JPH08300012A - Three-roll stretch reduction method fo metallic tube - Google Patents

Abstract

PURPOSE: To decrease angles in the peripheral direction of the inside surface of a product and to improve thickness deviation rate by arranging the rolls of roll stands imparting a specified angular displacement on a plane perpendicular to rolling pass line and executing rolling. CONSTITUTION: For example, after a steel strip 1 is heated to >=1200 deg.C in a heating furnace 2, both ends of the steel strip 1 are heated to 1380 deg.C with an edge heater 3. After that, by executing butt welding to both ends of the steel strip 1 with a tube making machine 4, the steel strip becomes a base tube 5. After stretch reducing this base tube 5 into a prescribed outside diameter and thickness with a stretch reducer 8 which is constituted of plural roll stands 7 making three rolls 6 which are arranged at the intervals of 120 deg. in the peripheral direction around the rolling pass line a set, the base tube is made into a product 10 by cutting it into a prescribed size with a cutting machine 9 and, after that, the product is transported to a cooling bed 11. Then, by executing rolling imparting the angular displacement that is a multiple of 9-15 deg. to the rolls 6 of the roll stand 7 on the plane perpendicular to the rolling pass line, the angles of the product 10 becomes >=24 angles and the out-of-roundness of the inside surface is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-roll drawing and rolling method for a metal tube, which reduces the internal surface swelling of the product generated during the drawing and rolling process.

[0002]

2. Description of the Related Art The drawing and rolling process of a metal tube is an important manufacturing process for determining a tube size such as an outer diameter and a wall thickness of a product by using a drawing and rolling machine. As shown in FIG. 6A, this squeezing and rolling mill has a plurality of roll stands 7 arranged continuously on a straight line along a rolling pass line.

The roll stand 7 is provided with three rolls 6 in the circumferential direction of the rolling pass line, and this roll arrangement is as shown in FIG.
As shown in (b), they are arranged at intervals of 120 degrees in the circumferential direction of the rolling pass line.

Conventionally, as shown in FIG. 7, this squeeze rolling mill has an angular displacement of a multiple of 60 degrees (0 degrees, 60 degrees) in a plane orthogonal to a rolling pass line in a roll stand of a set of three continuous rolls. ) Was arranged as.

Further, as a method for improving this, as shown in FIG. 8, in JP-A-58-25805, the angular displacement is arranged as a multiple of 30 degrees (0 degrees, 30 degrees, 60 degrees, 90 degrees). Things are also proposed.

[0006]

However, the displacement angle of the rolls of the roll stand consisting of a set of three rolls continuous by the above-mentioned reduction rolling mill is 6 in the plane orthogonal to the rolling pass line.
In the method of arranging the rolls every 0 degrees, as shown in FIG. 9A, rolling of the outer diameter and wall thickness of the pipe is repeated on each roll stand on the roll surface that divides the circumferential direction of the rolling pass line into six equal parts. , Hexagonal inner surface is generated in the circumferential direction of the product.

As a method for improving the above, Japanese Patent Laid-Open No. 58-258
In the method of arranging with an angular displacement of 30 degrees as disclosed in Japanese Patent Publication No. 05, etc., as shown in FIG. 9 (b), rolling of the outer diameter and wall thickness is performed on a roll surface that divides the circumferential direction of the rolling pass line into 12 equal parts. Since it is repeated on each roll stand, there is a problem in that a dodecagonal inner surface is formed in the circumferential direction of the product.

The present invention has been made to achieve a reduction in the squareness of the inner surface of the pipe. By arranging each rolling roll stand at an optimum angle in the circumferential direction of the rolling pass line, the circumferential direction of the product can be improved. The purpose is to reduce internal surface tension and improve the uneven thickness ratio.

[0009]

A three-roll squeeze rolling method for a metal tube according to the present invention comprises a plurality of roll stands arranged continuously and three rolls in the circumferential direction around the rolling pass line of each roll stand. In a three-roll squeeze rolling method in which the rolls are arranged at 120 ° intervals, the rolls of the roll stand are arranged and rolled with a multiple angular displacement of 9 ° to 15 ° in a plane orthogonal to the rolling pass line. It is what

According to a second aspect of the present invention, each roll stand arranged so as to have an angular displacement of a multiple of 9 to 15 degrees in the first aspect is divided into an arbitrary number of pairs, and the angular displacement within the pair is 60. And the angular displacement between adjacent pairs is 30 degrees or more.

A third invention is characterized in that the cycle in which the angular displacement within the pair is 60 degrees and the angular displacement between adjacent pairs is 30 degrees or more is repeated two or more cycles in the second invention. .

[0012]

The present invention is applied to the rolling pass line in the circumferential direction of 120
Since each roll arranged at an interval of 9 degrees is provided with an angular displacement of a multiple of 9 to 15 degrees in the circumferential direction of the rolling pass line, for example, a multiple of 15 degrees (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60
Angular displacement of 75 degrees, 90 degrees, and 105 degrees) is arranged as shown in FIG. As a result, the tube squeezed by the roll stand having an angular displacement of a multiple of 15 degrees is shown in FIG.
As shown in (c), rolling of the outer diameter and wall thickness of the pipe is repeated on each roll stand on the roll surface that divides the rolling pass line in the circumferential direction into 24 equal parts. The roundness of the inner surface of the product is improved.

Here, the reason why the angular displacement is limited to a multiple of 9 to 15 degrees will be described. If it is a multiple of 8 degrees or less, the number of roll stands will increase, resulting in higher equipment costs.
If it is a multiple of more than a degree, the effect of reducing the squareness is small.

The inventors of the present invention have developed rolls arranged at intervals of 120 degrees in the circumferential direction of the rolling pass line in multiples of 15 degrees in the circumferential direction of the rolling pass line (0 degrees, 15 degrees, 30 degrees, 4 degrees).
As a result of drawing rolling with angular displacement of 5 degrees, 60 degrees, 75 degrees, 90 degrees, and 105 degrees), the inner surface of the product became 24 square.

However, when the processing amount of the pipe is small, there is no problem, but when the processing amount of the pipe is large, there is a problem that the pipe is twisted during rolling and the inner surface of the product is not completely squared in the circumferential direction. Occurred.

The reason for this is that the roll caliber of the squeeze rolling mill is not a perfect circle and has a certain degree of ellipticity, so the shape of the pipe being rolled is not a perfect circle, and therefore the following rolling rolls are not. The metal tube twists in the direction that tries to match the shape of the caliber. For this reason, it is considered that the same surface is repeatedly rolled and the inner surface does not have a perfect 24-sided tension.

Therefore, various tests were conducted to improve this, and the following results were obtained. FIG. 4 is a graph showing the relationship between the roll angle displacement between adjacent roll stands and the tube twist angle. The twist angle is measured by measuring the twist angle in the circumferential direction of the seam portion between the roll stands with the rolling stopped and the tube stopped.

The black circles in the figure show the relationship between the angular displacement of the adjacent roll stands and the twist angle of the tube. As is clear from this figure, when the angular displacement of the adjacent roll stands is 60 degrees, the twist angle is the smallest, and it is found that there is no problem if it is 30 degrees or more.

Therefore, in order to set the angular displacement between the adjacent roll stands to 30 degrees or more, the roll stands arranged so as to have an angular displacement of a multiple of 9 to 15 degrees are divided into arbitrary pairs, and within the pair, The angular displacement is 60 degrees, and the angular displacement between adjacent pairs is 30 degrees or more (for example, 30 degrees, 45 degrees).
Roll stand arrangement.

Furthermore, when the cycle in which the angular displacement within this pair is set to 60 degrees and the angular displacement between adjacent pairs is set to 30 degrees or more is repeated for two cycles or more, the twisting of the pipe is caused in the entire roll stand where the rolling amount is large. Since it can be relaxed, uneven thickness is further improved.

[0021]

EXAMPLES The present invention will be described based on examples.

FIG. 1 is a schematic diagram of equipment showing an embodiment of the present invention. After the strip steel 1 is heated to 1200 ° C. or higher in the heating furnace 2, both ends (edge portions) of the strip steel 1 are heated to about 1380 ° C. by the edge heater 3. Thereafter, the pipe making machine 4 forge-welds both ends of the strip steel 1 to form the mother pipe 5. A roll stand 7 having a set of three rolls 6 of the mother tube 5 is drawn and rolled to a predetermined outer diameter and a wall thickness by a drawing and rolling machine 8 composed of a plurality of rolls, and then a predetermined number is cut by a cutting machine 9. After being cut to size, it becomes the product 10 and is then transported to the cooling floor 11.

The production conditions of the product are that the material of the strip steel 1 is low carbon steel, the width of the strip steel 1 is 445 mm, and the outer diameter of the mother tube inserted into the reduction rolling machine is 120.0 φmm. Outer diameter of the product is 21.7φmm, wall thickness is 2.8φmm
The reduction rate of the cross-sectional area from the mother tube to the product was 88.7%.

The number of stands of the reduction rolling mill of the present invention was 27 as shown in FIG.

In the present embodiment, as shown in Table 1, since the first stand group and the last stand group have a small pipe working amount, No. 1 and No. 2 of the first stand group and No. 19 to 27 of the last stand group. No. 3 to 1 of the middle stand group with a large processing amount of the pipe
For No. 8, the method of the present invention was used.

In the middle stand group, eight stands were set as one group, stand Nos. 3 to 10 were set to the first cycle, and stand Nos. 11 to 18 were set to the second cycle.

[0027]

[Table 1]

(Embodiment 1) In the drawing rolling mill of the present invention, each roll arranged at intervals of 120 degrees in the circumferential direction of the rolling pass line is a multiple of 15 degrees (0 degree) in the circumferential direction of the rolling pass line. , 15 degrees, 30 degrees, 45 degrees 60 degrees, 75 degrees, 90
The angle displacement pattern of the stand is as shown in Table 1. The first stand group and the final stand group were rolled at an angular displacement of 60 degrees, and both the first cycle and the second cycle of the intermediate stand group were rolled at a multiple of 15 degrees.

In Comparative Example 1, the first stand group, the intermediate stand group, and the final stand group were each rolled with an angular displacement of 60 degrees.

In Comparative Example 2, the first stand group and the final stand group were rolled at an angular displacement of 60 degrees, and the intermediate stand group was rolled at an angular displacement of 30 degrees.

FIG. 3 is a graph showing the relationship between the product thickness deviation and the roll angle displacement of the roll stand. The uneven thickness ratio (%) is obtained by subtracting the minimum pipe thickness from the maximum pipe thickness at one end of the product and dividing the value by the average product pipe thickness, and then multiplying by 100. . Table 2 summarizes the uneven thickness ratios of the products of Examples and Comparative Examples. As is clear from FIG. 3 and Table 2, the uneven thickness ratio of the product is higher than that when the roll angular displacement of the roll stand is 30 degrees and 60 degrees.

[0032]

[Table 2]

(Embodiment 2) In the drawing rolling mill of the present invention, the rolls arranged at intervals of 120 degrees in the circumferential direction of the rolling pass line are subjected to angular displacement in multiples of 15 degrees in the circumferential direction of the rolling pass line. And the angular displacement pattern of the roll stand is as shown in Table 1.

The initial stand group and the final stand group are 6
Rolling with an angular displacement of 0 degrees,
The angular displacement within the pair of cycles was shifted by 60 degrees, the angular displacement between adjacent pairs was shifted by 30 degrees or more, and the second cycle was performed with the same angular displacement as the second cycle of Example 1.

FIG. 3 is a graph showing the relationship between the product thickness deviation and the angular displacement of the roll stand. In FIG. 3, the mark Δ corresponds to the second embodiment.

As is clear from FIG. 3 and Table 2, the uneven thickness ratio of the product is such that the roll angle displacement of the roll stand is 30 degrees, 60 degrees.
And the case of Example 1 are improved.

(Embodiment 3) In the drawing rolling mill of the present invention, the rolls arranged at intervals of 120 degrees in the circumferential direction of the rolling pass line are subjected to angular displacement in multiples of 15 degrees in the circumferential direction of the rolling pass line. The angular displacement pattern of the roll stand is as shown in Table 1. The first group of stands and the last group of stands perform rolling with an angular displacement of 60 degrees, the angular displacement within the pair of the first cycle of the intermediate group of stands is 60 degrees, and the angular displacement of adjacent pairs is 30 degrees. As described above, the second cycle was also performed with the same angular displacement pattern as the first cycle.

FIG. 3 is a graph showing the relationship between the product thickness deviation and the roll angle displacement of the roll stand. In these FIG. 3, the mark “X” corresponds to the third embodiment.

As is clear from FIG. 3 and Table 2, the uneven thickness ratio of the product is 60 when the roll angle displacement of the roll stand is 30 degrees.
, Which is higher than those of the first and second embodiments.

In the present invention, the description has been given by taking the example of the number of roll stands of 27 rolls and the angular displacement of multiples of 15 degrees, but the number of roll stands of 20 to 50 rolls is an angle of multiples of 9 to 15 degrees. It goes without saying that the example of displacement can also be applied.

[0041]

As is clear from the above results, in the three-roll drawing rolling method, the rolls of the roll stand are rolled with a multiple of 9 to 15 degrees in the plane orthogonal to the rolling pass line. As a result, the squareness of the product is 24
The roundness of the inner surface of the pipe is improved because it is more than square.

Further, each roll stand is divided into an arbitrary number of pairs, the angular displacement within the pair is 60 degrees, and the angular displacement between adjacent pairs is 30 degrees or more.
It is possible to prevent the tube from twisting during rolling, reduce the inner surface squareness of the product, and improve the uneven thickness ratio.

[Brief description of drawings]

FIG. 1 is a schematic diagram of equipment used in an example of the present invention.

FIG. 2 is a configuration diagram of a roll stand of the reduction rolling mill used in the embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the product thickness deviation and the roll angle displacement of the roll stand.

FIG. 4 is a graph showing the relationship between the twist angle of a tube and the angular displacement of a roll between adjacent roll stands.

FIG. 5 is a schematic view showing a process of arranging a roll stand and a roll having an angular displacement of 15 degrees in a reduction rolling mill.

FIG. 6 is a drawing rolling machine, (a) is a perspective view, and (b) is a sectional view taken along line XX of (a).

FIG. 7 is a schematic diagram showing a process of arranging a roll stand and rolls having an angular displacement of 60 degrees in a reduction rolling mill.

FIG. 8 is a schematic diagram showing a process of arranging a roll stand and rolls having an angular displacement of 30 degrees in a squeeze rolling mill.

FIG. 9 is an explanatory diagram showing the relationship between the roll angle displacement of the roll stand and the inner surface tension of the product.

[Explanation of symbols]

 1 strip steel 2 heating furnace 3 edge heater 4 pipe making machine 5 mother pipe 6 roll 7 roll stand 8 drawing rolling machine 9 cutting machine 10 product 11 cooling floor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiro Ikeda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yuji Sugimoto 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Corporation (72) Inventor Kunio Todo 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside the Nippon Steel Pipe Corporation

Claims (3)

[Claims] 1. A three-roll squeeze rolling method in which a plurality of roll stands are continuously arranged and three rolls are arranged at 120 ° intervals in the circumferential direction around the rolling pass line of each roll stand. A three-roll squeeze rolling method for a metal tube, characterized in that the rolls are arranged and rolled with an angular displacement of a multiple of 9 to 15 degrees in a plane orthogonal to the rolling pass line. 2. The roll stands arranged with angular displacements in multiples of 9 degrees to 15 degrees are divided into an arbitrary number of pairs, and the angular displacement within the pair is set to 60 degrees so that the adjacent pairs are The three-roll drawing and rolling method for a metal tube according to claim 1, wherein the angular displacement is 30 degrees or more. 3. A three-roll throttle for a metal tube according to claim 2, wherein a cycle in which the angular displacement within the pair is 60 degrees and the angular displacement between adjacent pairs is 30 degrees or more is repeated for two cycles or more. Rolling method.