U.S. patent number 3,682,399 [Application Number 04/810,183] was granted by the patent office on 1972-08-08 for apparatus for comminuting and dispersing solid particles.
This patent grant is currently assigned to Vyzkumny Ustav Organickych Syntez. Invention is credited to Vladislav Bicik, Jan Kaspar.
United States Patent |
3,682,399 |
Kaspar , et al. |
August 8, 1972 |
APPARATUS FOR COMMINUTING AND DISPERSING SOLID PARTICLES
Abstract
Apparatus for comminuting dry solid particles to a size of one
micron or less comprises a vessel which contains a supply of balls
agitated by one or more disks mounted on a shaft which is coaxial
with and extends into the vessel. The comminuted material is
evacuated by gravity or by conveying a gas through the interior of
the vessel. The diameters of balls do not exceed 5 millimeters and
the diameters of agitating disks are between 70 and 90 percent of
internal diameter of the vessel.
Inventors: |
Kaspar; Jan (Pardubice,
CS), Bicik; Vladislav (Pardubice, CS) |
Assignee: |
Vyzkumny Ustav Organickych
Syntez (Pardubice, CS)
|
Family
ID: |
25203221 |
Appl.
No.: |
04/810,183 |
Filed: |
March 25, 1969 |
Current U.S.
Class: |
241/50; 241/54;
241/172 |
Current CPC
Class: |
B02C
17/16 (20130101) |
Current International
Class: |
B02C
17/16 (20060101); B02c 017/16 () |
Field of
Search: |
;241/46.02,47.50,171,172 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kelly; Donald G.
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims:
1. Apparatus for comminuting and dispersing solid particles to form
a mass of finely comminuted solid material, said apparatus
comprising a vessel having an internal chamber provided with inlet
means for admission of solid particles and outlet means for
evacuation of comminuted material; agitating means comprising a
drive shaft extending into said chamber and at least one
substantially disk-shaped agitating member provided on said drive
shaft in the interior of said vessel; a supply of discrete
dispersing elements in said chamber, said elements being arranged
to move in response to rotation of said agitating means to thereby
convert solid particles admitted through said inlet means into
finely comminuted material; a source of compressed gas; and second
inlet means for admitting gas from said source into said chamber so
that the thus admitted gas carries comminuted material toward and
into said outlet means.
2. Apparatus as defined in claim 1, wherein said vessel comprises a
cylindrical internal surface and wherein said shaft is coaxial with
said vessel.
3. Apparatus as defined in claim 2, wherein the diameter of said
disk-shaped agitating member is between 70 and 90 percent of the
diameter of said chamber.
4. Apparatus as defined in claim 2, wherein the angle of
inclination of the common axis of said shaft and said vessel with
reference to a horizontal plane does not exceed 45 degrees.
5. Apparatus as defined in claim 1, wherein said agitating means
comprises a plurality of agitating members spaced from each other
in the axial direction of said shaft by distances corresponding to
between 20 and 50 percent of the diameter of an agitating
member.
6. Apparatus as defined in claim 1, wherein said outlet means is
arranged to discharge comminuted material and gases upwardly from
said chamber.
7. Apparatus as defined in claim 1, wherein the maximum dimensions
of said dispersing elements are in the range of between 0.1 and 5
millimeters.
8. Apparatus as defined in claim 1, further comprising confining
means for retaining the dispersing elements and solid particles
whose size exceeds a predetermined value in said chamber.
9. Apparatus as defined in claim 8, wherein said confining means
comprises a filter in the region of said outlet means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improvements in apparatus for
comminuting and dispersing solid particles. More particularly, the
invention relates to improvements in apparatus of the class
including so-called ball mills, stream mills and like machines
wherein dry solid particles are comminuted by balls or analogous
dispersing elements which are agitated in the interior of a vessel.
Still more particularly, the invention relates to improvements in
apparatus which are especially suited for breaking up solid
granular or like material into minute particles with a size in the
range of one or more microns or a fraction of a micron. The
definition "breaking up" is intended to embrace reducing the size
of larger solid particles so that they yield smaller particles as
well as separating agglomerations of smaller particles into a mass
of discrete particles.
It was found that, once the material which is treated in
conventional ball mills or analogous apparatus reaches a certain
degree of fineness, no further refinement takes place even if the
material remains in the apparatus for extended periods of time.
Reference may be had, for example, to German Pat. Nos. 589,796,
592,105 and 642,127 which disclose such types of apparatus. It was
further found that the time required to reduce the size of solid
particles in conventional apparatus, especially if the particles
are to be converted into a mass of finely comminuted material, is
very long so that the operation of such apparatus is uneconomical.
This is attributed to the fact that conventional apparatus utilize
relatively large balls or analogous dispersing elements, normally
with a diameter of about 20 millimeters. If such balls are used to
break up particles to a size of about 0.001 millimeter, the ratio
of the size of particles of the ultimate product to the size of the
balls is about 1:20,000; therefore, the probability of satisfactory
impact of comminuted material against the balls depends too much on
the roughness of external surfaces of balls and on the speed at
which the balls are agitated in the interior of the vessel, i.e.,
on frequency of impact of balls against one another. As a rule, the
device which agitates the balls cannot be rotated at a speed which
exceeds a predetermined value. It was further found that, in
conventional apparatus, the efficiency does not depend on the
energy of collisions between particles of comminuted material and
the balls. The comminuting action is terminated when the comminuted
particles cease to move with reference to each other and with
reference to the balls. Some but not all of the above enumerated
problems are eliminated when the dispersing elements fill only a
certain portion of the interior of the vessel.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a novel and improved
apparatus which is capable of comminuting solid particles to a size
of one micron or less in a time-saving operation.
Another object of the invention is to provide an apparatus which
can break up agglomerations of coherent particles or which can be
used to break up discrete solid particles in a small area, faster
than in conventional apparatus, and with a higher degree of
efficiency.
A further object of the invention is to provide the apparatus with
novel agitating means for balls or analogous dispersing
elements.
Our invention is based on the recognition that the dispersing
elements can comminute solid particles with greater efficiency and
more economically if the mixture of solid particles and dispersing
elements is agitated at a high speed, if the ratio of maximum
dimensions of dispersing elements to maximum dimensions of admitted
solid particles is less than in conventional apparatus, and if the
dispersing elements and solid particles are maintained in motion by
novel agitating means. The agitating means is designed in such a
way that the entire contents of the vessel are kept in constant
motion and that the contents of the vessel fill the latter when the
apparatus is in use even though the combined volume of solids is
substantially less than the capacity of the vessel when the
apparatus is idle.
The novel features which are considered as characteristic of the
invention are set forth in particular in the appended claims. The
improved apparatus itself, however, both as to its construction and
its mode of operation, together with additional features and
advantages thereof, will be best understood upon perusal of the
following detailed description of certain specific embodiments with
reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a partly schematic and partly vertical sectional view of
a dispersing and comminuting apparatus which embodies one form of
our invention;
FIG. 2 is a fragmentary schematic sectional view of a second
apparatus;
FIG. 3 is a fragmentary schematic sectional view of a third
apparatus which constitutes a modification of the apparatus shown
in FIG. 2;
FIG. 4 is a fragmentary schematic sectional view of a fourth
apparatus which is similar to the apparatus of FIG. 3;
FIG. 5 is a fragmentary schematic sectional view of a fifth
apparatus comprising a rotary separator which is built into its
vessel;
FIG. 6 is a fragmentary schematic sectional view of a sixth
apparatus which comprises an externally mounted separator;
FIG. 7 is a fragmentary schematic sectional view of a seventh
apparatus which constitutes a modification of the apparatus shown
in FIG. 6;
FIG. 8 is a schematic partly sectional and partly elevational view
of a further apparatus with two externally mounted separators;
FIG. 9 is a schematic sectional view of a multi-stage separator
which can be utilized in the apparatus of FIGS. 1 to 8; and
FIG. 10 is a similar schematic sectional view of a modified
multi-stage separator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown an apparatus which
comprises a horizontal cylindrical vessel or container 1 which
contains a supply of dispersing elements 30. Such dispersing
elements (hereinafter called balls for short) may be of spherical,
ovoid, polygonal or other regular or irregular shape and are kept
in motion by agitating members 5 mounted on a horizontal drive
shaft 4 which is coaxial with the vessel 1. Particles of sand can
be used as dispersing elements. The shaft 4 extends through a
stuffing box 31 in the left-hand end wall 2 of the vessel 1 and is
journalled in bearings 32, 33 provided in brackets 34, 35 carried
by a base member 36. The left-hand end of the shaft 4 is fixed to a
pulley 37 which is driven by an electric motor or another suitable
prime mover through the intermediary of V-belts, not shown. The
vessel 1 is provided with an inlet 6 which is adjacent to the end
wall 2 and serves to admit dry solid particles which are comminuted
in the chamber 1a of the vessel and are thereupon evacuated by way
of an outlet 8 adjacent to the right-hand end wall 3 of the vessel.
A screen or filter 9 of fine mesh is installed in the outlet 8 to
confine the balls 30 in the chamber 1a. Since the dispersed
material is evacuated upwardly (by way of the outlet 8), the vessel
1 is preferably further provided with a second inlet 7 which admits
a gas serving as a carrier to entrain comminuted particles through
the interstices of the filter 9 and upwardly through the outlet 8.
The inlet 7 is connected to a source 38 of compressed fluid, e.g.,
air or an inert gas (such as nitrogen).
The vessel 1 includes a jacket 39 provided with an inlet 40 and an
outlet 41. The compartment defined by the jacket 39 serves to
accommodate circulating heating or cooling fluid (gas or liquid) if
and when a heating or cooling of solid particles is necessary. If
the fluid entering at 40 is a heating medium, the apparatus further
comprises a heat exchanger 42 which maintains the circulating
medium at a desired temperature. The vessel 1 (or the gas which is
admitted by way of inlet 7) is cooled if the particles admitted
through the inlet 6 are soft at room temperature or when the
treatment at room temperature or above room temperature would
adversely affect the color, quality or other characteristics of
treated material.
The mixture of balls 30 and solid particles preferably fills
between 40 and 85 percent of the chamber 1a. The volumetric ratio
of balls 30 to solid particles in the chamber 1a is between 0.3 and
10 to one, preferably between two and 10 to one, i.e., the volume
occupied by balls is preferably a multiple of the volume occupied
by solid particles. The remaining part of the chamber 1a (namely,
between 15 and 60 percent) is filled with gas. When the shaft 4 is
idle, the chamber 1a accommodates three layers including a lower
layer of balls 30, a median layer of solid particles, and an upper
layer of gas. Of course, finer solid particles penetrate into the
gaps between the balls 30 in the lower layer. When the shaft 4 is
rotated at a high speed, the gas, solid particles and balls 30 form
a homogeneous mixture which fills the entire chamber 1a.
The means for feeding solid particles from a hopper 43 or another
suitable source to the inlet 6 may comprise a screw conveyor 44 or
the like. The conduit connecting the source 38 with the inlet 7
preferably accommodates an adjustable pressure regulating valve 45
so that the operator can select the rate of admission and pressure
of the gaseous carrier as a function of the speed of comminuted
particles which are to be evacuated through the interstices of the
filter 9.
For example, the apparatus of FIG. 1 may employ a vessel 1 having
an internal diameter of 300 millimeters and an axial length of 420
millimeters, a total of seven agitating members 5 each having a
diameter of 260 millimeters, and the distance between adjoining
agitating members may be 60 millimeters. The valve 45 may be
adjusted to admit gas at the rate of 10 cubic meters per hour. The
pressure of gas which is admitted via inlet 7 need not be high.
Such gas must overcome the resistance of the filter 9 and the
resistance of filter or filters (to be described in connection with
FIGS. 8 to 10) which are used to separate the gaseous carrier from
finely comminuted material. As a rule, and particularly when the
outlet discharges comminuted material downwardly, the comminuting
and dispersing operation is carried out at normal pressure.
Nitrogen or another inert gas is employed when the apparatus is
used in an area where an explosion is likely to occur or when the
material to be comminuted should not be mixed with oxygen.
The interstices of the filter 9 should be small enough to prevent
escape of freshly introduced solid particles and/or the escape of
balls 30. It is normally sufficient if the size of interstices in
the filter 90 is about 50 percent of the size of particles which
are admitted by way of the inlet 6. The filter 9 may be a sheet of
textile material or a sheet which is formed with slits or other
types of openings. The size of particles which are admitted from
the source 43 is preferably less than 500 microns, most preferably
between 100 and 300 microns or even less than 100 microns. The
fineness of comminuted material depends on the grinding time; the
size of particles which are evacuated by way of the outlet 8 may be
in the range of one micron or even less than one micron. The
grinding time is variable and depends on the desired size of finely
comminuted material. Such grinding time may vary between one or
more minutes and one or more hours. In normal operation, the
contents of the chamber 1a are maintained at or slightly above room
temperature, for example, at 30.degree. C, provided that the
material admitted via inlet 6 is solid at such temperature.
If desired or necessary, the apparatus may be mounted in such a way
that the common axis of the shaft 4 and vessel 1 is inclined with
reference to a horizontal plane. The angle of inclination with
reference to such horizontal plane is preferably less than
60.degree., most preferably less than 45.degree. .
The ability of our apparatus to produce a stream of finely
comminuted particles with a size in the range of one micron or less
is attributed to the fact that we prefer to utilize relatively
small balls or analogous dispersing elements 30. At the present
time, we prefer to utilize dispersing elements having a maximum
transverse dimension in the range of 0.1 to 5 millimeters, most
preferably between 1-5 millimeters. As a rule, the ratio between
the maximum dimensions of dispersing elements and the maximum
dimensions of freshly admitted solid particles is between 10:1 and
10,000:1. A very satisfactory ratio is between 100:1 and 1,000:1.
The motor or other prime mover which rotates the shaft 4 is
preferably of the variable-speed type so that the speed of the
agitating members 5 can be varied within a wide range. The
rotational speed of these agitating members is preferably high to
insure an intensive dispersing and comminuting action which results
from repeated collision between the balls 30 and the solid
particles. The fact that the mass of dispersing elements is
relatively small does not affect the quality of dispersing and
comminuting action. The dispersing speed is proportional to the
frequency and intensity of collisions between the balls 30 and
solid particles; the factors which affect such dispersing speed
include the dimensions of balls 30, the ratio of the combined
volume of balls 30 to the combined volume of solid particles in the
chamber 1a, the ratio of the combined volume of balls 30 and solid
particles to the volume of the chamber 1a, the specific weight of
balls 30, the specific weight of solid particles, the size of solid
particles which are admitted via inlet 6, and the size of
comminuted material which is evacuated by way of the outlet 8. The
ratio of specific weight of the balls 30 to specific weight of
solid particles is normally between 0.1 and 8 to one. The nature of
the material of the balls 30 depends on the nature of solid
particles. Such material may be glass, ceramic, metal or plastic,
e.g., polyvinyl chloride, polystyrene, Teflon (trademark) and/or
others.
Another feature of our apparatus which contributes significantly to
intensive dispersing and comminuting action resides in that the
dimensions of agitating members are in a certain relationship to
dimensions of the vessel 1. It was found that the diameters of
agitating members 5 should be less than the diameter of the
cylindrical internal surface of the vessel 1, preferably between 70
and 90 percent of such internal diameter. It was further found
that, if the apparatus employs two or more agitating members, the
axial distance between such agitating members should preferably
correspond to between 20 and 50 percent of their diameter. The
agitating members 5 preferably resemble or constitute disks which
are provided with slots, holes or analogous recesses or openings
and/or with ribs or other protuberances to insure satisfactory
entrainment of balls 30 and solid particles when the drive shaft 4
rotates. It was found that disk-shaped agitating members undergo
little wear, even at very high speeds in the range of 5-30 meters
per second which are desirable to bring about satisfactory
agitation of the contents of the chamber 11.
The apparatus can be operated continuously or intermittently and
may be employed for comminuting and/or dispersing of different
sizes and/or types of solid particles. The valve 45 may be closed
to seal the inlet 7 from the source 38 if the nature of solid
material is such that it can be evacuated without resorting to a
gaseous carrier. As will be explained hereinafter, the gaseous
carrier which is discharged by way of the outlet can be
recirculated through the chamber 1a. Furthermore, at least those
parts of the apparatus which are subjected to extensive wear can be
provided with one or more coats or layers of highly wear-resistant
material.
FIG. 2 illustrates schematically certain details of a modified
apparatus. The main difference between the apparatus of FIGS. 1 and
2 is that the latter does not employ a gaseous carrier, chiefly
because the outlet 108 is arranged to discharge comminuted material
downwardly so that such material can be evacuated by gravity. All
such parts of the modified apparatus which are clearly identical
with or analogous to corresponding parts of the apparatus shown in
FIG. 1 are denoted by similar reference numerals plus 100. The
chamber of the vessel 101 accommodates a transverse partition 10 at
least a portion of which constitutes a filter or sieve to provide
interstices for passage of finely comminuted material which is
thereupon caused to leave the vessel by way of the outlet 108. The
partition 10 may form an integral part of the end wall 103 which is
preferably detachably secured to the cylindrical shell of the
vessel 101. In the embodiment of FIG. 2, the filter or sieve
constitutes the upper part of the partition 10. This partition may
consist of sheet metal which is formed with slits, round holes or
other types of interstices for passage of finely comminuted
material. When the shaft 104 rotates, the balls (not shown)
cooperate with the agitating members 105 to automatically transport
finely comminuted material from the inlet 106 toward the partition
10.
FIG. 3 shows a portion of a third apparatus wherein all such parts
which are clearly identical with or analogous to the parts of the
apparatus shown in FIG. 1 are denoted by similar numerals plus 200.
The inlet 206 for solid particles is provided in the upper portion
of the end wall 203 and the outlet 208 for finely comminuted
material is located in the lowermost part of shell of the vessel
201 adjacent to the end wall 202. In this apparatus, the filter 9
or 10 is replaced by another confining device which prevents escape
of dispersing elements and freshly admitted (non-communited) solid
particles from the chamber of the vessel 201. This confining device
comprises a ring 12 which is installed in the chamber of the vessel
201 and extends a relatively short distance toward the shaft 204,
and a disk 11 which preferably constitutes the leftmost agitating
member and defines with the adjoining end face of the ring 12 a
narrow annular gap or an annulus of discrete gaps through which
finely comminuted material is free to pass on its way toward the
outlet 208. It will be seen that the gap or gaps for evacuation of
communited material are defined by stationary and moving parts 12,
11.
The only important difference between the apparatus of FIGS. 3 and
4 is that the latter comprises a stationary ring 312 which is
adjacent to the inner side of the disk 311, i.e., the disk 311 is
located between the ring 312 and the end wall 302. All other parts
of the apparatus shown in FIG. 4 are denoted by numerals similar to
those employed in FIG. 3 plus 100. An advantage of the apparatus
shown in FIG. 4 is that finely comminuted material passes through
the gap or gaps between the parts 311, 312 under the action of
centrifugal force.
In the apparatus of FIG. 5, the means for confining dispersing
elements and freshly admitted solid particles in the chamber of the
vessel 401 comprises a rotary separator 13 which is preferably (but
not necessarily) installed in the end wall 403 and is driven by the
shaft 404 or by a separate drive 13a (indicated by phantom lines).
The separator 13 comprises a preferably conical rotor 13b which
defines a narrow annular gap with a stationary tube 13c for passage
of finely comminuted material into the outlet 408. The latter can
form an integral part of the tube 13c. The separator 13 can perform
the additional function of separating coarser and finer particles
of the material which enters the tube 13c. All other parts of the
apparatus of FIG. 5 are denoted by numerals similar to those
employed in FIG. 1 plus 400.
The apparatus of FIG. 6 constitutes a further modification of the
apparatus shown in FIG. 1. This apparatus comprises a separator 14
which is mounted externally of the vessel 501. The outlet 508 for
finely comminuted material is formed with a perforated wall and
extends into the separator 14 to receive the gaseous carrier and
the finely comminuted material. All coarser particles are returned
into the chamber of the vessel 501. The parts 502-507 correspond to
parts 2-7 of the apparatus shown in FIG. 1.
FIG. 7 shows an apparatus wherein the separator 15 for gaseous
carrier and comminuted material is mounted on the cylindrical shell
of the vessel 601. The outlet 608 evacuates comminuted material.
Coarser particles are returned into the vessel 601. The parts
602-607 correspond to parts 2-7 of the apparatus shown in FIG.
1.
FIG. 8 illustrates schematically an apparatus wherein the gaseous
carrier is recirculated through the chamber of the vessel 701. The
apparatus comprises two separators 16, 17 the first of which
separates comminuted material and gas from dispersing elements and
coarser solid particles and the second of which separates
comminuted materials from the gaseous carrier. The separator 16
comprises a rotor 16a which is provided with a filter or sieve
(e.g., a textile filter) having interstices just large enough to
permit entry of gas and comminuted material into a conduit 16b
which admits the mixture of gas and comminuted material into the
housing 17c of the second separator 17. This housing accommodates a
rotor 17a which is designed to retain comminuted solid material but
to permit entry of gaseous carrier into a conduit 17b connected to
the intake of a blower 18. The pressure side of this blower is
connected with the inlet 707 of the vessel 701. Solid particles
which cannot penetrate through the rotor 16a of the first separator
16 leave the latter's housing 16c by way of a return conduit 16d
which discharges its contents through the end wall 703 and back
into the chamber of the vessel 701. The outlet 708 for comminuted
material is provided in the bottom portion of the housing 17c. The
efficiency (separating action) of separators 16, 17 depends on the
size of interstices in their rotors 16a, 17a and on rotational
speed of such rotors. Each of these rotors can be driven by a
pulley or the like, not shown, preferably from a variable-speed
motor or transmission. The same motor or transmission can also
serve to drive the rotor of the blower 18 and to rotate the drive
shaft 704 for the agitating members 705. The numerals 702,706
respectively denote the left-hand end wall of the vessel 701 and
the inlet for solid particles. As described in connection with and
as shown in FIG. 1, the vessel of the apparatus can be heated or
cooled, depending on the nature of solid particles and/or on
certain other factors. It is also possible to employ in the
apparatus of FIG. 8 (or in the apparatus of FIG. 1 or 6 or 7) a
vessel which does not have a cooling or heating jacket and to
provide instead a heat exchanger (shown at 17e in FIG. 8) which
heats or cools the gaseous carrier upstream or downstream of the
blower.
It is further clear that the separator 16 and/or 17 of FIG. 8 can
be replaced by other types of separators without departing from the
spirit of our invention. For example, the apparatus can employ a
bag filter, a chamber filter or the like. Furthermore, the
separators 16, 17 of FIG. 8 can be replaced by a multi-stage
separator of the type shown in FIG. 9. This separator is designed
to segregate coarse solid particles and dispersing elements from
gases and comminuted material and to thereupon separate comminuted
material from gases. The mixture of solid particles, comminuted
material and gaseous carrier is admitted by suction into an outer
housing 19a by way of an inlet 19. The housing 19a accommodates an
upright hollow rotary outer filter 24 having interstices large
enough to permit passage of gases and comminuted material into the
interior of this filter. The solid particles which are too large
are intercepted by the filter 24 and descend by gravity into an
outlet 20 which returns them into the vessel, not shown. The
mixture of gases and solid comminuted material is separated in the
interior of the outer filter 24; thus, the gases are drawn into a
pipe 22 through the interstices of a hollow rotary inner filter 23
which is coaxially mounted in the outer filter 24. The filter 23
intercepts the comminuted material which descends by gravity into
an outlet 21 corresponding to the outlet 8 in the apparatus of FIG.
1. The numberals 25, 25a respectively denote gears which form part
of two independent drives for the filters 23, 24, i.e., each of
these filters can be rotated at a different speed. The upper
portions of filters 23, 24 rotate in antifriction gearings 26, 26a.
It is also possible to rotate the filters 23, 24 in different
directions.
FIG. 10 illustrates a modified multi-stage separator. All parts of
this separator which are clearly identical with or analogous to the
parts of the separator shown in FIG. 9 are denoted by similar
reference numerals plus 800. The main difference is that the
filters 823, 824 are rigidly connected to each other so that they
rotate at the same speed and in the same direction. The pipe 822
for the gaseous carrier can form part of the drive which rotates
the filters 823, 824.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without
omitting features which fairly constitute essential characteristics
of the generic and specific aspects of our contribution to the
art.
* * * * *