EP0470512A2 - Method of dressing metal bands passing through - Google Patents

Abstract

The invention relates to a method for straightening metal strips in a pass only by tension bending straightening. The strip to be straightened is tensile bent twice in succession in the direction of travel. In the first tensile bending process, the tensile bending straightening takes place with a comparatively small tensile stress and with a large bending deformation, while in the second tensile bending stretch the strip is subjected to only a slight bending with a significantly higher tensile stress. Through this successive different kind of stretch bending straightening, a flat strip is obtained which maintains its flatness even after a long storage period.

Description

Metal strips, the thickness of which has been reduced to less than 5 mm by repeated rolling, are not flat. They are wavy and have bumps. For this reason, they are often not suitable for further processing. For this reason, such tapes are subjected to a straightening process. A distinction is made between straightening and stretch-bending straightening. During tensile stretching, the strip is subjected to a tensile stress at which its yield strength is exceeded, so that the strip is plastically deformed, namely elongated. During stretch bending straightening, the strip is subjected to tensile stress and bent several times in opposite directions under tension. The yield stress in the area of the mutual bending is also exceeded and the strip is permanently elongated. Finally, it is also known to combine tensile stretching and stretch-bending straightening by first stretch-straightening and then tensile stretching. In this state of the art, tensile stretching is considered to be necessary in any case if a stretching degree of> 1% is used in straightening bending straightening, because it is then allegedly due to remaining residual stresses in the strip that bulges occur which are to be eliminated again by the subsequent pure tensile stretching in the plastic area (DE 35 25 343 C1). In practice, the various straightening processes are satisfactory, whether it is pure stretch stretching, stretch bending straightening or combined stretch stretching straightening and stretch stretching, not only because the strip is not satisfactorily flat after the treatment, but above all because after a longer aging period again adjust the flatness.

In addition, in the case of pure stretching and combined stretching and stretching in the pure stretch of train, no defined strip deflection over the bandwidth can be guaranteed. Since the belt is put under tension between two tensioning drums, it cannot be readily said in which area of the train path the belt stretching (elongation) takes place. If you define the distance as the distance between the centers of the two tensioning rollers, the desired belt elongation will not occur in this area, rather it must be assumed that the stretch zone is immediately in front of or behind the apex of the two tensioning rollers. The desired lengthening of the tape thus takes place on the contact sheet of the tensioning rollers, namely immediately before the point of deceleration of the braking roller or immediately after the point of impact of the pulling roller, because the tension introduced into the tape is higher at these points than in the actual train path, since here the a tensile stress dependent on the roller diameter is superimposed by the tension rollers generated, that is, added to this.

The belt extension on the circumference of tensioning rollers has considerable disadvantages. Since tensioning rollers of this type practically always have a rubber coating, the tension in the belt caused by imperfections in the rubber coating, different layer thicknesses and uneven wear of the coating and changing rubber coating properties, which does not correspond to the inner tension pattern of the belt to be straightened. The result is a tape that has significant residual stresses and thus flatness errors due to the large number of imponderables shown.

The object of the invention is to develop a method which avoids the disadvantages mentioned above and with which not only a flat belt can be produced, but also a permanent flatness is achieved due to the treatment of the belt.

This object is achieved procedurally in that the metal strip is subjected to tensile bending twice in one pass with different tensile stress, in that the bending deformation in the first tensile bending process is greater than in the second tensile bending process and in that the tensile stress in the second tensile bending process is at least 50% of the stretching limit stress of the strip and is substantially larger than the tensile stress during the first stretch bending process.

In direct contrast to the prior art, in which the tension is first stretched and then only stretched, the invention involves two tensile bending under different conditions. It has been shown that under the different tensile bending conditions during the first and second tensile bending processes, the strip leaving the second tensile bending section is absolutely flat and does not have the curvatures that it is known to in the prior art because of the tensile bending treatment. This effect is due to the fact that in the second tension bending process the desired plastic deformation of the strip using the usual means for bending, such as roller straighteners with small radii of curvature of the straightening rollers, can be carried out much more precisely than in a pure stretching stretch. It is surprising that in this way not only the desired flatness of the tape is maintained, but this flatness is also maintained permanently.

Good experiences with regard to the flatness and the preservation of the flatness have been made with a tensile stress during the first stretch bending process of 20% to 50% of the yield stress of the band and / or with a tensile stress during the second stretch bending process of approximately 80% - 90% of the limit stress of the band.

Preferably the band should be in the two Tension bending sections are lengthened differently, particularly in the first tension bending section than in the second tension bending section.

In the following, the invention is explained in more detail with reference to a drawing illustrating an exemplary embodiment, which shows a device for straightening metal strips in a pass in a schematic representation in a side view.

The device has two tensile bending sections 2-5 arranged one behind the other in the direction of travel of a strip B to be straightened. The belt B arrives via a pair of S-rolls 1, 1 'into the first draw bending section 2 and via a further driven S-pair of rolls 4.4' into the second draw-bending section 5 and from here via a third driven S-pair of rolls 7,7 ' a reel not shown. The drives of the S-roller pairs 1,1 ', 4,4', 7,7 'are tension controlled or degree of stretch controlled. A roller straightening apparatus 3, 6, whose straightening rollers, which have a small radius of curvature, bend the continuous belt B several times in the opposite direction, is arranged in each tension bending section 2.

In the device shown, the band B is subjected to a strong bending deformation and a weak tensile stress in the first tensile bending section 2 and a strong tensile stress and a weak bending deformation in the second tensile bending section 5. In the first tensile bending section, the tensile stress is 20 to 50% and in the second tensile bending section 5, 50 to 90% of the yield stress of the strip B. Depending on the tension set, a bending stress is superimposed on the tension by adjusting the straightening rollers of the bending straighteners 3.6 , which leads to the desired elongation of the band. So that the tension can be set independently of one another in both tension bending sections 2.5, the pair of S-rollers 4, 4 'is driven and therefore has a decoupling effect on both tension bending sections 2.5.

Claims (5)

1.Procedure for straightening metal strips exclusively by straightening the metal strip (B) with different tensile stresses in one pass, in which the bending deformation in the first tensile bending process is greater than in the second tensile bending process and the tensile stress in the second tensile bending process is at least 50% of the yield stress of the strip and is greater than the tensile stress during the first tensile bending process. 2. The method according to claim 1, characterized in that the tension in the first stretch bending process is 20 to 50% of the yield stress of the strip. 3. The method according to claim 1 or 2, characterized in that the tensile stress in the second stretch bending process is less than 90% of the yield stress of the strip. 4. The method according to any one of claims 1 to 3, characterized in that the band (B) is bent in the same direction at the beginning and end of a tension bending section. 5. The method according to any one of claims 1 to 4, characterized in that the band is curved in opposite directions at the beginning and end of a tension bending section, in particular the second tension bending section.

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