Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
1999-08-18
2001-08-07
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S265000, C148S275000, C148S696000, C148S703000
Reexamination Certificate
active
06270589
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a material used for a two piece can which is manufactured by a forming process including a drawing and ironing process. More specifically, it relates to a method of manufacturing a resin coated aluminum alloy sheet for a drawn and ironed can, wherein the resin coated aluminum alloy sheet is produced by coating a thermoplastic resin onto an aluminum alloy sheet, the resultant coated sheet being suitable for forming into a two-piece can, the wall of which is thinned by a forming process including a drawing and ironing process, and wherein the two-piece can is manufactured without cooling by water or lubricating by water-type lubricant, or cleaning the finished can.
PRIOR ART
As a two-piece can which is integrally formed with a can body portion and a bottom portion, a DI can (Drawn and Ironed Can) has so far been produced by drawing and ironing a tin plate or an aluminum alloy plate into a can. After the tin plate or the aluminum alloy plate is drawn into such DI can, it is cooled by a large quantity of water or lubricated by a water-type lubricant using several ironing dies continuously disposed, and punches until it is so thinned as to have a wall thickness of one third of the original wall thickness. Thereafter, the DI can is degreased and washed, dried and coated. Lately, Japanese Laid-open Publication No. Hei-6-312223 has disclosed a method for producing a two-piece can from a resin-coated metal sheet using a composite forming method including drawing and ironing process. This method differs from the conventional DI can producing method in that a resin-coated metal sheet to which a high temperature volatile lubricant is applied is drawn, and then redrawn and ironed at the same time (i.e., the composite forming method) under dry conditions without the use of water or water-type lubricant until the thickness of the two-piece can is sufficiently decreased. This composite forming method dispenses with the processes of degreasing, washing, drying, and coating the formed two-piece can, which makes it possible to produce two-piece cans without contaminating the environment. The present invention has been investigated to provide a resin-coated aluminum alloy sheet suitable for this composite forming method. As for the material suitable for the composite forming method, Japanese Laid-open Publication No. Hei-7-266496 discloses a material which is restricted with regard to yield strength, tensile strength, thickness, arithmetical mean deviation of profile, or the like, and also discloses the use of an aluminum alloy of JIS 3004 H19 as an example. The present invention has an object to provide a resin-coated aluminum alloy sheet suitable for the composite forming method as disclosed in Japanese Laid-open Publication No. Hei-6-312223. The composite forming method which is a target of the present invention comprises simultaneous operations of a redrawing process and an ironing process using a die in which a portion for redrawing and a portion for ironing are coupled in pairs. One of the characteristics of the composite forming method is that the shoulder radius of the die portion for redrawing is made smaller and this shoulder rounded portion works to bend and bend back a can piece so as to make thinner the wall thickness of the can piece. In this composite forming method, since the work piece is intensely bent and bent back with a very small shoulder radius that is only two or a few times the thickness of the work piece, the work piece often suffers surface coarseness or cracks, and under some circumstances it even suffers surface breaking due to the shoulder rounded portion. Even in cases where the can piece is safely formed without being broken at the shoulder rounded portion, the surface coarseness and cracks result in deterioration of the adhesion of the aluminum alloy sheet to the resin coating, which causes the can wall to easily suffer breaking in the next ironing operation. Therefore, the object of the present invention is to provide a resin-coated aluminum alloy sheet suitable for making a drawn and ironed can which is free from its wall breaking and has sufficient strength as a can, when the can is formed through a composite forming process including a bending and bending back operation at a die shoulder rounded portion of a small radius and a subsequent ironing operation, under dry conditions. The aluminum alloy of JIS 3004 H19 disclosed in Japanese Laid-open Publication No. Hei-7-266496 has enough strength, but it lacks substantial formability to achieve the aim of the present invention.
DISCLOSURE OF THE INVENTION
The present invention comprises a method of manufacturing a resin-coated aluminum alloy sheet for use in making a drawn and ironed can. The sheet-forming method comprises the steps of homogenization heat treating an aluminum alloy ingot containing essentially 0.5 to 2.0 wt % of Mn, 0.2 to 2.0 wt % of Mg, 0.05 to 0.4 wt % of Si and not more than 0.7 wt % of Fe as inevitable impurities, wherein (Si +Fe)<0.9 wt %, subjecting the resultant product to hot rolling by a normal manner to obtain a hot-rolled aluminum alloy sheet, subsequently subjecting the hot-rolled sheet to cold rolling, continuous annealing, another cold rolling at a reduction ratio of 30 to 50%, and a surface treatment, heating the thus surface treated aluminum alloy sheet at a temperature of 240 to 350° C. for a time within one minute, retaining the aluminum alloy sheet at a temperature of 220 to 300° C., and then coating both surfaces of the sheet with a thermoplastic resin, and immediately quenching the resultant product.
The present invention further comprises a method of manufacturing a resin-coated aluminum alloy sheet for a drawn and ironed can, which comprises the steps of homogenization heat treating an aluminum alloy ingot containing essentially 0.5 to 2.0 wt % of Mn, 0.2 to 2.0 wt % of Mg, 0.05 to 0.4 wt % of Si and not more than 0.7 wt % of Fe as inevitable impurities, wherein (Si+Fe)≦0.9 wt %, subjecting the resultant product to hot rolling by a normal manner to obtain a hot-rolled aluminum alloy sheet, subsequently subjecting the hot-rolled sheet to cold rolling, continuous annealing, another cold rolling at a reduction ratio of 50 to 80%, and surface treatment, heating the thus surface treated aluminum alloy sheet at a temperature of 240 to 350 0° C. for a time within one minute, retaining the aluminum alloy sheet at a temperature of 220 to 300° C., and then coating both surfaces of the sheet with a thermoplastic resin, and immediately quenching the resultant product.
Furthermore, the present invention is characterized in that the thermoplastic resin coated onto the aluminum alloy sheet is a thermoplastic polyester resin and the surface treatment applied onto the aluminum alloy sheet is etching and/or electrolytic chromic acid treatment and/or phosphoric acid chromating.
THE BEST MODE FOR CARRYING OUT THE INVENTION
A diversity of investigation has been made to obtain a resin-coated aluminum alloy sheet excellent in strength, formability, and adhesion, and also excellent in formable endurance in the drawing and ironing operations under dry conditions. Consequently, a method of manufacturing such a desired resin-coated aluminum alloy sheet has been developed by determining the composition of an aluminum alloy, kind of thermoplastic resin coating, type of surface treatment therefor, and so on. The present invention is explained in detail below referring to examples.
First, the reason for restricting the alloy composition of an aluminum alloy sheet used as a substrate of the resin-coated aluminum alloy sheet of the present invention is described. Each content of the alloy elements is hereinafter expressed by weight %.
[Mn]
Manganese is added to economically obtain strength of the aluminum alloy sheet. An amount less than 0.5% Mn does not have an effect. On the other hand, a Mn content exceeding 2.0% causes an Al—Fe—Mn system crystallized matter to be increased in the aluminum alloy s
Komai Masao
Kunishige Fumio
Shimizu Keiichi
Tanabe Jun-ichi
Taniguchi Ayumu
Browdy and Neimark
Oltmans Andrew L.
Sheehan John
Toyo Kohan Co. Ltd.
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