By Joyce Laird, contributing editor
Why are thin section ball bearings needed?
Thin Section Ball Bearings were developed to solve problems where standard deep groove ball bearings are not suitable. John A. Wallace, Vice President of Operations, AST Bearings LLC says that typical applications are those where there are space limitations, concerns with weight, and the loading and torque requirements still require the use of a ball bearing. “There are various definitions used in the industry and one of the more common is when the bore diameter is more than 4 times greater than the radial cross section, the bearing is considered a thin section. Cross-sectional size can vary, but it is typically two times the ball diameter.”
“Thin sections are available in a variety of configurations: radial, angular contact, 4 point contact, full complement, duplex pairs, and different cross sections,” Wallace adds. “The selection of a particular configuration is generally driven by the type and magnitude of loading required in the application.”
How do you select the best thin section bearings for an application?
Wallace says that although a typical bearing selection process can be used with thin section bearings, normally the space requirements will drive a designer to look at options within the family of thin section bearings. “Next, the loading and operational conditions will dictate the type of thin section ball bearing that is most suitable, i.e. radial, angular contact, duplex pair, 4 point contact etc. After considering the maximum static and dynamic loads, the desired bearing life, and catalog data – for size, speed and load ratings, the final type, size, and bearing arrangement can be selected.”
“Of course other application inputs must be considered. These include operating environment, rotational performance, mounting conditions, and temperature in order to determine the bearing specifications. Precision level, clearance, lubricant, and type of closure (shields or seals) also form a large part of specifying the correct bearing.”
Importance of understanding thin section bearing types
Once the application specifics such as space, load and other operating conditions are determined, the next thing to consider is the type of thin section bearing to use.
“Radial type bearings are used when loading is predominantly in the radial direction,” Wallace says. “They can also support limited axial and reversing loads. For this type, often, the best choice is available from standard series of bearings.”
“Angular contact types are used when there are higher thrust and axial loads,” he adds. “These types of bearings when used as duplexed pairs (matched sets), provide for increased load capacity and stiffness, as well as high rotational accuracy.”
Moving on to 4-point contact bearings, these have a unique raceway design that allows one bearing to handle radial, thrust, and over-turning moment loads. “Viewing the cross section, the raceway has the shape of a gothic arch instead of a true radius,” Wallace explains. “This arch creates 4 points of contact with the balls and raceway. Designers have the option of choosing a one 4 point contact bearing arrangement instead of two angular contact bearings. This saves on space and weight.”
Wallace notes that many thin section ball bearing applications have functional requirements which allow for their use within “instruments” in the broadest sense of the word. “These applications generally have demanding requirements with respect to rotational accuracy, repeatability, and torque. The tolerances of instrument bearings are generally equal to ABEC 5, or 5T, or better.”
“Thin section bearings are commonly available in both 52100 chrome steel as well as martensitic stainless steel for use if corrosion is of concern. Different sealing options are available that provide protection from contaminants. Various precision classes are available up to ABEC 5T, or 7F. Different ball separators are available that can be selected for non-standard operating conditions. All of these things must come into consideration when specifying.”
“Precision thin section ball bearings should be assembled at a clean work station. Tools and mating components should also be clean and free of burrs, dirt, chips, etc.,” Wallace says. “It’s a good practice to keep bearings in their original factory packaging until they are to be installed.”
“Great care must be taken with interference fits to avoid damaging the bearing. Thermal fitting can be used to minimize installation forces. Press tools should contact the ring that is being pressed for 360 degrees. Never transmit forces thru the balls to the rings. Push on the face of the ring that has the interference fit. Finally, always observe the match marks when mounting duplex bearings to ensure proper orientation.”
Wallace says that these bearings are used in many industries including aerospace, medical imaging, robotics, semiconductor, data storage, machine tools, packaging equipment, covering many different applications. Some interesting and diverse applications include:
Thin section ball bearings are often used where wiring or tubing is passing thru the bore in a hollow shaft or other arrangement.
Thin section ball bearings are also used in mechanisms such as Gimbal platforms, used in optical and targeting systems on ships and aircraft. Gimbals are also used in radar and satellite communications equipment, land, sea, and air-based.
Thin section ball bearings also find excellent applications in all types of work holding devices such as turntables, indexing and rotary tables.
They are also the perfect solution for smooth action in articulating parts such as in the elbows of robotics arms or other articulating joints.
Thin section ball bearings were developed for applications where space limitations are of the utmost importance. As the name implies, the difference between the inside and outside diameters of the rings has been minimized or thinned out. This requires the use of smaller balls due to the reduced cross section. “Of course this comes at a price by compromising load capacities. However, these bearings can still accommodate moderate radial thrust or combined loads”, Wallace says.
“Because there are so many important issues to consider when specifying any particular type of thin section bearing, it pays to discuss the application with your bearing supplier to ensure the correct match for a perfect application fit,” Wallace concludes.