My present invention relates to a method of continuously stretch leveling metal strip, especially strip with a thickness of 0.05 mm to 1.5 mm. The invention also relates to an apparatus which utilizes that method and to a method of operating the apparatus.
The invention especially relates to the continuous stretch leveling of metal strip of a thickness o 0.05 mm to 1.5 mm in which the strip passes from a braking-roll set, usually a four-roll bridle to a tensioning roll set, likewise usually a four-roll bridle, and is subjected between the two roll sets to a stretching in the plastic deformation range of the strip (hereinafter also referred to as the plastic range) to effect a straightening or leveling, i.e. an improvement in the planarity of the strip. A leveling in the plastic range can also be referred to as an elastic-plastic leveling since, in exceeding the elastic limit of the strip material as is required at the transition from the elastic range to the plastic range, there is some remaining residual elasticity in the strip material.
It is known to level this metal strip by a tension leveling process or in a tension leveling apparatus which has a brake roll set and a tension roll set. Both roll sets have as a rule two or more rolls which are looped by the strip.
For stretch leveling, a strip can be passed in such manner about two or more rolls which are operated with stepped torques or peripheral speeds so that between two rolls a stretching tension can be applied. Between the brake rolls sets and the tension roll sets, therefore, there can be a region in which the strip is subjected to tension, is stretched and is leveled.
In stretch leveling, there is a plastic elongation of the strip and a reduction of the strip thickness and strip widths. In prior systems, longitudinal stresses were produced and as a result of them, transverse stresses were created in the strip. As a consequence, greater longitudinal deformation could occur in the middle of the strip than would be present outwardly of the middle of the strip, resulting in residual stresses which were not uniform across the width of the strip.
To minimize the deformation which arose through stretch leveling and thus the central dishing of the strip and the nonuniform distribution of residual stresses therein, it has been proposed to provide between the braking roll set and the tensioning roll set a tension leveling roll path creating a stretching tension in the strip in the plastic range (see DE 39 122 676 C2).
It is the principal object of the present invention to provide a method of continuous stretch leveling of metal strip in which improved and even optimal planarity results can be achieved.
Another object of the invention is to provide a method of continuously stretch leveling metal strip of a thickness of 0.05 mm to 1.5 mm whereby problems which have been encountered with strip of such thicknesses heretofore are no longer a difficulty.
Still another object of this invention is to provide a method of stretch metal leveling strip which yields a product having fewer stresses or uncompensated stresses and which generally can be considered an improved product by comparison with prior art strip.
A further object of this invention is to provide an improved apparatus for stretch leveling metal strip.
Yet another object is to provide an improved method of operating an apparatus for stretch leveling a metal strip.
These objects are attained in a method of continuously stretch leveling metal strip which comprises the steps of:
The method can be practiced with an apparatus which comprises:
The method of operating the stretch leveling apparatus can comprise the steps of:
More particularly, according to the invention, between the two-roll sets and, preferably, a braking and tension roll set each of which comprises a four-roll set, each of which comprises a four-roll bridle, there are provided three or more stretching zones and in each of these stretching zones, there is a plastic deformation (elastic-plastic stretching) and/or a stretching in the elastic range. The third zone and, where provided, additional stretching zones quite surprisingly have been shown to give rise to a homogenization of the longitudinal stress distribution and the resulting length and width changes in the strip. The result is an optimum leveling or straightening and a significantly improved planarity of the strip.
According to the invention, the strip can be stretched in all of the three or more stretching zones in the plastic range. Preferably in accordance with the invention, however, when there are three such stretching zones, the strip is stretched in the inlet and outlet stretching zones in the plastic range and in the intermediate stretching zones between the inlet and outlet zones, i.e. in a middle zone, with a strip tension which lies only in the elastic range. The result is a rounding in the yield curve in the tension-yield diagram upon exceeding the elastic limit between the elastic and plastic region, apparently because the strip in the middle stretching zone represents a relief from the prior plastic deformation and itself has stresses which are eliminated in the subsequent plastic deformation. To optimize this effect, the strip tension in the central zone is ≦80% (less than or equal to 80%), preferably ≦50% of the elastic limit of the strip material. The strip should have a residence time in the central stretching zone ≦1 second (at least one second).
If, in accordance with the invention, there are more than three stretching zones between the tension and braking bridles, for example five stretching zones, the central stretching zones will be operated in the elastic range while the first two and last two stretching zones will be operated in the plastic range. In this case, whether the system has three, five or more stretching zones, the inlet and outlet stretching zones will operate in the plastic range while the central stretching zone can always be operated in the elastic range. The result is a system which has a particularly compact construction. Of course it is possible to coil the strip after it has traversed the inlet-side stretching zone or zones and to store the coil before the strip is uncoiled and subjected to the second, third or additional stretching operations. The intervening coiling has been found, surprisingly, to eliminate creep effects when the strip is subsequently coiled.
According to the invention, moreover, where the stretching zones are defined between rolls which are looped by the strip, each pair of such rolls can have at least the tension side roll of the respective pair formed as a concave/convex stretching roll with a variable geometry. With such tension rolls, the roll periphery can be adjustable between a convex or crown configuration and a concave configuration to enable dishing at the center of the strip and corrugations or waviness at the edges to be reduced or completely eliminated (see DE 42 30 243 C1).
To the extent that the apparatus must be matched to different strip widths, the strip can be subjected to the effect of one or more linear motors in specific stretching zones. The use of linear motors in inductive stretching of the middle strip is especially effective for nonferromagnetic materials, for example, bundmetal (zinc, copper, aluminum alloys) and enables a highly sensitive and precise adjustment of the stress distribution (see especially DE 197 19 994 A1).
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
In
In its basic construction the apparatus comprises a four-roll braking roll set or bridle 2 and a four-roll bridle forming a tension roll set 3. The tension roll set operates with a peripheral speed of its rollers which is greater than that of the braking roll set 2 and there is a stretch between the two-roll sets in which stretching of the strip is effected.
More particularly, there are in this stretch two stretching roll pairs or two-roll bridles 4, 5 and 6, 7 which define an inlet side stretching zone I between the two rolls 4, 5, an outlet side stretching zone III between rolls 6 and 7 and a central or intermediate leveling zone II between the two roll pairs 4, 5 and 6, 7. The roll 5 operates with a torque and a peripheral speed greater than the torque and peripheral speed of the roll 4. Roll 6 operates with a torque greater than that of roll 5 and roll 7 operates with a peripheral speed and torque greater than those of roll 6. At least the rolls 4 and 6, i.e. the upstream roll of the pairs 4, 5 and 6, 7 can be a concave/convex adjustable contour roll. In addition, the strip 1 in the individual stretching zones I, II, III can be acted upon by one or more linear motors as described in DE 197 19 994 A1.
In the travel of the strip 1 between the braking roll set 2 and the tension roll set 3, therefore, the strip traverses the leveling zones I, II and III in which the strip is leveled by tension in the plastic range and/or the elastic range. Preferably in the inlet leveling zone I and the outlet leveling zone III, the stretch leveling is effected in the plastic range and in the intermediate zone II only with a strip tension in the elastic range. The result is a rounding 8 of the yield curve 9 (
In
Finally in
Number | Date | Country | Kind |
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10323811.5 | May 2003 | DE | national |