Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Patent
1986-07-02
1988-09-06
Combs, E. Michael
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
72128, 72160, B21D 3716, B21D 102, B21D 302
Patent
active
047683635
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of levelling a two-layered clad metal sheet.
BACKGROUND ART
Two-layered clad metal sheets are known which have a base layer of a carbon steel clad with a covering layer of, for example, stainless steel, cupro nickel, etc.. The production of such a two-layered clad metal sheet encounters the following problem. Two layers of different metals have different amounts of thermal contraction when the clad sheet is cooled after levelling by a hot leveller. Therefore the clad metal sheet after cooled down to the room temperature exhibits a camber in such a manner that the metal layer of the greater thermal expansion coefficient is disposed on the radially inner side of the clad metal sheet.
More specifically, in ordinary process for rolling thick metal sheets, the hot sheet after the rolling is levelled by a leveller in order to remove any shape defect in the sheet, e.g., center buckle, edge wave, breadthwise camber and lengthwise camber. The hot-levelled sheet is then cooled on a cooling table. Any shape defect which is generated during the cooling is also levelled by a leveller after the cooling, whereby a flat sheet is obtained.
In the case of a two-layered clad steel sheet composed of a base sheet 1A and a covering layer 1B which have different values of thermal expasion coefficient, a breadthwise camber, which is much greater than that experienced by ordinary steel sheet, is caused during the cooling after the hot levelling, as shown in FIG. 22. In case of the two-layered clad sheet, a difference in the value of the thermal expansion coefficient exists between the base layer which is, for example, a carbon steel and a covering layer which is, for example, a stainless steel, as will be seen from FIG. 23. In consequence, two layers of the clad sheet exhibit different amounts of thermal contraction during the cooling down to the room temperature after the hot levelling, resulting in a large breadthwise camber. The amount y of the camber is maximized when the clad sheet has been cooled down to the room temperature. In the case of a two-layered clad sheet composed of a base layer of a carbon steel and a covering layer of a stainless steel, the camber amount y reaches 300 to 400 mm, although this amount y varies depending on the conditions such as the levelling temperature, sheet thickness, sheet width and the clad ratio, i.e., the ratio of the thickness of the covering layer to the total thickness of the clad sheet.
This heavy camber after the hot levelling causes the following inconveniences.
(a) It is difficult to convey the sheet by table rollers, when the sheet has a heavy camber.
(b) The sheet has to experience an impractically large number of passes during a subsequent cold levelling.
(c) If the camber is extremely heavy, it is practically impossible to level the sheet by an ordinary cold leveller.
The present inventors have already proposed, in Japanese Patent Unexamined Patent No. 42122/1984, a method for levelling a two-layered clad sheet, which has been successfully carried out.
According to this proposed method, the layer having the greater thermal expansion coefficient is forcibly cooled before or during the hot levelling so as to create a temperature difference between two layers, and the sheet is levelled in this state, so that the clad sheet shows only a small camber when cooled to the room temperature.
More specifically, referring to FIG. 23, the covering layer exhibits a greater amount of thermal contraction than that of the base layer. Thus, the base layer exhibits a thermal contraction .DELTA..epsilon.c when cooled down from a temperature Tc to the room temperature, whereas the covering layer exhibits the same thermal contraction .DELTA..epsilon.s when cooled to the room temperature from a temperature Ts which is below the temperature Tc. Thus, if the covering layer is cooled down forcibly to the temperature Ts while the base layer is maintained at the temperature Tc and the sheet is levelled in this state, both layers exhibit the same
REFERENCES:
patent: 3347076 (1967-10-01), Noda et al.
patent: 3613418 (1971-10-01), Nara et al.
Abe Hideo
Nagamine Tsuneo
Sasaki Toru
Takashima Norio
Watanabe Hideki
Combs E. Michael
Kawasaki Steel Corporation
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