Ball Screw Support Bearings Information
Ball screw support bearings are specially designed for use in ball screw or lead screw applications. Most ball screw support bearings are angular contact bearings with a steep contact angle, such as 60°, and are available in duplex, triplex, and quadruplex configurations. Other designs include bearings containing separate thrust and radial roller bearings in a single assembly. Cartridge designs are also available that include a housing, seals, and bearings.
The most important parameters to consider when specifying ball screw support bearings are the dimensions. These include bore, bearing, or housing outside diameter, outer ring width, and overall width. The bearing industry uses a standard number system for bearings with metric diameter bores. For bore sizes 04 and up, multiply by 5 to obtain the bore in millimeters. If the bore is a hex, this refers to the dimension across the flats. If the bore is tapered, this refers to the smaller diameter. The outside diameter of the bearing includes the housing if a housed unit, but excludes the flange if a flanged bearing. The outer ring width is the overall width of the outside of the bearing. The overall width of the bearing or bearing assembly includes the locking collar, if present.
Choices for ball screw support bearings include:
- one directional thrust bearing
- duplex set
- triplex set
- quadruplex set
A one directional thrust bearing is a one single directional thrust angular contact style bearing. Tolerates some misalignment. Same radial load as deep-groove bearings, but two to three times the thrust load. A duplex set is two matched bearings for use in ball screw support applications. A triplex set is three, matched bearings for use in ball screw support applications. A quadruplex set is four matched bearings for use in ball screw support applications. Some ball screw support bearings are pre-assembled in a flanged cartridge unit. The cartridge typically consists of a housing with boltholes parallel to the bearing axis, bearings, and seals. Ball screw support bearings can be preassembled in a block or pillow block unit. The bearing assembly has a mounting surface perpendicular to the bearing axis and is assembled via predrilled boltholes. The pillow block assembly typically includes seals. Combined needle roller bearings combine needle roller radial bearings with a ball or roller thrust bearing. These bearings can be used for combined radial and axial loading applications.
Special materials and plating options for ball screw support bearings include stainless steel, ceramic hybrid, and plating. Stainless steel is chemical and corrosion resistant and can have relatively high-pressure ratings. A ceramic hybrid bearing is constructed of steel inner and outer rings with ceramic (typically Si3N4) balls in place of steel. These bearings have several advantages over all steel bearings, such as higher speed and acceleration capability, increased stiffness, higher accuracy, lower friction and heat generation, reduced lubrication requirements, low thermal expansion, extended operating life. Bearings containing all ceramic balls are also nonconductive and are commonly used in electric motor applications. Common plating materials are cadmium and chrome.