A
sieve shaker has a rigid outer frame having longitudinally extending side beams and transverse end beams bridging the side beams, at least one cross bar in the frame extending generally parallel to the end beams, a mesh fixed to the cross bar and end beams, and spring elements resiliently supporting the cross bar on the frame for movement relative thereto. A drive reciprocates the outer frame at least generally parallel to the side beams and thereby also moves the cross bar. Thus the spring elements will transmit the movement of the outer frame to the inner cross bar with some delay. The mesh secured to the outer frame and cross bar will therefore be subdivided into panels that will be alternately tightened and slackened for excellent agitation of the material being sifted.
A standard
sieve shaker has a generally horizontal mesh, which term here is intended to cover any perforated sheet whether woven or not, whose ends at least are fixed to a frame that is reciprocated with at least some horizontal component. Thus particulate material placed on the mesh will be bounced about and those particles smaller than the mesh openings will fall through.
In order to maximize movement of the particulate material being graded it is known from German patent document 1,206,372 filed Sep. 26, 1964 by A. Wehner to fix the mesh to a plurality of horizontal and parallel bars each fixed to one of two frames with every other bar secured to the same frame. A drive is connected to and between the two frames to move them oppositely so that the mesh surface is subdivided into a plurality of different panels that move alternately, with half of the panels being pulled taut while the others are becoming slack and vice versa. Such a system is fairly complicated to build and its drive is quite expensive. Furthermore it is impossible to retrofit this system to an existing
sieve shaker whose mesh is held in a single panel that is moved all together.
