Guide to Working with Plastics -- A Choice of Good Connection: Hems or Seams in Flexible Film

The edges of plastic film and flexible plastic sheets can be heat-welded to form a variety of hems and seams that are useful for making such household items as shower curtains, garment bags and fit ted seat covers. An ordinary household iron is surprisingly handy for these fabrications, efficiently fusing such diverse plastics as polyethylene, polystyrene and polyvinyl chloride. But for very fine seams, such as those that seal the edges of plastic-wrapped prints and posters, you may need to rent special sealing tools—bar sealers and heat wands—from a plastics supplier or a hobby shop.

Insulate the work surface from an iron’s moderate heat with a sheet of heavy cardboard. To keep the plastic from sticking to the iron or the card board, sandwich it between two sheets of nonstick material such as cellophane or silicone-coated paper—most familiar as the peel-off paper on adhesive-backed plastics. If the iron has a nonstick coating, only the bottom layer of nonstick protective covering will be needed. Generally the iron should be set in the synthetics range and applied to the plastic for just a few seconds, but exact fusion times and temperatures depend on the composition and thickness of the plastic.

Experiment with scraps before attempting an actual project.

To guide the iron along a straight seam, butt it against a wooden straightedge; for a curved seam, cut a template from wood or heavy cardboard. No guide is necessary for seams made with heat wands or bar sealers, which will form straight seams automatically.

The precision of seams made with wands and bar sealers suits them welt to a technique called shrink wrapping, which uses a special plastic. As the term implies, this material can be wrapped around an object, sealed at the edges, and then shrunk—usually with a heat gun—to conform exactly to the shape of the enclosed object. Shrinkable plastic can also be seated with an iron, but the seams will be wider and less attractive.

Another sort of shrinkable plastic comes in tubular form and is most commonly used as a sleeve to gather wires into neat bundles. When heated, this tubular plastic shrinks to half its diameter without losing length. It’s available in diameters that shrink to .023 to 1 inch—in any length—and can be shrunk with a hot-air gun, an industrial hot-air blower or even with the heat of a cigarette lighter, because the material is nonflammable.

A Choice of Three Hems and Two Seams

===A range of seams and hems. Both the lap seam and the looped hem are made at the edge of the worktable, with the excess plastic over hanging the edge; the hidden seam and the other two hems are made at the center of the worktable, with the work supported on both sides. The lap seam joins two pieces of plastic film by simply overlapping and fusing their ends. The looped hem is folded back on itself and fused in a way that leaves an unsealed channel; a wire or a cord can be threaded through the channel. The hidden seam is formed by laying two sheets of plastic face to face and sealing their edges; when the sheets are opened out, the seam is on the underside of the work. The simple hem consists of a single fold, sealed on the underside of the work; for the reinforced hem, the fold is doubled.

64

===Forming a lap seam or a looped hem. Cover the work surface all the way to its edge With a nonstick protective covering. For a lap seam, overlap the two pieces of plastic about ¾ inch and position one edge of the seam along the edge of the work surface. Weight the seam along its center line with a straightedge. (If your iron lacks a nonstick base, place a layer of nonstick covering between the straightedge and the plastic.) Beginning at one end of the seam, lower the iron against the plastic, using the straight edge as a guide, and press down. Lift the iron, move it along the edge and press again. Continue until the seam is fused along its entire length. Then remove the straightedge and seal the other half of the seam.

For a looped hem, fold the plastic back on itself and line up the cut edge of the plastic with the edge of the worktable. Place the straightedge over the hem, covering enough of the fold line to provide a channel of sufficient width for the reinforcing cord. Fuse the area between the straightedge and the edge of the table.

===Fusing a hem or a hidden seam. For the seam, spread a sheet of nonstick protective covering over the work surface and lay the two sheets of plastic face to face over it, with their edges aligned. If, unlike the iron shown here, your iron does not have a coated soleplate, top the plastic with a second layer of protective covering. Place a straightedge over the layered materials, about ¾ inch in from, and parallel to, the edges of the plastic. Press down on the seam with the iron, as described above, using the straightedge as a guide. When the plastic sheets have cooled, spread them open, turning the seam to the back (inset).

For a simple hem, fold the plastic back on itself once; for a reinforced hem, fold it twice. Sandwich the plastic between two layers of protective covering and place a straightedge along the hem, covering about half its width.

Using the straightedge as a guide for the iron, press down on the hem as for the seam above. Then remove the straightedge and press down the free edge of the hem in the same way.

65

Shrink-wrapping with Heat Wand and Blower

1. Shrouding the object with film. Set up the heat-wand assembly, including the roll of plastic film, the heat wand and its heatproof pad, and the hot-air blower used in shrinking the film. Turn on the switch at the control box to ready the wand; it won’t actually heat, however, until you push the finger switch on the handle of the wand itself. Unroll enough film to cover the object being wrapped, and slip the object between the two layers of film. Slide the object toward you until it touches the seam at the end of the film.

2. Cutting and sealing the film. Set the heat wand on the plastic about 1 inch in from the edge of the object, pressing the film against the heatproof pad. Depress the switch on the handle of the wand, activating the heating element. Gently tug at one end of the plastic film until it separates along the wand, generally after a second or two. Turn the plastic-covered object and seal the remaining sides, about ½ inch beyond its edges. Nick this airtight plastic envelope with a razor blade in some inconspicuous spot to let air escape when the film shrinks.

66

3. Shrinking the film. Rest the plastic-wrapped object on a protective sheet of cardboard and direct a stream of warm air against it with the hot-air blower, moving the blower in a circle and holding it about 3 inches above the surface of the plastic. When the plastic on this side begins to bubble and wrinkle, turn the work over; heat the other side until it bubbles, then pulls taut and smooth. Repeat to smooth the first side.

Shrink Tubing Used to Bundle Wires Together

===Gathering wires into a bundle. Estimate the diameter of the bundled wires and choose shrink tubing manufactured to shrink to that diameter or slightly smaller. Cut tubing to the desired length; it can cover the entire length of the wires or grasp them only at intervals. Slide the tubing over the wires. Sweep a hot-air blower back and forth over the tubing until it grips the bundle tightly. A similar heat-shrinkable tubing, thick enough to protect bare wires in low voltage wiring splices, is available at electronics supply stores; ft must be heated with the open flame of a match or candle and thus should not be used to gather already-insulated wires, whose sheathings could be ignited.