Patent ID: 7497338
Filing Date: 2009-03-03
Classification: B07B

Abstract:
1. A sieve composing: a base; a circular sieve screen frame mounted on the base; a circular separator screen mounted in the frame; a vibrator arranged to vibrate the frame relative to the base; a resonator secured to or contacting the separator screen, wherein the resonator comprises a rod extending between spaced ends; and an ultrasonic transducer at one of said spaced ends to excite the resonator rod at a resonant frequency having a predetermined wavelength along the length of the resonator rod; wherein said resonator rod has at least a portion of its length which bends smoothly in a single direction of curvature though at least 90° and is formed as a spiral-like curve starting at or near the centre of the sieve screen, the curve having a progressively increasing radius of curvature and extending through at least 270° about said centre; and the rod has a radius of curvature at every point between said spaced ends which is greater than said predetermined wavelength.