CA1134337A

CA1134337A - Method and apparatus for processing dross

Info

Publication number: CA1134337A
Application number: CA000303240A
Authority: CA
Inventors: Paul J. Cromwell
Original assignee: Cromwell Metals Inc
Current assignee: Cromwell Metals Inc
Priority date: 1977-05-13
Filing date: 1978-05-12
Publication date: 1982-10-26
Also published as: SE7805504L; GB1603932A; JPS5415410A; DE2821399A1; IT7823413A0; IT1097252B; JPS5815179B2; NO781703L; FR2390507A1; SE8201313L

Abstract

#4964 .
METHOD AND APPARATUS FOR PROCESSING DROSS
ABSTRACT OF THE DISCLOSURE
The invention relates to the recovering of free metal en-trained in dross or skimmings obtained from melts of aluminum and aluminum based alloys wherein the dross has been partially prepared by prior art preparation processes. The invention is directed to the cleaning and preparation of the dross by the more effective removal of substantial portions of the oxide coatings on the dross. This results in the recovery of a sig-nificantly higher proportion of the free metal contained in the dross than is recovered using prior art cleaning and recovery processes. The dross, as partially processed by prior art methods, is sequentially fed through selected mechanical rolling and milling stages so as to separate aluminum oxide dust and aluminum concentrates from one another. The aluminum con-centrates may be utilized in conventional furnace recovery methods to produce aluminum ingot or may be further processed through selected stages to produce high quality aluminum pellets.

Description

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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

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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

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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 ` :

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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 . ' ;, .
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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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~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

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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~

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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.

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.. , 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 ':

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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 `, ~:~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 ~

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~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;

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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 ,, ,: : :,', -. . :',. . .. ..

~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 ': : .: ~ : : ;: ~ : : ` : ' '': : `

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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 ~
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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 -, - .; . ~ . ,: : . . :: :
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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 :: . . ,, , . . . ,: . : . :~ : : , - , ~: :

~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.
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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 , ; ~

~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 .

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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 ~3~33~7 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 _ 24 -~ 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 -25~

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~

. ~ . ., ~ .:

~.~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 :

.

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.

:~' `'. .. : :: ~.'' :':: :`:. ` ` ... :. :

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for reclaiming, in relatively high metallic concentrate form, metallic substances entrained in dross, said method comprising the steps of:
conveying said dross to a pair of roller means having a predetermined spacing, said dross comprising particles of a predetermined size range, compressing said dross to a limited degree without substantially crushing the same between said pair of roller means by passing said dross therebetween so as to substantially break the bonds between the metallic and non-metallic substances in said dross, and separating said non-metallic substances from said metallic substances so that relatively concentrated metallic substances remain whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

2. A method for reclaiming, in relatively high metallic concentrate form, metallic substances entrained in dross, said method comprising the steps of:
conveying said dross to a pair of roller means having a predetermined spacing, said dross comprising particles of a predetermined size range, compressing said dross to a limited degree without substantially crushing the same between said pair of roller means by passing said dross therebetween so as to substantially break the bonds between the metallic and non-metallic substances in said dross, milling said dross after passage thereof through said pair of roller means so as to disassociate said metallic and non-metallic substances one from the other, and separating said non-metallic substances from said metallic substances so that relatively high metallic con-centrates remain whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

3. A method for reclaiming, in relatively high metallic concentrate form, aluminum substances entrained in dross, said method comprising the steps of:
grading said dross into particles of a predetermined size range, conveying said dross to a pair of roller means, resiliently mounting said pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles, compressing, without substantially crushing, said dross in a resilient manner between said pair of roller means by passing said dross therebetween so as to substantially break the bonds between the metallic and non-metallic substances in said dross, milling said dross after passage thereof through said pair of roller means so as to disassociate said metallic and non-metallic substances one from the other, and separating said non-metallic substances from said metallic substances so that relatively high metallic con-centrates remain whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

4. A method for reclaiming, in relatively high metallic concentrate form, aluminum substances entrained in dross, said method comprising the steps of:
grading said dross into particles of a predetermined size range, conveying said dross to a pair of roller means, resiliently mounting said pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles, compressing, without substantially crushing, said dross in a resilient manner between said pair of roller means by passing said dross therebetween so as to substantially break the bonds between the metallic and non-metallic substances in said dross, and separating said non-metallic substances from said metallic substances so that relatively high metallic concentrates remain whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

5. A method for reclaiming, in relatively high metallic concentrate form, aluminum substances entrained in dross, said method comprising the steps of:
grading said dross into particles of a predetermined size range, conveying said dross to a pair of roller means, resiliently mounting said pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles, passing said dross between said pair of roller means to cause said roller means to yield and separate one from the other and exert a resilient compressive force on said dross particles without substantially crushing said dross particles so as to substantially break the bonds between the metallic and non-metallic substances in at least a substantial quantity of said dross particles, and separating said non-metallic substances from said metallic substances so that relatively high metallic con-centrates remain whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

6. A method for reclaiming, in relatively high metallic concentrate form, aluminum substances entrained in dross, said method comprising the steps of:
grading said dross into particles of a predetermined size range, conveying said dross to a pair of roller means that are resiliently mounted with respect to one another, said roller means having a predetermined spacing less than said predetermined size range of said dross particles, passing said dross between said pair of roller means to exert a resilient compressive force on said dross particles without substantially crushing said dross particles so as to substantially break the bonds between the metallic and non-metallic substances in at least a substantial quantity of said dross particles, and mechanically working said dross particles to cause said non-metallic substances to separate from said metallic substances so that relatively high metallic concentrates are obtained whereby metallic dust-like particles become disassociated from said metallic substances and are commingled with said non-metallic substances after separation of the latter from said metallic substances.

7. The method as set forth in claim 1 wherein said metallic substances comprise aluminum.

8. The method as set forth in claim 2 wherein said metallic substances comprise aluminum.

9. The method as set forth in claim 8 including resiliently mounting said pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles.

10. The method as set forth in claim 9 wherein said dross conveyed to said pair of roller means comprises particles greater than 1/40 of an inch but less than 1/20 of an inch in greatest dimension.

11. The method as set forth in claim 9 including separating said non-metallic substances from said metallic substances by passing both said substances over a screen means.

12. The method as set forth in claim 11 wherein said non-metallic substances are separated from said metallic substances by the additional step of passing the same through an air separator means.

13. The method as set forth in claim 3 further including the step of removing particles smaller than a predetermined size commingled in said dross prior to passing said dross between said pair of roller means.

14. The method as set forth in claim 3 wherein substances having magnetic properties are commingled in said dross and including the step of removing the former from the latter prior to passing said dross through said pair of roller means by passing said dross over a magnetic separating means.

15. The method as set forth in claim 1, 3 or 9 wherein said dross conveyed to said pair of roller means comprises particles greater than 1/20 of an inch but less than 1/10 of an inch in greatest dimension.

16. The method as set forth in claim 1, 3 or 9 wherein said dross conveyed to said pair of roller means comprises particles greater than 1/10 of an inch but less than 1/4 of an inch in greatest dimension.

17. The method as set forth in claim 1, 3 or 9 wherein said dross conveyed to said pair of roller means comprises particles greater than 1/4 of an inch but less than 1/2 of an inch in greatest dimension.

18. The method as set forth in claim 1, 3 or 9 wherein said dross conveyed to said pair of roller means comprises particles greater than 1/2 of an inch but less than 1 inch in greatest dimension.

19. The method as set forth in claim 1, 3 or 9 wherein said dross conveyed to said pair of roller means comprises particles greater than one inch but less than l-l/2 inches in greatest dimension.

20. The method as set forth in claim 3 wherein said dross conveyed to said pair of roller means comprises particles greater than 1-1/2 inches but less than 2 inches in greatest dimension.

21. The method as set forth in claim 2 including resiliently mounting said pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles.

22. The method as set forth in claim 2 including mounting said pair of roller means in a substantially rigid manner so as to have a fixed predetermined spacing therebetween, said roller spacing being less than said predetermined size range of said dross particles.

23. The method as set forth in claim 22 wherein said metallic substances comprise aluminum.

24. The method as set forth in claim 2 including the further step of conveying said relatively high metallic concentrates to a second pair of roller means having a predetermined spacing and compressing said metallic con-centrates between said second pair of roller means by passing the same therebetween so as to form said metallic concentrates into relatively thin, flake-like bodies.

25. The method as set forth in claim 24 wherein said metallic concentrates comprise aluminum.

26. The method as set forth in claim 25 further including the step of impacting said flake-like bodies by a plurality of milling surfaces so as to disassociate said metallic con-centrates and non-metallic substances one from the other, and separating said non-metallic substances from said metallic concentrates so that the latter remain as relatively higher metallic concentrates whereby metallic dust-like particles become disassociated from said metallic concentrates and are commingled with said non-metallic substances after separation of the latter from said metallic concentrates.

27. The method as set forth in claim 26 wherein said milling surfaces comprise knife-like surfaces.

28. The method as set forth in claim 26 including separating said relatively higher metallic concentrates and said non-metallic substances from one another by passing the same through an air separator means.

29. The method as set forth in claim 25 including resiliently mounting the first pair of roller means with respect to one another to have a predetermined spacing less than said predetermined size range of said dross particles.

30. The method as set forth in claim 29 further including the step of impacting said flake-like bodies by a plurality of milling surfaces so as to disassociate said metallic con-centrates and non-metallic substances one from the other, and separating said non-metallic substances from said metallic concentrates so that the latter remain as relatively higher metallic concentrates whereby metallic dust-like particles become disassociated from said metallic concentrates and are commingled with said non-metallic substances after separation of the latter from said metallic concentrates.

31. The method as set forth in claim 30 wherein said milling surfaces comprise knife-like surfaces.

32. The method as set forth in claim 30 including separating said non-metallic substances from said metallic concentrates by passing both over a screen means.

33. The method as set forth in claim 30 including separating said relatively higher metallic concentrates and said non-metallic substances from one another by passing the same through an air separator means.

34. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1/40 of an inch but less than 1/20 of an inch in greatest dimension.

35. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1/20 of an inch but less than l/10 of an inch in greatest dimension.

36. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1/10 of an inch but less than 1/4 of an inch in greatest dimension.

37. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1/4 of an inch but less than 1/2 of an inch in greatest dimension.

38. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1/2 of an inch but less than 1 inch in greatest dimension.

39. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than one inch but less than 1-1/2 inches in greatest dimension.

40. The method as set forth in claim 29, 30 or 31 wherein said dross conveyed to said first pair of roller means comprises particles greater than 1-1/2 inches but less than 2 inches in greatest dimension.