Reading failed bearings
Overheating and running dry: what the parts look like
Heat colours, soft deformed rollers, damaged cage windows and carbonised oil mark a bearing that lost its oil film. The cause is not always no oil.
Plastic yielding from heat
When there is not enough oil film to separate the surfaces, or the load is heavy enough to deform the steel permanently, the metal yields. Heat softens the rollers and cage, and the bearing quickly makes more heat. Root causes include too little or too much lubricant, the wrong viscosity, high loads and rough surface finish.
Not only no oil
Heat damage also starts with lubricant quality, high ambient temperature, heavy load or rough surface finish. Early signs are glazing, discoloration and fine surface pitting (frosting) before yielding appears.
- Hot, dry look with little oil residue points to loss of lubricant supply.
- Carbonised or cooked oil points to lubricant present but overheated.
- Hourglass wear in cage windows usually means the bearing became loose after earlier damage.
Takeaway. Heat damage is a result. Find out why the oil film failed: supply, quantity, grade, load or temperature.
Put it to work in the tool