模具设计与制造专业英语 黄义俊_ 电子教案统一模板(模具)Unit3.pptVIP

Unit 3 The Plastic Mold Design Unit 3 The Plastic Mold Design 3.1 Lesson 6 Plastics and Classification of Plastics Plastic means pliable or impressionable. It is defined as the capability of being deformed continuously in any direction without breaking apart.[1] Following this definition，plastics could include glass, metals, and wax．Thus, it is evident that name plastics is misleading and not exactly correct．Today, however, the name plastics is identified with the products which are derived from synthetic resins. The synthetic resins are made by various chemical processes．Plastics manufacturing is of comparatively recent date. Today plastics are commonly found in homes, automobiles, numerous other products and machines. Some machines which utilize electricity require plastic parts with electrical insulating properties. Plastics are usually shipped to manufacturing plants as pellets or powders, and they are melted (for thermoplastics ) just before the shaping process. Plastics are also available as sheet, plate, rod, and tubing, which may be formed into a variety of products.[2] Liquid plastics are used especially in the making of reinforced plastic parts. Plastics or polymers, commonly called plastics, fall into two broad classes: ? Thermoplastic molding materials—These include polymers such as ABS and polycarbonate used for toys, consumer electronic products, and more flexible kitchenware products.[3] The key feature is that these plastics can be heated to a viscous fluid, molded, and cooled in a reversible, time-and time-again manner. Because the thermoplastic materials are those which soften with heating and solidify and harden with cooling, they can be remelted and cooled time after time without undergoing any appreciable chemical change. ? Thermosetting molding materials — These include the melamine-formaldehyde used in hard plastic tableware and the epoxy resins used for glues and r