Abstrict An enclosed hammermill crusher having a closed-loop vent is described.
The crusher-enclosure has an upper vent opening in the housing above
the hammers where the hammer direction is upward, said vent opening
communicating with a closed-loop vent duct. The lower part of the
crusher housing is contiguous with a crushed particulate collector
which has sloping sides and a small discharge opening cummunicating
with a discharge conduit. The lower end of the vent duct connects
to the discharge conduit near the collector discharge opening, preferably
at about right angles to the discharge conduit. The inlet opening
for aggregate material in the top of the housing is above the hammers
where said hammers have a downward direction.
Claims I claim:
1. A vented hammermill crusher comprising:
a. a housing and rotary crusher means having an upper inlet opening
above that portion of the rotary crusher means where the crusher
direction is downward, a vent opening above that portion of the
rotary crusher means where the crusher direction is upwards,
b. a crusher particulate collector having a large upper opening
communicating with the housing bottom, said collector having sloping
sides and a small discharge opening,
c. a discharge conduit communicating with the discharge opening
of the collector, said conduit having substantially the same angle
as the collector wall relative to the horizontal and having an opening
therein,
d. a vent duct external to said housing connecting said vent opening
of the crusher housing and the opening in the discharge conduit,
said vent duct connecting to said discharge conduit at an angle
of about 90.degree. to the discharge conduit sidewall.
2. The vented crusher of claim 1 wherein said collector sloping
sides have a slope of from about 45.degree. to 60.degree. to the
vertical.
3. The vented crusher of claim 1 wherein said upper opening and
said vent opening are separated by a deflector plate.
4. The vented crusher of claim 1 wherein said crusher housing has
sidewalls and a top cover, said top cover having said vent opening
therein closely adjacent the crusher means.
5. The vented crusher of claim 1 wherein said deflector plate is
disposed at an angle of about 60.degree. to about 70.degree. with
respect to the top cover of said housing
6. The vented crusher of claim 1 wherein said vent opening communicates
with a vent housing having an angularly disposed delfector plate
and vent duct extending from said vent housing in a substantially
straight line for a short distance.
7. The vented crusher of claim 1 wherein said vent duct has a wall
in common with an outer wall of said crusher housing.
Description BACKGROUND OF INVENTION
1. Field
This invention relates to hammermill crushers, which are used in
the mineral industries for reducing the size of aggregate to a fine
size, i.e., a mesh size of about 8 to about 200. Because of the
fineness of the mill product, "dusting" or loss of fine
material has been a long-standing problem. The "dusting"
of "fines" lost from the mill may present a maintenance
and/or cleaning problem in production equipment. Furthermore, for
a mill in a sampling line the loss of any material may introduce
an error into the sample analyses. Part of the dusting problem results
because conventional hammermills act as an air-pump, drawing air
into the system by the rapid rotation of the hammers.
Introduction of large quantities of air into a particulate sampling
system further aggrevates the dusting problem and tends to dry the
particulate material, which causes an erroneous indication of moisture
content. Although these problems have existed, hammermills have
an important function in particulate sampling systems because of
their compactness, efficiency in reducing particle size, reliability
in producing particles of a constant size distribtuion and uniformity
of size, and ability to effect a substantial particle size reduction
to a fine particle size.
OBJECTS OF INVENTION
It is an object of the invention to provide a hammermill crusher
which has the ability to operate without a dusting problem.
A further object of the invention is to provide a hammermill which
operates without an undue loss of material.
Another object of the instant invention is to provide a hammermill
which operates without throwing undue quantities of air into the
system.
DESCRIPTION OF DRAWINGS
FIG. 1 is an elevational view of the vented hammermill crusher
of this invention.
FIG. 2 is a plan view of a vented hammermill crusher.
FIG. 3 is a plan view of an alternative construction for a vented
hammermill crusher.
DESCRIPTION OF INVENTION
An enclosed hammermill crusher having a closed-loop vent system
has been invented. The crusher enclosure has an upper vent opening
in the housing above the hammers where the hammer direction is upward.
This vent opening communicates with a closed-loop vent duct which
communicates with the discharge conduit connected at the bottom
of the crusher housing. The lower part of the crusher housing is
contiguous with a crushed particulate collector which has sloping
sides and is preferably conical or pyramidal in shape. A lower end
of the vent duct connects with the discharge conduit near the collector
discharge opening, preferably at right angles to the discharge conduit.
The inlet opening for aggregate material in the top of the housing
is above the hammer where said hammer has a downward direction.
In FIG. 1 an elevational view of the vented hammermill crusher
of this invention, the crusher housing 10 is cutaway to expose the
rotor 11 with hammers 12 attached near the periphery. The hammers
are thrown by centrifugal force, created during rotation of the
rotor, to pass close to the cylindrical shaped striking plate 13
to crush material to a very fine powder. The striking plate may
be discontinuous near the housing base or it may have very fine
holes therein to allow the pulverized material to escape into collector
means.
The inlet opening to the system for aggregate material is through
opening 14. An exit opening for discharge of air and circulation
of fines is through opening 15 wherein the air is traveling upward
and strikes deflector plate 16 and is deflected into the closed-loop
vent 17.
Deflector plate 16 serves two functions in the construction illustrated
in FIG. 1. First, it provides a wall for hopper 14a so that the
upper opening of the hopper is large to provide easy access to large
volumes of large aggregate and a smaller lower opening into the
mill to direct the aggregate into the proper area for pulverizing,
i.e., about the mid-point of the mill. Second, the deflector plate
16 is provided at an angle of about 60.degree. to about 70.degree.
to the top plate 14b of the mill to deflect the circulating air
into vent 17.
The bottom of the deflector plate 16 is located within plus or
minus 10.degree. of the crusher center line, i.e., as viewed in
FIG. 1. The center line passes vertically through the axle of the
rotor. The bottom of the deflector plate is preferably located directly
over the rotor axle and parallel thereto,
The vent exit housing 18 is constructed so that is has a base section
at an angle alpha to the flat top of the hammermill housing. The
angle alpha preferably has a minimum angle of about 20.degree. and
a maximum angle of about 60.degree.. It has been found that the
vent pipe 17 connected to the exit vent housing 18 preferably extends
for a short distance without having any curves in the vent pipe
so as to permit the air discharging through the vent housing 18
to continue the direction provided by vent housing 18 without an
immediate change in direction of flow. Vent duct 17 forms a closed-loop
connecting with the discharge pipe 19 at a point just below the
discharge opening from the conical or pyramidal shaped hopper 20.
The vent pipe 17 preferably meets the discharge pipe 19 at an angle
of about 90.degree. as indicated by the angle gamma on FIG. 1. The
angle of the discharge pipe 19 to the horizontal is preferably from
about 45.degree. to about 70.degree. and preferably 60.degree.,
as indicated by the angle beta in FIG. 1.
For commercially sized hammermills having a rotor diameter of about
20 inches, or larger, a vent duct 17 having a minimum diameter of
six inches is preferred.
FIG. 2 a plan view of the vented hammermill crusher of this invention,
illustrates the vent discharge housing 18 connected to the vent
pipe 17 and shows deflector plate 16 in the inlet opening 14. A
motor 21 drives the rotor. The top of the hammermill housing 22
is preferably a flat plate which supports the vent discharge housing
18.
The size of the inlet and outlet opening depend upon the size of
the hammermill. Also, the diameter of the vent depends upon the
size of the hammermill. Generally, these openings and vent pipe
may be greatly over-sized without affecting the operation of the
system. However, providing an under-sized opening and an under-sized
vent pipe builds up a back pressure which defeats the operation
of the system.
As indicated hereinabove, a minimum vent diameter is preferred
for hammermills with a rotor size of 20 inches.
FIG. 3 illustrates an alternative structure for the vented hammermill
crusher wherein a substantial portion of the vent means is made
an integral part of the crusher housing. Hopper 14a and deflector
plate are of similar construction and location as previusly indicated.
A second supplemental deflector plate 16a is located within the
integral upper vent duct 23 is slightly deflect the exhausting materials
into chamber 23a which has a curved outer wall 23b to turn the exhaust
stream downward into integral vertical vent duct 24 which uses one
wall of housing 10 as a duct wall. A deflector plate 24a directs
the exhaust into lower vent 25 which is similar in size, location
and shape to the lower portion of vent 17 illustrated in FIG. 1.
The structure of the mill of FIG. 3 is advantageous in that it
is compact and uses portions of the housing as portions of the duct.
The structure of FIG. 3 however, must provide a clean-out door
in the side of the duct to provide access to the clean-out door
normally located on the side of the hammermill where the direction
of the hammers is upward. The duct still may be hinged along a vertical
hinge to swing away from the hammermill housing to expose the clean-out
door. |