| 摘要 |
<p>A sieve screen (12) having flexible side walls (14) resiliently mounted to a frame (23), a rapping mechanism (21) actuated by a ram (18) fixed at one end relative to the frame and acting at its other end on a drive shaft (16) via a crank arm (20), the drive shaft (16) extending across the sieve screen (12) and being rotatably journalled in the respective side walls (14) of the sieve screen (12), the rapping mechanism (21) also having a rapping bar (21) connected to the drive shaft (16) by resiliently elongated arms (22), a mechanism to actuate the ram to cause it to move the rapping mechanism at intervals from a rest position wherein the rapping bar (21) is spaced a short distance from the sieve screen and the sieve screen (12) is supported by the frame to a primed position wherein the rapping bar (21) is spaced further away from the sieve screen and a predetermined distance above its rest position and the screen (12) is raised relative to the frame and thereafter to release the mechanism to allow the rapping bar and the sieve screen to fall back to the rest position with such force that the rapping bar (21) will cause the resilient arms (22) to bend sufficiently to cause the rapping bar (21) to strike the sieve screen (12).</p> |
