Plastics fall into two major groups, thermoplastics and thermosets. Thermoplastics are those plastics that are solid at room temperature, but when heated, they soften and can be reformed. These materials can be reused and recycled easily. Thermosets are those plastics that soften during original processing, but once finished, they cannot easily be reprocessed. Crude oil and natural gas supply the chemicals required for the production of plastics. When crude oil is "cracked" by fractional distillation, some fractions, such as octane, kerosene and oils are immediately useful. The companies producing plastics take the very small molecules, such as methane and ethane, and chemically combine them to make the large macromolecules of plastics .
A composite material is created by the combination of two or more materials: a reinforcing element and a compatible resin binder (matrix) to obtain specific characteristics and properties. The components do not dissolve completely into each other or otherwise chemically merge, although they do act synergistically. Normally, the separate components can be physically identified, as well as the interface between the components. Advanced composites containing materials such as carbon/graphite, boron or aramid fibers in an organic resin matrix are currently used mainly by the aerospace industries. However, these stiff, strong, lightweight materials are also used in various other commercial and industrial applications, ranging from aircraft structures to automobiles and trucks, from spacecraft to printed circuit boards, and from prosthetic devices to sports equipment. Products run the gamut from boat hulls and hockey shin guards to an advanced composite hinge for the retractable arm of the space shuttle .
After a component is manufactured, all or parts of its surfaces may have to be processed further or coated to impart certain properties and characteristics. Coating of critical surfaces is among important technological developments. Consider, for example, applications where temperatures are high and the environment is hostile, such as turbine blades and other components and surfaces of aerospace structures. In advanced propulsion systems, for example, coatings have important functions. First, they act as a thermal barrier to reduce the temperature to which parts are subjected. Second, they protect surfaces from oxidation due to gases such as hot oxygen, and from hydrogen, used for cooling, which otherwise could form brittle compounds .
Finishing processes are yet another classes of processes typically employed for providing protective and/or decorative surfaces on workpieces. Surface treatments include painting, thermal spraying, vapor deposition, electroplating and more [1-3].
- Rufe, P.D. "Fundamentals of Manufacturing, Second Edition." Dearborn, Mich.: Society of Manufacturing Engineers, 2002.
- DeGarmo, E.P.; Black, J.T.; Kohser, R.A. "Materials and Processes in Manufacturing, Ninth Edition." Hoboken, N.J.: John Wiley & Sons, 2003.
- Kalpakjian, S. "Manufacturing Engineering and Technology, Third Edition." Reading, Mass.: Addison-Wesley, 1995.