Roll screen for cleaning root crops

Claim 1

IN BEET SCREENING APPARATUS, THE COMBINATION OF AT LEAST TWO SCREENING UNITS, EACH MOUNTED AND ARRANGED TO PASS TRASH OF VARIABLE SIZE AND TO REJECT BEETS OF VARIABLE SIZE, EACH UNIT COMPRISING AN ELONGATE ROLL HAVING A SMOOTH SURFACE AND A SECOND ELONGATE ROLL HAVING A HELICAL FLIGHT ENCIRCLING AND EXTENDING ALONG ITS EXTERIOR SURFACE, SAID ROLLS BEING MOUNTED ON RESPECTIVE, SUBSTANTIALLY HORIZONTAL AXES WHICH EXTEND TRANSVERSELY TO THE FLOW OF BEETS BEING SCREENED BY SAID UNITS AND HAVING THEIR PERIPHERAL SURFACES SPACED TO PASS TRASH AND TO REJECT BEETS IN SAID FLOW, SAID HELICAL FLIGHTS BEING OF THE SAME HAND ON A SINGLE FLIGHT ROLL BUT OF OPPOSITE HAND ON ALTERNATE FLIGHT ROLLS AND EXTENDING FROM END-TO-END OF EACH OF SAID FLIGHT ROLLS EXCEPT FOR A MARGINAL PORTION AT ONE END OF EACH SUCH ROLL, WHICH IS LEFT SMOOTH AND DEVOID OF FLIGHT, SUCCESSIVE FLIGHT ROLLS HAVING THEIR SAID SMOOTH ENDS AT OPPOSITE SIDES OF SAID SCREENING UNITS.