Plastic is plastic, its all the same right? From a water bottle to a computer mouse, I never thought past the general term of “plastic”. That is, until I started my marketing internship at Poly-Cast. On my first day I was treated to a tour and shown all the different compounds we use in molding. “Poly” this, “lene” that, and more abbreviations than I could count. Luckily for me, and you the reader, I’ve been given a crash course in the different types of plastics and what factors need to be taken into consideration before choosing a resin. With the tens of thousands of plastic compounds available, and all types of additives that can be used in manufacturing, this post can’t tell you exactly what resin you need for your specific project, but can help give you an idea of some of the variables to think about as your project comes to life.
No this isn’t about turning on the air conditioning to get away from scorching temperatures in July, but the temperature at which the plastic will deform while bearing a load. Knowing the environment your product will be in helps cut down the list of possible resins as exposure to heat above the deflection temperature can compromise the component. Additionally, this is important in the injection molding process as the part is only safe to remove from the mold once it has cooled down sufficiently below the heat deflection temperature.
It sounds like a term that an over-enthusiastic trainer would use at your local gym, however this is an attribute of the material’s ability to resist deformation while bearing a load. Typically in a beam or rod shape, the part is bent and tested to see how much pressure can be applied before breaking.
Related to flexural strength, this describes the material’s tendency to bend, or thought of in a different way, how stiff it is. This is similar to elastic modulus, which is a test of the force required to pull something to the point of breaking. A major distinction between them comes from plastic, unlike metal, having a different stiffness when compressed (pushed in) as opposed to loaded with tension (pulled apart). This shifts the neutral surface line (think of it as the center of balance of the stress), so there is not an even split between the two forces.
Notched Impact Strength
Also known as an Izod Impact Strength Test (no relation to the clothing company) this is a measure of the plastic’s ability to withstand the force of an object hitting it. The application of the product will be able to give some guidelines as to how strong of a plastic you need. For example, in industrial or automotive products, there is a high likelihood of the object being hit or knocked around, so a higher impact strength rating will be required.
I hope this post was helpful to everyone, and got you thinking of the requirements that will be set by your new or even currently offered product. Watch for future posts as I learn more about the surprisingly complicated world of plastics. Feel free to comment below with suggestions for future topics.