Before the development of molded synthetic resins, electrical plugs and sockets were usually made of porcelain or molded of marble dust and shellac. In this use substitution has been almost complete. Wall plates for electric switches and outlets were usually of brass. Today molded tar-acid or molded urea resins are substituted in part. In neither of these examples has the substituted material any important effect upon the use of the product.
An example of a substitute material widening the usefulness of the product is afforded by a new computing scale, where a molded urea resin casing (substituted for metal in the older model) has aided in decreasing the weight and has improved the appearance. Another example is the use of laminated synthetic resin coil forms in radio frequency transformers which, because of their better electrical properties at high frequencies, have aided in the design of more compact units.
Examples of synthetic resins making possible a wholly new product are more difficult to find, but the following will serve as illustrations: Cast acrylate sheets to form curved cockpit enclosures for airplanes; molded acrylate buttons for reflecting road markers; and new special coatings, which make possible the use of metal cans for preserving foods and beverages hitherto impossible to can without loss of flavor.
Motives for substitution.
One of the most important reasons why a manufacturer may decide to substitute a synthetic resin for another material is the resulting economy in the sense of economy in total costs. As a rule, the synthetic resin will be more expensive pound for pound than the material for which it is substituted; but frequently the manufacturing cost is enough lower to more than make good the difference in material cost, because the resin part will come from the mold almost in finished form, whereas the part made of wood or metal will require considerable fabrication. In some cases there may be a saving in marketing costs. For example, the shades for large office fixture lights are now made of synthetic resin as well as of opal glass. The resin shades are less expensive to ship because they are lighter and require less expensive packing.
Another incentive toward substitution is to give novelty, and hence sales appeal, to an old product. In many cases the use of synthetic resins fits in with the present tendency to redesign an old-style product so that it will be more compact, have more pleasing lines, and more color.
Still another incentive toward substitution is to give the product greater usefulness, or lower costs in use. The great expansion in the use of synthetic resins in surface coatings has come about because, with these materials, coatings can be developed to fit special purposes, and dry rapidly, which means an important saving to those who use them.
Materials displaced by synthetic resins.
The wide range of uses to which synthetic resins are now applied implies that the materials displaced are numerous. For example, cast or wrought iron or steel is displaced in timing gears and in many small machine parts, such as cradle-type telephones; nonferrous metals in small machine parts and novelties, such as inexpensive bracelets; glass in lamp shades and in cosmetic containers; natural resins in lacquers; plastics, such as cellulose acetate in safety glass or cellulose nitrate in colored lacquers; other adhesives in bonding plywood; and cork or metal in bottle closures.