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 or 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 2-3 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.
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Ceramic hybrid bearings, the most common type of ceramic bearing, are constructed of steel inner and outer rings with ceramic (typically Si3N4) balls in place of steel. Common types of ceramic bearings are angular contact and conrad.
Cylindrical Roller Bearings
Cylindrical roller bearings have high radial-load capacity and moderate thrust loads. They contain rollers which are cylindrically-shaped, but crowned or end-relieved to reduce stress concentrations.
Slewing Rings and Turntable Bearings
Slewing rings and turntable bearings can accommodate axial, radial and moment loads. They are not mounted in a housing or on a shaft, but are instead mounted directly to a seating surface via mounting holes.
Spherical Roller Bearings
Spherical roller bearings are self-aligning bearings ideal for heavy-duty radial and axial loads. They utilize dual roller rows between a concave outer raceway and convex inner raceway to accommodate shaft deflection.
Super Precision and Spindle Bearings
Super precision and spindle bearings are high-precision bearings that are designed for use in machine-tool spindles and other precision applications. Most super precision bearings and spindle bearings carry a high quality-rating such as ABEC-7 or ABEC-9, and run coolly and smoothly at high speeds.
Tapered Roller Bearings
Tapered roller bearings use rollers with different-sized diameters on each end. The rollers and accompanying bearing components can accomodate axial and radial loads.
Thrust bearings are designed for pure thrust loads, and can handle little or no radial load. The rolling element in a thrust bearing can be a ball, needle or roller.