Method and apparatus for straightening sheet materials

Oct. 27, 1970 τ. sevenich etal 3,535,902

METHOD AND APPARATUS FOR STRAIGHTENING SHEET MATERIALS

Filed Feb. 29, 1968

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United States Patent Office

3,535,902

Patented Oct. 27, 1970

535 902 METHOD AND APPARATUS FOR STRAIGHTENING SHEET MATERIALS

Theodor Sevenich, Dortmund, and Peter Zens, Dortmund-Kirchderne, Germany, assignors to Hoesch Ak- _gtiengesellschaft, Dortmund, Germany

Filed Feb. 29,1968, Ser. No. 709,351

Claims priority, application Germany, Mar. 6, 1967,

1,602,461; Sept. 21, 1967, 1,602,468

Int. CI. B21d 1/02

U.S. CI. 72—160 8 Claims

ABSTRACT OF THE DISCLOSURE

Straightening sheet materials, especially sheet metal _lghaving at least a curvature in the transverse direction, by passing the sheet in a continuous movement in its longitudinal direction between two sets of straightening rollers having concave and convex outer surfaces, respectively, which act under pressure upon the convex and concave 20 sides of the sheet, respectively, so as to eliminate said curvature.

The present invention relates to a method and an apparatus for straightening sheet materials and especially 25 sheet metal which has a curvature extending transverse to the direction in which the material has been rolled in a hot-rolling mill.

In the production of sheet metal of any width it is the conventional procedure to wind the rolled sheet com- 30 ing from the rolling train and while still in a hot condition into a coil and then, after it has cooled, to unwind it from the coil in a cutting apparatus in which it is cut transversely and/or longitudinally to the rolling direction to the desired dimensions. While being unwound from 35 the coil, the sheet material is straightened and thereby plastically deformed in the longitudinal direction. This straightening operation, however, cannot prevent that residual stresses remain in the longitudinal direction of the sheet material and that the transverse components of ⁴⁰these longitudinal stresses will cause the material to curve in the transverse direction. These transverse curvatures must be thereafter eliminated in a separate straightening operation outside of the cutting apparatus.

For straightening uneven parts of metal sheets, these ⁴⁵sheets are generally passed through straightening machines which may be of different types. In one type of these machines the sheet material is passed between two superimposed rows of cylindrical straightening rollers which are rotatable in opposite directions and apply a pressure upon ⁵⁰the opposite sides of the sheet. Another known type of these straightening machines comprises cylindrical straightening rollers which are bent by means of bracing rollers so that the sheet material running therethrough will be stretched longitudinally at certain areas whereby ⁵⁵the waviness of adjacent areas of the sheet will be eliminated. Still another known type of straightening machines comprises short cambered straightening rollers which may be shifted axially on their shafts and act upon the particular areas of the sheet which are to be straightened. ⁶⁰There is also a straightening method known in which two different types of these machines are combined so that the sheet metal is at first straightened in its longitudinal direction and thereafter in a separate operation in the transverse direction by means of a flexible straightening ⁶⁵roller or a short straightening roller.

In all of these known methods the sheets to be straightened will be deformed in their direction of travel while the deformation which is attainable in the transverse direction is very small as compared with the longitudinal ' deformation. If it is necessary to eliminate transverse curvatures in the sheets, the latter must be passed several times through the straightening machine. Since repeated straightening operations cannot be carried out at all or only with great difficulty in a cutting apparatus, the known straightening methods and the machines for carrying out these methods are unsuitable for continuously eliminating the transverse curvatures of metal sheets.

It is an object of the present invention to overcome the above-mentioned disadvantages of the known straightening methods and apparatus and to provide a new straightening method in which sheets or strips of metal or other materials will be completely straightened in the longitudinal and transverse directions by being passed only once through a new type and arrangement of straightening rollers.

For attaining this object, the invention provides that the sheets or strips to be straightened are given an initial stress contrary to the transverse curvature and are deformed beyond the elastic limit of the sheet material by a rolling operation in the longitudinal direction in which they are produced by the rolling train of the mill. The extent to which the elastic limit of the material is to be exceeded in the transverse direction of the sheet is preferably determined by the sum of the transverse components of the longitudinal stresses and of the initial stress itself which the sheet has in its transverse direction.

The stresses which according to the invention are produced i® the transverse direction of the sheet should, however, preferably be kept far below the elastic limit of the material since they are not needed to effect a plastic deformation of the material in the transverse direction. The transverse curvature of the sheets is therefore eliminated merely by plastically deforming the material in the longitudinal direction to such an extent that the transverse components of the stresses which are produced by this longitudinal plastic deformation will be sufficiently increased by the transverse stresses themselves.

For straightening sheets or strips especially of metal by a single continuous operation, the invention provides an apparatus which comprises two rows of associated straightening rollers which are disposed within two different levels and are provided with concave or convex outer surfaces, respectively. The straightening rollers with convex surfaces are preferably provided in the upper row and the straightening rollers with concave surfaces in the lower row since the sheets are preferably passed through these rollers with their transverse curvature extending in the upward direction. Since according to the new method only a small stress is to be produced in the transverse direction of the sheet or strip material, the degree of curvature in the axial direction of the straightening rollers is preferably made very large. The diameter of these straightening rollers and their distances from each other therefore have to be only slightly larger than those of the conventional cylindrical straightening rollers in order to attain the required permanent plastic deformation of the sheets in their longitudinal rolling direction for completely straightening the sheets in all directions.

The features and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying diagrammatic drawings, in which—

FIG. 1 shows a perspective view of a complete set of straightening rollers according to the invention;

FIG. 2 shows a perspective view of a plate, for example, of sheet metal which has been wound from a coil and cut off transversely;

FIG. 3 shows a perspective view of a set of straightening rollers consisting of two upper convex rollers and one

3,535,902 lower concave roller for carrying out the first stage of the straightening operation;

FIG. 4 shows the lines of force in a sheet while the sheet is being bent about the lower concave straightening roller according to FIG. 3;

FIG. 5 shows a perspective view of a set of straightening rollers consisting of one upper convex and two lower concave rollers for carrying out the second stage of the straightening operation; while

FIG. 6 shows the lines of force in a sheet, for example, of metal, while the sheet is being bent about the upper convex straightening roller according to FIG. 5.

For carrying out the new method of straightening sheets or strips, for example, of metal, the invention provides a set of straightening rollers, as diagrammatically illustrated in FIG. 1, which comprises a row of lower rollers 1 with concave outer surfaces and a row of upper rollers 2 with convex outer surfaces. All of these straightening rollers 1 and 2 are ground so as to have substantially equal concave or convex curvatures c, respectively, as indicated in FIG. 3.

FIG. 2 illustrates a sheet, for example, of metal 3 which has been unwound from a coil and has then been cut transversely to the desired length. This sheet has a curvature a in its longitudinal direction and a curvature b in the transverse direction. Both these curvatures a and b are to be straightened so that the sheet will be completely plane. For this purpose, the invention provides that in a first working stage the sheet is passed through the set of straightening rollers as shown in FIG. 3. This first part of the straightening operation gives the sheet an initial tension in the direction opposite to the original transverse curvature b by bending it for the distance b-\-c. This results in a compressive stress Aj on the upper side of sheet 3 and in a tensile stress A₂ on its lower side, as indicated by the solid arrow heads in FIG. 4. These stresses Aj and A₂ by themselves do not exceed the elastic limit of the material. In the longitudinal direction of sheet 3, the stresses A, and A₂ produce the stress components Bt and B₂ as indicated in FIG. 4 by ordinary open arrow heads. The stress component Bi on the upper side of the sheet forms a tensile stress and the stress component B₂ on the lower side of the sheet a compressive stress. The stress components B_r and B₂ by themselves likewise do not reach the elastic limit of the material.

When the sheet 3 runs through the system of straightening rollers according to FIG. 3, it will be plastically deformed in the longitudinal direction about the lower concave straightening roller. This results in a tensile stress Ci on the upper side of the sheet and a compressive stress C₂ on its lower side, as indicated by the double open arrow heads in FIG. 4. In the transverse direction of the sheet, the stresses Ci and C₂ produce the stress components D, and D₂, as indicated by triple open arrow heads in FIG. 4. Since the stress component D_x on the upper side of the sheet is a compressive stress, it is added to the initial stress A_b while the stress component D_t is a tensile stress and therefore likewise added to the initial stress A₂. If the sheet is plastically deformed to a sufficient extent in the longitudinal direction of the stresses C_t and C₂, the sums of the stresses of the components Aj and Di and of the components A₂ and D₂ will also exceed the elastic limit of the material in the transverse direction and a plastic deformation of the sheet will take place in the transverse direction which eliminates the original curvature b of the sheet. The curvature a in the longitudinal direction of the sheet will, however, at first be increased by the straightening operation by means of the straightening rollers according to FIG. 3.

Since the entire roller arrangement as illustrated in FIG. 1 consists of several convex straightening rollers in the upper row and several concave straightening rollers in the lower row, the first stage of the straightening operation as above described will be followed immediately by the second stage by means of the roller arrangement according to FIG. 5. In this second straightening stage, the sheet will be stressed in the transverse direction in the same manner as in the first straightening stage according to FIG. 3. By bending the sheet in the transverse direction, the compressive stress Ei will be produced on the upper side of the sheet and the tensile stress E₂ on its lower side. These stresses are indicated in FIG. 6 by single open arrow heads. When runing through the roller arrangement according to FIG. 5, sheet 3 will be bent in the longitudinal direction about an upper convex roller 2. The stresses G, and G₂ which are then produced are indicated in FIG. 6 by double open arrow heads. These longitudinal stresses G, and G₂ produce the transverse components Η, and H₂ in the transverse direction, as indicated in FIG. 6 by triple open arrow heads. As may also be seen in FIG. 6, the stresses Ej and E₂ extend in the opposite direction to the transverse components H_t and H₂. Therefore the transverse components Hi and H₂ will reach the elastic limit of the material only after the latter has been plastically deformed in the direction of the longitudinal stresses G_x and G₂ to a greater extent than that which occurs during the passage of the sheet through the roller arrangement according to FIG. 3 in which the transverse components Dj and D₂ are formed which are produced by the longitudinal stresses B, and B₂, as indicated in FIG. 4. The roller arrangement according to FIG. 5 thus not only bends back the sheet so as to eliminate its deformation in the longitudinal direction which was produced by the preceding straightening stage by means of the roller arrangement according to FIG. 3, but it also eliminates the curvature a which originally existed in the longitudinal direction. The order of succession in which the individual straightening stages may be carried out may also be reversed and, if necessary or desirable, they may be repeated several limes.

The considerable advantage of the straightening method according to the present invention over the straightening methods as heretofore known is particularly the fact that the transverse curvature of a sheet or strip of metal of other material may be completely eliminated by passing it only once through the set of straightening rollers according to FIG. 1. It is another advantage of the new method that it also permits the different transverse curvatures of sheets and strips of different thicknesses to be completely eliminated by means of the same uniformly ground straightening rollers and by merely adjusting the upper and lower straightening rollers relative to each other so as to exert the required pressures upon the sheets or strips in accordance with their different thicknesses. If the method according to the invention is applied, it is therefore no longer necessary to carry out any additional expensive straightening operations outside of the cutting apparatus.

Although our invention has been illustrated and described with reference to the preferred embodiment thereof, we wish to have it understood that it is in no way limited to the details of such embodiment but is capable of numerous modifications within the scope of the appended claims.