Double Row Ball Slewing Bearings: LDB’s Innovation and Excellence

What is a Double Row Ball Slewing Bearing?

A double row ball slewing bearing is a large-scale precision rotary component that incorporates two independent rows of steel balls between the inner and outer rings. Unlike single-row slewing rings, which feature a single row of balls with four points of contact between each ball and the raceway, double row products offer two rows of ball bearings, two separate raceways, and eight points of contact for each ball. This fundamental difference allows double row bearings to handle higher loads and provide greater reliability compared to their single-row counterparts.

Single-row slewing rings are designed with a standard bearing raceway where each ball contacts the raceway at four points. This four-point contact design enables them to simultaneously withstand axial loads, radial loads, and tilting moments in a compact form. However, when applications demand higher load capacity or extended service life under continuous operation, double row ball slewing bearings become the preferred choice.

The same-diameter double row ball slewing bearing produced by LDB is specifically engineered for demanding applications such as wind turbine equipment and concrete pump trucks. In wind power equipment, for instance, the bearing is installed at the root of the propeller and functions as a side propeller, where it must endure constant rotation, vibration, and variable wind loads while maintaining precise alignment.

LDB’s double row ball slewing bearings are manufactured within an outer diameter range of 300 mm to 10,000 mm, accommodating both compact machinery and large-scale industrial systems. The ring materials are selected from 42CrMo, 50Mn, or C45 – all high-grade steel alloys known for their excellent hardenability, fatigue resistance, and impact strength. The balls or rollers are made from GCr15 bearing steel, a material specifically formulated for rolling element applications requiring high hardness and wear resistance. For cages, LDB offers steel 20 or ZL112 cast aluminum alloy; for spacers, nylon 6 or nylon 66 are available.

How Does a Double Row Ball Slewing Bearing Work?

The working principle of a double row ball slewing bearing centers on the separation of load paths. Because there are two distinct rows of balls and two separate raceways, each row can be optimized for specific load types. The upper row typically handles axial loads and tilting moments, while the lower row manages radial loads and supplementary axial forces. This division reduces internal stress concentrations and improves overall load efficiency.

When an axial load is applied downward onto the bearing, the upper row of balls compresses against its raceway, transferring force from the inner ring to the outer ring (or vice versa, depending on mounting orientation). If a tilting moment is introduced – for example, when a concrete pump truck’s boom extends outward – the load becomes uneven across the bearing circumference. The double row configuration resists this tilting by engaging both rows on opposite sides of the bearing, creating a restoring moment that maintains structural alignment.

The eight-point contact geometry (four points per ball, across two rows) provides a significant advantage in load distribution. Each ball contacts its respective raceway at four distinct points – two on the inner ring and two on the outer ring. This arrangement allows the bearing to distribute applied forces across a larger contact area, reducing peak stresses and extending fatigue life.

LDB’s engineering team utilizes finite element analysis during the design phase to optimize raceway curvatures, ball diameters, and ring thicknesses. For wind turbine applications – where the bearing is installed at the propeller root – this analysis ensures that the bearing can withstand not only static loads but also dynamic forces generated by wind gusts, blade pitch adjustments, and continuous rotation over decades of service.

Key Features of LDB’s Double Row Ball Slewing Bearings

LDB’s double row ball slewing bearings incorporate several distinctive features based on actual production specifications.

Eight-Point Contact Geometry – Unlike single-row slewing rings that offer four points of contact per ball, LDB’s double row design provides eight points of contact per ball (four on the upper row and four on the lower row). This increased contact area reduces stress concentration and enhances load distribution.

Wide Diameter Range – Outer diameters from 300 mm to 10,000 mm, accommodating everything from small industrial turntables to massive wind turbine yaw systems and concrete pump turntables.

Premium Material Selection – Ring materials include 42CrMo, 50Mn, and C45. Balls are manufactured from GCr15 bearing steel. Cages are available in steel 20 or ZL112 cast aluminum alloy. Spacers are offered in nylon 6 or nylon 66.

Raceway Hardness – The quenching hardness of the raceway reaches HRC 55-62, ensuring a hard, wear-resistant surface while maintaining sufficient core toughness to absorb shocks and impacts.

Flexible Gear Configurations – Available with no gear, internal gear, or external gear. Tooth type selection depends on the drive system design. For wind turbine applications, internal gearing is often preferred; for concrete pump trucks, external gearing is commonly used.

Lead Time – LDB offers a standard lead time of 30 days for custom orders.

Core Advantages and Competitive Edge

When compared to single-row slewing rings or other bearing types, LDB’s double row ball slewing bearings offer several distinct advantages.

Higher Load Capacity – Because there are two rows of balls and eight points of contact per ball, double row bearings can support significantly higher axial, radial, and tilting moment loads than single-row alternatives. This makes them ideal for applications where load requirements exceed the practical limits of four-point contact designs.

Greater Reliability – The redundant load path provided by two separate rows means that even if one row experiences uneven wear or localized damage, the other row can continue to support critical loads. This inherent redundancy translates directly into higher system reliability – a crucial factor for wind turbines and concrete pump trucks where unexpected downtime is costly.

Longer Service Life – Reduced contact stress per ball, combined with high-quality GCr15 ball material and raceway hardness of HRC 55-62, results in extended fatigue life. LDB’s double row bearings are engineered for continuous operation over many years, even under variable and impact loads.

Same-Diameter Efficiency – The same-diameter double row ball slewing bearing design offers optimized space utilization. By maintaining a consistent diameter while adding a second ball row, LDB maximizes load capacity without increasing the bearing’s physical footprint.

Application-Specific Engineering – For wind turbine equipment, the bearing is installed at the root of the propeller and acts as a side propeller. LDB customizes the bearing’s internal geometry, sealing system, and lubrication features to meet the unique demands of this application, including high cycle fatigue resistance and corrosion protection.

Flexible Material Choices – Clients can select from 42CrMo, 50Mn, or C45 ring materials based on their specific strength, weight, and cost requirements. Cage materials (steel 20 or ZL112 aluminum alloy) and spacer materials (nylon 6 or nylon 66) are similarly customizable.

30-Day Lead Time – In an industry where long production cycles are common, LDB’s 30-day standard lead time for custom double row ball slewing bearings provides a competitive advantage.

Main Configurations and Customization Options

LDB offers a range of configurations for double row ball slewing bearings.

By Gear Type

• No gear (plain) – For applications where rotation is driven externally, such as friction drives or separate pinion systems.
• Internal gear – Gear teeth are cut on the inner ring’s inner diameter. Common in wind turbines and other compact installations.
• External gear – Gear teeth are cut on the outer ring’s outer diameter. Widely used in concrete pump trucks, cranes, and excavators.

By Ring Material

• 42CrMo – High-strength alloy steel with excellent toughness and fatigue resistance. Suitable for heavy-duty applications including wind turbines.
• 50Mn – Medium-carbon manganese steel offering good hardenability and wear resistance.
• C45 – Unalloyed medium-carbon steel with reliable mechanical properties.

By Cage and Spacer Material

• Cage: Steel 20 (high strength, impact resistant) or ZL112 cast aluminum alloy (lightweight, corrosion resistant)
• Spacer: Nylon 6 or nylon 66 – both offer low friction and good wear resistance; nylon 66 provides higher temperature tolerance.

By Ball Material

• GCr15 – High-carbon chromium bearing steel. Provides high hardness, excellent wear resistance, and long fatigue life.

Industrial Applications

LDB’s double row ball slewing bearings are deployed across multiple industries, with two primary application areas standing out.

Wind Turbine Equipment – The same-diameter double row ball slewing bearing is installed at the root of the propeller (blade root), acting as a side propeller. This bearing allows the blade to pitch – adjusting its angle relative to the wind – which is essential for controlling rotational speed and optimizing energy capture. The bearing must withstand millions of load cycles over a 20+ year service life, resist environmental corrosion, and maintain precise rotational accuracy. LDB’s double row design, with its eight-point contact geometry and GCr15 balls, is specifically engineered for this demanding duty.

Concrete Pump Trucks – In concrete pump trucks, the slewing bearing is mounted between the chassis and the pump turret, allowing the boom to rotate 360 degrees. Double row ball bearings are preferred here because they must support not only the weight of the extended boom and concrete-filled piping but also the dynamic loads generated by pumping operations and wind forces. The higher load capacity and reliability of double row designs reduce the risk of field failures during concrete pours.

Additional Applications – Beyond these primary uses, LDB’s double row ball slewing bearings are also found in tower cranes, mobile cranes, aerial work platforms, harbor cranes, radar antennas, solar tracking systems, and industrial turntables.

LDB’s Manufacturing Excellence

LDB’s production process is built around precision machining, controlled heat treatment, and rigorous inspection.

Material Sourcing and Verification – Incoming ring materials (42CrMo, 50Mn, C45) and ball materials (GCr15) are verified for chemical composition and mechanical properties. Certificates are maintained for full traceability.

Precision Machining – Ring blanks are rough-turned, then finish-ground on CNC vertical lathes and grinding machines. Raceway profiles are machined to achieve the required geometry for eight-point contact. Gear teeth (if specified) are cut using hobbing or shaping processes.

Heat Treatment – Raceways undergo induction hardening to achieve HRC 55-62, providing a hard, wear-resistant surface while preserving core toughness. The specific heat treatment process is controlled to prevent distortion and maintain dimensional accuracy.

Assembly – Balls (GCr15), cages (steel 20 or ZL112 aluminum alloy), spacers (nylon 6 or nylon 66), and seals are assembled in a clean environment.

Inspection and Testing – Each bearing is tested for rotational torque, radial and axial runout, gear accuracy (if applicable), and raceway hardness. Non-destructive testing methods verify material integrity.

Packaging and Logistics – Finished bearings are coated with anti-corrosion oil and packaged in metal brackets or export-standard fumigation-free wooden boxes, ensuring safe delivery to customers worldwide.

Conclusion

Double row ball slewing bearings occupy a critical position in heavy machinery, offering higher load capacity and greater reliability than single-row alternatives. Luoyang LDB Bearing Co., Ltd. manufactures these components with careful attention to material selection, precision machining, and quality control – as reflected in the specifications of 42CrMo/50Mn/C45 rings, GCr15 balls, HRC 55-62 raceway hardness, and a 30-day lead time for custom orders.

The same-diameter double row ball slewing bearing produced by LDB is particularly well-suited for wind turbine equipment – where it is installed at the propeller root and acts as a side propeller – and for concrete pump trucks, where it enables reliable 360-degree boom rotation. With eight points of contact per ball, two separate raceways, and a wide outer diameter range from 300 mm to 10,000 mm, LDB’s double row ball slewing bearings deliver the performance, durability, and application-specific engineering that modern industries demand.

For clients seeking a trusted manufacturer who understands both the theoretical advantages of double row designs and the practical realities of production, LDB offers a compelling combination of technical capability, material quality, and responsive delivery.