Double row tapered roller bearings
Double-row tapered roller bearings are rolling bearings capable of supporting both radial and bidirectional axial loads. Their structural characteristics include two rows of tapered rollers and a shared inner or outer ring. The rollers maintain linear contact with the raceway, resulting in a significantly higher load capacity than ball bearings. They are widely used in heavy-duty applications such as automotive axles, construction machinery, and machine tool spindles. Compared to single-row tapered roller bearings, the double-row design improves bearing rigidity and rotational accuracy by adjusting clearance or preload, while simplifying the shafting structure and reducing installation space. Consequently, they are widely adopted in equipment requiring high load capacity and stability.
Double-row tapered roller bearings consist of an inner ring, outer ring, tapered rollers, a cage, and seals (on select models). The design and material selection of each component directly impact bearing performance. The inner and outer rings are typically made of high-carbon chromium bearing steel (such as GCr15), achieving a hardness of 60-65 HRC after quenching and tempering to ensure sufficient strength and wear resistance. The tapered rollers are made of the same material, with a surface super-finished to a roughness of Ra ≤ 0.08μm to reduce rolling friction. The cage is typically a stamped steel cage or solid brass cage. Stamped cages are low-cost and lightweight, suitable for low- and medium-speed applications, while solid cages offer superior strength and rigidity, making them suitable for high-speed and heavy-load applications. Some bearings feature dust covers or seals to prevent lubricant leakage and contaminant intrusion, extending bearing life. Seals are typically made of nitrile rubber or fluororubber, with a temperature range of -40°C to 120°C, meeting most operating requirements.
Double-row tapered roller bearings come in a variety of structural types. Based on the inner and outer ring configuration, they can be categorized as symmetrical or asymmetrical. Symmetrical bearings feature identical roller taper angles in both rows, ensuring even load distribution and suitable for symmetrical loads. Asymmetric bearings feature different roller taper angles in both rows, allowing them to withstand axial loads in different directions and are suitable for applications with unbalanced axial forces. Based on mounting method, they can be categorized as separable or inseparable. Separable bearings feature separate inner and outer rings for easier shaft assembly and adjustment. Inseparable bearings feature inner and outer rings connected by a cage and require installation as a single unit within the shaft. Common model series include the 35000 (double-row face-to-face) and 36000 (double-row back-to-back). Different bearing models feature varying contact angles (typically ranging from 10° to 30°). A larger contact angle indicates a greater ability to withstand axial loads.
The performance parameters of double-row tapered roller bearings primarily include dynamic load rating, static load rating, limiting speed, and clearance. These parameters are crucial for bearing selection. The dynamic load rating refers to the maximum load a bearing can withstand during its rated life (typically 106 revolutions). The dynamic load rating of a symmetrical double-row bearing is approximately 1.6-1.8 times that of a single-row bearing of the same size. The static load rating refers to the maximum load a bearing can withstand at rest or at low speed, typically 1.5-2.5 times the dynamic load rating. The limiting speed is affected by the cage type, lubrication method, and cooling conditions. The limiting speed of bearings with stamped cages is 10%-20% higher than that of bearings with solid cages, and can be increased by over 30% when using oil mist lubrication. Clearance is divided into radial and axial play. Excessive clearance will increase bearing vibration and noise, while insufficient clearance will increase heat generation and wear. During installation, the clearance should be adjusted using axial preload according to the operating conditions. The typical operating clearance is 0.01-0.05mm.
The installation, lubrication, and maintenance of double-row tapered roller bearings are crucial to their service life. During installation, use a specialized tool (such as a sleeve) to apply even pressure and avoid directly striking the inner or outer rings to prevent damage to the rolling elements and raceways. For separable bearings, first assemble the inner ring to the shaft, then the outer ring to the housing, and finally adjust the axial clearance. Grease and oil lubrication are available. Grease lubrication is suitable for low speeds (≤3000 rpm) and uses lithium-based grease or polyurea grease, filling 1/3-1/2 of the bearing’s internal space. Oil lubrication is suitable for high-speed applications and uses a lubricant with a viscosity grade of ISO VG32-100, supplied via splash lubrication or forced lubrication. During maintenance, regularly check bearing temperature, vibration, and noise. The normal operating temperature should be below 70°C. An abnormally high temperature may indicate insufficient clearance or poor lubrication. Lubricant should be replenished or replaced every 1000-2000 hours of operation to prevent aging and failure. Through proper installation, lubrication and maintenance, the service life of double row tapered roller bearings can reach more than 10,000 hours, giving full play to their advantages of high load capacity and high reliability.
