US3165267A - Comminution and beneficiation of refractory flour - Google Patents

Description

Jan. 12, 1965 w. H. OWEN ETAL 3,155,267

COMMINUTION AND BENEFICIATION OF REFRACTORY FLOUR Filed June 29, 1962 CALCINED FEED CALCINED FEED +28 f cRusHER +16 O DRY PAN v E E v v 28 MESH SCREEN SCREEN UNDERSlZE OTHER PRODUCTS V +48 |OO MESH SCREEN T PERMANENT -za +IOO IOO MESH MAGNETIC PULLEY MAGNETIC ELECTRO sEPARATOR MAGNETIC -2 +|oo PULLEY FREE OF IRON PERMANENT MAGNETIC QE' PULLEY cERAMlc STORAGE HOPPER STORAGE HOPPER 2 F/ WiLLIAM H O E A ATTORNEY United States Patent ()fiiice Bdhbib? Patented Jan. 12, 1955 3,165,267 COMMINUTIGN AND BENEFICIATION OF REFRACTORY FLQUR William H. Gwen and Robert K. Scott, Pittsburgh, Pa., assignors to Harbison-Walker Refractories (Jompany, Pittsburgh, 1221., a corporation of Pennsylvania Filed June 29, 1962, Ser. No. 206,373

' 8 Claims. (Cl. 241-24) This invention relates to comminution and beneficiation of refractory flour, and more particularly, to a method of producing very high purity refractory flour having utility as an investment molding material.

. In precision casting of metal parts by the so-called lost wax process, it is conventional to use a very finely divided refractory flour and a binder solution to make a precoatslurry. For example, an expendable, fusible, waxlike pattern is made, the dimensions of which are substantially identical in all respects to a metal part which.

is to be cast. This pattern is sequentially dipped into the pre-coat slurry of refractory fiourand binder, the excess slurry drained thereoif, and while still wet, subjected to a stuccoing or sanding with a coarse refractory grit. This sequence of steps is repeated the number of times necessary to fabricate a shell or sheath of a desired thickness about the expendable pattern. The expendable pattern is then melted out, leaving the desired mold.

This ceramic mold is usually of very thin wall section, i.e. to A, is usually mounted in some manner of back-up such as sand or steel shot either loosely consolidated or unconsolidated, and has molten metal poured thereinto produce the precision casting desired. These molds are used for but one casting.

The surface finishand quality of precision castings made from these molds is affected if, in any of the precoat slurries used, there exists occluded gases from such as air entrapped by poor mixing techniques, from gases generated by reactions between the refractory materials and the binder solution, etc.

The incidence of reaction between the refractory materials and binder solutions is considerably increased when the mold is rapidly heated to a high temperature during its contact with molten metal being cast. It is not uncommon for this molten metal to be poured into the mold at a temperature of 2900 F. and even higher. The gases which are generated under, such high temperature conditions cause pinholing ofthe metal casting. Furthermore, they sometimes cause reaction between the molten metal and the material of which the mold is made, in such a manner as to cause spaced areas of adhesion between the casting and the mold upon cooling. Such adhesion, during cooling, causes fissures or cracks to occur in the cast shape, because of variances in the surface tension of the cooling metal. Irony materials are one of the pri mary causes of such gaseous exudate and surface adhesion. Even in extremely small amounts, i.e. fractions of 1%, the irony-materials are detrimental.

Accordingly, it is an object of this invention to provide an improved method of comminution and beneficiation of refractory flour having particular utility as an investment molding media. It is another object of this invention to provide investment molding media substantially entirely free of those impurities which would tend to react with binder solutions or which would, under conditions of high temperature, produce gas which would pin hole or otherwise damage a precision casting.

It is yet another object of this invention to provide a very finely divided, refractory flour having less than about 0.001% metallic iron, on the basis of an oxide analysis. Audit is still another object of this invention to provide very'finely divided, iron-free mullite'flour having para ticular utility as an investment molding media for the so-called 10st Wax and like processes.

Briefly, according to one embodiment of this invention, a technical grade mullite (calcined bauxite substan tially entirely of mullite phase with minor amounts of corundum and glass) is provided, which has essentially less than 0.001%, by weight, metallic iron on the basis of an oxide analysis. This material is prepared by a process, which includes an initial crushing of a calcined feed to a mixture which is substantially all 16 mesh Tyler. This crushed material is subjected to an initial screening step, which provides three fractions. The first fraction is oversize or +16 mesh Tyler, which material is returned to the initial crushing step. An intermediate fraction is 16-]-4 8 mesh Tyler, and is subjected to subsequent treatment steps. The 48 mesh Tyler fraction is discarded. I I

The intermediate l6+48 mesh fraction is subjected to magnetic separation, and thence to further comminution in a ceramic-lined ballmill. The product of the ceramic mill is substantially all mesh Tyler, and is termed a flour in the art, which flour is substantially entirely free of irony materials.

A better understanding, other features, and further objects and advantages of this invention will become obvious, to those skilled in the art, from a study of the following'detailed description with reference to the drawings. In these drawings;

FIG. 1 is a schematic diagram of a preferred method of producing very finely divided beneficiated refractory flour, according to the concepts of this invention;

FIG.'2 is a schematic diagram of an alternative method.

' The present invention is applicable to almost all refractory materials which are capable of being reduced to a flour for use in such as investment molding procedures. It is, thus, applicable to silica, alumina-silica, alumina, zircon, Zirconia, calcia, periclase, periclasesilica, chrome, chrome-periclase, etc., and like minerals. For the purposes of explanation, however, this invention will be described in the manufacture of a very finely divided, beneficiated mullite flour from calcined bauxite (an alumina-silica type mineral). 1

As noted above, one of the primary purposes of the invention is to remove certain gas-forming agents, such as metallic iron and irony compounds, which would react in service to produce undesired effects on a metal part being cast. In actual laboratory tests on refractory investment materials, it was found that metallic iron, in amounts of only 50 parts .per million, was objectionable since it caused a sufficient volume of gas to be given off in service as to damage. a precision casting.

' Further, metallic iron reacts with water and other com- Thesereaction products often promote adherence of the investment molds to ferrous castings causing fissures to appear in the castings upon cooling.

,7 The hydrogen -gas,' mentioned above, is a reaction product of metallic iron and water or other combined hydrogen, and coalesces to. form small bubbles within the investment mold. These coalesced bubbles appear 3 as small gas cavities within the'm'old which rupture upon heating to cause fissures through the working face of the mold into which molten metal will flow, resulting in a pimpled surface on the resulting casting. V

7 Although some of the metallic ironand irony mate rials found'in the refractories used for investment molding are naturally-occurring, most of it appears to be picked up during grinding thereof to obtain the desired very finely divided flour state. Most of this contamina,

tion appears in the extremely fine fractions of this flour,

and in such a range as to be incapable of separation by magnetic treatment.

Referring now to FIG. 1, according to' this invention a quantity of bauxite havingthe following typical analysis (all partsby weight, and on the basis ofan oxide analysis): I

. Percent Silica (SiO 15.5 Alumina (A1 0 54.6' Titania (TiO 1.9 Iron oxide (R 0 0.8 Calcium oxide (CaO) 0.1

Magnesia (MgO) Q Trace Alkalies (Na OA-K 'Oi-Li O) 0.1 Loss on ignition T 27.2

was calcined to remove all free and substantially all chemically combined water, and to produce a calcined material having an ignition loss on the order of up to about 0.1%. This calcining step maybe carried out in such as a rotary kiln. an initial crushing step in a dry pan to produce a material substantially all of which is -16 mesh Tylerv Of course, if desired, a ball mill, rod mill, impact crushing mill, etc., can be used for this step. From the dry pan,

the material passes to a screening step; The screening step may be conducted. in such asthe Rotex screen of the Orville-Simpson Company, which -is described on The calcined material is fedv to page 958 of the Chemical Engineers Handbook, 3rd Edi- I tion. 1

Three fractions result from the screening step. The, first is a +16 .mesh Tyler or oversize fraction, which is recycled to the dry pan. The third fraction is a -48 mesh Tyler or'und'ersize, fraction, which is disposed of;

The intermediate or -16+48 mesh Tyler fraction is passed to a magnetic treatment to remove all of the iron and irony fluxes contained therein.

' the materialis sequentially subjected to a permanent magnet pulley or drum-type separator, an electromagnetic pulley-type separator, and then to a second permanent magnet-type separator;

The sequence of permanent magnet-icand electromagnetic treatment steps produces a product having essen- "tially less than 0.001%, by weight, metallic iron and' irony materials. I This material is fed. toa ceramic lined mill of the ceramic ball mill type to produce a refractory flour. The product from the ceramic-ball mill is for subsequent packaging as, desired.

Previously, it has notbeen thought commercially feasible to produce investment molding flour by ceramic milling, because of the. great expense involvedin large ceramic mill installations. However, by our preliminary 1 separation and isolation of an intermediate pre-ground fraction, particularly amenable to magnetic separation I treatment, all of the material whichis passed through the ceramic mill is product and there is no crushing of "material whichxmust be subsequently wasted.

In this treatment, 1

.fed to suitable;storage facilities, suchj'as a storagehopper,

2 is more difiicult to handle than the 48" mesh frac- I tion of the method of FIG. 1. In any event, the frac= tion which passesto. the magnetic separatingstepimust be entirely mesh, and is preferably all less than .16 mesh. I

Two samplesof. mullite flour, which were actually produced according to the method of FIG. 1, weresubjeeted to a very careful chemicalanalysis ina laboratory. The first sample was substantially entirely mesh Tyler and the second was substantially entirely 200 V mesh Tyler. Each of the samples was divided into two parts. A firstpart of each sample was tested qualita- *tively for the presence of iron or irony substances, by

wetting with water and adding concentrated hydrochloric acid. There Wasno evidence of-gas evolution from either 251 of the samples, as would have indicated the presence of iron. a

Quantitative chemical tests were then undertaken on the second portion of each of the samples. .The '150 mesh sample indicated 0.0002%, by weight, iron present. No evidence of iron'could be found in the 200 mesh sample. Y

The following is a brief synopsis of the method used to quantitatively analyze the material for metallic iron:

A 100.0;gram sample of material, as. received, was transferred to a .250 'r'nl. Erlenmeyer flask, and 501111.

of 4% HgCl solution was added. Using a trapto col lect. the condensate and a burner to ignite theeXit gas,

the airwas displaced from theflaskby a continuous flow of natural gas. Both the flask and sample were heated for 10 minutes, to just below ;boilingl of the sample. ,The flask was then cooled in ice -Water and the solution decanted through a 5 cm. #2 Whatman paper in a #1 Biichner funnel into a 250 ml; flaskcontaining 15 ml. of l-l H 80 The sample was washed by decantation using 25-30 ml; of cold water for each decantation. Thefiltratewas transferred (225rnl.) to

. a 600 ml. beaker and titrated with astandard Ce(SO solution using one'drop of o-phenanthroline-as anindicator. Itw'as then titrated to a colorless end-point. The sample was washed andthe' filtrate added to the titrated solution until the indicatorfshowed no color" change, or 1 drop of Ce (S0 wassufiicientto discharge the color, toassure complete removal'of ferrous salts from the saniple. 0.1 .ml. from the titrationwas d ducted for the blank, and percentage .otiron was cal-- culated. I r r I 7,

Calculation: I r

' .ml. O.2239

i Wt. sample' Nora-Preparation of Ce'(SO4 solution (0.05 8.4 grams of Ce(SO were dissolved in 'a solution containing l4 ml. of H 50 and 300 ml.-water, It was 1 thenffiltered through a #5 Whatman paper using suc-- tion, drluted t'o 500ml. and mixed .well. Treated as describedfiabove, it was standardized against 0.01001 to:

An alternative flow sheet, schematically shown in FIG. U

2 is useful for treating smaller quantities of ,material. It includes a-n-initial' calcining step, a' crushing step'to produce asubstantiallyr-ZS meshj', Tyler vmaterial, ja

first screening step to remove the oversize or, +28 mesh" 7 fraction ,for'recycle to the crushen-a subsequent=l00 meshscreening step to remove a -l00'n1esh waste-prod;-

0.0200 gram of iron wire. p p

In an actual industrial testusing iron-free :mullite flour, produced according to the'method hof FIG; 1, very high quality precisioncastings were obtained. In'addi- :-'tion to the precisionof the castings obtained in the absence of metallic ironand irony;, substance s, :it was dis-v covered that ain'old made of such a material resisted .wet-

ting bythe molteu'm'etali It is surmised that wetting, which had been noted with previous molding fmaterials; 7

had been the result of deposits of irony material on the working surface of the mold, which encouraged wetting of the mold by the molten metal. However, with the iron-free material of this invention, wetting was not noted.

Having thus described the invention in detail and with sufiicient particularity as to enable those skilled in the art to practice it, what we desire to have protected by Letters Patent is set forth in the following claims.

We claim:

1. Method of producing a refractory flour essentially free of irony material for use as an investment molding media, which comprises the steps of passing a selected refractory material to a preliminary size reduction stage, isolating an intermediate fraction substantially all of which rests on a 100 mesh Tyler screen from the reduced material, removing substantially all irony material from the intermediate fraction, passing the resulting material to a secondary size reduction treatment in a ceramic mill, said secondary size reduction treatment producing a refractory flour substantially all of which is -150 mesh Tyler and substantially entirely free of irony materials.

2. Method of claim 1, in which the selected refractory material is bauxite.

3. Method of producing a refractory flour essentially free of irony material for use as an investment molding media, which comprises the steps of passing a selected refractory oxide material to a calcining stage, passing the calcined material to a preliminary size reduction stage, isolating an intermediate fraction substantially all of which rests on a 100 mesh Tyler screen from the re duced material, removing substantially all irony material from the intermediate fraction, passing the resulting material to a secondary size reduction treatment producing a refractory flour substantially all of which is 150 mesh Tyler and substantially entirely free of irony materials.

4. Method of claim 3, in which the refractory material is bauxite.

5. Method of producing a refractory flour essentially free of irony material and having particular utility as an investment molding media, which comprises the steps of passing a selected refractory oxide to an initial crushing step to produce a material which is substantially all l6 mesh Tyler, passing the crushed material to a separation stage, said separation stage dividing the crushed material into three fractions, the first fraction being +16 mesh Tyler oversize, returning said oversize to the crushing step, a second fraction being l mesh Tyler and undersize, the third fraction being an intermediate l6-H00 mesh Tyler fraction, passing the intermediate fraction to a magnetic separation treatment, in which substantially all irony material is removed, passing the iron-free intermediate fraction to a fine crushing stage in a ceramic mill to thereby produce a refractory flour substantially calcining a selected refractory oxide material to remove all free water and substantially all chemically combined water, passing the calcined material to a separation stage, said separation stage dividing the crushed material into three fractions, the first fraction being +16 mesh Tyler oversize, returning said oversize to the crushing step, a second fraction being mesh Tyler and undersize, the ttu'rd fraction being an intermediate 16-|-l00 mesh Tyler fraction, passing the intermediate fraction to a magnetic separation treatment, in which substantially all irony material is removed, passing the iron-free intermediate fraction to a fine crushing stage in a ceramic mill to thereby produce a refractory flour substantially free of irony materials.

7. Method of producing a refractory flour essentially free of irony material for use as investment molding media, which comprises the steps of passing a selected refractory material to a preliminary size reduction stage, isolating an intermediate fraction substantially all of which passes a 16 mesh screen and rests on a 100 mesh screen, treating said material to reduce the irony content thereof to essentially less than 0.001%, passing the resulting material to a secondary size reduction treatment in a ceramic mill, said secondary size reduction treatment producing a refractory flour all of which is mesh Tyler and substantially entirely free of irony materials.

8. Method of producing a refractory flour essentially free of irony material and having particular utility as an investment molding media, which comprises the steps of passing a selected refractory oxide to an initial crushing step to produce a material which is substantially all -16 mesh Tyler, passing this crushed material to a separation stage, the separation stage dividing the crushed material into three fractions, the first fraction being substantially +16 mesh Tyler oversize, returning said oversize to the crushing step, a second fraction being 100 mesh Tyler and undersize, discarding said undersize, the third frac tion being an intermediate 16+100 mesh Tyler fraction, passing this intermediate fraction to a magnetic separation treatment in which the irony material content is reduced to less than 0.001%, passing this iron-free intermediate fraction to a fine crushing stage in a ceramic mill to thereby produce a refractory flour substantially free of irony materials.

References Cited by the Examiner UNITED STATES PATENTS 1,898,371 2/33 Hutchins 24124 X 2,269,912 1/42 Ladoo, et al. 241-24 2,468,321 4/49 Bland 24124 2,603,423 7/52 Buehl 24l24 X 2,618,530 11/52 Gardner 10638.27 2,840,480 6/58 Stoddard 106-3827 2,865,570 12/58 Nutting 241-24 J. SPENCER OVERHOLSER, Primary Examiner.

MORRIS LIEBMAN, Examiner.

Claims (1)

1. METHOD OF PRODUCING A REFRACTORY FLOUR ESSENTIALLY FREE OF IRONY MATERIAL FOR USE AS AN INVESTMENT MOLDING MEDIA, WHICH COMPRISES THE STEPS OF PASSING A SELECTED REFRACTORY MATERIAL TO A PRELIMINARY SIZE REDUCTION STAGE, ISOLATING AN INTERMEDIATE FRACTION SUBSTANTIALLY ALL OF WHICH RESTS ON A 100 MESH TYLER SCREEN FROM THE REDUCED MATERIAL, REMOVING SUBSTANTIALLY ALL IRONY MATERIAL FROM THE INTERMEDIATE FRACTION, PASSING THE RESULTING MATERIAL TO A SECONDARY SIZE REDUCTION TREATMENT IN A CERAMIC MILL, SAID SECONDARY SIZE REDUCTION TREATMENT PRODUCING A REFRACTORY FLOUR SUBSTANTIALLY ALL OF WHICH IS -150 MESH TYLER AND SUBSTANTIALLY ENTIRELY FREE OF IRONY MATERIALS.

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