Apparatus for comminuting materials to extremely fine size using a circulating stream jet mill and a discrete but interconnected and interdependent rotating anvil-jet impact mill

Apparatus for comminuting materials to extremely fine size includes a circulating stream jet mill and a discrete but functionally interconnected and interdependent rotating anvil-jet impact mill. New material is injected into the impact mill against a rotor, and the partly comminuted material is transferred to the jet mill with vortex feed into the jet mill. Uncomminuted material in the jet mill is reinjected into the impact mill. The two mills transfer the material back and forth until the particles are comminuted, classified, and removed from the jet mill. The anvil-jet mill is provided with stationary anvils and support for turning the rotor at increased velocity.

BACKGROUND OF THE INVENTION 
This invention relates to a method and apparatus for comminuting a wide 
variety of materials to an extremely fine size using a re-entrant 
circulating stream jet mill and a discrete but interconnected and 
interdependent jet and rotating anvil-jet impact mill. For the purposes 
described herein, extremely fine size means particles averaging below 20 
microns and, more specifically, below 10 microns including certain 
specified end products averaging less than 2 microns. 
Heretofore, various materials have been comminuted to intermediate average 
particle size using hammer mills with integral whizzer classifiers, ring 
roll and bowl mills with integral whizzer classifiers or wet bowl mills. 
The difficulty with wet bowl mills is that certain material tends to 
agglomerate when drying and, therefore, requires subsequent breaking up. 
Regardless, the mill best able to comminute particles to the lowest micron 
size has been the jet mill of which there have been three basic forms. The 
first such mill is disclosed in Luckenbach, U.S. Pat. No. 697,505 which 
uses opposed jet mills. Condensation and classifying problems, however, 
limited the usefulness of the Luckenbach mill. The next jet mill of any 
consequence was of the type disclosed in U.S. Pat. No. 1,935,344 and 
several kindred patents. This type of jet mill is in use today as the 
so-called "Majac Jet Pulverizer". It is described in its present form in 
the Fifth Edition of Perry's Chemical Engineering Handbook, Chapter 8, 
page 44. The Majac mill uses a whizzer type classifier making it superior 
in operation to the typical jet and anvil mill, such as disclosed in U.S. 
Pat. No. 2,487,088. 
The third and most universally used of all jet type communiting mills for 
low micron size is the re-entrant circulating stream jet mill disclosed in 
U.S. Pat. No. 2,032,827 and its prodgeny. This mill is often referred to 
as a Micronizer. 
There have been many attempts to improve upon the Micronizer since it was 
first introduced, and some of them have been significant improvements. The 
most successful improvement to the Micronizer for comminuting a wide range 
of materials is disclosed in U.S. Pat. No. 3,688,991, particularly in 
columns 7 and 8 and FIGS. 7 and 8. This mill, called the Cyclo-Jet, has 
been successfully used for the past 10 years for comminuting a wide range 
of materials with reduced consumption of energy. For example, the mill has 
been used to comminute talc at an energy cost of approximately 50% of the 
operating cost of previously known jet type mills. 
Not withstanding the success of the Cyclo-Jet, it too has inherent 
limitation in both its design and operation. To understand these 
limitations, it is important to note that the Cyclo-Jet is basically a 
combination of a rotating anvil-jet impact mill and a circulating stream 
jet mill. Circulating stream jet mills are complex devices despite their 
apparent simplicity of construction. There are numerous variables which 
must be balanced or coordinated to achieve the optimum comminution. Some 
of these variables include the diameter and peripheral height of the 
grinding and classifying chamber, the number and size of nozzles which in 
turn depend upon the kind of gas and its pressure, and the angle of the 
jet stream emitted by the nozzles. Another variable is the shape of the 
lateral walls which close the grinding and classifying chamber. These can 
be parallel plates or they can be axially divergent. If the latter, then 
consideration must be given to the angle of divergence and the radial 
extent thereof. Other factors include the location and structure of the 
material feed apparatus as well as the specific gravity and other 
characteristics of the matrial being fed. 
The advantage of the Cyclo-Jet mill disclosed in U.S. Pat. No. 3,688,991 is 
that the rotating anvil-jet section most efficiently comminutes coarser 
fractions of material while the circulating stream jet section is best for 
providing the finest grinding and classification. The problem is that that 
these two types of mill are not fully compatible when operating in a 
common grinding and classification chamber. For example, in many instances 
it is desirable to provide a circulating stream jet mill with diverging 
walls. This is not possible if the same mill has to include a shaft 
turning a rotor with anvils at its periphery. Still further, there are 
problems with supporting the rotor at the distal end of a shaft, as is 
necessitated by the presence of a centrally positioned outlet in a 
Micronizer. Experience has shown that distally mounted rotors tend to 
become unstable, particularly at high rotative velocities. Yet, experience 
has shown that such velocities are desirable. 
As indicated above, it is advantageous in some instances to provide 
diverging side walls for the grinding and classifying chamber of a 
circulating stream jet mill. This is not to say that parallel side walls 
do not have their uses. Parallel walls are preferred for grinding various 
precipitates and spray dried agglomerates. However, by and large diverging 
side walls are to be preferred. 
It is has been known for some time that the operation of a mill is improved 
by increasing the quantity of gas swirling within the grinding and 
classifying chamber. This is accomplished by providing diverging side 
walls. The amount of divergence is least for high specific gravity 
materials and greatest for low specific gravity materials. The amount of 
divergence is greatest at or adjacent the axis of the mill. FIG. 2 of U.S. 
Pat. No. 3,559,895 is a good illustration of a preferred form of 
circulating stream jet mill with diverging lateral walls. 
A Cyclo-Jet type mill such as illustrated in U.S. Pat. No. 3,688,991 has 
not yet successfully been provided with diverging walls and rotating disc 
and anvils. This inventor built a structure similar to the mill 
illustrated in FIG. 2 of U.S. Pat. No. 3,559,895 but with a 24 inch dish 
shaped rotor like the lower lateral wall in FIG. 2 of that patent. The 
rotor proved to be dynamically unstable, probably because of the great 
peripheral weight of the anvils. The rotor was modified to make it hollow 
approximately four inches radially outward from the shaft, but the 
vibration cracked the welds and the experiment was abandoned. 
In addition to unstable rotors, the Cyclo-Jet mill does not permit the use 
of anvils fixed on the peripheral wall of the chamber. This inventor tried 
welding ribs on the inner periphery of the chamber. This is sound practice 
in some impact mills, but is was counterproductive in the Cyclo-Jet mill 
because it interfered with classification of the finally comminuted 
product. The static anvils slowed the rotational velocity of the material 
laden gases at the periphery thus nullifying the increased gas velocity 
generated by the anvils on the rotor. See, for example, column 4, lines 
3-15 of U.S. Pat. No. 3,348,799 for a description of how the anvils on the 
periphery of a rotor assist in increasing the overall efficiency of a 
mill. 
In general, rotating anvil-jet impact mills comminute to finer particle 
size at higher rotor velocities. Although all materials do not require the 
same anvil speed for a desired average particle size, velocity tests using 
a 24 inch rotor with anvils on the periphery are significant. A Cyclo-Jet 
mill was modified so that the rotor could be turned at velocities of 
2,000, 3,600, 4,000 and 4,500 revolutions per minute. The product quality 
increased with increasing rotor velocity. However, the rotor showed signs 
of instability at 4,500 r.p.m. Today, approximately 4,000 r.p.m. is about 
the maximum rotor velocity in commercial use for a 24 inch mill. Of 
course, higher velocities are possible for mills having smaller rotor 
diameters. The maximum speed for a six inch mill is 12,000 r.p.m.; for a 
12 inch mill it is 8,000 r.p.m.; and a 20 inch mill can operate at 4,500 
r.p.m. These rotational velocities convert into peripheral (anvil) 
velocities of approximately 18,000 feet per minute for the six inch mill, 
25,000 feet per minute for a 12 inch mill, 23,000 feet per minute for a 20 
inch mill, and 25,000 feet per minute for a 24 inch mill. These velocities 
cannot be achieved using a dished rotor with anvils, because as indicated 
above with respect to the modified mill of FIG. 2 of U.S. Pat. No. 
3,559,895, the rotor becomes highly unstable at those speeds. 
Yet another problem with the Cyclo-Jet is that it cannot take advantage of 
improvements which have been made in the manner of feeding material into 
the circulating stream jet part of the mill. For a discussion of the 
problems encountered in feeding this type mill, see U.S. Pat. No. 
4,018,188 and 4,189,102. FIG. 1 of the latter patent illustrates a conical 
chamber dependent from one of the side walls of the grinding and 
classifying chamber. This conical chamber creates a vortex of material and 
injection gas which is merged with the gaseous vortex within the grinding 
and classifying chamber at approximately the jet tangent circle. In this 
manner the fluid carrying the feed material assists rather than detracts 
from the velocity of the main vortex. See also, U.S. Pat. No. 4,428,387 
which illustrates modifications of the same concept. 
Again, the Cyclo-Jet cannot be adopted to use these improved material feed 
means because the presence of both the rotor and the feed means would 
leave no place for a centrally positioned outlet. 
The present invention is directed to providing a method and apparatus for 
communuting materials to extremely fine sizes while overcoming the 
aforesaid limitations found in the Cyclo-Jet, yet retaining all of its 
benefits. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method and apparatus for comminuting 
materials to extremely fine size using a circulating stream jet mill and a 
discrete but innerconnected and interdependent rotating anvil-jet impact 
mill which overcomes the above-described limitations of the Cyclo-Jet mill 
to provide a mill with increased efficiency and a broadened field of 
application. In accordance with the present invention, a jet feed means 
injects new material to be comminuted into the impact mill against a rotor 
or its anvils. Thereafter, the thus partly comminuted material flows from 
a tangential port in the impact mill into a discrete re-entrant 
circulating stream jet mill by means of a vortex feed. The material is 
comminuted in the circulating stream jet mill with the finer fractions 
being classified and removed. However, the larger fractions are 
transferred back to the impact mill through a port in the peripheral wall 
of the circulating stream jet mill. From that port the material flows to 
jet injection means where it is reinjected against the rotor or its anvils 
in the impact mill. The two mills transfer the material back and forth 
until the particles are comminuted to an extremely finer size and then 
removed in accordance with the classification principles by which the 
circulating stream jet mill operates. 
The re-entrant circulating stream jet mill may be provided with diverging 
lateral walls to enhance its comminuting capability. Moreover, the mill is 
provided with a feed mechanism of the type which creates a vortex for 
feeding material to be ground into the circulating vortex within the 
grinding and classification chamber in the vicinity of the jet tangent 
circle. The comminuting capability of the rotating anvil jet impact mill 
may be enhanced by providing stationary anvils at preferred locations on 
the peripheral wall of the casing. Still further, the present invention 
provides for more stable rotor design whereby increased anvil velocity can 
be obtained for improved comminuting capability in the impact mill. 
The foregoing and other features of the apparatus and its method of 
operation described below comminute particles to extremely fine size with 
an efficiency and overall quality which heretofore has not been achieved. 
For the purpose of illustrating the invention, there is shown in the 
drawings a form which is presently preferred; it being understood, 
however, that this invention is not limited to the precise arrangements 
and instrumentalities shown.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings in detail, where like numerals indicate like 
elements, there is shown in FIGS. 1, 2 and 3, an apparatus 10 for 
comminuting materials to extremely fine size using two interconnected and 
interdependent mills comprising first a reentrant circulating stream jet 
mill 12 and second a rotating anvil impact mill 14. 
The re-entrant circulating stream jet mill 12 is generally the type known 
as an Micronizer and operates in accordance with the principles applicable 
to such mills except as hereinafter described. The circulating stream jet 
mill 12 includes a circular grinding and classifying chamber 16 defined by 
the annular peripheral wall 18 and opposed lateral walls 20 and 22. The 
walls 18, 20 and 22 are preferably held together with clamps or like 
devices for ready disassembly and cleaning. As illustrated, the lateral 
walls 20 and 22 diverge away from each other with the distance of greatest 
divergence being radially inward from the periphery toward the axis of the 
mill 12. The walls 20 and 22 diverge continuously from the peripheral wall 
to until they join the outlet 24 and the feed chamber 26 respectively. 
However, as described below, other configurations for the lateral wall can 
be used. 
The outlet 24 is a cylindrical duct for the finished material together with 
some of the fluid gases flowing within the chamber 16. The duct 24 extends 
through the lateral wall 20 and its opening is preferably coaxial with the 
axis of the chamber 16. 
Surrounding the annular peripheral wall 18 is an annular manifold 28 
connected through the duct 30 to a source (not shown) of gaseous fluid 
under pressure such as steam. 
A plurality of nozzles 32 are spaced at regular intervals around the entire 
peripheral wall 18. Each of the nozzles 32 is directed at an angle to the 
radius of the chamber 16 so that the fluid jet streams flowing from them 
move with both a forward and a radial component of direction. Thus, as is 
known in jet comminuting technology, the nozzles create a circulating 
vortex within the chamber 16. A duct 34 is connected through the manifold 
28 to an opening 36 in the peripheral wall 18. This duct provides for the 
flow of partly comminuted material from the comminuting and classifying 
chamber 16 to the jet and rotating anvil impact mill 14 as explained in 
more detail below. 
As indicated above, the mill 12 is also provided with a vortex feed means 
26 which comprises a cylindrical feed chamber closed at one end and 
opening into the apex of a lateral wall 22 at the other end. Although the 
feed chamber 26 is illustrated as cylindrical, it should be understood 
that it can assume other shapes, such as frusto-conical, provided that it 
has a circular cross-section. As illustrated, a duct 38 is connected to 
the peripheral wall of the feed chamber 26. Duct 38 conducts partly 
comminuted material from a port in the rotary anvil impact mill 14 into 
the feed chamber 26. The duct 38 is connected so that material flows into 
the feed chamber 26 in a direction that is generally tangential to the 
peripheral wall. In this manner, a vortical flow is created within the 
feed chamber 26. 
The rotating anvil-jet impact mill 14 comprises a chamber 40 which includes 
an annular peripheral wall 42 closed by opposed lateral side walls 44 and 
46. Mounted within the chamber 40 is a rotor 48 fixed to the shaft 50 by a 
key 52. A plurality of individual anvils 54 are fixed to the periphery of 
the rotor 48. As shown in FIG. 1, the anvils 54 are uniformly spaced 
around the outer periphery of the rotor 48 so that it is rotationally 
balanced. Although the anvils illustrated in FIGS. 1 and 3 are mounted 
only on the outer periphery of the rotor 48, it should be understood that 
in certain circumstances it may be desirable for the anvils to take 
different shapes and extend at least partly along the surface of the rotor 
in a radial direction as explained below. 
A plurality of regularly spaced stationery anvils 56 are positioned around 
the periphery of the annular wall 42 so as to be in opposed relation to 
the rotating anvils 54. The anvils 56 are not positioned along the 
entirety of the peripheral wall 42 for reasons explained below. 
The rotating anvil-jet impact mill further includes jet feed apparatus for 
feeding raw, uncomminuted material. The jet feed apparatus comprises a 
funnel 58 which is mounted on the nozzle and venturi mechanism 60. 
Material is fed in the conventional manner in that it flows from the 
funnel 58 and is entrained by the carrier fluid emitted from the nozzle 62 
connected to a source of high pressure gaseous fluid (not shown). The 
fluid and raw material are injected into a venturi passage 64 where they 
are accelerated and flow into the chamber 40. The feed mechanism 60 is 
mounted on the peripheral wall 42 so that material is directed into the 
feed chamber in opposition to the direction of rotation of the anvils 56. 
Specifically, fluid and material is directed generally tangential to the 
periphery of the rotor 48 and thus against the anvils 54. Thus, initial 
comminution occurs in the impact zone marked 66. 
It should be noted that the rotating anvils 54 also function as vanes for 
driving the gaseous fluid and entrained raw and partly comminuted material 
within the chamber 40. The centrifugal force imparted to the material 
tends to keep it adjacent the peripheral wall 42 and thus causes it to 
impact against the anvils 56. In addition, the material tends to flow in 
opposition to the direction of flow of the raw material emitted from the 
venturi 64. Thus, further comminution occurs as the material within 
chamber 40 impacts against raw material entering the chamber. 
The peripheral wall 42 is provided with a tangential port 68 to which is 
connected the duct 38. Still further, no anvils 56 are provided on the 
peripheral wall 42 for a substantial distance ahead of the port 68. 
Consequently, a certain portion of gaseous fluid and material can flow out 
of the chamber 40 through the duct 38 into the feed chamber 26. 
As previously indicated, partly comminuted material flows from the chamber 
16 through duct 34 back into the rotating anvil impact mill 14. It is 
accelerated into the mill 14 by means of a jet injection apparatus which 
comprises the nozzle 70 connected to a source of gaseous fluid (not shown) 
and the venturi 72. The duct 34 is connected between the nozzle 70 and 
venturi 72 so that the partly comminuted material is entrained in the gas 
emitted by nozzle 70. It is thereafter accelerated in the venturi 72 and 
carried into the chamber 40 against the rotating anvils 54 on rotor 48. As 
shown, the venturi 72 is connected at an angle to the radius of peripheral 
wall 42. Accordingly, the material flows into the chamber in a direction 
tangent to the periphery to the rotor 48 and it impacts against the 
rotating anvils 54 as well as any material flowing around the chamber 40 
adjacent the peripheral wall 42. Thus, further comminution takes place by 
impact against the anvil or against material within the chamber 40 in the 
zone 74. 
One advantage in providing a discrete rotating anvil-jet impact mill is the 
capability of higher rotor and anvil velocities by improving the support 
and drive structure for the shaft and rotor. Such an improved structure is 
illustrated in FIG. 3. As shown, the shaft 50 is keyed to a pulley 76 
driven by a belt 78 connected to a motor. The shaft 50 is supported by 
bearings on both sides of the chamber 40 of which only bearing 80 is 
illustrated inasmuch as the bearing on the opposing side is structurally 
the same. The shaft 50 extends through stuffing boxes 82 and 84. Only 
stuffing box 82 is illustrated in complete form inasmuch as stuffing box 
84 is structurally the same except it is positioned on the opposite side 
of chamber 40. 
Stuffing box 82 includes a flange 86 bolted, welded or otherwise fixed to 
the lateral wall 44. Flange 86 is provided with a plurality of 
conventional, heat-resistant packings 88 which are sealed into the box by 
means of a threaded gland 90. 
This structure provides support on both sides of the rotor and hence allows 
higher velocities. 
One of the difficulties with operating a rotating anvil jet impact mill is 
the tendency of the gas and material, which are above atmospheric 
pressure, to flow out of the mill along the drive shaft. This causes wear, 
particularly in the stuffing box, loss of stability, and difficulty in 
maintaining appropriate system pressure. To prevent this, each of the 
lateral walls 44 and 46 is provided with a open annular channel 92 and 94. 
Each of the channels surround the shaft 50 and is connected to a pipe 96 
and 98 respectively. Each of the pipes 96 and 98 is connected to a source 
of low pressure air. Still further, each of the channels 92 and 94 opens 
into the interior of the chamber 40 as indicated at 100 and 102. This 
allows low pressure gas to flow into the chamber without interfering with 
the flow of fluid and material within the chamber but at the same time 
preventing material and fluid from flowing along the shaft 50 thereby 
reducing the wear on the stuffing box. 
Another advantage of the design illustrated in FIG. 3 is that a hollow, 
water-cooled shaft can be provided. The structure shown in FIG. 4 of U.S. 
Pat. No. 3,688,991 operates at slow speeds but is inoperative at effective 
comminuting speeds, probably because the rotor and its shaft cannot be 
both statically and dynamically balanced. In accordance with the design in 
FIG. 3, the shaft can extend entirely through the casing 40 and be 
supported by bearings on both sides thereof. Still further, a nozzle 104 
can provide cooling fluid, such as water, which flows through the shaft 50 
and drains through the drain 106. Thus, the embodiment illustrated in FIG. 
3 provides a means for further improving the operation of the mill by 
cooling the stuffing box and other parts affected by heat. This may be 
particularly useful when steam is used as a gaseous fluid for carrying the 
material to be comminuted. 
In the operation of the comminuting apparatus illustrated in FIGS. 1, 2 and 
3, raw material is fed from the funnel 58 into the rotating anvil jet 
impact mill 14 where it is partly comminuted by impact against the 
rotating anvils 54. Typically, the anvils 54 are spaced approximately 1/4 
inch apart but this distance can be adjusted depending upon the materials 
being comminuted. Depending upon the pressure of the gas being used, some 
of the partly ground material flows out of mill 14 through duct 38 into 
feed chamber 26. There it flows in a vortical manner and is fed into the 
comminuting vortex within grinding and classifying chamber 16. The 
material is introduced at a point of low internal pressure and in a 
direction whereby it assists rather than detracts from the velocity of the 
operating vortex within chamber 16. 
The re-entrant circulating stream jet mill 12 operates in accordance with 
the general principles for such mills. As indicated above, it is provided 
with diverging lateral walls 20 and 22. It should be noted that the 
rotating anvils 54 act in the manner of fan blades to increase the 
velocity of the material-laden gas passing through duct 38 and into feed 
chamber 26. Thus they enhance the operation of feed chamber 26. The 
diverging walls 20 and 22 enhance the efficiency of the mill 12 by 
permitting an increased quantity of gas to flow within chamber 16. 
Material which has been comminuted to extremely fine size flows out through 
the outlet 24. Material which is partly comminuted flows through port 36 
and duct 34 into the space between jet 70 and venturi 72. At that point it 
is aspirated into the fluid, gas escaping from jet 70 and accelerated back 
into the mill 14. The material impacts the rotating anvils 54 and merges 
with the initial feed material and then returns as a thoroughly mixed feed 
and partly ground material to the feed chamber 26 as described above. 
The flow of material between mill continues until it has been comminuted to 
an extremely fine size. As indicated above, extremely fine size can be 
taken to be average particle sizes below 20 microns and, in most 
instances, below 10 microns. Indeed, for certain products it can be taken 
to mean particle sizes of less than 2 microns. 
A specific advantage of the present invention is that it permits the mill 
12 to be designed for optimum rotor speed independent of the size of the 
mill 12. Specifically, it allows even the smallest circulating stream jet 
mills to be used with rotating anvil-jet impact mills having maximum 
desireable anvil velocity. By way of example, a 24 inch circulating steam 
jet mill can be used with a 48 inch rotating anvil jet mill. This means 
that the rotor can revolve at half the revolutions per minute to achieve 
the same anvil velocity. This reduces wear and maintenance of the stuffing 
boxes as well as the bearings. This is particularly useful when 
comminuting spray dried and certain precipitated materials where 
velocities of 800 feet per second or greater provide improved comminution 
over lower velocities. 
Another advantage of having a discrete rotating anvil jet impact mill is 
the ability to use anvils 56 fixed to the inner periphery of the wall 42. 
Although this is sound practice in some impact mills, it is 
counter-productive if used in a Cyclo-Jet for producing finely classified 
product. Apparently, static anvils slow the rotational velocity of the 
material laden gases at the periphery and interfere with the speed of the 
classifying vortex. 
Referring now to FIG. 4, there is shown another embodiment of the present 
invention. Specifically, FIG. 4 illustrates a modified form of the 
re-entrant circulating stream jet mill designated 114. This mill is 
believed to be a preferred embodiment of circulating stream jet mill for 
use with a rotating anvil jet mill such as the mill 14 shown in FIG. 1. 
Only the parts of mill 114 which differ from the mill 12 are described in 
detail. Those parts of the mill 114 which are the same are indicated by 
the same number but with a prime associated therewith. Except where 
necessary for purposes of clarity, they will not be specifically referred 
to. 
The chamber 16' is closed by opposed lateral walls 116 and 118 which are 
divergent as illustrated. The point of greatest divergence is radially 
inward of the peripheral wall 18'. However, as illustrated, lateral walls 
116 and 118 include plane parallel portions indicated as 120 for the wall 
116 and 122 for the wall 118. 
Planar portion 122 of lateral wall 118 is positioned in the opening of feed 
chamber 124 which is cylindrical and functions in the same manner as feed 
chamber 26 in the embodiment of FIG. 1. Planar portion 122 is therefore a 
disk supported by a threaded post 126 bolted to the bottom of feed chamber 
124 by nut 128. Planar portion 122 is smaller in diameter than the opening 
of feed chamber 124 so as to provide a narrow annular opening into the 
mill proper. Feed material flows through this narrow circular opening 130 
into the interior of chamber 16'. Opening 130 is adjacent the circular jet 
tangent area for desirably feeding material from feed chamber 124. This 
arrangement is superior to the multiple feeding parts shown in U.S. Pat. 
Nos. 2,032,827 and 3,559,395. 
Mill 114 is a preferred form of re-entrant circulating stream jet mill 
which may be used with the rotating anvil jet mill of FIG. 1 or other 
embodiments thereof described herein. 
As indicated above, certain types of precipitated materials, as for 
example, titanium dioxide pigment and many spray-dried materials, are most 
effectively comminuted when the jets in the circulating stream jet mill 
entrain the partly ground material and scrub it along the lateral side 
walls. This scrubbing action comminutes the material by shear force in 
much the same manner that chalk is deposited on a chalk board. To be 
effective, the lateral side walls must be relatively close together 
because it is the expanding gas from the jets which provide this scrubbing 
or shearing action. The present invention provides an improved mill for 
comminuting of materials of the type which scrubbed along the surface of 
the lateral side walls. This is illustrated by reference to FIG. 5. 
As shown in FIG. 5, the comminuting apparatus includes a rotating anvil-jet 
stream mill 129 interconnected with a re-entrant circulating stream jet 
mill 131. Raw material is fed into the mill 129 from the funnel 132. 
Gaseous fluid from an appropriate source flows through nozzle 136. The 
gaseous material aspirates the raw material from funnel 132 and 
accelerates it in venturi 134. As shown, the venturi 134 is connected to 
the lateral wall 138 of chamber 135 at a position that is radially inward 
from the annular peripheral wall 144. Thus, the material is accelerated at 
an angle against the planar surface of rotor 140. This provides an initial 
scrubbing action. 
Rotor 140 is mounted on shaft 141. A plurality of anvils 142 are spaced at 
even intervals around the periphery of rotor 140. No fixed anvils are 
provided on the interior of annular wall 144 inasmuch as a shearing action 
for comminution is preferred. 
Material flowing within the chamber 135 is carried through duct 146 into 
the chamber 149. The material flows through the lateral wall 150 rather 
than into a feed chamber. The material is fed into the chamber adjacent 
the so-called jet tangent zone. 
The mill 131 includes an annular peripheral wall 154 with jets 155 
connected to the manifold 158. Manifold 158 is connected to an appropriate 
source of gaseous fluid through duct 160. The lateral walls 148 and 150 
are spaced through their radial extent so that the expanding jet laden 
with material scrubs both walls at the jet tangent circle. This point is 
chosen because the scrubbing effect would be minimized radially inward of 
the jet tangent circle whee only the finer fractions circulate. An outlet 
duct 152 is axially positioned in wall 148. 
Peripheral wall 155 is provided with a tangential outlet 161 connected to 
duct 162. Duct 162 is connected to a jet apparatus 164 comprising nozzle 
166 and venturi 168. Venturi 168 opens into the chamber 135 of mill 129 at 
a position spaced radially inward from the periphery of rotar 140. Thus, 
material flows out of mill 131 through duct 162. It is aspirated into the 
fluid escaping from nozzle 166 and accelerated against the surface of 
plate 140 to provide the scrubbing action. The material flows against 
rotor 140 in a direction opposite to the direction of rotation thereby 
enhancing the scrubbing action. 
It should be noted that the anvils 142 provide little if any comminuting 
action. Rather, in the embodiment of FIG. 5 they function mainly as fan 
blades for directing the flow of fluid within the chamber 155 and 
throughout the rest of the mill. For this reason, the anvils 142 can be 
made of a lighter construction than if they actually performed an anvil or 
impact action. 
The flow of material to and from each of the mills 129 and 131 is basically 
the same as the flow of material within the embodiment as illustrated in 
FIGS. 1-3, and therefore need not be described in detail. 
Although the embodiment of FIG. 5 performs particularly well for 
comminuting many precipitated materials and some spray-dried materials, it 
does not do well in comminuting tetrafluoroehylene (TFE) and combinations 
of TFE and polyethylene. For this purpose, another embodiment of the 
invention as illustrated in FIGS. 6 and 7 has been provided. This 
embodiment may use a re-entrant circulating stream jet mill such as is 
illustrated in FIG. 4 but with a discrete but interconnected rotating 
anvil jet impact mill as illustrated in FIGS. 6 and 7. 
As shown, the mill 170 includes a chamber 172 comprising an annular 
peripheral wall 174 and lateral side walls 176 and 178. A shaft 180 
extends through the chamber 172 and supports a novel rotor 182 which is 
best illustrated in FIG. 7. 
As shown, the rotor 182 comprises two concave discs 184 and 186 fixed to 
the shaft 180 by key means or the like. The discs diverge away from each 
other such that they are spaced farthest apart at their peripheries and 
abut each other adjacent the axis where they are joined to the shaft 180. 
Each of the discs 186 and 188 is provided with a plurality of fan blades 
188 spaced radially inward from the periphery thereof. 
The mill 170 is provided with a feed mechanism comprising the funnel 190, 
injector nozzle 192 and venturi 194 which function to feed raw material 
into the chamber through an opening in the peripheral wall 174. The manner 
of operation of this feed mechanism has been described in respect to other 
embodiments of this invention and therefore need not be further described. 
However, it should be noted that the venturi feeds the material through 
the peripheral wall 174 into the space between the two diverging discs 184 
and 186. 
Partly ground material is returned from the circulating stream jet mill 
through the duct 196. It flows into a zone between the injector nozzle 198 
and the venturi 200. In this manner, the returning partly comminuted 
material is aspirated into the fluid gas and accelerated through the 
venturi into the chamber 172. 
As illustrated in FIG. 7, the material flows into the chamber into the 
space between the two diverging discs 184 and 186. 
As best illustrated in FIG. 6, the venturies 194 and 200 direct the fluid 
and material into the chamber 172 against the direction of rotation of 
rotor 182. Moreover, their respective openings into the chamber 172 are 
spaced from each other at an angle of approximately 90.degree. about the 
peripheral wall 174. 
As previously indicated, the discs 184 and 186 are keyed to the shaft 180. 
Moreover, they are fixed to each other by any conventional means, such as 
bolts. They diverge from each other at an angle such that they are spaced 
apart at their periphery adjacent the annular wall 174 by a distance is 
approximately equal to or slightly greater than the port in the peripheral 
wall. 
By so shaping the discs, maximum advantage can be taken for the shearing 
action for comminuting materials such as TFE, polyethelyne or mixtures 
thereof. It has been determined that best results are obtained by using 
stainless steel for the discs 184 and 186. Still further, best results are 
obtained by injecting the raw material and the recirculated materials at 
an angle opposed to the direction of rotation. Thus, the venturi 194 is at 
an angle such that the material enters the space between the two discs 
radially outward from the shaft 180 and in a direction opposed to the 
direction of rotation for the discs. The same is true for the recirculated 
material entering from venturi 200 but at a different position on the 
annular wall 174. 
A series of tests was made to determine the relative percentage of 
reduction for TFE and mixtures of TFE and polyethelyne. It was determined 
that there is a reduction in the amount of energy required to comminate 
such materials. Further tests were made to determine the relative 
percentage of comminution in the circulating stream jet mill and the 
rotating anvil and jet mill. Although no conclusive proof was obtained, it 
does appear that on an energy basis the largest comminution was in the 
rotating anvil and jet mill while the circulating stream jet mill 
contributed mainly to classifying this difficult material. 
The embodiments of FIGS. 1-3, 4 and 5 illustrate the anvils as being on the 
outer periphery of the rotor. However, this is not always necessary. For 
some embodiments it may be desirable to otherwise position the anvil. In 
FIG. 8, the anvils 210 are mounted on one surface of the rotor adjacent 
the periphery thereof. This is useful where the direction of feed is 
through a lateral wall rather than the peripheral wall. 
In FIG. 9 the anvils 212 are on both the face of the rotor and its outer 
periphery. This is useful where the direction of feed is through a lateral 
wall but where it is also desirable to use stationary anvils 214 on the 
peripheral wall. 
From the foregoing, it should be apparent that by providing discrete but 
interconnected and interdependent re-entrant circulating stream and 
rotating anvil-jet mills, comminuting to extremely fine particle size can 
be provided. The use of such discrete but interconnected mills for the 
first time permits comminution to such particle size with increased 
efficiency by taking advantage of the combined interrelationship between 
the two mills while simultaneously operating the mills to their best 
advantage in an independent fashion. Examples include the capability of 
appropriate rotor and anvil design in the rotating anvil-jet mill and the 
use of diverging walls in the circulating stream jet mill. Other 
advantages include the capability of proper feed of the recirculating 
material in the circulating stream-jet mill and appropriate bearing design 
for high speeds in the rotating anvil-jet impact mill. of course, other 
examples of such advantages are described above. 
Finally, it should be noted that some but not all of the benefits of this 
invention may be obtained by not returning partly comminuted material to 
the rotating anvil jet mill. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and accordingly, 
reference should be made to the appended claims, rather than to the 
foregoing specification, as indicating the scope of the invention.