Needle roller bearings utilize needle-shaped rollers as rolling elements for rotational motion. Compared to ball bearings, needle roller bearings have a lower profile height and higher load capacity. Most radial needle bearings can handle axial forces exceeding 5% of the radial load. The rollers in radial applications run parallel to the shaft. As mechanical components, needle roller bearings help save space, making the entire mechanism more compact. These bearings play crucial roles in various products such as automobiles, motorcycles, printing machines, industrial robots, and construction machinery.
AUBEARING manufactures various types of needle roller bearings:
Roller and Cage Assemblies The cage and roller assemblies are easy-to-operate bearings with high load capacity despite their small size. The unique cage structure guides the rollers, ensuring stable operation even at high speeds. The design of cage assemblies ensures proper load distribution between rollers and raceways and controls radial internal clearances. They also feature high-speed capabilities and tolerance to shaft misalignment or load deflection. Cage and roller assemblies reduce stress concentration at roller ends due to moderate misalignment or shaft bending, thus extending bearing life. Common applications include planetary gears in automobiles, gearboxes, and robot reducers.
Drawn Cup Needle Roller Bearings AUBEARING's Drawn cup needle roller bearings feature a cage and full complement of rollers with a unique outer ring structure. These easy-to-install bearings have the thinnest outer rings among all rolling bearings while offering high load capacity, high maximum speed limits, and excellent wear resistance. Carefully selected alloy steels withstand high maximum allowable loads, and surface-hardened cages help bearings endure harsh conditions. Drawn cup needle roller bearings with integral seals are available in certain sizes. Lip contact seals limit bearing operating temperatures to -25°F to +225°F (-30°C to +110°C) throughout the installed bearing clearance range. Stamped outer ring bearings are designed to retain grease or non-pressurized oil inside the bearing while preventing contaminants from entering the raceway area. Standard lip contact seals are compatible with common lubricating oils and petroleum-based fuels but are adversely affected by certain fire-resistant hydraulic oils and most common solvents. Drawn cup needle roller bearings are as easy to handle and install as loose roller bearings but come in an assembled form. The housing (used as the outer raceway) is precisely stamped from low-carbon steel and surface-hardened without subsequent machining, making these bearings cost-effective. Common applications include general gearbox shaft supports, pulley supports, gear pumps, and guide bearings.
Solid Needle Roller Bearings Solid needle roller bearings provide maximum load capacity and high precision in compact spaces. These bearings are suitable for various operating conditions, with rings made from carefully selected vacuum-degassed bearing steels or carburizing steels, and rollers precision ground and heat-treated. Lightweight and extremely robust cages accurately guide rollers smoothly. High-quality materials offer high rigidity capable of withstanding heavy loads and impact loads. These bearings are available with or without inner rings; the type without inner rings uses the shaft directly as the rolling surface.
Spherical Needle Roller Bearings Spherical needle roller bearings have an outer raceway separated from the outer ring, which acts as a sleeve. The raceway features a concave external profile fitted with plastic rings. This allows needle roller bearings to compensate for minimal static misalignment of the shaft.
Needle Roller Bearings with Machined Rings Needle roller bearings with machined rings are used for applications requiring higher load capacity. They mainly come in two types: needle roller bearings without an inner ring and those with an inner ring. Bearings without an inner ring are used with hardened and ground shafts, allowing for larger shafts to provide higher rigidity. Bearings with an inner ring are used in applications where hardening and grinding of the shaft are not feasible or practical.
Needle Thrust Bearings Needle thrust bearings use roller and cage assemblies with surface-hardened cages made from two precisely pressed steel plates. The rollers are securely held in the cage, ensuring smooth rotation even under large axial loads. These bearings are compact, making them easy to replace within the same installation space as traditional thrust washers. Various configurations are available, including standalone units, integrated roller units, or units with different roller thicknesses to match installation conditions around the bearing. These components are designed to bear axial loads in limited spaces, using hardened steel cages to accommodate needle rollers. Despite typically occupying less space than conventional thrust washers, needle thrust bearings offer excellent friction characteristics and higher load capacity. Different thicknesses of individually hardened thrust washers are available if adjacent surfaces cannot be hardened to a suitable hardness level of 58 Rc or equivalent. Thrust needle and cage assemblies can withstand high speeds and axial loads. They are widely used in automatic transmissions, providing low friction in confined spaces.
To achieve desired bearing performance, selecting the appropriate needle roller bearings is just the beginning. Several specific factors affect bearing operation, including lubrication, hardness, and surface finish of the raceways, as well as bearing seats.
Lubrication: Oil lubrication is generally preferred, providing higher speeds by acting as a coolant, removing contaminants, and easier injection into the bearing load area. The best methods include positive feed, oil splash, or oil mist. Bearings may use grease lubrication when necessary. Bearings with cages typically have larger grease reservoirs, offering longer pre-lubrication life in situations where re-lubrication is not possible. Bearing life in such applications depends on grease life, which must be considered in life calculations. Seals help retain lubricants and exclude contaminants.
Raceway Surfaces: Good bearing performance depends on the material and geometric characteristics of the raceways.
Hardness: A key advantage of needle roller bearings is their ability to use mating surfaces as inner or outer rings, or both. Bearing rated loads are typically based on raceway hardness of 58 Rc or equivalent. If lower, the load-carrying capacity of the bearing-raceway combination decreases. Surface hardening, induction hardening, and through-hardening are acceptable treatments. If the shaft cannot be hardened to 58 Rc, separate inner rings are used. They are positioned on the shaft using shoulders or retaining rings.
Surface Finish: Excellent raceway surface finish is crucial for maintaining a good lubrication film between rollers and raceways. Rough surfaces allow high points to penetrate the lubrication film, leading to quicker fatigue and eventual seizure. Inner raceway finish should not exceed a Ra grade of 16 minutes, but better micro-finishing greatly extends service life. For full complement needle or roller and cage assemblies, an outer raceway finish less than 16 minutes provides optimal results. Ensure raceway surfaces are free of scratches and defects.
Geometric Shape: The ideal raceway surface for radial needle roller bearings is a perfect cylinder. Any deviation increases noise levels and shortens bearing life. Therefore, roundness of shafts and bearing seats should be maintained within half the recommended manufacturing tolerances or 0.0003 inches, whichever is smaller. Raceway taper causes increased roller stress and reduced bearing fatigue life. Perhaps more detrimental is raceway geometry causing uneven roller contact, such as uneven contact due to surface straightness or defects. Additionally, rollers should not hang over raceway surfaces. This can lead to stress concentration and early failure. Generally, for full complement bearings, the tilt of the shaft relative to the bearing centerline should not exceed 0.0010 inches per inch; for cage bearings, the tilt of the shaft relative to the bearing centerline should not exceed 0.0015 inches per inch. Shorter bearings can better withstand tilt.
Bearing Seats: Successful operation of drawn cup needle roller bearings requires correct installation to ensure proper outer shell size and roundness. Typically, simply pressing the bearing into place using basic tools and hand presses is sufficient. Axial positioning features are usually unnecessary. If the shell is made of steel or high-quality iron, its section may be small enough to be 11/2 to 2 times the bearing section. For light alloy shells, a similar section may suffice, but selecting appropriately smaller shell hole sizes is critical for correct bearing sizing and roundness. Heavy-duty needle roller bearings are installed in bearing seats with clearance fits if the load is stationary relative to the bearing seat; if the load rotates relative to the bearing seat, they are installed with a tight transitional fit. Regardless of the fit, use bearing seat shoulders and retaining rings or other positive axial positioning methods to secure the outer ring.
Bearing Materials - Bearing Cages separate rollers to evenly distribute loads around the bearing. They also reduce bearing noise, improve rolling conditions, and prevent slippage. Additionally, they contain rollers within a single component. Steel is the most common cage material in needle roller bearings. Plastic cages can be used where operating conditions allow. Lubrication and surface treatments reduce heat generated by friction. Some drawn cup needle roller bearing designs omit cages, containing a full complement of rollers. Full complement bearings combine maximum load capacity with the cost efficiency of drawn cup bearings. In this design, inward-turning lips retain rollers within the bearing rings. Tests have determined the following friction coefficients for caged and full complement needle roller bearing designs: Caged needle roller bearings: 15•10-4; Full complement needle roller bearings: 25•10-4.
Seals. Seals (if present) isolate rollers, cages, and lubricants from contaminants and moisture in harsh environments. Seals must withstand oxidation, high temperatures, and chemicals that bearings may encounter. Sealed bearings typically feature an inner ring inspection hole on the outer ring for relubrication. Seals are most effective when friction between the seal and bearing or shaft is minimized. Additional surface treatments or lubrication can reduce this friction. Bearings with integral seals operate at relatively lower speeds compared to open bearings. Seals are commonly made from acrylonitrile-butadiene rubber, polyurethane, or fluoroelastomer.
