Patent ID: 8651267

Claim:
A conveying screw apparatus ( 10 ) for transporting loose material; said apparatus ( 10 ) comprises: an Archimedes screw ( 21 ); a power unit ( 20 ) to rotate an Archimedes screw ( 21 ) pushing the loose material; a charging hopper ( 30 ) of the loose material in a tubular body ( 31 ) containing the Archimedes screw ( 21 ) and the loose material for at least a section of its feed path; the loose material being fed according to a first direction substantially parallel to a rotation axis (X) of the Archimedes screw ( 21 ); a feeding channel ( 40 ) of the loose material towards a user; the feeding channel ( 40 ) being connected in series to said tubular body ( 31 ); pushing elements of the loose material; said pushing elements being placed in said feeding channel ( 40 ); and a back flow preventing device ( 70 ), preventing the back flow of pushing air together with loose material; said device closing, in case, a through hole ( 63 ) to the feeding channel ( 40 ); wherein said back flow preventing device ( 70 ) comprises a shutter ( 71 ) provided with a plate ( 71 A), undergoing the action of first and second elastic means ( 81 , 90 ), which, in any opening/closing step of said through hole ( 63 ), is always substantially perpendicular to the first direction feeding the material in said tubular body ( 31 ); and wherein in said plate ( 71 A) there is said second elastic means in the form of a stiffening foil ( 90 ) made as a kind of “Belleville washer” so as to impart elasticity to said plate ( 71 A); said first elastic means ( 81 ) being in the form of a spring that applies a biasing force against said plate ( 71 A).