Abstract:
A method for straightening sheet, strips, sections, girders, etc. The method includes measuring the straightening forces of at least one of the straightening rolls in a straightening machine and adjusting the positions of the straightening rolls in accordance with the measured values. The method further includes individually measuring the straightening force acting perpendicularly on the axes of rotation of the straightening rolls, and/or the roll bearings and/or the frame, and automatically readjusting the straightening rolls in dependence upon these measured values in a range of the occurring varying pressure forces.

Description:
This is a continuation of U.S. application Ser. No. 07/441,765, filed Nov. 27, 1989 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for straightening rolled material, such as, sheets, strip, plates, sections, girders, etc. The method includes measuring the straightening forces of at least one of the straightening rolls in a roll straightening machine and adjusting the positions of the straightening rolls in accordance with the measured values. 
     2. Description of the Related Art 
     During the straightening procedure, vertical forces among other forces occur at the straightening rolls, wherein the vertical forces depend upon the properties of the material to be straightened, the dimensions of the straightening machine and the selected adjustments of the straightening rolls. These forces cause an elastic deformation of the straightening machine, particularly of the rolls, the bearings and the housing, resulting in a change (spring-back) of the roll positions which initially are usually adjusted without material to be straightened. Accordingly, the roll adjustments must be selected in such a way that the desired straightening effect is achieved with the changed adjustments occurring under load. Deviations of the properties of the material entering the straightening machine (temperature, width, thickness, modulus of elasticity, strength, yield point, etc.) from the values determining the selection of the roll adjustments usually lead to undesirable straightening results. For example, a change in strength leads to a changed curvature of the material leaving the straightening machine. Since changed properties of the material to be straightened result in changed straightening forces which, in turn, lead to changed spring-back values and, thus, to changed effective adjustments, it is apparent that the stability of the straightening result with scattered product parameters is essentially determined in part by the spring-back behavior of the straightening machine. The above results are based on practical experience in the past. For example, in high-strength, thick sheet metal, the spring-back may be even the dominating component of the effective roll adjustment. 
     The stiffness of the machine is also used for the approximate description of the spring-back behavior. A stiffness matrix is particularly suitable for the linearized description of the dependencies between individual roll forces and individual roll spring-backs. In addition, the elements of the matrix may depend on the respective point of operation. Computations have shown that a relationship exists between the property changes of the material entering the straightening machine (yield point) and the straightening results (curvature of the discharged material). For example, different machine stiffnesses have substantially different patterns. Similar relationships can also be shown for the parameters which depend on the thickness and width of the material. With respect to method technology, it is always an advantage if the scattering of the parameters have as little effect as possible on the bending process, i.e., functional patterns which are as flat as possible. 
     In straightening sheets, strips, plates, sections, girders, etc., the process is determined by the vertical positions of the straightening rolls selected in dependence on the desired straightening result and the properties of the material being straightened. Depending on the type and construction of the straightening machine, the upper and lower straightening rolls can be adjusted individually or jointly, as described by German Offenlegungsschrift 33 08 616 which discloses a method and an arrangement for straightening sheet metal. In addition to wedges and spindles, hydraulic piston-cylinder units can be used as adjusting devices. 
     In the known method described above, the adjustment and correction of the straightening roll gap is effected by means of control wedges which are in connection with pressure cylinders and spindle drives as displacement devices. The control wedges are arranged so as to extend in longitudinal direction of the straightening rolls and, therefore, are in the same manner in operative connection with the two bearings of the straightening roll. This results in one disadvantage that, when increased eccentric loads of the straightening rolls occur during the operation of the rolling mill due to changes of the cross-section and/or the strength of the rolled material, these eccentric increased loads are not immediately measured and, thus, cannot be corrected by adjusting the rolls without a time delay. This leads to an increased production of deficient finished products which must either be subjected to an expensive finishing operation or must again be melted down as waste. 
     Moreover, in this known method, the adjustment and correction of the straightening roll gap is not effected automatically, but manually. This causes a further time delay of the correction being made at the straightening rolls and increases the production of deficient final products. Also, in this known method, it is not possible to prevent elastic deformations of the straightening machine, particularly of the rolls, the bearings and the housing which not only negatively affects the straightening result of the material to be straightened, but also negatively affects the straightening machine. 
     It is, therefore, the primary object of the present invention to provide a method of the above-described type in which deviations and scattering of the properties of the material are determined without time delay and the consequences thereof are eliminated. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the abovedescribed method includes individually measuring the straightening force acting perpendicularly on the axes of rotation of the straightening rolls, and/or the roll bearings and/or the frame and automatically readjusting the straightening rolls in dependence upon these measured values in the range of the occurring varying pressure forces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE shows in graph form a comparison of the reduced influence the material has on the straightening machine in known straightening machines without compensation and the straightening machine of the invention with full compensation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the invention, each straightening force acting perpendicularly on the axes of rotation of the straightening rolls and/or the roll bearings and/or the housing of the straightening machine is measured individually. Thus, it is possible to measure directly at the straightening roll and correct without time delay any increased load occurring during the operation of the rolling mill, particularly also any eccentric increased load. 
     The correction of the straightening roll position in dependence on the measured value which occurs practically without time delay is achieved particularly by the automatic adjustment of the straightening roll. Thus, compared to the previously known methods, particularly increased loads occurring eccentrically on the straightening rolls, which are based on deviations and scattering of the material being straightened due to changes of the cross-section and/or strength of the material, are determined without time delay and are eliminated. This makes it possible to manufacture a faultless final product. 
     Moreover, the method steps of the present invention make it possible to eliminate any elastic deformations of the straightening machine, particularly of the rolls, the bearings and the housing and, thus, to facilitate the manufacture of a faultless straightened material. 
     The individual forces acting perpendicularly on the axes of rotation of the straightening rolls and/or roll bearings and/or housing of the straightening machine can be measured in the known manner very easily by a direct or indirect measurement, wherein the measurement of the straightening forces at the housing occur with the aid of the elastic deformations. In most cases, measuring devices of only a single known type are sufficient for this purpose. 
     For the adjustment of the straightening rolls, a known control device is provided which automatically carries out the correction of the straightening roll position which is adjustable during the straightening procedure, the correction being effected in dependence on the forces measured by means of the measuring devices and/or in dependence on the deformation distances measured by the measuring devices and possibly in dependence on the properties of the material being straightened, i.e., yield point, width, thickness, etc. The correction is effected in such a way that the parallel displacement of the straightening roll axes resulting from this correction extends in a direction which is opposite the direction determined by the displacement of the axes caused by the elastic deformations of the machine. As a result, deviations and scattering of the properties of the material being straightened does not affect the roll straightening machine. 
     In accordance with an advantageous feature of the invention, the adjustment or correction of the straightening rolls is carried out in dependence on the values measured on the material being straightened, such as, yield point, width, thickness, etc. As a result, the straightening results of the roll straightening machine are independent of the deviations and scattering of the properties of the material being straightened. 
     In accordance with a further development of the present invention, the adjustment or correction of the position of the straightening rolls is equal to the displacement of the straightening rolls due to the elastic deformation. As a result, a complete compensation of those influences, such as, elastic deformations, is achieved which emanate from the material being straightened and act on the straightening machine, particularly on the straightening rolls. This complete compensation causes the straightening machine to behave rigidly or almost indefinitely stiffly, while actual machine stiffness does not have to be high. In addition to a substantial reduction of the structural requirements of the straightening machine, the influence of deviations and scattering in the properties of the material being straightened are essentially reduced. As mentioned above, the FIGURE shows, compared to the previously known straightening machines without compensation (steep curve), the full compensation (flat curve) of the straightening machine according to the invention results in a substantial reduction of the influences of the material on the straightening machine. 
     It may also be very useful to effect an adjustment or correction of the straightening roll position which is greater than the displacement of the respective straightening roll carried out due to the elastic deformation. This corresponds to an over-compensation of the straightening machine, as indicated by the very flat or almost even curve in the FIGURE. An over-compensation of the elastic deformations which is suitably selected in dependence on the operation point of the straightening machine makes it possible to practically completely suppress an influence of the material being straightened on the straightening result over a wide scattering range (for example, of the strength) and, thus, to effect a stable behavior of the work process which in the past was not achieved. 
     The adjustment or correction of the straightening roll position may also be smaller than the displacement of the respective straightening roll effected on the basis of the elastic deformations. This corresponds to an only partial compensation of the influences of the material being straightened on the straightening machine. This may be advantageous if the number of straightening rolls which are adjustable under load is small relative to the total number of rolls. 
     The values for correcting the straightening roll positions are advantageously computed in accordance with the following formula and the corrections are effected in accordance with these values: ##EQU1## for i=1, . . . , k and j=1, . . . , 1+m, wherein Δp 1 , . . . , Δp k  : changes of the total number k of straightening roll positions adjustable under load, 
     F 1 , . . . , F 1  : measurement values of the total number l of force measuring locations, 
     u 1 , . . . , u m  : measurement values of the total number m of measured elastic deformations, 
     m ij  : partial derivatives of the straightening roll positions a 1 , . . . ,a k  belonging to Δp 1 , . . . , Δp k  by the measurable forces or elastic deformations: ##EQU2## C: multiplication factor which is adaptively adjustable manually and/or automatically in dependence on the product and /or depending on the straightening result, for example, between -2.5 and +2.5. 
     The correction values of the straightening roll positions can be very easily computed from case to case by means of PC computers and the straightening machine can be readjusted either force-controlled or position-controlled in dependence on the determined values. 
     The following numerical values may result, for example, in flat straightening machines: 
     Input Data 
     Number of rolls: 7 
     Roll diameter: 250 mm 
     Division: 150 mm 
     Sheet thickness: 10 mm 
     Sheet width: 3,500 mm 
     Yield point: 1,500 N/mm 2   
     Modules of elasticity for strip: 206,000 N/mm 2   
     Inlet curvature: 0.0 mm/m 
     Parallel stiffness: -1,060 kN/mm 
     Newton step width: 0.5 
     
         ______________________________________Roll       Position of Roll Apex                     StiffnessNo.        (mm)           (n/mm)______________________________________1          0.00           9999992          -13.28         9999993          0.00           9999994          2.11           9999995          0.00           9999996          17.50          9999997          0.00           999999______________________________________ResultsRoll  Contact point  Inclination                          Bending MomentNo.   (mm)     (mm)      (-)     (-)______________________________________1      37.95   -1.03     -0.3186 0.00002     124.12   -15.43    -0.2116 1.48003     253.65   -4.05      0.3993 -1.47614     416.87   1.72      -0.2749 1.46905     570.07   1.23       0.2467 -1.44516     738.90   13.13     -0.0891 1.32327     892.63   4.65       0.0591 0.0000______________________________________Roll Overstretching             Straightening Force                            Spring-backNo.  (-)          (kN)           (mm)______________________________________1    0.0000       1502.8         -4.86782    5.0054       4504.4         -4.86483    -4,5464      4991.2         -4.86434    3.9924       3551.8         -4,86585    -2.8315      3143.3         -4.86626    1.3231       2266.9         -4.86717    -0.0001       685.7         -4.8686______________________________________ Total straightening force: 10,323.0 kN Outlet curvature: -0.015 mm/m Geometrically permissible EPS: 5.282 (not exceeded) 
    
     The various features of novelty which characterize the invention are pointed out with particularly in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the FIGURE and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.