Monitoring lubrication condition and running clearance of rolling bearing via acoustic emission

Paper machines are equipped with hundreds of bearings, most of which are oil-lubricated rolling bearings. When steam is delivered through the axle and the inner ring of the bearing in the steam-heated drying cylinders, the difference in temperature between the bearing's inner and outer ring may become so high that the bearing's clearance is diminished or even eliminated due to the greater thermal expansion of the inner ring. Further, in certain special situations, the paper machine is to be run at a lower speed than normal. This prevents the metal surfaces from contacting each other, as the film of oil between the roller races and surfaces may be too thin. To determine these conditions, VTT is conducting research in co-operation with several Finnish companies. The research includes measurements carried out both with paper machines in the field and with test equipment in a laboratory setting. On the basis of tests performed on the equipment, the possibilities of using acoustic emission for monitoring critical operating situations of rolling bearings seemed very promising.