JPS6054207A - 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 type guiding device. CONSTITUTION:In forming the corners of a blank material having square cross section by plural sets of four-roll type roll guides and restrictingly guiding the material, at the inlet side just before a piercer; the gap between guide rolls 9 at each stage is gradually decreased from the 1st guide to make the roll gap at the final guide equal to the dimension of blank material, and the corner R of grooved bottom of the guide roll 9 at each stage is made equal to the R corresponding to every corner R of the prescribed cross section of blank material, and further the speed ratio (alpha) defined by VP=alpha.lambda.VP(VR: roll peripheral speed, lambda: elongation, VP: pusher speed), in fixed within a range of 0.9-1.3. In this way, a blank pipe free from rubbing-down flaw and eccentricity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Top Field of Application) The present invention is made of continuously cast bloom or billet with a rectangular cross section, and a set of freely rotating input guides are arranged at 80° intervals. ) Push drilling of a seamless steel pipe using multiple sets of 40-type roller blades consisting of four rolls arranged diagonally, a pusher, a pair of horizontal rolls with a circular hole shape, and a conical plug. It is related to rolling.

(Prior Art) FIG. 1 shows the principle of indentation piercing and rolling for manufacturing 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 from the rear by a butcher 4 using a pair of upper and lower horizontal rolls 3 having a circular hole shape and a conical plug 5 set at the center of the circular hole shape. During rolling, the circular hollow blank tube 2 is rolled while applying an indentation force over its entire length.

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 a rectangular cross-sectional material 1 is rolled through a circular hole shape 3, shear deformation tends to be concentrated 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 minimizes wall thickness deviation. It is necessary to prevent uneven thickness.

Currently, in order to prevent scratches on raw pipes, grinding and cleaning of the corners of the material are carried out off-line, or a third
This problem is prevented by installing a corner sizing mill having a pair of horizontal rolls 6 with Ponk hole shapes as shown in the figure between the heating furnace and the indentation rolling mill. In addition, to deal with uneven thickness of the raw pipe, 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, are combined in a 20- A single roller guide is installed just in front of the push-piercing 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 the soaring price and a decline in the price of 9,000 rupees.

(Purpose of the invention) Therefore, with the aim of omitting processes, rationalizing equipment, and increasing yield, we abolished offline grinder processing maintenance and horizontal 20-hole corner sizing mills, and in addition, continuous casting. We have invented an indentation piercing rolling method that allows the production of raw pipes with good wall thickness deviations and no scratches even when using square cross-section materials as they are.

(Structure 2 of the invention) The present invention provides an inlet guide immediately before a push-piercing rolling mill.
In place of the conventional 20-rule two roller guide, a plurality of sets of 40-rules, each of which rotates freely as shown in FIG. The second roller guide is installed, and the rolling setting conditions are as follows:
The roll gap of the 0-ru second roller guide is equal to the material size,
And the groove bottom corner R of each guide roll is gradually increased from the first kite to the final guide, and V+'?
= α・Enter @yP (VR: Roll circumferential speed, Entry: Stretching, vP:
The speed ratio α defined by pusher speed is 0.9 to 1.
3).

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. By actively restraining, the centering accuracy against the circular hole shape of the material is improved and the thickness unevenness of the raw tube is improved.
The reason why the guide roll gap is successively reduced from F) to make the final guide roll gap the same as the material dimensions is to prevent rolling stoppage due to guide clogging caused by material swelling due to indentation cull, and to prevent the final guide roll from stopping due to guide clogging. This is to ensure good centering performance, and to make all the guide roll groove bottom corners R of each kite equal to the predetermined corner R, the first guide roll is At the same time, this is to simplify the specifications of these guides by having the guide bear most of the roll load and lightening the load below the second guide.

Figure 6 compares the material restraint conditions of the 20-1 type roller guide (Figure A) and the 40-1 type roller guide (open mouth). While indirect reduction based on spreading is the main method, the 40-1 type allows effective forming because the corners of the material 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 push-in force of the pusher increases rapidly, and the +* curvature of 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.
Even if it becomes 3 or more, the pushing force hardly changes, and α is set to 1.
．． Setting it to 3 or more is meaningless. Not only that, but it also causes slips.

This is undesirable from the standpoint of energy efficiency as well as the formation of flaws.

Therefore, if α is set in the range of 0.8 to 1.3 depending on the rolling conditions, it becomes possible to simultaneously perform forming of the corner portion of the material using the 40-type roller guide and piercing rolling.

(Example) Next, a specific example will be described in which three sets of 401-type roller guides are used to simultaneously form the corner portion of a continuously cast rectangular cross-section material and press-pierce-roll it. The material has a cross-sectional dimension of 215φam.

Corner R8", corner radius of the material when it enters the circular hole shape of the piercing rolling machine is 2Q'ms, and the cross-sectional size of the piercing-rolled raw pipe is 2
50ψI, wall thickness f! It is 2.5 mm. Figure 9 shows the roll gap of each guide as 225m+*, 220+sm, 2
15IIm, and all groove bottom corners R of the guide roll are set to 20F, which is the same as the predetermined corner R. This is an example in which hole-rolling was performed while corner forming the material with am constant.

Figure 1θ shows an example of measuring pusher force when changing the speed ratio α from 0.7 to 1.3. Rolling was barely possible even at α = 0.9, but rolling stopped at α = 0.8. However, normal rolling was possible when α = 1.0 or more. Figure 11 shows the cross-sectional shape of the material at the circular hole entrance of the piercing rolling mill when α = 1.1 on the first guide entrance side. (The solid line is the material before sizing, the #1 line is the material after sizing), and the corner part is the target 20R.
It is molded as mm and has a bulge of approximately 2.51 mm.

Figure 12 shows the scratches caused by rubbing down on the raw pipe when α=1.1.
This is a comparison with the case where a 0-ru 2 roller guide is used, but as the groove bottom corner R of the guide roll becomes larger, the number of flaws decreases more rapidly with the final method, and at 20 mm, they almost completely disappear. It is clear that the final method has a great effect on preventing scratches.

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 this process and rationalize equipment, reducing material costs and equipment costs, improving yields, and making it possible to indent-pierce and roll raw pipes with no flaws and good uneven thickness.

[Brief explanation of the drawing]

11 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; FIG. Figure 3 is an explanatory view showing a horizontal 20-hole corner sizing mill with box hole shapes, Figure 4 is an example of the arrangement of the 20-hole two roller guides on the entrance side of the piercing rolling mill, and Figure 5 (
stomach). (B) is an example of the arrangement of the 40-type rollers and guides installed on the inlet side of the indentation rolling mill, and an explanatory diagram of the arrangement relationship of the four-cylinder guide rolls. Figure 7 is a front view comparing the difference in corner formability of a rectangular cross-section material by the guide rolls of the single-roll type roller guide and the 40-inch type roller guide, and the speed ratio α when using the 40-type roller guide. Figure 8 is a diagram comparing the swelling of materials according to
A chart showing the relationship between speed ratio α and pusher pushing force when using a 40-coil type roller guide, and FIG. 9 shows the implementation of the present invention when three 4-coil type a-ra guides are used. An explanatory diagram showing an example, FIG. 10 is a diagram illustrating an example of measurement of push-in force of a button shear according to the invention, and FIG. FIG. 12 is an explanatory diagram comparing the cross-sectional shape of the pipe, and FIG.
The figure is a chart comparing the wall thickness deviation ratio of the raw pipe according to the present invention with that of a 20-L double roller guide. ■... 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 box hole shape 7... Vertical guide roll with box hole shape 58... Horizontal guide roll with box hole shape engraved, 9... Guide roll. Patent applicant Representative patent attorney Tomoyuki Yafuki (and 1 other person) Figure 5 Figure 6 (Brazil Figure 9 10111 0 81 1111!It

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 round blank tube by inserting a billet having a rectangular cross section into the hollow cross-section path while applying pressure in the axial direction, the former step of 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, and when piercing and rolling the billet while rounding each edge of the cross section, the roll gap of the 40-le guide device of each stage is gradually decreased from the first stage guide device. Then, the roll gap in the final stage guide device is made equal to the cross-sectional dimension of the material, and the corner groove bottoms R of the guide rolls from the first stage 40-le guide device to the final stage 40-le guide device are all set to a predetermined value. The cross-sectional volume of the billet (material) (
The volume (corner) of the billet (material) cross section is made equal to the R corresponding to
While shaping the part to a predetermined corner R, vR=α・
The speed ratio α defined by input/vP (vR = rolling roll circumferential speed, input: stretching, Vp: pusher speed) is 0.8 to 1.3.
A seamless steel pipe rolling method characterized by indentation and perforation rolling performed within the range of .