MILLING MACHINE

Abstract: A milling machine comprises an elongate inner member (2) of annular transverse section having an outer surface thereto, an elongate, generally annular outer member (10) having an inner surface thereto and surrounding said inner member (2) to define a space therebetween, the inner and outer members (2, 10) being rotatable relative to one another about the central longitudinal axis of the machine, an inlet (22) at one end of the machine to said space, and an outlet (24) at the other end of the machine from said space, the outer surface of the inner member (2) and the inner surface of the outer member (10) being configured to provide, on relative rotation thereof, a co-operating action therebetween, the arrangement being such that material passing through the machine within said space follows a tortuous, but generally spiral path from the inlet (22) to the outlet (24), the co-operating action of the surfaces of the inner and outer members (2, 10) being such as to create, throughout the length of said spiral path, turbulent regions within the material whereby the particles therein wear against one another to reduce the sizes thereof.

Description: MILLING MACHINE TECHNICAL FIELD This invention relates to a milling machine, and more particularly to such a machine for the treatment of liquid/powder mixes to reduce the size of the particulate content, preferably to sub-micron size. BACKGROUND It is well-established practice in, for example, the paint, coating, ink and pharmaceutical industries to use bead mills to grind the powder of liquid/powder mixes to sub micron particle size. Such mills utilise large numbers of small beads agitated in a chamber, the product to be treated being pumped through the agitating beads to give a final grind/mill finish to the particles therein. Such an arrangement has a number of disadvantages, not the least of which are that the beads wear quickly during operation of the machine and need regular replacement, the removal, cleaning out and replacement of the beads is expensive and time consuming, the rotating internal parts of the machine are also subject to rapid wear and therefore need regular maintenance and/or replacement, and a large number of cycles/passes of the material through the machine is often required to produce the desired finish, resulting in the treatment itself taking a considerable length of time. SUMMARY OF THE INVENTION It would be desirable to be able to provide a milling machine for liquid/powder mixes which overcame the aforementioned disadvantage, and in particular which eliminated the requirement for beads and which effected the necessary treatment relatively quickly and without undue wear to the associated machine. According to the present invention, there is provided a milling machine comprising an elongate inner member of circular transverse section having an outer surface thereto, an elongate, generally annular outer member having an inner surface thereto and surrounding said inner member to define a space therebetween, the inner and outer members being rotatable relative to one another about the central longitudinal axis of the machine, an inlet at one end of the machine to said space, and an outlet at the other end of the machine from said space, the outer surface of the inner member and the inner surface of the outer member being configured to provide, on relative rotation thereof, a co-operating action therebetween, the arrangement being such that material passing through the machine within said space follows a tortuous, but generally spiral path from the inlet to the outlet, the co-operating action of the surfaces of the inner and outer members being such as to create, throughout the length of said spiral path, turbulent regions within the material whereby the particles therein wear against one another to reduce the sizes thereof. Ideally, within said turbulent regions, the material is subjected to pressure fluctuations and impulses such that, for any given region of the spiral path, material is moving in opposite directions to create said wearing action. In a preferred embodiment of the invention, the inner member is rotatable and the outer member is static . Conveniently the configurations of the outer surface of the inner member and the inner surface of the outer member each incorporate a plurality of sets of circumferentially spaced teeth. Preferably a first series of sets of peaked teeth on the inner member are axially aligned with a corresponding second series of sets of truncated teeth on the outer member, the external diameter of the teeth of the first series being substantially equal to the internal diameter of the teeth of the second series whereby, on rotation of the inner member, and on passage of material between said sets of teeth on the inner and outer members, said teeth effect a grinding action on said material . In a preferred embodiment of the invention the milling machine includes coolant flowing therethrough to dissipate heat generated within the material passing through the machine . Conveniently the outer member comprises a plurality of internally toothed annular elements alternating with a plurality of annular baffle plates, and the inner member comprises a plurality of externally toothed gear wheels axially aligned with the internally toothed annular elements of the outer member and alternating with a plurality of reduced diameter ring members defining spaces between adjacent externally toothed gear wheels and axially aligned with the baffle plates of the outer member, the baffle plates of the outer member projecting into the spaces between the externally toothed gear wheels of the inner member, the internally toothed annular elements and the baffle plates including interconnected coolant passages therein and therearound whereby coolant can flow through the length of the machine . Preferably each internally toothed annular element of the outer member has an annular coolant channel formed therein closely to surround the teeth thereof, each baffle plate of the outer member having an annular coolant channel formed in that part thereof projecting into the space between the associated externally toothed gear wheels of the inner member, the coolant channels in adjacent annular elements and baffle plates being interconnected to provide a continuous channel of generally spiral shape extending the length of the machine . Conveniently the direction of flow of the coolant is opposite to that of the material passing through the machine . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal section through a milling machine according to the invention,- Fig. 2 is a detail of Fig. 1 showing an internally toothed annular element of the outer member and an axially aligned externally toothed gear wheel of the inner member,- Fig. 3 is an end view in the direction of arrow A of the element and wheel of Fig.2; Fig. 4 is a detail of Fig. 3 to a larger scale, and Fig. 5 is an exploded isometric view of a baffle plate and the adjacent internally toothed annular element showing the coolant path. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the illustrated milling machine includes a central rotor indicated generally at 2 and comprising a series of axially spaced, externally toothed gear wheels 4 alternating with a series of reduced diameter spacer members 6, all mounted on, to be rotatable with, a drive shaft 8 powered by, for example, an hydraulic motor at speeds of up to, typically, 4000 rp . Clearly various other drive means could be used. The machine further includes a fixed annular sleeve or stator indicated generally at 10 and surrounding the rotor 2. The stator 10 comprises a series of axially spaced, annular elements 12 alternating with a series of annular baffle plates 14, the elements 12 being axially aligned with the gear wheels 4 of the rotor 2, and the baffle plates 14 being axially aligned with the spacer members 6 of the rotor 2 as clearly seen in Fig. l. More particularly, each gear wheel 4 is provided with a series of external, circumferentially spaced, peaked teeth 16, while the internal surface of the annular element is provided with a series of axially extending, circumferentially spaced grooves defining a series of truncated teeth 18 therearound the pitch of which is slightly greater than that of the teeth 16. A circumference through the peaks of the teeth 16 on a gear wheel 4 is of slightly smaller diameter than that of a circumference through the flats of the teeth 18 on an annular element 12, whereby a small gap exists between aligned teeth on the gear wheel 4 and the corresponding element 12. Each baffle plate 14 includes a radially innermost annular portion 20 projecting into the annular space between adjacent gear wheels 4 of the rotor 2. Each annular portion 20 terminates radially outwardly of the associated spacer member 6 of the rotor, thereby to define an annular space of generally U-shape in transverse section between adjacent gear wheels 4 and which connects with the aforementioned gaps between the aligned gear wheels 4 and annular elements 12. An inlet 22 for material to be treated is provided at one end of the machine to feed into the space between the rotor 2 and the stator 10, and an outlet 24 from said space for treated material is provided at the other end of the machine . On operation of the machine, the rotor 2 is rotated relative to the stator 10 by the hydraulic motor, and material to be treated is fed to the inlet 22. This material comprises a suspension of particles in a carrier liquid, the particles of which are to be deconglomerated, dispersed and milled to smaller, preferably sub-micron, size by passage through the machine . It will be appreciated that by virtue of the rotation of the rotor, the path of the material along the annular space between the rotor and the stator from the inlet 22 to the outlet 24 will be generally spiral. However, within said generally spiral path and at any position therealong, the material is subjected to constantly varying pressure impulses and fluctuations due to the configurations of the surfaces of the rotor 2 and the stator 10 to each side of said path. More particularly, and as perhaps best seen in Fig. 4, there are regions 26 within the stator 12, and in particular between the teeth 18 thereof, where material is relatively static, and adjacent regions 28 within the rotor 2, and in particular between the teeth 16 of the gear wheels 4, where material is travelling at substantial speed determined by the diameter of the rotor 2 and the output of the motor. The overall result is that material in the opposed regions 26, 28 creates a high pressure slipstream or slipline effect 30 of material at different speeds attempting to move in opposite directions, the particles in said material thereby being deconglomerated, dispersed in the carrier liquid and worn against one another to create a finely milled product. In Fig. 4, the material in the slipstream 30 has been omitted for clarity. This milling effect is further supplemented by passage of the material between the teeth 16 on the gear wheels 4 and the teeth 18 on the annular elements 12, while the tortuous nature of the path of the material through the machine is further determined by the presence of the portions 20 of the baffle plates 14 against the surfaces of which the material is incident during its generally spiral path through the machine. Clearly the precise nature of the tortuous path for the material as determined by the outer surface of the rotor 2 and the inner surface of the stator 12 can vary from that described and illustrated providing the turbulent regions within the generally spiral path are created to effect the desired grinding/milling of the particulate content of the material being treated. The elements of the rotor 2 may be other than gear wheels, while the configuration of the inner surface of the stator 10 can vary from that shown as long as it is such as to effect the necessary co-operation with the surface of the rotor 2 to create the desired effect. It will be appreciated that the described machine has distinct advantages over the so-called bead mills, in particular because the milling of the particles is substantially effected by particle to particle contact, this arrangement substantially reducing wear of the associated machine. Furthermore, the configuration of a machine, and the speed of rotation thereof, can be such as to enable a desired milling effect even to sub micron size to be achieved with a single pass through the machine . During passage of the material through the machine, and as a direct result of the particle to particle milling effect, a considerable amount of heat can be generated within the machine. The illustrated machine therefore incorporates means for dissipating this heat, in the form of a coolant passage within the stator and extending substantially spirally the length of the machine . More particularly, and with specific reference to Fig. 5, each element 12 has formed therearound an annular coolant channel 32 with an input to one side thereof and an adjacent output from the other side thereof separated by stop pin 34 whereby coolant can enter the channel 32 from one side of the element 12 through the input, flow around the element 12 as indicated by the arrows X in Fig. 5, and exit from the channel 32 through the output to the other side of the element 12. The portion 20 of each baffle plate 14 comprises a central annular member 34 within and spaced from a surrounding housing 36 to define an annular space 38 thereon of substantially U-shape in transverse section as best seen in Fig. 1. Each baffle plate 14 has a coolant input 40 to one side thereof aligned with the output from the adjacent element 12 and feeding into the space 38, and a coolant output 42 from the other side thereof aligned with the input to the adjacent element 12 and feeding from the space 38, whereby coolant entering through the input 40 flows around the portion 20 of the baffle plate 14 as indicated by the arrows Y in Fig. 5 and thence exits from the space 38 into the channel 32 of the next adjacent element 12. A stop plate 44 separates the input flow from the output flow. Thus it will be appreciated that the overall coolant passage extends spirally around each element 12 and baffle plate 14 the length of the machine, coolant flowing through the machine in a direction opposite to that of the material being treated. The proximity of the coolant to the material passing through the machine ensures that the material is maintained at a suitable working temperature under all operating conditions.

Claims: CLAIMS 1. A milling machine characterised by an elongate inner member (2) having an outer surface thereto, an elongate, generally annular outer member (10) having an inner surface thereto and surrounding said inner member (2) to define a space therebetween, the inner and outer members (2, 10) being rotatable relative to one another about the central longitudinal axis of the machine, an inlet (22) at one end of the machine to said space, and an outlet (24) at the other end of the machine from said space, the outer surface of the inner member (2) and the inner surface of the outer member (10) being configured to provide, on relative rotation thereof, a co-operating action therebetween, the arrangement being such that material passing through the machine within said space follows a tortuous, but generally spiral path from the inlet (22) to the outlet (24), the co-operating action of the surfaces of the inner and outer members (2, 10) being such as to create, throughout the length of said spiral path, turbulent regions within the material whereby the particles therein wear against one another to reduce the sizes thereof. 2. A milling machine as claimed in claim 1 in which the inner member (2) is rotatable and the outer member (10) is static. 3. A milling machine as claimed in claim 1 or claim 2 in which the configurations of the outer surface of the inner member (2) and the inner surface of the outer member (10) each incorporate a plurality of sets of circumferentially spaced teeth (16, 18) . 4. A milling machine as claimed in claim 3 in which a first series of sets of peaked teeth (16) on the inner member (2) are axially aligned with a corresponding second series of sets of truncated teeth (18) on the outer member (10) , the external diameter of the teeth (16) of the first series being substantially equal to the internal diameter of the teeth (18) of the second series whereby, on rotation of the inner member (2), and on passage of material between said sets of teeth (16, 18) on the inner and outer members (2, 10), said teeth (16, 18) effect a grinding action on said material. 5. A milling machine as claimed in any one of claims 1 to 4 and including coolant flowing therethrough to dissipate heat generated within the material passing through the machine . 6. A milling machine as claimed in claim 5 in which the outer member (10) comprises a plurality of internally toothed annular elements (12) alternating with a plurality of annular baffle plates (14) , and the inner member (2) comprises of plurality of externally toothed gear wheels (4) axially aligned with the internally toothed annular elements (12) of the outer member (2) and alternating with a plurality of reduced diameter ring members (6) defining spaces between adjacent externally toothed gear wheels (4) and axially aligned with the baffle plates (14) of the outer member (10) , the baffle plates (14) of the outer member (10) projecting into the spaces between the externally toothed gear wheels of the inner member (2) , the internally toothed annular elements (12) and the baffle plates (14) including interconnected coolant passages therein and therearound whereby coolant can flow through the length of the machine . 7. A milling machine as claimed in claim 6 in which each internally toothed annular element (12) of the outer member (10) has an annular coolant channel (32) formed therein closely to surround the teeth (18) thereof, each baffle plate (14) of the outer member (10) having an annular coolant channel (38) formed in that part (20) thereof projecting into the space between the associated externally toothed gear wheels (4) of the inner member (2) , the coolant channels in adjacent annular elements (12) and baffle plates (14) being interconnected to provide a continuous channel of generally spiral shape extending the length of the machine . 8. A milling machine as claimed in any one of claims 5 to 7 in which the direction of flow of the coolant is opposite to that of the material passing though the machine .

Inventors: COCKBAIN GEORGE STEWARTSON, COCKBAIN, GEORGE, STEWARTSON
Applicants: COCKBAIN GEORGE STEWARTSON, WITHDEAL LIMITED, COCKBAIN, GEORGE, STEWARTSON
Application year: 2000
Main classification: B02C19
IPC codes: B02C13, B02C17, B02C19