GB2174632A

GB2174632A - Regulation of flatness of cold-roller strip

Info

Publication number: GB2174632A
Application number: GB08610465A
Authority: GB
Inventors: Gerhard Richter; Axel Barten
Original assignee: Achenbach Buschhetten GmbH and Co KG
Current assignee: Achenbach Buschhetten GmbH and Co KG
Priority date: 1985-04-29
Filing date: 1986-04-29
Publication date: 1986-11-12
Also published as: DE3515459A1; JPS61249613A; IT8620041A0; FR2580959A1; IT8620041A1; GB8610465D0; FR2580959B3; IT1191721B; DE3515459C2

Abstract

Variations in tensile stress across the width 12 of the roller strip 8 are detected by a measuring roll 11. Where an elongated zone results in lower tension a corresponding heating device 6 upstream of the mill rolls is actuated to reduce the tension at entry to the rolls and thereby reduce the elongation by rolling. Roll coolant ensures that the heated zone is brought back to the same temperature as the rest of the strip. The heating devices 6 shown as a single row may be in two staggered rows across the width 12 of the strip. <IMAGE>

Description

SPECIFICATION Regulation of flatness of cold-rolled strip The invention relates to an apparatus for regulating the flatness of strip-like rolled stock, especially thin strips, for cold rolling mills.

The requirements of cold rolled thin-strip material as regards dimensional accuracy and accuracy of shape, have become considerably more stringent in the course of the development of rolling mill technology and subsequent treatment. An ideal cold-rolled strip will not only have a uniform thickness over the length and width, but will also lie completely flat.

Moreover, the flatness must also be maintained when the strip is subdivided in the subsequent treatment.

A measure of the degree of flatness of a strip is provided by the length distribution AL L over the width of the strip, which can be calculated from the measured strip tensions with the aid of the expression E in which Aa represents the difference of tension between two adjacent zones or fibres of the strip and E the modulus of elasticity of the material of the strip.

The requirements of dimensional stability and flatness of a thin strip cannot, however, be fulfilled. If, for example, one attempts to cold roll a hot strip, which is somewhat thinner at the edges than in the middle, so as to make it of completely uniform thickness throughout its width, this necessitates a relatively great reduction in the thickness and hence a relatively great elongation of the middle part of the strip which in turn leads to the formation of corrugations in this middle part.

If, however, the optimum possible flatness is sought after, then allowance must be made for the cross-sectional shape of the hot strip being transferred to the cold strip.

Flatness defects may become apparent after the rolling operation or not until the subsequent treatment is carried out. Flatness defects that appear during the rolling operation are essentially a result of differential elongation over the width of the strip resulting from a non-uniform deformation of the strip over the width thereof in the roll gap. During the subsequent treatment, for example when the strip is subdivided, flatness defects are often caused by the release of internal stresses produced during the rolling operation.

A distinction is made between flatness defects which can be eliminated by the application of tension and those which cannot be so eliminated. Defects which can be eliminated by the application of tension are those in which the strip deviates from flatness uniformly in the direction of its width. Moreover, oppositely directed internal stresses occur adjacent the upper and lower surfaces of the strip, these stresses being uniform over the entire width of the said strip. Unevennesses which can be eliminated by the application of tension are characterised by being confined rectilinearly to a single direction, i.e. to the longitudinal or transverse direction.

Flatness deviations which vary over the width and length of a strip are characterised by having curvilinear boundaries and cannot be eliminated merely by the application of tension. Thus, non-uniform internal stress distributions are present in the longitudinal and transverse directions. Such flatness defects occur in the form of corrugations in the middle and margins of the cold rolled strip.

The following serve as dimensional adjusting means or adjusting members in the known systems of regulating the flatness of thin-strip rolling mills:-the tilting of the rolls, the back bending of the rolls, the spraying of a coolant over the roll bodies in the region of the flatness defects that appear as long parts in the strip being rolled and the application of adhesive materials of semi-permanent consistency to the roll bodies in the region of the flatness defects which appear as short parts in the rolled strip (B BC-Nachrichten 62, 1980, pages 451 to 456).

The flatness adjusting systems for thin-strip rolling mills which are available on the market do not meet the stringent requirements in regard to strip quality.

The basic object of the present invention is to develop a flatness regulating apparatus for thin-strip rolling mills which is of increased accuracy compared with the known regulating devices.

This object is achieved by the features specified in the characterising clause of patent claim 1.

Suitable developments of the invention form the subject of the sub-claims.

The flatness regulating apparatus according to the invention for thin strip rolling mills is distinguished by the advantage which can be understood from the statement of object as well as the advantages referred to in connection with the following description of two embodiments.

There are shown in diagrammatic representation: Figure 1, a side elevation of a four-high rolling mill provided with a first arrangement of the flatness regulating apparatus according to the invention, Figure 2, a plan view of the rolling mill according to Fig. 1 and Figure 3, a plan view corresponding to Fig.

2 of a four-high rolling mill provided with a second arrangement of the flatness regulating apparatus.

The flatness regulating apparatus 5 according to Figs. 1 and 2, which is incorporated in a thin-strip four-high rolling mill with two working rolls 1, 2 and two backing rolls 3, 4 has a number of heating elements 6 which are arranged on the input side of the roll gap 7 side-by-side in a row extending transversely to the direction of movement a of the strip 8.

The heating elements 6 are mounted above and below the plane of the strip. The strip 8 can be heated zonally for a short time by the heating elements 6 up to 10 C or more.

In the second embodiment of the flatness regulating apparatus 9 according to Fig. 3, the heating elements 6 are arranged in two rows located one behind the other, the heating elements of each row being mounted side-byside and spaced apart by an interval equal to the width 10 of one heating zone and the elements in each of the two rows being offset with respect to those in the other row by an amount equal to the width of one heating zone.

Electric induction heating elements, especially microwave devices, radiant heat sources such as infra-red radiators, hot air heating elements and spray nozzles for applying heated roll oil may be used as the heating elements 6.

The flatness regulating apparatus, which is used in combination with a roll flexing device and a roll-cooling device, operates as follows: The tensile stress in the strip is measured continuously over the width 12 of the latter by means of a measuring roll 11 which is located on the output side of the roll gap 7.

The width of the measuring zones of the measuring roll 11 corresponds moreover to the width 10 of the heating zones in the strip corresponding to each of the heating elements 6. When a long part which gives rise to a flatness defect occurs in the strip 8 on the output side of the roll gap 7, the reduction in tensile stress that occurs in the region of the long part is detected by the measuring roll 11 which, by means of an electric control circuit, causes the emission of a control signal, which switches on the heating element located on the input side of the roll gap 7 over the region of the strip containing the long part. The strip part on the input side of the roll gap 7 in the region containing the said long part is heated briefly by the heating element 6 up to 10"C or more.As a result of the heating, the tensile stress in this region is reduced on the input side of the roll gap 7 and, due to the reduced tensile stress, there is a smaller reduction in the thickness of the strip in that part thereof entering the roll gap which has been cooled again to the temperature of the rest of the strip by the action of the roll coolant. The smaller reduction in the thickness of the strip in the roll gap results in a reduction in the elongation of the strip on the output side of the rolling mill in the region of the strip which contains the long part and hence an increase in the tensile stress by means of which the long part is eliminated.

The zonal alteration of the tensile stress in the thin strip on the input side of the roll gap constitutes a dimensional adjusting means which is operative in addition to the roll cooling and the roll bending during the regulation of flatness.

The regulation of flatness by varying the tensile stress over the width of the strip using zonal heating of the strip as the adjusting means operates substantially more accurately than regulation of flatness by zonal cooling of the rolls, since the heated parts of the thin strip are demarcated in a substantially more sharply defined manner than the cooled regions on the rolls which operate under the action of the coolant sprayed on them.

The document "BBC-Nachrichten 62" referred to above is a publication of Brown-Boveri Company of Mannheim. An off-print of the article in question is on file with U.K. Patent Application 8513133 in the name of the present applicants, together with a partial translation thereof.

Claims

1. Apparatus for regulating the flatness of strip-like rolled stock in cold rolling mills, characterised by heating elements arranged on the input side of the roll gap and transversely to the direction of travei of the strip so as to heat selected zones of the strip and thus reduce the tensile stress in the strip in those zones.

2. Apparatus according to claim 1, characterised by increasing the temperature of the strip in the said zones by up to 10 C.

3. Apparatus according to claim 1 or 2, characterised by the heating elements being arranged in a row.

4. Apparatus according to claim 1 or 2, characterised by the heating elements being arranged in staggered relationship to one another.

5. Apparatus according to any of claims 1 to 4, characterised by the heating elements being located above and/or below the plane of the strip.

6. Apparatus according to any of claims 1 to 5, characterused by electric induction heating elements, especially microwave devices.

7. Apparatus according to any of claims 1 to 6, characterised by hot air heating elements.

8. Apparatus according to any of claims 1 to 5, characterised by the use of radiant heat sources, especially infra-red radiators, as heating elements.

9. Apparatus according to any of claims 1 to 5, characterised by spray nozzles for applying heated roll oil to the strip being rolled.

10. Apparatus according to any of claims 1 to 8, characterised by the combination thereof with a roll bending device and a roll cooling device.