JPS6020082B2 - Manufacturing method for seamless steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a small diameter seamless steel pipe.

A mandrel mill tube manufacturing method is a method for efficiently producing seamless metal pipes, such as seamless steel pipes.

The mandrel mill tube manufacturing method is a method in which a mandrel is inserted into a circular tube that has been perforated by an appropriate method, and the tube is continuously rolled using a caliber row made up of a set of rolls, and then finish rolling is performed using a sizer or a stretch reducer. This method of continuously rolling a tube using a mandrel mill is referred to as a continuous tube rolling method, and includes the case where the moving speed of the mandrel during rolling is controlled. In the conventional continuous rolling method for tubes, most of the wall thickness reduction is performed in the first 2 to 4 calibers in the caliber row, the wall thickness is evened out in the middle 2 to 3 calibers, and the last 2 to 3 calibers are It is customary to loosen the tube from the mandrel and make it into a perfect circle.

At this time, the amount of change in the outer shape of the tube is generally only a small amount, about twice the amount of change in wall thickness. Recently, continuous cast blooms have come to be used directly as raw material for seamless steel pipes, including blooming and rolling.

The larger the cross section of such a continuous casting bloom, the better the casting efficiency, and the larger the cross section, for example, 200 mm or more, than the small cross section bloom used in the production of seamless steel pipes. Bloom's quality is also better. Therefore, when manufacturing small-diameter seamless steel pipes with an outer diameter of 17 mm to 25 mm by hot rolling,
Three types of material bloom cross sections are required, and tools corresponding to the number of material bloom sizes are required throughout the entire process from continuous casting machine molds to steel pipe products. There was also a huge waste of storage space. A primary object of the present invention is to provide a method for manufacturing small diameter spliced metal tubes from large cross-section blooms and a method for reducing the number of raw bloom sizes.

Furthermore, a second object of the present invention is to provide a method for manufacturing a small diameter seamless metal tube with excellent efficiency. The reason why this objective could not be achieved in the past is because of the following problems.

That is, for the first purpose, if the outer bulge reduction is large in the first pair of rolls of the '1' continuous rolling mill, poor biting will occur.

■ Even if the number of rolls is increased as an extension of the conventional continuous rolling method, the outer diameter reduction can be made large enough to achieve the above objective.On the contrary, the change in mandrel speed during rolling, which is a disadvantage of continuous rolling of pipes, becomes large. It was thought that this would deteriorate the dimensional accuracy of the finished pipe.

For the second purpose, [3' In the conventional method, the outer diameter reduction in the continuous rolling mill is extremely small, so if you want to obtain a product of the same weight, it is necessary to roll it thinner and longer in the previous process, which reduces the temperature. However, rolling with a continuous rolling mill became difficult.

Next, the present invention will be explained. Fig. 1 shows an example of the equipment layout in the case of implementing the present invention, in which a metal bloom with a polygonal cross section is used as the material. A metal heating furnace 1 that heats a polygonal cross-section metal bloom to a temperature that allows it to undergo hot working, a press roll punching machine 2 that punches the bloom into a cylindrical Qin tube or a cylindrical blank tube with a bottom, and then a plug inside the blank tube. Alternatively, there is an inclined roll rolling mill 3 that inserts a mandrel and rolls it, followed by a mandrel mill 4 (hereinafter referred to as a continuous rolling mill) that inserts a mandrel into the blank tube and rolls it continuously, and then a mandrel mill 4 that inserts a mandrel into the blank tube and rolls it continuously, and then a mandrel mill 4 that inserts a mandrel into the blank tube and rolls it continuously. A device 5 for extracting the mandrel, a device 6 for transporting the mandrel to the input side of the mandrel mill, and a metal tube heating furnace 7 for subsequently heating the raw tube to a temperature suitable for the next hot rolling process.
, a stretch reducer 8 that continuously tension-rolls the raw pipe, and a rolled material conveying device 9 that connects these devices. In the continuous rolling mill 4 that performs continuous rolling, the roll arrangement direction is 90 degrees out of phase between adjacent stands as shown in Fig. In particular, in the first roll pair groups a to c, a large rolling reduction is performed without using the mandrel M, and then the thickness reduction step i and rounding step n are carried out by the normal rolling method. Take.

That is, FIG. 2 shows the relationship between the mandrel M of the continuous rolling mill, the hollow piece date, and the roll caliber 10, and in the first roll pair groups a to c, the mandrel M diameter d is sufficiently smaller than the inner diameter of the hollow piece date. There is a gap between the two.

At this stage, hollow piece Nichigaiyo Do is D,, D2, D3
and the outer diameter is reduced. Here, the first roll pair group refers to the first two to four stand groups in the continuous rolling mill. Generally, the total outer diameter reduction (△
In the example of an 8-stand continuous rolling mill, DT) does not exceed 3 broadsides, but in the present invention, this is set to be sufficiently large.

Here, the total outer diameter reduction (△DT) is defined as follows with symbols as shown in FIG. △DT=D. -DnDo: Outer diameter of the hollow piece Dn: Caliber short diameter of the final roll pair When the dimensions of the tube after continuous rolling (hereinafter referred to as shell) are equal, the larger △DT is, the larger the outside diameter of the hollow piece is. We will start with the pipe material.

In order to consolidate the number of pipe cross sections, △DT must be 4 or more for industrial value to be produced, and it is preferably 5 or more. Note that the maximum value of ΔDT is determined by the number of roll sets (number of stands). If the number of rolls is increased, △D
Although T can be increased, in an industrial range, ΔDT can be up to about 9 degrees. In order to make ΔDT 4 or more, it is necessary to make the outer diameter of each of at least the first roll pair and the next roll pair 35 or more and reduce the outer diameter in all directions. Here, the pressure reduction (△Di)
is defined as follows. △Di=Di-2-D; i: Ranking of roll pairs from the entry side (i=1, 2...
・．．・・・． ...n) Di: Minor diameter of the caliber of the i-th roll pair Di-, = Do = Hollow Piece In the conventional continuous rolling method, it is difficult to achieve such a large outer rolling reduction, and it is difficult to achieve such a large outer rolling reduction without using a mandrel. It becomes possible only by doing the following.

When △Di becomes 35 Yanagi or more, poor biting starts to occur sporadically,
Frequently occurs on ships over 5 ships. In the present invention, a large rolling reduction is performed without using a mandrel at the beginning of continuous rolling.
When the front end of the tube engages at least the first pair of rolls,
When the biting has stopped, a pushing device follows the rear end of the tube to apply a pushing force to the rear end of the tube, and rolling is started. In other words, when △Di<35 (side), the biting is smooth even without a pushing device, and in such a case, it is meaningless to apply pushing force to the rear end of the tube. This is rather harmful as it causes crushing, bending and bulging of the pipe. 35mi△D'<50
(skin), the frequency of occurrence of defective biting is low, but when considering work stoppage due to defective biting, it is well worth having the pushing device follow the rear end of the tube.

When ΔDi≧50 (ribs), a pushing device is required. In either case, in the present invention, no pushing force is intentionally applied to the tube that is smoothly bitten, and crushing of the rear end of the tube, bending and bulging of the tube are prevented as much as possible. In order to do this, the pushing device is made to follow the rear end of the tube at a speed that is slower than the speed of the rear end of the tube after the front end is bitten, at least immediately before biting. Following does not include pushing forward or being pulled, but includes moving forward while the two are in contact. The above method is used not only when the front end of the tube is bitten by the first pair of rolls, but also without the action of a mandrel.
It can also be applied when biting after the second roll pair. The pushing device can be operated with the ability to exert a force greater than the yield stress of the tube. As the pushing device, for example, those described in Utility Model Application No. 53-174091 and Tokubuta No. 53-141073 can be used. - The maximum value of △Di is determined by the shape of the rear end of the tube that is deformed by the pushing force, and it is generally desirable that △Di be 8 ribs or less for thin-walled hollow pieces.

In addition, for thick hollow pieces, △Di depends on the strength of the rolling mill.
may be limited. Examples of the rolling method according to the invention are shown in Table 1 in comparison with the conventional rolling method.

In the example of an 8-stand continuous rolling mill, the total external reduction (△DT) of a continuous rolling mill does not generally exceed 3 rolls for a 28 yanagi in the conventional method, but in the method of the present invention, it does not exceed 3 in diameter. ■ 85
Side, size no. ■It is large at 65 willow.

Size No. (2) is described to show the tube size number aggregation of the present invention, and strictly speaking, it is not an embodiment of the present invention. Table 1: Problem '1' of the above-mentioned subordinate method due to the above-mentioned continuous rolling mill
1. Can solve [2- and '3}.

That is, the problem of poor engagement in {11] was improved by installing a pushing device and making it follow the rear end of the tube;
The problem of the amount of outer diameter reduction can be improved by reducing the outer diameter without using a mandrel at the beginning of continuous rolling.
The problem of the inclined rolling time in '3' can be improved by making the outer diameter after inclined rolling much larger than in the conventional method and shortening the length. In addition, the problem of '2' is that in the embodiment of the present invention shown in Table 1, the number of rolls is 8 pairs, which is the same as in the conventional method, so the number of rolls used for thickness reduction is reduced by 2 pairs, and the number of rolls used for thickness reduction is reduced by 2 pairs. The amount of change in speed of the mandrel during rolling is reduced, and a tube with good dimensional accuracy can be obtained. In the method of the present invention, if the number of rolls is increased and the last 8 pairs are rolled in the same way as in the conventional method, a tube with almost the same dimensional accuracy as the conventional method can be obtained, but in this case, the total external strain reduction (△
D,) can be made even larger, and the effect of the present invention becomes even greater.

[Brief explanation of the drawing]

FIG. 1 shows an example of general seamless metal production equipment for implementing the present invention, and FIG. 2 is an explanatory diagram of the continuous rolling process of the present invention. 1... Metal heating furnace, 2... Press roll perforator, 3... Inclined roll rolling machine, 4... Mandrel mill, 7... Reheating Furnace, 8...
・Stretch reducer, 10...Roll caliber, H
...Hollow piece, M...Mandrel. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. When a round blank tube that has been pierced and rolled is continuously rolled through a mandrel by a rolling device in which a plurality of pairs of driven rolls are arranged adjacently along a rolling line, In the group of roll pairs, set the outer diameter reduction (ΔD_i) to 35 mm or more per roll pair without using a mandrel, and start rolling by following the rear end of the tube at least when biting into the first roll pair. A method for manufacturing seamless steel pipes. However, the outer diameter reduction (ΔD_i) is ΔD_i = D_i_-_2-D_i where i is the rank of the roll pair from the entry side (i = 1, 2...
...n) D_i is the short diameter of the caliber of the i-th roll pair, and D_-_1 and D_0 are the outer diameters of the tube before rolling and are equal.