Plastic fasteners and components are used in many different industries including boating, aerospace, military, OEM, automotive, semiconductor, and many more. Plastic material properties vary widely even from one grade to another of the same plastic. There are plastic manufacturing terms that are used to describe and discuss the many variations found in plastic properties. It can be hard to keep up! In order to help you out, here are 10 commonly used plastic manufacturing terms explained:
Annealing is the process of heating a plastic gradually to above its glass transition point, maintaining that temperature for a specific period of time and then allowing it to cool to relieve internal stresses caused by manufacturing processes.
Creep is the tendency of a solid material to move slowly or deform permanently under the influences of stresses. Plastic manufacturing engineers designing for an application with consistent high pressure consider creep when choosing materials.
3) Conductive Plastics
Conductivity is the ability of a material to allow a current or charge to travel through it. Conductivity is the inverse of resistivity. Conductive plastics are hybrid polymers that are electrically conductive or static dissipative. These plastics are engineered to have specific conductivity characteristics using additives such as copper, silver, aluminum, carbon black, carbon fibers, etc.
4) Continuous Service Temperature
The continuous service temperature is the maximum temperature above which mechanical and electrical properties are significantly degraded over the life time of the product. Keeping a product at the continuous service temperature will not shorten the lifespan of the part. Note that this is different than the maximum service temperature, which can only be maintained for short periods without degradation.
The term “crazing” refers to small hair-like cracks beneath the surface of a plastic part. It sometimes is an indicator of imminent material fracture. Crazing is also often seen in ceramic glaze.
6) Flame Rating/UL 94
UL 94 is an internationally accepted plastics flammability testing standard created by Underwriters Laboratories. V stands for vertical flame and HB for horizontal burn. Expressed as V-0, V-1, and V-2. V-0 is a vertical burn that stops within 10 seconds. V-1 is a vertical burn that stops in 30 seconds and V-2 is one in which the vertical specimen stops burning in 30 seconds with the allowance of drips of flaming particles. HB is the designation for horizontal slow burn with a burning rate of <76mm/min where burning stops before 100mm.
7) Molding Shrinkage
The molding shrinkage is the amount a plastic will shrink after the molding process. As different plastics shrink at different rates, mold shrinkage rates must be considered to ensure the product is dimensionally correct.
The term “self-extinguishing” is somewhat loosely applied to describe the ability of a polymer to stop burning after a flame applied to it has been removed.
9) Stress Crack
A stress crack is an internal or external crack in a solid plastic body caused by tensile compressive or shear force.
Viscosity is the measure of a materials’ ability to resist flow. In fluids, viscosity can be understood as “thickness.” For example, glue is more viscous than water. In a solid, viscosity is understood the material’s ability to resist stress. In this way, viscosity is the opposite of creep. Interestingly, some scientists believe that certain materials such as glass and many polymers are actually extremely viscous fluids. As proof of this, these scientists point to the deformation of glass window panes due to gravity over time. However, this concept is somewhat in dispute.
Are there other plastic manufacturing terms you have questions about? Please let me know in the comments below and I’ll look up a definition for you. I’d also love to hear about any terms you’ve found useful.
To discover more plastic manufacturing terms, please download our complimentary Glossary of Plastic Manufacturing Terms.