Distributed ultrasonic lubrification of continuous steel casting

A critical point in the continuous steel casting process exists in the meniscus zone of the cooled mould, i.e. the region where the steel stream flowing out of the tundish nozzle starts to solidify, because of the sticking that occurs between the solid shell of steel and the mould. In this work a new system for the ultrasonic lubrication of the continuous steel casting is proposed and experimentally tested. The basic idea is to excite one of the mould natural vibration modes by means of a distributed ultrasonic source, composed of an array of power emitters, with each of them placed on an antinode of the mould. An experimental characterization of the vibrational behaviour of a square mould was first carried out. The most active resonance modes of the mould were detected with an effective experimental technique based on a simple impedance measurement, while the modal shape of the selected mode and hence the position of antinodes were obtained by means of interferometer measurements. A further experimental investigation was carried out by exciting mould vibrations with up to four piezoceramic disks placed on different sets of antinodes, and some positioning criteria to maximize the superposition effect were derived. Measurements obtained by exciting the mould with up to four Langevin-type power emitters, designed and manufactured to work at the mould selected resonance frequency, have shown that, by increasing the number of emitters, the ultrasonic power transmitted to the mould and, consequently, the maximum available displacement increases. Other practical advantages of the proposed system are highlighted and discussed.