Note: Descriptions are shown in the official language in which they were submitted.
CA 02203~62 1997-04-23
A SIZE REDUCTION APPARATUS FOR COMMINUTING MATERIALS
Field Of The Invention
The present invention relates to apparatus for reducing the particle size of free
flowing m~t~ri~l~ and, in particular, to apparatus for reducing the particle size of free
flowing m~teri~l~ by impact and attrition.
Back~round Of The Invention
Size reduction is among the oldest of the arts, yet it is still widely practiced and
e~enti~l to a broad sector of modern industry. In general mechanical comminlltion is
accomplished by one of two processes, rupturing by co,l,pression or bursting andattrition using kinetic energy. The first process is practiced using roller mills, jaw
crushers, pendulum mills or the like. The second process is practiced using h~mmer
mills, pin mills, jet mills or the like.
Modern methods for producing fine-grained materials are generally very energy
intensive and, consequently, tend to be costly. However, the demand for fine-grained
materials is quite high, so that any reduction in energy consumption that can berealized is very important. Many different types of mills have been invented forreducing particle size by impact and attrition. Among the most relevant to the present
invention are those described in British Patent 1 601 129, and United States Patents
2,750,120 and 4,697,743.
British Patent 1 601 129 to British Steam Specialities Limited was published on
October 28, 1981. It describes an apparatus for reducing the size of fatty and moist
materials and agglomerates which would normally block conventional size reducingapparatus. The apparatus comprises a grinding chamber having a frusto-conical
shaped, apertured side wall, and a blade element which is turned about an axis in the
grinding chamber to force material through the apertures in the sidewall. The blade
element is of an open planar frame construction and preferably made from round rod
that is shaped in an open frusto-conical profile. While this machine is eff1cacious for
its intended purpose, experimentation has shown that it is not well adapted for the size
reduction of hard materials.
CA 02203~62 1997-04-23
United States Patent 2,750,120 which issued June 12, 1956 to P~llm~nn
describes an apparatus for mechanically ~ integrating materials into small particles,
including materials that defy processing by conventional grinding devices. The
apparatus comprises a pair of impact shells respectively having facing, concave
5 configuration to form an impact chamber with a peripheral discharge slot. One of the
shells is mounted in a stationary position and the other is mounted to rotate with
respect to the first. A multi-bladed impact rotor is mounted for rotation inside the
impact chamber, the impact rotor having tips which provide limited clearance in a
restricted region adjacent the discharge slot to break the material to be comminuted
10 into small particles before it is discharged through the slot. The rotatable shell and the
impact rotor are preferably counter rotated to enhance the comminution of material.
While this m~.hine is apparently effective in reducing the size of a wide range of
materials, it is quite bulky, expensive to construct and not particularly energy efficient
because it requires two drive motors, one for impact rotor and one for the impact shell.
United States Patent 4,697,743 which issued October 6, 1987 to Bjorck et al.
describes a method and al)p~dlus for finely crushing particles of material in an impact
mill. The particles to be colllmillul~d are passed through a feeding tube or channel to
a crushing chamber cont~ining a rotor having its axle parallel to the feeding tube and
having first impact surfaces on the rotor impact the particles and drive them into
20 stationary impact surfaces located about a periphery of the crushing chamber and
positioned so that the particles impact them at substantially right angles to their line of
travel. In order to facilitate the efficient use of the kinetic energy, the crushing
chamber and the feed tube are evacuated so that the rotor rotates in a vacuum. Adischarge orifice is located on one side of the crushing chamber to permit crushed
25 particles to discharge by gravity from the chamber. A recirculation system may be
provided to recirculate oversized particles back through the crushing chamber. This
apparatus is particularly adapted to reducing hard materials to very small particle sizes
of 1011 or less. It is not adapted to the high volume, energy efficient size reduction of
food materials such as seeds or grains for the production of flours, pastes or granules.
CA 02203~62 1997-04-23
Summary Of The Invention
It is an object of the present invention to provide a simple, energy efficient
a~p~dlus for reducing the particle size of free flowing materials, including materials
that are tough, soft, hard, dry or oily.
It is a further object of the invention to provide an dpp~LldlUS for reducing the
particle size of free flowing materials which is inexpensive to construct and m~in1~in.
It is yet a further object of the invention to provide an apparatus for reducingthe particle size of free flowing materials which can produce particles of from about 25
mm to about lOIl in size in a single pass, with a short residence time in the
com~ lulion chamber.
In accordance with the invention, there is provided a size reduction apparatus
for comminuting m~teri~1~, comprising in combination: a housing surrounding a
commin11tion chamber, an impeller rotatable in the commin11tion chamber, a size
reduction screen disposed about a periphery of the comminution chamber, a propeller
l 5 disposed within the housing beneath the comminution chamber, the propeller being
disposed in a plane that is parallel to a plane of the impeller; a material inlet opening
in the housing for introducing material to be comminuted, the inlet opening being
adapted to permit the introduction of material into the comminution chamber; a
material outlet opening in the housing for ejecting comminuted material from thehousing; and, at least one shaft for turning the impeller to commin11te materialintroduced in to the comminution chamber and for turning the propeller to eject
comminuted material from the housing.
The size reduction dppaldlus for cor~ ;tlg materials in accordance with the
invention therefore provides a very simple machine which is inexpensively constructed
but is very efficient in comminuting a wide variety of materials useful in the food,
chemical, and pharmaceutical industries, to name but a few. The principal components
of the apparatus are an impeller which rotates inside a comminution chamber and a
propeller which rotates in a plane parallel with the impeller beneath the comminution
chamber and is disposed within a housing that surrounds the comminution chamber.The comminution chamber preferably has a solid top and bottom wall and a frusto-conical sidewall that is perforated to form a cornminution screen. The comminution
screen is preferably constructed of a plurality of screen segments which fit together
CA 02203~62 1997-04-23
end-to-end to form the frusto-conical screen. The screen segments are preferably made
from a thick steel stock that can be more than 200% thicker than the diameter of the
apertures through which comminuted material passes.
The segmented comminution screen has several advantages. First, it can be
5 made of heavier material than is possible if the screen is made in a single piece.
Second, if a segment is accidentally damaged, only the damaged segments need be
replaced. Third, segments of different aperture size or surface texture can be
interspersed to improve efficiency or to provide a comminuted material with a desired
range of particle sizes without multiple passes and post mixing.
The impeller can be made in any desired configuration, but preferably has an
outer cutting edge that rotates in close proximity to the comminution screen. Ingeneral, the larger a side surface area of the impeller, the more air flow is induced
through the machine and, consequently, the larger the particle size of the finished
product, regardless of other factors. Conversely, the smaller the side surface area of
15 the impeller, the less air is induced to flow through the comminution chamber. This
increases the residence time of material in the comminution chamber and therefore
reduces particle size, regardless of other factors.
The propeller serves the function of counterbalancing the air flow induced by
the impeller, serves as a beater to further reduce particle size, and ejects comminuted
20 material from the machine. The propeller is preferably driven by the same shaft as the
impeller. The orientation of the propeller with respect to the impeller is preferably
adjustable. The orientation of the propeller with respect to the impeller has an affect
on the residence time of material in the comminution chamber, and therefore has an
affect of particle size. An optimum angle between the propeller and the impeller25 depends on the material being comminuted and the desired particle size. In general, an
angle of about 45~ to 67~ provides the smallest particle size without affecting
throughput.
Comminuted material is preferably ejected from the machine through a
discharge tube which may be oriented in the direction of rotation of the
30 impeller/propeller, or in a direction counter to their direction of rotation. The
orientation of the discharge tube also has an affect on the residence time of material in
the machine and, therefore, an affect on the particle size of the comminuted material.
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If the discharge tube is oriented in the direction of rotation, the throughput increases
and the particle size increases, other factors being unchanged. On the other hand,
when the discharge tube is oriented in the opposite direction, the particle size is
decreased and the throughput decreases.
As a general rule, for any given material to be comminuted by the apparatus in
accordance with the invention, a given surface area per unit of time can be throughput.
Thus, for instance, if a coarse meal is to be produced from a grain, the weight per unit
of time throughput will be much greater than the weight per unit of time when a fine
flour is made from the same grain, but the surface area of the cornminuted material per
unit of time will remain about constant.
Brief Description Of The Drawin~s
The present invention will now be explained by way of example only and with
reference to the following drawings wherein:
FIG. 1 is an elevational view of a size reduction appaldl~ls installed in an
operational condition on an installation base;
FIG. 2 is an axial cross-section of the size reduction appalalus taken along lines
II-II of FIG. 1;
FIG. 3 is a radial cross-sectional view of the size reduction apparatus taken
along lines III-III of FIG. 2;
FIG. 4, which appears on sheet one of the drawings, is an elevational view of
one configuration for a comminution screen segment in accordance with the invention;
and
FIG. 5, which also appears on sheet one of the drawings, is an elevational view
of three preferred configurations for impellers for use in the size reduction apparatus in
accordance with the invention.
Detailed Description Of The Preferred Embodiment
FIG. 1 shows an elevational view of a size reduction apparatus, generally
indicated by the reference 10, in accordance with the invention installed on a support
base 12 and connected by a plurality of v-belts 14 to an electric motor 17 whichpowers the size reduction apparatus 10. The size reduction apparatus includes a
CA 02203~62 1997-04-23
tr~n~mi.~ion stand 16 which supports a comminution housing 18, the structure andfunction of which will be explained in detail with reference to FIGS. 2 and 3.
Attached to a top of the comminution housing 18 is a material inlet opening 20. The
electric motor 17 preferably has a torque rating of 15 to 50 horsepower.
FIG. 2 shows an axial cross-sectional view of the size reduction al~palaLus 10
taken along lines II-II of FIG. 1. As explained above, the si~ reduction al)palatus
includes a tr~n~mi~ion stand 16 which supports a comminution housing 18. The
comminution housing 18 is bolted to the tr~n~mi~ion stand 16 by bolts 22. The
tr~n~mi~sion stand 16 rotatably supports a drive shaft 24 which is equipped on its
lower end with a multi-groove pulley 26 to which the v-belts 14 (see FIG. 1) areconnected. Located within the comminution housing 18 is a comminution chamber,
generally indicated by the reference 28. The co~ inution chamber includes a top
plate 30, a bottom plate 32, and a peripheral comminution screen 34, the structure of
which will be explained in more detail with reference to FIGS. 3 and 4. Attached to
the drive shaft 24 and rotatable therewith is an impeller 36 located in the collllllinu~ion
chamber 34. The impeller 36 is preferably provided with two opposing blades affixed
to an impeller hub 38 which is in turn removably affixed to the drive shaft 24 using a
key, or the like. Positioned beneath the collllllillution chamber 28 and also attached to
the drive shaft 24 and rotatable therewith is a propeller 38. The propeller is likewise
keyed, or otherwise removably attached to the drive shaft 24.
The comminution chamber 28 is supported in the comminution housing by a
plurality of comminution chamber support brackets 33 which are secured to a top wall
56 of the comminl-tion housing by a pair of bolts 58. The comminlltion chamber top
plate is removable to permit the impeller 36 and the comminution screen 34 to beserviced. The collllllhlution chamber top plate 30 is clamped in place by a plurality of
brackets 60. Each bracket 60 is secured by a bolt which passes through a slot 64. The
bolt 62 is threaded into the comrninution housing top wall 56 and the comminution
chamber support brackets 33. When the bolt 62 is tightened with the bracket 60 in the
locking position (as illustrated) the comminution chamber top plate 30 is lockedsecurely in place. If all bolts 62 are loosened and the brackets 60 slid outwardly to a
released position, the comminution chamber top plate can be removed so that the
impeller 36 and the comminution screen 34 can be accessed for maintenance.
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Material to be comminuted is introduced through the material inlet opening 20.
The rate of introduction is dependent upon the power rating of the motor 17 (see FIG.
1) as well as the friability of the material to be comminuted. In general, it ispreferable to control the inflow of material to be comminuted through the material
5 inlet opening 20 using a computer controlled feed mech~ni~m such as described in
United States Patent 5,240,324 which is incorporated herein by reference. The
material is introduced through the material inlet opening 20 to the center of the
comminution chamber where it is forced outwardly by centrifugal force created by the
rotating impeller 36. The impact of the impeller with the material causes the material
10 to rupture. In addition, attrition of the material occurs between an outer end of the
impeller and the comminution screen 34, as will be explained in more detail withreference to FIG. 3. Once the material has been reduced in particle size, it is ejected
into the comminution housing where it may impact the propeller 38 and/or the walls of
the comminution housing 18. Because the apertures in the comminution screen 34 are
15 oriented at right angles to the direction of travel the impeller 36, the particles ejected
from the comminution chamber are an average considerably smaller than the aperture
diameter. Eventually, the comminuted material is ejected through the material outlet
21 which is preferably rotatable to be oriented in a direction that is aligned with the
direction of rotation of the impeller and the propeller or counter to the direction of
20 rotation of the impeller and the propeller as will be explained in more detail below. In
general, the propeller 38 serves three functions. First, it counterbalances air flow
through the size reduction apparatus 10 induced by the impeller 36. The extent of this
counterbalancing action is dependent on an angular relationship between the impeller
36 and the propeller 38 as will be explained in more detail with relation to FIGS. 3
25 and Table II. Second, the propeller acts as a beater which can be effective in further
reducing particle size. Finally, the impeller 38 creates a centrifugal force to eject
comminuted material from the size reduction apparatus 10 through the material outlet
21.
FIG. 3 shows a radial cross-sectional view of the size reduction apparatus 10
30 taken along lines III-III of FIG. 2. The impeller 36 rotates in the comminution
chamber 28, and the propeller 38 rotates in the comminution housing 18 beneath
comminution chamber 28. The side wall of the comminution chamber 28 is the
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,
comminution screen 34 which is preferably constructed from a plurality of
comminution screen segments 40. Each segment is locked in place in a groove 42 (see
FI(~. 2) located between a screen segment support bracket 44 and a ridge machined in
the respective top plate 30 and the bottom plate 32 of the comminution chamber 28.
The advantages of a segmented comminution screen are several. First, if a screensegment is damaged by foreign material entering the comminution chamber, that
segment can be replaced without the expense of replacing the entire screen. Second,
segments having di~elellt aperture sizes can be inserted to accommodate different
requirements in terms of particle size so that specific proportions of given particle sizes
can be produced in a single run without post mixing by properly adjusting the
apertures in the various segments of the comminution screen. Third, because the
segments are easier to machine than a single piece screen, the segments can be much
thicker than otherwise possible. The screen therefore lasts much longer and permits
the comminution of very hard materials, which would otherwise be impossible to
grind.
As shown in FIG. 3, the direction of rotation of the impeller 36 and the
propeller 38 are usually clockwise, though a counterclockwise rotation is equally
effective. Normally, the propeller 38 is preferably offset from the impeller 36 so that
they are not aligned. The offset is indicated in FIG. 3 by an angle A. The offset of
the propeller 38 from the impeller 36 affects to a certain degree the particle size of the
comminuted material because the propeller counterbalances air flow through the size
reduction aLp~alus 10 and therefore affects the residence time of material in the
comminution chamber 28. An ideal angle between the propeller 38 and the impeller36 depends upon the desired particle size and the material to be processed. In general,
testing indicates that an angle of about 45~ to about 67~ provides the greatest reduction
in particle size without affecting the throughput of the apparatus. This relationship is
discussed in more detail below in reference to Table II. As briefly described above,
the material outlet 21 is preferably rotatably attached to the comminution housing 18
so that it may be oriented in a direction counter to the direction of rotation of the
impeller 36 and the propeller 38 as shown in FIG. 3, or in alignment with that
direction of rotation (not illustrated). The orientation of the material outlet 21 also has
an affect on the particle size of materials comminuted by the size reduction apparatus
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. .
lO. In general, the orientation shown in FIG. 2 provides the greatest reduction in
particle size, though some increase in output temperature and some decrease in
throughput is experienced. As noted above, as a general rule, for any given material to
be comminuted by the size reduction al)p~dlus 10, a given surface area per unit of
time can be throughput using a motor 16 of a given power rating. Ch~nging the
orientation of the material outlet 21 is a further parameter for controlling particle size.
FIG. 4 shows a potential configuration for a comminution screen segment 40.
As noted above, the comminution of certain tough, dry or hard materials may be
facilitated by providing a textured surface on an inside surface of the comminution
screen segments 40. For instance, ridges or grooves 46 may be interspersed with
comminution apertures 48. Many other grooved or ridged configurations are also
possible, as will be al~pa~ t to those skilled in the art. It is well known that textured
surfaces on commimltion screens can facilitate the comminution of certain materials.
The screen segments 40 may be constructed from durable materials such as steel or
stainless steel. They are preferably tempered and may be case hardened or surface
treated with a wear resistant agent such as carbide steel, or the like.
FIG. S shows three preferred configurations for the impeller 36. Each impeller
has a shaft attachment portion 49 and a hammer portion 54. The first configuration is
the impeller shown in FIG. 2 wherein a substantially rectangular impeller fits closely
within the comll~hlulion chamber 28. This configuration induces the greatest air flow
through the size reduction apparatus 10. Air is drawn in along with material to be
comminuted through the material input opening 20. In general, the greater the air flow
through the size reduction apparatus 10, the greater the throughput and the greater the
particle size of the comminuted material, all other factors being constant.
The second configuration of the impeller 36 includes a rectangular or a
trapezoidal window 50 which reduces air flow through the size reduction apparatus 10
and consequently increase residence time in the comminution chamber, thereby
generally reducing particle size of the comminuted material. The third preferredconfiguration for the impeller 36 includes a narrow shank 52 which connects the inner
and outer ends of the impeller. This configuration induces the least air flow through
the chamber and consequently generally produces comminuted material of the finest
particle size. If very fine particles are to be output, this impeller is the preferred
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' '' 10
configuration Each of the impeller configurations is also preferably provided with a
hardened cutting insert which is welded, bolted or otherwise affixed to the hammer
portion 54 in a manner well known in the art to an outer end of the impeller 36. The
hardened insert may be constructed of a hardened steel, solid carbide or a metal coated
5 or penetrated with hard chrome, ceramic or carbide. The hardened cutting insert 54
helps extend the effective life of the impeller 36 arld consequently reduces
maintenance.
Table I shows test results of a variety of food materials cornminuted using a
size reduction a~aldl~ls 10 in accordance with ~e invention. Column 1 of the table
10 shows the material comminuted. Column 2 shows the product produced as a result of
the cornrninution, colurnn 3 shows the output in pounds per hour, column 4 shows the
particle size of the cornminuted material and colurnn 5 shows the power rating of the
motor that powered ~e size reduction a~p~lus 10 used for cornminution.
TABLE I
MATERIAL PRODUCT OUTPUT PARTICLE SIZE POWER
RATnNG
Oat Husk Powder 300 Ib/hr 50% <100 USS 40 amps
35% <40 USS
Wheat Bran Powder 350 Ib/hr 85% <100 USS 40 amps
Wheat Bran Increase Bulk 2000 IbAIr 34% <16 USS 40 amps
Density
Durum Wheat Flour 420 Ib/hr 77% <80 USS 4Q amps
Brown Rice Coarse Flour 900 Ib/hr 52% <100 11 40 amps
Brown Rice Fine Flour 500 Ib/hr 71% <100 ~1 40 amps
Cinnamon Bark Powder 400 Ib/hr 66% <100 !1 40 amps
60% <120 ~
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- ' 11
Mushroom and Powder 100 Ib/hr 60% <120 11 30 amps
Stems-Dried
-Shitake
Whole Hard Bread Flour 500 Ib/hr 52% <80 USS 40 amps
S Wheat
Flour Cake and High Ratio 1500 Ib/hr 99.5% <270 USS 40 amps
Pastry- Soft, Flour
Wheat
Chlorinated
Wheat Germ Flour 500 Ib/hr 75% <100 USS 35 amps
Whole Soybean Fine Flour 1150 Ib/hr 81% <100 USS 40 amps
Whole Soybean Coarse Flour 2000 Ib/hr 65% <100 USS 40 amps
Whole Soybean Meal 5200 Ib/hr 20% <100 USS 40 amps
80% ~20 USS
Depending on the particle size and the material to be comminuted, a size
reduction ~3al~lus 10 in accordance with the invention can output from 100 to 5200
lbs/hr at temperatures which range generally from 120~F to about 180~F. Most
materials process at about 120~F. Tough, dry materials are heat generating but if
throughput is controlled, the temperature at the material outlet 21 generally will not
20 exceed 180~F.
As discussed above, the angle A of separation between the propeller and the
impeller also has an affect on particle size without noticeably affecting output of the
size reduction apparatus 10 in accordance with the invention. Table II shows theresults of a test to determine the affect of angle A on the particle size of durum wheat
25 tailings processed by the size reduction apparatus 10. Column 2 of Table II shows the
angle A (see FIG. 2). Column 3 shows the output in pounds per hour of flour
produced during the test. Column 4 shows the particle size of the flour produced and
column 5 shows the power consumption.
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12
MATERIAL ANGLE A OUTPUT PARTICLE SIZE POWER
CONSUMPTION
Durum Wheat 90~ 750 lb/hr32%~80 USS Mesh 20 amps
Tailings 120~F
Durum Wheat 22.5 750 Ib/hr32%<80 USS Mesh 22 amps
Tailings 120~F
Durum Wheat 45.0 750 Ib/hr42%<80 USS Mesh 22 amps
Tailings 120~F
Durum Wheat 67.0 750 Ib/hr39%<80 USS Mesh 22 amps
Tailings
As is aLpa~ , the least power was consumed while producing about 750 lbs of
flour per hour when angle A was set at 90~. A fine flour was produced with about32% being less than 80 USS Mesh with an output temperature of about 120~F. An
angle A of 22.5 for the production of durum wheat flour consumed 22 arnps to
produce 750 lbs of flour per hour with no change in particle size, the particle size
being 32% less than 80 USS Mesh. The output temperature was also 120~. When
angle A was increased to 45~, the output remained constant at 750 lbs/hr and the power
consumption remained constant at 22 amps but the particle size of the flour was
20 reduced so that 42% was less than 80 USS Mesh while the output temperature
remained constant at 120~F. At 67~ for angle A, the output remained constant as did
the power consumption while the particle size increased slightly so that 39% was less
than 80 USS Mesh. In general, an angle A of 45~ to 67~ is preferred when the greatest
reduction in particle size is desired. If energy consumption is more important than
25 particle size then angle A should be set at about 90~.
While the examples documented above relate to the comminution of food stuffs,
it will be appreciated by those in the art that the size reduction apparatus 10 in
accordance with the invention is equally adapted to the comminution of chemicals,
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! ~
; ~ 13
pharmaceuticals, and other industrial products such as plastics, fibrous plant materials,
etc.
Changes and modifications to the illustrative embodiment will be apparent to
those skilled in the art. The scope of the invention is therefore intended to be limited
S solely by the scope of the appended claims.
