When it comes to injection molding, a common request we receive is advice on the right plastics to use in their projects. While we can only provide suggestions, one common point of confusion for our clients is the difference between thermoplastic and thermoset resins. As part of the injection process, both plastics are subjected to heat during the process, and it is in this difference (which you may have guessed to the thermo prefix) that truly separates these two types of plastics and give them their unique qualities.
As the name implies, thermoset plastics “set” after they cure during the injection molding process. Thermoset materials start as a liquid and when heated a chemical process creates permanent links between molecular chains (cross-links) during the curing process. These cross-links provide additional strength, but at the cost of reusability. A common thermoset plastic is Liquid Silicone Rubber (LSR).
The strong molecular bonds provide additional strength to the material, and in some instances, the inability for the plastic to re-melt can be a benefit. In general, thermoset plastics have:
While thermoset plastics have their strengths, they can also be weaknesses. This comes from not only their strengths but also their place in the industry in general.
Thermoplastics are the most commonly used type of plastic in injection molding, with two major points in favor of manufacturers: ease-of-use and recyclability. Thermoplastics come in the form of resin pellets. Depending on the needs of the client and the type of plastics, excess plastics from shearing and runners can be recycled back into the batch. A common example would be Acrylonitrile Butadiene Styrene or ABS plastic.
The ability to re-melt plastics provides both an incentive in manufacturing and as a green practice. It also provides a versatile platform for many different types of thermoplastics.
A thermoplastic’s strength can also be its greatest weakness. As it does not have the chemical cross-links and does have a higher melting point, it’s not for all applications.
Your choice ultimately lies with your requirements and budgets. Need help? Midstate Mold and Engineering can provide suggestions to our clients on the entire injection molding process, from mold design to parts production, though the final selection is always in your hands. Read our blog archives for more common thermoplastics and more suggestions on picking the right resins for your project. Ready to get started? Contact us today.
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