USRE23355E - Mold composition - Google Patents

Description

Reissued Apr. 10, 1951 MOLD COMPOSITION Burgess P. Wallace, Brooklyn, N. Y., assignor to Whitehead Brothers Company,

New York,

N. Y., a corporation of New Jersey No Drawing. Original No. 2,469,907, dated May 10, 1949, Serial No. 692,377, August 22, 1946. Application for reissue January 30, 1950, Serial a claims. (on. 22 1ss) Matter enclosed in heavy brackets I: appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to the expeditious and economical casting of high melting point, diflicultly oxidizable metals, such as iron, steel, bronze and the like, in so-called reversible water-tempered green molds and has for its particular objects the production of pattern-true castings of such metals having mirror-like surfaces, free from blow holes, pits, scabs and particularly from burnt-on sand grains whereby, as a consequence, it is unnecessary to resort to costly and tedious tumbling, wire-brushing and sand-blasting operations in order to obtain high grade castings.

Other objects of the invention are hereinafter set forth.

For generations, it has been the usual if not the universal practice in foundry operations, to cast grey iron and malleable iron, steel and bronze in molds formed of non-combustible refractory materials such as highly refractory grains of silica sand of varying degrees of fineness, naturally or artificially bonded with clays or with clay-like materials such as bentonite. In using such silica sand molds, however, one encounters a very serious difficulty in that the molten metal tends to fuse the bonding material both to the metal and to the sand grains in the surface of the mold with the consequence that rough castings will be obtained which are covered to a substantial depth by a layer of firmly adhering, burnt-on, fritted sand particles that require expensive equipment and considerable expenditure of time and effort to clean the'same. Many different methods are employed in an effort to minimize such so-called burn-on of the sand particles but they all depend in the last analysis upon the interposition of a carbonaceous film having a limited refractory value between the said surface of the mold and the flowing metal. For example graphite is frequently slicked or patted on the sand surfaces of the mold and the sand particles are completely covered thereby. Again, itis a common practice to employ a dust-on type of carbonaceous facing which is dusted on to the cope and drag surfaces of the mold in an attempt to separate the sand particles in the mold surface from the molten metal and thereby protect them from the fusing action of such metal. still other cases, finely divided sea coal or pitch is directly incorporated in the facing sand (the sand next to the metal of .such sand molds) for the purpose of generating in situ in such surfaces an,

amount of soot and soot-laden hydrocarbons which tend to coat the surface sand particles and thus separate them from the molten metal. It is generally recognized that, regardless of which protective procedure is employed, unless a sufficiently thick layer of carbon is applied to the mold or generated in the surface thereof, the hot metal will burn its way through such layer and contact directly with the sand particles in the mold surface and a burn-on of the silica particles will result. Not only are such facings expensive and their application time-consuming but frequently the mold surfaces are disturbed during the application thereof and consequently patterntrue castings cannot be obtained.

In the preparation of the aforesaid green sand molds, it is essential to impart thereto a green bond strength capable of resisting disintegration or fracture during the formation thereof and especially during the removal of the patterns therefrom as well as during the initial pouring of the mold. In addition to such green bond strength, the mold must be capable of withstanding the erosiv action of the molten metal and also be sufficiently refractory to preserve the dimensions of the mold cavities and the designs on the mold surfaces substantially unimpaired. These and other features are possessed by molds prepared in accordance with my invention as hereinafter set forth in detail.

My investigations have led to the discovery, that, contrary to the general belief that such refractory or incombustible materials, as above specified, are essential for forming metal-casting molds, that pattern-true castings far superior to those producible in sand molds can be obtained by the employment of molds composed substantially entirely, except for the indispensable bonding material, of combustible carbonaceous substances and containing no sand whatsoever. Furthermore that the'castings produced in this latter type of mold are not only entirely free from burnt-on sand conditions on all of the faces thereof but such surfaces possess a mirror-like finish entirely free from all imperfections which is characteristic thereof and quite unlike any castings made in the aforesaid ordinary sand molds. Since there is no adhering sand on the castings so produced in my improved mold, they do not have to be cleaned at all as nothing will be found adhering thereto after the casting is cooled and shaken out of the mold. Furthermore the employment of this novel molding media completely eliminates the necessity of employing facing compositions such as aforesaid and the very absence of the same facilitates the produc tion of faithful castings of extreme accuracy of pattern detail since nothing has been applied to the finished mold surfaces to distort the same.

ods:

Furthermore, since as is well known an excess of carbon produces-agreater fluidity; ingrey. iron, the metal-runs more freely and iron castings produced in such molds have sharper detail than those produced in ordinary sand molds.

' another important factor resides in theefactrthat,

carbon has a very low coeflicient of expansion and therefore complete molds-made, .WithnS Ufih carbonaceous molding media-do not. expand: 301- contract as much as sand molds and'ihence do not put strains on the metal as;it.solidifieswith the result that virtually no tears or cracks areQ evident. l

I am Well aware that it has been heretofore proposed to produce molding material by grinding together a major proportion of cokeand a min zr-pmporti nco e p i e and :to incorporate in the ground mixture asiuiicientaamountaof ,a,

;mold. The mold thus formed whenytempered with water has a very --moderate green bond strength, since the water constitutes the only bonding ,meclium and the green bond strength results solely fromits capillarity.. However, its hot bond strength is virtuallynil as the water zquickly evaporates when the mold is heated.

These molds are therefore wholly unable; to

withstand Zthe impact orerosive action of molten metal poured iDjtOgS'llCh molds. As aconsequence, dueto such erosive, action-on the mold, it is impossible to prQdur'ce pattern-true castings there-.

in. Moreover, the synthetic molding material employed in, such molds is substantially waterproofed 'by the melted pitch ingredient. incorporated therein and'consequentlysuch molding ;material is illadapted for -tempering ;with water in accordance with the prQcedure. usnallperna ployedgin making green sand -molds.,

In the preduction-of castings of ierrouszmetals,

bronze and other difiicultly-oxidizable metalspf ;rela tively;high melting points inaccordance. with my invention, it is preferable to proceedin ac,- eordance with :either of the following two math- (;1) Eighty parts of seventy-two (7 2) hour metallurgical coke, retort -carbon, anthr aci,te coal,

-peratureofseven hundred twenty-five (725?) C. "will not lose more :than forty-five (45 of .car-

bon,. is ground [until it has, a -,grai-n fineness] and selectively sized, in the welljmowzt manner .to; a grain fineness number between :o ne, hundred ninety (119.0) and .tWQ- hundred (200) asdetermined by the Foundry Sand Grading ClassificaylliOIl set forth inthe Foundry ,sandlt ti Island- 'book, fifth edition, 1944,. of 'theaAmerican Foundrymens Association. To this ground material is added ten (10) parts of an inorganic clay-like bondingmaterial, desirably bentoniteonfire clay, and (3) parts .of .a gummy ,adhesiveorganic bonding material, as dextrine or gumarabic. for

example, .the above materials being intimately mixed in a suitable mixer either .while dry ordn the presence of a small amount of water which latter gtends -to facilitate the wmoreaeven distribution of the bonding materials throughout the mass. resultant migrturaconstitutes a synthetic carbonaceous molding ;medium, -:which is ready for shipment to foundries wher it can be Still; itempered with the correct amount of Water and -fprrngdinto molds in the identical manner at present employed when using silica molding s nds.

liln athose-wcases; where the prepared molds are to be usedforthe production of heavy castings,

it is desirable to incorporate about to three nartapfia pitchy material, such as coal tar pitch,

10.1 sea coalii'n the above mixture in order to create a. $1 1 58 smoky atmosphere within the mold and to assist in freeing the clay-like bond from the casting.

1 2 Mrsa ndmethod,comprisesthe pre arationqofla moldingmedium which is .iree V fireman! clay-lik or other inorganic bonding substance, whatsoever, the same being accomplished by admixing with the aforesaid carbon base material about 3% to 8 by weight thereof-of anorganic, adhesive, water soluble bonding substance, such .asdext-rineor gum arable O S mB /2 to .of a water-sol,uble synthetic resin, desirably sci the citrogly,cerol type. There being no inurganic ingredient in such .a mixture, it is obvieuslyunnec sary s nwr Q at rs n bshm a with-such ba e even when prod cinsaVy-;castings.

The amount of theclay-like bonding substance emplQyfid ,should b between fi-ve and thirty percent by weight, of the finished molding I material when the same is employed at all and preferably the amount of. the gummy adhesive bondingsubstance admixed with the clay-like bonding,substanc zshould be between? ,a by weight of the. finished moldingr material, al thoughthe-samev can be dispensed with entirely if :not readily available .whenthe clay-like bond: ing material ,isemployed.

The carbon ingredientoi the molding material should have ,a refractory value substantially greater than =tha. t of a, ood grade. of charcoal .and, the-bentonite-and gummy bonding a ent 'ishonld be. preferably as ,finelydivided a'sthe. car.- I

.bona :eeu,s.- ;v material ;.that. ;.is employ-ed.

Instead :Qi. makin a. complete mold; of ,th aforesaid noyelimolding material, a mold canbs vformedfrom,ordinary molding sand except 1.01 the surface. layerhsayabout A to; 1/2 inch indepth which loan be formed-rfrom'said =no.v,elmolding .155 .g'raphite or like highly refractory, carbonaceous :material which, when heated to an ,averageytemmedium as. such .a facing will when tempered with water act exactly like the ;molding sand to ,thereariof itinsofar as; its moldability iscon- ,cerned and acfiprdingly will .iirmly adhere-to the backing to form an;effective protectinglayer that will absolutely prevent any contact between the backing. sandand the'molten metal with thereon sequence that thezeasti-ng obtained by pourin hot metal into the mqld -whenl finished will. corre- .spondin eyeryway to that obtainable by .ppur- ,;ing;hot .molten .metal int a mold formed-en ,tirely ,-,of;;my improved sand-freemoldin material.

- ;Due to, the presence of thebentonite or other .cl y-1ike'orgurnmy bondi ssnb ance 'i my imroved molding-material. a molderis oorlheap thereof ,will-gndt dryout during thB WOIIKi J adEE-Y as would-be theease were, lthe'tempering :water, Only, to be re ied up n as aforesaid-t em the material. Again.my;novelmolding.mat r alrcan.

'ius as i -2t as -of rdinary mo d ag sand-be e a ain.merelyby-ladd ag addinemp n ats for h t. e der d active in order to re-generate the molding material.

By the employment of my improved molding material, it is possible to realize all of the aforesaid advantages which were the objects of the invention while at the same time molds can be formed with the same facility and in the same manner as if ordinary molding sand was being employed and likewise the grain sizes of my carbon base material can be selected to correspond to the grain [sizes] fineness number of molding sands which had been previousl employed in a foundry desiring to use this new molding material, such [sizes] grain fineness number usually ranging from about 50 to 250 on the scale set forth in the said Foundry Sand grading classification.

While I have described certain preferred embodiments of my invention, various modifications thereof within the scope of the appended claims may be made without departing from the spirit of my invention.

Having thus described my invention, what I claim is:

1. An unbaked green mold for casting difiicultly oxidizable metals, consisting essentially of grains of highly refractory carbon of a ore-selected grain [sizes] fineness number and between about 50 and 250 on the scale set forth in the Foundry Sand Grading Classification in the Foundry Sand Testing Handbook, Fifth edition (1944), of the American Foundrymens Association, and containing a minor pro-portion, but at least about 5%, of bentonite intimately incorporated therewith and also between about 2% and 8% of an organic gummy adhesive [belonging to] selected from the group consisting of dextrine and gum arabic, said mold having excellent green bond strength, whereby the same is rendered capable of resisting disintegration o-r fracture during the formation thereof and especially during the removal of a pattern therefrom as well as during the initial pouring of the mold, and also having excellent hot strength, whereby the same is rendered capable of resisting the erosive action of the molten metal and of preserving designs on the mold surfaces substantially unimpaired; and said mold being essentially sand-free, at least to a depth of about one-quarter inch below the inner surface thereof.

2. An unbalcecl green mold for metal casting purposes, consisting essentially, at least to a depth of about one-quarter inch below the inner surface thereof, of grains of refractory carbon of a pre-selected grain fineness number and between about and 250 on the scale set forth in the Foundry Sand Grading Classification in the Foundry Sand Testing Handbook, Fifth edition (1944) of the American Foundrymens Association and a minor proportion, at least about 5%, of a clay-like bond selected from the group consisting of bentonite and fire-clay, said mold having excellent green bond strength whereby the same is rendered capable of resisting disintegratiOn or fracture during the formation thereof and especially during the removal of a pattern therefrom as well as during the initial pouring of the mold, and also having excellent hot strength, whereby the same is rendered capable of resisting the erosive action of the molten metal and of preserving designs on the mold surfaces substantially unimpaired.

3. An un-baked green mold for metal-casting purposes as claimed in claim 2, containing from 2% to 8% of an organic, adhesive, water-soluble bonding substance.

BURGESS P. WALLACE.

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

UNITED STATES PATENTS Number Name Date 2,299,860 Stoody Oct. 2'7, 1942 2,304,751 Hake Dec. 8, 1942 OTHER REFERENCES Dietert, Modern Core Practices and Theories, published 1942, pages 4-10, 16 and 42.