What is a Double Row Ball Slew Bearing?
It features a two-row ball structure and is widely used in mechanical equipment requiring high-precision rotation and heavy-load capacity. A double row ball slew bearing is a large rotational bearing designed to withstand **combined axial loads, radial loads, and overturning moments.
Basic Structure
– Double Row Ball Arrangement
Two independent rows of steel balls (rolling elements) are arranged in concentric raceways, allowing simultaneous distribution of loads in different directions.
– Inner and Outer Rings:
Precision-machined raceways on the fixed outer ring and rotating inner ring (or vice versa), often integrated with gear teeth to drive rotation.
– Seals and Lubrication:
Equipped with sealing rings to prevent contamination and lubrication ports for regular greasing to extend service life.
Core Functions
Multi-Directional Load Capacity:
-Axial Loads: Forces along the rotation axis (e.g., vertical pressure from cranes).
– Radial Loads: Forces perpendicular to the rotation axis (e.g., lateral forces from robotic arms).
– Overturning Moments: Torque caused by eccentric loads (e.g., twisting forces from wind turbine blades).
– High Rigidity Rotation
The double row ball structure distributes stress, minimizes deformation, and ensures smooth rotation.
Advantages and Disadvantages of Double Row Ball Slew Bearings**
Advantages:
High Load Capacity:
– Multi-directional load support**: Suitable for complex stress scenarios (e.g., wind turbines, cranes).
– Double row design**: Distributes loads across two rows, improving capacity by 30%~50% compared to single-row bearings and reducing localized stress.
Smooth Operation with Low Friction:
– Small ball contact area reduces friction, enabling precise control (e.g., medical devices, radar antennas).
– Low heat generation extends lubrication intervals and bearing life.
Compact and Integrated Design:
– Integration of gears (internal/external teeth), seals, and lubrication ports saves space.
– Ideal for applications with strict space constraints (e.g., industrial robot joints).
Versatility
– Material options (standard steel, stainless steel, anti-corrosion coatings) adapt to diverse environments (humid, corrosive).
– Suitable for low-speed heavy-load and medium-speed rotation scenarios.
Disadvantages
Limited Adaptability to Extreme Overturning Moments**:
– Prone to ball slippage under high overturning moments compared to **crossed roller bearings**, leading to localized wear.
– Extreme torque scenarios (e.g., heavy-duty machine tool turntables) require crossed or triple-row roller bearings.
High Installation Precision Requirements**:
– Base flatness tolerance must be ≤0.1 mm/m; deviations cause uneven raceway loading and accelerated fatigue failure.
– Demands experienced installers; improper installation risks early failure.
Higher Maintenance Costs**:
– Regular lubrication (every 500 operating hours) and seal replacement are critical; contamination shortens lifespan.
– Replacement in heavy machinery (e.g., wind turbines) requires costly disassembly and crane operations.
Cost-Performance Trade-offs**:
– More expensive than single-row ball bearings but weaker in load capacity than crossed roller bearings.
– Oversized models (e.g., diameter >5 meters) face manufacturing challenges and long lead times.
Application examples of this kind of bearings
In a wind turbine, the double-row ball slewing bearing is installed between the top of the tower and the nacelle:
– Axial force: The vertical pressure generated by the self-weight of the blades and the nacelle.
– Radial force: The lateral thrust caused by the wind shear force.
– Overturning moment: The torque generated by the aerodynamic imbalance during the rotation of the blades.
The load is dispersed through the two rows of balls, ensuring that the nacelle can yaw stably to align with the wind direction even under strong winds.
Factors Influencing the Price of Double Row Ball Slew Bearings
The price of double row ball slew bearings is affected by multiple factors, including raw materials, manufacturing processes, and market dynamics.
Material Costs:
– Steel Type:
– Standard bearing steel (e.g., GCr15) is cost-effective but corrosion-prone.
– Stainless steel (e.g., 440C) or specialty alloys (e.g., 42CrMo4) cost 30%~50% more but suit harsh environments (e.g., marine applications).
– Heat Treatment
– Processes like carburizing and surface hardening improve hardness and wear resistance but add 15%~25% to processing costs.
Size and Load Capacity:
– Diameter Range:
– Small bearings (diameter <1 meter): ¥10,000–¥50,000.
– Large bearings (diameter >3 meters, e.g., for wind turbines): ¥500,000–¥2,000,000 due to material and machining complexity.
– Load Rating:
– High-load designs (dynamic load rating >500 kN) require reinforced raceways and balls, increasing costs by 20%~40%.
Manufacturing Complexity:
-Raceway Machining Accuracy:
– High-precision grinding (Ra ≤0.4 μm) costs 30%~50% more than standard turning (Ra ≤1.6 μm) but extends service life.
– Gear Integration:
– Internal/external gear machining requires specialized equipment; each precision grade improvement (e.g., DIN Class 6) adds 10%~15% to costs.
– Seal Design:
– Multi-lip or labyrinth seals cost 20%~35% more than standard rubber seals but offer superior dust/water resistance.
Customization Requirements**:
– Non-Standard Designs**:
– Customized mounting holes or flange interfaces increase design and tooling fees (10%~20% of total cost).
– Special Coatings
– Zinc plating, Dacromet, or PTFE anti-corrosion coatings add 5%~15% to costs but suit chemical or marine environments.
Market Factors:
– Supply-Demand Dynamics**:
– Prices rise 10%~30% during high-demand periods (e.g., 2021 wind power installation surge).
– Regional Cost Differences
– Chinese-made bearings are 30%~50% cheaper than European/American equivalents due to lower labor and material costs.
Transportation and Installation Costs
– Logistics
Oversized bearings (e.g., 5-meter diameter) require special transport, with freight accounting for 5%~10% of total cost.
– Installation Complexity
High-precision installation (flatness ≤0.1 mm/m) demands professional teams, increasing labor costs by 5%~8%.
The double-row ball slewing bearing optimizes the load distribution through two rows of balls. It is a key component that balances the load-bearing efficiency and space occupation, and is widely used in heavy-duty rotating equipment that needs to bear complex loads. However, its installation accuracy and maintenance requirements are relatively high, and a comprehensive selection should be made according to the working conditions.
If you want to purchase bearings, you can get in touch with us. LDB-Bearing Company has advanced bearing manufacturing techniques and ensures strict compliance with national standards. Moreover, our R&D team has continuously received research and development funds, which guarantees that we won’t fall behind our peers. We can provide you with different bearings tailored to various industries. Meanwhile, we have a complete after-sales service system. Once you have any problems, we will reply to you immediately and offer reasonable solutions. If you’d like to know more, please feel free to contact us.