In certain industrial applications, standard bearings just don't cut it when it comes to delivering the precise performance required. That's where ultra-precision bearings step in. These bearings are designed to deliver exceptional accuracy and precision, making them perfect for demanding applications that require high-speed operation and pinpoint guidance. There are two main types of ultra-precision bearings: deep groove bearings and angular contact bearings.
Deep groove bearings feature full shoulders on both sides of the inner and outer raceways, which makes it easy to add seals or shields. These bearings can handle radial loads, thrust loads, or a mix of both. They’re available in numerous sizes, including miniature precision versions, and come with various cage options. Extremely versatile, deep groove bearings are among the most commonly used bearing types.
Angular contact bearings, on the other hand, have one full ring shoulder while the other ring shoulder is either partially or fully removed. This design allows for larger balls, offering greater load capacity and speed potential. Different cage designs are also available to cater to high-speed requirements. Angular contact bearings can support thrust loads or a combination of thrust and radial loads, but they cannot handle radial loads alone. When installed back-to-back or face-to-face, they can manage thrust loads in both directions.
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Angular contact bearings come in two varieties: separable or non-separable. These terms refer to whether the outer ring assembly can be detached from the inner ring. Separable angular contact bearings are particularly beneficial when installing in blind holes or in applications that require press fits.
When it comes to closures and cages for ultra-precision bearings, these components are crucial for protecting against internal damage during handling. Ultra-precision bearings often use closures made from high-performance materials like Teflon or stainless steel. There are two primary types of closures: shields and seals. Both are designed to prevent contamination and retain lubrication.
Shields are attached to the inner ring, while seals are fitted to the outer ring. Choosing between these depends on the priorities of your application—whether sealing efficiency, speed capability, or bearing torque is more important. Shields offer lower sealing efficiency but do not increase bearing torque or limit speeds. Seals provide stronger protection but restrict operating speed and increase torque and temperature.
Most bearing assemblies incorporate cages to ensure uniform ball spacing, reduce torque, and minimize heat buildup. Cages are available in various designs for both deep groove and angular bearings. Selection of the cage is typically based on the specific needs and purpose of the bearing.
Standard precision bearings usually use stamped steel cages. Ultra-precision bearings, however, employ cages made from materials such as stainless steel, bronze, or phenolic. These materials offer higher speeds and better loading capabilities. Cages can also be chosen to meet specialized requirements like low torque, high speed, lubrication-free operation, and reduced noise levels.
All precision ball bearings must adhere to Annular Bearing Engineers Committee (ABEC) standards, which align with ISO specifications. ABEC standards establish tolerances for critical bearing characteristics and dimensions, ensuring consistency within the industry.
The parameters covered by these guidelines include bore roundness and taper, width variation, bore and race runout, and radial runout. Higher ABEC numbers signify tighter tolerances—the higher the number, the better the bearing performs. ABEC 1 through 3 bearings are typically suited for general use, whereas ABEC 5 through 7 bearings are used for applications demanding higher precision and speed. Bearings from higher ABEC classes, intended for stationary housings, boast rounder balls and smoother raceways.
However, customers shouldn't automatically opt for the highest ABEC ratings. Higher-end bearings can be significantly more expensive, costing three to five times more than lower-end bearings. It’s essential to understand the specific needs of your application to make the right choice. Often, higher ABEC bearings aren't necessary.
To ensure optimal performance of ultra-precision bearings, users must set up their systems correctly. Two critical factors to consider are preloading and radial internal clearance. Users should carefully assess these elements to guarantee efficient operation under favorable conditions.
The bearings must have the appropriate radial internal clearance—the total maximum movement possible for the inner ring relative to the outer ring. This is also called "radial play." Proper radial internal clearance is vital because metals expand over time. Selecting the right clearance prevents metal ball bearings from seizing in their housings when expansion occurs. Bearings lacking sufficient radial play will fail due to interference and binding.
Preloading, conversely, involves removing internal clearance in a bearing. By applying a permanent thrust load, radial and axial play are eliminated, creating a very rigid setup. Preloading removes endplay and runout. This can be achieved through spring preloading, axial adjustment, or the use of duplex bearings.
Duplex bearings are matched pairs of bearings designed to provide built-in preloading. At installation, they are clamped together in face-to-face (DB), back-to-back (DF), or tandem (DT) configurations. Since each bearing has a matching preload offset, they counterbalance each other, enhancing axial and radial rigidity and enabling them to withstand bidirectional or heavy unidirectional thrust loads.
Shaft and housing fits are also important considerations when using ultra-precision bearings. Users should evaluate the bearing’s intended application before deciding on the appropriate fit tightness. Looser fits are necessary when axial movement must accommodate spring loading and thermal expansion or when axial clamping forces are involved. Assembly is simpler with looser fits. Tighter fits are ideal when the application requires heat transfer, vibration dampening, or support for heavy radial loading.
Lastly, users should determine whether ultra-precision bearings will perform better with grease or oil lubrication. Grease is the standard choice in most scenarios. However, oil should be considered for high-speed applications as it provides superior cooling and generates minimal torque. Oil must be replaced more frequently than grease, which lasts longer without maintenance.
Ultra-precision Bearings from Emerson Bearing
Emerson Bearing proudly serves as a leading distributor for many renowned bearing manufacturers. We offer ultra-precision bearings from top brands such as Barden, GMN, Nachi, NTN, and NSK.
Our team of experts can assist you in finding the right bearing for your specific application and requirements. We can help evaluate the various factors discussed above, including navigating ABEC standards, to equip you with the knowledge needed to avoid costly mistakes and downtime.
Contact us today to begin the bearing selection process.
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