Separator for a grinding machine

1. A grinding machine comprising:

a grinding head defining an opening;

a rotatable advancement member positioned within the grinding head;

an orifice plate positioned within the opening of the grinding head, wherein the orifice plate defines an upstream surface and a downstream surface, a plurality of grinding openings extending between the upstream surface and the downstream surface for discharging soft material through the orifice plate upon rotation of the rotatable advancement member, and one or more collection passages extending between the upstream surface and the downstream surface for discharging a mixture of soft material and hard material through the orifice plate upon rotation of the rotatable advancement member;

a separator assembly positioned downstream of the orifice plate, wherein the separator assembly receives the mixture of soft material and hard material from the one or more collection passages, the separator assembly including

a separator chamber defining a separator passage having an intake end, a discharge, and a plurality of perforations that communicate with the separator passage, wherein the separator passage receives the mixture of soft material and hard material at the intake end, and

a separator screw positioned within the separator passage of the separator chamber, wherein rotation of the separator screw causes separation of soft material from the mixture of soft material and hard material, wherein the soft material is discharged through the plurality of perforations and hard material is discharged through the discharge; and

a pin extending between the rotatable advancement member and the separator screw, wherein the pin and the separator screw rotate with the rotatable advancement member.

2. The grinding machine of claim 1 , wherein the separator screw has helical flights provided therein, wherein diameters of the helical flights change along a length of the separator screw.

3. The grinding machine of claim 1 , wherein the separator chamber includes a wall having a portion which is frustoconical.

4. The grinding machine of claim 1 , wherein the separator chamber includes a wall having the plurality of perforations therethrough.

5. The grinding machine of claim 1 , wherein the separator chamber has a portion that tapers between ends thereof, and wherein the separator screw has helical flights provided therein, wherein diameters of the helical flights match the portion of the separator chamber that is tapered.

6. The grinding machine of claim 1 , further comprising engagement structure between the pin and the separator screw for non-rotatably securing the separator screw to the pin.

7. The grinding machine of claim 1 , further comprising a knife holder mounted at an end of, and rotating with, the rotatable advancement member, wherein the knife holder has knife inserts mounted thereon, the knife holder being positioned adjacent the upstream surface of the orifice plate.

8. A combination comprising:

a grinding head defining an opening;

a rotatable advancement member positioned within the grinding head;

an orifice plate positioned within the opening of the grinding head, wherein the orifice plate defines an upstream surface and a downstream surface, a plurality of

grinding openings extending between the upstream surface and the downstream surface for discharging soft material through the orifice plate upon rotation of the rotatable advancement member, and one or more collection passages extending between the upstream surface and the downstream surface for discharging a mixture of soft material and hard material through the orifice plate upon rotation of the rotatable advancement member; and

a separator assembly positioned downstream of the orifice plate, wherein the separator assembly receives the mixture of soft material and hard material from the one or more collection passages, the separator assembly including

a separator chamber defining a separator passage having an intake end, a discharge, and a plurality of perforations that communicate with the separator passage, wherein the separator passage receives the mixture of soft material and hard material at the intake end,

a separator screw positioned within the separator passage of the separator chamber and connected to the rotatable advancement member, wherein rotation of the separator screw causes separation of soft material from the mixture of soft material and hard material, wherein the soft material is discharged through the plurality of perforations and hard material is discharged through the discharge, and

a pin extending between the rotatable advancement member and the separator screw, wherein the pin and the separator screw rotate with the rotatable advancement member.

9. The combination of claim 8 , wherein the separator screw has helical flights provided therein, wherein diameters of the helical flights change along a length of the separator screw.

10. The combination of claim 8 , wherein the separator chamber includes a wall having a portion which is frustoconical.

11. The combination of claim 8 , wherein the separator chamber includes a wall having the plurality of perforations therethrough.

12. The combination of claim 8 , wherein the separator chamber has a portion that tapers between ends thereof, and wherein the separator screw has helical flights provided therein, wherein diameters of the helical flights match the portion of the separator chamber that is tapered.

13. The combination of claim 8 , further comprising a knife holder mounted at an end of, and rotating with, the rotatable advancement member, wherein the knife holder has knife inserts mounted thereon, the knife holder being positioned adjacent the upstream surface of the orifice plate.