Process for production of draw-ironed can

Details Process for production of draw-ironed can Process for production of draw-ironed can

1991-03-13

1993-01-19

Larson, Lowell A.

Metal deforming

By use of closed-die and coacting work-forcer

Cup or shell drawing

723794, B21D 2228

Patent

active

051798549

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION



Technical Field

The present invention relates to a process for the production of a draw-ironed can. More particularly, the present invention relates to a process for the production of a draw-ironed can, in which the final can body is improved in the surface roughness and the necking workability and flanging workability are improved.


Background Art

Draw-ironed cans (sometimes referred to as "DI cans" hereinafter) formed of a tin-deposited steel sheet (tinplate) or an aluminum sheet are used in large quantities for beer cans and carbonated drink cans. These DI cans are prepared by draw-forming a metal blank into a cup having a relatively large diameter, redrawing the cup into a cup having a small diameter and subjecting the side wall portion of the cup to ironing working 2 or 3 times. According to need, the prepared DI cans are subjected to single-stage or multiple-stage necking working of reducing the diameter of the opening and then to flanging working to obtain can bodies to which easy-open lids are wrap-seamed.
In the production of DI cans, draw-forming and redrawing are indispensable steps. At this draw-redraw forming, the metal sheet shows such a plastic flow that the dimension increases in the height direction of the cup but the dimension decreases in the circumferential direction of the cup. Accordingly, in a cup obtained by draw-redraw forming, there is observed a tendency that the thickness of the side wall portion gradually increases toward the top from the bottom and the thickness is extremely large at the top end (open end) of the side wall portion.
Accordingly, the following defects are brought about when the above-mentioned redraw-formed cup is subjected to ironing working.
At the ironing step, the thickness of the side wall portion of the can is determined by the clearance between the radius of the outer surface of the punch and the radius of the inner surface of the die, and the thickness of the side wall portion is constant from the lower portion to the upper portion. However, the thickness of the upper portion of the cup is larger than the thickness in the lower portion. Accordingly, the ironing condition is severe and the thickness reduction ratio is high. At a high ironing ratio, barrel breaking is often caused at the ironing step, and wrinkling and flange cracking are often caused in the upper portion where necking working and flanging working are performed, resulting in occurrence of insufficient sealing (leakage). Moreover, the surface of the side wall of the can becomes rough and the metallic gloss is degraded, and in order to prevent the exposure of the metal, a coating having a larger thickness becomes necessary.
Application of an organic paint to the metal blank in advance or lamination of an organic resin film on the metal blank in advance, instead of formation of a coating on the formed DI can, is desirable in view of the productivity and environmental sanitation. However, the conventional draw-ironing process is defective in that the adhesion of the organic coating is drastically reduced in the upper portion of the side wall and the metal exposure measured as the enamel rater value (ERV) becomes extraordinarily large.


DISCLOSURE OF THE INVENTION

It is therefore a primary object of the present invention to provide a draw-ironed can where the above-mentioned defects of the conventional technique are overcome.
Another object of the present invention is to provide a draw-ironed can where the surface roughness of the final can body is improved, barrel breaking is prevented at the ironing step and the necking workability and flanging workability are improved.
Still another object of the present invention is to provide a process for the preparation of a draw-ironed can, in which the thickness reduction ratio at the ironing step is controlled to a relatively uniform level throughout the side wall of the cup from the lower portion to the upper portion.
A further object of the present invention is to provide a process especially suitable for the draw-ironing working

REFERENCES:
patent: 4346580 (1982-08-01), Saunders
patent: 4425778 (1984-01-01), Franek et al.
patent: 4962659 (1990-10-01), Imazu et al.
patent: 5014536 (1991-05-01), Saunders

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