Slewing ring bearings carry axial, radial and moment loads at once, in cranes, excavators, wind turbines, turntables and much more. When one fails, the cost is rarely just the bearing: there is downtime, damage to the structure around it and, in lifting equipment, a real safety risk. In the most serious cases, a failure can be fatal.
Almost every failure we see has one of four causes, and almost all of them give warning first.
1. Lubrication problems
- Not enough grease. Friction rises, the bearing runs hot and the raceways wear.
- The wrong grease. A grease without EP (extreme-pressure) additives, such as a non-EP2 grease, lets the lubricating film break down under high load, generating heat, thermal expansion and accelerated wear.
- Mixed greases. Relubricating with a grease that is not compatible with the original can make both ineffective.
- Contaminated grease. Dirt, debris or water in the lubricant wears the raceways from the inside.
See our lubrication guide for grease selection and intervals.
2. Installation problems
- Mounting surface not flat or not rigid, so the load concentrates in one part of the raceway.
- Bolts torqued incorrectly or unevenly, causing binding, heat and bolt fatigue.
- Incorrect preload and uneven loading.
- Loading plug or hardness gap left in the heavy load zone.
Our installation and maintenance checklist covers each of these step by step.
3. Overload and fatigue
Every bearing has load limits for load, speed and temperature, shown on its load chart. Repeated loading beyond them, or simply many cycles near them without maintenance, starts fatigue cracks in the raceways that can end in sudden failure. Heavy overloads can fracture the rings outright.
4. Corrosion
Salt water, chemicals, washdown and damp storage all attack the raceways and gear. Bearings stored in a humid place, or for longer than six months without fresh grease, can corrode before they are ever installed. For wet or corrosive service, ask about seals and corrosion protection when you specify the bearing.
Warning signs to act on
Stop and investigate if you see any of these:
- noise or vibration during rotation that is not normal
- rising operating temperature, or hot spots
- irregular rotating torque, or resistance that was not there before
- metal flakes or fragments in purged grease or in filters
- discoloration, peeling or scoring on visible surfaces
- grease leaking around, or damage to, the seals
- increasing axial or radial play
- equipment that no longer performs as it did
Don't treat a noisy bearing by adding grease and carrying on. Noise can mean internal damage, and extra grease only hides it for a while. If you find damage on the bearing, inspect the structure around it too.
How to prevent them
- Relubricate on a schedule, with a compatible EP grease, and relubricate early if you see discoloration, scoring or hot spots.
- Stay inside the load chart. If the application has changed since the bearing was selected, have the selection checked.
- Inspect proactively: purged grease, seals and the surrounding structure.
- Install it right the first time, following the bearing drawing and the checklist above.
Replacing a failed bearing
If a bearing has already failed and the machine is down, speed matters. Send us whatever you have:
- the part number, from any manufacturer. Over 800 SlewPro designs are already crossed to other brands, and you can look up the equivalent or use the Kaydon interchange yourself
- the drawing, or
- photos and the main dimensions: outside and inside diameter, height, bolt circles and gear details
Send it to our engineers and we will identify the replacement and tell you what, if anything, differs from the original.