Non-Metallic Bearings

This article takes a look at alternative-material, non-metal bearings, and it turns out the first bearings of that type - wood, in this case, were the norm - not an alternative.

Bearings make the world go ’round. Much like gears, bearings are used in practically anything you can think of—from toys to titanic machinery and beyond. Another similarity to gears: they’ve been around since the beginning of recorded history, as Timken Process Industries’ Steve Johnson, director–process technology, explains. (Ed.’s note: Statements from Timken in this article pertain to rolling element bearings only—ball, cylindrical roller, spherical roller and tapered roller. Other friction management systems such as fluid film bearings, magnetic bearings etc., were not considered.)

“I believe the first non-metal bearings were wood. The ancient Egyptians/ Greeks, etc., used wooden logs as simple roller bearings to move large objects. During the industrial revolution, early rolling element bearings were also wooden. In modern times, certainly low-cost plastic bearings have been used in toys, household appliances, etc., for many years.”

So there you go—this article is a look at alternative-material, non-metal bearings, and it turns out the first bearings of that type—wood, in this case, were the norm—not an alternative.

But there are indeed alternatives out there today. We now have bearings made from—or coated with—ceramics, reinforced and non-reinforced polymers, carbons and graphite, for example, with other, next-generation engineered materials almost sure to follow. And given the ever-fluctuating cost, quality and availability of steel worldwide, it is no wonder that non-metallic bearings have made tremendous gains in many markets and applications. “Full non-metal (ceramic) bearings are used in some space flight and semiconductor applications,” says Johnson. “Metal bearings with non-metal components such as polymer cages or ceramic rollers are used extensively in markets such as rail, light-vehicle systems and machine tools. The use of hybrid ceramic bearings in high-speed machine tool spindles as the standard has occurred over the last 15 years or so.” Tom Miller, Igus Inc. bearings unit manager/North America, adds this:

“Plastic bearings can be used in many different industries and applications. Just some of the industries in which plastic bearings are being used include automotive, medical, food and drug, farming, solar, bikes, packaging, textile, offshore, marine, aerospace and office furniture.

“Over the past few decades, the applications for self-lubricating plastic bearings have become almost endless. Some design engineers do not believe plastic—a material that most people equate with a disposable commodity like a plastic fork or spoon—will deliver superior performance. If you are using high-performance plastic bearings, they can be used in almost any application—from packaging machines and medical equipment to environments with chemicals, extreme loads or high temperatures.”

Looking at things from a leading material supplier’s perspective, Victrex technical manager Patrick Clemensen adds, “The largest markets for non-metal bearings are automotive transmissions, followed by industrial pumps, compressors and material handling applications.”

Speaking of automotive, one can safely assume that industry has been among the greatest consumers of bearings—of all kinds. “The auto industry has driven the use of non-metal bearings in some of the largest volume applications,” says Clemensen. “Victrex’s PEEK material advantages in automotive applications include high resistance against aging and creeping at high operating temperatures and high circumferential speeds.”

At Igus, Miller adds that “The automotive industry has certainly contributed to the increased use of self-lubricating plastic bearings, as they are an ideal choice for this sector. They are lightweight, dryrunning, dirt and dust-resistant, maintenance-free and corrosion-resistant. Plastic bearings also deliver extremely quiet operation and eliminate vibration, which is a key concern for many operators. In many instances, plastic bearings are replacing metal roller bearings in axle journals and can be used in place of metal bearings in shock absorbers thanks to their low static and dynamic friction properties.