Slewing bearings play a vital role in modern industrial equipment and mechanical systems. Whether it is construction machinery, wind power generation, or robotics, slewing bearings can provide smooth rotational motion and high load capacity to ensure efficient operation of equipment. However, faced with a wide range of bearing types on the market, how to choose the right slewing bearing? How does it work? What are the differences in requirements in different application scenarios? This article will provide you with a detailed analysis of the structure, working principle, application areas and selection guide of slewing bearings to help you gain a deeper understanding of this key mechanical component.
If you have any questions about the purchase, installation or maintenance of slewing bearings, you may wish to continue reading, we will provide you with comprehensive technical guidance and practical suggestions.
What Is a Slewing Bearing?
Basic Definition
Slewing bearings are special bearings designed to withstand axial, radial and overturning moments, usually consisting of an inner ring, an outer ring, rolling elements (such as balls or rollers) and a cage or spacer. Compared with ordinary bearings, slewing bearings usually have a larger diameter and are designed to support larger loads and slow rotation.
Effect
The main function of a slewing bearing is to achieve the slewing motion of a device or structure while bearing forces in various directions to ensure the smooth operation of the device. Common applications include:
- Engineering machinery (such as excavators, cranes, tower cranes), used to support and achieve rotational motion.
- Wind power generation (such as wind turbines), used to connect the wind wheel and the nacelle to achieve wind direction adjustment.
- Robots and automation equipment, used to provide high-precision rotation support for joints or rotating platforms.
- Military equipment (such as radars, tank turrets), used to ensure the stable rotation of the structure.
In general, slewing bearings play a vital role in modern industrial and mechanical systems, and can improve the rotational flexibility, load-bearing capacity and structural stability of equipment.
Working Principle and Structural Analysis of Slewing Bearings
Structural Analysis
The slewing bearing is mainly composed of an inner ring, an outer ring, rolling elements, spacers (or cages), seals, and a lubrication system.
Inner and outer rings
- The inner and outer rings are the main parts of the slewing bearing, usually made of high-strength alloy steel and quenched to improve the load-bearing capacity and wear resistance.
- The inner or outer ring usually has gears (internal or external teeth) to cooperate with the drive device (such as a reducer, gear transmission mechanism) to achieve slewing motion.
- In general, the fixed ring is installed on the support structure, and the other side is connected to the slewing part, and relative rotation is achieved by the rolling of the rolling elements.
Rolling element
- The rolling elements of the slewing bearing are usually balls (ball slewing bearings) or rollers (roller slewing bearings). Their shape and arrangement determine the load-bearing capacity and rigidity of the bearing.
- The rolling elements roll on the raceways of the inner and outer rings, thereby reducing friction and transmitting loads.
- According to the arrangement of the rolling elements, it can be divided into single-row, double-row or three-row structures to meet different load requirements.
Lubrication system
- Slewing bearings are usually lubricated with grease, and some high-load or high-precision applications may use oil bath lubrication or automatic lubrication systems.
- The main function of lubrication is to reduce friction, reduce wear, prevent rust, and play a certain role in heat dissipation.
- The bearing structure is usually equipped with a lubrication nozzle to facilitate regular replenishment of grease to ensure that an effective lubrication film is formed between the rolling element and the raceway.
Seals
- The sealing structure of the bearing is mainly used to prevent dust and impurities from entering the bearing and prevent grease leakage.
- Rubber sealing rings or metal sealing rings are used to ensure that the bearing can still operate stably in harsh environments.
How It Works
The working principle of the slewing bearing is to achieve smooth load transmission and reduce movement friction through the rolling of the rolling elements on the inner and outer ring raceways. Its working process is as follows:
Driving force input
- The driving force acts on the bearing through the outer gear ring or inner gear ring connected to the driving device (such as motor + reducer), causing it to rotate.
Rolling element action
- The rolling element (ball or roller) rolls between the raceways, allowing the inner and outer rings to rotate relative to each other and evenly transferring the external load to the supporting structure.
- The bearing can simultaneously withstand axial force, radial force and overturning moment, allowing the equipment to remain stable during operation.
Lubrication and friction control
- Grease forms a lubricating film between the rolling element and the raceway, reducing friction and wear and increasing the service life of the bearing.
- Through reasonable lubrication and sealing design, maintenance requirements can be effectively reduced and equipment reliability can be improved.
Main Types of Slewing Bearings
Single-Row Ball Slewing Bearing
Features:
- Using a single row of steel balls as rolling elements, it usually adopts a four-point contact structure.
- Compact structure, light weight, suitable for medium load and medium speed conditions.
- Applicable to excavators, tower cranes, rotary tables and other equipment.
Advantages:
✔Simple structure and low manufacturing cost.
✔Able to withstand large axial and radial loads.
Disadvantages:
✘Cannot withstand excessive overturning moment.
✘Suitable for medium speed, not for high-speed rotation applications.
Double Row Ball Slewing Bearing
Features:
- Double-row steel balls are used, usually a double-row four-point contact ball structure.
- Able to withstand large axial and radial loads and overturning moments.
- Commonly used in applications that require higher load-bearing capacity, such as large-tonnage cranes, heavy machinery, etc.
Advantages:
✔ Stronger load-bearing capacity, especially suitable for heavy-duty applications.
✔ Stable structure and long service life.
Disadvantages:
✘ Relatively complex structure and high manufacturing cost.
✘ Larger overall dimensions and heavier weight than single-row ball type.
Crossed Roller Slewing Bearings
Features:
- Rollers are used as rolling elements and are arranged in a cross pattern, usually in a two-row structure.
- Since the rollers are in contact with the rail line, the contact area is large and the rigidity is stronger.
- Suitable for equipment with high precision and high rigidity requirements, such as industrial robots, machine tool turntables, etc.
Advantages:
✔ High precision, able to achieve smoother rotation.
✔ Strong anti-overturning ability, suitable for high-precision working conditions.
✔ Better rigidity, can withstand large overturning torque.
Disadvantages:
✘ Due to the roller line contact, the friction resistance is large, not suitable for high-speed rotation.
✘ High production cost, strict processing accuracy requirements.
Summarize
| Type | Load Capacity | Rigidity | Application | Working Condition |
|---|---|---|---|---|
| Single-row Ball | Medium | Normal | Excavators, Tower Cranes | Medium Load, Medium Speed |
| Double-row Ball | High | Strong | Heavy Machinery, Cranes | Heavy Load, Medium Speed |
| Cross Roller | Very High | Excellent | Machine Tools, Robots | High Precision, Low Speed |
How to Choose a Suitable Slewing Bearing?
Load Calculation
The loads borne by slewing bearings usually include radial loads, axial loads, and overturning moments. Correct calculation of loads is crucial for bearing selection:
- Axial load (Fa): The main load type borne by slewing bearings, usually applied by the weight of the equipment, working load or external force.
- Radial load (Fr): Generally small, but cannot be ignored under certain working conditions (such as cranes and excavators).
- Overturning moment (M): Caused by eccentric loads or working torque, it affects the stability of the bearing.
- Calculation method: According to the working conditions of the equipment, use mechanical formulas or calculation tools provided by the manufacturer to ensure that the selected bearing can withstand the maximum working load and leave enough safety margin.
Speed ​​requirement
The speed of the slewing bearing determines its applicable working conditions, which generally depends on the operating speed and precision requirements of the equipment:
- Low-speed working conditions (<10 rpm): such as cranes and slewing platforms, four-point contact ball or cross roller slewing bearings are usually selected.
- Medium speed (10-100 rpm): suitable for automation equipment and industrial robots, cross roller bearings or angular contact ball bearings are more common.
- High-speed working conditions (>100 rpm): such as machine tool rotary tables, radar antennas, etc., it is recommended to use high-precision cross roller bearings or thin-walled angular contact ball bearings.
- Influencing factors: Lubrication method, manufacturing accuracy and rolling element type will affect the speed performance of the bearing, and comprehensive considerations should be made when selecting.
Environmental Adaptability
The working environment of the bearing determines its durability and maintenance requirements. The following factors should be considered:
Temperature:
- High temperature environment (>80°C): Use high temperature resistant grease and high temperature resistant materials (such as high temperature alloys, ceramic balls).
- Low temperature environment (<-20°C): Choose low temperature grease and avoid embrittlement of materials due to low temperature.
Humidity and corrosion:
- Anti-corrosion coating or stainless steel should be used in outdoor or marine environments.
- When there may be contact with chemicals, choose corrosion-resistant sealing design or special materials.
Dust and pollution:
- Construction machinery and mining equipment need to use bearings with good sealing to prevent foreign matter from entering.
- Regular maintenance and lubrication can effectively extend the life of bearings.
Other Considerations
- Installation space: Determine whether the bearing outer diameter, inner diameter and height are suitable for the equipment design.
- Lubrication method: Grease lubrication is suitable for low speed and medium load, and oil lubrication is suitable for high speed and heavy load.
- Service life: Calculate whether the bearing can meet the expected working time based on the L10 life.
Installation and Maintenance of Slewing Bearings
Correct Installation Steps for Slewing Bearings
1. Inspection and preparation
Before installation, the bearing and mating parts should be inspected:
- Inspect the mounting surface: Make sure the mounting surface is flat, smooth, and free of burrs, welding slag or other impurities.
- Inspect the bearing: Check whether the bearing has transportation damage or deformation, and confirm whether the bearing model and size match.
- Clean parts: Use gasoline or detergent to remove oil and dust from the bearing and mounting surface, and apply a layer of anti-rust oil.
2. Bearing in place
- Use lifting tools to carefully place the slewing bearing in the installation position to avoid impact or damage.
- Rotate the bearing and adjust it to the most suitable installation position.
3. Bolt fixing
- Use high-strength bolts that meet the standards (such as grade 8.8 or above).
- Tighten the bolts evenly and crosswise along the diagonal lines to prevent deformation or uneven force on the bearing.
- Use a staged tightening method: initial tightening (30% torque) → intermediate tightening (60% torque) → final tightening (100% torque).
- It is recommended to use a torque wrench to ensure that the tightening torque meets the specified requirements.
4. Check the installation accuracy
- Whether the bearing rotates smoothly, whether there is any jamming or abnormal noise.
- Measure the installation surface clearance to ensure that it is within the allowable range.
Lubrication and Maintenance of Slewing Bearings
1. Lubrication method
Lubrication is essential for the normal operation of slewing bearings. Common lubrication methods include:
- Grease lubrication: Use lithium-based grease, calcium-based grease and other greases, which are suitable for most equipment.
- Oil lubrication: Suitable for high-speed or high-load applications, but requires a sealing structure to prevent leakage.
2. Lubrication cycle
- After initial installation: Re-inject grease after 50 hours of operation.
- Normal use: Re-inject grease every 200-500 hours of operation.
- High load or harsh environment (such as high temperature, high humidity, dust environment): Appropriately shorten the lubrication cycle.
- Long-term out of service: Refill grease before re-activation.
3. Grease filling tips
- Use a refueling gun or automatic lubrication system to add grease.
- When rotating the bearing, add in batches to ensure that the grease is evenly distributed.
- Observe the overflow of grease. If it overflows slightly from the edge of the seal ring, it means that the amount of grease is added appropriately.
Common Faults and Troubleshooting Methods
| Fault Phenomenon | Possible Cause | Solution |
|---|---|---|
| Unusual noise (clicking, friction sound) | 1. Uneven installation 2. Loose bolts or insufficient preload 3. Foreign objects or insufficient lubrication |
1. Reinstall, ensuring flatness 2. Tighten bolts to standard torque 3. Clean bearing, add lubrication |
| Rotation stuck or high resistance | 1. Bearing deformation or damage 2. Insufficient lubrication or incorrect lubricant 3. Misaligned mounting holes |
1. Inspect and replace bearing 2. Apply proper lubricant 3. Adjust mounting holes |
| Excessive bearing clearance | 1. Severe bearing wear 2. Loose bolts |
1. Replace with a new bearing 2. Check and tighten bolts |
| Oil leakage or grease contamination | 1. Damaged seal ring 2. Excessive grease filling |
1. Replace the seal ring 2. Add proper amount of grease |
| Bolts break or loosen | 1. Insufficient bolt strength or fatigue failure 2. Insufficient tightening torque |
1. Use high-strength bolts 2. Tighten bolts to standard torque |
For more information, please click How To Repair Slewing Bearing? [Repair Process And Steps]
Market Trends and Future Development of Slewing Bearings
1. Technological innovation drives the upgrade of the slewing bearing market
With the development of industrial automation, intelligent manufacturing and high-end equipment, slewing bearings are moving towards higher precision, longer life and lower maintenance costs. Technological innovation has become a key driving force for market competition.
- Intelligent slewing bearings: Intelligent slewing bearings with integrated sensors, wireless monitoring systems and AI analysis technologies can monitor operating conditions in real time, such as temperature, vibration, load, etc., to achieve predictive maintenance and reduce equipment failure rates.
- High-precision manufacturing process: The advancement of high-end CNC machine tools, laser measurement technology and precision grinding technology has continuously improved the manufacturing accuracy of slewing bearings to meet the needs of high-end applications such as aerospace and medical equipment.
- Low-friction design and optimized lubrication: By optimizing the shape of rolling elements, improving the cage structure and introducing an efficient lubrication system, friction loss is reduced and the energy efficiency and service life of slewing bearings are improved.
2. Application of new materials to improve the performance of slewing bearings
Traditional slewing bearings are mostly made of alloy steel or stainless steel, and the application of new materials has greatly improved their performance and adapted to more demanding working environments.
- Ceramic materials: All-ceramic bearings or hybrid ceramic bearings (ceramic rolling elements + metal rings) are increasingly used in aerospace, high-speed machine tools and semiconductor manufacturing due to their excellent high temperature resistance, corrosion resistance and high rigidity.
- High-performance composite materials: such as carbon fiber reinforced polymer (CFRP) or polymer composite materials, can significantly reduce the weight of bearings, improve wear resistance and self-lubrication ability, and are suitable for lightweight and high-load conditions.
- New surface coating technology: New coating technologies such as DLC (diamond-like coating), ceramic coating and nano-lubricating film improve the wear resistance, corrosion resistance and self-lubrication of bearings, and are suitable for harsh environments and extreme conditions.
3. Market trends and future development
- Growth in the application of new energy and renewable energy: The demand for large slewing bearings (such as variable pitch bearings and yaw bearings) in the wind power industry continues to grow. At the same time, photovoltaic tracking systems and tidal energy equipment also put forward higher requirements for slewing bearings with environmental corrosion resistance and high reliability.
- Increased demand for robots and automation equipment: With the widespread application of industrial robots, collaborative robots and AGV (automatic guided vehicles), the market demand for small precision slewing bearings has increased significantly.
- Green manufacturing and sustainable development: The application of low-energy production processes, recyclable materials and environmentally friendly lubricants will drive the slewing bearing industry towards green manufacturing, which is in line with the global trend of carbon neutrality and sustainable development.
Conclusion
In the future, the slewing bearing industry will continue to develop driven by intelligence, high precision and new material applications. At the same time, with the expansion of new energy, robotics and high-end equipment manufacturing industries, market demand will continue to grow. Enterprises need to accelerate the pace of technological innovation and optimize material selection to enhance product competitiveness and meet the diverse needs of the global market.
