Choosing the Right Plastic
Plastics science has made tremendous strides over the years, rapidly advancing the ability to compound a variety of plastic materials with fillers and reinforcements that provide a tremendous amount of structural and chemical integrity. In fact, with proper material selection paired with design optimization, plastics can be as strong as metal and weigh far less.
Choosing the right plastic is a critical injection-molding step and can take some time, depending on the project. One of the greatest advantages of plastics is the availability of more than 25,000 engineered materials for manufacturing applications. New, higher-performance blends and hybrids can also be custom-designed to meet very specific performance requirements for complex, critical-use plastic parts and products.
Key considerations for the type of plastic that is selected for the project include:
- Chemical resistance
- Temperature resistance
- Impact resistance
- Frictional properties
- Flame resistance
A Plastics Primer
Plastics are made up of polymers, long chains of repeated molecule units. The ways in which the chains intertwine determine the plastic’s macroscopic properties. Typically, the polymer chain orientations are random and give the plastic an amorphous structure. Amorphous plastics have good impact strength and toughness. Examples include acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile copolymer (SAN), polyvinyl chloride (PVC), polycarbonate (PC), and polystyrene (PS).
If instead the polymer chains take an orderly, densely packed arrangement, the plastic is said to be crystalline. Crystalline plastics have lower elongation and flexibility than amorphous plastics, but better chemical resistance. Examples of crystalline plastics include acetal, polyamide (PA; nylon), polyethylene (PE), polypropylene (PP), polyester (PET, PBT), and polyphenylene sulfide (PPS).
The characteristics of plastics can be changed by mixing or combining different types of polymers and by adding non-plastic materials. Particulate fillers such as mineral, silica, ceramic, carbon powder/fiber, glass microspheres/fibers and powdered metal are added to increase modulus and electrical conductivity, improving resistance to heat or ultraviolet light and to reduce cost. Reinforcing glass fibers, carbon, stainless steel or Kevlar can be added to improve mechanical properties.
Kaysun has developed an extensive, in-house database based on 60 years of injection-molding work. We know, in detail, how plastics respond to various combinations of process variables. Our knowledge goes far beyond the basic information provided by the plastics manufacturer. For example, we know how individual plastics will flow and fill in the mold, based on parameters like melt temperature, flow rate, and cooling rate. This kind of data allows us to select the best plastic for the part, as well as design the best possible mold.
Material selection is a decision that is best made early in the design process. Utilizing Kaysun’s design and engineering teams allows them to share their in-depth knowledge of manufacturing processes and material science in the earliest stages of product development. Identifying the right material for the plastic part or product, up-front, is an essential step for determining the most efficient and cost-effective injection-molding process for the project—with an end product that meets or exceeds all performance requirements.
For specifics on how Kaysun has helped others in selecting the right material read our Smiths Medical case study.