Plan slewing bearing bolt preload, tightening sequence, friction control and installation records so the joint supports raceway and moment loads correctly.
Slewing bearing bolts do more than hold two parts together. Their preload creates the frictional joint that transfers operating forces, limits separation and helps the companion structure support the bearing rings. Incorrect bolt grade, uncontrolled friction or an uneven tightening sequence can reduce capacity even when every bolt appears tight.
The approved bearing calculation normally assumes a defined bolt size, strength class, preload and support condition. Installation must reproduce those assumptions. Any change to bolt material, washer, coating, lubricant or tightening method requires engineering review rather than a simple torque substitution.
Preload is the target, torque is only one method
The engineering target is bolt tension. Torque-controlled tightening estimates that tension through thread and bearing-surface friction, where most applied torque is consumed. Small changes in lubrication, coating, surface finish or reused hardware can therefore create large preload variation. Hydraulic tensioning, torque-angle or direct tension measurement may provide better control for critical large bolts.
Use the specified bolt, nut and washer system as a set. Confirm strength class, dimensions, manufacturer markings, coating and condition. Do not mix replacement hardware from different friction systems within one joint. Threads and seating faces must match the lubrication condition assumed by the approved tightening procedure.
Use a staged cross-tightening sequence
Seat the bearing on a verified clean and flat surface before tightening. Bring bolts up in multiple stages using a diametrically opposed pattern so the rings settle progressively. Tightening adjacent bolts around the circle from the start can trap uneven contact, distort the ring and leave early bolts below target after neighboring sectors are pulled down.
Mark completed bolts and record the tool, calibration status, target and operator. After the final stage, complete the specified verification pass. For large joints, divide the circumference into controlled sectors while maintaining the cross pattern. The exact sequence and number of stages must follow the machine or bearing installation instruction.
- Verify mounting flatness, cleanliness, bearing orientation and bolt specification.
- Install hardware finger-tight and confirm the ring seats without visible gaps.
- Tighten in a diametrically opposed pattern through approved intermediate stages.
- Reach final target using calibrated equipment and controlled friction conditions.
- Complete the required verification pass and preserve the tightening record.
Protect the frictional joint
Oil, paint, corrosion products or debris between the bearing and companion surface can reduce friction or settle after commissioning. Both conditions shift more operating load into the bolts. Keep seating faces in the condition required by the joint design and do not apply unapproved anti-seize compound to contact surfaces.
Bolt holes must provide the specified clearance without forcing the bearing into position. Oval holes, damaged threads or bolts bearing against one side of a hole are evidence of an interface problem. Correct alignment and structural causes before tightening rather than using the bolts to pull the assembly into place.
Commissioning and inspection baseline
After tightening, verify free rotation, gear backlash and seal condition. Record initial tilt clearance or another approved wear measurement at repeatable points. The baseline allows future inspections to identify change rather than relying on a single absolute reading with no installation reference.
Any post-commissioning bolt check must follow the equipment manufacturer procedure. Blindly applying the original installation torque to an in-service bolt can move or overload the joint, especially if friction has changed. Use an approved inspection method and investigate repeated loss of preload as a structural or load-path symptom.
Information required when the bolt system changes
Send the bearing drawing, bolt circle, hole geometry, clamped thickness, companion materials, surface condition, operating load cases and current tightening process. Engineering review should confirm separation safety, fatigue, preload range and tool access. The mounting-surface requirements are covered in the flatness and support stiffness guide, while dimensional model data begins in the standard model catalogue.
FAQ
Can I reuse slewing bearing bolts?
Only when the equipment manufacturer and approved procedure permit it. Critical joints often require new, traceable hardware.
Is tightening torque the same as bolt preload?
No. Torque is an indirect method whose result depends strongly on friction.
Why use a cross pattern?
It seats the rings progressively and reduces circumferential preload and distortion differences.
Engineering references
- Rothe Erde: Installation, lubrication and maintenance manual
- Kaydon/SKF: Slewing ring engineering and installation guide
For a drawing-based review, send MERYDOM the application, load cases, dimensions and required documentation. Final selection and service instructions must follow the approved drawing and equipment manufacturer requirements.