheating furnace. The rolling equipment has a structure in which several to 20 highly rigid rolling stands each consisting of 2 to 4 rolls are continuously arranged in series. The product is rolled to a predetermined size using tension. This Stretch Reducer-9 principle has an angle of 180° between its rotational axes in a plane perpendicular to the rolling direction.

This is a rolling method in which the outer diameter of the tube is reduced using two to four rolls of 120° or 90°, and the wall thickness is reduced by applying tension to the tube between rolling mills.

When rolling a tube using such a stretch reducer, there are the following problems. In other words, this is a phenomenon in which the wall thickness near the end of the tube becomes thicker than the center.

The reason why such a phenomenon occurs can be explained as follows. In a stretch reducer, the wall thickness is adjusted by the tension between the stands, but in actual rolling, tension is not generated unless the tip and rear ends of the raw tube are placed on the next stand. In other words, this tension is different between the state in which the tube is rolled by all the stands and the state in which the end of the tube passes through the stand, and a thickening phenomenon occurs as a result of the difference in the deformation of the tube.

This thickened portion near the end of the tube does not meet the dimensional specifications and is therefore discarded, which poses a major problem in terms of product yield. The present invention has been made to solve the problem of thickening the tube end and to improve the yield. That is, an object of the present invention is to carry out endless rolling to bring the tension during rolling to a state where the tube is always being rolled at all stands, thereby preventing the phenomenon of thickening. The gist of the present invention is that in a pipe rolling method, when a metal tube is subjected to reduction rolling in a line of tube drawing and rolling mills in which a plurality of rolling stands are arranged in series, the metal tube is rolled to a length in a preceding stage of the line of rolling mills. The direction is to connect.

The present invention will be explained in detail below.

When performing reduction rolling with tension applied to the tube, fluctuations in the value of the tension applied to the tube, i.e., the leading and trailing ends of the tube are simultaneously bitten by the rolling rolls of two or more rolling mills:
411. Inadequate wall thickness of the pipe (too thick) due to rolling under no tension due to
In order to prevent this from occurring, when supplying the rolled tube to the stretch reducer, it is necessary to sequentially connect the tubes in the length direction to eliminate unsteady parts related to tension application.

Welding, pressure welding, forge welding, a-blast welding, etc. can be considered as methods for joining pipes to continuously roll them, but stretch reducers (hereinafter referred to as 8R) provide deformation resistance to the pipes. The strength of the joint must be strong enough to withstand the tension applied during the rolling process.

Furthermore, in order to carry out continuous rolling, it is necessary to prevent the joining time of the tubes from becoming a factor that causes large fluctuations in the rolling speed. Endless rolling is a very effective method for achieving yield improvement and has been tried in various types of rolling.However, SR rolling is accompanied by difficulties in achieving endless rolling that are not seen in other rolling methods. . As mentioned above, this means that the tension between the stands is close to the deformation resistance, and because of this, the SR
This makes it possible to significantly reduce the wall thickness.

The magnitude of this inter-stand tension is also clear in one example shown below. In other words, even if two SR main tubes are cold welded and then charged into a reheating furnace and subjected to SR rolling, fractures may occur during rolling due to incomplete welding due to variations in welding conditions. It is.

Creating a joint that can withstand such tension requires nearly defect-free hot or cold welds, which can be quite difficult.

Therefore, the present inventors have completed the present invention after conducting various studies on a method that allows endless rolling by welding even if the welding is not completely defect-free. That is, the gist of the rolling method of the present invention is as follows.

(1) When a metal bus heated in a reheating furnace is reduced and rolled using a stretch reducer, the rear end of the leading bus is connected to the tip of the trailing bus in endless rolling.
Before the reheating furnace, the outer diameter of the tube end is processed to be smaller than the hole diameter of the final stand of the stretch reducer, and the pipes on both sides are welded together between the reheating furnace and the stretch reducer, and then immediately before rolling. An endless rolling method in a stretch reducer, characterized in that the joint portion is cooled to a temperature that is more than 100° C. lower than the rolling temperature of the main pipe.

(2) When a metal main tube heated in a reheating furnace is subjected to reduction rolling with a stretch reducer, in the endless rolling performed by joining the leading end of the leading main tube and the trailing end of the main tube, the stretching is carried out with the reheating furnace. After the pipes on both sides are joined by welding between the reducers, the pipe diameter of the joined part is made smaller than the hole diameter of the final stand of the stretch reducer by mechanical means such as a press, and the joined part is made into a base just before rolling. An endless rolling method in a stretch reducer characterized by cooling the pipe to a temperature that is at least (4°C) lower than the rolling temperature of the pipe.

The present invention will be explained in detail below.

If the bonding strength of the welded part is insufficient, this part 11'
.

All you have to do is lower the temperature by a few minutes. This is because deformation resistance increases at low temperatures, which also improves the fracture strength of the weld. However, if the temperature is lowered too much, it will have an adverse effect on the roll life, etc., and is not preferred in practice. Therefore, the pipe of the welded joint may be reduced by a stretch reducer to such an extent that it does not come into contact with the rolls during rolling.

In other words, after welding is performed in the circumferential direction of the joint between the leading and trailing bus tubes between the reheating furnace and the stretch reducer, the welded portion is compressed by a press or the like, and then the weld is welded immediately before rolling by the stretch reducer. The joint is cooled with water or the like.

In this case, the pipe shrinking process is usually a considerable amount of work, with a maximum of about % of the diameter of the main pipe. Further, the lower the temperature of the joint part is, the better, compared to the central part, but there is usually no effect unless the temperature difference is at least 30°C.

It is necessary to weld the joint all the way around the circumference, and it is normal to perform processing that has a groove and a root part, as shown in Fig. 1.

It is best to perform this process before the reheating furnace.

By the way, with this welding method, the outer surface of the tube can be strongly welded, but the inner welded part 1 shown in FIG. It is impossible to guarantee that there are no defects due to the occurrence of bumps, etc. Therefore, it is necessary to take this into consideration and operate on the safe side.

It should be noted that welding of pipes in the circumferential direction as described above requires complex equipment and procedures. Therefore, next, a method in which the order of the welding and tube shrinking processing described above is reversed will be explained. That is, the process involves shrinking both ends of the pipe in front of the reheating furnace, welding the butt part of the pipe between the reheating furnace and the stretch reducer, and cooling this welded part immediately before rolling. Naturally, it is necessary to shrink the pipe to a maximum of about % of the pipe diameter. Also, the cooling temperature of the welded part is 5% lower than the rolling temperature of the main pipe.
It is also necessary to lower the temperature by 0°C or more.

According to this method of shrinking the pipe ends before the reheating furnace, it becomes very easy to weld the abutting portions of the pipe ends. That is, as shown in FIGS. 2(A) and 2(-), the contracted end portions 3a and 3b are butted against each other with a groove, and welded in the same manner as normal overlay welding. Further, FIG. 3 shows an example in which the tube ends are cut diagonally and welded, and this method allows for more reliable connection. FIG. 4 shows cross sections at various positions in the case of oblique welding.

Although Figs. 2 and 3 above show the case where the tube reduction processing part has a round cross section, it may also have a square cross section as shown in Figs. 5, 6, and 7, which makes welding easier. It is considered easy.

Incidentally, the beveling process of the tube shrinking part may be performed before the reheating furnace, but if the process is performed immediately before welding, scale will not adhere and the conditions will be good for welding.

Next, examples of the present invention will be shown.

Example raw pipe: 101.6 m + φX 3.9 g + thick product: 48
．． 6 m + φ x 3.5 m thickness Reheat source temperature: 950°C Temperature at welded joint: 50°C Under the above conditions, the tube was rolled, the end was contracted, the joint was welded and cooled. The tube end shape and welding method were the same as the corner cross section and method shown in Figure 5. The results are shown in Figure '8.

As shown in FIG. 8, when the conventional rolling method and the method of the present invention are compared, it can be seen that the phenomenon of thickening at the tube end is significantly improved by the present invention.

[Brief explanation of drawings]

Fig. 1 is a sectional view for explaining the welding of the butt portion of the pipe ends, and Figs. 2 (a) and (b) are side views showing before and after welding of the round cross-section reduced pipe part in the method of the present invention. , Fig. 3 is a side view showing another example of the welding method for the round section reduced tube part, Fig. 4 (a)
, (b), (-) are A-A and B-B in Figure 3, respectively.
, CC sectional view, Figure 5 (a). (b) is the same as Fig. 2, in the case of a rectangular cross-section condensed tube part, and Figs. 6 and 7 (a), (b), () and) are side views showing the welding method of a rectangular cross-section constricted tube part. and its AA, BB, and CC sectional views are shown. Figure 8 shows the effects of the present invention by patent attorney Tomoyuki Yafuki (and one other person) Figure 1 gg Figure 2 (a) @31! l Figure 4 Figure 5R (A) Figure 6 #17 (A) (B) (C) Figure 8

Claims (2)

[Claims] (1) When a metal bus heated in a reheating furnace is stretched and rolled using a stretch reducer, the rear end of the leading bus is connected to the tip of the trailing bus in endless rolling. The outer diameter of the tube end is machined to be smaller than the hole diameter of the final stand of the stretch reducer in front of the heat furnace, and both mother tubes are welded together between the reheat furnace and the stretch reducer, and then immediately before rolling. An endless rolling method in a stretch reducer, characterized in that the joint portion is cooled to a temperature that is at least 1°C lower than the rolling temperature of the main pipe. (2) When a metal bus heated in a reheating furnace is subjected to reduction rolling with a stretch reducer, in the endless rolling performed by joining the leading end of the leading bus and the trailing head, the stretch between the reheating furnace and After welding the two main pipes between the reducers, the pipe diameter of the joint is made smaller than the hole diameter of the final stand of the stretch reducer by mechanical means such as a press, and the joint is connected to the mother pipe immediately before rolling. From the rolling temperature of the tube (
Capital) An endless rolling method in a stretch reducer characterized by cooling to a temperature lower than ℃.