Considerations for Plastic Parts
The viscoelastic nature of plastic means they respond to impact stress in ways similar to both liquids and solids. Like solids, they can keep their form, strengths, and elasticity, but like a fluid, they have some flow that is affected by the environment. This is different from how metal, ceramic, and even glass respond, which can create challenges for manufacturers using plastics for the first time.
One of the factors that this viscoelastic nature affects is impact resistance. This is the ability of plastic to withstand impact without cracking or shattering, and many types of plastic offer very high impact resistance. Understanding this function of plastic and how it affects the manufacturing process is crucial to today’s manufacturers.
Basics of Impact Resistance in Plastic Materials
Impact resistance is measured by how well a material can withstand a strike in a controlled environment. There are two basic tests: the Notched IZOD Impact and the Gardner Impact. The Notched IZOD Impact test sends a pendulum rotating downward to strike the plastic while it is on a mounting bracket. The Gardner Impact test drops a weight down onto an object that sits on the material. The weight or height required to damage the material using either test is what its impact resistance measure is. The higher the number, the more it resists damage. In no particular order, these are some plastics with high-impact resistance:
Remember that the tests used to rate the impact resistance of plastics occur in a controlled environment. They do not consider the effect of environmental factors that can change the actual impact resistance of the material. Still, understanding the impact resistance in a controlled environment will help manufacturers choose the right material for the job.
Choosing the Right Material for Impact Resistance Applications
Today’s manufacturers have many plastic materials to choose from as they seek the right material for a particular application. Finding the right one can be challenging.
The first place to look for information on a plastic material is its data sheet. This form will explain the material's tensile strength and impact resistance, allowing the manufacturer to narrow down their options. However, these sheets aren’t perfect, as they contain data from highly controlled testing. Thus, they should be the starting point only for the material selection.
Another way to choose is to talk to a plastics expert, like those at Piedmont Plastics. A plastics expert can help the manufacturer narrow their options even further to find the ideal plastic product for their particular manufacturing needs.
Factors Affecting the Impact Resistance of Plastic
Several factors affect the impact resistance of plastic. These include:
- Chemical makeup – HDPE, ABS, and polycarbonate are all highly impact-resistant plastics. Most of this is due to the chemical makeup that creates strong chemical bonds and tightly packed molecules.
- Temperature – Many strong plastics become tougher under warm temperatures but turn brittle under cool temperatures.
- UV light exposure – Exposure to the sun and other UV light sources can weaken a plastic and make it less impact resistant.
- Cut of the plastic – If you create sharp internal corners, you can reduce the impact resistance of the plastic in that area.
Design Considerations for Impact Resistance in Plastic Parts
Once a manufacturer has chosen a plastic, designing the part using that plastic begins. The design of the part can actually affect its impact resistance. In addition to the plastic chosen, consider these design factors:
- Radius – The radius should relate to the thickness of the part. Corners should be between 0.9 and 1.2 times the nominal thickness of the plastic part.
- Thickness of the wall – Keep the wall thickness consistent to reduce the risk of costly defects on the plastic parts.
- Draft – Draft is a tapering of the vertical walls of a plastic part that allows it to slip out of the mold during manufacturing. You need at least one to two degrees of taper, but you may need more depending on the design of your part.
All three of these factors can have an impact on how impact resistant the final product is. Use a strong plastic, then design the part in such a way that it maximizes the impact resistance of the final product.
Partner with Piedmont Plastics
Because plastics can behave very differently, working with someone who knows the materials well when choosing a plastic for your manufacturing needs is beneficial. Piedmont Plastics can assist you in finding the plastic products you need to manufacture strong, impact-resistant parts effectively. Reach out to our team today.