Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY MILL WITH CHARGING SYSTEM
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FIELD OF INVENTION
This invention relates to an improved system for chargin~
materials to a container under a protective atmosphere. More partic-
ularly it relates to a valve system for charging particulate materialto a batch-type rotary mill under seal to the air.
~ACKGROUND OF INVENTION
In milling certain types of materials it is often necessary
or desirable to have a positive control of the atmosphere within the
mill at all times. For example, readily oxidizable materials such as
aluminum, titanium, magnesium, lithium and fine powders of many
compositions are combustible or even explosive under certain
conditions or they may be contaminated by the presence of air. In
milling such materials the control of the atmosphere must extend to
charging and discharging of the mill without opening the mill to air.
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In designing apparatus to be used for metals and other
powders special consideration must be given to valve design when the
powders will come in contact with a valve because the powders will
find their way into valve parts and render the valve inoperable.
The problems encountered in milling powders are
particularly troublesome in the mechanical alloying of readily
oxidizable metals such as aluminum, titanium, magnesium, lithium, and
rare earths such as cerium. Mechanical alloying has been described
in detail in the literature and in patents. U.S. Patents No.
10 3,740,210, No. 3,816,080 and No. 3,837,930, for example, involve the
mechanical alloying of aluminum alloys and other composite materials
containing aluminum. In the practice of mechanical alloylng the
components of the product are charged in powder form into a high
energy milling device such as a ball mill where, in an environment
free of or reduced in amount of free or combined oxygen, the powders
that are dry or substantially dry are ground down to a very fine size
initially, prior to particle agglomeration in the latter stages of
the process. This initial grinding increases the total surface area
of the metallic powders significantly. Since any freshly exposed
surface is not oxidized, it is very hungry for oxygen to the extent
that the powders in this condition will burn and/or might explode
spontaneously if exposed to air. Thus, any port in the mill, for
example, for charge or discharge of powders, is a source of potential
danger from the standpoint of the quality of the product produced and
the possibility of a fire and/or an explosion.
In batch-type grinding mills it has been conventional to
provide charging devices which are normal to the mill. That is, when
the mill shell is positioned for loading, the charging device is in a
vertical position with the charge port at the top of the shell.
30 U.S. Patent 4,679,736 discloses a loading means having an improved
design. In the improved design the loading means is in a vertical
position when the mill shell is rotated so that the loading means is
on the side of the mill with unencumbered entry for the feed material
into the shell. Also disclosed is apparatus for utilizing the dis-
closed charging design in mills in which a protective atmosphere is
required. The present invention is particularly effective with the
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positioning design of the loading means of the aforementloned
disclosure.
The present invention involves a valve svstem for charging
rotary mills in a manner which will protect the charge material and
the environment in the mill during loading of the mill, while at the
same time it is designed to minimize the problem of wear of the valve
pzrts during operation of the mill.
The charge system of the present invention can be
incorporated into existing batch-type rotary mills, permitting them
to be charged and operated under protective conditions.
STATEMENT OF THE INVENTION
In the present invention a batch-type rotary mill for
processing powder and capable of operating under controlled
conditions is provided wlth an improved charging system. The mill
comprises a hollow rotatably mounted shell, means to rotate the shell
and at least one charge passage means, e.g. an orlfice, located in
the shell for passing material into the shell. The improved system
for charging material to the mill comprises a loading means sealably
secured to the shell over each charge passage means and sealable to
the atmosphere with respect to the charge passage means and a
sealable charging means mountable on the loading means, said loading
means comprising a loading conduit sealable to the atmosphere, and a
valve assembly at least part of which is disposed in the loading
conduit and sealable to the atmosphere, the sealable loading conduit
comprising a port of entry and an exit port for passage of the charge
material into the shell , said exit port being aligned with the
charge passage means in the shell for passage of the charge material
from the loading conduit into the shell, and the valve assembly
comprising a valve plug sealably mountable in the charge passage
means in the shell, valve opening means to remove the valve plug from
the hollow shell so as to permit charging of the hollow shell and
valve closing means to seal the valve plug in the shell, the valve
opening and closing means being operable while the loading means is
sealed to the atmosphere, whereby said mill can be loaded under seal
to the atmosphere. The sealable charging means, e.g. a receptacle
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sealable to the atmosphere mountable on the loadlng means, is used to
feed material to the loading means.
The valve system is designed so that in the open position
the valve plug extends into the shell and in the closed position the
valve plug seats sealably in the orifice with its inner face
substantially continuous with the inner circumference of the shell,
so that there are essentially no valve projections into the mill,
which pro~ections could be worn away by action of the mill. When the
valve plug is closed during operation of the mill, the interior of
the shell is essentially smooth and continuous. The valve plug can
be constructed of a material that is at least as wear resistant as
the interior of the shell so that no greater wear would be
attributable to the valve plug.
To charge the mill, the shell (which is maintained sealed
from the air) is rotated until the loading conduit is located in a
generally vertical position at the side of the mill. The design of
the loading conduit makes it possible for the charge material to flow
vertically downward into the mill when the loading conduit is at the
side of the mill. After removing the closure means, e.g. a blind
flange, from the loading means, a charge receptacle containing the
charge material is attached to the loading means at the entry port of
the loading conduit. The charge receptacle is sealed to the
atmosphere, e.g. by means of a valve device which can be opened to
permit flow of charge material to the mill. While the loading
conduit is sealed from the charge receptacle and the shell, it can,
if desired, be evacuated or purged, e.g. with a gas inert to the
charge material, using apparatus suitably placed in the system. Then
the valve plug is moved to the open position, e.g. extended into the
mill shell so as to minimize retention of the charge material on the
valve parts, and the valve of the charging receptacle is opened to
permit the charge material to flow into and through the generally
vertically disposed loading conduit into the shell.
After charging the material into the shell, the valve plug
is closed, the closure means sealably isolating the loading tube from
the mill. Then the charging receptacle with its sealing means is
removed from the mill. Thereafter the loading conduit can be
resealed wit'n the blind flange.
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There may be more than one loading means along the length
of the mill, as wil] be appropriate, for example, to the length of
the shell and the quantity of material to be charged.
The present invention applies to batch-type grinding mills,
e.g. ball mills, for processing particulate material. The grinding
media may be, for example, balls, rods, pebbles or other appropriate
media. The material processed in the mills may comprise elements,
compounds, mixtures, alloys, ceramics and combinations thereof.
Examples of elements which may be present as ma~or or minor
constituents of the product are nickel, copper, zinc, titanium,
zirconium, niobium, molybdenum, vanadium, tin, aluminum, chromium,
magnesium, lithium, iron, silicon, yttrium and rare earths, e.g.
cerium and lanthanum; examples of compounds are oxides, nitrides
and/or carbides of aluminum, magnesium, silicon, yttriumj cerium and
lS lanthanum; examples of alloys are master a]loys of aluminum-lithium
and aluminum-magnesium. The present inventlon is particularly useful
when the material to be processed must be charged to and/or processed
in a mill under a controlled atmosphere.
The invention is particularly useful for the processing in
a ball mill metal powders which are readily oxidized and are prepared
as dispersion strengthened materials or alloys by powder metallurgy
routes. Of necessity the milling of such materials must be carried
out in a controlled atmosphere, e.g., in a hermetically sealed or
purgative atmosphere, or in an environment of controlled gas flow
such as an inert gas, or in an atmosphere of inert gas which contains
specific amounts of process controlled agents, e.g. hydrocarbons,
alcohols, acids, etc. It will be understood, however, that the
present invention is especially useful generally, for processing in a
mill any materials where a controlled atmosphere is required or
beneficial. For example, the present invention can be used
advantageously for preparing by a powder metallurgy route dispersion
strengthened alloys having, e.g., nickel, titanium, chromium,
magnesium, copper, iron or aluminum as a maJor constituent.
As indicated above the placement and design of a loading
means as described in a co-pending patent application is used
advantageously with the present valve assembly.
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BRIEF DESCRIPTION OF DRAWING
A further understanding of the invention and its advantages
of the invention will become apparent from the following description
taken in conjunction with the accompanying drawing in which
Figure 1 is a diagrammatic view in cross-section of the
charging portion of a ball mill provided with the improved valve
assembly system of the present invention and showing the valve in the
charging mode with the charging receptacle in place on the loading
means and both ~the loading means and charging receptacle sealed to
the atmosphere.
Figure 2 is essentially the same view of the charging
portion of the mill as Figure 1, except that the valve plug is shown
in the closed position with the loading means sealed to the
atmosphere.
Figure 3 is a schematic diagram of a ball mill in
accordance with this invention showing the multiple loading means in
position for charging the mill.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to the drawings, Figures 1 and 2 sho~ a diagram-
matic view in cross-section of the charging portion 10 of a ball mill
comprising a portion of a rotatably mounted, hollow, cylindrical,
metal shell 11, having an orifice 12 for the passage of the charge
material into the mill, and sealably secured on the shell a loading
means 13 for charging powder into the mill while sealed to the
Z5 atmosphere. The loading means 13 comprises a loading conduit 14
having removable sealing means 15, e.g. a blind flange, and a valve
assembly 16. The loading conduit 14 has an entry port 17 and an exit
port ]8, and it may be fitted with a conduit valve (not shown). The
exit port 18 from the loading conduit is aligned with orifice 12,
providing a smooth, unencumbered, direct passage for the charge
material into the mill. The removable sealing means 15 is used to
seal the loading condui~ after shell 11 has been charged. Charging
receptacle 24, equipped with butterfly valve 25 (alternatively, a
slide gate or any other appropriate valve) is connected at the entry
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port 17 to the loading means 13 by means of bolts 26a and 26b through
flanges 28 and 50. The valve assembly 16 of the loadin~ means, in
turn comprises a valve plug 19 and a sealed valve activating means
for opening and closing the valve. The valve plug 19 is designed to
fit into sealable relationship with shell 11 so as to form a
hermetical seal on the shell with respect to the loading means 13 in
the orifice 12 when the valve is in the closed position. The valve
ac~iva,ing means is comprised of valve stem 20 flexibly connected at
connection means 31 to the valve plug 19 to allow for plug alignment.
(Alternative aLignment means may be provided.~ The valve stem 20
permits opening and closing of ehe valve plug 19 in shell 11 without
exposing material in the loading conduit 14 to the air. Loading
conduit 14 is adapted with a sealed entry means, viz. valve packing
21, packing nut 21a, and valve stem guide 20a for the valve stem 20.
Valve stem 20 extends outside the seal, providing a means for
controlling the opening and closing of the valve from a position
outside the sealed portion of the loading means 13 without exposing
the interior of the shell to air. Flexible bellows 32 also seal
powder out of the valve stem area. To seal the shell, orifice 12,
which may be any shape but is preferably round or elliptical, is
provided with a valve plug seat having a beveled rim 22, and valve
plug 19 is machined at rim 23 to mate securely with a valve plug seat
beveled rim 22 and seal the shell when the valve is in the closed
position. Alternatively, e.g., rim 23 or seal 22 may be the segment
of a sphere or other curve to improve valve seating and alignment.
Additionally an elastomeric-type material may be used to provide a
further seal between the valve plug and the orifice. In the
preferred embodiment angle a, i.e. the valve stem angle relative to
the horizontal is 45. If sealing faces 22 and 23 are at an angle of
about 45 to the valve stPm 20, then the lower portion of 22 are
beyond the vertical, eliminating surfaces on which powder may
accumulate. The valve plug 19 is constructed, for example, of an
abrasion resistant material so that it will not be worn away during
the grinding cycle of the mill. The valve stem 20 is provided with
means 29a and 29b (an orifice and pin, respectively) to hold It in
the closed position, and with a means 30, (a stem stop) to limit the
travel of the stem in open position. Alternatively, for example,
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stem 20 could be threaded for valve opening and closing. In
addition, by gauging the position of the stem 20 on the outside, it
i9 possible to determine if the valve is open for charging or seated
for running. Means for purging or evacuating the loading conduit i9
S provided by purge port 27, which is fitted so that a vacuum line
and/or purge gas line can be connected to the loading conduit.
Figure 1 shows schematically the valve plug in the open
position with a charging receptacle sealed to the entry port, and
Figure 2 shows the closed position of the valve plug with the blind
flange in place_ It will be understood that the orifice 12 will be
sealed with the valve plug during operation of the mill. In the
closed position there are no pro~ecting parts of the valve into the
interior of the mill shell 11. In the open position, in the
preferred configuration as explained above, the valve seat 22 is
vertically aligned with the loading conduit 14 at the lower end of
the orifice and horizontal at the upper end. This arrangement
provides for flow-through of charge material without encumbrances to
the passage of powder into the shell.
The mill shell may be, for example, cylindrical, spherical,
double or single conical, multi-flat sided, etc. The exact shape of
the mill shell is not critical to the invention. Mills may also be
double walled (or jacketed) for mill shell cooling. Water or other
cooling media may be passed through this space tor Jacket). Many
varieties of mills and mill adaptations may be used, but it will be
appreciated that these adornments are not a factor in this invention.
The loading means may be sealably mounted on the outer side of the
shell with, e.g. a flange. To obviate the need for alignment of the
loading port on the entire shell, the complete loading means assembly
including a section of the shell with the orifice can be mounted
separately into the shell. This arrangement would also be convenient
for repair and replacement of the loading means without otherwise
disturbing the mill.
Figure 3 shows a preferred embodiment of the present
invention in which a pair of loading means 13 and 13a are located on
the periphery of rotatably mounted shell 11 of a ball mill 40. The
ball mill comprises a pair of support members 33 and 34, a
cylindrical shell 11, mounted for rotation about an approximately
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horizontal axis on trunnion bearings 38 and 38a. The shell comprises
ends 35 and 36, a peripheral wall 37 and a pair of charging orifices
(concealed in the drawlng by the loading means 13 and 13a,
respectively). The charging orifices are sealable from the
atmosphere, respectively, by the pair of loading means 13 and 13a
secured on the shell 11 to cover the respective charging orifices.
The grinding medium, i.e. the balls, are not shown. At end 35 of the
drum ~s the driving means 39 for the mill which is not shown in
detail and not a part of the invention. When the loading means 13
and 13a are in the essentially vertical position so as to permit
charging of the mill under the force of gravity, the loading means 13
and 13a are on the side of the rotary mill shell 11, with a portion
of valve stems 20 and 20a visible. Shell 11 is sealed from the air
and is provided with a means ~not shown) for feeding into or
establishing in the shell a desired environment, e.g. nitrogen, argon
or other elemental or mixed gas with or without process control
additives, e.g. controlled amounts of hydrocarbons or oxygen or
carbon. Means to discharge material from the mill is not shown. A
suitable means of discharging the mill is disclosed, for example, in
U.S. Patent 4,679,736.
In operation of the improved valve assembly of the present
invention, the charge materials, e.g. metal powders, are charged
through the loading means under sealed conditions. While maintaining
the loading means under sealed conditions, charging receptacle 24
with valve 25 closed is attached to the loading means, the valve stem
20 is operated to move valve plug 19 into the open position, i.e.
extended into the rotary shell, thereby opening the orifice in shell.
Valve 25 is then opened, thereby releasing charge material from the
receptacle. The powder charge will then flow through the loading
conduit into the interior of rotary mill shell. After the powder
charge has drained from the charge receptacle through the loading
means into the shell, the valve stem 20 is used to retract and secure
the valve plug 19 to the shell face. The charge receptacle can then
be removed. The loading conduit is maintained sealed to the
atmosphere after the charge receptacle is removed.
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In the embodiment shown in the drawing the mill shell is
rotated about an essentially horizontal central axis. In another
embodiment of the invention the chargin~ system is adapted for
placement on a mill with the drum operated to rotate about a non-
horizontal axis.
Although the present invention has been described in
coniunction with preferred embodiments, it is to be understood that
modiEications and variations may be resorted to without departing
from the spirit and scope of the invention, as those skilled in the
art will readil~y understand. Such modifications and variations are
considered to be within the purview and scope of the inventicn and
appended claims.
