THREE MECHANICS WERE CHANGING CONVEYOR BELT ON INCLINED SLOPE BELT 14-100. INJURED EE WAS GUIDEING THE BELT ACROSS THE TOP OF RETURN ROLLERS ONBOTTOM SIDE OF BELT. RETURN ROLLER CAME OUT OF HANGER WHICH IN TURN STRUCK EE ON RIGHT SIDE OF LOWER BACK RESULTING IN CONTUSION AND ALSO STRAIN OF LOWER BACK. EE PLACED ON RESTRICTED DUTY DUE TO LIFTING .