Screening

Claim 2

A screening apparatus capable of separation of the components of a fluid pulp on the basis of size, the apparatus comprising a circular cross-section screen plate having screening apertures comprising a total open area of less than about 20 percent in the region of the plate having screening apertures, means defining a screening zone on one side of said screen plate, means defining an inlet for unscreened stock on said one side; means defining a rejects zone also on said one side for removal of rejected matter, a driven screen-cleaning rotor in the general form of a drum wall disposed on the other side of the screen platE and defining therewith an accepts zone, the drum wall having leading and trailing surface portions that slope relative to the direction of travel of rotor portions closest to the screen plate, said surface portions extending along the length of the rotor sufficiently to sweep fully, with generally uniform intensity, across respective apertures in said screen plate, said leading surface portions shaped to direct pulses through the apertures to dislodge over-size solids therefrom, said trailing portions shaped to assist accepts flow through said apertures, and an accepts outlet positioned to receive and discharge accepted fluid from said accepts zone adjacent said rotor and wherein beyond the region of the screen plate having screening apertures there are mutual extensions of said screen plate and said drum-wall spaced from each other a distance sufficiently close to prevent dissipation of pulses produced by said rotor adjacent the screening apertures.

Claim 3

The screening apparatus of claim 1 wherein the cross-sectional profile of said rotor in all planes perpendicular to the rotor axis that project through apertures of said screen plate is identical in form.

Claim 4

The screening apparatus of claim 1 wherein said apertures comprise narrow, elongated slots having a width less than 0.030 inches, said slots extending generally parallel to the axis of said rotor.

Claim 5

The screening apparatus of claim 1 wherein said accepts zone includes an accepts outlet aligned to intercept circulating fluid flowing from said accepts zone, and said rotor adapted to rotate relative to said aligned accepts outlet in a direction to impart forward pumping force to fluid proceeding towards said outlet.

Claim 6

The screening apparatus of claim 1 wherein said rejects zone includes an intermittently operable rejects valve having means to maintain it closed longer than opened, said valve being provided to withdraw a surge of fluid from the rejects zone thereby to remove rejects therefrom.

Claim 7

The screening apparatus of claim 1 wherein said sloped surface portions of said rotor are spaced no more than about one-half inch from the accepts side of said screen plate.

Claim 8

The screening apparatus of claim 1 wherein said apertures are elongated in the axial direction of said screen plate and said sloped surface portions are longer than and extend beyond the ends of elongated apertures of said screen plate.

Claim 9

The screening apparatus of claim 1 wherein said surface portions extend generally parallel to, but centered on axes spaced from the axis of said rotor.

Claim 10

The screening apparatus of claim 8 wherein said surface portions are of cylindrical form.

Claim 11

The screening apparatus of claim 8 wherein said surface portions are flat.

Claim 12

The screening apparatus of claim 1 wherein said surface portions comprise eccentric lobes that extend continuously along the rotor over the axial length of the screen plate.

Claim 13

The screening apparatus of claim 11 wherein said surface portions are of cylindrical form having axes offset on the order of one-fourth inch from the axis of said rotor.

Claim 14

The screening apparatus of claim 1 wherein said screen is cylindrical, said rotor is disposed within said screen, said screen plate is surrounded by a housing defining said screening zone.

Claim 15

The screening apparatus of claim 13 wherein said housing is of volute form and the inlet to the thus defined screening zone is tangential thus to maintain a uniform movement of the stock in the screening zone for moving solids dislodged from the screen plate by the rotor.

Claim 16

The screening apparatus of claim 3 having an inlet to a portion of the screening zone intermediate its ends and at each end thereof a rejects zone, each of said rejects zones including a rejects conduit, and valve means for regulating the rejects flow therethrough.

Claim 17

A screening apparatus capable of separation of the components of a fluid pulp on the basis of size, the apparatus comprising a circular cross-section screen plate having screeniNg apertures comprising a total open area of less than about 20 percent in the region of the plate having screening apertures, said apertures being elongated in the direction of the axis of said screen plate and having a length to width ratio of at least 20 to 1, means defining a screening zone on one side of said screen plate, means defining an inlet for unscreened stock on said one side; means defining a rejects zone also on said one side for removal of rejected material, an accept zone including an accepts outlet on the other side of said screen plate said accept zone being defined by a rotary wall disposed adjacent to but spaced from said screen plate, said rotary wall having leading and trailing surface portions that slope relative to the direction of travel of rotor portions closest to said screen plate, said sloped surface portions extending along the length of the rotor sufficiently to sweep fully, with generally uniform intensity, across respective apertures in said screen plate, said surfaces extending the full length of said elongated apertures and said surfaces shaped to create general screen-cleaning fluid pulses acting upon said screen plate, there being beyond the portion of said screen plate having said elongated apertures, mutual extensions of said screen plate and said drum wall spaced from each other a distance sufficiently close to maintain screen-cleaning fluid pulses at substantially full intensity at end rows of elongated apertures in said screen plate.

Claim 18

A screening apparatus capable of separation of the components of a fluid pulp on the basis of size, the apparatus comprising a circular cross-section screen plate having screeniNg apertures comprising a total open area of less than about 20 percent in the region of the plate having screening apertures, said apertures being elongated in the direction of the axis of said screen plate and having a length to width ratio of at least 20 to 1, means defining a screening zone on one side of said screen plate, means defining an inlet for unscreened stock on said one side; means defining a rejects zone also on said one side for removal of rejected material, an accept zone including an accepts outlet on the other side of said screen plate said accept zone being defined by a rotary wall disposed adjacent to but spaced from said screen plate, said rotary wall having leading and trailing surface portions that slope relative to the direction of travel of rotor portions closest to said screen plate, said sloped surface portions extending along the length of the rotor sufficiently to sweep fully, with generally uniform intensity, across respective apertures in said screen plate, said surfaces extending the full length of said elongated apertures and said surfaces shaped to create general screen-cleaning fluid pulses acting upon said screen plate, there being beyond the portion of said screen plate having said elongated apertures, mutual extensions of said screen plate and said drum wall spaced from each other a distance sufficiently close to maintain screen-cleaning fluid pulses at substantially full intensity at end rows of elongated apertures in said screen plate.

Claim 19

The screening apparatus of claim 16 wherein said surface portions have a clearance from said screen plate no greater than about one-half inch.

Claim 20

The screening apparatus of claim 16 wherein said surface portions comprise eccentric lobes of cylindrical form centered on axes off-set from the center of the rotor by about one-fourth inch.

Claim 21

The screening apparatus of claim 16 wherein said surface portions are flat.

Claim 22

The screening apparatus of claim 17 wherein said rotary wall has leading and trailing pulse-generating flat surface portions that slope relative to the direction of travel of rotor portions closest to said screen plate, said flat, sloped surface portions extending along the length of the rotor sufficiently to sweep fully, with generally uniform intensity, across respective apertures in said screen plate.

Claim 23

The apparatus of claim 20 wherein said rotor has a cross-section in the general form of a regular polygon having on the order of 10 flat sides.

Claim 24

The apparatus of claim 20 wherein the clearance of said rotor from said screen plate is on the order of one-fourth to one-half inch and has a rise greater than one-eighth inch.