Apparatus and methods for wet grinding

Wet grinding apparatus including a grinding unit having first and second outer plates forming a housing with an inner chamber. A rotatable disc is housed in the inner chamber. A drive shaft is attached to the rotatable disc and extends centrally through one side of the housing. The other side of the housing includes a central inlet port for allowing introduction of slurry solution. A peripheral edge surface of the housing includes one or more outlet ports. Inner surfaces of the first and second outer plates and both surfaces of the rotatable disc have a series of outwardly extending grooves which taper in depth from a central location of each disc to a peripheral portion of each disc. The rotatable disc further includes a plurality of central feed ports or openings in communication with grooves on each side of the rotatable disc. The grinding method and operation of the apparatus include feeding slurry solution containing particles into the grooves and rotating the rotatable disc to reduce the size of the particles in the slurry solution while transferring the slurry solution to the outlet or outlets of the grinding unit.

BACKGROUND OF THE INVENTION 
The present invention generally relates to apparatus for wet grinding and, 
more particularly, to the grinding of particles in a slurry solution down 
to particles having a size on the order of several microns or less. 
Generally, size reduction of particles in a slurry is accomplished in 
multistage processes. That is, large particles of grain such as whole 
grain, corn, rice and the like, or other solids are initially broken down 
in size by conventional milling apparatus such as roll crushers, hammer 
mills, shredders and other similar devices depending on the product being 
ground. As one example, hammer mills may be suitable for use in dry 
grinding processes, wet grinding processes or both and may include a 
rotating cylinder or drum with attached "hammers" which crush particles 
against a stator screen. Hammer mills generally work under the principle 
of forcing particles through the holes in the stator screen to produce 
particles of a size commensurate with the size of the screen holes. Hammer 
mills are used in the distilling industry to dry grind grain which is 
later slurried with water in a separate tank to prepare the grain for 
fermentation. Disadvantages of hammer mills include the possibility of 
explosions resulting from the production of large amounts of dust, high 
maintenance costs associated with regular replacement of stator screens, 
and loss of product and damage to product from heat produced during the 
grinding process. 
U.S. Pat. No. 4,813,617 ('617) issued on Mar. 21, 1989 to Knox, Jr. et al., 
which names the present inventor as a co-inventor thereof, addresses the 
problem of obtaining both maximum grinding efficiency and maximum 
throughput volume in a wet grinding machine. The '617 patent provides 
apparatus for very efficiently grinding large particles such as corn and 
the like down to smaller particles, for example, on the order of 1/8" in 
diameter, on a continuous high throughput volume basis. The '617 patent 
successfully accomplishes this objective by combining both large and small 
slots in a stationary stator and using a rotating bladed rotor disposed 
within the stator. Larger particles are reduced in size through shearing 
action between the blades of the rotor and the edges of the large slots in 
the stator and smaller particles are reduced in size through shearing 
action between the rotor blades and the small slots in the stator. Large 
particles are transferred out of the stator through the large slots and 
small particles are transferred out of the stator through both the large 
and small slots. The apparatus disclosed in the '617 patent presents a 
significant improvement over past grinding methods in terms of the size 
reduction and throughput volume potential of a single step grinding 
apparatus capable of reducing relatively large particles down to particles 
having an average diameter, for example, of 1/8". 
Regarding apparatus and methods for reducing particles from a size on the 
order of 1/8" to a size of several microns or less, ball mills, hammer 
mills and homogenizers have been used in the past. Apparatus of this type 
have several undesirable features and cost implications. First, in order 
to obtain smaller and smaller particle sizes the holes in the stator 
screen or, for example, the balls or beads of a ball mill must be smaller 
to obtain smaller particle sizes. As the screen holes, balls or beads get 
smaller so to does the throughput volume of the grinding apparatus using 
these grinding or size reduction means. Thus, past fine grinding methods 
produce very low volumes of finely ground product. 
Also, the costs associated with the manufacture, operation and maintenance 
of these machines is very high. For example, the costs associated with 
manufacturing minute openings in the screens used in a hammer mill are 
high especially when considering that the screens must be replaced 
constantly. The costs of manufacturing and maintaining a typical 
homogenizer are high due to the costs of the high pressure pumps, high 
powered motors and many other precision components. 
Other problems have arisen using past methods to produce particle sizes on 
the order of several microns or less such as the undesirably long milling 
times, which may stretch up to 30 hours and which add to the costs of 
using ball mills, hammer mills and homogenizers. In the case of ball 
mills, due to the long milling time involved, these mills must be 
surrounded by cooling jackets which further add to their cost and 
complexity. 
Accordingly, there is a need in the art for apparatus and methods for 
reducing the size of particles from sizes easily produced by apparatus 
such as that shown in the '617 patent, down to sizes on the order of 
several microns or less in a fast and efficient manner by producing 
continuous high throughput volumes of dispersions and emulsifications 
containing such particles. 
It has therefore been one objective of the invention to provide a wet fine 
grinder capable of continuously grinding particles contained in a slurry 
solution without clogging and without significant wear on the size 
reducing or grinding components of the apparatus. 
It has been another objective of the invention to produce high throughput 
volumes of particles of a size on the order of several microns or less 
quickly and efficiently on a continuous in-line basis as opposed to a 
single batch basis. 
It has been still another objective of the invention to significantly 
reduce the amount of time and number of grinding steps necessary to reduce 
large amounts of slurry solution containing relatively large particles 
into a slurry solution containing particles of several microns or less in 
size. 
It has been yet another objective of the invention to provide apparatus for 
grinding particles in a batch of slurry contained in a tank as well as 
apparatus for grinding particles contained in slurry solution traveling in 
a fluid line and continuously recirculating slurry solution through each 
grinding apparatus. 
It has been still a further objective of the invention to use the slurry 
solution itself as a lubricant and a coolant for the grinding components 
of the apparatus to substantially reduce wear on grinding components of 
the apparatus. 
SUMMARY OF THE INVENTION 
To these ends, the present invention provides at least two plates or discs 
having opposed flat surfaces and a plurality of outwardly extending 
grooves in each flat surface for containing and grinding particles in a 
slurry solution. At least one of the discs is rotated at high speed with 
respect to the other of the discs to facilitate size reduction of 
particles located in opposed grooves of different discs. The slurry 
preferably enters the spaces created by the grooves at a central inlet of 
one or more of the discs and is transferred to the periphery of the discs 
by centrifugal force created through rotation of at least one of the 
discs. The slurry is then preferably recirculated to the central inlet to 
continuously circulate the slurry through the slots in the discs. In the 
preferred embodiments, the slots in the discs are tapered in depth along 
their length such that their deepest points are proximate the central 
inlet of the discs and their most shallow points are proximate the 
periphery of the discs. Furthermore, the grooves in each disc preferably 
end short of the periphery of the disc. 
More particularly, a first preferred embodiment of the invention comprises 
an in-line grinding unit which includes a housing formed by two outer 
plates or discs. One of these outer discs includes an elevated land having 
a major face. A plurality of equally spaced grooves extend radially 
outwardly from a central slurry inlet port in the disc to a point 
proximate the outer periphery of the raised land. 
A rotatable plate or disc includes similar grooves on both of its major 
faces and has a central threaded bore which allows the disc to be mounted 
to a rotatable drive shaft. This rotatable disc further includes feed 
openings spaced around and proximate to the central threaded bore. These 
feed openings extend through the rotatable disc from the first major face 
thereof to the second major face thereof and each feed opening 
communicates with an inlet end of one groove on the first major face and 
the inlet end of one groove on the second major face, 
The second outer plate or disc forms a housing with the first outer plate 
or disc by including a flange portion which extends at right angles to the 
outer plates or discs and is attached to the first outer plate or disc 
radially outward of the raised land to form a chamber containing the 
rotatable disc. This chamber is substantially equal in height to the 
maximum thickness of the rotatable disc. The second outer plate or disc 
includes a central bore through which the drive shaft of a motor, for 
example, extends and further includes a plurality of radially spaced 
outwardly extending tapered grooves similar to the tapered grooves in both 
the first outer plate or disc and the rotatable plate or disc. 
In this first preferred embodiment, the outer peripheral surface of the 
flange of the second outer plate or disc includes an outlet port through 
which ground slurry is transferred by way of centrifugal force created by 
the rotating disc within the chamber of the housing. The outer peripheral 
edge of the rotating disc includes notches which accumulate ground slurry 
and carry it around the outer edge of the rotating disc to the outlet 
port. This design provides a pumping action which effectively pumps the 
slurry out of the chamber in the housing to the outlet port such that it 
may then be recirculated to the central inlet port of the grinding unit or 
fed into a receiving tank. 
The second preferred embodiment of the present invention is very similar to 
the first embodiment in that two discs form a housing which contains a 
rotatable disc and each of the discs include grooves which interact with 
one another to provide a disintegrating action as well as a transfer path 
from central portions of each disc to at least one outlet in the outer 
periphery of the housing. In the second preferred embodiment, the grinding 
apparatus is submerged in a tank of slurry containing particles and the 
slurry is initially forced into the central inlet port by atmospheric 
pressure acting on the top surface of the slurry solution in the tank. The 
slurry solution that contains the particles is then drawn into and 
transferred along the grooves of each disc as a result of centrifugal 
forces created by the rotating disc. The particles in the slurry are 
disintegrated between the rotating disc and the discs which form the 
housing before the slurry exits through peripheral outlets in the housing. 
The slurry is thereby constantly recirculated from the tank into the 
central inlet port of the grinding unit, through the grooves in each of 
the discs, and back into the tank. 
Each of the above described embodiments work on similar principles. That 
is, as the slurry material advances radially outwardly along the grooves, 
the particles are repeatedly reduced in size by shearing action between 
the advanced edge of one of the housing plates and the trailing edge of a 
groove in the rotating disc. Moreover, particles constantly collide with 
one another and are subjected to fluctuating pressures within the 
intermittently registering grooves of adjacent discs to cause further 
disintegration of the particles as they travel outwardly within the 
grooves. In addition, particles caught between the flat surfaces of the 
discs are reduced in size through a rolling action of the particles 
between the flat surfaces. If the particles are fibrous, then the fibers 
making up the particles are rolled into and compacted against each other 
to reduce the sizes of the particles. 
As the particles are reduced in size, they travel radially outwardly along 
the grooves into shallower and shallower portions of the grooves and are 
finally reduced to sizes which are generally less than the distance 
between first and second flat surfaces of the rotating disc and the 
respective opposed flat surfaces of the outer housing plates or discs. 
After the particles have been ground, the slurry containing the particles 
exits the apparatus and may then be recirculated back to the inlet. In its 
preferred use, the invention is particularly applicable to the grinding of 
particles down to sizes of, for example, less than 5 microns. However, the 
apparatus may be dimensioned for grinding or disintegrating particles 
having greater diameters as well. This would merely require changing the 
depth of the grooves, the spacing between the rotating disc and the 
housing plates or discs, and other dimensions of the apparatus 
accordingly. 
Further objects and advantages of the invention will become more readily 
apparent through the following detailed description taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before describing the preferred embodiments of the present invention, 
reference is first made to FIG. 1 which illustrates a conventional wet 
grinder 1 which is used in a batch of slurry material to reduce the size 
of particles contained in the slurry material. The wet grinder 1 includes 
a plurality of baffles 2 radially extending from the lower end of a drive 
shaft 3 and rotatably received in a circular screen structure 4. The 
screen structure 4 is typically held between upper and lower flanges (not 
shown). In operation, the wet grinder 1 is lowered into a batch of slurry 
material and the drive shaft 3 is rotated to draw slurry material into an 
inlet end 5 of the screen structure 4 through the lower flange (not 
shown). Once the slurry material is drawn into the screen structure 4, 
part of the material is forced through the screen openings 6. Many larger 
particles may not be able to be forced through the openings 6 in the 
screen structure 4 by the baffles 2. Also, devices such as the one shown 
in FIG. 1 reduce particles to a size which is limited by the size of the 
holes 6 in the screen structure 4 and, although the holes 6 may be formed 
in very small sizes through processes such as photoetching, by doing so 
the screen structure 4 becomes very fragile and easily subject to 
deformation. Moreover, problems related to clogged screen holes 6 and low 
throughput volume of ground slurry material often arise with devices of 
this type. 
A first preferred embodiment of the present invention is illustrated in 
FIG. 2 and comprises an in-line wet grinding apparatus 10 having a 
mounting base 11 and a drive means in the form of a motor 12 directly 
coupled to a drive shaft 13. The drive shaft 13 extends along the 
longitudinal axis of the apparatus 10 inside a drive shaft housing 14. The 
drive shaft housing 14 includes an access port 14a for allowing 
maintenance to be performed on components within the housing 14. The drive 
shaft 13 is supported by bearing assemblies 15, 16 contained in the drive 
shaft housing 14. A flange portion 17 of the drive shaft housing 14 is 
located at one end thereof opposite the motor 12 and is attached by bolts 
18 to a grinding unit 20. 
Referring now to both FIGS. 2 and 3, a preferred embodiment of the grinding 
unit 20 includes a grinding unit housing 21 having outer discs 22, 23 
which together form an inner chamber which receives an inner rotary disc 
24. One of the outer discs 22 includes a flange portion 25 which is 
connected to the other outer disc 23 by bolts 28 received in apertures 23a 
of disc 23 and threaded holes 25a in flange portion 25. The grinding unit 
housing 21 further includes a slurry inlet 30 and a slurry outlet 31. The 
slurry inlet 30 preferably extends through the center of disc 23 and the 
slurry outlet 31 extends through the flange portion 25 of disc 22. The 
slurry inlet 30 and slurry outlet 31 may vary in size according to the 
flow requirements of the particular grinding operation. The slurry inlet 
30 and slurry outlet 31 have respective female threaded portions 30a, 31a 
for connecting fittings and fluid lines thereto. Of course, male threaded 
portions or other connecting means, such as quick-connect fittings, may be 
substituted for the female threads shown. 
As previously mentioned, the outer discs 22, 23 preferably form a housing 
or stator within which the inner rotary disc 24 rotates. The inner 
surfaces 26, 27 of each respective outer disc 22, 23 contain a series of 
grooves 34, 35. As shown best in FIG. 2, each groove 34, 35 preferably 
tapers in depth from a respective inlet end 36, 37 to a respective outlet 
end 38, 39. Each of the grooves 34, 35 are deeper at their respective 
inlet ends 36, 37 than at their respective outlet ends 38, 39. The inlet 
ends 37 of each of the grooves 35 in disc 23 communicate with the slurry 
inlet 30 at the center of disc 23. 
As further shown in FIG. 2, the rotary disc 24 includes a series of tapered 
grooves 41, 42 in both of its major faces 43, 44. The grooves 41, 42 
extend from respective inlet ends 46, 47 to respective outlet ends 48, 49. 
Notches 45 are formed in the peripheral edge surface of the rotary disc 24 
and each notch 45 is in line with the outlet ends 48, 49 of two parallel 
grooves 41, 42 in opposite sides 42, 43 of the rotary disc 24. Like the 
grooves 34, 35 in discs 22 and 23, the grooves 41, 42 are each preferably 
tapered such that they are deeper at their respective inlet ends 46, 47 
than at their respective outlet ends 48, 49. 
A central threaded aperture 51 of disc 24 allows a threaded end of the 
drive shaft 13 to be attached to the rotary disc 24. The drive shaft 13 
preferably rotates the inner disc 24 at a speed which is preferably in 
excess of 1000 rpm and may be, for example, 3450 rpm in a direct couple 
system between the motor 12 and the drive shaft 13. Of course, the actual 
speed will depend on the viscosity of the liquid containing the particles 
and/or the overall viscosity of the slurry solution. An annular pattern of 
spaced feed openings 52 are formed about the periphery of the drive shaft 
mounting aperture 51. Each feed opening 52 communicates with one inlet end 
46 of a groove 41 on one side of the rotary disc 24 and one inlet end 47 
of a groove 42 on the other side of the rotary disc 24. These feed 
openings 52 allow slurry solution to be introduced into the inlet 30 of 
disc 23 and fed from the grooves 35 in disc 23 into the grooves 42 in the 
rotary disc 24 which face away from the inlet 30 as well as the grooves 34 
in disc 22. 
A mechanical liquid seal is provided to keep the slurry solution within the 
grinding unit 20 and includes a rotary seal member 53 which is preferably 
formed of a ceramic material. The rotary seal member 53 is recessed into 
and rigidly attached to the rotary disc 24 intermediate the central drive 
shaft opening 51 and the spaced feed openings 52. A second spring loaded 
seal component 54 is held against the rotary component 53 by a mounting 
bracket 56 having an O-ring 57 in a lower surface thereof. The bracket 56 
is fastened to outer disc 22 by a plurality of bolts 58. Thus, liquid 
seals are created between the rotary seal member 53 and the lower portion 
54a of the spring loaded seal component 54, between the top portion 54b of 
the spring loaded seal component 54 and the bracket 56, and between the 
O-ring 57 and the outer surface of disc 22. One suitable seal assembly is 
marketed by Garlock Mechanical Packing Division, Mechanical Seals, a 
division of Colt Industries, under PK Form No. 70-20B. 
A second embodiment of the invention is shown in FIG. 4 and comprises an 
in-tank grinding apparatus 110 mounted by a suitable bracket 111 to a tank 
of slurry solution 126. The grinding apparatus 110 includes a motor 112 at 
an upper end thereof operatively connected to a rotating drive shaft 113. 
Like the drive shaft 13 of the first embodiment, the drive shaft 113 is 
supported by suitable bearing assemblies 115, 116. At the lower end of the 
drive shaft 113, the grinding apparatus 110 includes a grinding unit 120 
formed by a housing having outer plates or discs 122, 123. 
There are only two significant differences between the in-line design shown 
in FIGS. 2 and 3 and the in-tank design shown in FIG. 4. One difference is 
that the in-tank grinding apparatus 110 includes elongated support rods 
114 in place of a drive shaft housing. These elongated support rods 114 
extend substantially between the motor 112 and the grinding unit 120 and 
are sized according to the depth of the tank in which the grinding 
apparatus is intended to be used. Thus, the drive shaft 113 and the 
support rods 114 are of a length which allows the motor 112 to be 
positioned above the top surface of the slurry material 126 and the 
grinding unit 120 to be positioned near the bottom of the tank of slurry 
solution. 
The other difference between the two embodiments resides in the fact that a 
plurality of outlet ports 131 are formed in the flange portion 125 of disc 
122 as opposed to a single outlet port. The use of a plurality of outlet 
ports 131 allows ground slurry to exit the grinding unit 120 in greater 
volumes than would a single outlet port. This allows slurry to be more 
quickly recirculated back to the inlet port 130 of the grinding unit 120 
and further increases the volume of slurry moving through the grinding 
unit 120. Except for the use of a plurality of outlets 131, the inner 
design of the grinding unit 120 including the grooves (not shown)in the 
inner faces of the outer discs 122, 123 and the design of the grooved 
rotary disc (not shown), is identical to the design of the like components 
in the grinding unit 20 including discs 22, 23 and 24 shown in FIGS. 2 and 
3 and described in detail above, This detail therefore need not be 
repeated in the description of the second embodiment. 
In operating the embodiments shown in FIGS. 2 and 3 of the present 
invention, and with specific reference to FIG. 2, slurry solution 
containing particles enters the grinding unit 20 through the inlet port 30 
by way of a fluid line (not shown) connected to the inlet port 30. The 
slurry solution is then drawn into the grooves 35 of disc 23 by the 
partial vacuum or negative pressure created by centrifugal forces of the 
rotating disc 24. The slurry solution also enters the feed apertures 52 in 
the rotating disc 24 and thereby reaches the series of grooves 42 in the 
rotating disc 24 as well as the series of grooves 34 in disc 22. The 
maximum initial size of the particles in the slurry solution entering the 
grinding unit 20 is limited by the maximum combined depth of a groove in 
disc 23 and a groove 41 in the rotary disc 24 added to the distance 
between faces 27, 43 of discs 23, 24, respectively. Likewise, the maximum 
initial particle size is also limited to the maximum combined depth of a 
groove 34 in disc 22 and a groove 42 in the rotary disc 24 added to the 
distance between faces 26, 44 of discs 22, 24, respectively. The feed 
openings 52 are also formed large enough to allow transfer of the maximum 
size of particles as defined above to prevent blockage of the feeding 
openings 52 by oversized particles. As shown in FIG. 3, feed apertures 52 
are formed with a diameter which is not appreciably greater than a maximum 
width of tapered grooves 41 to which feed apertures open at the inlet ends 
46 thereof. More specifically, apertures 52 are formed with a diameter 
which is approximately equal to a maximum width of tapered grooves 41 at 
inlet end 46. The slurry solution is preferably run through a classifier 
prior to entering the grinding unit 20 in order to filter out particles 
larger than the maximum initial size which may be effectively processed by 
the grinding unit 20. Of course, the dimensions of the outer discs 22, 23, 
the inner rotary disc 24, the grooves 34, 35, 41, 42 in each disc, and the 
feed openings 52 may be varied according to the specific grinding needs 
and the particular slurry material to be ground. 
Once the slurry solution is transferred into grooves 34, 35, 41 and 42, the 
slurry solution is transported outwardly within the grooves 34, 35, 41 and 
42, through centrifugal force created by the rotating disc 24. As the 
slurry solution is transported along the tapered grooves 34, 35, 41 and 
42, the particles in the slurry solution are continuously ground and 
disintegrated at least until they reach a maximum size which is defined by 
the distance between the major surfaces 43, 44 of the rotary disc 24 and 
each respectively opposed inner surface 26, 27 of the outer discs 22, 23. 
This maximum size results because each of the grooves 34, 35, 41 and 42 
tapers up to the respective surfaces 26, 27, 43 and 44 a short distance 
inside of the peripheral edges of these surfaces 26, 27, 43 and 44. Thus, 
small surface areas 26a, 27a, 43a and 44a are left outside the outlet ends 
38, 39, 48 and 49 of the respective grooves 34, 35, 41 and 42. The 
distance between surfaces 26 and 44 as well as the distance between 
surfaces 27 and 43 therefore essentially govern the maximum output 
particle size. The maximum output particle size may therefore be 
controlled by varying these distances through specific dimensioning of the 
apparatus. The distance between surfaces 27 and 43 and surfaces 26 and 44 
may each be, for example, 0.010" and the grinding unit 20 will still 
produce particles on the order of several microns or less to achieve 
extremely find grinding of particles in a slurry solution. Thus, it will 
be appreciated that the plates or discs 22, 23, 24 need not be spaced 
apart by 5 microns to obtain particles of 5 microns, for example. The 
combined effects of the high speed rotation of at least one disc, the 
shearing effects of the tapered grooves, and the high speed collisions 
between particles cause the particles to be disintegrated to a size 
smaller than the spacing between the flat surfaces 26, 27, 43, 44 of the 
respective discs 22, 23, 24. 
Separate cooling means are generally not necessary since the slurry 
solution itself acts as a lubricant and coolant as it flows through the 
grinding unit 20. Of course, a cooling jacket may be used around the 
grinding unit 20 if necessitated by a particular grinding operation. 
When the slurry solution reaches the outer peripheral edge of the rotary 
disc 24, the slurry solution is transferred along the inner edge of flange 
portion 25 of disc 22 to the outlet port 31 by notches 45 in the rotary 
disc 24. In this regard, the notches 45 in the rotary disc 24 provide a 
pumping action, similar to a centrifugal pump, to continuously feed slurry 
material through the outlet port 31. To provide a continuous grinding or 
disintegration action, the outlet port 31 may be connected by suitable 
fluid lines and fittings to a slurry supply and back to the inlet port 30 
such that the slurry solution in the supply is continuously recirculated 
through the grinding unit 20. Alternatively, the inlet port 30 may be 
connected to a slurry supply and the outlet port 31 may be connected to a 
separate receiving tank. 
The operation of the in-tank grinding apparatus 110 shown in FIG. 4 is very 
similar to the operation of the in-line grinding apparatus 10 described 
above with reference to FIG. 2. The only significant difference is that 
the grinding unit 120 is placed into a batch of slurry material 126 such 
that slurry material is constantly forced into the inlet 130 of the 
grinding unit 120 by atmospheric pressure exerted against the top surface 
of the slurry material 126. The slurry material travels into the grinding 
unit 120 and the particles in the slurry are ground or disintegrated in a 
manner identical to that described above with reference to FIG. 2. 
However, rather than being transferred out of the grinding unit 120 
through a single outlet port, the slurry material preferably exits the 
grinding unit 120 through several outlets 131. The slurry material 126 
contained in the tank is constantly recirculated through the grinding unit 
120 until substantially all of the slurry material 126 in the tank has 
passed through the grinding unit 120. 
Although preferred embodiments of the present invention have been shown and 
described above, one of ordinary skill will readily recognize numerous 
modifications thereto. For example, although the grinding units are shown 
to include a rotary disc having grooves on both sides thereof and outer 
plates each having inner grooves opposing the grooves in the rotary disc, 
the grinding unit could readily be modified into a two disc system having 
one series of grooves on each disc in opposed relation. Furthermore, the 
grinding unit may be designed with suitable multiple drive shaft and/or 
gear systems such that more than one of the discs are rotated at one time. 
For example, the grinding unit could be design using conventional drive 
mechanisms such that adjacent discs rotate in opposite directions so as to 
increase the difference in their relative speeds and thereby increase the 
resulting particle disintegration. In addition, the design of the grooves 
in the various discs may be varied by, for example, extending their 
lengths by forming them in patterns other than the radially extending 
patterns shown and described herein. One alternative is to form them 
shaped as curves extending from their inlet ends to their outlet ends. The 
grooves may be tapered in width as well as depth from an inlet end to an 
outlet end thereof, for example, such that they are wider at the inlet 
end. For coarser grinding applications, the grooves may be left untapered 
in depth. Finally, the grooves may have concavely shaped bottom surfaces 
as opposed to flat bottom surfaces as shown. This would, for example, 
prevent buildup of slurry material in the grooves. 
Other modifications will become readily apparent to the artisan of ordinary 
skill and applicant intends to be bound only by the scope of the appended 
claims.