Part temperature Plastic material

Unlike metals and ceramics, plastics absorb water. The amount of water absorption depends upon the specific type of plastic. The key properties—mechanical, electrical, and optical—are seriously affected. Water also tends to act as a plasticizer and lowers the softening temperature of the part (1). Plastic materials that absorb a large amount of water normally affect the dimensional stability of the product. The plastic product designer must take into account the water absorption characteristics of the plastic materials to avoid premature failures. 

A number of areas in which plastics are used in electrical and electronic design have been covered there are many more. Examples include fiber optics, computer hardware and software, radomes for radar transmitters, sound transmitters, and appliances. Reviewed were the basic use and behavior for plastics as an insulator or as a dielectric material and applying design parameters. The effect of field intensity, frequency, environmental effects, temperature, and time were reviewed as part of the design process. Several special applications for plastics based on intrinsic properties of plastics materials were also reviewed. 

The use of primers is also advisable if the bonded parts are to be subjected to temperature changes, damp conditions, tension compression, shear forces, etc. Some porous substrates and plastic materials also require primers. Primers can be applied to a thoroughly prepared surface by brushing, spraying or dipping to form a thin film. All primers contain flammable solvents and therefore safety precautions are essential. 

The middle or naphthalene oils separate in that part of the fractionating column with a temperature of 410-460°F. Products include dyes, perfumes, plastic materials, pharmaceutical and photographic materials. After the deposit of naphthalene, creosote oil is left. This has been used as a wood preservative. Heavy or anthracene oils are obtained at the bottom of the fractionating column, at temperatures between 460°F and 680°F. 

Engineering polymers comprise a special, high-performance segment of synthetic plastic materials that offer premium properties. When properly formulated, they may be shaped into mechanically functional, semiprecision parts or structural components. The term "mechanically functional" implies that the parts will continue to function even if they are subjected to factors such as mechanical stress, impact, flexure, vibration, sliding friction, temperature extremes, and hostile environments. 

Solid phase pressure forming (SPPF) combines the use of pressure forming and plug-assist to form crystalline plastics at temperatures below their normal forming range, 5 to 8% below the crystalline melting temperature, in order to produce stiffer parts with less material. 

Die Swell Compensation. The polymer melt swells when it exits the die, as explained previously. This die swell is a function of the type of plastic material, the melt temperature, the melt pressure, and the die configuration. The die must be compensated for die swell so that the extruded part has the corrected shape and dimensions. Molds and dies for different fabrication processes will be described later in more detail when the processes are discussed. 

Moisture is absorbed by adhesives and other plastic materials to various degrees and can accumulate in voids within the bond line during assembly, testing, and operation. The absorption of moisture in adhesives as well as in other polymeric materials, such as molding compounds, has been proven to cause failures when parts are subsequently solder reflowed and exposed to the high solder melt temperatures of 200 °C and above. The rapid evaporation and expulsion of the moisture result in stresses that cause cracking and delamination, a phenomenon referred to as popcorning. 

Production of EPS. Plastic materials on the polystyrene basis occupy with its production volume the third position in the world, following polyolefin and pol5rvinyl chloride. Polystyrene (PS) is made from styrene (vinyl benzene), which is liquid at ordinary temperatures and can be polymerized well in a unit or suspension. In the basic methylene chain, which forms a polystyrene molecule, a six-part aromatic circle (phenyl) is linked to every other carbon instead of hydrogen. 

Drape forming (also called oven forming) is carried out commercially on small and large parts where the plastics material is pre-heated in an oven to the forming temperature, placed in a mould and held in place while it cools. Applications include windscreens, seat backs and bottoms, covers and doors. 

The shrinkage behavior of different resins and the part geometry must be considered. Generally shrinkage is the difference between the dimension of the mold at room temperature (72°F) and the dimensions of the cold blown part, usually checked 24 hours after production. The elapsed time is necessary to allow the part to shrink. Trial and error determines what time period is required to ensure complete shrinkage. Coefficients of expansion and the different shrinkage behaviors depend on whether plastic materials are crystalline or amorphous (see Chapter 1). 

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