Abstrict A centrifugal impact crusher has an enclosed table to ensure that
substantially all the material deposited on the table is impacted
against the anvils that surround the table. The table includes spaced-apart
upper and lower plates that have radially oriented impellers sandwiched
between them to direct material being thrown off of the table by
centrifugal force to exit the table at the proper angle to achieve
maximum fracture upon striking the anvils. The impellers have projecting
tabs which fit into receptacles in the upper and lower plates and
the plates are squeezed together to hold the tabs in the receptacles
and lock the plates and impellers together in a rigid table assembly.
The upper plate has a central opening through which material is
deposited onto the table. A funnel directs material fed into the
crusher through an infeed plenum and into the central opening in
the upper plate to ensure that all of the material reaches the table.
Recirculation plenums extend from an outlet plenum located below
the table up to the infeed plenum. The rotating table acts as a
fan which draws air into the infeed tube along with the material,
and this airflow creates a pressure differential across the table
that causes air to flow through the recirculation plenum. The recirculation
air includes dust and particulate matter which is either sent back
through the crusher to be more finely crushed or is removed by filters.
Claims What is claimed is:
1. A centrifugal impact crusher having an enclosed chamber, an
infeed plenum that opens into the chamber, a rotating table having
a series of radially arrayed impeller blades on its upper surface
located in the chamber below said infeed plenum, a plurality of
anvils located in the chamber around the periphery of the table
substantially coplanar with the upper surface thereof, an outlet
plenum defined in the chamber below the table, and one or more recirculating
plenums that extend between the outlet plenum and the infeed plenum,
said crusher comprising:
(a) a flow restrictor, having a defined flow area, located in the
infeed plenum upstream of said recirculation plenums; and
(b) means for changing said flow area.
2. The crusher of claim 1 wherein said flow restrictor includes
a series of hollow cylindrical tubes each having a different diameter,
and said means for changing comprises:
(a) flanges associated with each of said tubes; and
(b) means for releaseably attaching said flange to said infeed
plenum.
3. A centrifugal impact crusher having an enclosed chamber, an
infeed plenum that opens into the chamber, a rotating table having
a series of radially arrayed impeller blades on its upper surface
located in the chamber below said infeed plenum, a plurality of
anvils located in the chamber around the periphery of the table
substantially coplanar with the upper surface thereof, an outlet
plenum defined in the chamber below the table, and one or more recirculating
plenums that extend between the outlet plenum and the infeed plenum,
said crusher comprising:
(a) adjustable flow control dampers located in said recirculation
plenums;
(b) first access ports defined in said recirculation plenums downstream
of said flow control dampers; and
(c) second access ports defined in said recirculation plenums upstream
of said flow control dampers.
4. A table for a centrifugal impact crusher of the type having
an enclosed chamber, an infeed plenum that opens into the chamber,
a rotating table having a series of radially arrayed impeller blades
on its upper surface located in the chamber below said infeed plenum,
a plurality of anvils located in the chamber around the periphery
of the tables substantially coplanar with the upper surface thereof,
an outlet plenum defined in the chamber below the table, and one
or more recirculating plenums that extend between the outlet plenum
and the infeed plenum, said table comprising:
(a) a lower plate;
(b) an upper plate that overlies said lower plate and defines a
central opening that communicates with the infeed plenum;
(c) upwardly and downwardly projecting tabs on said impeller blades:
(d) said upper and lower plates defining receptacles for receiving
said tabs;
(e) one of said upper and lower plates a plurality of threaded
holes defined therein;
(f) the other of said upper and lower plates having a plurality
of openings defined therein with one of said openings being aligned
with each of said holes;
(g) threaded fasteners that extend through said openings and into
threaded engagement with said holes; wherein
(h) said openings and holes being located in said plates such that
said fasteners are located in the shadow of the impeller blades
and not be contacted by material being crushed.
5. A method for crushing material in a centrifugal impact crusher
of the type having an enclosed chamber, an infeed plenum that opens
into the chamber and through which particulate matter is introduced
into the crusher, and rotating table having a series of radially
arrayed impeller blades on its upper surface located in the chamber
below said infeed plenum, a plurality of anvils located in the chamber
around the periphery of the table substantially coplanar with the
upper surface thereof, an outlet plenum defined in the chamber below
the table, and one or more recirculation plenums that extend between
the outlet plenum and the infeed plenum, said method comprising:
a. providing inlet ports in said recirculation plenums; and
b. introducing additional particulate matter which has not previously
passed through said infeed plenum into said inlet ports to increase
the concentration of particulate matter in the air passing through
said infeed plenum to a desired level.
6. A method for crushing material in a centrifugal impact crusher
of the type having an enclosed chamber, an infeed plenum that opens
into the chamber and through which particulate matter and air are
introduced into the crusher, a rotating table having a series of
radially arrayed impeller blades on its upper surface located in
the chamber below said infeed plenum, a plurality of anvils located
in the chamber around the periphery of the table substantially coplanar
with the upper surface thereof; an outlet plenum defined in the
chamber below the table into which particulate matter that is thrown
off of said rotating table against said anvils and is fractured
is urged by gravity and one or more recirculation plenums that extend
between the outlet plenum and the infeed plenum through which is
selected portion of fractured particulate matter is reintroduced
into the infeed plenum, said method comprising:
a. providing inlet ports in said recirculation plenums; and
b. introducing additional air, which did not pass through the crusher
with the fractured particulate matter when it was initially fractured,
into said inlet ports to decrease the concentration of particulate
matter in the air passing through said infeed plenum to a desired
level.
7. The method of claim 6 including the further step of heating
said air before it is introduced into said inlet ports.
8. The method of claim 6 including the step of adding moisture
to said air before it is introduced into said ports.
9. A method for crushing material in a centrifugal impact crusher
of the type having an enclosed chamber, an infeed plenum that opens
into the chamber, a rotating table having a series of radially arrayed
impeller blades on its upper surface located in the chamber below
said infeed plenum, a plurality of anvils located in the chamber
around the periphery of the table substantially coplanar with the
upper surface thereof, an outlet plenum defined in the chamber below
the table, and one or more recirculation plenums that extend between
the outlet plenum and the infeed plenum, said method comprising:
a. providing adjustable flow control dampers in said recirculation
plenums;
b. providing first access ports in said recirculation plenums downstream
of said flow control dampers;
c. providing second access ports in said recirculation plenums
upstream of said flow control dampers;
d. removing air and airborne particles from said second ports for
processing said airborne particles;
e. introducing particulate matter into said first port.
10. The method of claim 9 including the step of introducing air
into said first port.
11. The method of claim 10 including the step of heating said
air before it is introduced into said first port.
12. The method of claim 10 including the step of adding moisture
to said air before it is introduced into said first port.
13. A method for crushing material in a centrifugal impact crusher
of the type having an enclosed chamber, an infeed plenum that opens
into the chamber, a rotating table having a series of radially arrayed
impeller blades on its upper surface located in the chamber below
said infeed plenum, a plurality of anvils located in the chamber
around the periphery of the table substantially coplanar with the
upper surface thereof; an outlet plenum defined in the chamber below
the table, and one or more recirculation plenums that extend between
the outlet plenum and the infeed plenum, said method comprising:
a. providing adjustable flow control dampers in said recirculation
plenums;
b. providing first access ports in said recirculation plenums downstream
of said flow control dampers;
c. providing second access ports in said recirculation plenums
upstream of said flow control dampers;
d. at least partially closing said dampers;
e. introducing air and particulate matter into said first port.
14. The method of claim 13 including the further step of heating
said air before it is introduced into said inlet port.
15. The method of claim 13 including the step of adding moisture
to said air before it is introduced into said inlet port.
16. A method of crushing material in a centrifugal impact crusher
of the type having an enclosed chamber, an infeed plenum that opens
into the chamber, a rotatable table having a series of radially
arrayed impeller blades on its upper surface located in the chamber
below said infeed plenum, a motor for rotating said table, a plurality
of anvils located in the chamber around the periphery of the table
substantially coplanar with the upper surface thereof, an outlet
plenum defined in the chamber below the table and one or more recirculation
plenums that extend between the outlet plenum and the infeed plenum,
said method comprising:
a. providing adjustable flow control dampers in said recirculation
plenums; and
b. modulating the position of said dampers in a manner such that
said motor operates at its maximum efficiency for the material being
crushed and the desired table speed.
Description BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a centrifugal impact crusher, and in
particular to such a crusher in which 100% of the material fed into
the crusher is impacted against the crushing anvils and in which
the amount of dust is significantly reduced.
Centrifugal impact crushers have successfully been used for crushing
a wide range of materials. A use that has recently been suggested
for centrifugal impact crushers is in the production of cement.
Cement has traditionally been ground from clinker in ball mills
using a two-step process. The clinker is first rough ground in a
first section of the ball mill having large balls, and the ground
material from the first section is then reground in a second section
having smaller balls. When ball mills are used to grind large particles,
such as occur with clinker, they consume excessive amounts of energy,
and thus they are not well-suited for this purpose. German patent
DE3815217 using a centrifugal impact crusher for the first section
in crushing clinker, since centrifugal impact crushers handle material
of this size much more efficiently than ball mills. However, the
smaller second stage ball mill required to grind fine enough to
produce cement does not handle large material well and the first
stage device must reduce all of the material passing through it
in the required amount. Prior art centrifugal impact crushers were
designed to crush materials such as rock where a wide size range
of crushed material is not only allowable, but actually desired.
A substantial amount of material deposited onto the rotating table
of prior art centrifugal impact crushers does not even strike the
crushing anvils and thus is uncrushed. This means that when centrifugal
impact crushers are used for the first stage of clinker reduction,
the material must be sorted and a portion of it reground which increases
the cost of using centrifugal impact crushers for clinker. Furthermore,
cement creates tremendous amounts of dust when it is crushed in
the violent manner that exists in a centrifugal impact crusher,
and this dust creates significant problems.
While complete reduction and dust handling are critical when crushing
clinker, dust creates problems when other materials are crushed
as well. In many materials dust is handled by wetting the material.
While wetting is obviously unworkable with cement, water makes sorting
of other materials more difficult and it increases wear. In addition,
when rock is crushed to sand, it is important that dust be separated
from the sand and this cannot be done when the material is wetted
during crushing.
The foregoing shortcomings and limitations of prior art centrifugal
impact crushers are overcome in the subject invention by providing
a table having spaced-apart upper and lower plates that have impeller
blades sandwiched between them. The upper plate has a central opening
through which material is deposited onto the table. Thus, the table
is enclosed which forces substantially all of the material thrown
off of it by centrifugal force to be impacted against the anvils.
In addition, an annular retainer plate fits above the anvils and
extends radially inward to the periphery of the upper plate. The
retainer plate covers what little area there is for material that
is thrown off of the enclosed table to miss the anvils.
The impellers have tabs protruding from their upper and lower surfaces
which fit in conforming receptacles located in the upper and lower
plates. The upper and lower plates are joined to one another by
bolts or pins, and when the bolts are tightened or wedges inserted
into the pins the tabs are seated in the receptacles and the plates
and impellers form a rigid table assembly. The tabs cover a substantial
portion of the impellers and, as a result, impeller attachment is
spread over a large surface area which prevents the impeller connector
breakage that is common with devices of this type due to the centrifugal
force created by the high rotational speed and due to material striking
the impellers.
In order to reduce dust and ensure uniform fine crushing, recirculation
plenums extend from an outlet plenum at the bottom of the crusher
shell to an infeed plenum through which material is fed into the
crusher. The rotating table in the crusher acts as a fan which creates
a negative pressure above the table and a positive pressure below
the table. This pressure differential between the infeed plenum
above the table and the outlet plenum below the table draws air
into the recirculation plenums. Since the recirculation plenums
receive air from beneath the table, dust and particulate matter
resulting from the crushing is entrained in the air and this material
passes through the recirculation plenums and back into the crusher.
The recirculation plenums have first ports in them which permit
particle-laden air to be removed from the plenums and the particles
removed by filters or separators if desired. In addition, there
are second ports in the recirculation plenums that permit specified
amounts of graded material to be introduced into the crusher to
insure crushed material of a particular size, or permit the addition
of heated or moisture-laden air into the crusher. A flow restrictor
located above the infeed plenum restricts the air that enters the
crusher with the material in order to establish significant flow
through the recirculation plenums. The infeed plenum is connected
to the central opening in the upper plate of the table so that all
of the material and dust-laden air in the infeed plenum reaches
the table.
Accordingly, it is a principal object of the subject invention
to provide a centrifugal impact crusher in which 100% of the material
deposited in the device is thrown off of the table and impacted
against the crushing anvils.
It is a further object of the subject invention to provide such
a device in which the table is enclosed.
It is a still further object of the subject invention to provide
such a device having a retaining plate over the anvils which prevents
material from passing over them.
It is a still further object of the subject invention to provide
a centrifugal impact crusher having an air recirculation system
that recirculates air and entrained particles from the bottom of
the crusher back into the infeed plenum.
It is a yet further object of the subject invention to provide
such a crusher in which the air and entrained particles in the recirculation
system can be filtered to remove the particles.
It is a still further object of the subject invention to provide
such a crusher in which it is possible to regulate the amount of
air that is drawn into the crusher with the material being crushed.
It is a further object of the subject invention to provide such
a crusher in which particulate matter, heated air or moisture-laden
air can be introduced into the recirculation system.
The foregoing and other objectives, features and advantages of
the present invention will be more readily understood upon consideration
of the following detailed description of the invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view, in cross section, of a centrifugal
impact rock crusher embodying the features of the subject invention.
FIG. 2 is a sectional view taken along the line 2--2 in FIG. I,
partially broken away to show hidden detail.
FIG. 3 is a plan view of the crusher of FIG. 1.
FIG. 4 is a detail view of an alternate embodiment of a portion
of the crusher.
FIG. 5 is a side elevation view, in section of flow restrictors,
which are elements of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENTS
Referring to FIG. 1 of the drawings, a crusher comprises a cylindrical
shell 10 that is mounted on a rectangular frame 12. The shell is
covered by a lid 14 that is releasably secured to the shell by means
of locks 16. Located medially in the shell is a pedestal 18 that
rotatably journals a shaft 20 having a table assembly 22 mounted
on its upper end. The lower end of the shaft 20 carries a pair of
pulleys 23 that are driven by electric motors 24 through belts 26.
The table assembly 22 includes a flat circular lower plate 28 that
is attached to the shaft 20 and is covered with a replaceable wear-resistant
liner 30. The center section of the liner is in the shape of a cone
32. An upper plate 34 is attached to the lower plate and a plurality
of radially oriented impellers 36 are sandwiched between them. The
lower surface of the upper plate is covered with a replaceable wear-resistant
liner 35.
Referring now also to FIG. 2 the impellers 36 have tabs 38 protruding
from their top and bottom surfaces, and the top and bottom plates
have receptacles 40 in them which matingly receive the tabs. In
one embodiment, shown in FIG. 1 the lower plate has threaded openings
42 located in it that receive bolts 44 that extend through aligned
openings 46 in the upper plate. Thus, when the bolts are tightened,
the plates are pulled together and the impellers are secured between
them. In another embodiment, shown in FIG. 4 the bolts are replaced
with pins 100 having slots 102 at their extremities and the nuts
are replaced by wedges 104. The tabs constitute a relatively large
percentage of the impellers thereby creating a strong bond between
the impellers and plates that will not easily break during operation
of the crusher, even when it is operated at high rates of speed
and large forces act on the impellers. The large size of the tabs
is necessary since the tabs transfer the entire shear load between
the impellers and the remainder of the table. Since the bolts 44
or pins 100 do not carry the bulk of the shear loads, but merely
hold the assembly together, their location is not critical and they
can be placed entirely in the shadow of the impellers so that they
are not impacted by the material being crushed and thus will not
be subject to extensive wear. In order to further protect the bolts
or pins, they are covered by replaceable wear-resistant shields
48. The upper plate 34 has a central opening 49 through which material
is deposited onto the lower plate 28.
Located around the periphery of the shell 10 coplanar with the
table assembly, are a plurality of anvils 50 that material thrown
off of the table assembly by centrifugal force is impacted against.
The fractured material drops between the periphery of the table
assembly 22 and the anvils into an outlet plenum 51 provided in
the shell below the table assembly. Appropriate removal devices
(not shown) remove the crushed material from the outlet plenum and
out of the crusher. The anvils 50 and their mounting system 52 are
conventional for centrifugal impact crushers. Mounted above the
anvils is an annular retainer ring 54 that extends inwardly to approximately
the outer periphery of the upper plate 34.
Material is fed into the crusher through an infeed assembly 56
that is mounted on the lid 14. The infeed assembly includes a hollow
cylindrical tube 58 that is attached to the lid and forms an infeed
plenum 59. A funnel 60 extends from the bottom of the tube 58 into
the opening 49 in the upper plate 34. Thus, all of the material
passing through the infeed plenum 59 is directed into the table
assembly. A hopper 61 located at the top of the crusher is connected
to the tube 58 through a flow restrictor 62. In the preferred embodiment
illustrated, the flow restrictor 62 includes a pair of back-to-back
tube assemblies, each comprising a hollow tube 63 having a flange
65 at one end, which permits them to be joined together and to the
tube 58 by means of bolts 67. Referring now also to FIG. 5 preferably
there is a series of flow restrictors each having a different diameter
"D" thereby permitting the flow restriction flow area
to be changed as required.
Located around the bottom of the shell 10 is a set of openings
64 that open into the outlet plenum 51. A matching set of openings
66 located around the periphery of the tube 58 open into the infeed
plenum 59. Each opening 64 is connected to a mating opening 66 through
a recirculation plenum 68. A covered first port 70 is located in
each recirculation plenum to permit a filtering system (not shown)
to be connected to the plenums. An adjustable damper 71 is located
in each recirculation plenum downstream of the first port 70. In
addition, a covered second port 73 is located in each recirculation
plenum downstream of the damper.
The crusher of the subject invention is operated like other centrifugal
impact crushers, however, for several reasons provides improved
performance. First, the enclosed table assembly 22 causes substantially
all of the material deposited on it to be thrown radially outward
such that it impacts the anvils 50 and becomes crushed. The retainer
plate 54 covers the only area where material thrown off of the table
could escape impacting the anvils, so that 100% of the material
deposited on the table is crushed. In addition, the close connection
between the infeed tube 58 and the upper plate 34 of the table assembly,
created by the funnel 60 ensures that all material deposited in
the hopper 61 at the top of the crusher is deposited on the table.
Furthermore, the enclosed table assembly and close connection between
the infeed tube and the table significantly reduces dispersion of
the dust that is generated during crushing.
A much larger factor in the reduction of dust is the recirculation
plenums 68. The rotating table assembly acts as a fan to draw air
into the hopper 61 along with the material being crushed. Thus,
a negative pressure is created above the table in the infeed plenum
59 and a positive pressure is created below the table in the outlet
plenum 51. This pressure difference causes air to flow through the
recirculation plenums 68 from the outlet plenum back into the infeed
plenum. The flow restrictor 6 accelerates the air passing through
the infeed plenum to create a venturi effect which increases the
amount of air that flows through the recirculation plenums. The
amount of this venturi effect can be adjusted as required by replacing
the flow restrictor with one having a different flow area. Since
the recirculated air has dust and particulate matter entrained in
it, this material is passed back trough the crusher where it is
crushed to a greater degree. If filters or separators are attached
to the outlets 70 dust can be removed from all or a portion of
the air entering the recirculation plenum. The relative amount of
the recirculation air that is filtered depends upon the setting
of the dampeners 71.
The dampers 71 can also be used to obtain the most efficient operation
of the motor 24. As indicated above, the rotating table operates
as a fan which draws air into crusher through the inlet plenum 58
and the recirculation plenum 68. The more air that is drawn through
the crusher the more "pump work" that must be accomplished
by the motor. Thus, when little or no recirculation is required,
the damper can be partially closed to reduce the airflow to the
minimum necessary level and thereby maximize the efficiency of the
crusher.
In addition to recycling airborne particulate matter from the outlet
plenum and removing particles through filtration, the recirculation
plenums can be utilized to add particulate matter or alter the moisture
content of the material being crushed. This is accomplished by introducing
particulate matter, heated air or moisture laden air into the first
port 70. The process can be implemented in a number of different
ways. If the crusher is being used to crush clinkers prior to introduction
into a ball mill, the material fed into the ball mill must be within
a specified size range which will not always be achievable by crushing
in a single pass through a centrifugal impact crusher. To achieve
such close control, the damper 71 is partially closed and a large
portion of the particulate matter is diverted out of the recirculation
plenums through the second port 70 where it is captured by filters.
The captured material is then sorted by grade and selectively introduced
back into the recirculation plenum through one of the first ports
73 such that the material that ultimately is discharged from the
crusher falls within the desired size range. Alternatively, particulate
matter can be introduced into the crusher through the first port
to achieve the proper blend without removing material from the second
port for filtering.
With some materials, such as clinker, it is important that moisture
is minimized during crushing to prevent caking of the material.
In this case dried or heated air can be introduced into the first
port to compensate for moisture in the material itself or in the
air drawn into the funnel 61 with the material. On the other hand,
with other materials moisture is critical in the crushing process
to reduce dust. In this event metered quantities of moisture-laden
air can be introduced into the crusher through the first port.
The terms and expressions which have been employed in the foregoing
specification are used therein as terms of description and not of
limitation, and there is no intention, in the use of such terms
and expressions, of excluding equivalents of the features shown
and described or portions thereof, it being recognized that the
scope of the invention is defined and limited only by the claims
which follow. |