AU2010202771A1

AU2010202771A1 - A centrifugal grinding system

Info

Publication number: AU2010202771A1
Application number: AU2010202771A
Authority: AU
Inventors: John Charles Turner
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-07-01
Filing date: 2010-06-30
Publication date: 2011-01-20
Anticipated expiration: 2030-06-30
Also published as: AU2010202771B2

Description

1 OF 31 AUSTRALIA Patents Act 1990 5 COMPLETE SPECIFICATION 10 Invention Title: 15 A CENTRIFUGAL GRINDING SYSTEM The invention is fully described in the following statement: 20 2 OF 31 A CENTRIFUGAL GRINDING SYSTEM The present invention relates to the size reduction of solid material in a centrifugal grinding mill. BACKGROUND 5 Many products in common use by society require the use of finely ground solid material. These products are used in all manner of products such as pharmaceuticals, food, paints, filled paper, filled plastics and building products such as cement etc. Often the product properties depend heavily on the size distribution of the component ground material and in addition in recent years the use of ultra fine ground materials even down to the nanometer scale has grown 10 significantly as new material properties have been attributed to the smaller particle size. Much of the grinding of bulk commodities and minerals is carried out in the conventional technology tumbling mills such as ball mills. Tumbling mills are the workhorse of the cement industry for example simply because they are reliable, simple to operate and are effective. 15 They are however extremely energy intensive but inherently low efficiency. The specific power input achievable with such mills being typically less than 30 Kwatts/m 3 of grinding chamber volume. As a consequence of the low specific power input a conventional tumbling mill is a large expensive item of capital equipment. The low power input arises from the limitation of grinding forces to those due to gravity alone. Another characteristic of the tumbling mill is the 20 wide particle size distribution of the mill output and its limitation to producing output with a relatively large particle size due to the large interstitial space of the ball mass. If a higher proportion of smaller particle sizes are required then the interstitial volume of the ball mass must be reduced which implies smaller and therefore lighter balls. In turn this reduces the energy of impact between the balls and therefore reduces the grinding rate. Accordingly the 25 conventional technology tumbling mill is simply not suited to producing the smaller particle size distribution increasingly required for modern materials. Another inherent disadvantage of the ball mill is the cost of the grinding media or balls. Not only must the grinding chamber be initially charged with media but also it must be replaced as it wears down in size. In summary the tumbling mill is capital intensive, expensive to run, very large, not energy efficient and not 30 suited to producing the small particle sizes increasingly needed today. In order to provide a realistic alternative to the tumbling mill for most of the existing applications a mill must provide in combination: superior energy utilisation, continuous operation, reliability of operation, lower whole of life cost and be capable of real time operational optimisation. 35 The limitations of the tumbling mill have been recognised for a long time and numerous other grinding methods have developed in order to address one or more of the foregoing shortcomings. In particular stirred mills and various forms of centrifugal mills have been developed and found application in various industries. Of particular interest here is the 40 development of the centrifugal mill in its various types.

3 OF 31 The principal of the centrifugal mill is to replace or at least augment gravity as the force producing the grinding energy. All centrifugal mills consist of one or more grinding chambers rotating about their own axis whilst orbiting about another substantially parallel axis such that the contents of the grinding chamber or chambers is continuously cascading and impacting 5 with itself, any grinding media present and the walls of the grinding chamber. High specific energy inputs can be obtained utilising this mechanism as the centrifugal forces generated can be greater than 50 times gravitational force. With centrifugal mills (as with tumbling mills) there is an optimum density of grinding chamber 10 contents (grinding furnish and grinding media if any) wherein for a given angular velocity the effective grinding energy per unit volume of grinding chamber is at a maximum. Increasing or decreasing the grinding chamber contents density above or below the optimum point will result in lower grinding energy per unit volume of grinding chamber. In addition within a centrifugal mill grinding chamber it is possible to profile the grinding energy density throughout the length 15 of the said chamber by profiling the internal diameter of the chamber. Exploitation of this mechanism is of little or no value unless the grinding chamber length to diameter ratio is greater than 2 and preferably greater than 3. For the purposes of differentiation within this specification and in order to classify the prior art 1 20 have classified centrifugal mills into 2 broad categories. Mills where the axis of orbit lies within the locus formed by the extremity of the grinding chamber as it rotates about its axis of rotation (locus of rotation) I term "internal orbit mills" and mills where the axis of orbit lies on or outside the locus of rotation of the grinding chamber I term "external orbit mills". Figures 1A and 1 B illustrate the geometry of each type. Clearly internal orbit mills are restricted to having one 25 grinding chamber per mill whereas external orbit mills may have a plurality of grinding chambers per mill. Also clearly the radius of orbit of the internal orbit mill is restricted to the radius of the locus of rotation of the grinding chamber. Whilst higher centrifugal forces are attainable in an external orbit mill for the same rotational speed by virtue of the increased radius they have a very clear disadvantage of by necessity having a complex infeed and 30 outfeed system. Furthermore where there are a plurality of grinding chambers modulating the infeed to each individual chamber becomes difficult if not impossible in practice. These operational disadvantages have prevented the widespread acceptance of this mill geometry for large scale bulk grinding. 35 External orbit grinders with a plurality of grinding chambers have an inherent advantage in that they are automatically in balance other than for differences in the amount of material to be ground in each grinding chamber. This advantage and the higher centrifugal forces available with the higher radius of orbit appear to have encouraged a disproportionate amount of development and innovation of the external orbit machine over the internal orbit machine. 40 For the purposes of additional differentiation I have further classified centrifugal mills as being of fixed ratio or variable ratio. The fixed ratio mill has a fixed ratio between the rotational speed 4 OF 31 of orbit and the rotational speed of the grinding chamber. The variable ratio mill has a variable ratio between the rotational speed of orbit and the rotational speed of the grinding chamber. A variable ratio mill will in general have an independent drive train driving the grinding chamber to that driving the mill orbit. Whilst fixed ratio mills have an advantage of simplicity their 5 operational efficiency and absolute power consumption cannot be optimized in real time by modulating the ratio and additionally they cannot be made to transition into a different operating mode such as idle or any mode more suited to the rectification of an operational problem such as choking. 10 For yet further purposes of differentiation I have further classified centrifugal mills as being continuous or batch mills. The prior art mills are generally shown as either horizontal or vertical and indeed most are designed for and rely on one particular orientation to work. 15 Early forms of the centrifugal mill are described in US patent 405810. Intemal and external orbit machines are illustrated. All are batch machines and all are fixed ratio machines in general intended more for husking grain than mineral grinding. 20 Further early forms of centrifugal mill are described by Pendleton US patent 458662. Internal orbit batch mills and external orbit continuous mills are illustrated all of which are fixed ratio where the grinding tube is held substantially in a fixed absolute rotational orientation by a linkage. 25 A vertical continuous external orbit mill of fixed ratio is illustrated in US patent 569828. A recognition that other than a 1:1 ratio of rotational to orbit speed was of benefit is given in US patent 2937814 where a simple relationship of rotational speed ratio to radii ratio is given for radii ratios of 2 and above - ie for external orbit mills. An external orbit batch mill with a 30 variable ratio facility and an external orbit continuous mill with fixed ratio are illustrated. Canadian patent 1089428 describes an internal orbit continuous mill of fixed 1:1 speed ratio utilising a system of 2 eccentric bearings and oscillating linkages to provide the orbital motion. The grinding chamber itself not being free to rotate. 35 Gamblin - US patent 5029760 describes an external orbit, fixed ratio 1:1 centrifugal mill whereby the rotational orientation of the 2 grinding tubes is maintained substantially fixed by means of linkages somewhat in the manner as that proposed by Pendleton in earlier prior art. Continuous operation is envisaged through small diameter flexible tubes located in the end 40 plates of the grinding tubes. In a later patent Gamblin describes a similar grinding system but with a single grinding tube and continuous operation through flexible tubes at both ends of the grinding tube.

5 OF 31 US patent 5232169 describes an external orbit continuous ball mill with a plurality of small grinding chambers and a pneumatic conveying system for the infeed and ouffeed. 5 Numerous specifications describe external orbit centrifugal mills with features designed to overcome the significant operational problems associated with maintaining a continuous infeed and outfeed to a plurality of orbiting grinding chambers. They include US patents 5364036, 5522558, 5513806. 10 US patent 6086242 describes in significant detail an external orbit, variable ratio, centrifugal mill with independent drive trains for the main rotor and the grinding chambers. In reviewing the prior art and the existing utilisation for centrifugal grinders it became apparent that a principal reason for the technology not being taken up to any great extent for the bulk 15 grinding operations such as cement was the difficulty in providing a reliable and acceptably large feedrate to the grinding chambers of external orbit machines. In more recent years some developments with designs that partially overcome this difficulty have been made. US patent 5375783 Gamblin describes a variation on his proposals described above whereby a 20 grinding tube of a fixed ratio, external orbit machine is enclosed at the ends and flexible tubes connected into the sides of the grinding tube in order to provide infeed and outfeed. Such a system requires the grinding tube to orbit with a fixed rotational orientation. Whilst the specification also proposes the use of multiple grinding tubes this arrangement is impossible to achieve as the tubes and flexible hoses would interfere. 25 A hybrid centrifugal mill in the form of a nutating chamber is described in US patent 4733825. In this design the axis of rotation of the chamber is not parallel to the axis of orbit of the chamber but rather the axes intersect at what is referred to as the nutation point. The design approximates an internal orbit machine. By virtue of its design the mill can only be a fixed ratio 30 mill of 1:1 ratio. A vertical mill is described and the relatively large infeed opening on the central axis of the machine allows the use of a simple infeed system. Further developments in this mill are detailed in US patent 7070134. Whilst this design seems to substantially improve the infeed characteristics of the mill and has demonstrated that specific power inputs of greater than 2000 Kwatt/m 3 of grinding chamber are possible the design suffers from a number of shortcomings 35 that have precluded its use for bulk grinding applications such as cement. In particular the significant out of balance force from the rotor cannot be counter-balanced, leading to a complicated and expensive support bearing arrangement. The outlet openings in the bulbous shaped grinding chamber are of necessity smaller than ideal. It is difficult to place a large area outlet with a surface that is substantially in the same plane as the direction of travel of the 40 ground material and grinding media. The design of the chamber is such that there is close to homogeneous mixing of infeed with ground material throughout the grinding chamber which leads to a wide particle size distribution in the outfeed and an increased tendency for the outlet 6 OF 31 screen to choke with oversize particles. In addition the fixed ratio precludes the option of fine tuning the grinding process by varying the speed ratio. It is an object of the present invention to address or ameliorate some of the above 5 disadvantages and limitations or to at least provide the public with a useful choice. Note The term "comprising" (and grammatical variations thereof) is used in this specification in the 10 inclusive sense of "having" or "including" and not in the exclusive sense of "consisting only of". Throughout this specification the terms "secondary rotor" and "grinding chamber" refer to the same thing and are used interchangeably. 15 Throughout this specification the term "grinding" as it relates to this invention also includes the process of mixing as the invention can equally be used for mixing as for grinding. Throughout this specification the term motor applies equally to a motor/gearbox combination. 20 DEFINITIONS Annular Type Cavity By annular type cavity we mean a cavity bounded on the outside by a substantially cylindrical surface and bounded on the inside by a substantially cylindrical surface but not necessarily 25 coaxial whereby the radial depth of the annular cavity varies with angular position. Drive Transmission System By drive transmission system we mean a train of an at least one rotational drive components arranged to transmit rotary motion from an input shaft to an output shaft 30 External Orbit Grinder By external orbit grinder we mean a centrifugal grinding machine wherein the rotational axis of orbit of the grinding chamber lies outside the locus of the radial extremity of the grinding chamber as it rotates. 35 Fixed ratio Grinder By fixed ratio grinder we mean a centrifugal grinding machine wherein the rotational speed of orbit of the grinding chamber is a fixed ratio to the rotational speed of the grinding chamber. 40 Grinding Energy Density 7 OF 31 By grinding energy density we mean the total energy of collisions per unit volume of chamber between the 3 components in the grinding chamber - the walls, the grinding furnish and the grinding media if any. 5 Grinding Furnish By grinding furnish we mean the material to be ground that is fed into the grinder. We also include the material being ground in the grinder. Internal Orbit Grinder 10 By internal orbit grinder we mean a centrifugal grinding machine wherein the rotational axis of orbit of the grinding chamber lies inside the locus of the radial extremity of the grinding chamber as it rotates. Lifter Bars 15 By lifter bars we mean internal radial protrusions from the wall of a grinding chamber designed to prevent the contents of the grinding chamber from sliding around the internal wall of the said grinding chamber and to promote collisions between the contents of the grinding chamber and collisions between the contents of the grinding chamber and the walls of the grinding chamber. The lifter bars are generally substantially ridge like running substantially in the longitudinal axis 20 of the said grinding chamber. Liquid Ring By liquid ring we mean the ring of liquid that forms on the inside surface of a rotating vessel when the centrifugal force exerted on the liquid as it rotates overcomes the gravitational force 25 tending to collapse the ring. Liquid Ring Depth By liquid ring depth we mean the radial depth of a liquid ring from the liquid surface to the inside surface of the rotating vessel. 30 Liquid Ring Control System By liquid ring control system we mean a control system that alters the liquid ring depth. Modulating Counterweight System 35 By modulating counterweight system we mean an at least one counterweight with an adjustable moment of inertia with respect to the main rotor axis of rotation that can be adjusted such that the centrifugal force on the said at least one counterweight can be modulated. Motion Control System 40 By motion control system we mean a system of rotational speed control wherein the rotational speeds of a plurality of axes of rotation can be controlled absolutely and/or with respect to each other.

8 OF 31 Net Counter-Balancing Mass By net counter-balancing mass we mean the aggregate sum of all individual component counter-balancing masses. 5 Radius of orbit By radius of orbit we mean the radius from the centre of rotation of a main rotor to the axis of rotation of a secondary rotor. 10 Rimming speed By rimming speed we mean the rotational speed at which a liquid ring becomes stable and is not collapsed by gravity. Variable Ratio Grinder 15 By variable ratio grinder we mean a centrifugal grinding machine wherein the rotational speed of orbit of the grinding chamber is not a fixed ratio to the rotational speed of the grinding chamber and wherein the rotational speed of orbit and the rotational speed of the grinding chamber can be varied independently of each other. 20 BRIEF DESCRIPTION OF THE INVENTION In a broad form of the invention there is provided an internal orbit (as defined herein), variable ratio (as defined herein), continuous centrifugal grinding mill system comprising: 25 a. a supporting framework, b. a main rotor supported within bearing arrangements by said supporting framework, c. a grinding chamber as a secondary, substantially tubular rotor supported and carried by the main rotor to form a rotor assembly and 30 wherein said secondary rotor has an axis of rotation substantially parallel to the axis of rotation of said main rotor, d. a main rotor drive system, e. a secondary rotor drive system, f. a grinding chamber infeed system, 35 g. a grinding chamber discharge system and wherein the axis of rotation of said main rotor lies within the locus formed by the outer extremity of the secondary rotor as it rotates about its axis and wherein said main rotor and said secondary rotor can rotate continuously and 40 independently about their respective axes of rotation and wherein said main rotor drive system powers the rotation of said main rotor and wherein said secondary rotor drive system powers the rotation of said secondary rotor 9 OF 31 independently of the rotation of said main rotor and wherein an at least one infeed opening in one end of said secondary rotor allows grinding furnish and or grinding media to be admitted to said secondary rotor and wherein an at least one discharge port in said secondary rotor allows ground material to be 5 extracted from said secondary rotor and wherein said centrifugal grinding mill is intended to be operated in a continuous manner. Preferably said discharge port and said infeed opening are one and the same. 10 Preferably said infeed system utilises a stationary feed-tube protruding into said infeed opening and wherein said infeed opening can rotate around said feed-tube without interfering with it. Preferably said secondary rotor is supported at each end by bearing arrangements fitted to the 15 main rotor. Preferably said main rotor is substantially tubular. Preferably said main rotor drive system comprises a motor or motor gearbox arrangement 20 driving the main rotor through a gear engaged with a ring gear mounted on said main rotor. Preferably said main rotor drive system comprises a motor or motor gearbox arrangement driving the main rotor through a transmission drive belt system engaged with a drive pulley mounted on said main rotor. 25 Preferably said main rotor drive system comprises an at least one roller or wheel engaging with an at least one circumferential track on the main rotor and wherein said at least one roller or wheel is powered. 30 Preferably said secondary rotor has a coaxial drive shaft integral with or rigidly connected to it. Preferably said coaxial drive shaft is connected directly to the motor shaft of a motor mounted on the body of the main rotor and rotating with it. 35 Preferably the frame of said motor has a slip ring assembly coaxial with the axis of rotation of the main rotor and rotating with it for the purposes of at least supplying power to said motor. Preferably said coaxial drive shaft is connected through a drive transmission system to an input drive shaft coaxial with said main rotor axis of rotation at the opposite end of the grinder to the 40 infeed opening.

10 OF 31 Preferably said drive transmission system is a planetary gear set with outer gear driving a planetary gear. Preferably said outer gear of said planetary gear set is directly supported, substantially on its 5 outer circumference by a bearing arrangement. Preferably said input drive shaft is directly connected to the shaft of a motor fixed rigidly to the body of the main rotor such that said motor is coaxial to said main rotor and rotates with it. 10 Preferably the frame of said motor has a slip ring assembly coaxial with the axis of rotation of the main rotor and rotating with it for the purposes of at least supplying power to said motor. Preferably said drive transmission system is a system of belts and pulleys fixed to the main rotor and rotating with it. 15 Preferably said drive transmission system is a universal drive shaft with a constant velocity joint at each end. Preferably said secondary rotor has sacrificial wear resistant linings on its internal walls. 20 Preferably said sacrificial wear resistant lining at the infeed end of said secondary rotor is in the form of a screw to assist with feeding the grinding furnish into said secondary rotor. Preferably a fluid is used to at least assist with conveying ground material to said at least one 25 discharge port of said secondary rotor. Preferably said fluid admitted to said secondary rotor is pressurised. Preferably said pressurised fluid is fed from a plenum substantially sealed against the infeed 30 end of said secondary rotor. Preferably said plenum has a perforated plate forming one component of the seal against the end of said secondary rotor. 35 Preferably said at least one discharge port in said secondary rotor has a grate like insert or cover in order to prevent grinding media or oversize ground material from exiting the grinding chamber. Preferably said grate like insert or cover forms a substantially planar surface with an internal 40 wall of said grinding chamber.

11 OF 31 Preferably said grate like insert or cover uses slots in order to prevent grinding media or oversize ground material from exiting the grinding chamber. Preferably said substantially planar surface is substantially at right angles to the axis of rotation 5 of said grinding chamber. Preferably said at least one discharge port of said secondary rotor discharges into a discharge cavity within the main rotor. 10 Preferably said discharge cavity has an at least one discharge opening in the shell of the main rotor for discharging ground material from said main rotor. Preferably said secondary rotor has an at least one lifter bar (as defined herein) attached to or being integral with the wall of said secondary rotor. 15 Preferably said at least one lifter bar is in the form of a helix along the longitudinal axis of said secondary rotor. Preferably a plurality of lifter bars form both clockwise and counter-clockwise helixes along the 20 longitudinal axis of said secondary rotor. Preferably said main rotor has an at least one counterweight fixed within it or on it to substantially offset the off-centre mass of the secondary rotor and its contents. 25 Preferably said main rotor has a modulating counterweight system as defined herein to offset any change in the off-centre mass of the secondary rotor. Preferably said modulating counterweight system is adjustable in real time. 30 Preferably said modulating counterweight system is adjusted and controlled by a controller utilising an output from an at least one vibration sensing transducer such as an accelerometer as a process variable input. Preferably said modulating counterweight system comprises an at least one fixed mass 35 modulated in radial position by suitable means such as lead screws. Preferably said modulating counterweight system uses a rotating liquid ring as defined herein of adjustable liquid ring depth as defined herein. 40 Preferably said rotating liquid ring depth is adjusted by means of an at least one control valve.

12 OF 31 Preferably said at least one control valve is mounted on the main rotor. Preferably said liquid used in the rotating liquid ring is formulated to give a specific gravity greater than that of water. 5 Preferably said liquid used in the rotating liquid ring is a concentrated solution of inorganic salts with a specific gravity greater than 1.3. Preferably said main rotor has an at least one slip-ring assembly fixed to and rotating coaxially 10 with said main rotor such that electrical power and/or data signals and/or pressurised fluid can communicate between the rotor of said slip-ring assembly attached to the rotating main rotor and the stator of said slip-ring assembly attached to the stationary said supporting framework. Preferably wireless control signals and or data signals are passed to and from a 15 transmitter/receiver attached to the main rotor and a stationary transmitter/receiver. Preferably said rotor assembly has an at least one rotary seal assembly wherein a seal surface rotating with said secondary rotor seals against an opposing seal surface connected to and inside said main rotor such that fluid and or particulate matter is restricted from passing axially 20 within the rotor assembly past said seal assembly. Preferably a plurality of said rotating seal arrangements form an at least one enclosed annular type cavity with outer wall being a main rotor external wall, inner wall being the secondary rotor extemal wall and end walls being said rotating seal arrangements and supporting diaphragms. 25 Preferably pressurised fluid is admitted to said at least one enclosed annular type cavity for the purposes of at least cooling the rotor assembly. Preferably said main rotor drive system and said secondary rotor drive system are variable 30 speed systems such that the rotational speed of said main rotor and the rotational speed of said secondary rotor can be varied independently of one another. Preferably said variable speed systems are controlled by a motion control system as defined herein such that the absolute and relative rotational speeds and/or relative rotational positions 35 of said main rotor and said secondary rotor are maintained accurately. Preferably said motion control system uses a motion control unit. Preferably said motion control unit is in digital communication with an HMI such that rotor drive 40 parameters are available in real time to grinder operators and adjustment to rotor drive parameters can be made in real time.

13 OF 31 Preferably accurate rotational speed and position data for the main rotor and the secondary rotor are provided to said motion control system by rotary encoders connected to suitable points on the drive systems of each rotor. 5 Preferably the absolute rotational speed of said main rotor and the relative (to the main rotor) rotational speed of said secondary rotor are modulated in order to maintain in isolation or in combination an aim grinding power input, aim grinding efficiency and an aim ground material particle size distribution. 10 Preferably in isolation or in combination accurate real time continual or continuous measurements of motor torque, motor power and motor speeds are used to impute grinder performance. Preferably the internal surface of the secondary rotor is profiled so as to alter the grinding 15 energy density in different regions of the chamber. Preferably the internal diameter of said secondary rotor is reduced at the infeed end region and/or the drive end region of said secondary rotor. 20 Preferably the internal diameter of the secondary rotor is profiled from smaller to larger in an at least one region along the longitudinal axis of said secondary rotor. Preferably a remote sensing bulk density measuring transducer such as a radar or microwave reflection transducer is used to measure the bulk density of the contents of the grinding 25 chamber. Preferably an over arching supervisory control system is used to control in combination at least the grinder infeed rate and rotor rotational speeds as well as any or all of the grinder parameters: 30 a. grinder temperature, b. ground material outfeed temperature, c. overall main rotor rotational balance, d. grinder power. 35 Preferably said grinding mill system can be oriented at any angle from horizontal to vertical. In another broad form of the invention there is provided a method for the size reduction or mixing of solid material in a continuous grinder; said method including the steps of: 40 a. feeding a grinding furnish through a feed-tube into the secondary rotor of an internal orbit, variable ratio, continuous centrifugal grinding mill, 14 OF 31 b. rotating the secondary rotor and the main rotor of said grinding mill at rotational speeds above the rimming speeds for said rotors such that a grinding action is set up within said secondary rotor, c. maintaining optimum absolute and relative rotational speeds and/or 5 positions of said rotors by controlling said rotational speeds with variable speed systems, d. substantially keeping the main rotor in balance, e. discharging the ground material through an at least one discharge port in said secondary rotor, 10 f. controlling in real time any or all of the following parameters so as to provide optimum grinding results: feed rate, discharge rate, rotational speeds, rotor balance and temperatures. 15 BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawings wherein: 20 Figure 1a is schematic representation of the rotation of a main rotor and a secondary rotor of an external orbit grinding machine. Figure 1b is schematic representation of the rotation of a main rotor and a secondary rotor of an internal orbit grinding machine. 25 Figure 2 is a schematic perspective of the main rotor and the secondary rotor of an internal orbit grinding machine. Figures 2A, B, C are schematic representations of end elevations of an internal orbit grinding 30 machine detailing the geometry with respect to the grinder infeed. Figure 3 is a partially sectioned side elevation of a preferred form of internal orbit grinding machine. 35 Figure 3A is an end elevation of an internal orbit grinding machine showing a belt drive arrangement for the main rotor. Figure 3B is an end elevation of an internal orbit grinding machine showing a geared drive arrangement for the main rotor. 40 Figure 3C is an end elevation of an internal orbit grinding machine showing the main rotor supported within two arrays of rollers with one array being driven.

15 OF 31 Figure 3D is a side elevation of an internal orbit grinding machine showing the main rotor supported within two arrays of rollers with one array being driven. 5 Figure 4 is a fully sectioned view of the internal orbit grinding machine shown in figure 3. Figure 4A is a larger scale detailed sectioned view of a preferred rotary seal arrangement shown in figure 4. 10 Figure 4B is a larger scale sectioned view of a preferred form of main rotor and secondary rotor support bearing arrangement and secondary rotor drive arrangement shown in figure 4. Figure 4C is section CC from figure 4B showing a preferred discharge port arrangement. 15 Figure 4D is the same sectional view as figure 4C showing a preferred arrangement of lifter bars. Figures 4E, 4F and 4G are schematic cross sections illustrating 3 preferred forms of secondary rotor infeed and discharge configuration. 20 Figures 5A, B, C & D are sectioned views or elevations of 4 preferred forms of secondary rotor drive arrangements. Figures 6A, B and C are sectional schematic views of a preferred form of modulating 25 counterweight arrangement utilising a variable depth liquid ring. Figure 7 is a partially sectioned schematic view of a preferred form of liquid ring control system. Figures 8A, B, C & D are sectioned views of a preferred form of inlet arrangement for a 30 pressurised fluid carrier system for an internal orbit grinding machine. Figure 9 is a schematic view of a preferred form of motion control system for the main and secondary rotors of a centrifugal grinding machine. 35 Figures 10A, B & C are side elevations of an internal orbit grinding machine in the horizontal, angled and vertical orientations respectively. Figures 11 A, B, C & D are sectional views of 4 preferred profiles of grinding chamber internal diameter. 40 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 16 OF 31 With reference to figure 1A and by way of example there is shown a schematic representation of the rotations of a main rotor and a secondary rotor of an external orbit grinding machine wherein secondary rotor axis of rotation 2 is connected to a main rotor with axis of rotation 4 and follows an orbit 3 around the said main rotor axis of rotation 4. The radial extremity of the 5 said secondary rotor within the said main rotor follows a circular locus 1 as the said secondary rotor rotates. The main rotor axis of rotation 4 lies outside the said locus 1 thereby making the representation one of an external orbit machine as defined herein. With reference to figure 1B and by way of example there is shown a schematic representation 10 of the rotations of a main rotor and a secondary rotor of an internal orbit grinding machine wherein secondary rotor axis of rotation 2 is connected to a main rotor with axis of rotation 4 and follows an orbit 3 around the said main rotor axis of rotation 4. The radial extremity of the said secondary rotor within the said main rotor follows a circular locus 1 as the said secondary rotor rotates. The main rotor axis of rotation 4 lies inside the said locus 1 thereby making the 15 representation one of an internal orbit machine as defined herein. Rotations of said rotors can be in either direction there being no limitation on combinations of rotational directions. With reference now to figure 2 there is shown a perspective view of an internal orbit grinding machine 10 with main rotor 5 supporting and carrying secondary rotor 6. Said main rotor 5 20 rotates about axis 4 whereas secondary rotor 6 rotates about axis 2. Said rotational directions can be either way as shown by the directional arrows being double ended. The secondary rotor 6 is supported in the main rotor 5 by a suitable support arrangement such as bearings (not shown). 25 Preferably the length to diameter ratio of the secondary rotor is greater than 1. More preferably it is greater than 2 and even more preferably it is greater than 3. A coaxial infeed opening 9 in the end of secondary rotor 6 allows a feed-tube 7 to protrude into said secondary rotor 6 for the purposes of admitting grinding furnish (not shown) into the 30 grinding chamber 6. The diameter of the said infeed opening 9 is set with regards to the required feed rate to the grinding machine and the requirement to ensure containment of the grinding media and grinding furnish within said secondary rotor. Preferably said feed-tube 7 is circular in cross section and coaxial to the main rotor. More 35 preferably said feed-tube 7 is stationary without the need to rotate or nutate about an access. Referring now to figures 2A, B and C wherein schematic representations of end elevations of an internal orbit grinding machine are shown. Referring specifically to figure 2A the internal surface 6i of main rotor rotates about axis 4. The secondary rotor rotates about axis 2. The 40 distance between the orbit of the axis of rotation of the secondary rotor and the axis of rotation of the main rotor is h as shown. The secondary rotor has an infeed opening 9 in the end of the rotor with circumference 9c and diameter Do as shown. The diameter of the internal surface 5i 17 OF 31 of secondary rotor is Di as shown. In order for a feed-tube to remain stationary and protrude inside infeed opening 9 there can be no interference between surface 9c and the infeed tube as the main rotor rotates. The relationship governing the maximum diameter of the infeed tube for a given infeed opening diameter Do and distance between axes of rotation h is: 5 Dt(max) = Do - 2h Referring now to figure 2B and by way of non limiting example there is shown a feed-tube 7 of maximum diameter Dt for infeed opening diameter Do. 10 Referring now to figure 2C and by way of further non limiting example there is shown a feed tube 7 of maximum diameter Dt for infeed opening diameter Do wherein the infeed opening diameter is equal to the internal diameter of secondary rotor Di. This represents the extreme case wherein the secondary rotor is completely open ended. Whilst such a configuration may 15 be suboptimal for grinders in the horizontal orientation it is not necessarily so for grinders in a vertical or angled orientation such as illustrated in figures 1OB and 10C. In use and with reference to figures 2, 2A, 2B and 2C grinding furnish is fed into the secondary rotor 6 by suitable means such as feed-tube 7. The main rotor 5 is rotated at a speed above 20 the rimming speed for objects within the secondary rotor 6. The rotation of the secondary rotor 6 is in general in the opposite direction to that of the main rotor 5 but may be rotated for some applications in the same direction. The rotational speed of the secondary rotor is set such the contents within the secondary rotor are continuously cascading within the rotor 6 and colliding both together and with the internal walls of the rotor. Comminution of the material to be ground 25 is achieved through a combination of rolling or sliding action and high energy collisions. In general the higher the rotational speed is, the higher the centripetal acceleration is and consequently the higher the force between particles and the average energy of collision. Variation of the rotational speed of the secondary rotor 6 with respect to the main rotor speed offers a mechanism to vary the grinding action from mostly rolling and sliding to mostly chaotic 30 collisions. Grinding can be autogenous wherein only grinding furnish is present within the grinding chamber and collisions are between pieces of grinding furnish or between the walls of the grinding chamber and pieces of grinding furnish. Alternatively grinding media such as steel or ceramic balls can be trapped within the grinding chamber thereby subjecting the grinding furnish to very powerful inter-grinding media collisions. 35 Referring now to figure 3 and figure 4 wherein there is shown in partially sectioned side elevation and fully sectioned side elevation respectively, a preferred form of internal orbit grinding machine 11 mounted within support framework 14 in turn supported on robust foundation 15. 40 Main rotor 5 is rigidly connected at the infeed end to end plate 121 running within bearing arrangement 18. Main rotor 5 is rigidly connected at the opposite end (the drive end) to end 18 OF 31 . plate 43 running within bearing arrangement 19. Preferably each said bearing arrangement comprises a rolling type bearing or a plurality of rolling type bearings fitted side by side (not shown). 5 With reference now to figures 3C and 3D there is shown in 2 elevations another preferred bearing arrangement whereby main rotor 5 is supported by and free to rotate within a plurality of rollers or wheels 201 set out in an at least one suitable array. The rollers or wheels 201 run on an at least one circumferential track 200 fixed to main rotor 5. A suitable arrangement being a track at each end of the main rotor with an array of 3 wheels or rollers per track. The wheels 10 or rollers are in turn supported by appropriate support arrangements such as cantilevered supports 202 and trunnion support arrangements 203. Note that the supports for the uppermost wheels or rollers in figure 3D are not shown for the purposes of clarity. Referring now again to figure 3 and figure 4 main rotor end plates 121 and 43 carry the 15 secondary rotor on an axis of rotation parallel to but offset from the axis of the main rotor. Thus when the main rotor 5 rotates about its axis of rotation it carries the secondary rotor 6 in an orbit around the main rotor axis of rotation. The diameter of the orbit being equal to twice the said offset. 20 Main rotor 5 is driven by motor 13 (shown partially obscured) by means of a suitable drive arrangement. There are numerous drive arrangements that would suffice for the purpose and those skilled in the art would choose one suitable for the particular application. Referring now to Figure 3A by way of non limiting example only there is shown a preferred form 25 of drive arrangement in end elevation. Drive motor 13 drives rotor 5 through toothed pulley 13a and toothed belt 17a meshing with and driving toothed pulley 17 fitted to the circumference of rotor 5. Referring now to Figure 3B by way of further non limiting example only there is shown another 30 preferred form of drive arrangement in end elevation. Drive motor 13 drives rotor 5 through a gear set comprising driving gear 13b and driven ring gear 17 fitted to the circumference of rotor 5. In another preferred form of drive arrangement for the main rotor, the rotor is driven directly by 35 an at least one roller or wheel engaging with an at least one circumferential track on the rotor. Referring now to figures 3C and 3D by way of non limiting example only there is shown main rotor 5 (with feed tube 7) supported by 2 circumferential tracks 200 each rotating within 3 rollers 201. Drive motors 13c power the 3 rollers on the track at the non feed tube end of the rotor. 40 Referring again now to figure 3 secondary rotor 6 is rigidly attached to end plate 122 at the infeed end. End plate 122 is supported within the main rotor end plate 121 by a suitable -- - 19-OF 31 bearing arrangement 20. In figure 3 the said bearing arrangement 20 comprises 2 single rolling type bearings fitted side by side but those skilled in the art would select a bearing arrangement that suited the particular application. 5 Referring now to figure 4B where a larger scale sectioned view of the drive end of the grinder is shown. Main rotor end plate 43 is supported within bearing arrangement 19 and in turn supports secondary rotor shaft 30 at bearing arrangement 21. In figure 4B the said bearing arrangement 21 comprises a single rolling type bearing but those skilled in the art would select a bearing arrangement that suited the particular application. Secondary rotor shaft 30 is 10 integral with or attached by suitable means to drive end secondary rotor end plate 46. Drive end secondary rotor end plate 46 is in turn attached rigidly to the shell of the secondary rotor 6 by suitable means such as flange and fastenings 47. Accordingly secondary rotor 6 can rotate freely within the main rotor 5 and supported by main rotor end plates 121 and 43 and bearing arrangements 20 and 21 at the infeed and drive ends respectively. 15 Still with reference to figures 4 and 4B various retaining rings 44 are shown. Preferably said retaining rings serve to retain the various bearing arrangements in place and/or provide rotary seals to at least protect the said various bearing arrangements. 20 Still with reference to figures 4 and 4B, preferably secondary rotor 6 is driven rotationally through secondary rotor drive shaft 30, whilst it in turn orbits around the main rotor with radius of orbit h, by a suitable drive arrangement that allows the secondary rotor to be driven independently of the main rotor. Preferably the axis of rotation of the secondary rotor drive input shaft 42 coincides with the axis of rotation of the main rotor. Preferably the offset drive 25 connection between the secondary rotor drive shaft 30 and the secondary rotor drive input shaft 42 is through a suitable drive transmission system. There are a number of suitable drive transmission system for driving the secondary rotor whilst it orbits and those skilled in the art would select an arrangement that suited the particular application. Four preferred forms of drive transmission systems are shown in figures 5A - 5D. 30 With reference now to figure 5A there is shown in sectioned view a preferred drive arrangement 50 utilising a planetary gear train. Input shaft 42 is connected to and drives outer gear 29. Outer gear 29 meshes with planetary gear 32 that is rigidly connected to secondary rotor drive shaft 30. Now with reference to figure 4B that also shows a planetary gear assembly 35 with outer gear 29 and planetary gear 32. Preferably outer gear 29 is supported substantially on its outer circumference within suitable bearing arrangement 31 in order to maintain accurate alignment of rotating elements and reduce stresses in shaft 42 and outer gear 29. According to the arrangement described the said secondary rotor drive motor (not shown) is aligned with the said main rotor axis of rotation 4 and the said secondary rotor is driven rotationally about axis 40 of rotation 2 whilst orbiting around main rotor axis of rotation 4 with radius of orbit h.

20 OF 31 With reference now to figure 5B there is shown in sectioned view a further preferred drive arrangement 51 utilising drive belts and pulleys. Preferably said drive belts and pulleys are toothed. Input shaft 42 is connected to and drives first toothed pulley 54. First toothed pulley 54 drives first toothed belt 55 that in turn drives second toothed pulley 56 rotating on lay shaft 57. 5 Said lay shaft being supported by a suitable bearing arrangement (not shown) mounted on the main rotor and thereby rotating with it. Second toothed pulley 56 is sufficiently wide to accommodate first toothed belt 55 and second toothed belt 58 side by side. Second toothed belt 58 being driven by second toothed pulley 56 drives third toothed pulley 59 connected rigidly to secondary rotor drive shaft 30 thereby rotating the secondary rotor. According to the 10 arrangement described, the said secondary rotor drive motor (not shown) is aligned with the said main rotor axis of rotation 4 and said secondary rotor is driven rotationally about axis of rotation 2 whilst orbiting around main rotor axis of rotation 4 with radius of orbit h. With reference now to figure 5C there is shown in elevation a further preferred drive 15 arrangement 52 utilising a universal drive shaft 65 and two constant velocity joints 60a and 60b. Input shaft 42 is connected to and drives first constant velocity joint 60a. First constant velocity joint 60a is rigidly connected to drive shaft 65 that is in turn rigidly connected to second constant velocity joint 60b. Second constant velocity joint 60b is rigidly connected to secondary rotor drive shaft 30 thereby rotating the secondary rotor. According to the arrangement 20 described said secondary rotor drive motor (not shown) is aligned with the said main rotor axis of rotation 4 and said secondary rotor is driven rotationally about axis of rotation 2 whilst orbiting around main rotor axis of rotation 4 with radius of orbit h. With reference now to figure 5D there is shown in partially sectioned view a further preferred 25 drive arrangement 53 utilising a planetary gear train or similar drive arrangement integral with drive motor. Secondary rotor drive motor 12 is mounted coaxially with main rotor such that the axis of rotation of the said motor 12 coincides with the main rotor axis of rotation 4. The frame of said drive motor 12 is connected to the main rotor most conveniently by means of flange mounting 64. Thus the frame of said drive motor 12 rotates with the main rotor 5. Connected to 30 and rotating with the frame of said motor 12 is tail shaft 62. Preferably said tail shaft 62 is supported at the end by bearing arrangement 63. Preferably slip ring assembly 61 is mounted on said tail shaft 62. Preferably electrical power flows to the motor via the said slip ring assembly 61. Said motor 12 can equally be an hydraulic motor wherein said slip ring assembly 61 would pass at least hydraulic fluid between its stator and rotor. Preferably input 35 shaft 42 is connected to and drives outer gear 29. Preferably outer gear 29 meshes with planetary gear 32 rigidly connected to said secondary rotor drive shaft 30. Preferably said outer gear 29 is supported substantially on its outer circumference in a bearing arrangement (not shown) in the manner illustrated in figure 4B. According to the arrangement described said secondary rotor drive motor (not shown) is aligned with the main rotor axis of rotation 4 and 40 said secondary rotor is driven rotationally about axis of rotation 2 whilst orbiting around the said main rotor axis of rotation 4 with radius of orbit h.

21 OF 31 In another preferred form of the drive arrangement described in the immediately forgoing paragraph but not illustrated in the drawings the secondary rotor drive motor output shaft is connected directly to the secondary rotor drive shaft without the use of an intermediate drive arrangement such as a planetary gear set. Thus the motor frame orbits with the secondary 5 rotor. The tail shaft however remains coaxial with the main rotor axis of rotation. Whilst this arrangement simplifies the construction of the grinder it introduces an offset mass on the main rotor. This arrangement is particularly suited to an hydraulic motor wherein the slip ring assembly would pass at least hydraulic fluid between its stator and rotor. 10 Referring again now to figure 4, preferably the secondary rotor 6 has a sacrificial wear resistant lining 28 on the inside cylindrical wall. Preferably the said wear resistant lining 28 is replaceable. Preferably the inside surface of said lining necks in at the infeed end to the reduced diameter of the infeed opening 9. Preferably a baffle 26 is supported within the secondary rotor 6 by radial support legs 27 to assist with preventing grinding media (not 15 shown) and/or grinding furnish 120 from exiting the grinder through infeed opening 9. Preferably the said grinding furnish 120 is fed into the grinding chamber through feed-tube 7 by suitable means such as a screw conveyor (not shown). Preferably the conical shaped internal wall of the grinding chamber 28a assists with the infeed of the said grinding furnish 120 to the grinding chamber proper as the centrifugal force forces the said grinding furnish into the region 20 of maximum diameter within the said grinding chamber. In another preferred form of this embodiment the conical shaped region at the entrance of the grinding chamber 28a is in the form of a screw (not shown) such that the said grinding furnish 120 is effectively screwed into the said grinding chamber. 25 Preferably as the grinder operates, the grinding furnish migrates through the grinding chamber being progressively reduced in particle size as it goes. Ground particles exit the grinding chamber through suitable exit ports in the walls of the grinding chamber. Referring now to figure 4B and figure 4C that is section CC from figure 4B there is shown a 30 preferred embodiment of the invention for the discharge of ground material 120g from the grinding chamber 6. Preferably ground material 120g is carried towards the exit ports 24 by a carrying fluid. For dry grinding applications the fluid would be gaseous such as air and for wet grinding applications the fluid would be a liquid such as water. Preferably the fluid is admitted to the grinding chamber under pressure or is drawn from the said grinding chamber by means 35 of a negative pressure applied to the downstream side of the said exit ports 24 or a combination of the two is used. With reference now to figures 8A, B, C & D there is shown a preferred arrangement for admitting pressurised fluid to the said grinding chamber for at least the purposes of assisting with the discharge of ground material and/or providing cooling. Preferably a stationary annular shaped plenum 94 surrounds feed-tube 7. Preferably a flat end 40 wall 91 of the said plenum has perforations 95 in a substantially annular array and is in sliding contact with flat seal surface 92 fixed to the infeed end of the secondary rotor 93. Said sliding contact providing a seal between the plenum 94 and the end of the secondary rotor 93.

zz U, 1I Preferably said substantially annular array of perforations extend out to a maximum radius substantially equal to the distance from the axis of rotation of the main rotor to the outer extremity of the secondary rotor infeed opening 9. Thus as the main rotor rotates about its axis of rotation the infeed opening 9 of the secondary rotor sweeps around the said array of 5 perforations. Preferably pressurised fluid 90 enters the plenum 94 and discharges through the perforations 95 into the infeed opening 9 of the secondary rotor. With specific reference now to figures 8A & B, the secondary rotor position is shown with infeed opening 9 uppermost and substantially above the feed-tube 7. Infeed opening circumference 9c is shown on figure 8B. Now with specific reference to figures 8C & D the secondary rotor position is shown 1800 . 10 rotated from that of figures 8A & B and with infeed opening 9 substantially below the feed-tube 7. Infeed opening circumference 9c is again shown on figure 8D. With reference again now to figures 4B and 4C, in a preferred arrangement the faces of the exit ports are located substantially on a plane aligned with the plane of centrifugal force within the 15 grinding chamber. le perpendicular to the axis of orbit of the grinding chamber. Preferably the exit ports are located in the drive end wall of the grinding chamber. Preferably the said drive end wall comprises the drive end secondary rotor end plate 46 covered by sacrificial wear resistant lining 35. Preferably exit port grates 24 are fixed within each port opening within the said end wall. Preferably said exit port grates have slots 24a or the like such that oversize 20 ground particles (not shown) and grinding media (not shown) cannot go through the grates. Such an arrangement minimizes the incidence of choking of the said exit port grates 24 as the cascading grinding furnish and grinding media if any tends to "wipe" any build up of oversize ground material on the said grates clear. 25 Preferably said exit port grates are easily removable without having to dismantle the grinder. Still with reference to figure 4B, preferably the ground material 120g passes through the said exit port grates 24 and into discharge chamber 8d within the main rotor 5. Preferably a combination of centrifugal action and friction with the carrying fluid moves the ground material 30 120g out through an at least one discharge opening 8 in the shell of main rotor 6. With reference now to figure 4, preferably the ground material 120g exits the shell of main rotor 6 and into a suitable collection chamber 23. Preferably ground material 120g is removed from said collection chamber through a suitable opening 25. 35 Now with reference to figures 4E, 4F and 4G and by way of non limiting examples only there is illustrated 3 alternative preferred configurations of entrance and exit porting. Secondary rotor 6 rotates within main rotor 5. Feed-tube 7 projects into the grinding chamber through infeed opening 9. Now with specific reference to figure 4E grinding furnish 220 enters the grinding chamber through feed-tube 7 at the infeed opening end and ground material 221 is discharged 40 through an at least one discharge port 24 fitted within the circumferential shell of grinding chamber 6. Now with specific reference to figure 4F grinding furnish 220 enters the grinding chamber at the infeed opening end through feed-tube 7 and ground material 221 is discharged z3 Ut 31 through discharge port 24 fitted to the end of discharge tube 222 fitted coaxially within feed tube 7. The advantage of this configuration being the elimination of discharge ports fitted into the shell or end plate of the grinding rotor and the consequent simplification of manufacture and maintenance. Now with specific reference to figure 4G grinding furnish 220 enters the 5 grinding chamber through feed-tube 7 terminating at the non infeed opening end or some intermediate axial position within the grinding chamber. Ground material 221 is discharged through the infeed opening 9 which in this instance also acts as the discharge port. These examples illustrated are not comprehensive and the configuration of infeed and discharge will depend on the application. 10 Now with reference to figure 4D there is shown a preferred arrangement of lifter bars wherein an at least one longitudinal ridge-like radial lifter bar 6a protrudes into the grinding chamber cavity. In figure 4D, 4 such lifter bars are shown but the number and depth dl of the lifter bars is a function of the type of grinding furnish and the rotational speed of the grinder. The lifter bars 15 prevent the contents of the grinding chamber from "swirling" as a mass around the grinding chamber and promote collisions between the grinding furnish, grinding media and walls of the grinding chamber. In a preferred embodiment of this arrangement of lifter bars a wear resistant coating (not shown) covers the inside surface of the grinding chamber and the lifter bars. In a further preferred embodiment the lifter bars are formed from the wear resistant coating itself 20 (not shown). In yet a further preferred embodiment the lifter bars are in the form of a helix to promote movement in the axial direction within the grinding chamber. In yet a further preferred embodiment a plurality of lifter bars are in the form of clockwise and counter-clockwise helixes. Such an arrangement promoting more collision activity within the grinding chamber. 25 In another preferred embodiment of the invention there is provided an at least one rotary seal assembly between the inside of the main rotor and the outside of the secondary rotor. Said seal assembly being a preferred means of at least retaining lubricating fluid and/or cooling fluid and/or retaining particulate material such as ground material within a discharge region and/or preventing particulate material or other impurities from entering clean environments such as 30 bearing cavities. The said seal assembly may take one of many forms depending on the application. Rotary seals both static and energized and of many different configurations and form and manufactured from a variety of materials are commercially available and those skilled in the art will be able to specify a particular seal to suit the application and purpose. Preferably there is a plurality of said seal assemblies displaced axially along the length of the secondary 35 rotor so as to create an at least one annular type cavity between the said seal assemblies. Said annular type cavities being suitable for admission of fluids for the purposes of at least lubricating, cooling and purging. With reference now again to figure 4 and by way of non limiting example only there is shown a 40 preferred sealing assembly 16 at the infeed end of the grinder and similar preferred sealing assembly 34 at the drive end of the grinder. Preferably said sealing assemblies sealing each end of an annular type cavity between the inside surface of the main rotor 5 and the outside 4 Ur 1 surface of the secondary rotor 6. Now with reference to figure 4A there is shown the preferred sealing assembly 16 in larger scale. Preferably main rotor 5 has an annular shaped body 118 fixed to it by suitable means such as screw fasteners 119. Preferably body 118 carries a first seal component 117 that mates with a second seal component 116 carried by second annular 5 shaped body 115 fixed by suitable means to secondary rotor 6. Preferably said seal components 117 and 116 are held in sliding contact together thus sealing the cavity on one side of the said seal assembly from the cavity on the other side of the said seal assembly. Preferably either or both of the said seal components 116 and 117 can be energised (not shown). By energised we mean forced against one another by suitable means such as springs 10 (not shown) or a pneumatic device (not shown) or the like. In another preferred embodiment of the invention there is provided a counterweight fixed to the main rotor of the grinding machine such that the mass of the secondary rotor assembly and its contents orbiting about the main rotor axis of rotation is substantially offset and the main rotor 15 assembly is substantially in balance. Referring now to figures 3 and 4 counterweight 22 is shown fixed to the shell of main rotor 5 in an angular position about the main rotor axis of rotation substantially 180* from the centre of mass of the said secondary rotor. Preferably said counterweight is manufactured from a substance with a density as high as practicable such as lead. 20 In yet a further preferred embodiment of the invention there is provided a modulating counterweight system as defined herein wherein an at least one counterweight has an adjustable moment of inertia to be used either by itself or preferably in conjunction with a fixed counterweight system. A modulating counterweight system has the advantage of being capable 25 of being modulated such that changes in the mass of the secondary rotor caused by changes in the quantity of ginding media and/or grinding furnish within the grinding chamber or erosion of the sacrificial wear linings can be compensated for without time consuming balancing trials and adjustment of balancing weights. Preferably said modulating counterweight system is adjustable in real time. Preferably said real time adjustment utilises the signal from an at least 30 one vibration sensor such as an accelerometer mounted at least on the supporting framework for the main rotor. Said modulating counterweight system must modulate the centrifugal force generated by the counterweight used. Said centrifugal force is given by the following equation: CF = Mw 2 R 35 Where CF = The centrifugal force M = The mass of the counterweight w = The angular velocity R = The radius of gyration of the counterweight 40 Since w is the same for both the secondary rotor and the counterweight the centrifugal force can only be modulated by modulating the mass of the counterweight and/or modulating its radius of gyration. 5 In one preferred form of modulating counterweight system an at least one fixed mass is modulated in position radially by suitable means such as lead screws. In another preferred form of modulating counterweight system the mass of the counterweight is modulated, such as a modulating amount of liquid in a rotating counterweight vessel. 10 Preferably a modulating counterweight will act at both ends of the main rotor or be distributed along the length of the main rotor or be centrally placed such that the main rotor is in balance at both ends. 15 Referring now to figures 6A, B and C there is shown in schematic form a sectional view of a preferred form of modulating counterweight system utilising a rotating liquid ring. Main rotor shell 5 contains secondary rotor 6 with its centre of mass offset from the axis of rotation of the main rotor. Preferably a fixed counterweight 22 acts to substantially offset the fixed mass of secondary rotor 6. Preferably liquid 70 is admitted into the generally annular cavity between the 20 inside of main rotor 5 and the outside of secondary rotor 6. Preferably the rotational speed of main rotor 5 is above the rimming speed as defined herein for the rotor. Liquid 70 is retained as a liquid ring against the inside surface of the main rotor 5. Referring now to figure 6A the liquid ring depth d is less than the radial distance e from the inside surface of main rotor 5 to the closest point of the circumference of secondary rotor 6. In this case no counter balancing effect 25 is generated. Referring now to figure 6B The liquid ring depth d is greater than e and accordingly a counter balancing force in the opposite direction to the net centrifugal force from the off centre secondary rotor is generated from 2 effects. A first buoyancy effect B is generated due to the displacement of the fluid 70 by the secondary rotor 6 in the force field generated by the rotating motion. Said buoyancy effect being equal to the weight of the fluid 30 displaced by the immersed portion of the said secondary rotor wherein the weight per unit mass of the fluid in this arrangement is the centrifugal force exerted per unit mass. Said buoyancy effect acting toward the axis of rotation of the main rotor and therefore offsetting directly the net centrifugal force from the orbiting secondary rotor. Said buoyancy effect increasing with increasing, liquid ring depth d to a maximum at the point where the liquid ring 35 surface intersection with the outside circumference of the secondary rotor 6 coincides with the intersection 74a of a radial plane 74 from the centre of rotation and at 900 to the radial plane between the axis of rotation of the main rotor and the centre of mass of the secondary rotor. Thereafter with increasing liquid ring depth the net buoyancy effect B is reduced as the incremental increase in liquid ring depth d produces an incremental buoyancy acting in the 40 opposite direction to B. Still with reference to figure 6B a second counterweight effect f is generated by the offset mass of the rotating liquid ring caused by the smaller volume of liquid on the secondary rotor side of plane 74. Now with reference to figure 6C there is shown the Z. UP 31 particular case of when the entire generally annular cavity is full of liquid 70. This case is the case of maximum counter balancing effect for whilst the buoyancy effect B is lower than its maximum, f is at its maximum and wherein the increase in f more than offsets the reduction in B. 5 Preferably the liquid used in the modulating counterweight system has as high a specific gravity as is practicable. One preferred type of liquid is a concentrated aqueous solution of inorganic salts wherein specific gravities of about 1.3 are achievable with many commonly available salts and specific gravities of up to 2.0 are achievable with some commonly available 10 salts such as zinc chloride. With reference now to figure 7 there is shown as a cross sectional schematic view a preferred form of liquid ring depth control system. Preferably liquid ring 70 is maintained within the generally annular cavity between main rotor 5 and secondary rotor 6. The said liquid ring is 15 prevented from axial movement out of the generally annular cavity by rotary seals (not shown) according to a preferred embodiment of the invention described above. Preferably a pressurised liquid supply 78 is routed onto the main rotor 5 through a suitable rotary union or liquid slip ring assembly 36. Preferably pressurised liquid is admitted into the generally annular cavity by control valve 77 acting in accordance with a control signal routed through control line 20 75a. Preferably control line 75a is connected to slip ring assembly 36. Preferably liquid 70 can be discharged by means of centrifugal action from the said generally annular cavity through control valve 76 acting in accordance with a control signal routed through control line 75b. Preferably control line 75b is connected to slip ring assembly 36. For simplicity slip ring assembly 36 is shown as a duel control signal and liquid slip ring assembly but separate slip 25 ring assemblies for each purpose may be mounted in separate locations on the main rotor without diminishing the effectiveness of this embodiment of the invention. In another preferred means of control signal transmission (not shown) control lines75a,b connect to a suitable control signal generator mounted in or on the main rotor 5 and wherein 30 the said control signal generator is in wireless communication with a stationary control signal transmitter mounted remotely from the grinder. Still with reference to figure 7, preferably liquid from the liquid ring 70 discharges through control valve 76 and into discharge tube 81 and thence into a circular collection trough 82. 35 Preferably discharged liquid 70e runs to the bottom of said trough 82 and is discharged through pipe 83. Preferably discharged liquid 70e can be recycled back through the control system after suitable treatment such as cooling, filtering etc. In operation the liquid ring control system modulates the depth of the liquid ring by modulating 40 outlet control valve 76 such that the counterweight effect is modulated so as to minimize vibration of the grinder as measured by suitable vibration sensors such as accelerometers (not 27 OF 31 shown). In addition the flow rate of liquid through the grinder is modulated by modulating inlet control valve 77 so as to provide at least a controlled cooling effect. In another preferred embodiment of the invention a suitable motion control system controls in 5 real time the speeds of rotation of the main rotor and the secondary rotor such that they bear a defined ratio and relative direction to one another and/or a defined positional relationship to one another. There are numerous commercially available motion control systems available capable of maintaining speeds and relative positions to high degrees of precision. In one preferred form of this embodiment three phase electric motors driving the main rotor and the 10 secondary rotor are operated in closed loop vector mode using variable frequency drive modules under the supervision of a motion control unit as defined herein. Said motion control unit being in digital communication with a suitable human-machine interface or HMI. Note: Motion control units can alternatively be referred to as motion coordinators or servo 15 controllers. In this application their function is to control the angular speed and/or the position of the main and secondary rotors by monitoring their real time positions as defined by a suitable transducer such as a rotary encoder, compare them set points defined within the controlling software and then alter the angular speeds and/or positions so as to minimize the differences between actual and set point. This "servo control loop" is typically closed at greater 20 than 4 times per millisecond. With reference now to figure 9 and by way of non limiting example only a suitable motion control system is shown in schematic form. Preferably main rotor drive motor 12 has rotary encoder 48 fixed to the shaft of the motor and generating digital pulse stream 107 that defines 25 the angular position and speed of the motor and thereby the main rotor in real time. Preferably digital pulse stream 107 is used by the variable frequency drive module 103 and by the motion control unit 105 and accordingly the said digital pulse stream 107 is split into 2 parallel and identical digital pulse streams by signal splitter 102. Preferably variable frequency drive module 103 accepts electric power from suitable power supply 112 and outputs controlled frequency 3 30 phase electric power 114 to motor 12. Preferably variable frequency drive module 103 accepts control signal 110 from motion control unit 105. Still with reference to figure 9, preferably secondary rotor drive motor 13 has rotary encoder 100 fixed to the shaft of the motor and generating digital pulse stream 108 that defines the 35 angular position and speed of the motor and thereby the secondary rotor in real time. Preferably digital pulse stream 108 is used by the variable frequency drive module 104 and by the motion control unit 105 and accordingly the digital pulse stream 108 is split into 2 parallel and identical digital pulse streams by signal splitter 101. Preferably variable frequency drive module 104 accepts electric power from suitable power supply 112 and outputs controlled 40 frequency 3 phase electric power 113 to motor 13. Preferably variable frequency drive module 104 accepts control signal 111 from motion control unit 105.

28 OF 31 Still with reference to figure 9, preferably said motion control unit 105 accepts from and passes to HMI 106, data using data link 109 allowing grinder operators to make operational settings and adjustments to the rotational speeds of both motors 12 and 13. In operation the rotational speeds and/or relative rotational positions can be varied "on the run" in order to react to 5 changing operational circumstances. Operation of the motors in closed loop vector mode allows real time measurement of actual motor torque that is a very sensitive indicator of grinding performance and an early indicator of process upsets thereby allowing rapid, automatic response from the motion control system 10 and/or the process control system (not shown) and/or the grinder operators. By way of further specific non limiting example and still with reference to figure 9 preferably power supply 112 is a 3 phase alternating current supply, motor supplies 113 and 114 are 3 phase alternating current variable frequency supplies, control signals 110 and 111 may be 15 standard analogue signals or digital signals and data link 109 is a standard field bus or Ethernet link or similar. Preferably the absolute rotational speed of the said main rotor and the relative (to the main rotor) rotational speed of the said secondary rotor are modulated in order to maintain in 20 isolation or in combination an aim grinding power input, aim grinding efficiency and an aim ground material particle size distribution. In another preferred form of the invention the grinder can be oriented at any angle from horizontal to vertical depending on the application. The operation of the said grinder is not 25 adversely affected by orientation. In general where throughputs are larger an angled or vertical orientation is preferred. With reference now to figure 10A there is shown a preferred arrangement wherein the grinder is in the horizontal orientation with feed-tube 7 protruding into the secondary rotor infeed 30 opening. Motor 12 is driving the secondary rotor and motor 13 (partially obscured) is driving the main rotor. Ground material is collected in collection chamber 23 and discharged through outlet 25. With reference now to figure 1 OB there is shown a preferred arrangement wherein the grinder 35 is in an angled orientation with feed-tube 7 protruding into an infeed opening extension 122 of the secondary rotor infeed opening. Motor 12 is driving the secondary rotor and motor 13 is driving the main rotor. Ground material is collected in collection chamber 23 and discharged through outlet 25. 40 With reference now to figure 10C there is shown a preferred arrangement wherein the grinder is in a vertical orientation with feed-tube 7 discharging into an infeed opening extension 123 of the secondary rotor infeed opening. Motor 12 is driving the secondary rotor by means of 29 OF 31 toothed belt 124 and motor 13 is driving the main rotor by means of toothed belt 125. Ground material is collected in collection chamber 23 and discharged through outlet 25. In another preferred embodiment of the invention the internal surface of the grinding chamber 5 is profiled so as to alter the grinding energy density as defined herein in regions of the chamber. For a given angular velocity the average centripetal acceleration of the contents of the grinding chamber is a function of the internal grinding chamber diameter. Accordingly higher energy collisions can be expected in regions of higher diameter. In addition the centrifugal force will tend to migrate the contents of the grinding chamber to the regions of 10 higher diameter. An equilibrium is established whereby the tendency of contents to migrate into the regions of higher diameter and energy density will be offset by the tendency of contents to be ejected from the regions of higher diameter and energy density by the increased number and intensity of collisions. By judicious profiling of the grinding chamber diameter the grinding energy density itself can be profiled through the longitudinal axis of the said grinding chamber. 15 Referring now to figures 11 A - 11D wherein this embodiment is further illustrated by way of non limiting examples. With specific reference to figure 1 1A wherein by way of non limiting example only a preferred 20 profile of internal grinding chamber diameter is shown. Internal diameter of grinding chamber 6 is at a minimum at point 130 and increases to a maximum diameter at point 131 uniformly over the length of the said grinding chamber. Grinding furnish 120 enters the said grinding chamber from feed-tube 7 and is subjected to uniformly increasing grinding energy density from collisions with walls, grinding furnish and grinding media (not shown) as the diameter increases 25 and also as the contents density increases as the grinding furnish migrates towards the larger diameter. The average particle size of the grinding furnish reduces as it migrates through the said grinding chamber. At point 131 of maximum diameter the grinding energy density is at a maximum and as a consequence end wall liner 35 and exit port grates 24 are subjected to increased wear and erosion. 30 With specific reference to figure 11 B wherein by way of non limiting example only another preferred profile of internal grinding chamber diameter is shown. Internal diameter of grinding chamber 6 is at a minimum at point 130 and increases sharply to point 132. The sharp increase in diameter over the relatively short length assists in keeping the entrance region of the said 35 grinding chamber substantially clear of grinding furnish 120 and grinding media (not shown). The grinding chamber internal diameter increases from point 132 to maximum diameter at point 131 uniformly over the remaining length of the said grinding chamber. Grinding furnish 120 enters the said grinding chamber from feed-tube 7 moves more rapidly from the entrance region and is then subjected to uniformly increasing grinding energy density from collisions with 40 walls, grinding furnish and grinding media (not shown) as the diameter increases and also as the contents density increases as the grinding furnish migrates towards the larger diameter. The average particle size of the grinding furnish reduces as it migrates through the said 30 OF 31 grinding chamber. At point 130 of maximum diameter the grinding energy density is at a maximum and as a consequence end wall liner 35 and exit port grates 24 are subjected to wear and erosion. 5 With specific reference to figure 1 1C wherein by way of non limiting example only another preferred profile of internal grinding chamber diameter is shown. Internal diameter of grinding chamber 6 is at a minimum at point 130 and increases sharply to the point of maximum diameter 133. The sharp increase in diameter over the relatively short length assists in keeping the entrance region of the said grinding chamber substantially clear of grinding furnish 120 and 10 grinding media (not shown). The grinding chamber internal diameter remains uniform between points 133 and 134. Grinding furnish 120 enters the said grinding chamber from feed-tube 7, moves more rapidly from the entrance region and is then subjected to uniform and high intensity grinding energy density from collisions with walls, grinding furnish and grinding media (not shown) between the points 133 and 134 that is the region of maximum diameter. The 15 average particle size of the grinding furnish reduces as it migrates through the said grinding chamber. At point 134 the diameter reduces sharply over a short length to point 131 at the end wall of the said grinding chamber. As a consequence there is a reduction in grinding energy density between points 134 and 131 and end wall liner 35 and exit port grates 24 are subjected to a reduced level of wear and erosion. 20 With specific reference to figure 11D wherein by way of non limiting example only another preferred profile of internal grinding chamber diameter is shown. Internal diameter of grinding chamber 6 is at a minimum at point 130 and increases sharply to point 135. The sharp increase in diameter over the relatively short length assists in keeping the entrance region of the said 25 grinding chamber substantially clear of grinding furnish 120 and grinding media (not shown). The grinding chamber internal diameter increases from point 135 to maximum diameter at point 136 uniformly down the longitudinal axis of the said grinding chamber. Grinding furnish 120 enters the said grinding chamber from feed-tube 7 moves more rapidly from the entrance area and is then subjected to uniformly increasing grinding energy density from collisions with walls, 30 grinding furnish and grinding media (not shown) as the diameter increases and also as the contents density increases as the grinding furnish migrates towards the larger diameter. The average particle size of the grinding furnish reduces as it migrates through the said grinding chamber. At point 136 the diameter reduces sharply over a short length to point 131 at the end wall of the said grinding chamber. As a consequence there is a reduction in grinding energy 35 density between points 134 and 131 and end wall liner 35 and exit port grates 24 are subjected to a reduced level of wear and erosion. With reference again now to figures 1OA-C, in another preferred embodiment of the invention there is provided a remote sensing bulk density measuring transducer 126 such as a radar or 40 microwave reflection transducer to measure the bulk density of the contents of the grinding chamber. Preferably the said transducer is directed through the infeed opening of the said 31 OF 31 grinding chamber. Said transducer giving real time measurements of the said bulk density to assist with real time control of the grinder and the infeed rate to it. In another preferred embodiment of the invention an over arching supervisory control system is 5 used to control in combination at least the grinder infeed rate and rotor rotational speeds as well as any or all of the following grinder parameters: a. Grinder temperature b. Ground material discharge temperature 10 c. Overall main rotor rotational balance d. Grinder power In Use 15 In use the system herein described allows effective grinding either autogenously or with grinding media in a grinder with high specific energy per unit volume of grinding chamber. By using centrifugal force the grinding intensity can be significantly increased above that of tumbling mills. Independent speed control of the main rotor and the secondary rotor provides 20 an effective mechanism for changing the size reduction dynamics from rolling and sliding to chaotic collisions; for optimizing the efficacy of the grinding process and additionally providing a means of circumventing grinding process disruptions such as choking. The infeed and outfeed of the grinder is simplified compared to conventional centrifugal grinding mills and accordingly the invention is more suitable for higher volume grinding applications. Use of a modulating 25 counterweight system reduces the vibration associated with the grinder thus allowing higher rotational speeds and longer component service life. The above describes only some embodiments of the present invention and modifications obvious to those skilled in the art can be made thereto without departing from the scope and 30 spirit of the present invention.

Claims

1. An internal orbit (as defined herein), variable ratio (as defined herein), continuous centrifugal grinding mill system comprising: 5 a. a supporting framework, b. a main rotor supported within bearing arrangements by said supporting framework, c. a grinding chamber as a secondary, substantially tubular rotor supported and 10 carried by the main rotor to form a rotor assembly and wherein said secondary rotor has an axis of rotation substantially parallel to the axis of rotation of said main rotor, d. a main rotor drive system, e. a secondary rotor drive system, 15 f. a grinding chamber infeed system, g. a grinding chamber discharge system and wherein the axis of rotation of said main rotor lies within the locus formed by the outer extremity of the secondary rotor as it rotates about its axis and 20 wherein said main rotor and said secondary rotor can rotate continuously and independently about their respective axes of rotation and wherein said main rotor drive system powers the rotation of said main rotor and wherein said secondary rotor drive system powers the rotation of said secondary rotor independently of the rotation of said main rotor and wherein an at least one 25 infeed opening in one end of said secondary rotor allows grinding furnish and or grinding media to be admitted to said secondary rotor and wherein an at least one discharge port in said secondary rotor allows ground material to be extracted from said secondary rotor and wherein said centrifugal grinding mill is intended to be operated in a continuous manner. 30

2. The grinding system of claim 1 wherein said discharge port and said infeed opening are one and the same. 35

3. The grinding system of claim 1 wherein said infeed system utilises a stationary feed-tube protruding into said infeed opening and wherein said infeed opening can rotate around said feed-tube without interfering with it.

4. The grinding system of claim 1 wherein said secondary rotor is supported at each 40 end by bearing arrangements fitted to the main rotor. 2 OF 7

5. The grinding system of claim 1 wherein said main rotor is substantially tubular.

6. The grinding system of claim 1 wherein said main rotor drive system comprises a motor or motor gearbox arrangement driving the main rotor through a gear engaged with a ring 5 gear mounted on said main rotor.

7. The grinding system of claim 1 wherein said main rotor drive system comprises a motor or motor gearbox arrangement driving the main rotor through a transmission drive belt 10 system engaged with a drive pulley mounted on said main rotor.

8. The grinding system of claim 1 wherein said main rotor drive system comprises an at least one roller or wheel engaging with an at least one circumferential track on the main rotor and wherein said at least one roller or wheel is powered. 15

9. The grinding system of claim 1 wherein said secondary rotor has a coaxial drive shaft integral with or rigidly connected to it.

10. The grinding system of claim 9 wherein said coaxial drive shaft is connected 20 directly to the motor shaft of a motor mounted on the body of the main rotor and rotating with it.

11. The grinding system of claim 10 wherein the frame of said motor has a slip ring assembly coaxial with the axis of rotation of the main rotor and rotating with it for the purposes of at least supplying power to said motor. 25

12. The grinding system of claim 9 wherein said coaxial drive shaft is connected through a drive transmission system to an input drive shaft coaxial with said main rotor axis of rotation at the opposite end of the grinder to the infeed opening. 30

13. The grinding system of claim 12 wherein said drive transmission system is a planetary gear set with outer gear driving a planetary gear.

14. The grinding system of claim 13 wherein said outer gear of said planetary gear set is directly supported, substantially on its outer circumference by a bearing arrangement. 35

15. The grinding system of claim 12 wherein said input drive shaft is directly connected to the shaft of a motor fixed rigidly to the body of the main rotor such that said motor is coaxial to said main rotor and rotates with it. 40

16. The grinding system of claim 15 wherein the frame of said motor has a slip ring assembly coaxial with the axis of rotation of the main rotor and rotating with it for the purposes 3 OF 7 of at least supplying power to said motor.

17. The grinding system of claim 12 wherein said drive transmission system is a system of belts and pulleys fixed to the main rotor and rotating with it. 5

18. The grinding system of claim 12 wherein said drive transmission system is a universal drive shaft with a constant velocity joint at each end.

19. The grinding system of claim 1 wherein said secondary rotor has sacrificial wear 10 resistant linings on its intemal walls.

20. The grinding system of claim 19 wherein said sacrificial wear resistant lining at the infeed end of said secondary rotor is in the form of a screw to assist with feeding the grinding furnish into said secondary rotor. 15

21. The grinding system of claim 1 wherein a fluid is used to at least assist with conveying ground material to said at least one discharge port of said secondary rotor.

22. The grinding system of claim 21 wherein said fluid admitted to said secondary rotor 20 is pressurised.

23. The grinding system of claim 22 wherein said pressurised fluid is fed from a plenum substantially sealed against the infeed end of said secondary rotor. 25

24. The grinding system of claim 23 wherein said plenum has a perforated plate forming one component of the seal against the end of said secondary rotor.

25. The grinding system of claim 1 wherein said at least one discharge port in said secondary rotor has a grate like insert or cover in order to prevent grinding media or oversize 30 ground material from exiting the grinding chamber.

26. The grinding system of claim 25 wherein said grate like insert or cover forms a substantially planar surface with an internal wall of said grinding chamber. 35

27. The grinding system of claim 25 wherein said grate like insert or cover uses slots in order to prevent grinding media or oversize ground material from exiting the grinding chamber.

28. The grinding system of claim 26 wherein said substantially planar surface is substantially at right angles to the axis of rotation of said grinding chamber. 40 4 OF 7

29. The grinding system of claim 1 wherein said at least one discharge port of said secondary rotor discharges into a discharge cavity within the main rotor.

30. The grinding system of claim 29 wherein said discharge cavity has an at least one 5 discharge opening in the shell of the main rotor for discharging ground material from said main rotor.

31. The grinding system of claim 1 wherein said secondary rotor has an at least one lifter bar (as defined herein) attached to or being integral with the wall of said secondary rotor. 10

32. The grinding system of claim 31 wherein said at least one lifter bar is in the form of a helix along the longitudinal axis of said secondary rotor.

33. The grinding system of claim 32 wherein a plurality of lifter bars form both 15 clockwise and counter-clockwise helixes along the longitudinal axis of said secondary rotor.

34. The grinding system of claim 1 wherein said main rotor has an at least one counterweight fixed within it or on it to substantially offset the off-centre mass of the secondary rotor and its contents. 20

35. The grinding system of claim 1 or claim 34 wherein said main rotor has a modulating counterweight system as defined herein to offset any change in the off-centre mass of the secondary rotor. 25

36. The grinding system of claim 35 wherein said modulating counterweight system is adjustable in real time.

37. The grinding system of claim 35 wherein said modulating counterweight system is adjusted and controlled by a controller utilising an output from an at least one vibration sensing 30 transducer such as an accelerometer as a process variable input.

38. The grinding system of claim 35 wherein said modulating counterweight system comprises an at least one fixed mass modulated in radial position by suitable means such as lead screws. 35

39. The grinding system of claim 35 wherein said modulating counterweight system uses a rotating liquid ring as defined herein of adjustable liquid ring depth as defined herein.

40. The grinding system of claim 39 wherein said rotating liquid ring depth is adjusted 40 by means of an at least one control valve. 5 OF 7

41. The grinding system of claim 40 wherein said at least one control valve is mounted on the main rotor.

42. The grinding system of claim 39 wherein said liquid used in the rotating liquid ring 5 is formulated to give a specific gravity greater than that of water.

43. The grinding system of claim 42 wherein said liquid used in the rotating liquid ring is a concentrated solution of inorganic salts with a specific gravity greater than 1.3. 10

44. The grinding system of claim 1 wherein said main rotor has an at least one slip-ring assembly fixed to and rotating coaxially with said main rotor such that electrical power and/or data signals and/or pressurised fluid can communicate between the rotor of said slip-ring assembly attached to the rotating main rotor and the stator of said slip-ring assembly attached to the stationary said supporting framework. 15

45. The grinding system of claim 1 wherein wireless control signals and or data signals are passed to and from a transmitter/receiver attached to the main rotor and a stationary transmitter/receiver. 20

46. The grinding system of claim 1 wherein said rotor assembly has an at least one rotary seal assembly wherein a seal surface rotating with said secondary rotor seals against an opposing seal surface connected to and inside said main rotor such that fluid and or particulate matter is restricted from passing axially within the rotor assembly past said seal assembly. 25

47. The grinding system of claim 46 wherein a plurality of said rotating seal arrangements form an at least one enclosed annular type cavity with outer wall being a main rotor external wall, inner wall being the secondary rotor external wall and end walls being said rotating seal arrangements and supporting diaphragms. 30

48. The grinding system of claim 47 wherein pressurised fluid is admitted to said at least one enclosed annular type cavity for the purposes of at least cooling the rotor assembly.

49. The grinding system of claim 1 wherein said main rotor drive system and said secondary rotor drive system are variable speed systems such that the rotational speed of said 35 main rotor and the rotational speed of said secondary rotor can be varied independently of one another.

50. The grinding system of claim 49 wherein said variable speed systems are controlled by a motion control system as defined herein such that the absolute and relative 40 rotational speeds and/or relative rotational positions of said main rotor and said secondary rotor are maintained accurately. 6 OF 7

51. The grinding system of claim 50 wherein said motion control system uses a motion control unit.

52. The grinding system of claim 51 wherein said motion control unit is in digital 5 communication with an HMI such that rotor drive parameters are available in real time to grinder operators and adjustment to rotor drive parameters can be made in real time.

53. The grinding system of claim 50 wherein accurate rotational speed and position data for the main rotor and the secondary rotor are provided to said motion control system by 10 rotary encoders connected to suitable points on the drive systems of each rotor.

54. The grinding system of claim 49 wherein the absolute rotational speed of said main rotor and the relative (to the main rotor) rotational speed of said secondary rotor are modulated in order to maintain in isolation or in combination an aim grinding power input, aim grinding 15 efficiency and an aim ground material particle size distribution.

55. The grinding system of claim 49 wherein in isolation or in combination accurate real time continual or continuous measurements of motor torque, motor power and motor speeds are used to impute grinder performance. 20

56. The grinding system of claim 1 wherein the internal surface of the secondary rotor is profiled so as to alter the grinding energy density in different regions of the chamber.

57. The grinding system of claim 56 wherein the internal diameter of said secondary 25 rotor is reduced at the infeed end region and/or the drive end region of said secondary rotor.

58. The grinding system of claim 56 or claim 57 wherein the internal diameter of the secondary rotor is profiled from smaller to larger in an at least one region along the longitudinal axis of said secondary rotor. 30

59. The grinding system of claim 1 wherein a remote sensing bulk density measuring transducer such as a radar or microwave reflection transducer is used to measure the bulk density of the contents of the grinding chamber. 35

60. The grinding system of claim 1 wherein an over arching supervisory control system is used to control in combination at least the grinder infeed rate and rotor rotational speeds as well as any or all of the grinder parameters: a. grinder temperature, 40 b. ground material outfeed temperature, c. overall main rotor rotational balance, 7 OF 7 d. grinder power.

61. The grinding system of claim 1 wherein said grinding mill system can be oriented at any angle from horizontal to vertical. 5

62. A method for the size reduction or mixing of solid material in a continuous grinder; said method including the steps of: a. feeding a grinding furnish through a feed-tube into the secondary rotor of an 10 internal orbit, variable ratio, continuous centrifugal grinding mill, b. rotating the secondary rotor and the main rotor of said grinding mill at rotational speeds above the rimming speeds for said rotors such that a grinding action is set up within said secondary rotor, c. maintaining optimum absolute and relative rotational speeds and/or positions 15 of said rotors by controlling said rotational speeds with variable speed systems, d. substantially keeping the main rotor in balance, e. discharging the ground material through an at least one discharge port in said secondary rotor, 20 f. controlling in real time any or all of the following parameters so as to provide optimum grinding results: feed rate, discharge rate, rotational speeds, rotor balance and temperatures.

63. A grinding system as herein described and with reference to the accompanying 25 drawings.