What Are The Properties of Slewing Bearings?

Slewing bearings, also known as slewing rings or turntable bearings, are large-diameter rotational bearings that can support axial loads, radial loads, and tilting moments, either individually or in combination. Their properties are critical to their performance in various applications. 

Slewing Bearings Properties

1. Load Capacity:

Axial Load Capacity: The ability to support loads perpendicular to the bearing's plane of rotation (vertical loads). This is usually expressed as a static and dynamic axial load rating.

Radial Load Capacity: The ability to support loads parallel to the bearing's plane of rotation (horizontal loads). This is also expressed as static and dynamic radial load ratings. Radial load capacity is often lower than axial load capacity.

Tilting Moment Capacity: The ability to resist overturning moments that try to tilt the bearing. This is often the limiting factor in many applications. A large tilting moment capacity prevents excessive edge loading and bearing failure.

2. Rotation Speed:

Maximum Speed: Slewing bearings typically operate at relatively low speeds. Exceeding the maximum allowable speed can lead to excessive heat generation and bearing damage. The allowable speed depends on the bearing's size, lubrication, and operating conditions.

3. Accuracy and Stiffness:

Rotational Accuracy: Refers to the precision of rotation. Factors affecting accuracy include manufacturing tolerances, bearing clearance, and deformation under load.

Stiffness: The resistance to deformation under load. Higher stiffness results in less deflection under load, which is important for applications requiring precise positioning. Stiffness is affected by the bearing's design, size, and material.

4. Friction and Torque:

Friction Torque: The resistance to rotation caused by friction between the rolling elements, raceways, and seals. Lower friction torque is desirable for reducing power consumption and heat generation.

Starting Torque: The torque required to initiate rotation from a stationary position.

Running Torque: The torque required to maintain rotation at a given speed.

5. Material:

Raceways and Rolling Elements (Balls or Rollers): Typically made of high-carbon chromium bearing steel (e.g., 52100 steel) for high hardness, wear resistance, and fatigue strength.

Rings: Can be made of various materials, including:

Forged Steel: Common for most applications, offering good strength and durability.

Stainless Steel: Used in corrosive environments or applications requiring hygiene.

Aluminum: Used for weight reduction in some applications.

Seals: Typically made of nitrile rubber (NBR) or other elastomers to prevent contamination and retain lubricant.

6. Size and Weight:

Outer Diameter: Can range from a few inches to several meters, depending on the application.

Inner Diameter: Similar range as outer diameter.

Width: The axial dimension of the bearing.

Weight: Can vary from a few pounds to several tons.

7. Operating Temperature:

Temperature Range: Slewing bearings have a limited operating temperature range. Exceeding the allowable temperature can degrade the lubricant, reduce bearing life, and potentially cause material damage. The specific range depends on the materials and lubricant used.

8. Environmental Resistance:

Corrosion Resistance: The ability to withstand corrosion from moisture, chemicals, or other environmental factors. Stainless steel or special coatings may be used to enhance corrosion resistance.

Dust and Dirt Resistance: Seals are crucial for preventing dust and dirt from entering the bearing, which can cause wear and damage.

9. Lubrication:

Grease Type: As mentioned previously, proper grease selection is critical. Lithium-based greases with EP additives are commonly used.

Lubrication Method: Typically grease lubrication, applied through grease fittings. Oil lubrication may be used in some applications.

10. Gear Type (if geared):

External Gear: The gear teeth are on the outside of the bearing ring.

Internal Gear: The gear teeth are on the inside of the bearing ring.

No Gear: The bearing is smooth, requiring an external drive mechanism.

Gear Material and Hardness: Important for durability and wear resistance.

11. Other Important Considerations:

Bearing Type: Ball bearings, roller bearings (cylindrical, tapered, or cross-roller), and wire race bearings each have different load capacities, stiffness, and friction characteristics.

Preload: Some slewing bearings are preloaded to eliminate play and increase stiffness.

Mounting Considerations: The flatness, rigidity, and alignment of the mounting surfaces are crucial for proper bearing performance.

Understanding these properties is crucial for selecting the right slewing bearing for a specific application and for ensuring its reliable performance. Always consult the manufacturer's specifications and guidelines.