Metal deforming – By use of non-deforming work-gripping clamp and relatively... – By individually non-deforming clamps
Reexamination Certificate
1999-07-23
2001-04-17
Crane, Daniel C. (Department: 3725)
Metal deforming
By use of non-deforming work-gripping clamp and relatively...
By individually non-deforming clamps
Reexamination Certificate
active
06216521
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for improving the planeness of metal sheets by stretching, and particularly high strength aluminum alloy sheets.
DESCRIPTION OF RELATED ART
Industrial manufacturing of metal sheets usually results in planeness defects despite all precautions taken, which cause expensive internal scrap in order to respect standards and specifications in force in this field. For example, these defects may consist of a general deformation of the sheet, called “camber” when this deformation is a longitudinal curvature about an axis perpendicular to the rolling direction, and “transverse bow” when it is a curvature about an axis parallel to the rolling direction, using the terms in European standard EN 485-3. Deformation may also be local, either in a particular area of the sheet, or concentrated at one or several vertices, which for example may be measured. It may concern “wavy edges” when one edge of the sheet is longer than the central part, or corrugations originating from rolling. Standards known to the expert in the field specify planeness tolerances as a function of the thickness, particularly by defining a total maximum deflection over the length or width or over a chord with a minimum length. For example, this is the case in European standard EN 485-3 (October 1993 edition) for hot rolled aluminum alloy sheets, and standard EN 485-4 (October 1993 edition) for cold rolled aluminum alloy sheets.
The operation to improve planeness consists of stretching the sheet or the strip, causing plastic deformation of the metal that elongates the shortest fibers. There are two frequently used techniques for correcting these defects: leveling by rolls, and stretching. Leveling by rolls consists of passing the sheet between two series of parallel rolls placed alternately below and above the sheet, the rolls being nested. The strip or sheet is then alternately deflected in one direction and then in the other to obtain plastic deformation. Roll leveling machines cannot completely correct planeness defects unless these defects are not too severe; in the case of thick sheets with high mechanical properties, the leveling effect that can be obtained in this way is often insufficient, or even non-existent, particularly after quenching. This is why there are hardly any machines that can accept sheets more than 25 or 30 mm thick.
There are several variant roll leveling machines in which the sheet remains fixed and the rolls, mounted on a mobile cage, move together with respect to the sheet. Thus, U.S. Pat. No. 3,552,175 defines a technique for leveling metal strips using at least three rolls placed alternately above and below the strip, which ensures that the strip which is fixed at both ends and is tensioned, is deflected at all locations at least once alternately in one direction and then in the other, each deflection leading to permanent elongation. In this technique, permanent elongation is the result of deflection obtained by the effect of the rolls, and not by stretching applied to the ends of the strip. Examples deal with very thin strips (between 0.08 and 0.13 mm), and it is doubtful that this technique could be applied to rolled aluminum alloy products with a significantly greater thickness.
Patent GB 1 179 089 describes a machine that is a combination between a stretcher and a low power rolling mill. After tensioning the steel strip to its yield strength, the rolling mill is made to pass from one end of the strip to the other. This technique does not lead to a significant permanent elongation.
Tension consists of stretching the plate, the ends of which are trapped between two jaws, to apply a permanent controlled elongation of a few percent to it. This technique is used particularly for thick sheets. The stretching machine comprises a fixed head with jaws and a mobile head comprising the other jaws. The efficiency of this technique is not satisfactory in some cases, and particularly in the case of quenched sheets. For example, for heat treated aluminum alloy sheets, in other words alloys in the 2000, 6000 and 7000 series using the designation of the Aluminum Association, it is well known that the quenching operation induces significant deformations and therefore a strong transverse bow effect, in addition to dispersed and random planeness defects; this does not disappear easily during stretching.
Patent GB 2 066 120 describes a technique for leveling metal sheets that consists of a combination between leveling by rolls and stretching. A relative movement between the sheet fixed between two jaws at the ends, and a set of parallel leveling rolls placed alternately below and above the sheet, subjects the plate to the leveling effect by rolls and by applied stretching, each of which results in a permanent deformation beyond the yield strength of the material, in a different manner. Nevertheless, this device is more like a tensioned leveling machine using nested leveling rolls, than stretching by tension. The permanent deformation of the sheet obtained using this technique is very low, of the order of 0.1 to 0.2% per leveling pass since it is obtained mainly by the bending effect on nested leveling rolls, since the contribution of stretching is low. The sheet or strip is fixed at each end in jaws rigidly attached to a fixed head, the set of leveling rolls being displaced with respect to the fixed heads, or at one of its ends in jaws fixed to a mobile head that moves with respect to the group of leveling rolls.
In many cases, the improvement in planeness is not the only objective of applying stretching to the sheet. Permanent cold deformation of a sheet or strip improves some mechanical properties, particularly the yield strength, and relaxes internal stresses caused by quenching, which is particularly important for thick sheets intended to be machined. In this case, the deformation must be carried out in a very controlled manner in order to obtain a product with reproducible characteristics, which is easier with a stretcher than with a roll leveling machine, at least in the case of medium and thick sheets.
Therefore, there are three major disadvantages with the technique described in Patent GB 2 066 120; since the stretching force is simply equal to the resistance to be overcome to pull the sheet through a set of leveling rolls, the contribution of stretching to the total deformation is difficult to control and remains too low to significantly improve some mechanical properties of the sheet, and it cannot sufficiently eliminate some planeness defects and internal stresses induced by quenching sheets.
Furthermore, some standards require that controlled stretching is applied to the sheet; for example, standard EN 2126 specifies controlled stretching between 1.5% and 3% for the manufacture of 7075 alloy sheets (using the designation of the Aluminum Association) in T651 temper (as defined in EN 515) with a thickness of between 6 and 80 mm. This process requirement cannot be satisfied using a roll leveling machine or the device described in Patent GB 2 066 120.
SUMMARY OF THE INVENTION
Thus, the purpose of the invention is to improve the planeness of metal sheets, and particularly quenched metal sheets, and particularly to eliminate transverse bow effects and local deformations along the longitudinal or transverse direction due to quenching.
Its purpose is a process for improving the planeness of metal sheets consisting of stretching the metal by tension between two jaws until a permanent controlled elongation of more than 0.5% is achieved, and preferably more than 1% and even better more than 1.5%, and maintaining a transverse pressure on at least one of the faces of the sheet, at least during part of the time that this stretching is applied.
The invention also relates to different methods of applying this transverse pressure:
rolls transversely applied with pressure on at least one of the faces of the sheet, and subject to an application force onto the sheet,
“anti-bow” bars consisting of a metal bar transversely applied with pressure on one of the face
Garbil Michel
Heymes Fabrice
Hochenedel Vincent
Crane Daniel C.
Dennison, Scheiner Schultz & Wakeman
Pechiney Rhenalu
LandOfFree
Process for improving the planeness of a metal sheet does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for improving the planeness of a metal sheet, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for improving the planeness of a metal sheet will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2456655