Aggregate attrition systems, methods, and apparatus

1. An attrition mill, comprising:

a tank, said tank having a sidewall defining an interior volume, said sidewall positioned between a lid and a bottom surface of said tank;

an inlet in fluid communication with said interior volume;

an outlet in fluid communication with said interior volume, said outlet vertically displaced from said inlet;

a motor;

a shaft assembly, said shaft assembly comprising:

a shaft, said shaft being removably coupled to said motor, said shaft being operably coupled to said motor for rotation of said shaft about a vertical axis, said shaft extending along the vertical axis through an opening in the lid toward the bottom surface and terminating at an end spaced apart from the bottom surface, wherein the lid supports the shaft for rotation about the vertical axis and the end is free of support for rotation about the vertical axis;

a first propeller, said first propeller comprising a first axial core having a first axially extending outer wall, said first propeller comprising a first plurality of propeller blades mounted to said first axial core, said first propeller removably mounted to said shaft, said first propeller disposed at a first height;

a second propeller disposed at a second height along said shaft, said second height being higher than said first height;

a first spacer disposed between said first propeller and said second propeller, said first spacer removably covering a first portion of said shaft, said first spacer abutting said first axial core of said first propeller; and

a second spacer disposed between said second propeller and said opening, said second spacer removably covering a second portion of said shaft, wherein at least one of said spacers at least partially supports at least one of said propellers

an access opening in said sidewall of said tank;

an access door displaceably mounted to said tank, said access door having a first position in which said access opening is covered by said access door, said access door having a second position in which said access opening is not covered by said access door, wherein said access opening is sized such that at least one of said first and second propellers is removable from said tank through said access opening.

2. The attrition mill of claim 1 , wherein said second propeller is removably retained on said shaft assembly.

3. The attrition mill of claim 1 , wherein said first propeller, said second propeller, said first spacer and said second spacer cooperate to prevent material in said interior volume from contacting said shaft.

4. The attrition mill of claim 1 , wherein said second spacer extends at least partially through said opening.

5. The attrition mill of claim 1 , wherein first spacer is supported at least partially by said first propeller.

6. The attrition mill of claim 1 , wherein said second propeller is supported at least partially by said first spacer.

7. The attrition mill of claim 1 , wherein said second spacer is supported at least partially by said second propeller.

8. The attrition mill of claim 1 , wherein said first spacer rests on said first propeller.

9. The attrition mill of claim 8 , wherein said second propeller rests on said first spacer.

10. The attrition mill of claim 1 , wherein at least one of said first and second spacers comprises a shell made of a first material and a lining made of a second material.

11. The attrition mill of claim 1 , wherein an annular gap is disposed between said shaft and at least one of said first and second spacers.

12. The attrition mill of claim 1 , wherein one of said shaft and said second propeller includes a keyway, and wherein the other of said shaft and said second propeller includes a keyseat, wherein a key engages said keyway to said keyseat such that rotation of said shaft causes rotation of said second propeller.

13. The attrition mill of claim 1 , wherein said access opening is sized such that said shaft assembly is removable from said tank through said access opening.

14. The attrition mill of claim 1 , further comprising:

a bushing mounted to said shaft, said bushing disposed at or near an upper end of said shaft, said bushing being disposed at least partially outside of said tank.

15. The attrition mill of claim 1 , wherein an annular gap is disposed between said shaft and said second spacer, and wherein said bushing extends at least partially into said annular gap.

16. An attrition mill, comprising:

a tank, said tank having a sidewall defining an interior volume, said sidewall positioned between a lid and a bottom surface of said tank;

an inlet in fluid communication with said interior volume;

an outlet in fluid communication with said interior volume, said outlet vertically displaced from said inlet;

a motor;

a shaft assembly, said shaft assembly comprising:

a shaft made of a first material, said shaft being removably coupled to said motor, said shaft being operably coupled to said motor for rotation of said shaft about a vertical axis, said shaft extending along the vertical axis through an opening in the lid toward the bottom surface and terminating at an end spaced apart from the bottom surface, wherein the lid supports the shaft for rotation about the vertical axis and the end is free of support for rotation about the vertical axis;

a first propeller removably mounted to said shaft, said first propeller disposed at a first height;

a second propeller comprising an axially extending core and a plurality of propeller blades attached to said axially extending core, said second propeller disposed at a second height along said shaft, said second propeller being removably supported on said shaft, said second height being higher than said first height;

a spacer disposed between said first and second propeller and at least partially supported by said first propeller, said axially extending core of said second propeller resting on said spacer; and

a lining made of a second material, said lining applied to said spacer, wherein said lining protects said spacer from contact with fluid in said interior volume; and

an access opening in said sidewall of said tank;

an access door displaceably mounted to said tank, said access door having a first position in which said access opening is covered by said access door, said access door having a second position in which said access opening is not covered by said access door, wherein said access opening is sized such that at least one of said first and second propellers is removable from said tank through said access opening.

17. The attrition mill of claim 16 , wherein said second propeller comprises a blade, said blade having an inner end and an outer end, said inner end having an inner end height, said outer end having an outer end height, said blade having an upper surface, said upper surface having a chamfer such that said outer end height is less than said inner end height.

18. The attrition mill of claim 16 , further comprising:

a baffle slidingly received in an opening in a lid of said tank, said tank extending vertically substantially along an inner sidewall of said tank.

19. The attrition mill of claim 1 , wherein at least one of said propeller blades is disposed at an angle At with respect to horizontal.

20. The attrition mill of claim 19 , wherein said angle At is 45 degrees.

21. The attrition mill of claim 19 , wherein said angle At is approximately 40 degrees.

22. The attrition mill of claim 19 , wherein said angle At is less than 45 degrees.

23. The attrition mill of claim 1 , wherein said tank is generally cylindrical, and wherein said access door is arcuately shaped.

24. The attrition mill of claim 16 , wherein at least one of said propeller blades is disposed at an angle At with respect to horizontal.

25. The attrition mill of claim 24 , wherein said angle At is 45 degrees.

26. The attrition mill of claim 25 , wherein said angle At is approximately 40 degrees.

27. The attrition mill of claim 16 , wherein said tank is generally cylindrical, and wherein said access door is arcuately shaped.