Title of Invention

A GROOVE CONTOUR OF THE SUBSTANTIALLY CIRCULARLY GROOVED ROLLS OF A REDUCING MILL

Abstract

(1694/MAS/96) The present invention relates to a groove contour of the substantially circularly grooved rolls of a reducing mill with three-high rolling stands, especially for rolling thick-walled tubes with a wall thickness/diameter ratio greater than 0.25 characterized by the fact that the groove contour of each roll has a diameter enlargement in the region of the groove base, in which the material area rolled in the roll discontinuity of the respective preceding groove in the direction of roll can be deformed.

Full Text

The invention relates to the groove contour of the substantially circularly grooved rolls of a reducing mill with three-high rolling stands especially for rolling thick-walled tubes with a wall thickness/diameter ratio greater than 0.25. In order to roll thin-walled tubes, reducing mills according to the prior art normally do not use circular groove forms. Instead, such reducing mills use elliptical grooves formed by three curvatures, the short semiaxes of which are located in the groove base. The long semiaxis is located in the groove discontinuity and is larger than the short semiaxis of the preceding groove. This measure represents an attempt to prevent the rolled material from emerging into the roll gap and in this way to avoid roll gap markings. However, the technical limits of such groove forms are reached in rolling tubes with wall thickness ratios greater than 0.1. In these cases, so-called "polygon formation" occurs, i.e., the internal contour of the tube deviates from the desired circular shape. In an extreme case, such polygon formation can result in an almost hexagonal internal cross-section, which severely limits the usefulness of the tube. It is nearly impossible to roll thick-walled tubes using the known oval groovings. Instead, groovings that are more nearly circular in shape and can better suppress polygon formation must be used. These correlations are discussed in the "Archive of Iron and Steel Metallurgy dash Eisenbuettenwesen), Vol. 41, No. 11, November 1970, pp. 1047 - 1053. In conclusion, this known prior art proposes that reducing mills use special grooving for the thick-walled portions of the program of a tube rolling train. The special grooving strives to encompass the tube on all sides during the rolling process, i.e., to achieve a substantially circular groove. It is possible to adopt such a measure because roll gap markings are significantly less likely to appear on the external surfaces of thick-walled tubes than on those of thin-walled tubes. The groove opening should be selected in such a way that the difference in length between the shortest and longest contact areas is minimal, i.e., in such a way as to create a rectangular contact surface between the roll and the tube. When the principle stated in the cited publication is applied, however, it has been shown that an even contact surface cannot be achieved between the tube and the roll in pass sequences with small groove openings. Using standard roll pass dressing technology, a contact surface with three peaks, which are located in the groove base and at the groove discontinuities, respectively, is created. This is described on p. 1052, Figure 11 of the aforementioned publication. In very thick-walled tubes with a wall thickness/diameter ratio greater than 0.25, the peaks in the contact surface between the roll and the rolled material again result in internal non-circularities on the tube and thus have a significant negative impact on tube quality. Furthermore, friction is increased, so that the rolls abrade more intensely. Starting from the prior art as described in the "Archive of Iron and Steel Metallurgy," Vol. 41, No. 11, November 1970, the present invention is based on the object of improving the groove contour of rolls with substantially circular grooving according to the prior art in such a manner that undesired peaks in the contact surface between the roll and the rolled material are avoided or at least flattened. To attain this object, it is proposed according to the invention that the groove contour of each roll have, in the region of the groove base, a diameter enlargement, in which it is possible to deform the material rolled in the roll discontinuity of the preceding groove in the direction of roll. By deliberately enlarging the groove diameter in the region of the groove base, it is possible to shorten the contact length in this region, and thus to obtain an even contact surface. As a result, the tube is no longer subjected to disproportionate stresses in the region of the groove base, because the distinct peaks found in the prior art can be largely flattened. It is particularly advantageous for the diameter enlargement, starting from the groove diameter, to equal approximately 0.5% to 1.0% of the groove diameter and to extend on both sides of the groove base center at a circumferential angle of roughly 10° to 15°. Given these dimensions, good tube results have been obtained, i.e., a nearly right-angled contact area between the roll and the rolled material. In a measure that improves the invention, there is, in addition to the diameter enlargement in the groove base of the roll, a diameter enlargement in the region of the groove discontinuity. This latter diameter enlargement can be achieved, for example, by enlarging the transition radius at the edge of the roll to 3 - 5 mm. It has been shown that when such radii (which are less than 3 mm in the prior art) exist, significant improvement in deformation ratios can be achieved and the groove contact peaks can be significantly reduced even at the edge of the groove of a roll. Accordingly, the present invention provides a groove contour of the substantially circularly grooved rolls of a reducing mill with three-high rolling stands, especially for rolling thick-walled tubes with a wall thickness/diameter ratio greater than 0.25, characterized in that the groove contour of each roll has a diameter- enlargement in the region of the groove base, in which the material area rolled in the roll discontinuity of the respective preceding groove in the direction of roll can be deformed. An example of the invention is shown in the drawings and described below. The drawings show: Figure 1 & lA Front view of a partially-cut grooved roll according to the invention with a tube that is entering; Figure 2 Projection of the contact area between the tube and the grooved roll according to the invention, on the horizontal. In Figure 1, reference number 1 indicates one of three grooved rolls according to the invention that comprises the total groove. The indicated grooved roll rotates around the rotational axis 2. The tube to be rolled is marked with reference number 3. The substantially circular groove 4 of the roll 1 has, in the region of the groove base at 5, an enlarged diameter, i.e., a deepening of the groove base. According to the invention, there are further groove enlargements in the region of the groove discontinuity at 6; specifically, in the form of radii enlargements at the edge of the grooved roll 2. To assist understanding. Figure 1 shows the conventional groove form by a dashed line at 7. The conventional groove form is also shown in Figure 2, which depicts the projection of the contact area between the tube 3 and the roll 1. The contact peaks created in the conventional groove at 8 in the region of the groove base 9 of the grooved roll 1 and in the area of the groove discontinuity 10 on both edge sides of the roll 2 are clearly visible. These peaks 8 and 10 are created on the entry side of the roll 2 and result in the described internal non-circularity in the finished tube 3. The contact area of the tube with the roll according to the invention is shown in Figure 2 in a darker shade. It is clear that the peak 8 and 10 are largely eliminated, resulting in an almost rectangular contact area with the contact length 11. The diameter enlargements 5 (in the groove base) and 6 (in the area of the groove discontinuity) are responsible for this change in contact area. WE CLAIM : 1. A groove contour of the substantially circularly grooved rolls of a reducing mill with three-high rolling stands, especially for rolling thick-walled tubes with a wall thickness diameter ratio greater than 0.25, characterized in that the groove contour of each roll (1) has a diameter enlargement (5) in the region of the groove base, in which the material area rolled in the roll discontinuity of the respective preceding groove in the direction of roll can be deformed. 2. The groove contour as claimed in claim 1, wherein the diameter enlargement (5), starting from the groove diameter, equals 0.5% to 1.0% of the groove diameter and extends on both sides of the groove base center at a circumferential angle of 10° to 15". 3. The groove contour as claimed in claims 1 and 2, wherein in addition to the diameter enlargement (5) in the groove base of the roll (1), there is a diameter enlargement (6) in the region of the groove discontinuity. 4. A groove contour of the substantially circularly grooved rolls of a reducing mill, substantially as herein described with reference to the accompanying drawings.

Documents:

1694-mas-1996 abstract duplicate.pdf

1694-mas-1996 abstract.pdf

1694-mas-1996 claims duplicate.pdf

1694-mas-1996 claims.pdf

1694-mas-1996 correspondence others.pdf

1694-mas-1996 correspondence po.pdf

1694-mas-1996 description (complete) duplicate.pdf

1694-mas-1996 description (complete).pdf

1694-mas-1996 drawings.pdf

1694-mas-1996 form-2.pdf

1694-mas-1996 form-26.pdf

1694-mas-1996 form-4.pdf

1694-mas-1996 form-6.pdf

1694-mas-1996 others.pdf

1694-mas-1996 petition.pdf