Plastic Material Selection: Engineering, High-Performance, and Imidized Plastics

Many manufacturers are making the switch from metal to industrial plastics for both structural and bearing and wear applications. In general, plastics have many beneficial qualities that make it a superior alternative to metal components, such as lighter weights, better coefficient of friction, and quieter operation, to name just a few. But just like metal alloys, plastic materials have a wide range of characteristics. Choosing the right plastic material for your application is a complex and critical process. 

The most common mistake that manufacturers make in material selection is under-specification for their requirements. Selecting a plastic that doesn’t have the necessary thermal properties, strength, or chemical resistance is sure to result in part failure. It’s common for manufacturers who have tried an under-specified plastic to give up on plastics altogether and go back to using metal components. Their logic? Plastics didn’t work. 

On the opposite end of the spectrum, some manufacturers may have deployed a high performance plastic where a more economical option would do the trick. In this case, the perception of plastics follows that they are too expensive to make sense for the application.

The Plastics Pyramid

With so many industrial plastics to choose from, materials are commonly organized into a pyramid to demonstrate the differences between different families of amorphous and crystalline plastics. At the bottom, you find commodity plastics such as acrylic, ABS, polypropylene, HDPE, and PVC. Commodity plastics are cost-effective, and depending on the material, can offer good chemical resistance and machinability (although not all plastics in this category exhibit these qualities). 

Moving up a level in the pyramid, you find engineering plastics such as nylon, acetal, UHMW-PE, and polycarbonate. While again, materials at this level vary in characteristics, this family of materials can be suited for general structural or bearing and wear applications, featuring moderate temperature resistance and strength. 

For more specialized and demanding applications, the top two tiers of the pyramid house high-performance plastics and imidized plastics. High-performance plastics such as PEEK, PPS, and PTFE can withstand high service temperatures while exhibiting excellent chemical resistance. Imidized plastics, once considered suited only for aerospace applications, are becoming more widely specified for thermal insulators, high-performance bearings, electrical connectors, and ablative structures. Imidized plastics include polyamide-imide (PAI), polybenzimidazole (PBI), and polyimide (PI), which feature the highest temperature resistance and load bearing capabilities, among other features. 

Using the Plastics Pyramid in Material Selection

The plastics pyramid effectively demonstrates the differences between families of polymer types. But within each family, there are important variances between materials that make each one best suited for particular types of applications. 

To narrow your selection, it’s important to know the answers to the following questions:

• What’s your part’s function? Is it a structural or bearing and wear application? 
• At what temperature will the part operate?
• How much load will the part be subjected to, and at what speed?
• What kind of chemicals are present in the application? 
• What is the impact resistance required?
• Will the part be used outdoors or require UV resistance?

Cope Plastics has developed an online tool to help you narrow down your material selection from the thousands of available materials to a few options. But once you’re left with your final options, there’s more to explore before landing on the perfect material for your application. 

Looking at a plastic’s characteristics alone isn’t enough. It’s important to consider how the forces of your application interact. Just because a material (plastic or nonplastic) has attractive characteristics doesn’t mean it will function well in your application.

Take coefficient of friction for example. While PTFE has a very low coefficient of friction (COF), the COF of PTFE decreases dramatically under load. Nylatron GSM has a higher COF in a side-by-side comparison, but its COF actually increases when under load. Due to the complexity of factors that interact in applications, it’s crucial to engage an experienced technical plastics expert when making your final material decision.

The Right Plastics Partner is Important, Too

We mentioned the importance of working with an expert in selecting a plastic material for your application. It’s also important to choose an expert backed by a team that has the resources necessary to fully support you. 

Sourcing materials to cut and machine in-house? Not all plastics distributors offer the same range of materials. Most large plastic manufacturers place caps on their distribution, so in this industry, relationships are key. When selecting a materials partner, it’s beneficial to choose a company with a direct relationship with the manufacturer. This helps ensure you receive a quality product at the fairest possible price. 

Contracting out your fabrication? The above still applies, but you have more to consider. When selecting a partner, it’s a good idea to gain an understanding of how your parts will flow through their production cycle. Can your fabrication partner provide space to stock inventory? How large is the equipment arrangement? These factors will dramatically influence the lead times you will experience once you begin working together.

Expert Advice and Vast Resources: Cope Plastics Has It All

Choosing the right material and the right plastics partner involves considering a host of different factors. It’s an important choice to the success of your business. If you have any of these questions on your mind, then Cope Plastics may be the perfect partner for you. 

With one of the largest equipment arrangements in the country, Cope Plastics’ fabrication operation is backed by an experienced team of technical and engineering experts (and robots) who can help guide you in everything from material selection to part design to testing. Also, since we’ve been in business for 74 years, Cope has built relationships with the world’s leading plastics manufacturers to give customers access to the best quality materials at all levels of the plastics pyramid. 

If you’re facing challenges with a specific application, our team is ready to help. You might be amazed to discover what the right material, backed by the right team, can make possible in your business.