Tag Archive for: slewing ring assembly

What Is a Slewing Bearing?

A slewing bearing is a large rotating component that supports heavy loads while enabling rotation between two structures. These bearings handle axial loads, radial loads, and tilting moments simultaneously. They are essential in cranes, excavators, wind turbines, and other heavy machinery.

Most slewing bearings are manufactured as single-piece rings. However, when the required diameter exceeds manufacturing or transportation limits, a different approach becomes necessary. Segmented slewing bearings solve this problem by dividing the bearing into multiple sections that are assembled on site.

Why Segmented Slewing Bearings Exist

The demand for ever-larger machinery has pushed slewing bearing diameters beyond what traditional manufacturing and logistics can handle. Offshore installation vessels, ultra-large tunnel boring machines, and giant mining equipment require bearings that measure 10 meters or more in diameter.

Manufacturing limits

Single-piece slewing bearings can be manufactured up to certain diameters depending on the manufacturer’s equipment. Beyond a certain size, manufacturing becomes impractical or impossible with conventional processes.

Transportation constraints

Even if a bearing could be manufactured as a single piece, transporting it presents another challenge. A 15-meter diameter bearing cannot be shipped by standard road or rail. Specialized transport would be prohibitively expensive and logistically complex. Segmented designs solve this problem by allowing shipment in standard containers or on conventional trucks.

Site access limitations

Many project sites—offshore platforms, remote mining locations, underground tunnels—have limited access for large equipment. Segmented bearings can be transported in manageable sections and assembled on site using available lifting equipment.

The industry has responded to these challenges. In 2024, a segmented roller slewing bearing with an outer diameter of 23.4 meters was delivered, consisting of 68 individual segments, for a 2,000-tonne offshore installation crane. This bearing is designed for a service life of 25 years.

How Segmented Slewing Bearings Are Designed

Designing a segmented slewing bearing requires solving problems that do not exist with single-piece bearings. The joints between segments must maintain structural integrity, load-carrying capacity, and sealing performance.

Segmentation strategy

The number of segments depends on the bearing diameter and transportation constraints. Smaller segmented bearings may have 4 to 8 segments, while the largest designs can have 60 or more. Each segment is manufactured with precision to ensure proper fit and alignment during assembly.

Joint design

The joints between segments are critical to performance. They must transfer loads across the connection without creating stress concentrations. Bolted connections are common, with precision-machined mating surfaces to ensure proper load transfer. Some designs use additional keyways or dowels to handle shear forces.

Raceway continuity

The raceway must be continuous across segment joints to allow smooth rolling element passage. Any discontinuity would cause impact loads, noise, and accelerated wear. Manufacturing tolerances are extremely tight to ensure proper alignment when segments are assembled.

Sealing continuity

Seals must also be continuous across joints. Segmented seal designs allow the seal to bridge the gap between segments while maintaining contact with the raceway. This prevents contaminant ingress and lubricant loss at the joints.

Induction-hardened raceways

Modern segmented bearings use induction-hardened raceways rather than replaceable raceway plates. This design eliminates the need for screwed raceway segments, reducing weight and improving cross-section efficiency. The hardening process is performed on each segment before assembly, with careful control to ensure uniform hardness across the entire assembled raceway.

Manufacturing Segmented Slewing Bearings

Manufacturing segmented slewing bearings requires capabilities beyond those needed for single-piece bearings. Each segment must be manufactured to exacting tolerances, and the assembled bearing must perform as a single unit.

Segment manufacturing

Each segment is forged, machined, and heat-treated individually. The raceway is induction-hardened to achieve 55-62 HRC surface hardness with adequate case depth. Gear teeth, if present, are also hardened. After heat treatment, segments are precision-ground to final dimensions.

Quality control

Dimensional inspection verifies that each segment meets specifications. The curvature of the raceway, the flatness of mounting surfaces, and the position of bolt holes are all critical. Any deviation would cause misalignment during assembly, leading to premature failure.

Pre-assembly testing

Before shipment, segments may be pre-assembled at the factory to verify fit and function. This identifies any issues before the bearing reaches the project site, where correction would be far more difficult and expensive.

Applications for Segmented Slewing Bearings

Segmented slewing bearings serve applications where single-piece bearings are impractical or impossible. These are typically the largest and most demanding machines in operation.

Offshore installation cranes

A 23.4-meter segmented bearing delivered in 2024 was for a 2,000-tonne offshore installation crane. These cranes lift massive offshore wind components and oil platform modules. The bearing must handle enormous loads while maintaining precise control in a marine environment.

Tunnel boring machines

The largest tunnel boring machines require main bearings that exceed single-piece manufacturing limits. Segmented designs allow these machines to be built with cutter head diameters of 15 meters or more. The bearing must support the cutter head while withstanding extreme thrust and tilting moments.

Mining equipment

Large mining excavators and draglines use segmented slewing bearings when their size exceeds manufacturing capabilities. These machines operate in harsh conditions with heavy shock loads.

Wind turbine test stands

Test facilities for large wind turbine drivetrains may use segmented bearings to support the rotor assembly during testing. The bearing must handle the full rotor weight and operating loads.

Installation and Assembly of Segmented Slewing Bearings

Assembling a segmented slewing bearing on site requires careful planning and execution. The process differs significantly from installing a single-piece bearing.

Site preparation

The mounting surface must be flat, level, and rigid. For large bearings, the foundation is often constructed with embedded anchor bolts or mounting plates. The surface flatness is critical—any deviation would cause uneven load distribution when the bearing is assembled.

Segment positioning

Segments are lifted into position using cranes or other lifting equipment. Each segment is aligned with its neighbors and temporarily secured. Guide pins or alignment fixtures help achieve proper positioning.

Bolting and torqueing

Once all segments are in position, the connection bolts are tightened to specified torque values. The tightening sequence is critical to ensure even load distribution across the joints. Hydraulic tensioners may be used for large bolts.

Raceway alignment

After assembly, the raceway continuity is checked. Any steps or misalignment at the joints must be corrected before the bearing is put into service. This may require adjustment of the segment positions or additional machining on site.

Seal installation

Seals are installed across the joints to maintain continuity. The seal material must be compatible with the operating environment and lubricant.

Maintenance Considerations for Segmented Slewing Bearings

Segmented bearings require maintenance similar to single-piece bearings, with additional attention to the joints.

Joint inspection

The segment joints are potential weak points. Regular inspection should check for bolt loosening, joint opening, or seal damage at the connections. Any issues should be addressed promptly to prevent escalation.

Lubrication

The lubrication system must ensure that all segments receive adequate lubricant. Grease channels and fittings are distributed around the bearing circumference. The joints may require additional attention to ensure proper lubricant distribution.

Monitoring

Condition monitoring systems can track bearing performance over time. Vibration, temperature, and rotational resistance are key indicators. Any change from baseline performance warrants investigation.

How LDB Bearing Supports Ultra-Large Diameter Applications

LDB Bearing designs and manufactures high-quality slewing bearings for heavy machinery applications. Products use verified 42CrMo forged alloy steel with induction-hardened raceways achieving 55–62 HRC and gear teeth hardened to 50–60 HRC.

LDB’s capabilities:

• Custom design: Application-specific bearings engineered for individual project requirements
• Quality manufacturing: ISO 9001-certified manufacturing with documented inspection reports and full material traceability
• Precision engineering: Capabilities to meet the tight tolerances required for demanding applications
• Global reach: Serving 73 countries with over 500,000 units in service

While LDB specializes in a comprehensive range of slewing bearing sizes and types, the company understands the challenges of ultra-large diameter applications. For projects requiring segmented bearings, LDB offers engineering support and quality assurance to help ensure successful outcomes.

Contact LDB Bearing today to discuss your slewing bearing requirements.

FAQs

1. What is a segmented slewing bearing?
A segmented slewing bearing is a large-diameter bearing manufactured in multiple sections that are assembled on site. This approach overcomes manufacturing and transportation limits for bearings exceeding 10 meters in diameter.

2. Why use a segmented design instead of a single-piece bearing?
Segmented designs solve manufacturing limits (equipment cannot produce larger single pieces), transportation constraints (large bearings cannot be shipped conventionally), and site access limitations (segments can be transported in standard containers).

3. How large can segmented slewing bearings be?
Segmented slewing bearings have been produced with outer diameters exceeding 23 meters. A 23.4-meter bearing with 68 segments was delivered in 2024.

4. What are the challenges in segmented slewing bearing design?
Key challenges include joint design (transferring loads across connections), raceway continuity (maintaining smooth rolling element passage), and sealing continuity (preventing contamination at joints).

5. How are segmented slewing bearings assembled?
Segments are positioned with cranes, aligned with guide pins, bolted to specified torque, and checked for raceway continuity. Seals are installed across joints to maintain protection.