Friction Induced Vibrations of a Vertical Long Flexible Shaft

Abstract

A soot blower is used to blow off soot on tubes in a tubular heat exchanger, or a gas heater. The soot blower has a long flexible tube, that is, a lance tube, about 10 m long and 76 mm in diameter, which is put slowly into/out of a gas heater. Steam flows through the lance tube and is discharged at the free end to blow off soot. The lance tube, rotating slowly about its axis at about 12 rpm, is supported at an intermediate position by a support bearing, that is, a lance bearing. Vibrations and noises occurred in operation while a lance tube is put into a gas heater. They are considered self-excited vibrations due to friction between the lance tube and the lance bearing. Experimental study is done to clarify the mechanism of the vibration. Accordingly, backward whirling motion of a shaft is observed. Analytical study is also done which clarify the mechanism and characteristics of friction induced vibrations.