tapered roller bearings
Tapered roller bearings are rolling bearings capable of supporting both radial and axial loads. Their rolling elements are tapered rollers, and the raceways of the inner and outer rings are conical surfaces. They feature high load capacity, compact structure, and easy installation and adjustment. They are widely used in automotive rear axles, machine tool spindles, construction machinery, and steel rolling equipment. The structural characteristics of tapered roller bearings enable them to withstand both radial and large unidirectional axial loads. Furthermore, as the axial load increases, their radial load capacity also increases, making them an ideal choice for heavy-duty transmission systems.
The structure of a tapered roller bearing consists of an inner ring, outer ring, tapered rollers, and a cage. The structures and functions of these components work together to ensure the bearing’s performance. The inner ring, also known as the shaft ring, has an inner bore that fits tightly against the shaft and rotates with it. The outer surface of the inner ring is a tapered raceway, the raceway angle of which matches the cone angle of the rollers. The outer ring, also known as the seat ring, has an outer diameter that fits into the bearing seat bore and is usually stationary. The inner surface of the outer ring is a tapered raceway that, together with the inner ring raceway, forms a space for the rollers. The tapered rollers are truncated cones with a flat end face that contacts the inner ring’s rib to transmit axial forces. The rollers’ tapered surfaces contact the raceways of the inner and outer rings to transmit radial forces. The cage’s function is to evenly separate the rollers to prevent collision and friction. Cage materials are typically stamped steel, brass, or phenolic resin, and are selected based on the bearing’s operating environment and speed. The contact angle of tapered roller bearings (the angle between the raceway generatrix and the radial plane) is generally 10°-18°. The larger the contact angle, the greater the ability to withstand axial loads.
The material selection and heat treatment process for tapered roller bearings play a decisive role in their performance and life. High-carbon chromium bearing steel (such as GCr15 and GCr15SiMn) is typically used for the inner ring, outer ring, and rollers. This material offers high hardness, excellent wear resistance, and good contact fatigue strength. After quenching (oil quenching at 830-860°C) and low-temperature tempering (150-180°C), it can reach a hardness of 61-65 HRC. The core of the rollers maintains a slightly lower hardness (58-62 HRC) to ensure a certain level of toughness. For bearings operating in high-temperature environments (>120°C), heat-resistant bearing steel (such as Cr4Mo4V) is required, which maintains sufficient hardness and strength even at high temperatures. For corrosive environments, stainless steel (such as 9Cr18) is required and must undergo appropriate heat treatment. Material purity significantly impacts bearing life. The oxygen content in GCr15 steel must be kept below 15 ppm, and the inclusion level must not exceed level 2, otherwise premature fatigue failure may occur.
The manufacturing process for tapered roller bearings is complex, requiring multiple steps to ensure precision and performance. The inner and outer rings are processed as follows: forging the blank → spheroidizing annealing → turning → heat treatment (quenching and tempering) → grinding → superfinishing. The grinding process includes internal grinding, external grinding, raceway grinding, and rib grinding. The raceway roundness must be ≤0.005mm, the taper angle error ≤±30″, and the surface roughness Ra ≤0.1μm. Superfinishing can further reduce the surface roughness to Ra 0.025μm, improving contact accuracy. The rollers are processed as follows: cold heading → polishing → heat treatment → taper grinding → end face grinding → superfinishing. The rollers’ taper roundness error is ≤0.001mm, the taper angle error is ≤±10″, the surface roughness Ra ≤0.025μm, and the end face flatness is ≤0.001mm. Cage processing varies depending on the material. Stamped cages are produced using a blanking, punching, and forming process, while brass cages are produced by turning or die-casting. Bearing clearance must be adjusted during assembly by selecting spacers of varying thicknesses. Radial clearance is controlled within 0.01-0.05mm, and axial clearance is controlled within 0.03-0.1mm. Excessive or insufficient clearance can affect the bearing’s rotational accuracy and lifespan.
The installation, use, and maintenance of tapered roller bearings significantly impact their performance and lifespan and must be performed in strict accordance with specifications. During installation, pay attention to the bearing’s orientation. Tapered roller bearings are designed to withstand unidirectional forces, so the large end should face the direction of the axial force. Paired bearings should be installed face-to-face or back-to-back to withstand bidirectional axial forces. The inner ring typically has an interference fit (tolerances of M6 and K6) against the shaft, while the outer ring typically has a clearance fit (tolerances of H7) against the bearing housing. During installation, use a special tool (such as a sleeve) to strike the inner or outer ring, avoiding direct impact with the rollers and raceways to prevent damage. The operating temperature must be controlled during use. The maximum operating temperature of GCr15 bearings does not exceed 120°C. If the temperature exceeds this, heat-resistant bearings must be used. The lubrication method is selected according to the speed. Grease (such as lithium-based grease) is used in low-speed applications (speed <1000r/min), and lubricating oil (such as total loss system oil L-TSA46) is used in high-speed applications (speed >3000r/min). The amount of grease filled should be 1/3-1/2 of the internal space of the bearing. Too much grease will cause heat.
