What is Double Row Ball Slewing Bearing?

What is Double Row Ball Slewing Bearing?

A double row ball slewing bearing has three raceways. Steel balls and spacers can be directly arranged into the upper and lower raceways. Based on the load conditions, two rows of steel balls with different diameters are arranged. This open assembly is highly convenient, with both the upper and lower arc raceways having a load-bearing angle of 90°, enabling them to withstand significant axial forces and overturning moments. When the radial force exceeds 0.1 times the axial force, the raceways require special design. Double row ball slewing bearings have relatively large axial and radial dimensions and a compact structure. They are particularly suitable for medium-to-large diameter applications such as tower cranes, truck cranes, and other material-handling machinery.

Double ball bearings are considered high-end bearings. These bearings contain multiple small steel balls arranged around the shaft. When the fan blade or shaft rotates, the balls rotate accordingly. Since they are spherical, friction is reduced, and there is no risk of oil leakage.

The advantages of double ball bearings include a long lifespan (approximately 50,000–100,000 hours) and excellent anti-aging performance, making them suitable for high-speed fans. The disadvantages are higher manufacturing costs and higher noise levels at equivalent rotational speeds (due to doubled friction points).

Double ball bearings are fully embedded within the fan, with no direct contact between the rotating parts and the external environment. In a sealed environment, the bearing’s operating conditions remain stable. Therefore, large fans operating at 5,000 RPM typically use double ball bearings. In contrast, hydraulic bearings feature a unique recirculating oil path, which minimizes the likelihood of lubricant leakage.

Composition of Double-Row Ball Slewing Bearings

Inner and outer rings

An annular structure made of high-strength steel, with an inner ring usually fixed to a rotating shaft and an outer ring connected to a fixed base. The raceways are machined on the contact surface of the inner and outer rings to provide a rolling path for the balls.

Two rows of balls

Two rows of balls symmetrically distributed between the inner and outer rings, mostly made of high-quality steel or ceramic. Simultaneous rayal and axial loads and torques are accommodated through multi-point contact, significantly increasing load-bearing capacity.

Cage (Isolation Block)

It is used to fix the position of the balls, ensure that they are evenly distributed and avoid collisions with each other. Materials include metal, plastic, or fibers to optimize the stability of the ball movement.

Sealing device

Typically constructed of rubber or metal seals, mounted on the edge of the bearing, it prevents the ingress of dust and impurities and maintains internal lubrication.

Lubrication system

Grease/oil fills through the oil injection hole or integrated oil circuit to reduce friction and dissipate heat for performance at high rotational speeds.

Special Design Supplements:

Some double-row structures adopt split inner rings (such as double inner ring riveting design), which compensates for installation errors through loose mating and riveting mechanisms to enhance structural adaptability. In addition, spacers can be used to adjust the axial spacing of the two rows of balls to optimize the load distribution.

Principle of Double-Row Ball Slewing Bearings

The principle of double-row ball slewing bearings is based on the synergy of double row balls, and the core mechanism is as follows:

Load distribution: Two rows of balls are symmetrically distributed in the inner and outer ring raceways, bearing radial and axial loads and torques at the same time, and evenly distributing the load through multi-point contact to reduce the pressure of single balls.

Rolling friction optimization: The ball rolls between the raceways, the friction coefficient is significantly lower than the sliding friction, and the lubrication design reduces energy loss and ensures the stability of high-speed rotation.

Enhanced rigidity: The double-row structure increases the number of contact points, improves the radial and axial rigidity, suppresses deformation, and adapts to the needs of high precision.

Torque resistance: The double-row layout strengthens the anti-overturning moment performance, which is suitable for slewing motion scenarios that need to transmit large torque.

Through the dynamic balance of double-row balls, the synergistic optimization of high load-bearing, low friction and structural stability is realized to meet the needs of precision slewing support under complex working conditions.

Features of Double-Row Ball Slewing Bearings

The characteristics of double-row ball slewing bearings can be summarized into the following six core dimensions, and through the collaborative innovation of structural design and material technology, high-performance support under complex working conditions can be realized:

Three-dimensional load carrying capacity

The double-row balls are symmetrically distributed in the inner and outer ring raceways, which can bear the radial load (perpendicular to the axis of rotation), axial load (parallel to the axis of rotation) and overturning moment (torque) at the same time, forming a three-dimensional mechanical balance. For example, in the case of high torque transmission on a crane rotating platform, the double-row structure distributes the load to more contact points through the synergy of two rows of balls, reducing the pressure of the single beads by about 40%. This design significantly increases the overall load carrying capacity of the bearing, making it suitable for heavy machinery that requires multi-directional force support.

Torque resistance and stiffness strengthening

The cross-arrangement of the double-row balls significantly improves the overturning moment resistance. Taking wind yaw bearings as an example, the double-row design can improve the torque resistance by 2-3 times compared with single-row bearings, ensuring stable rotation under strong wind impacts. At the same time, the double-row structure improves the radial and axial rigidity of the bearing and reduces the deformation by increasing the number of contact points, and is suitable for equipment that requires high precision (such as machine tool spindles), and its radial runout can be controlled within 0.002mm.

Low friction and efficient transmission

The rolling friction of the balls on the raceway is significantly lower than the sliding friction, and with grease or oil lubrication, the coefficient of friction can be reduced to 0.001-0.003, which is close to the state of fluid lubrication. For example, the spindle bearings of high-speed machine tools use phenolic cages, which reduce noise and frictional losses, and support high-speed rotation above 20,000 rpm. This low-friction characteristic not only reduces energy loss, but also effectively dissipates heat and ensures the stability of the bearing at high speeds.

Compact structure and long life

The double-row ball design achieves high load-bearing capacity in confined spaces and is compact, making it suitable for space-constrained applications such as industrial robot joints. At the same time, by optimizing load distribution and material selection, such as silicon nitride ceramic balls, the fatigue life of the bearings can be extended by up to 2-3 times that of conventional single row bearings. For example, double-row ball slewing bearings for EPBs can reach a mileage of more than 10 km.

Sealing and lubrication systems

Rubber or metal seals are usually installed on the edges of the bearings to form a multi-level seal protection against the ingress of dust and impurities and to maintain internal lubrication. For example, mining machinery uses contact rubber seals in combination with metal dust caps, while high-speed rotating equipment, such as industrial robots, uses labyrinth seals to reduce lubricant leakage. In addition, some bearings integrate intelligent lubrication technologies, such as an oil-air lubrication system, which can precisely control the amount of lubricating oil and reduce power consumption by 50%.

Materials & Finishes

The inner ring, outer ring and ball of the bearing are mostly made of high-strength steel (such as GCr15), which has a hardness of HRC60-65 and a compressive strength of more than 2000MPa after quenching and tempering treatment. Ceramic balls, such as silicon nitride, are suitable for high-temperature, lightweight applications, with a density of only 40% of steel and a low coefficient of thermal expansion. Surface treatment processes (e.g., carburizing, quenching, superfinishing) further improve raceway hardness and finish, increase contact fatigue life by more than 3 times, and raceway roughness Ra≤0.04μm.

Summary: Double-row ball slewing bearings balance high load carrying capacity, rigidity and rotational flexibility through the synergistic effect of double row balls, and are key mechanical components to cope with complex loads and precision rotation needs. Its characteristics are mainly reflected in three-dimensional load bearing, torque strengthening, low friction and efficient transmission, compact structure and long life, multi-stage sealing lubrication and material surface optimization, which are widely used in heavy machinery, wind power, industrial robots and other fields.

Applications of Double-Row Ball Slewing Bearings

Construction machinery

Rotating support for large equipment such as cranes, excavators, and shield machines can withstand high loads and overturning moments to ensure stable operation.

Energy equipment

Wind power yaw system and photovoltaic tracking bracket can adapt to the needs of complex loads and high-precision angle adjustment, and improve power generation efficiency.

Industrial automation

Robot joints and precision turntables can achieve high-speed rotation and nano-level positioning to ensure the stability of intelligent manufacturing equipment.

Transportation

The drive motor and train steering system of new energy vehicles reduce energy consumption and extend the transmission life through low-friction design.

Special equipment

Medical CT equipment, aerospace equipment, provide high-reliability support in extreme environments, and meet the needs of precision positioning.

Core advantages: three-dimensional load bearing, torsional strengthening, compact structure and long life, suitable for multi-directional force complex working conditions.

Maintenance & Troubleshooting

Maintenance and Fault Diagnosis of Double-Row Ball Slewing BearingsThe maintenance of double-row ball slewing bearings needs to follow a systematic process to ensure their performance and life.

Lubrication management is the key link: choose lithium grease, composite aluminum grease or molybdenum disulfide spray according to the working conditions, the grease injection amount is controlled at 1/3 to 1/2 of the internal space of the bearing, the grease injection cycle can be calculated by formula, and it is usually replenished every 100-200 hours of operation, and excessive grease will cause a significant increase in temperature rise.

The sealing system needs to be checked regularly, the rubber seal is replaced every 2-3 years, the labyrinth seal is cleaned up every 6 months, the combination of stainless steel and fluorine rubber seal should be used in humid environments, and the protective cover and air curtain protection are required for dust conditions. During installation, it is necessary to ensure that the coaxiality deviation is ≤0.05mm/m, and the preload must be controlled by the spacer sleeve to avoid local load concentration or friction heating caused by poor alignment or overtightness.

Operation monitoring is an important means to prevent failures: the normal temperature should be ≤ 80°C, and the temperature rise rate should exceed 5°C/hour, and the machine should be stopped immediately for troubleshooting; In the case of vibration accelerations of more than 5 m/s², spectral analysis is required to identify internal damage such as ball spalling. When abnormal noise occurs, the high-frequency acoustic noise is usually caused by lubrication failure, and the lubricant needs to be replenished or replaced; Low-frequency squeaks can be caused by excessive clearance or poor alignment, requiring readjustment of preload or calibration of concentricity.

When the temperature rise is too high, check the lubrication status, seal fit and actual load, reduce the speed if necessary and use the thermal imaging camera to locate the hot spot. Modern maintenance technologies are becoming more intelligent, with predictive maintenance of bearings with integrated temperature/vibration sensors via the IoT platform, oil analysis to detect metal particle levels (above 100 ppm indicating increased wear), and life assessment to calculate remaining life based on Miner theory.

The Price of Double-Row Ball Slewing Bearings

The price of double-row ball slewing bearings varies significantly due to the model, size, accuracy and application scenarios, and the price span from micro to large products can reach hundreds of times: micro bearings (inner diameter ≤ 10mm) are about 2-10 yuan / piece for domestic ordinary type, and 30-50 yuan / piece for imported precision type (such as NSK); Small and medium-sized bearings (inner diameter 10-50mm) domestic industrial-grade products are 10-200 yuan/piece, and imported high-precision bearings are up to 200-500 yuan/piece; Among the large heavy-duty bearings (inner diameter >50mm), the products for construction machinery are about 500-3000 yuan/piece, and the customized bearings for wind power or high-end equipment can reach 10,000 yuan. Prices are mainly influenced by size and load capacity, material (30%-50% premium for stainless steel/ceramic ball bearings), sealing grade (10%-20% markup for shield/sealed types) and brand (imported brands are usually 3-5 times higher than domestic brands). It is advisable to obtain a real-time quote for the specific model through a professional platform or authorized dealer, taking into account the additional costs of special needs such as customized design or adaptation to extreme operating conditions.

Supplier of Double-Row Ball Slewing Bearings

LTZC double-row ball slewing bearings are made of GCr15 bearing steel (hardness HRC60-65) and superfinishing grinding process (Ra≤0.04μm) to achieve three-dimensional load carrying capacity, reduce the pressure of single beads by 40%, and increase the service life by 2-3 times compared with traditional single row bearings. The company offers miniature to large full-size sizes and supports customized services such as ceramic balls, multi-level seals, and smart sensor integration. Through technological innovations such as carburizing and quenching, 3D printing cages, the products have both lightweight and impact resistance, and have been successfully applied to wind power yaw systems, new energy vehicle drive motors and other scenarios, helping customers improve equipment efficiency and reliability.