Fabricated plastic parts and semi-finished shapes include molded, cast, extruded, and machined parts made from any polymeric materials. They are often supplied as bars, films, plates, profiles, rods, and shims.
Plastic parts and shapes can be made from many different materials. Among the array of material types, some of the most commonly used are polyamide, polyethylene, polyvinyl chloride, polyacetal, fluoropolymer, and acrylic.
Polyamide is a commonly used polymer for molding high-strength engineered components. Polyamides are also used to produce strong hot-melt adhesives. Polyamides provide higher strength than polyethylene or other commodity-type polymers. Nylon is a well-known example of a polyamide engineering resin that is also used to mold plastic parts.
Polyethylene is the most widely used plastic resin and is a base polymer for other variations of polymers. It is used to form a variety of common or commodity-plastic components. High density (HDPE) and ultra-high molecular weight polyethylene (UHMW PE) have good friction and mechanical properties. They are used in medical devices, wear parts, and engineered components.
Polyvinyl chloride is a thermoplastic polymer widely used in construction because it is cheap, durable, and easy to assemble. It can be made softer and more flexible by the addition of plasticizers. It is a controversial material because of the toxins it may liberate during its production and lifetime.
Polyacetal or polyoxymethylene (POM) is a thermoplastic used in precision parts that require high stiffness, low friction, and excellent dimensional stability. It provides a higher strength material compared to polyethylene-type polymers. However, polyacetal materials are susceptible to oxidation at elevated temperatures. DuPont’s Delrin® is a common polyacetal engineering resin that is also used to mold plastic parts.
Fluoropolymers including polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) are used in applications requiring superior chemical resistance. PTFE is used in applications requiring superior chemical resistance or low friction.
Acrylic polymers are formed by polymerizing acrylic acids through a reaction with a suitable catalyst. Acrylics provide excellent environmental resistance and have faster-setting times than other resin systems.
Plastic Part Selection Considerations
Shapes and Sizes
Plastic parts and shapes are listed according to dimensions such as thickness, length, width, inner diameter (ID), and outer diameter (OD). Hollow stock is usually tubular or pipe-shaped and contains an open internal bore. Round stock is often used with valves. Plastic shapes with square, spherical, angular, rectangular, hexagonal, tubular, I-shaped, and T-shaped cross-sections are also available.
Performance Properties and Features
Fabricated plastic parts and semi-finished shapes are supplied in a variety of chemical and/or polymer systems, and may be filled or unfilled. These different types of plastics provide different mechanical, thermal, and optical properties.
Mechanical properties include tensile strength, tensile modulus, and elongation. Thermal properties include temperature range, thermal conductivity, and the coefficient of thermal expansion (CTE). Resistivity, dielectric strength, and dielectric constant are important electrical properties to consider. Optical properties cover index of refraction, a measure of the speed of light in a material, as well as transmission.
Features such as electrical insulation and thermal insulation are also important to consider, especially based upon the application. For example, products that prevent electromagnetic interference (EMI), radio frequency interference (RFI), and electrostatic discharge (ESD) are available. Typically, they have high electrical conductivity and low electrical resistivity. Flame retardant materials are used to fabricate plastic shapes and parts that can resist ignition or reduce the spread of flames when exposed to high temperatures. Dampening materials are used to reduce sound, vibration, or shock.
Applications for Plastic Parts
Fabricated plastic parts and semi-finished shapes are used in many industries and applications. Some plastic shapes are used in aerospace, automotive, marine, military, and tooling applications.
Others are designed for electrical power and high voltage products such as generators, transformers, circuit breakers, and motor assemblies. Plastic shapes that are designed for semiconductors and integrated circuit (IC) packaging are also available.
Fabricated plastic parts and semi-finished shapes that are suitable for medical, pharmaceutical, and food processing must meet the requirements of agencies such as the Food and Drug Administration (FDA) or the U.S. Department of Agriculture (USDA).