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.
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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 measures impact resistance by swinging a pendulum downward to strike a plastic sample mounted in a bracket. The Gardner Impact test measures impact by dropping a weight onto a material sample. In both cases, the force or height required to damage the material indicates its impact resistance: the higher the value, the greater its ability to withstand impact.
In no particular order, here are some plastics known for high-impact resistance:
Top Impact-Resistant Performance Plastics
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ABS
Acrylonitrile butadiene styrene is a durable, impact-resistant material commonly used in automotive components, consumer goods, and protective housings.
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HDPE (High Density Polyethylene)
HDPE offers strength, low weight, and resistance to chemicals and moisture, making it ideal for food and beverage equipment, industrial components, and marine applications.
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Polycarbonate
Polycarbonate is a high-performance, impact-resistant thermoplastic known for its clarity, strength, and weatherability, making it suitable for applications such as eyewear lenses, bullet-resistant glass, construction materials, and automotive parts.
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PETG
Strong and versatile, PETG plastic sheet can be used in various applications, including signage, displays, medical implants, and beverage containers.
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PTFE (Polytetrafluoroethylene)
PTFE plastic sheet and rod offer unmatched chemical resistance, high temperature performance, and low friction properties for industrial, electrical, and mechanical applications.
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 select the appropriate 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 options. However, these sheets aren’t perfect, as they contain data from highly controlled testing. Thus, they should only be the starting point for material selection.
Another option is to consult a plastics expert, like the team at Piedmont Plastics. With the right technical guidance, manufacturers can further narrow their options and select the ideal plastic material for their specific application and performance requirements.
Factors Affecting the Impact Resistance of Plastic
Several factors affect the impact resistance of plastic, including:
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Chemical Makeup
HDPE, ABS, and polycarbonate offer high impact resistance thanks to their strong molecular structure and chemical bonding.
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Temperature
Many strong plastics become tougher under warm temperatures but turn brittle under cool temperatures.
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UV Light Exposure
Exposure to the sun and other UV light sources can weaken a plastic and make it less impact resistant.
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Cut of the Plastic
By creating sharp internal corners, manufacturers can reduce the impact resistance of the plastic material.
Design Considerations for Impact Resistance in Plastic Parts
Once a manufacturer has selected a plastic material, the part design process begins. Design choices can significantly impact overall impact resistance. In addition to material selection, consider the following 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.
Wall thickness: 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 a large effect on the impact resistance of the final product. Use a strong plastic, then design the part in such a way that it maximizes the impact resistance of the material.
Partner with Piedmont Plastics
Because plastics can perform very differently depending on the application, it’s beneficial to work with an expert when selecting the right material for your manufacturing needs. Piedmont Plastics can help you choose the best plastic products to produce strong, impact-resistant parts with confidence. Contact our team today for more information!
