I am not a metal worker so excuse my ignorance. I have a question about about Alumina Zirconia sanding belts. I am sanding cast iron strips 2"x14" and am using 40 60 and 80 grits. It seems that the belts lose their cutting ability fairly quickly, say in about 10-15 min of use. The belts seem to dull and cutting slows significantly. I have tried reversing the direction with seeming improvement. I have read that this type of abrasive is very hard and does not fracture easily causing it to dull. I am using a 6x46 stationary belt sander and applying as much pressure as I can without overloading the motor. How long should I expect the paper to stay relatively sharp and is there a way to renew the grit (create new fractured edges) as one can do with a grinding wheel and a silicon carbide stick? Thanks for your help.