Note: Descriptions are shown in the official language in which they were submitted.
33~ ~
BACXGROUND OF ~E INVENTION i;
_ _
This inven~ion relates gei~erally to the recovering o the
free metal entrained in dross or skimmings obtained ~rom ~h~
production of aluminum or aluminum based alloys.
In the course of conventional aluminum melting operat~ons,
oxidas, nitrides and other non-metallic impurities accumulate
on the surface of the molten metal. Prior to tapping of th~
molten metal these non-metallic~ are removed ox skimmed from the
surface of the melt~ Substantial quantities of aluminum metal
will be unavoidably entrained with the non-metallics and also be
removed with the non-metallics. ~his mixture of non-metallics,
free alwninum and alumiDum alloy is termed aluminous dross or
skim~ For convenience, this mixture of non-metallics and free ~ -
aluminum i~r aluminum alloy will hereinafter, in the specifica- -
tion and the appended claims, be referred to as aross.
As stated above, the dross derived from aluminous metal
melt unavoidably contains a substantial proportion of free metal
and/or alloy as a result of the usual stirring of the melt and ~`~
rakiny off of the floating material. During the raking, skim-
ming and removal of the dross from the top of the metaL melt,
the dross becomes compressed into pasty mud-like masses. These
masses of dross, when removed from the furnace will vary rom
small lumpi3 on the order o~ one inch in dimension and smalLer to
large lumps approaching one foot in dimension for example. The
amount o free metal and/or alloy in the dross may vary from 30yO
- 2 -
' ~
337
to g5% by weight depending upon a number of factors, such as
the composition of an alloy being meited, the melting proceduro
followed, and the care with which the dross is skimmed or raXed
from the meltO If a batch of hot dross removed from a malt is
allowed to stand, some free metal will accumulate at the bottom
o~ the mass, but the l~rger part o~ the ~ree metal will remain
intimately mixed with non-metallics in the form of globules or
small par~icles and will not readily separate from the non
metallic portion~ Aliso, upon being exposed to the abmosphere,
the hot dross may begin to react with the air, if the reaction
ha3 not already started within the f~rnace; and if ~he reaction
is not stopped, a large part of the available metal will be
lost. iThe separation of the free metal from the non-metallic
portion of the dross has been a dif~icult problem. se~eral
methodq used or proposed for effecting separation are meltioned
below.
Xn one ~ethod, the dross is cooled to room temperat~re as
quickly as possible, screened, crushed as in a ball mill, and
then screened again. By this mechanical means of separation, the
coarser metal particles can be separated and recoveredO However,
the bulk of the free metal in the dross is in the orm of small
particles which heretofore has made recovery by mechanical mean~
unattractive.
In another method the hot dross is stirred into a heel of
molten aluminum or aluminum alloy. This method is not efficient
because in agitating the dross in the molten metal heel, nearly
as much metal is beaten into the dross as is removedO
~ .
: . ~ :
~ ~ ~3~3 `~ :
In still another process, after skimming o the droRs, it
is fed without further preparation into recovery ~urnaces,
fluxed with salt for example, and metal recoverie~ are ohtainedO
This process is not efficient because of low metal recoverie~0
high energy costs per ~ound of metal recovered and a seriou~
disposal problem o~ the resulting slag which, berause of it
salt content, has become envir~nmentally unacceptable~
Common salt, i.e. sodium chloride, is employed in this
process due to the low cost of the material. More expensive
salt type fluxes may be used to increase metal recovery to a
limited extent, but then such additional C05t for flux offset~
the increased effactiveness related theretoO ~owever, while
tha cost of sodium chloride is low, the recovery of molten
metal involved has also been very low. These low recoverie~
are due to the fact that common salt fails to efficiently
attack the o~ide coatings on the small droplets of aluminum
material entrapped in the aluminous dross. The use of common
3alt has a further disadvantage in that substantial heat is
re~uired to melL the salt, its melting point being at a tempera-
ture o~ approximately B00 degrees CO (approximately 1480 degrees
F.). I~ satisfactory melting i9 to be made possible, the salt
bath must be heated at a temperature substantially above its
melting point in order to have sufficient fluidity, and it must
be kept at this temperature during the introduction o~ the alumi~
nous dross and during melting down. For example, where the salt
` :
.. _ 4
~ - ~
i33~
melts at 1480 degrees F~, the bath would have to be heated to a
temperature on the order of 80 degrees F. higher, or about 1560
degrees F. in this inst~nce. For melting and treatiag ~luminum,
the maximum temperature permissible for best results is approxi- ~-
mately 1500 degrees F. Above this temperature deterioration of
the quali~y o the metal and undes irable fumes result. Further- `
more, when the aluminous dross-salt flux mixture is heated to ~;;
1560 degrees F., it possesses a considera~le dissolving power
for all metals which come into consideration as impuritiesO In
addition, the hot common salt melt strongly attacks furnac~
lining.
According to a more recent process, hot dross, which may be
either the dross a~ removed from the melting furnace or cold
dross which has been reheated, is placed in an inclined rotatable
drum open to the air, and the dross is rotated therein for a
short period of ~ime. If the dross is not already burning when
introduced into the drum, ignition is started by the addition `~
o suitable salts. In this process, a portion of the finely
divided ree metal is consumed in reacting with the air to pro-
vide the heat essential for raising the temperature of the ~ass
Consequently, the recovery o~ metals is not as high as desired.
Metal recoveries on the order o2 65% to 70% o2 the available
. ' ;, .
:,
-5- ``
` : ' ' . . ' '~' . :' ' ` ~ ' `: ' : : . ; . . :
~.3~33~
metal have been achieved by this method, but on the average the
recovery has been found ~o be below 60%o ~n addition, it i9
difficult to control the furnace tempexature when employing
this process, and generally the tempexature is well above 1500
degrees F. with the attendant disadvantages thereof, :
With respect to all of the prior art methods for recoveri~g
aluminum metal, it is to be understood that dro~s, as generally
referred to hereinabove, exists in particles and chunks of
material of various sizes~ A representative sample of dross,
after initial con~en~ional milling and screening preparation,
may contain the following size ranges, aluminum content and
recovexable aluminum using the better of the recovery methods
described heretofore:
, ~
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U~a \ ~:
U~
~,
C ~ ~ ¦
h U
~ C I
O ~ 2
O o o o
O .~ a~ In Z S!;
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a. Q~
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a) U
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,1 ~ O ao ~ z 2;~ ;
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h O 1l)
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V~ t
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~he size ra~ges of -.10 inch and down, if subjected to the ~ -
heat of the furnace, would be consumed in the heat of th~
fuxnace and lostO $herefoxe, these size ra~ges are generally
screened off and sold as low percentage metallic content ~
aluminum oxide du~t
~si~g a represe=tative sample of dross, screen~ng off the
-.10 inch size range, and using the balance for furnace re- ;~
covery, the foIlowing approxi~ate results are obtained using ~.
the generally accepted aluminum xecovery methods described.i
heretoforeO
-8-
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r~ ~ o ~ rl ~ ~ ~ ~ ~
r 1 O O O O
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q~
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a) :~ ~ o o ~
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o ~r tD Ul I~ ::
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~n ~u O O O O O ~-
o o o o o :-
O t:: O O O O ~ .:
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o ~ o ~r ~D O O
i4 ~LI N h N ~1 i~
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U
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rl ~-1 r~ N
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., __.. _____ ._ _ ... _... ., ~ _ .
', . ' `: : :'':''::: :: : ` : , ' " ' :: ' ;
~5~3~3~
Therefore, using prior art methods of metallic recovery,
~ubstantial portions of the contained aluminum or aluminum alloy
in the low grade, smaller dross pa~icl~ are lost in the re- ~;
covery process. This results in a metal recovery, by weight, of ~;
'b approximately 5a% of the dross load or approximately 71% oE the
contained metallicsO
It i5 to be further understood that conventional prior art
milling methods could be employ d to mill dross for an extended
s
period of time with the resulting dross having an increased
metallic % content. ~owever, this is not done for at least two
reasons. ~irst, it would require significant amounts of energy
' ,?' to mill the dross for prolonged periods of time which is econo-
~; mically impractical. Secondly, if the dross were continuously
milled ~or a prolonged period of time, the milling would tend
to di~integrate some o~ the metal into dust which would combine
with the oxides whereby such disintegrated metal could not be
used to charge a furnaceO
Therefore, with respect to the current state o~ the art, it
will become readily apparent that the present invention re-
presents a significant breakthrough in the processing of dross
as hereinafter shown~
10~
' :
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:. .. - ,, : : ..
: ~. -, . .. : . . . .. .
~ , : , : .
~3~37
Accordingly, one ob~ect of the present invention is to
provide a new and substantially improved process for recovering
metallic substances entrained in dross.
In one particular aspect the present invention provides
a method for reclaiming, in relatively high metallic concentrate
form, metallic substances entrained in dross, the method com-
prisin~ the steps of: conveying the dross to a pair of roller
means having a predeter~ined spacing, the dross comprising
particles of a predetermined 9i ze range, compressing the dross
to a limited degree without substantially crushing the same
~between the pair of roller means by passing the dross there-
between so as to substantially break the bonds between the
metallic and non-metallic substances in the dross, and separating
the non--metallic substances from the metallic substances so
that relati~ely concentrated metallic substances remain whereby
metallic dust-like particles become disassociated from the
metallic substances and are commingled with the non-metallic
substances after separation of the latter from the metallic
substances.
In summary, raw dross may initially be screened, milled,
screened and separated into three fractions, for example, as
familiar to those skilled in the art. The particles of these
fractions may be one-quarter of an inch and larger, one-quarter
oE an inch down to one-tenth of an inch and one-tenth of an
inch and down in size. This initial preparation and sizing
is prior art and not part of the present invention.
--11-- -
cb/ /~ "~1~
33~
.. ,
Dross concentrates or particles larger than one inch,
for examp].e, wh:ich approximates 20% oE a representative sample ~;
of partially prepared dross concentrates, are already high
grade, high % metallic concentrates to a degree sufficient for
final processing. The si~e ranges on the order of one inch and
':
. `~
30 ;
~ 12-
.,, ,, . . . , , ., ., . " . . ..
,. : ; ~
~3~33~
smaller are sub-divided and processed by the method and
apparatus o~ the instant inventionO
A sub-divided size range, low grade dross concentrate is
screened and conveyed to a first pair of roller means h~ving i~
a predetermined spacing. The rollers are preferably spring or
otherwise resiliently mounted to a}low movement of the rollers
away from one another as the dross passes therebetweenO ~he
rollers compress the dross particles or concentrates to a
limited degree without substantially crushing the same so as
to break the bonds between the metallic and no~-metallic sub-
stances in the dross. The dross concentrates, so compressed,
are screened to remove the limited amount of oxides which fall
of~ as a result of the roller action. The screened dross, in
the compressed conditio~, is then conveyed to a hammermill
which loosens and removes the oxides from the aluminum in a
highly effective manner due to the prior breaking of the bonds
between the ~etallic and oxide substances by the rollersO The
oxides are then screened out to yield aluminum concentrates
significantly free of oxides. These resulting concentrates
may be charged into a recovery furnace or conveyed to a second
pair of roller means. The second pair of rollers substantially
crush the high grade aluminum concentrates into flattened high `~
grade aluminum flakes. A small percentage of oxide material
-13-
`,
~:~L3~3~7
,:' -
is removed by the action of the seco~d rollers.
At ~his point, the al~minum flakes may be further processedas fQllows.
(1) The flakes may be charged into a furnace ~'or recove~y
of the contained metai as aluminum ingot with recovery ratios
being approximately the same as partially prepared dross c~n-
centrates sized larger than one inch in dimension.
~ 2) The aluminum flakes may be processed through a
series of ham~ermills to convert the same into high purity
aluminum pellets sized on the order of one-tenth of an
inch and smaller, for exampla. The larger shredded pieces
tend to ball up into substantially pure aluminum pellet~.
The smaller shredded pieces also tend to ball up into
aluminum pellets, but of lesser puri~y because they become
intermixed with tiny pieces of oxide not removed by the process.
~ 3) The substantially pure aluminum pellets may be charged
into a ~'urnace for recovery of the contained metal as aluminum
ingot with recovery ratios better than the recovery ratio o~' ~
paxtially prepared dross concentrates sized larger than one ,`
inch as referred to hereinaboveO
The present invention also describes apparatus for commi-
nuting a metallic substance, such as high grade alumi~um con-
centrates or scraps, into metallic particles. ~he apparatus
aomprises a mill with a plurality o~ cutting knives having
- 14 ~
` .
~3~7
leading edges formed to slice through the metallic substan~es.
The foregoing and other objects, advantages and characteri
æing features of the present invention will become clearly
apparent from the ensuing detailed description and an illustra;
tive embodiment thereof, taken together with the accompanying
drawings wherein like referenced characters denote liXe parts
throughout the various views.
BRIEF DESCRIPTIOM OF T~E DRAWIN~S
Figs. lA and lB schematically represent exemplary apparatus
employed in practicing the present invention to recover aluminum
metal from dross wherein the dross is fed into a conveying means
at the left side of Fig. lA and the recovered products are re-
ceived at the right-hand side of Fig~ lB
Figs. 2A and 2B respectively represent a chunk of dross, pre~
viously milled and sized by prior art methods, on the order of
one-quarter to three-quarters of an inch in dimension and having
on the ordex respectively of 65% and 75% by weight of aluminum
me.tal combined with non-aluminum materials such as ferrous and ~
oxide suhstances; ;
FigsO 3A and 3B are views correspondingly similar to Figs.
2A and 2B representing the dross after it has passed through
the first pair of rollPr means whereby the bonds between the
metal and oxides are substantially broken;
-15-
~;
;'
.
.. . ~ . : . . . ~ . . , . . - -. , . ,.. . - .. . - . .
3~7
Figs. 4A and 4s correspondingly represen~ aluminu~ con- ;
centrates and non aluminum dust substances separated ther2from
after the dross has passed through the irst pair o~ roller
means and hammer mill associated therewith,o
Fig. 5 illustrates aluminum concentrates after passing
through the second pair o~ roller means wherein the concentrate
have been substantially flattened;
Fig. 6 represents aluminum particles after having passed ~`
through the hammer mill means following the second pair o~
roller means wherein the concentrates have been further cleaned;
Fig. 7 is an illustration of the cutting edge of a knife
associated with the mill illustrated in Figs. 8 and 9;
Fig. 8 is a side view of a mill, with portions thereof
shown in section, for conver~ing chunk aluminum into aluminu~
pe llets comprising particles of a predetermined si7e range, and
FigO 9 is a transverse view in section taken about on line
9-9 of Fig. 8 showing the hammer mill illustrated therein.
DETAIIED DESCRIPl~ION O_T E_E~IO~ .
IA considering a detailed description of an embodiment of
the method comprising in part the present invention and an em-
bodiment o~ the apparatus associated therewith, it is to be
understood that the non-aluminum, oxide dust in combination with
varying degrees of aluminum dust recovered from the dross ha~ a
-16-
,, ,: : :,', -. . :',. . .. ..
~3~33 7
substantial market value, as ior example in the exothermic
industry as it relates to ~he manufacture of stael. The alumi
num dust entrained in the non-aluminum substances is subject to
oxidation and correspondingly is a source of con iderable heat
necessary in the manufacture of steel, all of which is well
known to those skilled in the art. As energy in general becomes
more expensive, it will become still more desirable in the steel
industry to improve the quality of manufactured steel with a
view towards avoidance of reprocessing steel products which ca~
be costly in an energy sense. This represents but one o~ the
useq ~ r the aluminum/oxide dust provided by the present in-
vention and illustrates the importance thereof in view oX
current and potential future energy problems. Of course, the
value of recovering aluminum concentrates from the d~oss in
selective degrees of purity by a mechanical process is readily
apparent to all familiar with this art.
Dross as such,wh~ch is intended to include aluminum,
aluminum alloys and other similar metals, may be purchased by
a dross processor from a metal producer wherein the dross will
have particles or chunks of very small size to chunks sized on
the order of one foot in dimension, for example. By way o
example, a one hundred thousand pound load of raw aluminum dross
may contain on the order of 75% to 80% by weight of metallic
aluminum combined with non-aluminum substa~ces, The relatively
-17-
': : .: ~ : : ;: ~ : : ` : ' '': : `
:~3~3~'~
larger chunks of dross ge~erally contain a higher percentage by
weight of aluminum metal than the smaller chunks and for purposes
of description aluminwm is considered to mean pure aluminum as
well as aluminum alloy. Dross chunks on the order of two inches
in dimension and larger may accorclingly be ~easibly processed
for me~al recovexy in urnaces employing prior art procedures
and the present invention is of less significance with respect
to dross chunks of this siza than with re~pect to those on the
order of two inches in dimension and smaller. In other words,
the realtively smaller amount of oxide on the larger, high
metallic content dross chunks creates a lesser problem in
recovering the metal therefrom. However, as discussed and to
. .
be discussed, as the size of ~he dross chunks decrease, it be-
comes progressi~ely more dif~icult to process the same for
recovery in a furnace. The smaller the dross chunk becomes, it
has a relatively ~arger surface area. The relatively larger
surface area subjects the smaller concentr*es to destruction in
the heat of the furnace. The~smaller the dross chunk becomes,
i~s relative non metallic oxide coating increases entraining a
a relatively smaller p~rcent of metal within the concentrate.
In this regard, the oxides act to ihsulate the entrained ~luminum
and salt fluxes have less efficiency in attacking the oxide
coatings and consequently less o~ the entxained metal is
releas~d. Also, because of their lower density, a good portion
of the released metal from the smaller dross chunks ars now
subject to being burned up in the heat of the furnace. Accord-
~J inyly, as referred to abo~e, the prior art methods of recovering
18 ~
~ ,.
.' ' ' . ' , ` , ' ' '' . , '~.' ' ` ' ' ' ;' '
i " ., - , , ~ ~, "~ " ~
`~ .
~L3~33~ ~
metal from dros~ chunks particularly in the size range on the
order of two inches i~ dimension and smaller have not beea
efficient --- recovering for example on the order of 90yo of
the entrained metal in 3i~es near two inches if properly pre-
pared to only less than half of the entrained metals m size~
near one tenth of an inch. Therefore, the method to he describ-
ed, although applica~le in general to metallic dros , i~
specifically applica~le to aluminum dross
- l=a -
, - .; . ~ . ,: : . . :: :
., ,.: :: : :: :: :i - ::
` ~3~
chunks or par-ticles of smaller siæe.
~ urning now to Fig. lA, dross which has been previously
milled and screened from whole dross into particle siæes ranging
for example from one-tenth of an inch to one-quarter o~ an inch
are placed in hopper 10 and conveyed upwardly by a bucke~
elevator 12 to a aouble deck screen 14. It is to be understood
~hat the instant method is more efficient when the dross charged
into hopper 10 has been appropriately sized into selected size
ranges. With respect to dross particles two inches in dimension
and smaller, the size ranges of dross for charging in~o hopper
10 could include 1/40 to 1/20 of an inch in dimension, 1/20 to
1/10 o an inch, 1/10 to 1/4 of an inch, 1/4 to 1/2 of an inch,
1~2 to 1 inch, 1 to 1-1/2 inches and 1-1/2 to 2 inches. Of
course these ranges could be varied somewhat within the scope of
the inven~ion. As shown in Figs. 2A and 2B, a typical particle
or chunk o dross will include mètallic p~rticles 2Q, oxide
.
su~stances 18,;ferrous subs~ances 16 and other fore~gn-substances 23
Figs~ 2B, 3B and 4B are included only to illustrate ~he
larger percentage of metal in larger dross particles when com-
pared to Figs. ~A, 3A and 4A. For example, Fig. 2A may repx~sent
metal content on the order of 65% ~or a one-~uarter inch particle
while Fig. 2B may represent metal conten-t on the oxder of 75%
for a three--quarter inch particle.
Oxide and aIuminum dust having particles smaller than one-
twentieth of an inch for example pass downwardly through the
double deck screen 14 into hoppex 22 and are collected as an
end product for uses referred to hereinabove. In referring to
the separatio~ of non-metallic substances from metallic sub-
stances/concentrates, it is to be understood tha-t minute
- 19 -
:: . . ,, , . . . ,: . : . :~ : : , - , ~: :
~3433 7
particles of metal substantially in the form of dust, ~ill be
commingled with the non-metallic substances whichalso will
be of minute particulate sizeA ~ecessarily, the dust collected
in hopper 22 will h~ve a v,arying percentage of aluminum du~t
commingled therein. Container 22a may simply be a removable
barrel for receiving the aluminum oxide dust rom hopper 22.
I}edross material not falling throughthe double decX screen
14 passes onto a magnetic separating means 24 which removes loose
ferrous substances such as 16, subsequent to which the dross i9
conveyed to hopper 260 ~he dross in hopper 26 is in turn fed
to a c~nveyor 28 which conveys the dross material to a vibraL.ing
feeder ~0 which ~eeds the dross material to a first pair of ' ~,
spaced roller means 32.
The rollers 32 are pre~erably resiliently mounted with
xespect to ~e another as for example by means of springs 33. The
rollers 32 have a predetermined spacing less than the selected
size range o~ dross particles passed therebetween whereby the
rollers 32 may resiliently separate one from the other upon
passage of the dross therebetween. For example,,for dross 1/10
to 1/4 of an inch ~ed to rollers 32, the spacing therebetween
could be on the order of 1/20 of an inchO The spacing would bc
correspondingly increased or decreased for other dross si7.e
ranges so that it is less than the smallest size of particles
passed therethrough. The rollers 32 are adj~sted to compress
the dross passed therebetween to a limited degree without
substantially crushing the dross so as to substantially break -
the bonds between the metallic and non-metallic substances there~
ln. ~he spring pressure on the rollers, w~ich can be adjusted
independently of the spacing, should be increased or decreased ,
respectively for the larger or small dros~ sizes so as to impart
the above effect on the dross.
,' ,
- 20 -
3~
The limited compression imparted by xollers 32 can be
appreciated from a comparison of Eigures 2 and 3 respectively
representing dross on the input and outputs sides of rollers
32. As illustrated in Fig. 3, bxeaking of the bonds between
the metallic and non-metallic substances is intended to be
repres~nted in a schematic sense by the fracture iines 21. Of
course oxide bonds on the surface of the aluminum particles
would be broken~ The limited compression imparted by rollers
32 is to be contrasted with prior art roll crushers which in
good part pulverize or disintegrate dross passed therebetween.
In so doing, the oxide substances such as 18 become ground into
the metallic substances so that they are not readily separable
there~rom upon subsequent milling as are the oxides subjected
to the limited co~pression of the instant method. In this
xegard, the springs 33;'function to avoid lmparting undue com-
pression on the dross passed thxough the rollers. However, it
is within the scope of this invention that rollers 32 could
have fixed mountings with respect to one another, thereby not
being resiliently separable. In this arrangement, the over-
sizing of the dross passed between the rollers would have to be
restricted to a narrower range so as to insure that only an
appropriate amount of compression and ;~paction be imparted to
the dross.
The crushed dross flows rom the rollers 32 up an inclined
conve~or means 34 to hopper 36 which feeds a bucket elevator
1'``'
38. The bucket elevator 38 feeds the dross onto a single
21
,
; ~
~341t~
deck vibrating screen 40 which screens out non-aluminum
and aluminum dust su~stances in a manner similar to the
collection of such substances in hopper 22 described herein~
above. ~he dross materials which do not fall through screen
40 into the underlying hopper 42 and container 42a are passed ~-
~Fig. lB) to a hammer mi}l means 440 ~ammer mill 44 is of
a type well known to those skilled in the art a~d which im
pacts the dross, previously fractured to a limited degree,
so as to knock off loose oxide materials. In this regard
the prior compressing of the dross by rollers 32 is signi-
ficant 90 as to enable mill 44 to disassociate the oxides
from the metal after rollers 32 have broken the bonds there-
between. ~owever, hammer mill 44 does not necessarily de~
form the aluminum particles and chun~s, as viewed in Fig. 4,
but yields particles of dross having significantly higher `
percentage of metal content ~concentrates) with oxide~ com-
pletely removed in fact from some of the surface area of the
metal.
An air separator or separating means 45 is i~ fluid com~
munication with the lower housing of mill 44 which pulls a
certain amount of non metallic and metallic dust from the
housing to a remotely located baghouse 47 for example~
~ he dross as processed by the hammer mill 44~(Fig. 4) falls
-22-
.
~3~3;3~
to the underlying conveyor 46 which passes the same to hopper
48 and the bucket elevator 50 associated therewith. BucXct
elevator 50 transports the chunks of aluminum concentrate~
and disassociated oxide materials not pulled ofi by air
separator 4S upwardly onto a single deck vibrating scree~ -
52. The resulting relatively high metallic concentrates
m~y be passed to another magnetic separator tnot shown)
and onto vibrating feeder 540 The milled non-metallic
substances as well as minute aluminum particles which ma~
be present fall through screen 52 into hopper 56 as an end
product, in a manner similar to that described with respe~t :
to screens 40 and 140 In actual practice, it has been found
that the limited compression imparted by rollers 32 removes .
on the order of 7 to 8 per cent of the original oxides present :~
and at the further step of milling as at 44 or example re-
moves a significant additional amount of non metallic sub-
stances ~oxides) on the order of 11-12 per cent of the
original non-metallic substancesO
~he dross or aluminum concentrates conveyed to vi~ ;
brating feeder 54 are a marketable product, without the need
for further processing, within the context of the present
invention. Further processing, as within the scope of this
invention, would inGsease the purity of the concentrates
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but at the cost, of course, of further processing operations. :
The concentrates provided at feeder 54 have been cleaned of :;
oxides to such a degree that they may be charged into, for
example, a swarf furnace for recovery of metal in ingot fonm,
as well known in the prior art. The charging of relative}y
clean concentrates, as prGvided by ~he instant invention, into
a swarf furnace is to be contrasted with the prior art methods
of charging considerably less pure concentrates lnto a rotary
furnace for the recovery of metal which involves all of the
drawbacks referred to previously hereinaboveO .
Alternatively, the concentrates on feeder 54, instead of
being taken off as an end product, may be passed to the spacad
rollers 58 which deform the aluminum concentrates into
flattened, flake-like pieces as illustrated in Fig. 5.
Rollers 58 preferably include ~ixed mountings whereby the
concentrates from feeder 54 are compressed into flakes such
as illustrated in Fig. 5 which may be on the order of 1/16 of ~-
an inch thick for example with respect to 1/10 to 1/4 of an
inch dross originating in hopper 10. The spacing of rollers 58
would be set to a corresponding degree and could be increased
or decreased, respectively for larger or small dross sizes
originating in hopper 10. The ~lakes fall to the underlying
screen 59 which passes some additional aluminum and oxide dust
into hopper 61 and associated container 61a.
At this point the flakes include a somewhat higher
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~ 3~337
percentage metal content than the concentrates con~eyed
to feedex 54O Consistent with the approach of the present
invention, the ~lakes residing on screen 59 may be pulled
off as a marketable product not requiring further pro-
cessingn With respect to conversion to ingot iorm, the
fla~es may be viewed as more desirable than the concen~
trates conveyed to ~eeder ~4 since the ~lakes or example
have a higher density and accordingly will sink below the
surface of a swarf furnace more rapidly as a consequenceO
Of course, it is important that the charge to the swar
urnace (concentrates/flakes) sink below the furnace
surface so as to avoid potential combustion with the
atmosphere.
Should it be desired to convert the flaXes on
screen 59 to yet a more pure form, the flakes may be
conveyed from screen 59 to a hammer mill 60, one embodi- ;:
ment of which forms part of the present invention and is
illustrated in Figs. 7-9.
The Fig. 5 flakes are processed by mill 60 and ~low
through passage 80 to a cyclone type o air separation
means 81. Cyclone 81 is a device well known to those :~
skilled in the art wherein the milled flakes would enter
the cyclone at a tangential angle so as to create a low
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337
pressure area in the ce~tral portion of the cycloneO
The low pressure draws aluminum and oxide dust in~o .
the central portion which pass in turn through conduit
83 to a xemotely located baghouse 920 ~aghouse 92 empties
into an underlying removable container ~2a which is similar
to containers 61a, 56a, etcO The heavier metallic parti-
~les in cyclone separator 81 drop to a second mill 78
underlying the cyclone 81. The output from mill 78 i9
conveyed through passage 84 to a second cyclone means 85
which is similar in all respects to cyclone 81 and which
conveys aluminum and oxide dust to conduit 83 and the ::
oaghouse 920
Metallic concentrates, which may be in the form of
pellets as shown in FigO 6, fall from cyclone 85 to the ;~:
underlying screen means 88. The aluminum pellets falling
onto scxeen 88 are of a higher purity than the Fig. 5
type flakes charged into mill 60 in view of the oxides
removed by cyclones 81 and 85, and further in view of the
oxide, as well as aluminum dust, which passes through screen
88 to the underlying hopper 96 and container 96aO The
pellets residing on screen 88 are in turn conveyed to
hopper 98 and to the underlying container 98a as an end
product~
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. ~ . ., ~ .:
~.~3~33~ `~
The pellets or concentrates collected in container
98a are the most desirable of the vaxious products pro-
duced by the instant invention since they are of the
relatively greatest purity. of cour-e, the pellets m
container 98a necessitate more processing than the other
concentra~es ;~rc-vided by the instant invention which are
o~ lesser purity in correspondence to their degree o$
processing. Accordingly, a user of the subject invention
will be able to selectively process metallic concentrates
to various degrees of purity based on operating expenses
and market conditions, etcO
Mills 60 and 78 may be conventional in nature, having
generally hlunt blades which result in the formation o~
spherical-like pellets as illustrated in Fig. 6.
In addition, the mills 60 and 78 may be of a type,
as de3cribed hereinbelow to form part of the instant in-
vention, which would result in the concentrates collected
in hopper 98 being in a sliced, flake-like configuration.
The ha.~mer mill 60 in Figs. 8 and 9 includes a
housing 62 and a rotary hub 64 which is mounted on shaft
66 ~or rotation within the housing. Shaft 66 may be driven
by an electric motor for example in a clockwise direction
as shown in Fig. 8 A plurality of cutting knives 68 are :
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.
3~
pivotally mounted about the periphery of hub 64 by
fastening means 70.
Fig~ 7 illustrates a transverse ~iew of a cutt~ng ..
knife 68 wherein the knife includes a slicing blade con~
figuration along both of its side edges. In this regard,
the cutting knives have interchan:geable leading and trailing
edges which can he employed to prolong the useful life of
the cutting knife as will be more fully described hereinbelow.
In addition, cutting knives 68 include mounting apertures 72
at both ends thereof. Through use of mounting apertures 72
eithex end of a cutting knife may be mounted to hub 64 in an
interchangeable manner so that the useful operating life of ~ :
the cutting knives can be exte~ed. In addition, an opening
74 is provided at the top vf housing 60 through which
aluminum concentrates are fed to the mill. In addition,
a substantial amount of air is also drawn into the mill
through opening 74. The bottom portion of housing 62 in-
cludes a plurality of openings 76 of a predetermined
dimension which function as a screening means to insure that
the aluminum material has been sliced or milled to a certain
. size before passing to the su~sequent mill 78 i~ndicated in
Fig. lB~
-.28 -
, ~."\~;~
~ . ~ . . . .
Mill 78 is functionally equivalent to mill 60.
The size of its openings 76 which may be smaller than
those in mill 60 so that the aluminum concentrates or`~
chips are further reduced in size. With respect to
~ig. lB and 8, the milled product from mill 60 passes
through the apertures 76 into the base of housing 60 and
passes into a tubular passage 80 which connects with
cyclone 81. Mill 60 tends to draw in a substantial amount
of outside air through opening 74 which in turn results
in an air flow through the base of the housing of mill 60
and through passage 80 to the cyclone 81 so as to provide
a motive for~e to the milled aluminum. The cyclone 81. .
feeds the aluminum in process to mill 78 which inturn'.
passes the further processed aluminum to passage 84. The
second mill 78 funct'ions to further induce an air flow
through the cyclones and the passage 84.
In summary, it is to be understood that metallic
concentrates having varying degrees of purity are selectively
provided by.the afQresaid method and apparatus from dross which
herertofore has had a significantly lessex value in terms of
aluminum metal recovery for example. 'The commingled oxide
and aluminum dust collected at various points in the sub]ect
process, although including varying percentages of aluminum
. -29-
., .. ~ , .
:.' ~. .
~ 3~3;3 7
dust, are quite marketable as for example in the manufactureof steel.
The combination of processing steps provided by the first
pair of rollers 32 and mill 44 are fundamental in providing the
metallic concentrates in progressively greater degrees of purity
at selected stages in the instant method. As statèd, it is
preferable that rollers 32 be spring loaded SQ as to facilitate
the imparting of a limited compression to the dross passing
therebetween or the reasons set forth hereinabove. In turn,
the subsequent milling action provided by mill 44 complements
the limited compression imparted by rollers 32 to e~fectively
clean the dross to a significant degree. As described, the
concentrates provided on screen 52, following mill 44, are
a valuable product and may be charged, for example, directly
into a furnace for metal recovery in~ingot form. of course,
the concentrates on screen 52 may be further cleaned to a
higher degree of purity by further processing through rollers
58. In turn~ the flake-like particles passing from rollers 58
to screen 59 may be considered an end product of the in~ant
invention or the flakes on screen 59 may be subjected to further
milling and separation steps to yield concentrates or pellets
o~ yet still higher purity.
It is also within the scope of the present invention that
metallic scrap material, such as aluminum turnings for example,
,: ~
~3'~33~7
could be fed directly to rolle~s 58 for c~nversion into
aluminum chips by processing through the mill described in
Figs. 7 through 9~ In this regard, it is believed that the
h = er mill described in Figs. 7 through 9 is uniqu~ in
operation in view of the cutting knives 68 which tend to slice
through the metallic material processed therethroughO
From the foregoing, it is apparent that the objects of
the present invention have been fully accomplished~ As a
result of this invention a vastly improved method is provided
for recovering metallic substances from dross material. Further
more, the method may be e~ployed to convert irregularly si~ed
chunks of metallic scrap into milled chips having a sliced-liXe
configuration. The method is mechanical in nature and may be
employed on a production line basisO In addition, a novel and
unique mill is provided for converting alu~inum chunks or
compressed flakes into al~nin~n chips of predetenmined aimension.
Having thus described and illustrated my invention, it
will be understood that such description and illustration is by
way oP example only and that such modifications and changes as
may suggest themselves to those skilled in the art are intended
to ~a}l within the scope of tbe present invention as limited ~;
only ~y the appended claims.
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