How To Choose Between Internal And External Gear Slewing Bearings

How To Choose Between Internal And External Gear Slewing Bearings

What Are Internal Gear Slewing Bearings And External Gear Slewing Bearings?

Internal gear slewing bearings and external gear slewing bearings are the two primary configurations of slewing bearing, essential components enabling rotational motion under heavy loads in countless industrial machines. Both types feature rolling elements (balls or rollers) contained between concentric inner and outer rings, facilitating smooth, low-friction rotation around a central axis. The fundamental distinction lies in the location of the gear teeth. Internal gear slewing bearings have their gear teeth machined onto the inner surface of the outer ring. Conversely, external gear slewing bearings have their gear teeth machined onto the outer surface of the outer ring. This seemingly simple difference in gear placement drives significant variations in their performance characteristics, optimal applications, and integration requirements.

How To Choose Between Internal And External Gear Slewing Bearings?

Selecting the right slewing bearing type hinges on carefully evaluating several key aspects of your application:

Available Space and Structural Constraints: This is often the primary driver.

Internal Gear Bearings: The gear teeth are recessed within the bearing's outer diameter profile. This makes them inherently more compact radially and ideal where space is extremely limited around the perimeter of the bearing. Their design also naturally shields the gear teeth from direct exposure to external contaminants like dust, debris, and weather.

External Gear Bearings: Require sufficient radial clearance around the outer diameter of the bearing to accommodate the protruding gear teeth and the meshing pinion drive. They are best suited for applications where ample space exists around the bearing circumference for easy pinion access and integration.

Torque Transmission and Load Capacity Requirements:

Internal Gear Bearings: Generally offer a good balance for medium loads and torque requirements, commonly found in smaller to mid-sized equipment. While capable, their typically smaller gear diameter compared to external bearings of the same overall size can limit maximum torque transmission capacity.

External Gear Bearings: Feature a larger effective gear diameter relative to the bearing size. This allows for more teeth to be engaged simultaneously with the pinion, resulting in significantly higher torque transmission capability and superior load handling capacity, especially crucial for very heavy machinery and high-torque applications.

Drive Efficiency and Operating Conditions:

External Gear Bearings: The larger gear diameter generally provides superior efficiency in low-speed, high-torque scenarios. The increased contact area between pinion and gear spreads the load more effectively.

Internal Gear Bearings: Can perform comparably at higher speeds but might exhibit slightly lower efficiency under very high torque loads due to the smaller gear diameter and potentially higher contact stresses. Lubrication access can sometimes be more challenging.

Environmental Conditions and Protection Needs:

Internal Gear Bearings: Offer superior inherent protection for the gear teeth. The recessed location shields them from direct impact, splash, and airborne contaminants. This makes them highly suitable for harsh environments (dusty, wet, corrosive) or applications where minimal maintenance is desired. Achieving high IP (Ingress Protection) ratings is often easier.

External Gear Bearings: The exposed gear teeth are more vulnerable to contamination, wear, and damage from the operating environment. While easier to clean and inspect visually, they typically require more frequent maintenance (cleaning, lubrication) and potentially additional protective guarding or sealing solutions in demanding conditions.

Cost Considerations and Budget:

Internal Gear Bearings: Generally carry a higher initial cost. Machining gear teeth on an internal surface is more complex, requires specialized tooling, and is often more time-consuming than external gear machining. Heat treatment processes can also be more challenging.

External Gear Bearings: Are typically more cost-effective to manufacture, especially for larger diameters and in higher production volumes. The external teeth are easier to machine, inspect, and harden.

Characteristics Of Internal Gear Slewing Bearings And External Gear Slewing Bearings

Internal Gear Slewing Bearings:

Gear Location: Teeth on the inner surface of the outer ring.

Radial Space Efficiency: Excellent – compact outer profile.

Gear Protection: High – teeth are recessed and shielded.

Torque Capacity: Moderate to High (depending on size/design).

Manufacturing Complexity: Higher – internal machining.

Relative Cost: Higher.

Maintenance Access: More difficult – gear teeth less accessible.

Sealing: Generally easier to achieve higher sealing effectiveness.

External Gear Slewing Bearings:

Gear Location: Teeth on the outer surface of the outer ring.

Radial Space Requirement: Larger – needs clearance for teeth and pinion.

Gear Protection: Lower – teeth are exposed.

Torque Capacity: High to Very High – larger effective diameter.

Manufacturing Complexity: Lower – external machining.

Relative Cost: Lower.

Maintenance Access: Easier – gear teeth readily accessible.

Pinion Mounting: Simpler integration with drive systems.

Applications For Internal Gear Slewing Bearings And External Gear Slewing Bearings

The distinct characteristics of each type naturally lend them to different industrial sectors and machinery:

Internal Gear Slewing Bearings: Excel in applications demanding compactness, environmental protection, and precision, often under moderate loads:

Radar Antennas & Satellite Communication: Where compact size, precision rotation, and weather protection are paramount.

Military Equipment (Turrets, Missile Launchers): Requiring ruggedness, reliability in harsh conditions, and space efficiency.

Robotics & Precision Automation: Especially robotic arms and indexing tables needing smooth motion within confined spaces.

Medical Imaging Equipment (CT Scanners): Needing precise, quiet rotation and compact design.

Packaging Machinery: Where space is limited and protection from dust/lubricants is beneficial.

Solar Trackers: Increasingly popular due to compactness and environmental resilience.

External Gear Slewing Bearings: Dominate applications requiring maximum torque, heavy load handling, and where space is less constrained:

Tower Cranes & Mobile Cranes: Handling massive loads and requiring high torque for slewing the boom.

Wind Turbines (Yaw & Pitch Drives): Subjected to enormous, unpredictable loads and requiring very high torque transmission.

Excavators & Heavy Construction Equipment (Swing Drives): Enduring extreme shock loads and dirt in demanding environments.

Mining Machinery (Bucket Wheels, Stackers/Reclaimers): Handling abrasive materials and requiring immense torque.

Material Handling Equipment (Large Forklifts, Port Cranes): Lifting and moving heavy cargo efficiently.

Industrial Mixers & Large Valves: Where high torque is needed to rotate heavy drums or valve components.

Price Factors Influencing Internal Gear Slewing Bearings And External Gear Slewing Bearings

The cost of both internal gear slewing bearings and external gear slewing bearings is influenced by a complex interplay of factors:

Gear Type & Manufacturing Complexity: As discussed, internal gears are inherently more expensive to produce due to the complexity of machining and heat-treating teeth on an internal surface. External gears are simpler and cheaper to manufacture.

Bearing Size & Dimensions: Larger diameter bearings, regardless of gear type, require more material, larger machining centers, and more complex heat treatment, significantly increasing cost. Height (cross-section) also impacts material usage.

Load Capacity & Design Complexity: Bearings engineered for higher static/dynamic loads, moment capacities, or specific stiffness requirements involve more complex internal designs (e.g., more rows of rolling elements, specialized raceway profiles), better materials, and stricter manufacturing tolerances, raising costs.

Material Selection: The grade and quality of steel used (e.g., standard 42CrMo4, higher grades like 50Mn, or specialized case-hardening steels) significantly impact cost. Corrosion-resistant materials (e.g., stainless steel variants) add substantial expense.

Precision & Tolerance Requirements: Bearings requiring ultra-high precision (e.g., for radar or medical use) or very tight tolerances for gear profile, runout, or preload demand more sophisticated manufacturing and inspection processes, increasing cost.

Heat Treatment & Surface Hardening: The specific hardening process (e.g., induction hardening, carburizing) and the required depth and hardness profile for raceways and gears affect cost. Achieving consistent hardness on internal gears is more challenging.

Sealing & Protection: Integrated sealing solutions (multi-lip seals, labyrinth seals), special coatings (zinc plating, paint, Dacromet, Geomet), or requirements for specific IP ratings add cost. Internal gears might need less complex sealing for the teeth themselves, but overall bearing sealing requirements still apply.

Customization: Standard catalog bearings are generally cheaper. Bearings requiring custom bolt patterns, lubrication systems, special flanges, integrated sensors, or unique dimensional specifications incur significant engineering and setup costs.

Quantity & Economies of Scale: Larger production runs spread fixed costs (tooling, setup) over more units, reducing the per-bearing cost significantly. Prototypes or small batches are much more expensive per unit.

Certification Requirements: Meeting specific industry standards (e.g., DNV-GL, ABS, CE) or undergoing rigorous testing protocols adds administrative and testing costs.

Geographic Origin & Logistics: Manufacturing location, import duties, taxes, and shipping costs for large, heavy components influence the final price.

Partnering With A Reliable Slewing Bearing Supplier

Selecting the optimal internal or external gear slewing bearing is critical, but ensuring its quality, performance, and longevity is equally important. This requires partnering with a reputable manufacturer known for engineering expertise, precision manufacturing, rigorous quality control, and responsive technical support. LYRADRIVE stands as a leading supplier in this field. We offer a comprehensive range of both standard and highly customized internal gear and external gear slewing bearings, engineered to meet the most demanding specifications across diverse industries like construction, renewable energy, material handling, and industrial automation. LYRADRIVE leverages advanced manufacturing capabilities and stringent quality assurance processes to deliver durable, high-performance slewing solutions backed by expert application engineering support to ensure the perfect bearing fit for your unique requirements. Contact LYRADRIVE to discuss your specific slewing bearing needs and experience the difference quality engineering makes.