GB2038204A

GB2038204A - Grinding mill with adjustable separator

Info

Publication number: GB2038204A
Application number: GB7941418A
Authority: GB
Original assignee: Babcock Product Engineering Ltd
Current assignee: Babcock Product Engineering Ltd
Priority date: 1978-12-01
Filing date: 1979-11-30
Publication date: 1980-07-23

Abstract

The invention provides a grinding mill in which ground material is entrained in a gas stream to carry it away from the grinding elements (1,2 and 3). Means (14,20; 106,120) is provided by which the maximum cross-section of the flow path from the grinding elements may be varied. A baffle (10; 110) forming a boundary of a path through which ground material may pass from the grinding elements may also form a boundary of a path by which oversized material may return from the area of greatest cross-section to the grinding elements. <IMAGE>

Description

SPECIFICATION Improvements in or relating to grinding mills This invention relates to grinding mills and is concerned to provide a grinding mill such that the grade reaching the outlet from the mill may be varied. The invention may be embodied in modifications of the ,so-called E-type mill in which a ring of grinding balls is held, and acts, between two grinding rings that are rotated relatively to each other.

According to the present invention, there is provided a grinding mill of the kind in which the material being ground passes through a set of grinding elements and the ground material is carried in a gas stream from the grinding elements to an outlet, means being provided whereby the maximum cross-section of the path from the top of the grinding elements to the outlet can be varied.

By way of example, embodiments of the invention will now be described with reference to the accompanying, somewhat schematic, drawings in which Figures 1 and 2 show vertical, axial, cross-sections through two grinding mills that are modifications each of the other.

Each of the mills that are illustrated is essentially a mill of the so-called E-type. The mill includes a ring of grinding balls 1 held between an upper grinding ring 2 that is fixed and a lower grinding ring 3 that rotates. Material to be ground passes radially outwardly between the grinding rings. A circle of jets 4 is arranged to discharge air upwardly past the outer periphery of the rings to entrain ground material and carry it upwards to the outlet 5 from the casing 6 in which the grinding surfaces are contained.

Extending concentrically with, and vertically upwardly from, the ring 2 is an annular baffle 10 of which the side walls 10a and 10b converge upwardly at equal angles to the vertical. The inner side walls of the casing 6 are provided with a lining 14 of which the lower part, 1 4a is of frusto-conical form. The part 1 4a converges slightly towards the wall 10b, but in other embodiments it may be parallel to the wall 10b. From a level below the tops of the baffle 10, the lining provides an upper part 14b, that meets the part 14a and diverges outwardly.

Extending concentrically downwardly into the space within the baffle 10, is a core member 20 of which the outer surface is frusto-conical and parallel to the wall 10a and to the part 14b. The maximum cross-section of the flow path for material leaving the grinding zone and passing to the outlet 5 is determined by the axial position of the core 20 relative to the lining 14. To enable its position to be adjusted, the core is suspended by threaded rods 21 that co-operate with nuts that abut the top wall 6a of the casing 6 so that by adjusting the positions of the nuts along the rods 21, the height of the core 20 can be varied. The upper surface 20a of the core is pitched so that any material falling on to it will roll off into the conveying air or back to the grinding zone.

The wall 10a of the baffle 10 is parallel to the outer surface of the core 20 and the space between them provides a return passage by which material that is not carried to the outlet may return to the grinding zone.

In operation, material to be ground passes radially outwardly between the grinding rings 2 and 3 to be entrained by the air supplied through the jets 4. Of the material carried up by the air, some will pass to the outlet 4, whilst some will drop out, and pass between the walls 1 0a and the surface of the core 20 back to the grinding zone. The grade of the material that passes to the outlet can be varied by varying the maximum cross-section at the upper end of the baffle 10. As the area increases, the velocity falls and it is possible to envisage changes in the grade that is carried to the outlet 5 between, perhaps 99.9% less than < inch to 99.9 /0 less than 1 /6 inch.

In a modification of what has been described, it is envisaged that the height of the lining 14 might be altered to vary the maximum cross-section at the upper end of the baffle in the passage of the ground material from the grinding zone to the outlet.

In the embodiment that is shown in Figure 2, the baffle 110 is in the form of a regular cylinder. The wall 106 of the casing with which the baffle 110 co-operates to form the up-flow path is also a cylinder, parallel to the baffle. Only the upper part 1 20b of the outer surface of the core 120 is frusto-conical and the extent to which this lies below the upper level of the baffle will determine the maximum flow path for the entrained material. The height of the core 120 can be adjusted by nuts working on bolts 21, whilst the other essential parts of the mill, such as the grinding rings 2 and 3 and the grinding balls 1 are similar to those of the previous embodiment.

In both embodiments, the baffle is mounted on the upper grinding ring 2 so that it will move with the grinding rings 2 to the extent that the ring wears in use.

1. A grinding mill of the kind in which the material being ground passes through a set of grinding elements and the ground material is carried in a gas stream from the grinding elements to an outlet, means being provided whereby the maximum cross-section of the path from the top of the grinding elements to the outlet can be varied.

2. A grinding mill as claimed in claim 1 in which means is provided to define a return path by which material reaching the region of maximum crosssection and not conveyed downstream of that region may return to the grinding elements.

3. A grinding mill as claimed in claim 2 in which the grinding elements are arranged in a horizontal ring, an annular baffle extends upwards from the ring, the path through which ground material passes from the grinding elements being defined by the outer surface of the baffle and an encircling annular wall, and the path through which ground material may return to the grinding elements including the inner surface of the baffle and a core member that

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to grinding mills This invention relates to grinding mills and is concerned to provide a grinding mill such that the grade reaching the outlet from the mill may be varied. The invention may be embodied in modifications of the ,so-called E-type mill in which a ring of grinding balls is held, and acts, between two grinding rings that are rotated relatively to each other. According to the present invention, there is provided a grinding mill of the kind in which the material being ground passes through a set of grinding elements and the ground material is carried in a gas stream from the grinding elements to an outlet, means being provided whereby the maximum cross-section of the path from the top of the grinding elements to the outlet can be varied. By way of example, embodiments of the invention will now be described with reference to the accompanying, somewhat schematic, drawings in which Figures 1 and 2 show vertical, axial, cross-sections through two grinding mills that are modifications each of the other. Each of the mills that are illustrated is essentially a mill of the so-called E-type. The mill includes a ring of grinding balls 1 held between an upper grinding ring 2 that is fixed and a lower grinding ring 3 that rotates. Material to be ground passes radially outwardly between the grinding rings. A circle of jets 4 is arranged to discharge air upwardly past the outer periphery of the rings to entrain ground material and carry it upwards to the outlet 5 from the casing 6 in which the grinding surfaces are contained. Extending concentrically with, and vertically upwardly from, the ring 2 is an annular baffle 10 of which the side walls 10a and 10b converge upwardly at equal angles to the vertical. The inner side walls of the casing 6 are provided with a lining 14 of which the lower part, 1 4a is of frusto-conical form. The part 1 4a converges slightly towards the wall 10b, but in other embodiments it may be parallel to the wall 10b. From a level below the tops of the baffle 10, the lining provides an upper part 14b, that meets the part 14a and diverges outwardly. Extending concentrically downwardly into the space within the baffle 10, is a core member 20 of which the outer surface is frusto-conical and parallel to the wall 10a and to the part 14b. The maximum cross-section of the flow path for material leaving the grinding zone and passing to the outlet 5 is determined by the axial position of the core 20 relative to the lining 14. To enable its position to be adjusted, the core is suspended by threaded rods 21 that co-operate with nuts that abut the top wall 6a of the casing 6 so that by adjusting the positions of the nuts along the rods 21, the height of the core 20 can be varied. The upper surface 20a of the core is pitched so that any material falling on to it will roll off into the conveying air or back to the grinding zone. The wall 10a of the baffle 10 is parallel to the outer surface of the core 20 and the space between them provides a return passage by which material that is not carried to the outlet may return to the grinding zone. In operation, material to be ground passes radially outwardly between the grinding rings 2 and 3 to be entrained by the air supplied through the jets 4. Of the material carried up by the air, some will pass to the outlet 4, whilst some will drop out, and pass between the walls 1 0a and the surface of the core 20 back to the grinding zone. The grade of the material that passes to the outlet can be varied by varying the maximum cross-section at the upper end of the baffle 10. As the area increases, the velocity falls and it is possible to envisage changes in the grade that is carried to the outlet 5 between, perhaps 99.9% less than < inch to 99.9 /0 less than 1 /6 inch. In a modification of what has been described, it is envisaged that the height of the lining 14 might be altered to vary the maximum cross-section at the upper end of the baffle in the passage of the ground material from the grinding zone to the outlet. In the embodiment that is shown in Figure 2, the baffle 110 is in the form of a regular cylinder. The wall 106 of the casing with which the baffle 110 co-operates to form the up-flow path is also a cylinder, parallel to the baffle. Only the upper part 1 20b of the outer surface of the core 120 is frusto-conical and the extent to which this lies below the upper level of the baffle will determine the maximum flow path for the entrained material. The height of the core 120 can be adjusted by nuts working on bolts 21, whilst the other essential parts of the mill, such as the grinding rings 2 and 3 and the grinding balls 1 are similar to those of the previous embodiment. In both embodiments, the baffle is mounted on the upper grinding ring 2 so that it will move with the grinding rings 2 to the extent that the ring wears in use. CLAIMS

3. A grinding mill as claimed in claim 2 in which the grinding elements are arranged in a horizontal ring, an annular baffle extends upwards from the ring, the path through which ground material passes from the grinding elements being defined by the outer surface of the baffle and an encircling annular wall, and the path through which ground material may return to the grinding elements including the inner surface of the baffle and a core member that extends into baffle and, above the baffle, provides a bonding of the region of maximum cross-section.

4. A grinding mill as claimed in either of claims 3 and 4 in which the height of the core member relatively to the baffle is adjustable, and the maximum cross-section depends upon the extent to which the core member projects into the baffle.

5. A grinding mill as claimed in either of claims 3 and 4 in which the maximum cross-section is determined by the outer surface of the core and an annular surface surrounding the core and projecting above the baffle, the surfaces being movable axially relatively to each other and being such that the maximum separation between them above the baffle is determined by their relative axial position.

6. A grinding mill as claimed in claim 5 in which said outer and annular surfaces are co-axial inverted frusto-conical surfaces having equal, or nearly equal, semi-vertical angles.

7. A grinding mill as claimed in either of claims 5 and 6 in which the annular surface is provided by a lining mounted on, and reciprocable relatively to, the casing of the mill.

8. A grinding mill as claimed in any of claims 3 to 8 in which means is provided for discharging air upwardly past the grinding elements into the path through which ground material passes from the grinding elements.

9. A grinding mill as claimed in any of claims 3 to 8 in which the baffle means provides two frustoconical surfaces converging upwardly, and the encircling annular wall and the surface of the core member that co-operates with the inner surface of the baffle are each in the form of a frusto-conical surface of the same semi-vertical angle as that of the surface of the baffle means with which itco- operates.

10. A grinding mill as claimed in any of claims 3 to 5 in which the baffle is provided by a cylindrical wall that is parallel to the encircling annular wall and, above the baffle, the core provides an outer frusto-conical surface.

11. A grinding mill substantially as described with reference to, and as illustrated, by either of the accompanying drawings.