Picking Your Plastics Option
Continuing on with our manufacturing series, I’ll spend the next few weeks diving specifically into plastics. Our world today exists because of advances in plastic manufacturing. Nearly everything we touch or use has plastic components in them. This week we’ll start with Thermoset plastics.
From the highest level, there are two classes of plastic: Thermoset and Thermoplastic. Thermoplastic is the most popular class of plastic used in manufacturing. These plastics are made by melting pellets and forming them into a shape with a tool. These plastics can be re-melted or ground up into pellets again and recycled to be used for other parts. Thermoset plastics are manufactured by mixing two different agents together with heat, and then allowing a chemical reaction to take place where irreversible bonds are formed. Because of this, thermoset plastics can’t be reused or recycled. But they have numerous advantages.
Thermoset plastics were the first type of plastics developed. They are typically used in applications where they will be in contact with chemicals, high heat, or need high structural integrity. Thermoset materials can be used in cases where a chemical might eat away at thermoplastic polymers. This includes some industrial cleaners or lab chemicals. Thermoset materials can be used in applications with temperatures over 300°C. Whereas Thermoplastic typically melts at 100 – 120°C. This is especially important with medical equipment that needs to be sterilized in an autoclave, or with engine components or electrical applications that see high heat. And they can be easily made with variable wall thickness to either add more structure to certain areas of your part while having thinner (light weight) walls in other areas of the part.
While there are many different types of thermoplastic manufacturing options, thermoset plastics tend to only be manufactured through a liquid molding process. The liquid molding processes are RIM and RTM. Reaction Injection Molding (RIM) is where two separate liquid agents, polyol and isocynate, are heated up, then injected through a mixing nozzle into a mold cavity. At this point the chemical reaction takes place and the part is formed.
Resin Transfer Molding (RTM) is where the resin material is mixed with a catalyst at the nozzle and injected into the mold cavity where is then sets and forms the part.
The link below is specifically about RIM molding. But the process for RTM is quite similar.
Stay tuned for next week where we start covering thermoplastic manufacturing techniques!