How to Install a Slewing Bearing: Step-by-Step Guide for Heavy Machinery
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.
Slewing bearings are precision-engineered components. They arrive from the manufacturer with specific tolerances, hardening patterns, and surface finishes. However, even the highest-quality slewing bearing will fail prematurely if installed incorrectly. Proper installation ensures the bearing performs as designed and achieves its expected service life.
Why Proper Installation Is Critical for Slewing Bearing Service Life
Proper installation is the bridge between a quality slewing bearing and reliable operation. A poorly installed bearing will fail regardless of its material grade or manufacturing precision.
The consequences of improper installation
When a slewing bearing is installed on an uneven or non-rigid mounting surface, the load does not distribute evenly across the rolling elements. Some rollers carry far more load than others, creating stress concentrations that lead to raceway indentation and spalling. Loose bolts allow the bearing to shift under load, causing misalignment and accelerated wear. Over-tightened bolts can stretch or fracture, risking catastrophic failure.
Industry data shows that a deviation of just 0.5mm in alignment can create contact pressures 300% higher than intended in specific raceway zones. This localized overloading dramatically shortens slewing bearing life. Proper installation prevents these problems before they start.
The key factors in successful installation
Successful slewing bearing installation depends on four factors: a flat and rigid mounting surface, correct bolt torque, proper positioning of the hardness gap, and adequate initial lubrication. Each factor is essential. Neglecting any one compromises the entire installation.
How to Install a Slewing Bearing Properly
This section walks through the complete installation process step by step. Follow these steps carefully to ensure your slewing bearing performs as designed.
Step 1: Prepare the Mounting Surface
Before installing a slewing bearing, inspect both the bearing and the mounting structure. The bearing should be free of damage, corrosion, or contamination from shipping and storage. Remove preserving agents from the slewing bearing’s contact surfaces and gearing using an alkaline cleaning agent. Do not let solvent enter the seals or raceway.
Check the mounting surface flatness. The structure must be rigid and flat to ensure even load distribution across the slewing bearing. If the surface is not completely supported, rework it before proceeding. Use a feeler gauge to check for gaps between the bearing and the mounting surface.
Important: Hardness Gap Positioning
Every slewing bearing ring has an unhardened section between the beginning and end of raceway hardening. This is marked with an “S” on the interior or exterior diameter. Position this “S” mark outside the main load area when the application’s primary load direction is known. This simple step prevents premature failure in the slewing bearing’s most vulnerable zone.
Step 2: Position and Align the Slewing Bearing
Use appropriate lifting equipment rated for the slewing bearing’s weight. Attach lifting straps to designated lifting points, ensuring even weight distribution. Lower the slewing bearing onto the mounting surface, aligning it with pre-marked positions and bolt holes. Use guide pins or alignment tools to help precisely position the slewing bearing.
The installation position of the slewing bearing must match the drawing. Do not force the bearing into position. If bolt holes do not align, investigate the cause rather than applying excessive force.
Step 3: Install Bolts for the Slewing Bearing
Bolts are critical to slewing bearing performance. The bolt joints must handle the full load of the bearing.
Bolt Selection and Preparation
Fixing bolts normally belong to strength class 10.9 according to DIN ISO 267. Clearance holes should be designed per DIN EN 20273 medium range. Use a thread-locking compound to prevent loosening from vibration.
Tightening Procedure
Tighten the slewing bearing bolts in a cross-pattern (star pattern) to ensure even pressure distribution. Follow these stages:
- First stage: Tighten to 30-50% of final torque
- Second stage: Tighten to 70-80% of final torque
- Third stage: Tighten to 100% of specified torque
Use a calibrated torque wrench. Hydraulic tensioners may be necessary for larger slewing bearings. The table below shows reference tightening torques for common bolt sizes:
| Bolt Size | Class 10.9 Torque (Nm) | Class 8.8 Torque (Nm) |
|---|---|---|
| M12 | 117-137 | 79 |
| M16 | 279-338 | 193 |
| M20 | 558-661 | 387 |
| M24 | 954-1,136 | 666 |
| M30 | 1,890 | 1,350 |
Note: Values based on μ ≈ 0.14. Consult manufacturer specifications for exact values for your slewing bearing.
Post-Installation Bolt Checks
After the slewing bearing has operated for a short period (typically a few hours), recheck the bolt torque and retighten if necessary. Bolts can creep or elongate due to settling of the mounting structure.
Step 4: Check Gear Backlash in the Slewing Bearing
If your slewing bearing includes integral gear teeth, check tooth flank clearance. The minimum clearance should be 0.03-0.04 times the module on the three teeth marked in green. After final fixing of the slewing bearing, check flank clearance over the entire circumference.
Step 5: Lubricate the Slewing Bearing
Most slewing bearings require initial greasing before operation. Use the manufacturer-recommended grease and fill grease points until fresh grease exits the seals. This ensures lubricant reaches all rolling elements and flushes out any remaining preservative.
Final Checks for the Installed Slewing Bearing
Rotate the slewing bearing to ensure smooth, consistent movement. Any binding or tight spots indicate installation problems that need investigation. The bearing should rotate freely without unusual noise or resistance.
Check vertical clearance between the slewing bearing and mounting surface to confirm correct seating.
Verify seals are intact and properly placed to prevent contamination.
How LDB Supports Proper Slewing Bearing Installation
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.
LDB’s installation support:
- Technical documentation: Detailed installation instructions and torque specifications
- Engineering support: Application engineering for bolt selection and mounting design
- Quality assurance: ISO 9001-certified manufacturing with dimensional records retained for every bearing
- Global reach: Serving 73 countries with over 500,000 units in service
Proper slewing bearing installation extends service life and prevents premature failure. Understanding the key steps—surface preparation, hardness gap positioning, bolt torque, and backlash checking—enables reliable operation. LDB offers the technical expertise and quality assurance that equipment manufacturers and operators need.
Contact LDB Bearing today to discuss your slewing bearing installation requirements.
FAQs
1. What is the hardness gap (“S” mark) on a slewing bearing?
The hardness gap is the unhardened section between the beginning and end of raceway hardening, marked with an “S”. Position this mark outside the main load area to prevent premature failure.
2. How should slewing bearing bolts be tightened?
Tighten bolts in a cross-pattern (star pattern) in three stages: 30-50%, 70-80%, and 100% of final torque. Use a calibrated torque wrench and follow manufacturer specifications.
3. What is the minimum tooth flank clearance for a slewing bearing?
The minimum clearance should be 0.03-0.04 times the module. Check clearance on the three marked teeth and over the entire circumference after final installation.
4. How do I check if the mounting surface is suitable for a slewing bearing?
Check flatness with accurate measurement instruments. Use a feeler gauge to verify the bearing surface is completely supported. Rework the surface if it does not meet specifications.
5. When should I retighten slewing bearing bolts after installation?
Recheck bolt torque after the bearing has operated for a short period (typically a few hours). Bolts can settle due to structure settling and may need retightening.