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Views: 0 Author: Site Editor Publish Time: 2025-12-15 Origin: Site
A slewing gear is a large rotational component that combines a slewing bearing with gear teeth on its inner or outer ring. It supports axial loads, radial loads and overturning moments while allowing a machine structure to rotate through a pinion or other drive mechanism.
Slewing gears are also commonly called slewing ring gears or geared slewing rings. They are mainly used in cranes, excavators, wind turbines, port machinery, mining equipment and industrial turntables that require controlled rotation under heavy loads.
These three terms are closely related, but they do not always refer to the same component.
| Term | Meaning | Primary function |
|---|---|---|
| Slewing bearing | A large bearing that supports combined loads and rotational movement | Supports loads and guides rotation |
| Slewing gear | A slewing bearing with integrated internal or external gear teeth | Supports loads and transmits drive torque |
| Slewing drive | A packaged drive unit containing a slewing bearing, drive gear, housing and sometimes a motor | Provides a complete enclosed rotary drive |
A slewing bearing may have internal gear teeth, external gear teeth or no gear. When gear teeth are machined directly into one of the bearing rings, it can be described as a geared slewing ring or slewing ring gear.
A slewing drive is a more complete assembly. Depending on its design, it may use a worm gear or spur gear to drive the slewing bearing.
A slewing gear supports the rotating structure and transfers torque from the drive system.
The operating process can be summarized as follows:
A motor or hydraulic drive turns the pinion.
The pinion meshes with the teeth on the slewing ring.
Torque is transferred to the geared inner or outer ring.
Rolling elements allow the two bearing rings to rotate relative to each other.
The bearing carries axial, radial and moment loads during rotation.
One bearing ring is normally fixed to the stationary structure, while the other is connected to the rotating structure. The mounting bolts, supporting structure and pinion alignment all affect the operating accuracy and service life of the system.
A typical geared slewing ring includes:
The inner ring forms one side of the bearing raceway. Depending on the design, it may contain mounting holes or internal gear teeth.
The outer ring connects the bearing to the surrounding structure. External gear teeth can be machined around its outer diameter.
Balls or cylindrical rollers transfer loads between the two rings while reducing rotational resistance.
The raceway guides the rolling elements and carries contact loads. Raceway geometry, hardness and surface quality influence load capacity and fatigue life.
Gear teeth transmit torque from the pinion to the rotating bearing ring. Important gear parameters include module, pressure angle, number of teeth, tooth width, accuracy and hardness.
The cage or spacers maintain appropriate separation between the rolling elements.
Seals help retain lubricant and reduce the entry of dust, water and other contaminants.
Lubrication holes allow grease to be added to the bearing raceway. Gear teeth normally require separate lubrication.
An external gear slewing ring has teeth around the outside of the outer ring. The drive pinion engages with the external teeth.
Its main advantages include:
Easy access for gear inspection
Convenient pinion installation
Flexible drive arrangement
Suitable for many cranes and construction machines
Because the gear teeth are exposed, external gear slewing bearings require appropriate lubrication and protection against dust, moisture and impact.
External gear designs are commonly used in excavators, cranes, concrete placing equipment, lifting platforms and material-handling machinery.
An internal gear slewing ring has teeth machined into the inner diameter of one bearing ring. The pinion and gear mesh are positioned inside the bearing.
Its potential advantages include:
Compact drive arrangement
Better protection for the gear mesh
Reduced exposure to external contamination
More space around the outside of the bearing
Internal gear slewing bearings are often selected when installation space, gear protection or machine layout makes an internal drive arrangement preferable.
View an example of a cross roller slewing bearing with internal gear.
A gearless slewing ring does not have teeth on either bearing ring. It supports the load and guides rotation, while a separate mechanism supplies the driving force.
Gearless designs may be used when:
The machine already has a separate drive system
Gear transmission is not required
Rotation is produced by hydraulic cylinders, chains or other mechanisms
The bearing is mainly required for load support
View a single-row ball slewing bearing without gear.
| Configuration | Gear position | Main advantage | Key consideration |
|---|---|---|---|
| External gear | Outside the outer ring | Easy inspection and flexible pinion installation | Gear teeth need external protection |
| Internal gear | Inside the inner ring | Compact and better protected gear mesh | Installation and inspection space must be considered |
| Gearless | No integrated gear | Simple bearing structure | Requires a separate rotation mechanism |
There is no universally superior gear configuration. The correct design depends on the available space, required transmission ratio, pinion position, environmental conditions and supporting structure.
Gear configuration determines how the bearing is driven, while the internal bearing structure determines how loads are carried.
A single-row four-point contact ball slewing gear uses one row of balls in a specially designed raceway.
It can carry:
Axial loads
Radial loads
Overturning moments
This structure provides a compact size and relatively low weight. It is commonly used in excavators, truck cranes, aerial platforms and small to medium lifting equipment.
A double-row ball slewing gear uses two rows of balls to provide greater load capacity and structural stiffness.
It may be selected for applications requiring:
Higher axial load capacity
Larger overturning moment capacity
Greater structural rigidity
A larger bearing diameter
A cross roller slewing gear uses cylindrical rollers arranged alternately at right angles.
This structure provides:
High rigidity
Good rotational accuracy
High moment load capacity
Compact radial dimensions
Cross roller slewing bearings are commonly used in machinery that requires both load capacity and stable rotational accuracy.
A three-row roller slewing gear uses separate roller rows to carry axial loads, radial loads and overturning moments.
It is generally selected for large and heavily loaded equipment such as:
Large cranes
Port handling machinery
Offshore equipment
Mining machinery
Heavy industrial turntables
Because the loads are distributed across different roller rows, this structure can provide high load capacity for large-diameter applications.
Slewing gears are designed to carry several types of loads simultaneously.
Axial load acts parallel to the rotational axis. Examples include the vertical weight of a crane upper structure or industrial platform.
Radial load acts perpendicular to the rotational axis. It may result from lateral forces, machine movement or external working loads.
An overturning moment is created when a load acts at a distance from the center of rotation. This is a major selection factor for cranes, excavators and lifting machinery.
The gear teeth must transmit the required drive torque without excessive tooth stress, wear or deformation.
Excavators, cranes and mining equipment may experience sudden changes in load. These operating conditions should be included in the bearing and gear calculations.
Slewing gears allow the crane upper structure, boom and load to rotate relative to the undercarriage or supporting base. Applications include tower cranes, crawler cranes, truck cranes, deck cranes and harbor cranes.
An excavator slewing gear supports the upper structure and transfers torque from the swing drive. It must withstand digging forces, vibration, shock loads and frequent directional changes.
Geared slewing rings are used in wind turbine yaw and pitch systems. Yaw bearings help rotate the nacelle toward the wind, while pitch bearings support controlled blade-angle adjustment.
Harbor cranes, ship deck cranes and loading equipment use slewing gears to rotate heavy structures under changing loads and harsh environmental conditions.
Stacker reclaimers, bucket-wheel excavators and bulk material systems require large slewing bearings capable of supporting heavy loads and continuous operating cycles.
Large production lines, welding positioners and assembly platforms use slewing ring gears for controlled rotation and positioning.
Selecting a slewing gear requires more than choosing an outside diameter. The following information should be evaluated.
Provide axial load, radial load and overturning moment values. Both maximum and normal operating loads should be considered.
Important gear information includes:
Internal or external gear
Gear module
Pressure angle
Number of teeth
Tooth width
Gear accuracy
Gear hardness
Required drive torque
Pinion dimensions
Required backlash
The inside diameter, outside diameter, overall height, mounting hole positions and surrounding installation space must match the machine structure.
Specify the maximum speed, normal operating speed, rotation angle, operating frequency and whether the bearing rotates continuously or intermittently.
Choose between single-row ball, double-row ball, cross roller or three-row roller structures according to load capacity, stiffness, weight and dimensional requirements.
Dust, moisture, salt, extreme temperatures and corrosive materials affect the required seal, lubricant, material and surface treatment.
The mounting surface must provide adequate rigidity and flatness. Improper installation can cause uneven load distribution, gear misalignment and premature wear.
Insufficient, unsuitable or contaminated grease can increase raceway wear and gear tooth damage.
Too little backlash may cause binding and abnormal heat. Excessive backlash may produce impact, noise and positioning errors.
Incorrect pinion position can concentrate the load on one side of the gear tooth and cause uneven wear.
Insufficient bolt preload can allow movement between the slewing bearing and mounting structure.
Loads or moments exceeding the design conditions can damage raceways, rolling elements, gear teeth or mounting bolts.
Damaged seals may allow dirt and water to enter the raceway while permitting grease to escape.
An uneven or insufficiently rigid mounting structure can distort the bearing rings and create localized loading.
To support reliable operation:
Lubricate the bearing raceway at the specified intervals
Apply suitable lubricant to the gear teeth
Inspect seals for cracking, separation or leakage
Check mounting bolt preload
Monitor abnormal noise, vibration and temperature
Inspect gear teeth for pitting and uneven wear
Check pinion alignment and gear backlash
Remove dirt and contaminants from exposed gear teeth
Record operating changes during regular inspections
Maintenance intervals should be determined according to load, operating frequency, temperature, contamination and equipment manufacturer requirements.
LYXQL manufactures large-size slewing bearings with internal gear, external gear and gearless configurations. Available bearing structures include single-row ball, double-row ball, cross roller, three-row roller and ball-and-roller combination designs.
To evaluate a slewing gear for a new machine or replacement project, provide:
Bearing drawing or required dimensions
Axial, radial and moment loads
Gear module and number of teeth
Internal or external gear requirement
Operating speed and duty cycle
Pinion data
Mounting hole requirements
Working temperature and environment
Required material, hardness and accuracy
LYXQL can evaluate standard and non-standard slewing ring gear requirements according to the application parameters.
Contact LYXQL to discuss your slewing gear application.
A slewing gear is a slewing bearing with integrated internal or external gear teeth. It supports axial, radial and moment loads while transmitting torque from a drive pinion.
Not always. A slewing bearing may have internal gear teeth, external gear teeth or no gear. The term slewing gear generally refers to a geared slewing bearing or slewing ring gear.
A motor or hydraulic drive turns a pinion that meshes with the slewing ring gear. The pinion transfers torque to one bearing ring, causing the connected machine structure to rotate.
An internal gear has teeth inside the bearing ring and offers a compact, protected gear arrangement. An external gear has teeth around the outside and generally provides easier pinion installation and inspection.
Typical applications include cranes, excavators, wind turbines, port machinery, mining equipment, material-handling systems and industrial turntables.
Required information normally includes bearing dimensions, axial and radial loads, overturning moment, gear type, module, number of teeth, pinion data, speed, duty cycle and operating environment.
