JPH0785804B2 - Steel pipe rolling method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rolling method for rolling a seamless steel pipe, which improves the inner surface properties of the seamless steel pipe and eliminates uneven thickness in the circumferential direction of the pipe, so-called uneven thickness. Regarding

(Prior Art) Generally, a seamless steel pipe is manufactured by a hot extrusion or rolling method. In the rolling method, for example, an inclined drilling machine,
The product is perforated and stretched by sequentially passing through a plug mill, a reeler, and a stretch reducer. Thus, one of the quality requirements for seamless steel pipe is to minimize the uneven thickness of the above-mentioned product, and the other is to prevent internal flaws and to obtain smooth internal texture. Especially.

If the uneven thickness is large, it is difficult to perform accurate thread cutting when threading the axial end of the tube.In addition, the pressure crush strength of the steel pipe decreases, and the temperature in the cross section during heat treatment of the steel pipe -It causes problems such as large variations in the material properties of the product in the cross section due to non-uniformity in time relationship.

Such uneven thickness is caused by uneven heat at the time of heating the material in the heating furnace, eccentricity of the inner plug in each mill, and whirling.

On the other hand, the inner surface property directly determines the quality of the product, and if a flaw having a depth of a predetermined value or more occurs, it is treated as a defective product. This flaw is also unavoidable in the current rolling method.

That is, in a plug mill, for example, as described in the 3rd edition of the Iron and Steel Handbook, Vol. III (2), pages 953 to 970, the plug inside is exposed to the pressure and heat due to vigorous rolling, and therefore a particularly remarkable tool. Wear occurs, and this is printed on the inner surface of the material, causing inner surface flaws.

For the two problems, the former is expected to have the effect of eliminating uneven thickness by the inclined rolling mill, or measures such as preventing uneven heat in the heating furnace are taken, but it is not a fundamental solution. The actual condition is that uneven thickness of 5-10% is usually produced as a product.

Also, in the latter, measures for alleviating severe conditions such as improvement of tool material and lubricant or use of mandrel instead of plug have been taken, but this has not been a fundamental solution.

(Problems to be Solved by the Invention) In the present invention, it is impossible to solve the problems of the inner skin and uneven thickness in the conventionally known type rolling mills. It is a solution by adoption. This rolling method makes it possible to roll a steel pipe with an excellent inner surface texture without uneven thickness by newly installing it in the middle of the existing mill or replacing part of it.

(Means and Actions for Solving Problems) The gist of the present invention is to insert a mandrel into a hollow shell and to use a rolling mill having a roll axis in the axial direction of the mandrel to roll the mandrel and the roll. In the rolling method, the hollow shell is rolled in the circumferential direction of the tube. The present invention will be described below.

It is easily presumed that the cause of the deterioration of the inner skin is that the stress and thermal load on the internal tool are too large. That is, for example, in a plug mill, the roll on the outer surface is repeatedly subjected to load, but cooling is also performed during this period. However, the internal plug is exposed to heat load during rolling of one material without being cooled and is in a one-way sliding state. Therefore, if this condition is relaxed, that is, if a longer tool is used for deformation, the heat input per unit length is small, and it is even better if the tool can be rotated without slipping.

On the other hand, although the cause of uneven thickness is known as described above,
It is also known that the uneven thickness once generated cannot be corrected unless a rolling method is adopted to release the metal in the circumferential direction. It is known that it can be corrected to some extent by a so-called empty fir, which is rotated by a so-called inclined rolling mill without an internal plug, but it is still not possible to make it zero. The method of solving both of these two is the following processing method.

That is, if a mandrel can be inserted inside the hollow shell and rolled in the circumferential direction instead of the longitudinal direction, the metal flow directions of the material and the tool will match and the deformation will be smooth.

As the mandrel rotates, the deformation becomes smooth.

Since it is handled by more tools than a plug, the heat input is reduced.

As a result, the tool will not be worn. At the same time, the following effects occur.

When there is uneven thickness in the raw pipe, it is applied in the longitudinal direction at the same time, so metal flow occurs in the circumferential direction, that is, the outer diameter becomes large in the thick part and the uneven thickness is corrected. It However, since the cross-sectional area hardly changes even if the size of the uneven thickness changes, the outer diameter in the longitudinal direction becomes substantially uniform. Even if there is a slight change in outer diameter, it can be made uniform in the subsequent steps.

However, the only problem with such a rolling method is that such hollow shells generally reach 5 to 20 m, so equipment for simultaneous reduction in the longitudinal direction becomes impractical. Therefore, as a solution to this problem, a method was devised in which rolling was divided in the longitudinal direction and rolling was partially applied.

The present invention will be described in detail with reference to FIG. In this case, the rolling mill is composed of two rolls 1 and 2, a part of the raw tube 4 having the mandrel 3 inserted therein is placed in the longitudinal direction at the center thereof, and the rolls are preliminarily opened. Simultaneously with the rotation of the roll, the roll gap is gradually tightened to a predetermined position, and the deformation of the material from the thick portion is started in the circumferential direction.

At this time, as shown in the principle in FIG. 2, the rolls 1 and 2 start to be rolled down at the same time on the upper and lower surfaces, but their longitudinal positions are not the same at the top and bottom. Therefore, although the mandrel 3 tries to bend, the reduction is small, and since the force in the opposite direction acts on the peripheral portion of the mandrel 3, the deformation balances at the position where the load is the same as a whole, and the uneven thickness is gradually eliminated. , Finally, it becomes uniform in all cross sections. Also, since the rotation direction of the roll and mandrel and the metal flow direction of the material match,
This is the same state as normal strip rolling, and the tool is not particularly worn.

At this time, in order to perform stable rolling, the roll side may have a slight inclination, and the roll may also have a profile such that the gap between the mandrel and the roll is constant. Sometimes you have a. The cross-sectional shape will be slightly distorted due to pipe expansion, but this will be correct as it will be corrected in a later step. Moreover, the shape of the seam may become uneven by repeating rolling a plurality of times, but this is not a practical problem if the deformation is gradually performed by providing a smooth step at the end of the roll. .

FIG. 3 shows an example of roll arrangement. Two rolls, three rolls, and four rolls are used. In order to stabilize the rolling, the roll may have a slight inclination with respect to the axis of the roll, and the roll may have a profile in order to compensate for the accompanying change in the roll gap.

The rolling procedure will be described with reference to FIG. A mandrel bar 7 coated with a lubricant is inserted into the raw pipe 6 and is transferred by a feed roller into a rolling mill. After the first part is rolled, the material is further transferred by a feed roller or an extract roller and then The part is rolled. The mandrel is withdrawn after all rolling is completed.

FIG. 5 shows another rolling procedure. In advance, the mandrel 7 stands by in the rolling mill, the material is inserted by the feed roller, and the first rolling starts. As soon as the rolling is finished, the next part is rolled one after another, and after the rolling, the mandrel is pulled out of the machine.

(Example) FIG. 6 compares the product thickness unevenness when a hollow tube having a spiral uneven thickness is rolled by a plug mill and when the method of the present invention is applied. By applying the method of the present invention, the uneven thickness became almost zero, and at this time, the inner surface properties were smooth and no flaws were generated.

(Effects of the Invention) According to the present invention, it is possible to obtain a beautiful steel pipe having a small inner wall thickness and a beautiful inner surface in the production of the steel pipe.

[Brief description of drawings]

FIG. 1 is an example of the structure of a rolling mill according to the present invention, FIG. 2 is a principle diagram for correcting uneven thickness, FIG. 3 is an example of roll arrangement, and FIG. 4 is a process diagram for carrying out the present invention. The figure is a process drawing showing another rolling procedure of the present invention. FIG. 6 is a graph showing the effect of the method of the present invention in comparison with the conventional method. 1,2 …… upper and lower rolls, 3,7 …… mandrel, 4,6 …… element pipe, 5 …… rolling machine.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Seki, Inventor Hiromi Seki 1-1-1, Emitsu, Hachiman-to-ku, Kitakyushu, Fukuoka Prefecture, Nippon Steel Corporation 3rd Technical Research Laboratory (56) Reference JP-A-59-113908 ( JP, A)

Claims (4)

[Claims] 1. A mandrel is inserted into a hollow shell, and the hollow shell is rolled between the mandrel and rolls in the circumferential direction of the tube by a rolling mill having a roll axis in the axial direction of the mandrel. A rolling method characterized by the above. 2. The rolling method according to claim 1, wherein a rolling machine having two rolls, three rolls and four rolls is used as the rolling mill. 3. The rolling method according to claim 1 or 2, wherein a part of the pipe in the longitudinal direction is rolled and then the remaining part is rolled. 4. A rolling method according to any one of claims 1 to 3, wherein a plurality of rolling mills are randomly arranged and rolled.