Note: Descriptions are shown in the official language in which they were submitted.
~5~
VERTICAL GRINDING MILL
The present invention relates to a vertical yrind-
ing mill used to pulverize emery, alumlna, etc. into fine or
ultrafine particles by grinding.
In conventional grindiny mills the material which
is to be pulverized is fed into the upper end of the mill
and the end product in the form of fine particles is trans
ported from the upper end of the mill by means of an air
current. Air is introduced to the lower end of the mill in
order to establish the current necessary to carry the par-
ticles out of the mill. Normally air is blown into the
housing of the mill through an inlet opening which is loca-
ted at one side of the lower end of the mill housing. As a
result, there is a tendency for the current particles to
accumulate in the area of the lower end of the housing which
is remote from the input passage used to introduce the air
current to the housing. This reduces production efficiency
and effectively reduces the capacity of the grinding apparatus.
According to one aspect of the present invention
there is provided a vertical grinding mill which overcomes
the difficulties described above and which has a high degree
of production efficiency.
In accordance with a further aspect oE the present
invention, there is provided a vertical grinding mill which
comprises a shell for containing the material to be pul
verized and grinding medium, a vertical screw shaft rotatably
mounted in the shell so as to extend through a top wall of
the shell for agitating the material and the grinding medium
- 1 -
~%~
to pulverize the material to fine particles, means for driv-
ing the screw shaft, collector means for collecting the fine
particles, and means for forming a fluid current -to -take -the
fine particles out of the shell and pass them through the
collector means, characterised in that the screw shaft is
hollow and has its bottom end open at the bottom of -the shell.
Other features and objects of the present invention
will become apparent from the following description ta~en
with reference to the accompanying drawings, in which:
Fig. 1 is a partially sectional schematic view of
the first embodiment;
Fig. 2 is a sectional view taken along the line
II - II of Fig. l;
Fig. 3 is a partially sectional view showing
another example of the classifying member;
Figs. 4 - 6 are partially sectional schematic views
of the second to fourth embodiments; and
Fig. 7 is a similar view of a prior art apparatus.
The same or similar reference numbers are employed
to designate the same or similar parts.
A conventional grinding mill of this type is shown
in Fig. 7. A vertical screw shaft 2 is rotatably mounted in
a vertical shell 1. Grinding medium _ such as steel balls
is filled in the shell. While rotating the screw shaft, the
material a to be pulverized is fed into the shell. The
material is pulverized to fine particles by friction between
the material and the grinding medium. The fine product par-
ticles c are carried by air current out of the shell and
collected by means of a collector 3 such as a bag filter and
a cyclone. The air current formed by a fan ~ is introduced
through an intake nozzle 5 into the bottom of the shell 1
and leaves the shell at its top with the fine particles.
Since the air current is blown into the shell from one side
of its bottom, the product particles will be unevenly dis-
tributed as shown in E~ig. 7 with a dotted line, and thus
will not be smoothly discharged out of the shell. Therefore,
the production efficiency was relatively low and the capacity
was small for a large apparatus size.
Referring to Fig. 1 illustrating the first embodi-
ment, a vertical grinding mill comprises a vertical cylin-
drical shell 10 having its top and bottom walls closed, and
a screw shaft 11 turnably supported in -the center of the
cylindrical shell 10 by means of thrust and radial bearings
(not shown). The screw shaft extends through the top wall of
the shell 10 and is rotated by drive means (not shown). The
screw shaft 11 is hollow and has its upper end connected to
a source of air and its lower end open near the bottom of
the shell 10. Because the inside of the shell is under
negative pressure, air flows through the screw shaft 11 into
the shell 10 from its bottom.
The shell 10 is provided at its upper portion with
an inlet 12 for the grinding medium _ and an inlet 13 for
the material to be pulverized. Through the inlet 12, the
grinding medium such as ceramic, gravels or steel balls is
filled up to the level L in Fig. 1. Through the inlet 13,
the material to be pulverized is fed into the shell 10 by a
~ 25~
screw conveyor or the like, keeping airtiyhtness. As the
screw shaft 11 rotates, the grin~iny
-- 4 --
~2~6~f~
medium and the material to be pulverized are moved in
the direction of arrow and agitated. As a result, the
material is pulverized to fine particles c by friction
between the material and the grinding medium.
At the upper portion of the shell 10, a conical
classifying member 14 is mounted on the screw shaft 11.
As shown in Fig. 2, blades 15 are provided at regular
intervals on the inner wall of the shell 10 so as to
be opposed to the classifying member 14. The blades
15 are curved toward the direction of rotation. Above
the classifying member 14, is formed a suction port 16
to which a suction fan 18 is connected through a product
collector 17 such as a bag filter and a cyclone. This
fan 18 puts the inside of the shell 10 under negative
pressure, so that air will flow into the screw shaft
11 from its top.
In order to obtain particles of a desired size or
assure a smooth operation, the apparatus should be operated
on the basis of the result of measurement of such parameters
as the level of the material in the shell, the speed
of air flow in the shell, the particle size of the product,
etc. The level of the material may be detected either
by means of a level indicator or by measuring the difference
between pressure at the suction port 16 and pressure
at top of the screw shaft 11. The speed of air flow
~5~
may be measured at top of the screw shaft 11 by use of
an orifice or a Venturi tube. The level of the rnaterial
in the shell may be controlled by adjusting the arnount
of material supplied, and the speed of air flow rnay be
controlled by adjusting the r.p.m. of the fan. An outlet
19 is provided to take the grinding medium out of the
shell.
In operation, when the screw shaft 11 starts to
rotate and the material to be pulverized is fed into
the shell, the shaft will agitate the material and the
grinding medium, so that the material will be pulverized
to fine particles by friction between them. On the other
hand, when the suction fan 18 is started, air will flow
through the screw shaft 11 downwardly into the bottom
of the shell 10 and spread uniformly in all directions.
This air current will flow up in the shell 10, swirling
up between the classifying member 14 and the blades 15.
The air current passing therebetween carries up the fine
particles, which pass through the suction port 16 and
are collected in the collector 17. The coarse particles
are separated when passing between the blades 15 and
the classifying member 1~.
Since the air from the bottom of the screw shaft
11 spreads uniformly in all directions and disperses
the grinding medium and the material to be pulverized,
_ ~ _
~;~S6~
they will not stay at the same position. Since the suction
from the fan 18 puts the inside of the shell 10 under
a negative pressure, the requirement for sealing to avoid
pollusion of the work environment is not so severe and
the operation is easy to control.
Also, because the flow rate through the suction
port 16 can be easily controlled by adjusting the suction
fan 18, particles having a uniform particle size can
be obtained.
Fig. 3 shows another example of the classifying
member 14' which comprises a vane wheel rotatably mounted
on the screw shaft 11 and adapted to be rotated by a
motor 20. An annular member 15' triangular in section
may be formed on the inner wall of the shell 10. The
provision of the members 15' makes easy the formation
of swirlig air flow. But, the classifying members 14,
14' and the blades 15 and the triangular members 15'
may be omitted. Even if they are omitted, coarse particles
will drop by their own weight without being sucked through
the suction port 16.
Referring to Fig. 4 showing the second embodiment,
which is a vertical grinding mill of a wet type, a hollow
screw shaft 11 is mounted in the center of a cylindrical
shell 10 as in the first embodiment. The screw shaft
is supported by means of a support means 34 such as thrust
"` ~.;;~56~
and radial bearings so as to extend through the upper
wall of the shell 10. It is driven by drive means (not
shown) and has its bottom end open at the bottom of the
shell.
The shell is formed at its top with an inlet 32
through which both the material a to be pulverized and
the grinding medium b are fed into the shell 10. The
top of the screw shaft 11 is connected to a pump 18'
through a product collector 17. Suction from the pump
18' puts the inside of the shell 10 under a negative
pressure. This causes water or chemical liquid to flow
through the inlet 32 into the shell 10, down to its bottom,
up through the screw shaft 11 to the product collector
17. The material to be pulverized may be fed with water
in the form of slurry.
In operation, firstly the screw shaft 11 is driven
and the pump 18' is started to form the current of fluid.
When the material to be pulveri~ed is fed, it is pulverised
to fine particles by friction between the material and
the grinding medium. The product particles c are carried
by the abovesaid current through the screw shaft 11 upwardly
and are collected by the product collector 17.
As in the first embodiment, since the inside of
the shell is under negative pressure, the requirement
for sealing is not severe and control of the operation
7-
~56~
is easy.
Next, referring to Fig 5 showing the third embodiment,
a hollow screw shaft 11 is rotatably supported in the
center of a shell 10, as in the other embodiments. The
screw shaft 11 has its upper end connected to the blow
side of a fan (not shown) and its lower end open at the
bottom of the shell 10.
The material a to be pulverized and the grinding
medium b are fed through a rotary valve 42 and an inlet
43 into the shell, keeping airtightness. To the top
of the shell is connected a product collector 17. A
major difference from the first embodiment is that air
is blown into the shell 10 from top of the screw shaft,
whereas in the first embodiment air is sucked into the
shell because its inside is under negative pressure.
In operation, after the screw shaft 11 has started
to rotate and an air current flowing down through the
screw shaft and up the shell 10 to the collector 17 has
been formedl, the material to be pulverized is fed. The
material is pulverized to fine particles, which go up
in the shell 10, carried by the abovesaid current, and
are collected by the product collector 17.
The air current from the open bottom of the screw
shaft 11 spreads uniformly in all directions, dispersing
the grinding medium and the material to be pulverized
, 9
---8
~2s6a~
without allowing them to stay at the same position.
The product particles smoothly go up in the shell over
the whole periphery in the shell.
In this embodiment, as shown by dotted lines, the
collector 17 may be connected to the bottom of the shell
10 to take the product particles therefrom.
Next, referring to Fig. 6 showing the fourth embodiment,
the screw shaft 11 is rotatably supported in the shell
10 by means of a thrust bearing and radial bearings (not
shown)~ It is rotated by drive means (not shown) and
is open at its bottom end.
To the top of the screw shaft 11, a material feeder
55 is connected airtightly to feed the material to be
pulverized from the bottom of the shaft 11 into the shell
10. To the top of the shell, the suction side of a fan
18 is connected through a classifier 21 and a collector
17. The operation of the fan forms an air current flowing
into the screw shaft 11 into the shell 10 through the
classifier 21 and collector 17 to the fan.
In operation, the shaft 11 is firstly rotated and
the abovementioned air current is formed. In this state,
the material to be pulverized is fed from the material
feeder 55 through the screw shaft 11 into the shell 10.
The material will be uniformly fed into the shell from
the bottom of the shaft 11 and be pulverized to minute
particles by friction with the grinding medium The
fine particles are carried upwardly by the air current
formed by the fan and are classified by the classifier
21 and the product collector 17. The coarse particles
classified by the classifier 21 are fed back to the shell
10 through the screw shaft 11.
In the second to fourth embodiments, the screw shaft
11 may be formed at its lower portion with a plurality
of small holes 60 through which air, the product particles
and the material to be pulverized can pass. In the first
embodiment, slits 61 are formed at bottom of the screw
shaft 11 instead of the small holes 60.
Although in the first, third and fourth embodiments
air is used, dry hot air may be used instead. In this
case, dry product particles can be obtained.
Although the classifying member 14 is provided on
the screw shaft in only the first embodiment, it may
be provided in any of the other embodiments.
Although all the embodiments except the second one
are of a dry type, they can be converted to a vertical
grinding mill of a wet type such as the second one by
replacing the fan with a pump.
