RU2379141C2 - Rolling mill for manufacturing of seamless pipes and operation method of rolling mill - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: rolling mill contains, as minimum, one rolling mill with at least two rolling rolls (1, 2) which jointly form circle (3) of tubular blank (4). During rolling process inside tubular blank (4) it is placed draw bar (5). Forming rolls (1, 2) in operation position and draw bar (5) form thickness of walls (d) of rolled pipe. For reduction of necessity in rods at keeping of quality of rolling by invention it is provided that vertical relative to longitudinal axis (L) cross section of draw bar (5) allows shape, differs from shape of circle. In addition invention relates to operation method of such rolling mill. ^ EFFECT: seamless pipes with equal thickness of wall. ^ 12 cl, 7 dwg

Description

The invention relates to a rolling mill for the manufacture of seamless pipes, especially steel, having at least one rolling stand with at least two rolling rolls that jointly roll the pipe billet around the circumference; during the rolling process, the mandrel bar is placed inside the tube billet, and the rolls in the working position and the mandrel bar form the wall thickness of the rolled tube. In addition, the invention relates to a method of operating such a rolling mill.

Rolling mills of this kind have been known in the art for quite some time. For example, documents DE 33 10 769 C2, DE 195 32 643 C2 and DE 26 41 555 A1 can be indicated. They describe that a seamless pipe can be obtained by placing a mandrel bar in the hollow block, on which the tube blank is formed into the desired pipe. To obtain a pipe of cylindrical profile, the mandrel bar must have a circular cross section, and the rolling rolls processing the outer surface of the tube billet must have a corresponding shape, that is, have a semicircular contour in a radial section. With the corresponding position of the rolling rolls relative to the mandrel bar, a deformation zone is formed having the desired annular shape, which the tube stock takes during rolling.

A problem arising in the manufacture of a seamless pipe is shown in FIGS. 1-3. They depict a different mutual arrangement of the rolling rolls 1 and 2, the tube stock 4 and the mandrel bar 5.

The ideal option is presented in figure 1. Here, the rolls 1 and 2 form the volume 3 of the tube stock 4; a mandrel bar 5 is located inside the tube billet 4. Accordingly, for each tube that is made from the tube billet 4, a separate pair of rolling rolls 1 and 2 and an own bar of the mandrel 5 are necessary in order to obtain the ideal mutual position shown in Fig. 1. This means that by using mandrel rods with different diameters, the desired wall thickness of the tube blanks can be adjusted.

To reduce the number of mandrel rods with the required diameters, usually within certain boundaries, the radial position of the rolls relative to each other is varied. Radial adjustment is achieved by opening or closing the caliber of the rolling compared to the average position shown in figure 1, which is neutral with respect to the uniformity of wall thickness.

Figure 2 shows that both rolls 1 and 2 in order to reduce the average thickness of the tube stock close to each other; the distance between the axes of rotation of both rolls is reduced. Based on the greatly enlarged geometric ratios shown in the drawing, it is immediately evident that the tube blank at the top and bottom has a smaller wall thickness with respect to the thickness on the left and right. This results in a non-circular section with a maximum wall thickness at the edges of the deformation zone.

Another option is depicted in figure 3, where both the rolls 1 and 2 in order to increase the average wall thickness of the tubular billet allotted from each other; the distance between the axis of rotation of both rolls 1 and 2 increased. It can be seen that now the tube stock from above and below has a relatively large wall thickness compared with a smaller thickness on the left and right. We also get a non-circular section with a maximum wall thickness in the middle of the deformation zone.

Thus, although changes in the average wall thickness of tube blanks can be made, but, as shown, the movement of the rolls leads to a change in the shape of the deformation zone during rolling between the rolls and the mandrel bar and to deviation from the ideal circular cross section. This leads to an increase in the unevenness of the wall thickness of the pipes. So that the wall thickness of the pipes remains within the limits of possible tolerances, the movement of the rolling rolls relative to each other is possible to a limited extent. Therefore, the use of more mandrel rods of various diameters is required.

In addition, the problem is complicated by the fact that in the manufacturing process requires four to five mandrels of one or another diameter. In addition, mandrels are usually made of expensive heat-resistant steel. This means that it is necessary to have a relatively large and costly fleet of rods for the required pipe sizes. Consequently, large investments are required, which is a big economic problem, especially with the initial equipment of production.

Therefore, the object of the invention is the creation of a rolling mill of the type described above and the method of its operation, which allows for a smaller number of mandrel rods to provide the desired range of produced pipes with sufficient quality, that is, to guarantee good roundness of the pipes.

This problem, in accordance with the invention, is solved by the fact that the mandrel bar vertically relative to its longitudinal axis has a shape deviating from a regular circle.

The mandrel rod in its vertical section relative to the longitudinal axis can, in principle, have an oval shape.

A preferred embodiment of the invention provides that the mandrel bar in a vertical section of the axis has a shape relative to its longitudinal axis that is substantially formed by at least two arcs of the same radius, while the radii of the arcs are more than half the smallest diameter of the mandrel bar.

In this case, a special design of the mandrel bar provides that its vertical cross section has a shape relative to the longitudinal axis formed by two arcs of the same radius.

If in the direction of movement of the rolled products to provide for the consistent use of several pairs of rolls with their relative deployment relative to each other, you can achieve a very good roundness of the rolled pipes. In this case, it is desirable that the mandrel bar in a vertical section with respect to its longitudinal axis have a shape formed by four or more arc segments; the number of arc segments must be even. As mentioned above, this design is applicable if in the direction of movement of the rolled products provides for the consistent use of at least two pairs of rolls in one or more rolling stands; however, the pairs of rolls should be slightly deployed relative to the longitudinal axis of the mandrel bar.

The intermediate segment between the two arcs forming the profile of the mandrel bar can be rounded. The highest radial points of the transverse profile of the mandrel bar should be located symmetrically on its circumference. The cross-sectional shape of the mandrel bar must be symmetrical with at least one symmetry line.

Rolling rolls in radial section should have a rolling surface in the form of an arc segment.

A great advantage is also the equipment of the rolling mill with rotary devices with which the mandrel bar can be rotated and held in a certain position. In this way, it is possible to exert an active influence on the wall thickness of the pipe, which will be explained in more detail. Swivel devices can be included in the movable support assembly of the mandrel bar.

For each rolling stand, two, three or four rolling rolls are preferably provided.

By rolling mill is meant, first of all, a hot rolling mill operating in continuous or cyclic mode. The invention can also be used in pilger or cold rolling of pipes.

In the proposed method of operating such a rolling mill in the direction of movement of the rolled pipes, in accordance with the invention, it is provided to measure the wall thickness of the pipe after processing them in at least one of the rolling stands and to compare these data with predetermined parameters; at the same time, the measured actual parameters of the wall thickness are brought closer to those set with the help of an adjusting device that sets the desired angle of rotation around its longitudinal axis of the mandrel bar, which has a transverse profile different from the ideal circle.

Thanks to this solution, it becomes possible to roll the same pipe assortment with fewer rods. The number of rods, which is very important to reduce the initial investment, can be significantly reduced, which positively affects the efficiency of production. The operation of the mill is also simplified.

The number of mandrel rods can in particular be reduced on continuous rolling mills or broaching installations on the mandrel. Moreover, the quality of rolled pipes does not deteriorate.

The drawings show one embodiment of the invention. The following is shown:

figure 1 - a pair of rolls, tube billet and mandrel bar in the context with respect to the longitudinal axis of the mandrel bar and in accordance with the prior art;

figure 2 - a pair of rolling rolls, tube billet and the mandrel bar shown in figure 1, with the rapprochement of the rolling rolls in accordance with the prior art;

figure 3 - a pair of rolling rolls, a tube billet and the mandrel bar shown in figure 1, with the remote position of the rolling rolls in accordance with the prior art;

figure 4 - mandrel rod in a vertical section in relation to its longitudinal axis in accordance with the invention;

figure 5 - a pair of rolling rolls, a tube billet and a mandrel bar in a vertical section in relation to its longitudinal axis in accordance with the invention, while the rotary devices are shown schematically;

in Fig.6 - a pair of rolling rolls, a tube billet and the mandrel bar shown in Fig.5, with the convergence of the rolling rolls;

in Fig.7 - a pair of rolling rolls, a tube billet and the mandrel bar shown in Fig.5, with the remote position of the rolling rolls.

In accordance with the invention, FIG. 4 shows a mandrel bar 5 in a vertical section with respect to its longitudinal axis L. It can be seen that the cross section of the mandrel bar 5 does not have the shape of a regular circle, but somewhat deviates from it. In this case, the sectional shape approaches the oval.

In this particular case, it is envisaged that the cross section of the mandrel bar 5 is formed by two arcs 6 and 7 located symmetrically to the line of symmetry 11. The radii R of both identical arcs 6 and 7 are greater than half of the smallest diameter D of the mandrel core 5. Accordingly, at two opposite segments along the radii are the highest points 9 and 10, on which roundings 8 are provided.

In the standard case, along with the mandrel bar 5, rolling rolls are also shown in FIG. 5. Both partially shown rolling rolls 1 and 2 form a circle 3 of the tube billet 4, interacting with the mandrel bar 5 located inside the tube billet 4. When rolling the tube billet 4 in the position shown in Fig. 5, a pipe with almost the same wall thickness d is obtained. After rolling, the pipe has a not quite perfect round profile, but deviations from the ideal shape are small and are within tolerances.

If it is necessary to reduce the outer diameter of the pipe or the thickness of its walls d, then the rolls 1 and 2 converge (Fig.2), as shown in Fig.6. Due to the shape of the mandrel bar 5, a pipe with almost the same wall thickness d is also obtained here, and deviations from the ideal shape also occur, but they are also within tolerances.

If it is necessary to increase the outer diameter of the pipe or the thickness of its walls d, then operations can be performed as shown in Fig. 7. Here, the mandrel bar 5 by means of rotary devices 12, which are shown schematically in FIG. 5, is rotated 90 ° about its longitudinal axis L so that it faces downward and upward with its protruding sides. Rolling rolls 1 and 2 moved further apart, that is, the caliber increased. It is clear that now, using the same mandrel rod 5, it is possible to roll pipes of a much larger diameter, while the deviations from the ideal shape that arise are within tolerances. The wall thickness d is fairly uniform around its circumference.

Thus, it became possible to rotate the mandrel bar 5, which has a non-circular shape, around its longitudinal axis L to make matching, which ensures rolling of the pipes in a wide range of their diameter and wall thickness.

Thus, mandrel rods with an irregular circular cross section are used, which are constructed mirror-like with respect to the formation of a gap between the rolling rolls when they move from the middle position. The mandrel rods can purposefully rotate around its longitudinal axis and lock in position.

The shank of the mandrel bar has functional surfaces to achieve accurate angular positioning of the bar to achieve the described effect.

Rotary devices 12 allow targeted rotation of the mandrel bar 5. On rolling mills with adjustable feed of the mandrel bar, the rotary devices are integrated into the movable shaft support assembly.

In order to avoid premature wear of the bar profile when positioning rolling rolls that do not require maximum angles of rotation of the bar, neutral intermediate positions of the angle of rotation are established.

The proposed profiled mandrel rods can be used not only on rolling mills with rolling stands having two rolls, but also on rolling mills with three or more rolls in one rolling stand. Profiled rods can be used especially effectively if, when processing a workpiece, the final pipe wall thickness is achieved not only by using the final rolling gauge, but also by a sequential combination of two or more rolling gauges. A profiled rod for a rolling stand with two rolls should have a four-sided oval profile, and for a rolling stand with three rolls - a six-sided oval profile.

A particular advantage is achieved when using the device for measuring the wall thickness of the rolled pipes located behind the rolling mill. The adjusting device associated with the pipe thickness control unit can compare the actual and set value of the wall thickness to act on the rotary device 12 so that the actual parameters approach the set parameters. If, for example, an excess of the nominal pipe wall thickness d is established at the highest point 13 of the pipe (FIG. 6), then the adjusting device of the mandrel bar 5 can turn the rolling tools from the position shown in FIG. 6 in the direction shown in FIG. Fig.7 extreme position, which will reduce the thickness of the rolled wall of the pipe d. When reducing the nominal size of the pipe wall d, it can accordingly be increased by reverse rotation of the mandrel rod 5 from the position in Fig.7 to the position in Fig.6.

The contour of a profiled rod can be formed from opposite arcs or from opposite curvilinear curves. Intermediate segments may be rounded.

The profiling shape is selected taking into account the fact that the rolling gauge is in the middle position and deviations in the thickness of the pipe walls do not exceed the parameters of the prior art.

List of conventions:

one rolling roll 2 rolling roll 3 circle four pipe billet / pipe 5 mandrel bar 6 arc 7 arc 8 rounding 9 highest radial point 10 highest radial point eleven line of symmetry 12 rotary devices 13 highest point d pipe / billet wall thickness L mandrel shaft axis R radius D smallest mandrel bar diameter

Claims (12)

1. The method of operation of the rolling mill for the manufacture of seamless pipes, especially steel, comprising at least one rolling stand with at least two rolling rolls (1, 2), which together roll the surface (3) of the tube stock (4) in this case, during the rolling process, the mandrel bar (5) is placed inside the tube billet (4), and the rolls (1, 2), when they are in the working position and the mandrel bar (5), form the wall thickness of the rolled pipe, characterized in that direction of movement of rolled pipes measuring the actual wall thickness of the pipes (d) after processing them in at least one of the rolling stands and comparing these data with the given parameters, using the adjusting device acting on the rotary device (12), specify the angle of rotation of the longitudinal axis (L) of the mandrel bar ( 5) having a transverse profile different from the ideal circumference, for bringing the measured actual parameters of the wall thickness closer to the set ones. 2. Rolling mill for the manufacture of seamless pipes, especially steel, containing at least one rolling stand with at least two rolling rolls (1, 2), which jointly roll the surface (3) of the tube billet (4), during the rolling process, the mandrel bar (5) is placed inside the tube billet (4), and the rolls (1, 2), when they are in the working position and the mandrel bar (5), form the wall thickness of the rolled pipe, characterized in that the mandrel bar ( 5) in a vertical section with respect to its longitudinal axis (L) II, has a shape different from the ideal circle, while the rolling mill is equipped with a control device acting on the rotary devices (12) to rotate the mandrel bar (5) in a certain position around the longitudinal axis (L) and hold it, and the mandrel bar (5) has functional surfaces for adjusting the rotation. 3. The rolling mill according to claim 2, characterized in that the mandrel bar (5) in the vertical section with respect to its longitudinal axis (L) has an oval shape. 4. The rolling mill according to claim 2, characterized in that the mandrel bar (5), in a vertical section with respect to its longitudinal axis (L), has a shape formed by at least two arcs (6, 7) of the same radius ( R), while the radii (R) of the arcs have a value that is more than half the smallest diameter of the mandrel bar (D). 5. The rolling mill according to claim 4, characterized in that the mandrel bar (5), in a vertical section with respect to its longitudinal axis (L), has a shape consisting of four or more arc segments (6, 7), wherein the number of arc segments (6, 7) is even. 6. A rolling mill according to claim 5, characterized in that in the direction of movement of the rolled pipes, it is envisaged the sequential use of at least two pairs of rolls (1, 2) in one or more rolling stands, while the pairs of rolls (1, 2) are rotated relative to the longitudinal axis (L) of the mandrel bar (5). 7. The rolling mill according to claim 4, characterized in that the intermediate segment between the two arcs (6, 7) forming the profile of the mandrel bar (5) has a rounding (8). 8. A rolling mill according to claim 4, characterized in that the highest radial points (9, 10) of the transverse profile of the mandrel bar (5) are located symmetrically on its circumference. 9. A rolling mill according to claim 4, characterized in that the cross-sectional shape of the mandrel bar (5) is symmetric with at least one symmetry line (11). 10. The rolling mill according to claim 2, characterized in that the rolling rolls (1, 2) in radial section have a rolling surface in the form of an arc segment. 11. A rolling mill according to claim 2, characterized in that the rotary devices (12) are included in the movable support assembly of the mandrel bar. 12. The rolling mill according to claim 2, characterized in that the rolling stands are equipped with two, three or four rolling rolls (1, 2).

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