GB2572528A

GB2572528A - Milling apparatus

Info

Publication number: GB2572528A
Application number: GB1721757.1A
Authority: GB
Inventors: Allen John
Original assignee: Cheshire Dispersion Co Ltd
Current assignee: Cheshire Dispersion Co Ltd
Priority date: 2017-12-22
Filing date: 2017-12-22
Publication date: 2019-10-09
Also published as: CN208373217U; GB201721757D0

Abstract

A milling apparatus (10, Fig 1) comprises a rotatingly driven centrifuge grinding separator (24 Fig 1 and figures 3-4). Separator (24) as upper and side slotted/perforated walls 28, 30, an open ended separator chamber (32). When side walls 30 rotate a grinding charge contained within the apparatus, is forced from the centre of the centrifuge grinding separator upwards /downwards and over/under the separator periphery and back in to the open ended separator chamber. Slots are shown by elements 36a-g and 38a-d. Separator (24) may be formed of a single piece of material and may have an upper wall 28 with an outer surface that slops upwardly towards the centre thereof. Attrition pegs (42, 43 Figs 4a & 4b) may also be provided.

Description

The present invention relates generally to an apparatus for and a method of milling, wet grinding, mixing, dispersing, emulsifying, homogenizing and similar functions hereinafter referred to as milling.

Background

A milling apparatus is known which comprises a milling chamber for containing particulate material such as granules or beads hereinafter termed the grinding charge. Such a milling apparatus generally comprises an agitating means for submitting this grinding charge and a material to be milled or otherwise treated within the chamber to intense agitating and shearing forces. The agitating means typically comprises one or more impellers or discs that in use cause the material to be milled to flow through the milling chamber and to be submitted to intense agitation and shearing forces in admixture with the grinding charge. In known milling apparatus a separation device is required to contain the grinding charge so as to separate it from the milled material. Such apparatuses are conventionally referred to as sand mills, agitated bead mills or pearl mills depending on the nature of the grinding charge and or the manufacturer's preference.

Patent document number WO2006/131698A2 describes a milling apparatus comprising a milling chamber loadable with a grinding charge; an inlet to the milling chamber via which a material to be milled is introduced into the milling chamber; and an outlet from the chamber via which milled material is extracted from the milling chamber. A rotatingly driven centrifuge grinding separator is located within the milling chamber. The separator comprises: an upper plate formed with a plurality of diagonally formed through slots; a lower plate formed with a plurality of diagonally formed through slots; and a ring located between the upper and lower plates formed with a plurality of diagonally formed through slots.

An object of the present invention is to provide milling apparatus, centrifuge grinding separators and method of milling which enable improved and less expensive milling of material, and to enable reductions in the cost of manufacturing milling apparatus and centrifuge grinding separators.

Summary

According to a first aspect of the present invention, there is provided a milling apparatus comprising at least one milling chamber for containing a grinding charge and a material to be milled, within which is located an associated rotatingly driven centrifuge grinding separator, which separator comprises: an upper wall formed with a plurality of through slots; a side wall formed with a plurality of through slots; and an open ended separator chamber defined by internal surfaces of the upper wall and the side wall; arranged such that rotation of the side wall formed with a plurality of through slots continually pressurizes such a grinding charge so as to force such a grinding charge from the centre of the centrifuge grinding separator upward and over the periphery of the separator and downward and under the periphery of the separator and drawing such a grinding charge back into the open ended separator chamber of the separator.

The grinding separator is advantageously formed from a single piece of material. The outer surface of the upper wall may have a sloping section which extends upwardly towards the centre of the plate.

The milling apparatus may further comprise an inlet to the milling chamber via which a material to be milled is introduced into the milling chamber; and an outlet from the chamber via which milled material is extracted from the milling chamber. The inlet is advantageously positioned so as to cause a material to be milled to flow directly into the open ended separator chamber of the centrifuge grinding separator.

A set of rotating attrition pegs may be located on the periphery of the separator so as to rotate with the separator and a set of stationary attrition pegs is located in the milling chamber in a facing arrangement with the rotating attrition pegs.

The milling apparatus may additionally comprise a drive shaft wherein the drive shaft rotatingly drives the centrifuge grinding separator and a drive motorwherein the motor rotatingly drives the drive shaft.

The motor is preferably a variable speed motor and the apparatus preferably additionally comprises a micro-processor for controlling the speed of the motor wherein temperature control of the material to be milled is achieved by varying the speed of the motor to maintain the temperature below a preset temperature limitation.

The through slots in the upper wall may extend from an outer surface of the upper wall to an inner surface of the upper wall and may be formed so that, in the direction of rotation of the upper wall, the outer leading edge of each slot precedes the inner leading edge of that slot.

The through slots in the side wall may extend from the outer surface of the side wall to the inner surface of the side wall and may be formed so that, in the direction of rotation of the side wall, the inner leading edge of each slot precedes the outer leading edge of that slot.

The milling apparatus advantageously further comprises a screen operable to retain the said grinding charge in the milling chamber.

According to a second aspect of the present invention there is provided a centrifuge grinding separator for a milling machine which separator comprises: an upper wall formed with a plurality of through slots; a side wall formed with a plurality of through slots; and an open ended chamber defined by internal surfaces of the upper wall and the side wall arranged such that rotation of the side wall formed with a plurality of through slots continually pressurizes such a grinding charge so as to force such a grinding charge from the centre of the centrifuge grinding separator upward and over the periphery of the separator and downward and under the periphery of the separator and drawing such a grinding charge back into the open ended chamber of the separator.

The grinding separator is advantageously formed from a single piece of material. The through slots in the upper wall may extend from an outer surface of the upper wall to an inner surface of the upper wall and may be formed so that, in the direction of rotation of the upper wall, the outer leading edge of each slot precedes the inner leading edge of that slot.

According to a third aspect of the present invention there is provided a method of milling using a milling apparatus according to the first aspect of the present invention, comprising the steps of: loading the grinding chamber with a grinding charge; introducing a material to be milled into the grinding chamber; and rotatingly driving the centrifuge grinding separator.

Description

Embodiments of the invention will now be described by way of example and with reference to the following drawings in which:

Figure 1 shows a sectional view through a milling apparatus according to a first aspect of the present invention;

Figure 2 shows an exploded view of the milling apparatus of Figure 1;

Figure 3a shows a perspective view of the upper side of a centrifuge grinding separator according to the second aspect of the present invention;

Figure 3b shows a perspective view of the lower side of the centrifuge grinding separator of Figure 3a;

Figure 4a shows a perspective view of the upper side of an alternative embodiment of the centrifuge grinding separator of Figures 3a and 3b; and

Figure 4b shows a perspective view of the lower side of the alternative embodiment of the centrifuge grinding separator of Figure 4a.

Referring to Figures 1 and 2, a milling apparatus 10 according to the present invention comprises a main drive shaft 12 mounted for use in the vertical orientation secured by a bearing housing 14, upper bearing flange 16, lower bearing flange 18, upper bearing 20 and lower bearing 22. The bearing housing 14 provides support for the rotating shaft 12. The bearings are high temperature bearings which contribute maintaining concentricity of the shaft 12 during rotation. The shaft 1 is driven by pulleys and belts from a primary drive motor which is single or variable speed in operation (not shown). The shaft 1 carries at its lower end a centrifuge grinding separator 24. The shaft also passes through a seal housing 26. The seal is a double mechanical seal which is operable to contain liquid within the milling chamber and is supported by a pressurized vessel (not shown) which delivers pressurized barrier fluid to the mechanical seal and dissipate the heat load absorbed into the barrier fluid from the mechanical seal.

Referring also to Figures 3a and 3b, in accordance with the present invention a centrifuge grinding separator comprises an upper wall 28, a side wall 30, an open ended chamber 32 and a lower flange 34 extending circumferentially around the opening to the open ended chamber 32. The open ended chamber 32 is defined by the inner surfaces of the upper wall 28 side wall 30 and the flange 34.

The centrifuge grinding separator 24 is formed from a single piece of material. This is enabled by virtue of the open ended chamber 32 which allows for the centrifuge grinding separator 24, of the present invention, to be cast and/or machined out of a single block of material using fewer steps of manufacturing compared to a separator having the closed or substantially closed chambers of the prior art, which are formed using, for example, an upper plate, central ring, and lower plate which are attached to each other to form a separator. Therefore, the centrifuge grinding separator 24, of the present invention, can be manufactured at a lower cost compared with those of the prior art. Moreover, being formed from a single piece of material and having the open ended chamber 32 advantageously provides for a relatively light-weight centrifuge grinding separator 24 with improved stability and milling performance and lower energy consumption relative to prior art milling apparatus and separators.

The upper wall 28 comprises one or more upper wall slots 36a-h which extend through the upper wall 28 between the inner surface and outer surface thereof.

The side wall 30 comprises one or more side wall slots 38a-d spaced apart around the circumference of the side wall 30 and extending through the side wall 30 between the inner surface and outer surface thereof. Only one side of the side wall can be seen in the drawings. However, it will be appreciated that the side wall slots are spaced around the complete circumference of the side wall

30.

The slots 36 and 38 are preferably diagonally formed through the upper and side walls, 28 and 30, respectively.

More preferably, on the upper wall 28, the diagonal slots 36 are formed from the bottom of the upper wall to the top of the upper wall such that the part of the slot at the top of the upper wall precedes the part of the slot at the bottom of the upper wall in the direction of rotation of the upper wall. The upper leading edge of each slot precedes the lower leading edge of each slot. The slots are centered on and extend along an arc, the points on which are all equidistant from the centre of the upper wall. However, in an alternative embodiment, the slots 36 can be formed so that they diverge from such an arc, either towards the direction of the peripheral edge of the upper wall 28 or towards the centre of the upper wall 28.

Also, more preferably, the diagonal slots 38 are formed in the side wall 30 from the outer surface of the side wall 30 to the inner surface of the side wall 30 such that the part of the slot at the inner surface of the side wall precedes the part of the slot at the outer surface of the ring in the direction of rotation of the side wall 30. The inner leading of each slot precedes the outer leading edge of each slot. The slots 38 extend at an angle to a radius of the side wall 30.

The angle of the slots 36 and 38 may be between 30° and 60° relative to the respective upper and side wall, 28 and 30, and preferable between 40° and 50° and more preferably approximately 45° relative to the respective upper and side wall, 28 and 30.

The flange 34 provides a peripheral channel 40 around the circumferential periphery of the open ended chamber 32.

Referring to Figures 4a and 4b, an alternative embodiment of centrifuge grinding separator 24 comprises a plurality of attrition pegs 42 and 43, disposed, is use, to extend from the centrifuge grinding separator 24 in an upwards direction and downwards direction, respectively.

The centrifuge grinding separator 24 is secured to the shaft 12 through a shaft spacer 45 by a number of cap head screws. The shaft spacer 45 provides additional stability for the shaft 12 and thereby mitigates vibration resulting in an improved and more efficient milling process.

A main milling chamber 44 is suspended from the seal housing 26 which carries a number of shaft seals 46, and is flushed with liquid via suitable holes (not shown).

The milling chamber 44 is equipped with a number of stationary attrition pegs 47 (shown in Figure 1).

The milling chamber 44 further comprises a side water cooling annulus 48 and jacket 50 an upper water cooling annulus 52 and jacket 54 and a lower water cooling annulus 56 and jacket 58, which are operable in combination to cool the milling chamber 44.

In use, the milling chamber is partially filled using known technology with a grinding charge of particulate material having a diameter of between 0.1 mm to 3 mm. The apparatus according to the present invention requires a quantity of grinding charge equivalent to 45% - 55% of the volume of the milling chamber and preferably about 50% of the volume of the milling chamber. This is less than required in prior art milling apparatus. Therefore, lower grinding charge volumes are to be used.

The material to be milled is caused to flow through appropriate inlet and outlet ports 60 and 62, respectively, and is directed to the centre of the open ended chamber 32 of the centrifuge grinding separator 24. At the same time the motor is operated to rotate shaft 12 thereby causing the centrifuge grinding separator 24 to develop the appropriate intense agitation, shearing, attrition and separation conditions within the milling chamber. The rotating centrifuge grinding separator 24 causes the material to be milled to be forced outward and into and through the grinding charge. The escape of the grinding charge is prevented by the separation effect of the centrifuge grinding separator on the material to be milled and the grinding charge. The heavier grinding charge is pulled back into the centrifuge grinding separator by the action of the diagonally formed slots 36 in the upper wall 28 and through the opening of the open ended chamber 32.

A suitably disposed screen 64 ensures the grinding charge remains in the milling chamber 44.

The milling apparatus described above has several advantages arising from forming the centrifuge grinding separator and grinding chamber as shown.

The chamber 32 of the centrifuge grinding separator 24 being open generates increased forces and velocity resulting in an improved and more intense grinding charge pressure between the periphery of the centrifuge grinding separator 24 and milling chamber wall which results in significantly improved grinding effects. This is achieved because the majority of the grinding charge, displaced by the material to be milled, is sucked in from the internal wall of the milling chamber 44 through the relatively large open end of the centrifuge grinding separator chamber 32 io wherein it is evenly distributed within the open ended chamber 32 and naturally separated from the material to be milled before being jetted again through the slots and the action repeats itself again. The even distribution of the grinding charge within the open ended chamber 32 provides an intense grinding action and particle to particle abrasion as it increases the number of regions of uniform open spaces between the individual particles of grinding charge. Therefore, improved particle size reduction is achieved on the material to be milled giving very fine particle products and a more uniform and predictable size of particle.

This also creates lower volume high intensity grinding zones and more uniform milling of the material.

The grinding zones are maintained throughout the operation by the efficiency of the centrifuge grinding separator causing the grinding charge to behave in a predetermined circular motion and to be concentrated around the inner and outer periphery of the centrifuge grinding separator.

Aggressive grinding forces are also created between the rotating pegs 42 and 43 and stationery pegs 47. When in use, pegs 42, 43 and 47 work in with the grinding charge within the milling chamber 44 to provide attrition to the material being milled within the milling chamber 44.In use, the pegs 42, 43 and 47 also causes agitation and displacement of the grinding charge within the milling chamber 44.

A definite separation of the grinding charge from the product to be milled is achieved and so no secondary separation device is required.

During operation of the milling apparatus 10, the temperature of the milling chamber 44 is kept cool using a side cooling annulus 48 and jacket 50 an upper cooling annulus 52 and jacket 54 and a lower cooling annulus 56 and jacket 58. In use, an externally cooled fluid is circulated around the milling chamber 44 through the cooling annulus 48, 52 and 56. The cooled fluid absorbs excess heat from the milling chamber 44. The jackets 50, 54 and 58 insulate the cooling annulus 48, 52 and 56.

Temperature control of the milling chamber 44 is achieved by preset temperature limitations through a micro-processor so as to control the input speed through variable speed drive.

The milling apparatus according to the present invention is a grinding machine, such as a wet grinding machine which is comprised of a main drive shaft supported by a bearing/seal housing which is driven by V Belts and pulleys via a primary electric motor. The grinding chamber is suspended from the seal housing in a vertical configuration which is wide and shallow. Suspended at the lower end of the main drive shaft are the main rotational elements (centrifuge grinding separator). Within the grinding chamber, particulate grinding materials are housed. The material to be milled is passed through a suitable inlet 60 and is dispersed through the grinding charge before leaving the machine via a suitable outlet 62 in continuous operation. The material to be milled and the grinding charge are separated at the periphery of the centrifuge grinding separator. Therefore, no other separation device is required.

Accordingly, the milling apparatus 10 and method, according to the present invention, provides a more efficient milling process which enables the production of a better quality, more uniform milled product to be processed at a reduced cost, relative to the prior art apparatus and methods.

Also, the centrifuge grinding separator 24, according to the present invention, is easier to manufacture, is of a reduced weight and provides a more stable and uniform separation and milling process with improved grinding action and particle to particle abrasion relative to the centrifuge grinding separators of the prior art. The relatively light-weight centrifuge grinding separator 24 reduces the power io consumption and thereby provides a more low cost milling process relative to prior art milling apparatus and methods.

Claims

1. A milling apparatus comprising at least one milling chamber for containing a grinding charge and a material to be milled, within which is bcated an associated rotatingly driven centrifuge grinding separator, which separator comprises:

an upper wall formed with a plurality of through slots;

a side wall formed with a plurality of through slots; and an open ended separator chamber defined by internal surfaces of the upper wall and the side wall;

arranged such that rotation of the side wall formed with a plurality of through slots continually pressurizes such a grinding charge so as to force such a grinding charge from the centre of the centrifuge grinding separator upward and over the periphery of the separator and downward and under the periphery of the separator and drawing such a grinding charge back into the open ended separator chamber of the separator.

2. A milling apparatus as claimed in claim 1, wherein the grinding separator is formed from a single piece of material.

3. A milling apparatus as claimed in any of the preceding claims, wherein the outer surface of the upper wall has a sloping section which extends upwardly towards the centre of the plate.

4. A milling apparatus according to any of the preceding claims, further comprising:

an inlet to the milling chamber via which a material to be milled is introduced into the milling chamber; and an outlet from the chamber via which milled material is extracted from the milling chamber.

5. A milling apparatus according to claim 4 wherein the inlet is positioned so as to cause a material to be milled to flow directly into the open ended separator chamber of the centrifuge grinding separator.

6. A milling apparatus according to any one of the preceding claims wherein a set of rotating attrition pegs is located on the periphery of the separator so as to rotate with the separator and a set of stationary attrition pegs is located in the milling chamber in a facing arrangement with the rotating attrition pegs.

7. A milling apparatus according to any one of the preceding claims additionally comprising a drive shaft wherein the drive shaft rotatingly drives the centrifuge grinding separator and a drive motor wherein the motor rotatingly drives the drive shaft.

8. A milling apparatus according to claim 7 in which the motor is a variable speed motor and the apparatus additionally comprises a micro-processor for controlling the speed of the motor wherein temperature control of the material to be milled is achieved by varying the speed of the motor to maintain the temperature below a preset temperature limitation.

9. A milling apparatus according to any one of the preceding claims wherein the through slots in the upper wall extend from an outer surface of the upper wall to an inner surface of the upper wall and are formed so that, in the direction of rotation of the upper wall, the outer leading edge of each slot precedes the inner leading edge of that slot.

10. A milling apparatus according to any one of the preceding claims, wherein the through slots in the side wall extend from the outer surface of the side wall to the inner surface of the side wall and are formed so that, in the direction of rotation of the side wall, the inner leading edge of each slot precedes the outer leading edge of that slot.

11. A milling apparatus according to any of the preceding claims, further comprising a screen operable to retain the said grinding charge in the

12. A centrifuge grinding separator for a milling machine which separator comprises:

an upper wall formed with a plurality of through slots;

a side wall formed with a plurality of through slots; and an open ended chamber defined by internal surfaces of the upper wall and the side wall arranged such that rotation of the side wall formed with a plurality of through slots continually pressurizes such a grinding charge so as to force such a grinding charge from the centre of the centrifuge grinding separator upward and over the periphery of the separator and downward and under the periphery of the separator and drawing such a grinding charge back into the open ended chamberof the separator.

13. A centrifuge grinding separator as claimed in claim 11, wherein the grinding separator is formed from a single piece of material.

14. A centrifuge grinding separator as claimed in claim 11 or 12, wherein the through slots in the upper wall extend from an outer surface of the upper wall to an inner surface of the upper wall and are formed so that, in the direction of rotation of the upper wall, the outer leading edge of each slot precedes the inner leading edge of that slot.

15. A centrifuge grinding separator as claimed in claims 11 to 13, wherein the through slots in the side wall extend from the outer surface of the side wall to the inner surface of the side wall and are formed so that, in the direction of rotation of the side wall, the inner leading edge of each slot precedes the outer leading edge of that slot.

16. A method of milling using a milling apparatus according to any one of claims 1 to 11, comprising the steps of:

loading the grinding chamber with a grinding charge;

introducing a material to be milled into the grinding chamber; and rotatingly driving the centrifuge grinding separator.