JPS6054204A - Rolling method of seamless steel pipe - Google Patents

Abstract

PURPOSE:To obtain a blank pipe free from flaw and wall-thickness deviation by specifying the gap between guide rolls, the dimensions of the grooved-bottom corners of roll, and the speed ratio based on a prescribed definition, at each stage, in forming the corners of a blank material having square cross section by a four-roll guiding device. CONSTITUTION:At the inlet side just before a piercer, the corner parts of a blank material 1 having square cross section are formed and restrictedly guided by plural sets of four-roll type roll guides consisting each of four rolls 9 arranged at 90 deg. intervals on the diagonals slanted by 45 deg. in the cross section perpendicular to the rolling direction. In this case, as the set conditions for rolling, the corner R of grooved bottom of each guide roll 9 is gradually enlarged from the 1st guide to the final one, and further, the speed ratio (alpha) defined by VR= alpha.lambda.VP(VP: roll peripheral speed lambda: elongation, VP: speed of pusher) is fixed within a range of 0.9-1.3. In this way, a blank pipe free from rubbing down flaw and wall-thickness deviation is obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is made of continuously cast bloom or billet with a rectangular cross section, and a set of freely rotating entry guides are arranged at 90° intervals and 45° diagonal lines. Using multiple sets of 40-rule two roller guides consisting of four rolls arranged above,
This invention relates to indentation piercing rolling of a seamless steel pipe using a butcher, a pair of horizontal rolls having a circular hole shape, and a conical plug.

(Prior Art) No. i5 shows the principle of indentation piercing rolling for producing a hollow tube with a circular cross section from a material with a rectangular cross section. Continuously cast material l with a rectangular cross section such as bloom or billet is cast by a pair of upper and lower horizontal rolls 3 having circular holes and a conical plug 5 set at the center of the circular holes.
The circular hollow blank tube 2 is rolled while applying a pushing force over its entire length by a pusher 4 from behind.

This method of rolling allows the direct use of continuously cast rectangular cross-section materials, resulting in low material costs, and compressive force is applied to the inside of the raw tube that is rolled with plugs, resulting in good quality raw tubes with no internal defects. is obtained. On the other hand, as shown in Fig. 2, since the rectangular cross-section material 1 is rolled through the circular hole shape 3, shear deformation tends to concentrate at the corners of the material, which tends to cause scratches caused by the rolls. Since the pushing force is applied from the rear, if the centering of the material with respect to the hole shape is poor, eccentricity of the plug will occur, and uneven thickness of the raw pipe will likely worsen.

In seamless steel pipe rolling, it goes without saying that the most important issue is to ensure that the product has no defects and that uneven thickness is kept to a minimum. It is necessary to prevent this.

Currently, in order to deal with scratches caused by abrasion on raw pipes, it is necessary to perform off-line grinota treatment on the corners of the material, or
This is prevented by installing a corner sizing mill having a pair of horizontal rolls 6 with box holes as shown in the figure between the heating furnace and the indentation rolling mill.

In addition, in order to deal with uneven thickness of the raw pipe, a 20-wheel drive system is used that alternately combines a pair of horizontal guide rolls 8 and a pair of vertical guide rolls 7, each having a box hole shape that rotates freely, as shown in Fig. 4. A type roller guide is installed just in front of the indentation rolling mill to prevent these problems.

However, in this push-hole rolling method, each process or equipment is only effective for one problem, and when viewed as a whole, it is not only wasteful in terms of process, but also reduces material and equipment costs. There are problems such as high prices and a decline in yield.

(Purpose of the invention) Therefore, for the purpose of omitting step -I, rationalizing equipment, and improving yield, we abolished the offline grinder processing and the horizontal 20-hole corner sizing mill.
In addition, we have invented a push-piercing rolling method that allows us to use a continuously cast rectangular cross-section material as it is, without causing scratches and producing a blank tube with good wall thickness unevenness.

(Structure 1 of the invention) The present invention provides an entry side guide immediately before a push-pull piercing rolling machine.
Instead of the conventional 20-L 2 roller guide, one set of freely rotating 40-L 2 roller guides as shown in FIG. A roller guide is installed, and the rolling setting conditions are as follows:
- Make the roll gap of the second roller guide equal to the material size, and gradually increase the groove bottom corner R of each guide roll as the first guide becomes the final kite. It is configured by setting a speed ratio α defined by circumferential speed (input: stretching, Vp: pusher speed) in the range of 0.8 to 1.3.

The 40-type roller guide has a rectangular cross-section material corner R that is continuously cast online and is molded to the desired dimensions to prevent scratches on the outer surface of the raw tube. This restraint has the effect of improving the centering accuracy for the circular hole shape of the material and improving the uneven thickness of the raw tube, but the guide roll gap from the first guide to the final guide is all made to be the same as the material size. The purpose of this is to securely form the corner part by firmly restraining the material and to ensure good centering performance.
The reason why is made gradually larger is to prevent scratches caused by the guide rolls by shaping the corner portions reasonably, and to distribute the load on the guide rolls almost equally.

Figure 6 compares the material restraint conditions of the 20-1 type roller guide (Figure 1) and the 40-1 type roller guide (low). In contrast to indirect reduction based on width expansion, the 40-1 type allows effective forming because the material corners can be directly reduced using guide rolls. Furthermore, while the 20-1 type has two sides of the material restrained, the 40-1 type has four sides restrained, so it is possible to ensure centering accuracy equal to or higher than that of the 20-1 type.

The purpose of setting the speed ratio α in the range of 0.8 to 1.3 is to prevent rolling stoppage due to guide clogging caused by material bulging due to excessive pushing force. As shown in Figure 7, when α is 0.8 or less, the roll speed of the piercing mill is slower than the pushing speed of the pusher, so the amount of metal on the entry side increases compared to the exit side, and the material inside the kite increases. The bulge in the cross section increases. As a result, as shown in FIG. 8, the pushing force of the pusher increases rapidly, and the bulge in the cross section of the material increases, exceeding the forming limit of the guide, causing the material to jam in the guide, and rolling to stop. When α is 0.8 or more, the roll speed becomes faster, so the above-mentioned phenomenon disappears and normal rolling becomes possible, and especially when α is 1.0 or more, this tendency becomes remarkable. However, α is 1.3
Even if the pushing force becomes more than 1, the pushing force hardly changes.
Setting it to 3 or more is meaningless. Therefore, if α is set in the range of 0.8 to 1.3 depending on the rolling conditions, 4
It becomes possible to simultaneously perform forming of the corner portion of the material and piercing rolling using the 0-1 type roller guide.

(Example) Next, a specific example will be described in which three sets of 401-type roller kites are used to simultaneously perform corner forming and push-piercing of a material having a continuously cast rectangular cross section. The material has a cross-sectional dimension of 215φ■.

Corner R82, material corner R when entering the circular hole shape of the piercing rolling machine is 20 ■, cross-sectional dimension of the piercing rolled blank pipe is 25
It has a diameter of 0φ■ and a wall thickness of 82.5m+n. Figure 9 shows that the roll gap of each guide is 215rsm, which is the same as the material size.
The groove bottom corner R of the guide roll is set at 10 am.

This is an example in which hole-rolling was carried out while forming the corners of the material while changing the resistance sequentially to 15Rmm and 20Rmn+.

Figure 1θ shows an example of measuring the pleasure pushing force when changing the speed ratio α from 0.7 to 1.3. Even when α = 0.8, rolling was barely possible, but when α = 0.8, rolling was possible. was stopped, and normal rolling was possible when α=1.0 or more.

Figure 11 compares the cross-sectional shape of the material at the circular hole entrance of the piercing rolling mill when α = 1.1 with the material cross-sectional shape at the first guide entry side (the solid line is the material before sizing, the chain line is the material after sizing). ), and the corner part has the desired 20RI
It is shaped like Im and has a bulge of about 3m11.

Figure 1S12 compares the abrasion flaws on the raw pipe when α=1.1 with that when a 20-roll two-roller guide is used. It is clear that the final method has a great effect of preventing scratches because the number of scratches decreases more rapidly and is almost completely eliminated at 2QRmm.

Figure 13 compares the thickness deviation of the raw tube between the final method and the 20-L type roller guide.The thickness deviation of the base tube is almost the same as that of the 20-L type roller guide, but it is slightly smaller. The effect of preventing uneven thickness due to high centering accuracy is recognized.

(Effects of the Invention) As is clear from the above, the present invention allows continuous casting materials to be used as they are without the need for off-line grinder processing or corner sizing mills, which were conventionally required. It has become possible to omit processes and rationalize equipment, reducing material and equipment costs, improving yields, and making it possible to indent-pierce-roll blank pipes with no flaws and good uneven thickness.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the principle of indentation piercing and rolling for manufacturing a circular cross-section hollow shell from a square cross-section material, and FIG. 2 is an explanatory diagram showing the state of contact between the square cross-section material and the circular hole shape. Fig. 3 is an explanatory view showing a horizontal 20-hole corner sizing mill with box hole shapes, Fig. 4 is a side view of the arrangement of the 20-hole two roller guides on the entrance side of the piercing rolling machine, and Fig. 5 (
stomach). (B) is a side view of the arrangement of the 40-roll second roller guide installed on the inlet side of the indentation rolling mill and an explanatory diagram of the arrangement relationship of the four guide rolls. A front view comparing the difference in corner formability of a rectangular cross-section material by the guide rolls of the 40-ru type roller guide and the 40-ru two roller guide.
Figure 7 is a chart comparing the swelling of the material depending on the speed ratio α when using a 40-inch roller guide, and Figure 8 is a diagram comparing the swelling of the material depending on the speed ratio α when using a 40-inch roller guide.
A chart showing the relationship between the speed ratio α and the pushing force of the pusher when using a 0.01 mm roller guide, and FIG. 9 shows an example of the present invention when three 40 mm type roller guides are used. FIG. 1O is a diagram showing an example of measurement of the pushing force of the pusher according to the present invention. FIG. Explanatory diagram comparing the shape, 1st
Figure 2 shows the occurrence of scratches on the raw pipe according to the present invention.
FIG. 13 is a chart comparing the uneven thickness of the raw pipe according to the present invention with that of a 20-1 type roller kite. l... Rectangular cross section material, 2... Hollow tube with circular cross section, 3... Horizontal roll with circular holes carved, 4... Pusher, 5... Conical plug, 6... Horizontal roll with a box hole shape 7... Vertical guide roll with a box hole shape 8... Horizontal guide roll with a box hole shape 9... Guide roll. Patent applicant Agent: Tomoyuki Yafuki (and 1 other person) Figure 5 Figure 6 (a) Figure 9 (2) Figure 1O Figure 11

Claims (1)

[Scope of Claims] A plug supported by a mandrel is provided at the center of a circular path formed by a pair of upper and lower rolling rolls each having a semicircular hole, thereby forming a hollow cross-sectional path, In the process of manufacturing a nine element tube by inserting a billet having a rectangular cross section into the hollow cross section path while applying pressure in the axial direction, a step before the hollow cross section path constituted by the pair of pressure rolls and the plug. A 40-ru guide provided in multiple stages in which each ridge portion in a plane perpendicular to the rolling direction of the billet is rounded and functions to align the center of the hollow cross-sectional path with the cross-sectional center of the billet. The device constrains and guides the billet while rounding each edge of the cross section of the billet while piercing and rolling it. The groove bottom corner R of each guide roll is gradually increased from the first stage 40-le guide device to the final stage 40-le guide device, and the cross-sectional volume of the billet (raw material) is The (corner) portion is formed into a predetermined corner R, and the speed ratio α defined by vR = α・Ent・VP (VR: rolling roll circumferential speed, entry: stretching, Vp: pusher speed) is set to 0.9 to 1. A seamless steel pipe rolling method characterized by indentation and perforation rolling with settings within the range of 1.3.