Bearing solution saves money

When a UK-based elec­tric­i­ty pro­duc­er was expe­ri­enc­ing fre­quent break­downs due to bear­ing fail­ures in two indus­tri­al fan units, the plant request­ed the ser­vices of NSK to pro­pose and imple­ment a suit­able solu­tion. After per­form­ing an appli­ca­tion review as part of NSK´s AIP (Added Val­ue Pro­gramme), a change of bear­ing and fix­ing arrange­ment led to sig­nif­i­cant cost savings.
The two direct-dri­ve over­hung fans, which are sup­port­ed by spher­i­cal roller bear­ings in plum­mer blocks, oper­ate 24/7. As pri­ma­ry total air fans, their role is to feed air to the boil­er at a rate of 8 m³/second with an out­put pres­sure of 13 kPa. How­ev­er, the bear­ings in each unit were fail­ing every three months on aver­age, a sit­u­a­tion that would take three engi­neers 10 hours to rem­e­dy each time, incur­ring high costs per breakdown.
The long time and high cost of replace­ment was large­ly due to the size of the task. Each fan is around 3.5 m in diam­e­ter and attached to the end of a 2 m long, 135 mm diam­e­ter shaft. Shaft rota­tion is 1487 rpm, pow­ered by a direct­ly cou­pled 350 kW elec­tric motor.
NSK´s com­pre­hen­sive appli­ca­tion review includ­ed a failed bear­ing exam­i­na­tion from the dri­ve and non-dri­ve end bear­ings. A num­ber of issues, includ­ing fret­ting cor­ro­sion, were not­ed to the exter­nal diam­e­ter of the out­er ring. It was also clear that both bear­ings exhib­it­ed a race­way which had sup­port­ed an axi­al load; evi­dent from a wider and more pro­nounced run­ning band. This is unusu­al as the fan con­fig­u­ra­tion had a fixed and free-end arrange­ment — to allow for shaft expan­sion from oper­at­ing tem­per­a­tures — thus the free end should only sup­port a radi­al load.
As the free end bear­ing at the ener­gy plant exhib­it­ed axi­al load­ing, the com­pa­ny was able to attribute the root cause of the ongo­ing fail­ures to incor­rect bear­ing arrange­ment. High-capac­i­ty Spher­i­cal Roller Bear­ings with­in SNN Plum­mer Blocks were there­fore rec­om­mend­ed, along with cor­rect­ing the fix­ing arrange­ment. The Spher­i­cal Roller Bear­ings use state-of-the-art mate­ri­als that make them suit­able for high speeds and loads. Offer­ing spe­cial ring tol­er­ances to with­stand vibra­tion, shock loads and mis­align­ment, the bear­ings are heat sta­bilised up to 200°C. Fur­ther­more, high-capac­i­ty Spher­i­cal Roller Bear­ings were the pre­ferred choice as the inter­nal design is more reli­able for direct-cou­pled over­hung indus­tri­al fan units, thanks large­ly to inner ring ribs that pro­vide bet­ter roller guidance.