Air sifter

Claim 2

An air sifter comprising a sifter housing, a plurality of dust separators, each having an air inlet and an air outlet, arranged in crown fashion around the sifter housing, a fan which is mounted to rotate upon a vertical axis in the lower part of the sifter housing and which has an axial air inlet on one side and is closed on the other side, a system of substantially closed conduits which connects the air outlets of the dust separators to the air inlet of the fan, and which includes a plenum chamber at the top of the sifter housing, to which is connected a vertical suction conduit that is located centrally in the sifter housing and leads air downward to the axial air inlet of the fan, and through which passes at least one channel constituting a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, the inlets of the dust separators being connected to the upper portion of the sifter housing to receive air, laden with fine material, which is discharged from the sifter housing under the pressure created by the fan, and a material outlet at the bottom of the sifter housing, for the discharge of coarse material which has separated from the fine material in the feed material falling from the material inlet in countercurrent to the air ascending in the air sifter housing from the fan.

Claim 3

An air sifter according to claim 2 wherein each dust separator comprises a central dip pipe which constitutes an air outlet and which is connected to the plenum chamber.

Claim 4

An air sifter comprising a sifter housing, a plurality of dust separators, each having an air inlet and an air outlet, arranged in crown fashion around the sifter housing, a fan which is mounted to rotate upon a vertical axis in the lower part of the sifter housing and which has an axial air inlet on one side and is closed on the other side, a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan, a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, a pre-distributor plate and a scatter plate, both mounted to rotate upon a vertical axis above the fan in the sifter housing, a sleeve-like hood surrounding and spaced from the pre-distributor plate, the pre-distributor plate being located below the material inlet, to receive material therefrom and to distribute it against the interior of the hood, and the scatter plate being located below the hood, to receive material falling from the hood and to disTribute it into the air ascending from the fan, the inlets of the dust separators being connected to the upper portion of the sifter housing to receive air, laden with fine material, which is discharged from the sifter housing under the pressure created by the fan, and a material outlet at the bottom of the sifter housing, for the discharge of coarse material which has separated from the fine material in the feed material falling from the material inlet in counter-current to the air ascending in the sifter housing from the fan.

Claim 5

An air sifter comprising a sifter housing, a plurality of dust separators, each having an air inlet and an air outlet, arranged in crown fashion around the sifter housing, a fan which is mounted to rotate upon a vertical axis in the lower part of the sifter housing and which has an axial air inlet on one side and is closed on the other side, a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan, a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, a pre-distributor plate and a scatter plate, both mounted to rotate upon a vertical axis above the fan in the sifter housing, a sleeve-like hood surrounding and spaced from the pre-distributor plate, the pre-distributor plate being located below the material inlet, to receive material therefrom and to distribute it against the interior of the hood, and the scatter plate being located below the hood, to receive material falling from the hood and to disTribute it into the air ascending from the fan, the inlets of the dust separators being connected to the upper portion of the sifter housing to receive air, laden with fine material, which is discharged from the sifter housing under the pressure created by the fan, and a material outlet at the bottom of the sifter housing, for the discharge of coarse material which has separated from the fine material in the feed material falling from the material inlet in counter-current to the air ascending in the sifter housing from the fan.

Claim 6

An air sifter according to claim 3 wherein the fan, the scatter plate and the pre-distributor plate are mounted upon a common vertical shaft which is connected at its top to drive means and is guided below the fan by a bearing supported by adjustable radial struts.

Claim 7

An air sifter according to claim 3 wherein the scatter plate and pre-distributor plate are mounted upon a first central drive shaft and the fan is mounted upon a second drive shaft coaxially surrounding the first drive shaft, the shafts are connected at their lower ends to separate drive means, and an annular pneumatic conveyor channel is disposed at the base of the sifter housing for extracting the coarse material.

Claim 8

An air sifter comprising a sifter housing, a plurality of dust separators, each having an air inlet and an air outlet, arranged in crown fashion around the sifter housing, a fan which is mounted to rotate upon a vertical axis in the lower part of the sifter housing and which has an axial air inlet on one side and is closed on the other side, a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan, a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, an annular baffle disposed above the fan comprising a ring of shutters through which the air is directed spirally inward and is thus set in rotary motion, the inlets of the dust separators being connected to the upper portion of the sifter housing to receive air, laden with fine material, which is discharged from the sifter housing under the pressure created by the fan, and a material outlet at the bottom of the sifter housing, for the discharge of coarse material which has separated from the fine material in the feed material falling from the material inlet in countercurrent to the air ascending in the sifter housing from the fan.

Claim 9

An air sifter comprising a sifter housing, a plurality of dust separators, each having an air inlet and an air outlet, arranged in crown fashion around the sifter housing, a fan which is mounted to rotate upon a vertical axis in the lower part of the sifter housing and which has an axial air inlet on one side and is closed on the other side, a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan, a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, an annular baffle disposed above the fan comprising a ring of shutters through which the air is directed spirally inward and is thus set in rotary motion, the inlets of the dust separators being connected to the upper portion of the sifter housing to receive air, laden with fine material, which is discharged from the sifter housing under the pressure created by the fan, and a material outlet at the bottom of the sifter housing, for the discharge of coarse material which has separated from the fine material in the feed material falling from the material inlet in countercurrent to the air ascending in the sifter housing from the fan.

Claim 10

An air sifter according to claim 6 wherein the annular baffle is arranged to guide falling coarse material inside the baffle onto the top of the fan to be scattered centrifugally thereby.

Claim 11

An air sifter according to claim 7 wherein the fan has a cover plate to receive and scatter the falling coarse material.

Claim 12

An air sifter comprising a sifter housing, a plurality of dust separators, arranged in crown fashion around the sifter housing, each having an air inlet connected to the upper portion of the sifter housing and an air outlet, and a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, wherein the improvement comprises a material outlet at the bottom of the sifter housing, for the discharge of coarse material, a fan which is located above the material outlet, is mounted to rotate upon a vertical axis in the lower part of the sifter housing, has an axial air inlet on one side and is closed on the other side, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, and the fan discharging air radially into the coarse material falling past the fan toward the material outlet, thereby stripping the last of the fine material from the coarse material, and a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan to return clean air to the fan.

Claim 13

An air sifter comprising a sifter housing, a plurality of dust separators, arranged in crown fashion around the sifter housing, each having an air inlet connected to the upper portion of the sifter housing and an air outlet, and a material inlet leading into the upper portion of the sifter housing, for introducing feed material to be separated, wherein the improvement comprises a material outlet at the bottom of the sifter housing, for the discharge of coarse material, a fan which is located above the material outlet, is mounted to rotate upon a vertical axis in the lower part of the sifter housing, has an axial air inlet on one side and is closed on the other side, the upper side of the fan being provided with a cover plate to prevent feed particles from falling into the fan, and the fan discharging air radially into the coarse material falling past the fan toward the material outlet, thereby stripping the last of the fine material from the coarse material, and a system of substantially closed conduits connecting the air outlets of the dust separators to the air inlet of the fan to return clean air to the fan.

Claim 14

An air sifteR according to claim 9 wherein each dust separator inlet is in the form of a pipe extending generally tangentially from the upper portion of the sifter housing.

Claim 15

An air sifter according to claim 7, wherein each of the dust separators comprises a central dip pipe which constitutes an air outlet, and which is connected to a system of conduits leading to the axial air inlet of the fan.

Claim 16

An air sifter according to claim 8 wherein the system of conduits connecting the air outlets of the dust separators to the air inlet of the fan includes a hollow vertical shaft which rotates with the fan.

Claim 17

An air sifter according to claim 9 wherein an annular passage is provided immediately inside the sifter housing, leading from the outer periphery of the fan to the inlets of the dust separators.

Claim 18

An air sifter according to claim 13 wherein the annular passage is provided with an adjustable throttle member for regulating the proportion of the air flow that is bypassed through the annular passage.