Interview: Bearings—Plastics vs. Metal

Metals have long been considered the materials of choice for bearings. But igus Inc. has been making plastic bearing for years, and engineers there have some insights on their benefits. In this interview, Nicole Lang, Product Manager for dry-tech bearings and linear systems at igus, gives an overview on plastic bearings, how they compare to metal versions, and the advantages of plastics.

How do plastic and metal bearings compare in terms of cost and performance?

Generally speaking, plastic bearings are very comparable to their metal counterparts in terms of cost. If you compare plastic bearings with other plain metal bearings, typical per piece prices are very similar. However, plastic bearings eliminate any need for maintenance and constant re-lubrication. So over the lifetime of the bearing, self-lubricating plain plastic bearings are usually more cost-effective.

For performance comparisons, we need to look at a simple plastic and a composite plastic. For example, in a lot of cases, simple plastics do not offer the same wear resistance or strength as a composite, so it’s hard to compare them to metal bearings. Composite plastics, on the other hand, usually hold up well against plain bearing metal counterparts.

Are there any applications plastic bearings can handle and metal ones can’t?

Plastics excel in applications where there could be shock or impact loads. Plastics are inherently more elastic. For example, among our bearing plastics, we have some that are very elastic and some that are less, and they can both absorb shocks and vibrations.

Plastics also do better in applications where there is exposure to moisture or the bearing will be completely submerged. Plastic bearings resist corrosion and several composite plastics have minimal swell.

Applications where weight might be a concern also favor plastics. These include automotive, bicycles, recreational vehicles, and aircraft interiors, to name just a few.

Applications with a large amount of dirt and dust can also benefit by using plastic bearings. Dirt and dust can score or scrape metal linings, causing damage to the bearing and premature wear. This type of environment will also cause problems for a lubricated bronze bearing, since dirt and dust can get stuck within the lubricant, causing binding or seizing as well as premature wear.

Plastic bearings can also offer FDA compliance with some combinations and are RoHS-compliant—standards most metal bearings cannot meet.

Are there any unsung or little-known advantages to plastic bearings?

Plastic bearings offer many advantages (most of those mentioned above). But oftentimes, people don’t realize is that due to the wide variety of composite plastic blends, there are bearing materials that withstand extreme temps (482°F long-term and approaching 600°F for short-term exposures).

What are the advantages of the ability to order plastic bearings in various colors?

Color is not always a concern. But for some customers, it may be important to “hide” the bearing when aesthetics matter. In addition, we have had many clients in the packaging industries who want components in colors that are detectable and stand out. That’s the main reason we have three food-grade materials that are blue.

Why do some engineers, designers, and purchasing agents say they cannot or will not use plastic bearings?

A lot of it is perception. For those familiar with the previous industry standard (metal bearings), they believe metal is stronger. It appears stronger and it is a material that people associate with strength. That being said, it is common to underestimate the strength of composite plastics and their abilities. As mentioned earlier, plastic bearings, thanks to their elasticity, can withstand shock and impact loads that could shatter metallic bearings.

Are European, Asian, and other non-U.S. companies and engineers more or less likely to use plastic bearings than those in the U.S.?

I have heard from my colleagues that plastic bearings face the same challenges that they do in the U.S. In general, most people are misled to believe that metal is better. In recent years, there has been a slight shift in perception. Most still feel a metallic bearing is better, but there are more people starting to discover plastics’ capabilities.

What will it take to convince designers that plastic bearings can improve designs, save money and weight, and meet the requirements for many applications?

We eagerly want to prove to them that plastic will not only work, but oftentimes work better. To do this, we offer free samples for testing or we will do the testing for them. In addition, we have an online expert system that compiles all of our standard testing for each material in different conditions and on different shafts. From that, we then can tell them the number of hours the bearing will last in their applications.