Advances in Tin Cans; Lasers Help in Welding Smooth Seam

Some manufacturers contend that the seams on tin can are unsightly and make labeling and decoration more difficult. Technological advances in the welding process are reported to make these seams less noticeable and, in turn, more attractive cans are known to be created.

In recent years, several companies are known to have begun welding cans with laser beams instead of the conventional thin copper electrode strip. Although many people in the can industry suggest it will probably be several years before laser welding is widely used in consumer products, the technique is said to become a common method of can manufacturing.

Laser welding is said to cut production costs and it uses about 45 percent less energy than the traditional method, called resistance welding.

''Laser welding is a technology that's just getting started in the United States,'' said Fred L. Church, editor of Modern Metals, published from Chicago. ''Its use here is targeted primarily for the aerosol can business because that's where the technology is considered to be best used.''

Most beverage cans, Mr. Church said, are now made with two pieces of metal. In these cans, there is no side seam because the cylinder and the base are formed from just one piece of aluminum. But aluminum is considered to be too weak for some food and pressurized products, so such cans are usually made from three metal pieces: a top, a base and a rectangular sheet of tin-plated steel, which must be welded to form a cylinder. In resistance welding, the thin area of overlap on the curved sheet is fused by intense heat conducted through a copper electrode.

A 1,325-watt carbon-dioxide laser, by contrast, melts the steel at the edges of the sheet, fusing the edges and forming an almost seamless cylinder. After the welding, the can passes through a set of rollers that smooth the welded area, preparing it for the subsequent labeling or paint spraying.

The process is controlled by a computer that shuts off the laser if the beam strays from the thin welding area. The biggest driving factor behind the development of laser welding is supposed to be the fact that it makes the cans more esthetically attractive. In the conventional method of welding cans with copper electrodes, there is a seam that's an eighth of an inch or so. With laser welding, that seam is down to almost nothing. Laser-welded cans are likely to appeal to can customers because they are better to place labels on.

The New York Times

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