Anti-plugging discharge grates

1. A grinding mill, comprising:

a shell defining a mill shell chamber therein in which a charge including grinding balls and ore-bearing rocks is positioned, the shell being rotatable in a predetermined direction about a central axis thereof for comminution of the ore-bearing rocks to produce a mixture including a fluid and worn rock pieces from the ore-bearing rocks, wherein the commnution of the ore-bearing rocks forms the grinding balls into worn grinding balls;

a discharge end wall attached to the shell, the discharge end wall extending between an outer edge thereof connected to the shell and an inner edge thereof at least partially defining a central opening in the discharge end wall; and

a discharge end wall system, comprising:

a plurality of discharge grate assemblies; and

a plurality of pulp chambers located between the respective discharge grate assemblies and the discharge end wall, for directing the mixture received therein toward the central opening, to exit the grinding mill therethrough,

wherein each said discharge grate assembly is positioned to screen the mixture flowing from the mill shell chamber into each said pulp chamber respectively as the shell rotates about the central axis,

wherein each said discharge grate assembly is rotatable with the shell about the central axis between a lowered condition, in which the mixture is flowable through at least part of each said discharge grate assembly into the pulp chamber adjacent thereto respectively, and a raised condition, in which the discharge grate assembly is positioned above the charge, and

wherein each said discharge grate assembly comprises:

a body comprising a plurality of elongate apertures therein, formed to screen the mixture flowing therethrough from the mill shell chamber into the pulp chamber,

wherein each said aperture extends between respective first and second ends thereof, the first end having a predetermined first end width and the second end of the aperture having a predetermined second end width that is larger than the first end width,

wherein each said aperture is defined by aperture walls formed in the body; and

wherein the aperture walls comprise first and second end walls that are at least partially rectilinear and partially define the first and second ends respectively, the first and second end walls being formed to impede the worn grinding balls and the worn rock pieces in the mixture from lodging in the aperture.

2. The grinding mill according to claim 1 , wherein the aperture walls additionally comprise first and second side walls respectively extending between the first end wall and the second end wall.

3. The grinding mill according to claim 2 , wherein the first and second side walls are at least partially rectilinear.

4. The grinding mill according to claim 3 , wherein:

the body comprises an at least partially planar front side facing the mill shell chamber; and

each of the aperture walls defines an aperture wall edge thereof at which each said aperture wall intersects the front side of the body.

5. The grinding mill according to claim 4 , wherein the aperture wall edges of each said aperture wall defining the second end engage the worn grinding balls and the rock pieces having diameters larger than the second end width to locate the centers of gravity of the worn grinding balls and the rock pieces having diameters larger than the second end in the mill shell chamber width, to impede lodging thereof in each said aperture respectively.

6. The grinding mill according to claim 5 , wherein the aperture wall edges of each said aperture wall defining the first end engage the worn grinding balls and the rock pieces having diameters larger than the first end width to locate the centers of gravity of the worn grinding balls and the rock pieces having diameters larger than the first end width in the mill shell chamber, to impede lodging thereof in each said aperture respectively.

7. The grinding mill according to claim 3 , wherein each said aperture is partially defined by a center line thereof extending between a first middle point of the first end wall and a second middle point of the second end wall.

8. The grinding mill according to claim 7 , wherein the body of each said discharge grate assembly is elongate and extends between inner and outer ends thereof, the inner end being located proximal to the central axis of the mill shell, and the outer end being located distal to the central axis.

9. The grinding mill according to claim 8 , wherein the center lines of the apertures are located at least partially transverse to a middle line of the body extending between the inner and outer ends thereof.

10. The grinding mill according to claim 9 , wherein the apertures are located spaced apart from each other in the body with the center lines of the apertures being located orthogonal to the middle line of the body.

11. A discharge grate assembly in a discharge end wall system in a mill shell of a grinding mill, the mill shell defining a mill shell chamber therein in which a charge including grinding balls and rocks is positioned, the mill shell being rotatable about a central axis thereof for comminution of the rocks to produce a mixture including a fluid and worn rock pieces from the rocks, wherein the comminution of the rocks forms the grinding balls into worn grinding balls, the discharge grate assembly comprising:

a body having a front side facing the mill shell chamber and an opposite rear side, the body comprising a plurality of apertures for permitting the fluid and the rock pieces having a predetermined maximum permitted size sufficiently small to pass through the apertures into a pulp chamber located adjacent to the rear side of the body,

wherein each said aperture is defined by aperture walls formed in the body, each said aperture extending between first and second ends thereof, the first end being defined by a first rectilinear wall having a predetermined first end width and the second end of the aperture being defined by a second rectilinear wall having a predetermined second end width that is greater than the first end width, to impede the worn grinding balls and the worn rock pieces from being lodged in the aperture.

12. The discharge grate assembly according to claim 11 , wherein the aperture walls additionally comprise first and second side walls extending between the first and second end walls, the first and second side walls being rectilinear.

13. The discharge grate assembly according to claim 12 , wherein:

the body comprises a planar front side facing the mill shell chamber;

each of the aperture walls defines an aperture wall edge thereof at which each said aperture wall intersects the front side of the body; and

the aperture wall edges of each said aperture wall defines the second end engage the worn grinding balls and the rock pieces having diameters larger than the predetermined maximum permitted size to locate the centers of gravity thereof in the mill shell chamber, to impede lodging thereof in each said aperture respectively.

14. A discharge end wall system mounted on a discharge end wall of a mill shell in a grinding mill, the mill shell defining a mill shell chamber therein in which a charge including rocks and grinding balls is positioned, the mill shell being rotatable about a central axis thereof for comminution of the rocks to produce a mixture including a fluid and worn rock pieces, wherein the comminution of the rocks forms the grinding balls into worn grinding balls, the discharge end wall system comprising:

a plurality of pulp lifters radially arranged on the discharge end wall relative to the central axis, the pulp lifters being located to partially define pulp chambers; and

a plurality of discharge grate assemblies positioned between the pulp chambers and the mill shell chamber, for screening the mixture moving into the pulp chambers from the mill shell chamber,

wherein each said discharge grate assembly comprises a body with a plurality of elongate apertures therein for screening the mixture,

wherein each said elongate aperture is defined by aperture walls formed in the body, the aperture walls comprising first and second end walls and first and second side walls extending between the respective first and second end walls,

wherein each said aperture is defined by a center line thereof intersecting each of the first and second ends at midpoints thereof, and

wherein the first and second end walls are rectilinear and located orthogonal to the center line of the aperture.

15. The discharge end wall system according to claim 14 , wherein:

the first end wall and the first and second side walls of each said aperture define a first end of the aperture formed to permit the worn grinding balls and the rock pieces having a predetermined first end permitted size to pass therethrough; and

the second end wall and the first and second side wall define a second end of the aperture that is larger than the first end, to permit the worn grinding balls and the rock pieces having a predetermined second end permitted size therethrough.

16. The discharge end wall system according to claim 15 , wherein the body of each said discharge grate assembly extends between an inner end that is located proximal to the central axis and an outer end located proximal to the outer perimeter, and the body is partially defined by a center body line thereof dividing the body into two equal parts.

17. The discharge end wall system according to claim 16 , which, wherein the apertures are formed in the body such that the respective center lines thereof are located transverse relative to the center body line.

18. The discharge end wall system according to claim 17 , wherein:

the body comprises an at least partially planar front side facing the mill shell chamber; and

each of the aperture walls defines an aperture wall edge thereof at which each said aperture wall intersects the front side of the body.

19. The discharge end wall system according to claim 18 , wherein the aperture wall edges of said aperture walls defining the second end engage the worn grinding balls and the rock pieces having diameters larger than the predetermined second end permitted size to locate the centers of gravity thereof in the mill shell chamber, to impede lodging thereof in said aperture.

20. The discharge end wall system according to claim 18 , wherein the aperture wall edges of said aperture walls defining the first end engage the worn grinding balls and the rock pieces having diameters larger than the predetermined first end size to locate the centers of gravity thereof in the mill shell chamber, to impede lodging thereof in said aperture.

21. A discharge grate assembly in a discharge end wall system in a mill shell of a grinding mill, the mill shell defining a mill shell chamber therein in which a charge including rocks is positioned, the mill shell being rotatable about a central axis thereof for comminution of the rocks to form the rocks into worn rock pieces and to produce a mixture including a fluid and the worn rock pieces, the discharge grate assembly comprising:

a body having a front side facing the mill shell chamber and an opposite rear side, the body comprising a plurality of apertures for permitting the fluid and the rock pieces having a predetermined maximum permitted size sufficiently small to pass through the apertures into a pulp chamber located adjacent to the rear side of the body,

wherein each said aperture is defined by aperture walls formed in the body, each said aperture extending between first and second ends thereof, the first end being defined by a first rectilinear wall having a predetermined first end width and the second end of the aperture being defined by a second rectilinear wall having a predetermined second end width that is greater than the first end width, to impede the worn rock pieces that are larger than the predetermined maximum permitted size from being lodged in the aperture.

22. The discharge grate assembly according to claim 21 , wherein:

the body comprises an at least partially planar front side facing the mill shell chamber;

each of the aperture walls defines an aperture wall edge thereof at which each said aperture wall intersects the front side of the body; and

the aperture wall edges of each said aperture wall define the second end engage the rock pieces having diameters larger than the predetermined maximum permitted size to locate the centers of gravity thereof in the mill shell chamber, to impede lodging thereof in each said aperture respectively.