Repair and Remanufacturing of Large Slewing Bearings: A Cost-Effective Alternative
What Is a Slewing Bearing?
A slewing bearing—also called a slewing ring or turntable bearing—is a large-diameter rotational bearing that supports heavy loads while enabling rotation between two structures. It handles axial loads, radial loads, and tilting moments simultaneously. These bearings are essential in cranes, excavators, wind turbines, tunnel boring machines, and other heavy equipment where large structures must rotate.
Large-diameter slewing bearings often reach several meters in diameter with wide raceways. They are precision-engineered components that are expensive to manufacture and time-consuming to replace. When a slewing bearing fails, a new bearing can take weeks or months to deliver due to the complex manufacturing process and long supply chains. This creates significant downtime for equipment operators.
Why Consider Repair and Remanufacturing for Slewing Bearings?
Replacing a large slewing bearing is costly and time-consuming. The bearing itself is expensive—often costing tens of thousands of dollars or more. The replacement process requires specialized equipment, skilled labor, and extended downtime. For equipment operators, every day of downtime means lost production and revenue.
Repair and remanufacturing offer a practical alternative. Depending on the level of repair, savings can range from 40% to 70% compared to the cost of a new bearing. Kaydon reports that remanufactured bearings typically cost 50% less than new OEM bearings. The lead time for remanufacturing is significantly shorter—Kaydon offers four-week turnaround for bearings up to 8 feet in diameter. Trasmec reports delivery time reductions of up to 80% compared to new production.
A slewing bearing with only 30% of its calculated service life remaining can still be well worth remanufacturing. SKF notes that remanufacturing can extend bearing life cycle by 50% or more while reducing total lifecycle costs. Some bearings can even be remanufactured multiple times without compromising performance.
Environmental benefits are another consideration. Remanufacturing uses significantly less energy and materials than producing a new bearing, resulting in lower CO₂ emissions. This makes remanufacturing a more sustainable choice for environmentally conscious operators.
When Is a Slewing Bearing Eligible for Remanufacturing?
Not every damaged slewing bearing can be repaired. The bearing must meet certain criteria to be eligible for remanufacturing.
Bearing condition: The best candidates are bearings removed before serious degradation occurs. Once the damage progresses beyond a certain point, repair becomes impractical or impossible. Bearings that have experienced severe cracking, broken teeth, or extensive raceway spalling may not be repairable.
Hardened case depth: The remaining hardened layer depth is critical. If regrinding the raceway would remove too much of the hardened case, the bearing cannot support the required loads. RBC Bearings applies a design rule of 11% of the rolling element diameter as the minimum effective case depth required for most applications.
Structural integrity: The bearing rings must be free of cracks or other structural damage. Non-destructive testing (NDT) methods such as magnetic particle inspection and ultrasonic testing detect hidden defects.
Most bearings can be remanufactured: Kaydon states that it can remanufacture any bearing up to 26.25 feet (8 meters) in diameter, regardless of design, configuration, or original manufacturer. High-quality bearings with stable performance are particularly good candidates.
The Slewing Bearing Remanufacturing Process
The remanufacturing process for slewing bearings follows a systematic approach. The specific steps depend on the condition of the bearing and the level of repair required.
1. Initial Inspection and Assessment
The process begins with a thorough inspection. The bearing is cleaned and examined for damage. Key measurements include:
- Turning torque: Measures rotational resistance
- Free-state clearance: Checks internal clearance
- Gear condition: Inspects teeth for wear, pitting, or breakage
- External features: Documents overall condition
Non-destructive testing identifies hidden defects. Magnetic particle inspection detects surface cracks, while ultrasonic testing checks for subsurface defects and measures hardened case depth. Hardness readings are recorded to verify that the raceway still meets specifications.
An engineering analysis determines whether the bearing can be remanufactured and at what level. A formal inspection report is provided to the customer with recommendations.
2. Disassembly and Cleaning
The bearing is fully disassembled. All components—rings, rolling elements, spacers, cages, and seals—are separated and cleaned. This allows thorough inspection of each part.
3. Raceway Repair (Level 3 and 4 Repairs)
For bearings with worn or damaged raceways, the damaged surface is removed and rebuilt. Several methods are used:
Plasma-Transferred Arc (PTA) Welding: This advanced welding process applies a new cladding material to the damaged raceway. PTA welding offers a small heat-affected zone, high automation, and deposition rates up to 15 kg/h. The cladding material bonds metallurgically to the base material. Researchers have developed a complete repair process chain using PTA welding to restore damaged slewing bearing raceways.
The process chain involves:
- Removing the entire damaged raceway (milling out the worn surface)
- Applying repair welding using a specially developed alloy as cladding
- Heat treatment to improve service life properties
- Machining to reach nominal dimensions
- Incremental forming to generate residual compressive stresses
Precision grinding: In some cases, the raceway is reground to restore the proper geometry and surface finish. This optimizes load-carrying capability. Care must be taken to ensure sufficient hardened case remains.
New induction hardening: For bearings with high wear, the raceway may undergo a new induction hardening process after repair.
4. Component Replacement
Rolling elements (balls or rollers) are always replaced with new ones during remanufacturing. Cages, spacers, and seals are also replaced as needed. Some bearings require replacement of a major component such as an inner or outer ring—this is the highest level of remanufacturing (Level 4).
5. Reassembly and Final Inspection
The bearing is reassembled with new rolling elements and seals, then packed with fresh lubricant. Final inspection verifies all critical features meet specifications. A test report documents clearance and torque measurements. Remanufactured bearings typically come with a one-year warranty, just like new bearings.
Levels of Slewing Bearing Remanufacturing
Bearing manufacturers classify repairs by level, depending on the extent of work required:
| Level | Description | Typical Candidates |
|---|---|---|
| Level 1 | Clean, inspect, lubricate, repackage | Bearings with storage damage only |
| Level 2 | Clean, inspect, polish raceways, replace seals, reassemble | Bearings at ~50% of theoretical life |
| Level 3 | Full race grinding, replace rolling elements and cages, new seals | End-of-life bearings, abnormal clearance |
| Level 4 | Replace major components (inner or outer ring), plus Level 3 work | Heavily damaged bearings |
Warning Signs That a Slewing Bearing Needs Attention
Identifying slewing bearing problems early increases the chances of successful remanufacturing. Watch for these warning signs:
Metal particles in grease: Metal flakes or dark discoloration in the expelled grease indicates active internal wear. This is the most reliable indicator of raceway damage. Clean grease should be smooth and uniform. Metal particles mean the bearing surfaces are deteriorating.
Abnormal noise: Grinding, clicking, or rhythmic popping during rotation indicates raceway or gear damage. A rhythmic knock repeating at regular intervals often indicates brinelling—localized raceway deformation. Continuous grinding usually means raceway damage.
Uneven or jerky rotation: Hesitation, binding, or uneven movement during rotation suggests worn rolling elements or raceways. Resistance at specific points often points to a localized defect such as a crack or deformed raceway.
Excessive play: Visible rocking of the upper structure—especially with the boom extended—means the bearing clearance has exceeded its wear limit. For excavators, axial clearance exceeding 2.0mm to 3.0mm is considered the red line.
Grease leakage: Visible grease leaking around the seal indicates seal failure. Once the seal is compromised, contaminants enter the bearing cavity and accelerate wear rapidly.
How LDB Bearing Supports Cost-Effective Solutions
LDB Bearing designs and manufactures high-quality slewing bearings and slew drives 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 commitment to value:
- Quality manufacturing: ISO 9001-certified manufacturing with documented inspection reports and full material traceability
- Comprehensive product range: All major slewing bearing types with internal, external, or gearless configurations
- Engineering support: Application engineering for load calculations, finite element analysis, and custom designs
- Global reach: Serving 73 countries with over 500,000 units in service
While LDB specializes in new slewing bearing manufacturing, the company understands the importance of lifecycle management. Proper selection, installation, and maintenance extend bearing life and maximize return on investment. When replacement becomes necessary, LDB offers quality alternatives to help equipment operators maintain productivity with minimal downtime.
Contact LDB Bearing today to discuss your slewing bearing requirements and explore the most cost-effective solution for your application.
FAQs
1. How much can I save by remanufacturing a slewing bearing instead of buying new?
Savings typically range from 40% to 70% compared to the cost of a new bearing. Kaydon reports savings of approximately 50%, while Trasmec reports 40-70% savings.
2. How long does slewing bearing remanufacturing take?
Lead time is significantly shorter than new production. Kaydon offers four-week turnaround for bearings up to 8 feet in diameter, with slightly longer lead times for larger bearings. This compares to weeks or months for new bearings.
3. What types of slewing bearings can be remanufactured?
Most slewing bearing types can be remanufactured, including four-point and eight-point contact ball, crossed roller, and three-row roller bearings. Diameters up to 26 feet (8 meters) can be handled.
4. How many times can a slewing bearing be remanufactured?
Some bearings can be remanufactured multiple times without compromising performance. Each remanufacturing cycle extends the bearing’s service life. The practical limit depends on the remaining material and hardened case depth.
5. What is the warranty on remanufactured slewing bearings?
Reputable manufacturers like Kaydon offer a full one-year warranty on remanufactured bearings, the same as new bearings.
