Bearing
What Does it Take to Make a Bearing?
Bearings are what make the world go around. Without them, many modern machines could not exist. And without heat treatment, bearings could not do their job.
Bearings take a variety of forms for different types of jobs. They include air, babbit, ball, magnetic and roller. Did you know that the first practical caged roller bearing was invented in 1760? Caged ball and roller bearings prevent the bearing elements from rubbing against each other, which causes additional friction.
Steel developments in the 1800s transformed the manufacture and use of rolling-element bearings. Anti-friction rolling-element bearings are manufactured from two basic types of steels: through-hardened and case-carburized. Through-hardened components, as the name implies, have the same hardness all the way through the part. Case-carburized components, on the other hand, denote a hard surface but a softer interior. These bearings are typically case hardened by carburizing the surface followed by a conventional austenitize, quench and temper hardening process.
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So, what exactly does it take to make a bearing? To gain further insight, Industrial Heating asked expert Mike Schneider, FASM, The Timken Company. Here’s what he had to say.
“Bearings are, for many, an unseen, taken-for-granted item. It’s just part of the package you buy. In actuality, a bearing is a highly engineered product that needs to be matched to the performance requirements of the application. They also require a lot of attention, and a lot of work, for proper heat treatment. But a well-designed process will yield good, consistent results and reward you with a long-term relationship with bearing manufacturers.
“While the market offers polymer, ceramic and nonferrous bearings for a wide variety of industries, this article will focus solely on heat-treated steel bearings used in non-aerospace applications.”
Click on the links below to see what else Schneider has to say on bearing production.
Material Selection
The majority of bearing designs use steel and are classified as either bearing steels or case-carburized grades.
Melting
Steel cleanness is critical to the performance of most bearing applications, and literature has shown a direct relationship between how many inclusions are present in the steel and bearing life.
Material Conversion (Forging)
There are three mainstream material-conversion options: machining from tubing, machining from bar or machining from a forging.
Material Testing/Verification
At a minimum, the end user should carefully read their casting certificate from the steel provider to ensure all customer requirements are met.
Preparation for Heat Treatment
It is wise to visually inspect incoming bearing components for damage, especially on the raceways. Damage at this point will lead to “NCU,” or “no clean up,” at grind and a complaint from your customer.
Part Loading/Fixturing
As with gear manufacturers, distortion is a concern for bearing manufacturers. The loading arrangement and heating rate used has a significant effect on distortion in either through hardening or case carburizing.
Furnace Preparation
For through-hardening grades – whether a martensitic or bainitic structure is desired – decarburization, added carburization and intergranular oxidation (IGO) are not acceptable.
Process Performance and Success Metrics
Performance and success for through-hardened, high-carbon components as well as carburized or surface-treated components will be reviewed.
Part Cooling and Quenching
Distortion is very important to bearing races, and final dimensional results are critical to bearing performance.
Post-Process Verification
Hardness and microstructure testing are very important to verify the process. Of course, dimensional control is vital, and statistically based testing is a must.