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Slewing bearings are often called the “joints of machinery.” Although they look similar on the outside, their internal structures differ significantly, and so do their load capacities, rotational accuracy, and adaptability to working conditions. Choosing the right type directly determines the operating performance and service life of the equipment.

I. Single-Row Four-Point Contact Ball Slewing Bearing

Structural features: A single row of balls runs in a peach-shaped (Gothic-arch) raceway. Each ball makes two-point contact with both the upper and lower raceways — four-point contact in total — with a contact angle of generally 45°.

Performance features:

• Capable of withstanding simultaneous bidirectional axial loads, radial loads, and tilting moments; the moderate load capacity suits most small-to-medium load applications.
• Low rolling friction and low starting torque ensure smooth, energy-efficient operation, making it suitable for higher speeds and frequent start-stop cycles.
• Compact axial height, minimal space requirement, and easy installation.

Typical applications: Small and medium cranes, the slewing mechanisms of small excavators and wheel loaders, rotary worktables, amusement rides (carousels and Ferris wheels), medical equipment, and light machinery.

II. Double-Row Ball Slewing Bearing (with Differing Ball Diameters)

Structural features: Two rows of balls of different diameters. The upper row of larger balls primarily carries axial loads and tilting moments, while the lower row of smaller balls mainly carries radial loads.

Performance features:

• Load capacity and anti-overturning (tilting) resistance are significantly higher than those of the single-row four-point contact ball type, enabling it to handle medium-to-heavy loads.
• Retains the low friction and smooth rotation advantages of ball bearings, maintaining stable slewing even under heavy loads without noticeable jamming.
• Point contact between balls and raceways provides good adaptability to mounting base deformation, allowing relatively relaxed requirements on base surface accuracy.

Typical applications: Tower cranes, portal cranes, port handling machinery, floating cranes, and medium-sized marine lifting equipment.

III. Three-Row Roller Slewing Bearing

Structural features: Three rows of cylindrical rollers. The upper and lower rows respectively handle upward and downward axial loads and tilting moments, while the radial row carries radial loads. Each row can be selected independently, allowing the dimensions to be optimized for each load direction.

Performance features:

• Line-contact loading gives this type the highest load capacity of all slewing bearing designs, making it particularly suited to extremely large axial loads and tilting moments.
• High rigidity and strong impact resistance ensure stable structure under heavy loads and a long service life.
• Higher roller friction and lower rotational speed mean relatively lower rotation flexibility; it also demands high stiffness and flatness of the mounting base.
• Extra-large-diameter products can adopt segmented raceway designs for easier machining and transport.

Typical applications: Large open-pit mining excavators, heavy-lift cranes on large crane ships and wind turbine installation vessels, tunnel boring machines (shield machines), and heavy metallurgical equipment.

IV. Crossed Roller Slewing Bearing

Structural features: Cylindrical rollers are arranged alternately at 90° to one another along the raceway, with the axes of adjacent rollers mutually perpendicular — one set carries axial loads and the other radial loads. The raceway is V-shaped.

Performance features:

• A single bearing simultaneously withstands axial loads, radial loads, and tilting moments with balanced load distribution.
• Excellent rigidity and high rotational accuracy allow precise control of the slewing angle, meeting precision positioning requirements.
• Compact structure with small axial height, ideal for space-constrained installations.
• Low friction and smooth operation, while still accommodating moderate speeds.

Typical applications: Industrial robot joints, CNC rotary tables and indexing tables, high-end astronomical telescopes, medical devices, radar antenna pedestals, and other precision equipment.

V. Selection Guidelines

(1) Selection by Load

• Light loads: where axial load, radial load, and tilting moment are all small (e.g., small amusement rides and light construction machinery), choose the single-row four-point contact ball type for the best cost-effectiveness.
• Medium loads: for applications such as medium-sized tower cranes and wheel loaders, choose the double-row ball type, which balances load capacity and rotation performance.
• Heavy loads: for severe heavy-duty conditions such as large mining excavators and wind turbine installation vessel cranes, choose the three-row roller type; for space-constrained heavy-duty precision equipment, the crossed roller type may be considered.

(2) Selection by Accuracy For equipment requiring extremely high rotational accuracy — industrial robots, astronomical telescopes, CNC rotary tables, and the like — the crossed roller type is the preferred choice. General construction machinery has relatively lower accuracy requirements as long as load capacity is met, so the remaining types can be selected based on load.

(3) Selection by Space and Mounting Conditions When installation space is limited, prioritize the crossed roller type for its compact structure. When the mounting base is relatively flexible or prone to deformation, ball types (point contact) offer better adaptability. For large equipment with rigid bases and ample space, the three-row roller type — with the strongest load capacity — is preferred.

(4) Other Key Factors

• Speed and start-stop frequency: for continuous high-speed rotation, prioritize ball types; for heavy-load low-speed applications, choose roller types.
• Operating environment: in dusty conditions (e.g., mining), enhance sealing; in marine or high-humidity environments, apply anti-corrosion coating and stainless steel components; for extreme high- or low-temperature conditions, select matching grease.
• Gear configuration: choose internal gear, external gear, or gearless design according to transmission needs, and verify the module, tooth count, and tooth surface hardness.
• Safety factor: select the static load safety factor according to the working conditions (1.1–1.25 for steady operation; 1.5 or higher for impact or safety-critical applications); for lifting equipment, also include the lifting inertia factor.
• Lubrication and maintenance: replenish grease at prescribed intervals and regularly inspect the raceways, gear teeth, and seals.

VI. Comprehensive Comparison of the Four Structural Types

In terms of load capacity, the three-row roller type, with its line-contact loading, offers the strongest axial load capacity and tilting resistance, making it suitable for heavy-duty applications such as mining excavators and wind turbine installation vessel cranes. The double-row ball type and the crossed roller type rank in the middle, handling medium-to-heavy loads. The single-row four-point contact ball type offers moderate capacity, suited to small-to-medium-load equipment.

In terms of rotational accuracy, the crossed roller type achieves the highest accuracy thanks to its alternating roller arrangement and balanced loading, making it the first choice for precision equipment such as industrial robots, astronomical telescopes, and CNC rotary tables. The single-row four-point contact ball type and the double-row ball type provide relatively high accuracy, adequate for general construction machinery. The three-row roller type offers moderate accuracy — its strength lies in heavy-load capacity rather than precision.

In terms of speed and friction, ball bearings feature low friction and low starting torque, suiting them to higher speeds and frequent start-stop operation. The crossed roller type, also based on rolling contact, runs smoothly with low friction. The three-row roller type has higher roller friction and lower speed, making it better suited to heavy-load, low-speed rotation.

In terms of structural compactness, the crossed roller type has the smallest axial height and occupies the least space. The single-row four-point contact ball type also features a small structural height. The double-row ball type ranks in the middle, while the three-row roller type is the largest — but in return it offers the strongest load capacity.

In summary, each of the four structural types has its own strengths: choose the single-row four-point contact ball type for cost-effectiveness and flexible rotation, the double-row ball type for a balance of load capacity and rotation performance, the three-row roller type for severe heavy-duty conditions, and the crossed roller type for high precision and compact spaces.

Conclusion

Besides the common types described above, slewing bearings also include double-row ball types with equal diameters, ball-and-roller combined types, and others, each suited to specific working conditions. Selection should take loads, accuracy, speed, space, environment, and maintenance conditions into overall consideration, with load capacity verified against the current industry standard JB/T 2300-2018 Slewing Bearings. If you have any questions about selection, contact the Ximark Slewing Bearing Factory — our professional engineers will recommend or customize the right model for your actual working conditions. A properly selected slewing bearing is the foundation for efficient, stable equipment operation and a longer overall machine service life.