US2441695A - Casting mold - Google Patents

Description

@Ross REFEENCE May 1s, 1948.

R. c. FEAGIN ET AL CASTING MOLD Filed may s1, 1944 mag/4,

Patented May 18, 1948 CASTING MOLD Roy C. Feagn, Flushing, and Eric H. Zahn, Pound Ridge, N. Y., assignors to Austenal Laboratories,

Incorporated, New York, N. Y., a corporation of New York Application May 31, 1944, Serial No. 538,166

(ci. 221s9) 7 claims. 1

This invention relates, in general, to the art of casting, and hasparticular relation to improvements in the coating of the casting surfaces of refractory molds.

While the particular embodiment of the invention which we shall describe hereinafter in connection with the drawing has to do with the coating of the casting surfaces of refractory molds for casting articles of high fusing metals and alloys, it is to be understood that the invention is not limited to the character or use of the mold except to the extent that such limitations are expressly included in the appended claims.

One of the main objects of the present invention is to provide, for the casting surfaces of refractory molds, an improved coating having a high degree of surface smoothness; also relatively great strength and substantial resistance to water.

f Another object of the invention is to provide i i ,I

' ing the molten material, such as a high fusing metal or alloy, into the mold.

Another object of the invention is to provide improvements of the character set forth which will render possible precision casting of articles which have extreme hardness and are difficult to finish, whereby such articles are cast consistently with a high degree of surface smoothness and detail, and require little, if any, finishing of the articles after the casting operation. Another object of the invention is to provide an improved method of applying the coating material to the low fusing destructible pattern from which the coating and bonding or anchoring material are transferred to the mold body. Another object of the invention is to provide an improved refractory mold having its casting surface coated with the improved coatingmaterial and having the coating bonded to the mold body in accordance with the present invention.

Further objects and advantages of the invention will become apparent from vthe following detailed description, taken Ain connectionj with the accompanying drawing in which: j

I I 4f IP-sr 2 Figure 1 is a schematic view showing in simplied form a pattern of an article to be cast;

Figure 2 is a view similar to Figure 1; showing the pattern provided with a sprue element, and also showing applied to the pattern the coating for forming the smooth casting surface on the mold body;

Figure 3 is a view similarto Figure 2; showing applied to the coated pattern the material for bonding or anchoring the coating to the mold body:

Figure 4 is a fragmentary microscopic section taken on the line 4-4 of Figure 2;

Figure 5 is a fragmentary microscopic section taken on the line 5-5 of Figure 3;

Figure 6 is a more or less schematic sectional view showing one illustrative manner in which the refractory mold is formed about the pattern;

Figure 7 is a fragmentary microscopic section taken on the line 'I--1 of Figure 6;

Figure 8 is a sectional View through the completed refractory mold after eliminating the pattern; and

Figure 9 is a fragmentary microscopic section taken on the line 8-9 of Figure 8.

Referring to the drawing, the reference character I0 designates a pattern of an article to be cast. While this pattern I0 is shown as comprising a cylindrical body I I having a base flange I2, it is to be understood that the shape of the pattern will vary according to the article to be cast and that the pattern shown in the drawing is of simplified form for purposes of illustration. It may be shaped, for example, for use in casting turbine buckets of the character disclosed and claimed in the copending application of Albert W. Merrick, Serial No. 422,421, led December 10, 1941, now Patent 2,381,459, or it may be shaped for use in making dental castings or in casting other articles, as suitable and desired.

The pattern I0 is preferably formed of low fusing material, such as wax, or of any of the other destructlble materials well known in the art. The pattern may be cast under force or pressure in known manner so as to reproduce accurately the desired article as to dimensions y and configuration, and as to all fine detail.

Having produced the pattern I0 of Figure'l,

we attach to such pattern a sprue element I3 having, at its outer end, a pouring basin forming part I4. The element I3 and part I4 are formed of low fusing material, preferably corresponding with thematerial of the pattern I0.

The pattern Ill,l of Figure 2, with the sprue I3 and its basin forming part I4 attached thereto, is then coe-.ted with the coating material which is to form the casting surface of the refractory mold. This coating material, in its preferred form, is prepared by mixing a suitable quantity of comminuted refractory material-with-a binding agent and a' film forming which will harden by air-drying. We prefer to use, as the refractory material, silica finely ground, for.- example, to approximately 00 mesh or finer. The use of a finely ground refractory material produces a smooth coating which resultsin a casting having'a high degree-ofisurfacefsmocthness and possessing the maximum of ydetail present in the pattern itself. Other refractory materials, such as fused uartz, fused alumina, Zircon, zirconia, mullte, fused magnesia', and t'-lil'e` may 5e employed.

In order to producea coating which will be flexible tothe desiredextent, l cerin-is preferably employedintherefractorymixor forming thel primary' investment coating. Due toits hygroscopic character, it-preveritsY rapidm drying of the coating,` and-subsequently, thevcrack'ing andipeeling of the coatingfromthe pattern. The best range of this constituent is from approximately tov approximately 201% of the liquidcontent .of themix.l

Sodiumlsilicate or water lass ispreferably added to the Ex as the Bininglagent for the refractory constituent of-thecoating. This Vbinding agent is preferably-'employed in quantity sufcient to' add strength-to' the. refractory. mix, both in the dried-stage and in the fired stage, preparatory to receiving` the molten metal' or alloy; While-itis not. highly desirable to use an: excessiveV amountof silicate -in the coating,- this substance should constitute at least approximately'10%, and preferably from approximately 10% -toapproximately 40%, ofthe liquid constituents Bindersv otherI than sodium silicate 4 tough film on drying from solution. Solutions of these materials may be gelled by the addition of acids, saltsI and or g nts.

For the purpose o assuring a smooth coating of the pattern with the refractory mix, a wetting agent-suchas.Wetanol (sulfa-tu. h drocar-Y o sulfonate), and-"erosol OT (sodium dioc't l s fo'cuccinate) grgiclyr (shatei'w 4` hi-Her alcohols) or the like-ls preferably used n e mix. The range of such substance may vary'from approximately .01% to approximately 1.0%4 of total Weight. Excessive use of the wetting' agent' may form bubbles in the coating composition.- resulting in rough castings, and therefore should be avoided.

In order to minimize bubble formation in the mixture-and 'in -the coating on the pattern, a defoamin is preferably employed in the mix.

Oct a cb is a suitable defoaming agent, but

o other 'dei'oa'ii` ng agents-such as Fomax (mixpercen age .o' t ingre nt may vary from approxlmately .01% to approximately 0.10%.

One typical composition embodying the present invention and suitable as therefractory coating mix isasfollows:

atefr -i i i cc 290 Glycerin -cc- Water 'glassicc 90 3 Hydrochioric acid (4.42% by weight) cc e5 6% Jammonium algnate solution cc 15 Octylalcohol cc 0.3

7.5% Wetanol cc 7.5

3,5 otters Flint 1bs 2.3

AnotherV composition embodying the present invention and suitable as the refractory coating x is'as -follows:

Water -cc-- 290 4 Glycerine nnfifl cc 45 Water glass y cc 180 may be used in the refractory mix for forming 6% ammonium .313m te solution ccn 15 thefprimary investment-coating, as will hereinu octyllalcohoynh cc 0 3 after appeal* i y 7.5% Wetanol solutio ...D L-f.b I,.a. cc 7.5 Hydrochloric acidislpreferably. added to the 4 Potta-255mm g ,1bs 2,4 :amr-ge ingagentfor the binder. i ,i n Itreacts` with the silicate to. form a Another composion S'Wtable as the refractory hydroussilicic. acid gel. Other acids may be coating' mins ST0 lows used, suchas sulphurlc, hosphoric-,lac,1 'g., and Water cc 290 the-like. The'presence'of al small aunt ofacid 50 Glycerin cc 45 isindicated as highlyvdesirable. The' acid c011- Water glass cc 90 tenbmaygbe- Varied fr0mf0'% tO-EDDTOXimately Hydrochloric acid (4.42% by weight) cc 65 25 of the liquidcontent ofthr'efractry mix Octyl alcohol cc 0,3 which 4forms-the primary investment coating. A .5% Wetanol cc 7.5 higher acid contentl is preferably avoided Since ottersFlint lbs 2.3 itlmay produce instantaneous gelling, resulting in a lumpy mix within the' refractorycomposi- Referring' for, example to the rst'mentlrfed u typical coating composition, this composition On'theIebYprOdMmg an pnsamsfton.' clng' may-be termed the primaryinvestment coating. bn; tgfrlpi gggtongg, After the constituents are cofibimrd'lhrg 0o oughly mixed, the pattern I0 is completely coated andlmore rasistant to water-also, somewhat harderwe preferably add ammonium alglnate to the refractory mix. Th' percen age o is constituent can be varied widely, depending upon the particular characteristics desired in theprimary investment coating. We contemplate varying the 4content of 'ammonium alginatefr'om approximately 130% to approximately.10.`0`% ofthe 'totalweightof-themix. 'Ifhiamaterial serves as a. low temperature filmforming binder, `and gives the coating.- composition .the advantageous characteristics abovesetforth.- Similar-materials can be used whichlfall1inJthe1class-comprising al lum alginate and other M `ginates. a gin and alginates form a hard,

with-thismaterlal, as'shown, forv example, at l5 inFigure'Z of ythe drawing. The coating-of the pattern is preferably accomplished bydipping the pattern inthe coating solution. This. is quickerI than spraying the-coating `on-the pattern. Dipping also assures more 'uniform and smooth coating of al1-surfaces ofthe pattern. We do not,hcwever., atleast withincertain aspects of the present-invention, intend-to be limited to this-particularmethod.. of.- applying the coating l5 to the pattern. Where the dipping method ofapplyfing the. coating is .not expressly included intlieclaims, we intend`to' cover the primary investment coating. per se, regardlessof Whether it is applied b'y dipping..spraying, stucc'oing,

tagte-nari;

painting it on the pattern, or in other situable manner.

After the pattern I has been thoroughly coated with the primary investment material I5, and while the coating I is still wet, the surface is thoroughly covered, for example, by sprinkling it with refractory (preferably silica) in coarse particle form, grade from approximately 50 to 100 mesh. Other refractory materials, such as those referred to in describing the composition of the coating I5, may, of course, be employed. The layer of coarse refractory particles covering the coating I5 is shown at I6. The sprinkling of the wet pattern with the coarse refractory particles is termed sanding Alfter the wet pattern has been thoroughly sanded, the excess coarse refractory particles are shaken off and the dipped and sanded pattern -is allowed to dry. The coarse refractory particles I8, as applied to the surface of the coating I 5, penetrate the coating I5 to varying depths, and are thus effectively bonded in place.

After air-setting of the dipped and sanded pattern the primary coating consists of a roughened exterior surface brought about by the bonding and drying of the coarse refractory particles on its surface. This roughened surface interlocks with the secondary investment composition forming the body of the mold, effectively to bond or anchor the coating in place. Moreover, the sanding operation assists in fixing the coating I5 in place by preventing a drainage or flowing thereof along the surface of the pattern, formexample from the high points of the pattern.

f We have found it desirable, under certain circumstances, to provide a heavier primary coating for producing certain types of castings. This can be accomplished on a commercial scale by dipping and sanding" the destructible pattern as above described, permitting the dipped and sanded pattern to air-dry, and subsequently repeating the operation of dipping and sanding to build up the thickness of the primary coating to the desired degree.

-fThe application of the outer coating I6 of coarse refractory particles also tends to prevent cracking or crazing of the primary investment as it sets or dries, the layer of the primary investment remaining in contact with the pattern being appreciably thinner than when it is initially applied, due to the flow thereof between the particles of the outer coarse layer I5. This also has the advantage of tending to eliminate or reduce any difference in expansion of the primary investment relative to the investment material constituting the body of the mold.

After the pattern is coated and sanded and the coating has dried, a suitable mold of refractory material is formed about the pattern,

including the sprue I3 thereof, which sprue is l allowed to extend through the wall of the refractory mold so as to permit the escape of the material of the pattern and to form an ingate for the fluid metal. The refractory mold may be formed about the pattern in any known or suitable manner. This procedure therefore will not be described in detail except to state that the secondary investment material for forming the body of the mold is indicated at in Figure 6, whereas the completed refractory mold is indicated at 26 in Figure 8. The plate I1 is shown as having a coating of wax or other suitable material at I8 to which the basin forming element I4 is waxed or otherwise suitably secured at 20. The investment sleeve 2|, preferably of heat resistant alloy, is shown as having an asbestos liner 22 and an inner paper liner 23, and as waxed to coating I8 at 24.

The material used in forming the body of the mold 26 may be, in general, any suitable refractory ller and a suitable binder. The refractory filler may be in comminuted form, silica or any of the other refractory materials well4 known in the. art. In general, in such materials the bulk of the refractory ller is usually present in the form of coarse or large particles of a particle size "mint" larger than the particle size of the refractory particles I6 applied to the pattern in the "sanding operation. The use of coarse refractory particles in the secondary investment material for forming the mold body provides desirable porosity in the mold for the escape of air and gases in the casting operation, as well understood in the art.

While any 'suitable binder may be employed in the secondary investment material 25, we preferably use an investment having a tetra-ethyl silicate binder, or the investment material disclosed and claimed in the copending application of Paul F. Collins, Serial No. 450,619, filed July 11, 1942, now Patent 2,380,945, issued August '7. 1945. Any of the other binders known in the art, or suitable for refractory mold materials, may, of course, be employed. The binder for the primary coating material is preferably the same, or selected to match the binder for the secondary investment material, although, this may vary within the scope of the present invention.

When the refractory mold 26 has solidified or set suciently, it is subjected to heat at a temperature about or slightly abpgathafuslng 13913113. 1J/,

of the material of 'ta'ttn this material when me'lte, esc'a' ping th e opening 28 formed inrnprue I3. This lea rthecaetmgrcavny 21 with the smooth, strong, and water-resistant coating I5, and the coarse refractory material' I6 securely bonding the coating to the refractory mold material. In forming the mold 26 about the pattern the wet investment material 25 fiows into and fills the interstices in the rough outer surface of the coating. The resulting bonding or anchoring of the coating to the body of the refractory mold 26 prevents, as already pointed out, separation of the coating from the body of the mold, and cracking and breaking of the coating (with resulting defects in the casting), particularly when the mold is heated to a high temperature preliminary to casting and in pouring the molten material, such as a high fusing metal or alloy. into the mold.

Upon completion of the mold 26, metal having the desired properties for the finished casting is poured or otherwise introduced into the mold cavity 21. The resulting casting, which may have extreme hardness and be diicult to machine, has a high degree of surface smoothness and detail, and requires little, if any, finishing of the article after the casting operation. After the casting has been made, the refractory mold 26 may be broken to permit removal of the casting.

We do not intend to be limited to the precise details or to the precise embodiment of the invention shown and described, as variations in the details and other embodiments are contemplated within the scope of the appended claims.

We claim:

l. A refractory mold comprising a body of comminuted refractory material having a casting surface covered with a coating comprising a comminuted refractory material of relatively fine 7. partielesize and alayer of comminuted refractory material of particle size coarser than the particle size of the refractory material of said' coating and n'ertthan the particle size of the refractory material ofthe mold body, said last mentioned layer ofrefractory material being substantially coextensive with said coating and interposed between the coating and the mold body to anchor the coatingfto the mold body.

2-. A refractorymold comprising a body of comminuted refractory. material having a casting surface covered with a coating comprising acomminuted refractory material of relatively fine particle size and a binding agent, and a layer of comminuted refractory material of particle size coarsertban theparticle size of the refractory Y material 'of 4said coatingv and nner than the particle size of the refractory material of the mold body, said last mentioned layer of refractory material being substantially coextensive with said coating-and interposed Abetween the coating and the mold body tobond and anchor the coating to the-mold-bod-y.

Sil-A refractory mold comprising a body of comminuted refractory material having a casting-surfacecovered with a coatingrcomprising a comminuted refractory material of relatively fine particlesize; abinding agent and a-filmforming constituent,- and a layer of comminuted refractory materialof particle size coarser than the-particle vsize of therefractory material of saidcoatingand finer than the particle size of the refractory material ofthe mold body, said lastmentioned layer of refractory material beingsubstantiaily coextensive with said coating aadinterposed between the coating and the mold body to -bond vand anchor the coating to the mold body.v

4. A refractory moldy comprising a body of comminuted refractory material having a'casting'surfacecovered with a coating comprising a comminuted refractory'm-aterial of relatively fine particle size, a binding agent and a water-soluble alginate acting asa nlm-forming constituent, and -avlayer of comminuted refractory material'of particle size coarser than the particle sizeof the refractory material of said'coating and finer than the particle size of the refractory material of the mold body, said last mentioned layer ofrefractory material being substantially coextensive with said coating-and interposed between the coating and the mold body to bond and anchor the coating tothe mold body.

- 5s The method of fabricating a mold having a refractory mold body provided with a smooth casting surface', which comprises, dipping a fusible pattern into-a iiuid mixture of finely-divided refractory material and aA binding material, withdrawing said ypattern from said mixture whereby it will be provided vwith a coating thereof, applying to saidcoating while it is at least .f partially wet a refractory material having aparticle size larger than the particle size of theiine- 1y divided refractory material in saidcoating, drying the coating with said last mentioned fre- 5 fractory material thereon, and investing said coated pattern in a settable investment compo'- sition comprising a lrefractory material of larger particle size than that of said refractory material applied to said coating.

6. The method of fabricating a mold having sa refractory mold bodyl provided with a smooth casting surface, which comprises, coating a fusible pattern with a fluid mixture of finely divided refractory material, a binding material and a film forming constituent, partially drying said coating, dusting said partially dried' coating with a refractory material having. a particle size coarser than that of said finely divided refrac-l tory material, drying said coated and dusted pattern, and investing said pattern so coated, dusted -and dried, in a settable investment composition containing a refractory material of larger particle size than that of said'refra'ctoryfmaterial used for dusting.

7. The method of fabricating a mold having a refractory mold body provided with a casting surface which comprises coating a fusible pattern with a mixture of finely divided refractoryfma'- terial and a binding material; applying tol said so coating while it is still at least partially-'weta refractory material having a particle size larger than the particle size of the finely divided're= fractory material in said coating, drying fthe coat'- ing with -said last mentioned refractory -material settable investment composition comprising a refractory material of larger particle sizethan that of said refractory material applied to said coating.

40 ROY C. FEAGIN.

ERIC H. ZAHN.

REFERENCES CITED The following references are of record`in`the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Gregory, Uses and Applications of Chemicals ao and Related Materials, pages 18 and 19.

thereon, and investing said coated pattern-in a

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