Slewing bearings are important components in tunnel boring machines (TBMs) where large axial loads, radial loads and overturning moments must be supported within a large rotating structure. The right slewing bearing design helps maintain reliable rotation, structural rigidity and long service life under demanding tunneling conditions.
Unlike conventional rolling bearings, slewing bearings are designed specifically for large-diameter rotating structures and can accommodate combined radial loads, axial loads and tilting moments. Different TBM designs may require different slewing bearing configurations depending on load conditions, machine dimensions, rotation speed and mounting requirements.
Why Are Slewing Bearings Important in TBMs?
A tunnel boring machine operates under demanding mechanical conditions. During excavation, the rotating structure can experience substantial axial thrust, radial forces and overturning moments. These loads may vary depending on excavation conditions, machine configuration and operating cycles.
A TBM slewing bearing therefore needs to provide more than simple rotational support. It must maintain the relative position between rotating and stationary structures while carrying combined loads over long operating periods.
High Load Capacity
Supports substantial axial and radial loads generated during tunneling operations.
Moment Resistance
Provides resistance to overturning and tilting moments caused by eccentric or uneven loading.
Large Diameter
Designed for large rotating structures where conventional bearings may not be practical.
What Loads Do TBM Slewing Bearings Handle?
Axial Loads
Axial loading is one of the most important considerations in many TBM applications. Excavation forces and machine thrust systems can generate substantial axial loads that must be transferred safely through the bearing.
Radial Loads
Radial forces can result from the weight of rotating components, cutting equipment, support structures and uneven operating conditions. The bearing must provide sufficient radial capacity and rigidity to maintain stable operation.
Tilting Moments
Large-diameter TBM bearings can experience significant overturning moments. These moments create uneven load distribution across the raceway, making bearing geometry, rolling element size and mounting stiffness important factors in the design.
Types of Slewing Bearings for Tunnel Boring Machines
Different TBM structures require different slewing bearing configurations. Three important designs for heavy-duty applications are single-row four-point contact ball slewing bearings, double-row ball slewing bearings and three-row roller slewing bearings.
Four-Point Contact Ball Slewing Bearings
A compact design capable of accommodating combined radial and axial loads as well as tilting moments.
View ProductsDouble-Row Ball Slewing Bearings
Two rows of balls provide increased load capacity and improved resistance to overturning moments.
View ProductsThree-Row Roller Slewing Bearings
Multiple roller raceways provide very high load capacity and rigidity for particularly heavy structures.
View ProductsFour-Point Contact Slewing Bearings for TBMs
Four-point contact ball slewing bearings use a raceway geometry that allows the balls to accommodate loads acting in different directions. This makes them suitable for applications where radial loads, axial loads and moment loads occur simultaneously.
Their relatively compact structure and ability to handle combined loading make four-point contact designs a practical option for rotating structures where space, weight and load capacity must be balanced.
When selecting this type of slewing bearing for a TBM, engineers should consider the bearing diameter, axial load, radial load, tilting moment, rotation speed, lubrication and mounting conditions.
Double-Row Ball Slewing Bearings
Double-row ball slewing bearings use two rows of rolling elements to increase load-carrying capacity compared with a single-row ball design. The two-row arrangement can also provide improved resistance to overturning moments.
This configuration can be considered when a TBM structure requires higher capacity while retaining a ball-based slewing bearing design. The stepped-bore configuration can also be incorporated into applications where the mounting arrangement requires different raceway or bore dimensions.
Three-Row Roller Slewing Bearings for Heavy TBMs
For particularly heavy TBM structures, three-row roller slewing bearings can provide a higher-capacity solution. Separate roller raceways distribute different load components and provide high resistance to combined axial, radial and moment loading.
The larger contact area between rollers and raceways allows these bearings to achieve high load capacity and structural rigidity. They are particularly suitable when bearing stiffness and load capacity are more important than achieving high rotational speed.
Three-Row Roller vs. Ball Slewing Bearings
Ball-type slewing bearings can offer a compact and versatile solution for combined loading, while three-row roller slewing bearings are generally better suited to applications where extremely high load capacity and rigidity are required.
How to Select a Slewing Bearing for a TBM
Slewing bearing selection should begin with the actual load and operating conditions rather than simply choosing a bearing according to its diameter.
1. Combined Loads
Determine the axial load, radial load and tilting moment under both normal and maximum operating conditions.
2. Bearing Diameter
Consider the required inside and outside diameter together with the available installation space and structural stiffness.
3. Rotation Conditions
Evaluate rotation speed, operating cycle, acceleration, vibration and possible shock loading.
4. Lubrication & Sealing
Lubrication intervals, contamination, sealing performance and maintenance access should be considered during selection.
Mounting and Installation
The bearing mounting structure must provide adequate stiffness and dimensional accuracy. Improper mounting can lead to uneven raceway loading, increased stress and premature bearing damage even when the bearing itself has sufficient theoretical load capacity.
For large TBM slewing bearings, the mounting flange, bolt arrangement, housing deformation and installation tolerances should therefore be evaluated together with the bearing.
JYHY Slewing Bearings for Tunnel Boring Machines
JYHY Group manufactures and supplies large and heavy-duty slewing bearings for demanding industrial applications. Our product range includes different slewing bearing configurations for applications requiring high axial capacity, radial load capacity and resistance to overturning moments.
Depending on the TBM design and load requirements, suitable configurations may include single-row four-point contact ball slewing bearings, double-row ball slewing bearings and three-row roller slewing bearings.
For TBM projects, bearing selection should be based on the actual load spectrum, dimensions, rotation requirements and mounting conditions. JYHY can evaluate a suitable bearing configuration based on application data and technical drawings.
Conclusion
Slewing bearings play an important role in TBM rotating structures where high axial loads, radial loads and tilting moments must be supported simultaneously. Four-point contact ball slewing bearings provide a compact solution for combined loading, while double-row ball and three-row roller designs can provide increased load capacity and moment resistance for heavier applications.
The right bearing should be selected according to the complete operating condition rather than bearing size alone. Load combination, bearing diameter, rigidity, rotation, lubrication, sealing and mounting conditions should all be evaluated before final selection.