By Tom Miller, Bearings Unit Manager, igus North America
Steel, ceramic, or plastic—which material is the best for your application? Here are several tips to narrow your choice
Ball bearing components are available in different types of materials, each with its own set of features and benefits. Thus, weighing the pros and cons of a specific kind of ball bearing is an important part of the design process.
The three main types of ball bearings are steel, ceramic and plastic. While every ball bearing is comprised of four main parts—an outer race, an inner race, a cage and balls—each has its own set of characteristics and benefits.
Steel Ball Bearings
Partly because they are an older technology, steel ball bearings are a trusted component for use in many designs. Typically, these bearings are comprised of all-steel parts, but they are available with different types of steel races and balls, or with a phenolic cage.
Steel ball bearings suit robust applications handling extremely high loads and fast rotations per minute (rpm) and some feature a radial load capacity of up to 30,000 pounds. Another advantage is that steel ball bearings tend to be more precise due to the clearance that can be achieved.
However, steel ball bearings do have some disadvantages. They are heavy, noisy and, depending on the grade of steel, lack chemical resistance. They require constant lubrication, which means time and cost spent on maintenance. Steel is also susceptible to corrosion in humid or wet environments. Furthermore, in medical applications, its magnetic properties can cause problems.
In addition, there are such a high number of steel ball bearing manufacturers that prices can vary greatly, ranging from inexpensive to extremely costly. This could be perceived as an advantage or disadvantage but, either way, the options can be overwhelming at times.
Ceramic Ball Bearings
The most common type of ceramic ball bearing is often considered a hybrid, which indicates the outer race, inner race, and cage of the bearing is comprised of steel, while the balls are made from ceramic. The ceramic material enables the bearing to run faster while maintaining a cooler operating temperature and simultaneously reducing noise and vibration.
Ceramic ball bearings tend to be more corrosion resistant, more rigid and lighter weight than most steel ball bearings. Lower coefficients and higher speeds are also possible and, since they are nonconductive, ceramic ball bearings can be used in electrical applications. In addition, most ceramic balls bearings can operate in temperatures up to 1,800° F.
With these advantages, ceramic ball bearings are an attractive option. However, these types of bearings are expensive, which is a strong argument in itself for seeking out an alternative, such as plastic ball bearings.
Plastic ball bearings
While plastic ball bearings are a newer technology, they have advantages that are not offered by steel or ceramic ball bearings. Plastic ball bearings are comprised of all-plastic races and a plastic cage and are typically available with a choice of three different types of balls: plastic, glass, or stainless steel. The choice of material is often dependent on the environment in which the bearing will be used.
Plastic balls are best for applications where weight and noise are most critical, while glass balls boast less magnetic properties than 316 stainless steel balls. Glass balls are ideal when a metal-free option is needed. And, compared to stainless steel balls, they still offer a significant weight advantage.
Whatever configuration, plastic ball bearings suit applications with normal to high speeds and have a number of attractive features. Thanks to their plastic construction, plastic ball bearings are self-lubricating, corrosion resistant and are quiet in operation. Another advantage is that they are lightweight: while a ceramic ball bearing weighs about one third of its steel counterpart, a polymer ball weighs the least out of all three types.
However, there are instances where plastic ball bearings should not be used, including applications with high loads or long-term temperatures exceeding 300° F.
Every manufacturer offers its own versions of ball bearings with varying features. A manufacturer of steel ball bearings, for example, often offers its products in a number of different types of steel, including a 300 series (soft stainless), a 400 series, or chrome steel.
Plastic bearings are available in different materials too. For example, the line of xiros® plastic ball bearings from igus® comes in three different thermoplastic race materials:
• A500 for extreme chemical resistance and temperatures reaching 302° F
• B180 for high wear resistance and temperatures up to 176° F
• C160, which can also be used in chemical-exposed applications, but where the temperature remains 176° F or lower.