US3213497A - Method of treating an investment mold - Google Patents

Method of treating an investment mold Download PDF

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Publication number
US3213497A
US3213497A US324872A US32487263A US3213497A US 3213497 A US3213497 A US 3213497A US 324872 A US324872 A US 324872A US 32487263 A US32487263 A US 32487263A US 3213497 A US3213497 A US 3213497A
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United States
Prior art keywords
alcohol
mold
refractory
shape
investment
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US324872A
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English (en)
Inventor
Robert K Scott
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Harbison Walker Refractories Co
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Harbison Walker Refractories Co
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Publication date
Application filed by Harbison Walker Refractories Co filed Critical Harbison Walker Refractories Co
Priority to US324872A priority Critical patent/US3213497A/en
Priority to AT877564A priority patent/AT246346B/de
Priority to DE19641433964 priority patent/DE1433964B1/de
Priority to FR993561A priority patent/FR1415980A/fr
Priority to GB44769/64A priority patent/GB1027419A/en
Application granted granted Critical
Publication of US3213497A publication Critical patent/US3213497A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
    • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
    • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
    • B22C1/205—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of organic silicon or metal compounds, other organometallic compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/02—Sand moulds or like moulds for shaped castings
    • B22C9/04—Use of lost patterns

Definitions

  • this invention relates to an improvement in the process disclosed in copending application Serial No. 317,039, filed October 17, 1963 (now abandoned), and owned by the same assignee as the instant invention.
  • This invention rel-ates to the manufacture of refractory molds of the type used for making precision metal castings. More particularly, the invention relates to a process of treating refractory patterns which are subsequently to be used for casting of molten metal.
  • the single invesment casting process includes preparation of a plurality of refractory molds from the same permanent master pattern or mold.
  • the permanent mold can be termed a positive (identical to the shape to be cast); and the refractory investment is the negative into which molten metal is cast.
  • the double investment casting process is quite similar to the single investment one, in that a permanent mold is repeatedly used to make refractory invesments for the actual casting of molten metal. There is a difference, however, in the refractory investment. It has a backup .Or base portion, which can be identical to that used in the single investment mold process. However, in the double investment system, the molten metal contacting portions are coated with a layer of specially size graded refractory material to provide extremely smooth surfaces.
  • Both the single investment and double investment processes utilize substantially the same material (with the exception just noted). These materials include a refractory aggregate and a binder.
  • binder Most generally, the preparation of a binder is considered the most critical part of the process, since it had to be carefully and critically prepared according to a most precise recipe.
  • One commonly used type of binder includes a mixture of alcohol (ethyl alcohol for example), an acid (such as hydrochloric acid), a small amount of water, and an organic silicate (such as ethyl silicate), sometimes with additional ingredients added.
  • micro-crazing is beneficial, since it prevents gross cracking. It is accomplished by torching or burning the surfaces of the refractory immediately upon its reaching a self-sustaining or set state. I have not found micro-crazing desirable. I believe one completely free of even minute cracks is preferable.
  • I utilize a prehydrolyzed ethyl silicate solution and a pretreated refractory grain in a system of the type disclosed and claimed in copending application Serial No. 317,039, identified above.
  • the gel formed from this system is weak, initially; but continues to develop strength when permitted to stand.
  • a mold prepared by this and prior similar systems is allowed to stand in open air too long, evaporation of alcohol from exposed surfaces produces shrinkage of such surfaces, sufiicient to cause cracking or crazing before the gel is strong enough to prevent shrinkage.
  • a remarkably satisfactory and preferred impervious plastic sheet material which can be used according to the practice of this invention, is Saran wrap, a commercially available product.
  • This material is made from thermoplastic resins obtained by the polymerization of vinylidene chloride or co-polymerization of vinylidene chloride with lesser amounts of other unsaturated compounds.
  • other flexible film or sheet material which is impervious to air and alcohol fumes, and which will resist chemical reaction, i.e. inert to the organic and inorganic constituents of the gelling investment, can be used.
  • a rigid container if available, which can be sealed to the atmosphere, can be used, since it also will serve to enclose an alcohol-rich atmosphere about the investment.
  • refractory grain which is conventionally used for making refractory investments
  • satisfactory grain include alumina, calcined clay which analyzes mostly SiO and A1 0 on an oxide basis, mullite, silica, calcined high alumina materials such as bauxite and diaspore, fused corundum and fused mullite, sill-imanite, various spinel minerals such as chrome ore, zirconia (preferably stabilized zirconia), etc.
  • the refractories used for making investment molds should be carefully screened so as to provide a uniform product.
  • the grains may be of a size so that 50%, by weight, is in the range 6+3O mesh, the rest mostly in the 30 mesh range. From 20 to 40% can be smaller than 200 mesh. (All of these sizes are according to the United States Standard series of screens.)
  • the size graded grain is treated with a solution of a volatile organic solvent and an organic base.
  • the organic base is of the amine type, preferably having from 8 to 22 carbon atoms, and of the type of alkali metal and alkaline earth salts of chemically basic organic compounds as are discussed in the copending application above identified.
  • the refractory grain is coated by treating them with one of the amine-type materials, just discussed, so that at least a major portion of the exposed surface area of the refractory grain of the batch (at least about 50%) is covered.
  • the amount of the coating may run from 0.1 to about 2%, by weight, based on the weight of the refractory. The preferred range is 0.3 to 0.7% by weight.
  • Coated grains are treated with a gelling binder.
  • a preferred gelling binder is prepared from:
  • the resulting binder and treated refractory grain mixture is about as follows: 400 grams of a refractory consisting essentially of 20% 8 on 30 mesh calcined flint clay, the balance being -100 mesh mullite, and the mixture treated with 0.55% Duomeen C (or 0.2% diethylmethylamine-this being preferred), is mixed with 100 cc. of a binder solution containing 18% SiO by weight, derived from ethyl silicate (40% SiO content), water to allow 83% hydrolyzation (about 6 cc.
  • hydrochloric acid or other inorganic acid such as sulfuric or nitric acid to yield a pH of approximately 2 (about 1 cc.)
  • ethyl alcohol to reduce the SiO content to the above mentioned to 18% (from 50 to 55 cc. of ethyl alcohol).
  • Duomeen C is a coconut oil derivative of 1,3-propylenediamine. After thorough mixing, the resulting slurry is poured over a master pattern, where gelation occurs in about 3 minutes at 75 F.
  • a preferred refractory grain is the commercial product of commerce, identified by the trade name Flintmull GG3, a product of the Harbison-Walker Refractories Company. This commercial product is a mixture of calcined flint clay and mullite.
  • the preferred coating agent is Duomeen C, a product of the Armour Chemical Company.
  • the mixture of binder and coated refractory is poured into a master pattern, allowed to gel to a state sufiicient to resist light finger pressure, the master pattern is stripped from the refractory, and the refractory investment is inserted in a plastic bag which is tied to close the investment off from the atmosphere.
  • the time necessary for the refractory to remain covered by the plastic is visually determined; for example, when all surfaces are of a uniform color and no wet areas are obvious, the bag may be removed. I found it very satisfactory, using the preferred composition, above discussed, to remove the bag after about 1 to 2 hours, followed by air drying for a similar or longer period. If desired, the bag may remain longer; for example, overnight (12 or so hours).
  • the investment may be placed in an oven to ignite any residual alcohol.
  • the in vestment can be heated to a temperature of on the order of 2000 F. to obtain some ceramic bonding through the refractory material to thereby obtain improved strength.
  • a method of preventing micro-crazing and cracking of gelling investment molds of the type made from a slurry of (l) a refractory, and- (2) an alcohol and lower alkyl silicate bonding solution which comprises the steps of, pouring the slurry about a master pattern, allowing the slurry to initially gel only to a self-sustaining shape about said master pattern, immediately stripping the pattern from the shape, immediately encapsulating the shape in means defining an air and alcohol vapor-impervious cavity, said means sealing said cavity from the atmosphere, said cavity being larger than the mold it encapsulates and of such size and configuration as to retard the evaporation of alcohol from the mold and to promote and allow the formation of an alcohol-rich atmosphere about exposed surfaces of the mold by evaporation of alcohol from the mold, maintaining the shape in the cavity for at least about an hour until all surfaces of the mold are substantially uniform in color and with no wet areas being obvious.
  • said refractory is selected from the group consisting of alumina, calcined clay, mullite, silica, bauxite, diaspore, fused corundum, fused mullite, sillimanite, chrome ore, and mixtures thereof.
  • a method of preventing micro-crazing and cracking of gelling investment molds of the type made from a slurry of (1) a refractory, and (2) an alcohol and lower alkyl silicate bonding solution which comprises the steps of pouring the slurry about a master pattern, allowing the slurry to initially gel only to a self-sustaining shape about said master pattern, immediately stripping the pattern from the shape, immediately encapsulating the shape in an air and alcohol vapor-impervious plastic bag, said bag being sealed from the atmosphere and of such size and configuration as to retard the evaporation of the alcohol and to promote the formation of an alcohol-rich atmosphere about exposed surfaces of the mold by evaporation of alcohol from the mold, maintaining the shape in the bag until all surfaces of the mold are substantially uniform in color and with no wet areas being obvious.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Mold Materials And Core Materials (AREA)
US324872A 1963-11-19 1963-11-19 Method of treating an investment mold Expired - Lifetime US3213497A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US324872A US3213497A (en) 1963-11-19 1963-11-19 Method of treating an investment mold
AT877564A AT246346B (de) 1963-11-19 1964-10-15 Verfahren zur Verhinderung der Bildung von Rissen und Sprüngen in Präzisionsformen
DE19641433964 DE1433964B1 (de) 1963-11-19 1964-10-16 Verfahren zum Behandeln von Giessformen
FR993561A FR1415980A (fr) 1963-11-19 1964-11-02 Traitement de modèles
GB44769/64A GB1027419A (en) 1963-11-19 1964-11-03 Improvements in or relating to the production of refractory moulds

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US324872A US3213497A (en) 1963-11-19 1963-11-19 Method of treating an investment mold

Publications (1)

Publication Number Publication Date
US3213497A true US3213497A (en) 1965-10-26

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US (1) US3213497A (de)
AT (1) AT246346B (de)
DE (1) DE1433964B1 (de)
GB (1) GB1027419A (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3314117A (en) * 1965-05-10 1967-04-18 British Ind Corp Method of manufacturing a foundry core
US3445250A (en) * 1967-02-28 1969-05-20 Nalco Chemical Co Precision metal casting molds comprising alumina coated silica and a refractory
US4043853A (en) * 1976-03-05 1977-08-23 Saladino Matthew L Method of renovating a series of identical bathtubs
US5014763A (en) * 1988-11-30 1991-05-14 Howmet Corporation Method of making ceramic cores
US5126082A (en) * 1988-11-30 1992-06-30 Howmet Corporation Method of making ceramic cores and other articles

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2025376A (en) * 1932-04-12 1935-12-24 Du Pont Cellophane Co Inc Conditioned material and method of preparing same
US2795022A (en) * 1953-04-09 1957-06-11 Shaw Process Dev Corp Method of making moulds
US2948935A (en) * 1958-04-07 1960-08-16 Richard T Carter Process of making refractory shell for casting metal
US2979790A (en) * 1957-08-09 1961-04-18 Shaw Process Dev Corp Molds
GB876805A (en) * 1959-06-11 1961-09-06 Howe Sound Co Improvements in making refractory shell molds
US3148422A (en) * 1961-07-20 1964-09-15 Monsanto Chemicals Production of shell moulds
US3172176A (en) * 1964-03-26 1965-03-09 Greenwood Ronald Method of making ceramic molds

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2025376A (en) * 1932-04-12 1935-12-24 Du Pont Cellophane Co Inc Conditioned material and method of preparing same
US2795022A (en) * 1953-04-09 1957-06-11 Shaw Process Dev Corp Method of making moulds
US2979790A (en) * 1957-08-09 1961-04-18 Shaw Process Dev Corp Molds
US2948935A (en) * 1958-04-07 1960-08-16 Richard T Carter Process of making refractory shell for casting metal
GB876805A (en) * 1959-06-11 1961-09-06 Howe Sound Co Improvements in making refractory shell molds
US3148422A (en) * 1961-07-20 1964-09-15 Monsanto Chemicals Production of shell moulds
US3172176A (en) * 1964-03-26 1965-03-09 Greenwood Ronald Method of making ceramic molds

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3314117A (en) * 1965-05-10 1967-04-18 British Ind Corp Method of manufacturing a foundry core
US3445250A (en) * 1967-02-28 1969-05-20 Nalco Chemical Co Precision metal casting molds comprising alumina coated silica and a refractory
US4043853A (en) * 1976-03-05 1977-08-23 Saladino Matthew L Method of renovating a series of identical bathtubs
US5014763A (en) * 1988-11-30 1991-05-14 Howmet Corporation Method of making ceramic cores
US5126082A (en) * 1988-11-30 1992-06-30 Howmet Corporation Method of making ceramic cores and other articles

Also Published As

Publication number Publication date
GB1027419A (en) 1966-04-27
AT246346B (de) 1966-04-12
DE1433964B1 (de) 1969-09-25

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