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Machining Plastics (Thermoplastics and Thermoset Plastics) from Cutting Tools Chicago

Plastics (Thermoplastics and Thermoset Plastics) technical information from Cutting Tools Chicago aka General Cutting Tools in Chicago, Illinois.  Plastic materials are derived mainly from petroleum products. The types, trade names, and compositions of the various modern plastics form a long list, with more being developed as required to meet specific design and application needs in industry.
A Thermoplastic is a plastic in which the finished molded part may be remelted for remolding. A thermoset plastic is a plastic in I i the chemical reaction cannot be reversed, thus allowing the part to be cast only once. Thermoplastics are extruded, injection molded, and cast in dies. Thermoset plastics usually are compression molded. Some of the thermoplastics are also formulated for thermoset applications, such as the urethanes. Table 4.56 lists the common trade names, suppliers, SAE symbols, and plastic “family” names for most plastics.

Common plastics and compositions. Listed here are some of the more prevalent plastics and compositions.

  • ABS (acrylonitrile-butadiene-styrene) Acetal (Delrin, Celcon)
  • Acetate (cellulose)
  • Acrylic (Lucite, Plexiglas)
  • Benelex
  • Epoxy, epoxy glass
  • Diallyl phthalate, Melamine
  • Mylar (polyester film)
  • Nylon
  • Phenol formaldehyde
  • Phenolic laminates
  • Polycarbonate (Lexan)
  • Polyester glass
  • Polyethylene
  • Polypropylene
  • Polyimide
  • Polystyrene
  • Polysulfone
  • Polyurethane
  • Polyvinyl chloride (PVC)
  • RTV (room temperature vulcanizing) silicones, Styrofoam (polystyrene)
  • Teflon (PTFE, polytetrafluoroethylene), urea-formaldehyde

Common plastics and typical uses
Acetal (Delrin, Celcon). Properties: High modulus of elasticity, low coefficient of friction, excellent abrasion and impact resistance, low moisture absorption, excellent machinability, ablative. Typical uses: bearings, gears, antifriction parts, electrical components, washers, seals, insulators, and cams.

Acetate (Cellulose). Properties: Odorless, tasteless, nontoxic, grease resistant, high impact strength. Typical uses: badges, blister packaging, displays, optical covers, and book covers.

Acrylic (Plexiglas, Lucite). Properties: unusual optical clarity, high tensile strength, weatherability, good electrical properties, ablative. Typical uses: displays, signs, models, lenses, and electrical and electronic parts.

Benelex (Laminate). Properties: high compressive strength, machinable, resists corrosion (alkalis or acids), good electrical insulation, high flexural, shear, and tensile strength. Typical uses: work surfaces, electrical panels and switch gear, bus braces (low voltage only), and neutron shielding.

Diallyl phthalate, Melamine. Properties: high strength, chemical resistant, low water absorption, medium-high temperature use. Typical uses: terminal blocks and strips, dishware, automotive applications, and aerospace applications.

Epoxy glass. Porperties: high strength, high temperature applications, flame retardant, low coefficient of thermal expansion, low water absorption. Typical uses: high quality printed circuit boards, microwave stripline applications, VHF and UHF applications, electrical insulation, and service in temperature range of -400 to 500°F.

Mylar (polyester film, polyethylene terephthalate). Properties: High dielectric strength, chemical resistance, high mechanical strength, moisture resistant, temperature range 70 to 105°C, does not embrittle with ago. Typical uses: Electrical and industrial applications and graphic arts applications.

Nylon. Properties: Wear resistant, low friction, high tensile strength, excellent impact resistance, high fatigue resistance, easy machining, corrosion resistant, lightweight. Typical uses: Bearings, bushings, valve seats, washers, seals, cams, gears, guides, wheels, insulators, and wear parts.

Phenol formaldehyde (Bakelite). Properties: Wear resistant, rigid, moldable to precise dimensions, strong, excellent electrical properties, economical, will not support combustion. Typical uses: Electrical and electronic parts, handles, housings, insulator parts, mechanism parts, and parts that are to resist temperatures to 250°C.
Phenolic laminates. Properties: Immune to common solvents, lightweight, strong, easily machined. Typical uses: Bearings, machined parts, insulation, gears, cams, sleeves, and electrical and electronic parts.

Polycarbonate (Lexan). Properties: Virtually unbreakable, weather resistant, optically clear, lightweight, self-extinguishing, thermoformable, machinable, solvent cementable. Typical uses: High voltage insulation, impact resistant injection moldings, glazing, bulletproof’, glazing, and plumbing fittings. The strongest thermoplastic.

Polyester glass. Properties: Extremely tough, high dielectric strength, heat resistant, low water absorption, antitracking electrically, self-extinguishing, machinable. Typical uses: Insulators and bus braces, switch phase barriers, general electrical insulation, mechanical insulated push rods for switches and breakers, contact blocks, and terminal blocks.
Polyethylene. Properties: Transparent in thin sheets, water resistant. Typical uses: Bags for food storage, vapor barriers in construction, trays, rollers, gaskets, seals, and radiation shielding.

Polypropylene. Properties: Good tensile strength, low water absorp¬tion, excellent chemical resistance, stress-crack resistant, electrical properties. Typical uses: Tanks, ducts, exhaust systems, gaskets, laboratory and hospital ware, wire coating, and sporting goods.

Polystyrene. Properties: Outstanding electrical properties, excellent machinability, ease of fabrication, excellent chemical resistance, oil resistant, clarity, rigidity, hardness, dimensional stability. Typical Lighting panels, tote boxes, electronic components, door panels (refrigerators), drip pans, displays, and furniture components.

Polysulfone. Properties: Tough, rigid, high-strength, high-temperature thermoplastic, temperature range –150 to +300°F, excellent electrical characteristics, good chemical resistance, low creep and cold flow properties, capable of being autoclaved repeatedly. Typical uses: Food-processing and medical industries, electrical and electronics, appliance, automotive, aircraft, and aerospace uses.

Polyurethane. Properties: Elastomeric to rock-hard forms available, high physical characteristics, toughness, durability, broad hardness range, withstands severe use, abrasion resistant, weather resistant, radiation resistant, temperature range –80 to 250°F, resistant iii common solvents, available also in foam types. Typical uses: Replaces a host of materials that are not performing well; extremely broad range of usage; replaces rubber parts, plastic parts, and some metallic parts.

Polyvinyl chloride (PVC). Properties: Corrosion resistant, formable, lightweight, excellent electrical properties, impact resistant, low water absorption, cementable, machinable, weldable. Typical uses: Machined parts, nuts, bolts, PVC pipe and fittings, valves, and strainers.

RTV silicone rubber. Properties: Resistant to temperature extremes 1 75 to 400°F), excellent electrical characteristics, weather resistant, good chemical resistance; FDA, USDA, and UL approved. Typiccal uses: General-purpose high-quality sealant, gasket cement, food contact surfaces, electrical insulation, bonding agent, glass tank construction, and countless other applications.
Styrofoam. Properties: Low water absorption, floats, thermal insulator, extremely lightweight. Typical uses: Insulation board for Domes and buildings, cups, containers, thermos containers, shock absorbing packaging, plates (food), and flotation logs.

Teflon (PTFE). Properties: Unexcelled chemical resistance, cryogenic service, electrical insulation, very low friction, high dielectric strength, very low dissipation factor, very high resistivity, machinability. Typical uses: Valve components, gaskets (with caution, due to cold flow), pump parts, seal rings, insulators (electrical), terminals, bearings, rollers, bushings, electrical tapes, plumbing tapes, and machined parts; bondable with special etchant preparations.
Urea-formaldehyde. Properties: Hard, strong, molds accurately, low water absorption, excellent electrical properties, ablative, economical, will not support combustion. Typical uses: Electrical and electronic parts, insulators, small parts, and housings.
Properties of Materials: General and Specific.

All manufacturers of plastic materials provide material specification sheets when so requested. Material analysis sheets likewise are sup¬plied by metal providers, forges, and foundries when so requested. The material test report is generated by one of the various materials test laboratories nationwide, but it must be purchased by the company requesting the analysis. Owing to the rise in imported materials that may or may not meet the requirements of the SAE, ASTM, AISI, ASM, and ANSI standards, material confirmation by way of laboratory analysis is necessary in many instances. Materials that do not conform to the standards applicable for a given material, as specified on the engineering drawings, pose a serious safety prob¬lem for manufacturers of industrial and consumer products and their users. When in doubt about a material’s performance, have the material analyzed at a testing laboratory. The material supplier is responsible for the specifications of the material that it sells. If you order a type 304L stainless steel per SAE or ASTM specifications, the material must conform to these specifications both chemically and mechanically.

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