Ordinarily the molds used are made of hardened steel, highly polished. They must stand working pressures of several thousand pounds per square inch. The mold is placed in a hydraulic press, heated by steam, electricity, or gas, and the molding material is placed in the mold. The press is closed and heat and pressure are applied. The temperatures used range between 250° F. and 365° F., and the pressures between 1,000 and 8,000 pounds per square inch. The molding time depends on the shape and size of the article and on the composition of the molding material. As little as one-half minute is required for small objects and as long as 10 minutes for large objects. Average molding time is about 3 minutes. The article is removed from the mold, allowed to cool, and is then trimmed, sanded, filed, or polished. Since the mold is highly polished, the finishing operation is usually needed only to remove the flash. Inserts, such as metal parts (binding posts, electrical contacts, etc.), or inlays of polished metal in name plates, and signs, are often molded in; gear shift knobs are molded over a hollow metal core; rubber inserts are used in castors, electrical plugs, and similar objects. The molding operation is an art, and has made remarkable progress in recent years. Many articles molded of tar-acid resins are well-known to the public. The automotive industry is the best customer, using such molded parts as gear shift knobs, horn buttons, accelerator pedals, light switches, ignition parts, and distributor heads. Other well-known applications are builders’ hardware, electrical switch plates, switches and fixtures, fountain pens, radio parts, telephone parts, handles for stoves, vacuum cleaners, and other appliances, buttons, buckles, costume jewelry, camera cases, radio cabinets, small containers, and hundreds of others. The importance of tar-acid resins in molded articles is shown by the fact that more than 75 percent of all synthetic resin molded articles made in 1937 used this type of resin as a binder. Production of tar-acid molding resins. Domestic production of tar-acid molding powders and pellets was reported to the Tariff Commission by 15 makers in 1937. Most of these firms have specialized in resin development and manufacture. Among the well-known brands are Bakelite, Durez, Durite, Resinox, Indur, and others (see p. 153 for list of trade names). Statistics of production and sales of tar-acid resins used in molding were collected separately for the first time in 1935. They show a net resin output of about 21,000,000 pounds, with sales of 18,000,000 pounds or about 40 percent of the total tar-acid resins. The average unit value was 17 cents per pound. In 1937 the production of tar-acid resins for molding exceeded 32,000,000 pounds, again about 40 percent of the total. These statistics are based on net resin and do not include fillers, modifiers, pigments, or inert material of any kind. CAST PHENOLIC RESINS Process of manufacture.