US3836372A

US3836372A - Methods and materials for treating investment casting patterns

Info

Publication number: US3836372A
Application number: US00253177A
Authority: US
Inventors: R Horton
Original assignee: Precision Metalsmiths Inc
Current assignee: Precision Metalsmiths Inc
Priority date: 1972-05-15
Filing date: 1972-05-15
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: JPS5120407B2; JPS4941221A

Abstract

Investment casting patterns are treated with a liquid mixture consisting essentially of an aqueous dispersion of colloidal refractory particles and a medium comprising a watersoluble organic liquid in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by water-base refractory slurries used in the production of ceramic shell molds and bulk investment molds.

Description

,1 o r, i 1, l-1 Unite tts tent 1191 1111 3,836,372 Horton Sept. 17, 1974 [54] METHUDS AND MATERIALS FOR 2,842,445 7/1958 Emblem 106/3835 TREA'HNG INVESTMENT CASTING 3,258,348 6/1966 Reuter 106/3835 3,270,382 9/1966 Emblem et a1. 106/383 PATTERNS 3,326,269 6/1967 Schneider 106/383 [75] lnventor: Robert A. Horton, Chesterland, 3,399,067 8/1968 Scott 106/383 Ohio 3,748,157 7/1973 Moore 106/383 3,754,946 8/1973 Moore 106/383 [73] Assrgnee: Precision Metalsmith, Inc.,

Cleveland, Ohlo Primary Examiner-Lorenzo B. Hayes [22] Filed: May 5 1972 Attorney, Agent, or Firm-Watts, l-loffmann, Fisher &

Heinke Co. [21] Appl. No.: 253,177

[57] ABSTRACT [52] US. Cl 106/3822, 106/3827, 106/383, Investment casting patterns are treated with a liquid 106/3 8.35, 106/389 mixture consisting essentially of an aqueous dispersion [51] lint. (I1 B28b 7/36 of colloidal refractory particles and a medium com- [58] Field of Search 106/383, 38.35, 389, prising a watersoluble organic liquid in order to render 106/3822, 38.27; 164/25, 26 the pattern surfaces hydrophilic and thereby promote uniform surface coverage by water-base refractory [56] References Cited slurries used in the production of ceramic shell molds UNITED STATES PATENTS and bulk investment molds.

2,380,945 8/1945 Collins 106/383 15 Claims, N0 Drawings METHODS AND MATERIALS FOR TREATING INVESTMENT CASTING PATTERNS BACKGROUND OF THE INVENTION The present invention relates generally to the investment casting art, and more specifically to methods and materials for treating investment casting patterns to promote uniform surface coverage of the patterns by' water-base refractory slurries used in the production of ceramic shell molds and bulk investment molds.

As is known to those familiar with the art of investment casting, ceramic shell molds and bulk investment molds are made using disposable patterns which typically are composed of organic material, such as wax, synthetic resin, or a wax and synthetic or natural resin composition. The patterns are surrounded with refractory slurry which is allowed to harden, the patterns being subsequently destroyed to form the mold cavities. Bulk investment molds are produced by dipping an assembly of patterns in refractory slurry, sanding the coated patterns while wet with coarse refractory particles, and drying the coating to form a thin, hard layer. After this dipcoat or pre-coat has dried, the pattern assembly is placed in a flask and the flask is filled with a cementitious refractory material known as investment which hardens to form the bulk of the mold. In some instances, as when using a plaster-base investment, the dip coat or pre-coat can be omitted. Ceramic shell molds are usually prepared by forming a plurality of hardened refractory layers around a pattern assembly in the same manner as the dipcoat in the production of bulk investment molds. The steps of dipping, sanding and drying are repeated until a refractory shell of the desired thickness has been built up around the pattern assembly.

A problem encountered in the production of both types of investment molds described above is that of the refractory slurry failing to wet the surfaces of the patterns, as is necessary to obtain uniform pattern coverage and to form a dense, void-free mold face capable of reproducing the pattern detail. In extreme situations where the slurry does not have the ability to wet the patterns at all, most of the slurry will run off the patterns when they are withdrawn from the slurry bath so that the pattern surfaces are substantially bare. In less severe cases, the slurry coating gradually withdraws or recedes from some areas of the pattern surfaces, a condition referred to as dewetting. Although gross withdrawal or dewetting can be alleviated to some extent by sanding or stuccoing the slurry coating immediately after the dipping operation, localized dewetting may still occur throughout the coating so that castings made in the molds have a condition of overall surface roughness.

The most common condition encountered in the production of shell molds is that the slurry, while appearing to coat the patterns satisfactorily, does not actually wet difficult areas, such as tiny holes, narrow slots, serrations, sharp corners, etc. Castings made by use of such improperly coated patterns exhibit characteristic defects such as small globules of metal corresponding to air bubbles which the slurry did not displace from the pattern and indistinct detail in areas where the slurry covered over a negative feature in the pattern surface instead of penetrating into it. The same types of problems encountered in forming ceramic shell molds also may be encountered in forming bulk investment molds. This is particularly true when a precoat is applied to the patterns before investing, since the precoat operation is identical to that of applying the first slurry coating in shell forming operations. When the precoat is eliminated and the investment is poured directly around the patterns, failure of the investment slurry adequately to wet the patterns can result in an inability of the slurry to displace air bubbles and a failure to penetrate fine detail of the patterns, etc.

The wetting problem is of particular significance because of the extensive use of water-base slurries, i.e., slurries formulated with aqueous binders, in the investment casting industry. This is due to the fact that the organic pattern materials commonly employed in investment casting processes, including jewelry and dental casting, are not readily wetted by water. In spite of the wetting problems attendant to the use of aqueous binders, such binders are widely used in formulating dipcoat slurries and investments for a number of reasons. Water-base binders do not present the fume and fire hazards accompanying the use of solventbase systems, e.g. ethyl silicate-alcohol systems. In addition, aqueous binders are economical and readily available. Aqueous colloidal silica sols, for example, are frequently employed in formulating water-base slurries for ceramic shell operations and for precoat slurries used in making bulk investment molds. Aqueous colloidal silica-type slurries are often used for the first slurry coating which is applied directly to the patterns even in systems relying primarily upon ethyl silicate as a binder for subsequently applied coatings. Aqueous slurries based on sodium silicate as a binder also are used for ceramic shell mold operations and precoats for investment operations. Slurries used as the investment in making bulk investment molds contain such binders as gypsum plaster, metallic phosphates, calcium aluminate, sodium silicate, colloidal silica and others.

It has been conventional to add wetting agents to water-base slurries in attempts to improve the ability of the slurries to wet organic patterns. Typical wetting agents which have been used include sodium dioctyl sulfosuccinate, various polyoxyethylene ethers and complex phosphate esters. Many of these wetting agents are not completely compatible with the slurries and cause localized gelling if added improperly. Even when properly added, the agents can cause a gradual thickening of the slurry. Furthermore, the use of wetting agents generally promotes the formation of air bubbles in the slurry and foam on the top of the slurry bath. In some instances, lower shell strengths result when particular wetting agents are used, and this may be due to the formation of air bubbles and thickening of the slurry. Among other disadvantages, it has been found that certain wetting agents lose their effectiveness with time after having been added to the slurry baths. This makes it necessary to monitor the slurries after they have been formulated and to add fresh quantities of the wetting agent at periodic intervals.

Recently it has been suggested that the wetting problem could be alleviated by coating disposable patterns with fumed silica particles. Fumed silica is a submicroscopic pyrogenic silica made by the vapor phase hydrolysis of silicon tetrachloride at a temperature of about 1100C. Because of their elevated temperature origin, fumed silicas are characterized by having the sil' ica particles sintered together in chain-like formations having a branched structure. In practice, the fumed silica is suspended in alcohol and applied to the pattern surfaces by dipping. After the suspension has dried, the pattern surfaces are hydrophilic and can be wetted by aqueous slurries.

While the use of fumed silica in the manner described represents a significant improvement over the use of wetting agents, there are distinct disadvantages which limit its usefulness. Fumed silica is of an extremely fine, light powdery consistency so that it is difficult to handle during weighing and mixing. High shear mixing equipment which is not readily available in investment casting foundries is required to dispense fumed silica in the liquid medium. Even when such equipment is available, it is difficult to obtain a stable dispersion or suspension so that settling often occurs during transit, in storage and in use. This requires that the mixture be constantly restirred. Also, due to the fact that fumed silica has a chain-like structure as distinguished from being discrete particles, it tends to form a network structure when dispersed in the liquid medium which results in a strong thickening effect. Consequently, the viscosity of the dispersion is sensitive to concentration and undue thickening can occur simply because of evaporation of the medium. This necessitates that the dispersion be monitored in use and that additional quantities of the medium be added as it is required.

SUMMARY OF THE INVENTION The present invention provides for the treatment of disposable investment casting patterns composed primarily of organic material by a process and with a liquid mixture which is effective to render the pattern surfaces hydrophilic. Patterns rendered hydrophillic by being processed according to the invention are readily wetted by water-base slurries used in the production of bulk investment molds and ceramic shell molds, whereby uniform coverage of the patterns, including penetration of the slurry into all of the intricate surface detail, is obtained. 7

The new pattern treating liquid mixture provided by the invention consists essentially of discrete colloidal refractory particles dispersed in a liquid medium which at least in part includes an organic liquid characterized by the capability of wetting the pattern, the colloidal refractory being present in the mixture in an amount of at least about 0.5 percent by weight and the organic liquid being present in an amount sufficient to cause the mixture to wet the pattern. Preferably, the organic liquid is included in an amount exceeding about 6 percent by weight of the mixture. In more specifically preferred embodiments, the liquid mixture is formulated by mixing an acidic, aqueous sol of colloidal refractory particles with at least one organic liquid characterized by being soluble in water in all proportions and by a surface tension value of less than 28 dynes per centimeter at C. The most preferred organic liquids have a surface tension of less than 24 dynes per centimeter at 20C. and are more volatile than water. In accordance with the preferred method of the invention, a disposable organic pattern is coated with the liquid mixture, as by dipping, and is then dried to deposit the colloidal refractory particles on the pattern surfaces and thereby render the pattern surfaces hydrophilic.

Since the new mixture is formulated with liquids, the problems associated with the handling of extremely dusty materials such as fumed silica are eliminated. The liquids are easily mixed together with little or no agitation so that special high shear mixing equipment and the like is not required.

As distinguished from the network structure formed by fumed silica when dispersed in a liquid medium, the mixture of the present invention is characterized by a dispersion of discrete colloidal refractory particles. These discrete refractory particles do not have the same thickening tendency as fumed silica and the liquid mixture maintains a usable viscosity over a wide range of refractory concentration. As a result, the effect of evaporation on viscosity is minimal so that there is usually no need to monitor the mixture as it is used. Normal additions to replace the amounts of the liquid removed by dipping patterns is usually sufficient to maintain the mixture in a usable condition for extended periods of time. Another important advantage of the new mixture is that the colloidal refractory particles have no tendency to settle so that the mixture is completely stable. This avoids the necessity of constantly restirring the mixture.

Other advantages and a fuller understanding of the invention will be had from the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the present invention involves the steps of coating disposable investment casting patterns composed primarily of organic material with a liquid composition consisting of a hydrophilic agent in the form of colloidal refractory particles dispersed in a liquid medium which is at least in part an organic liquid capable of wetting the patterns. The patterns, which may be easily coated by dipping them into the liquid, are dried to deposit the colloidal refractory on their surfaces and thereby render the pattern surfaces hydrophilic. It has been found that patterns treated in the foregoing manner to render their surfaces hydrophilic are readily wetted by the water-base refractory slurries used in the production of bulk investment molds and ceramic shell molds.

It is preferred to formulate the liquid pattern treating composition using an aqueous sol of colloidal refractory material as the hydrophilic agent and by mixing the sol with a compatible liquid medium which contains the organic liquid or liquids in an amount at least suffi cient to cause the mixture to wet the pattern surfaces. By compatible it is meant that the liquid medium is sufficiently miscible with the sol to form a single phase mixture. Acid stabilized, aqueous colloidal refractory sols are especially suitable for use because they are miscible with the required organic liquids to form a stable mixture. Alkali stabilized sols also are usable, but they usually must be acidified prior to formulating the mixture in order to prevent the organic liquids from gelling or precipitating the colloidal refractory.

Various aqueous sols of colloidal refractory material are available commercially and have been found satisfactory for use as the hydrophilic agent. Examples of the known sols are aqueous or water-base colloidal silica sols, aqueous colloidal zirconia (ZrO sols, and aqueous colloidal aluminosilicate sols. The commercially available sols typically have a colloidal refractory content ranging from about l5 to percent by weight and a particle size ranging from about 2 to millimicrons. Such sols function satisfactorily for purposes of the present invention.

The aqueous sols are included in the mixture in an amount such that the colloidal refractory content is sufficient to render the surfaces of the pattern to which the mixture is applied hydrophilic. The minimum amount of colloidal refractory should be about 0.5 percent by weight of the mixture, and the preferred range of the refractory content is from 1.5 percent to 5 percent by weight of the mixture. While considerably larger amounts of the refractory can be used, it has been found that a refractory content in excess of about 5 percent by weight does not produce significant improvements in the formation of the desired hydrophilic film on the treated patterns and is uneconomical. Furthermore, mixtures containing extremely large amounts of colloidal refractory in relation to the or ganic liquid, for example, a mixture of one part by volume organic liquid and parts by volume of a colloidal silica sol having a silica content of 34 percent by weight, have certain disadvantages. Such mixtures are slow drying which is inconvenient. The slow drying rate combined with the excessive refractory concentration may make it difficult to obtain optimum uniform coverage when the mixture is applied to a pattern.

The primary function of the organic liquids is to impart to the mixture the capability of wetting the patterns so that the colloidal refractory will be deposited substantially uniformly on their surfaces after drying. Accordingly, the organic liquid must have the property of wetting the particular patterns which are to be treated. There are many different pattern material blends employed in the investment casting industry and, depending upon their composition, these blends exhibit a range of wettability characteristics, i.e., are susceptible to being wetted by a particular organic liquid in different degrees. The usual pattern blends consist of natural and/or synthetic waxes or a blend of such waxes with a natural and/or synthetic resin. Other organic patterns which find some use are composed of synthetic resins, such as polystyrene. It has been discovered that organic liquids having low values of surface tension are capable of wetting the largest number of these different pattern material compositions, and that the usefulness of organic liquids in terms of their broad applicability decreases as the surface tension in creases. The preferred liquids have surface tension values less than 28 dynes per centimeter measured at C., and the most preferred liquids which are useful in formulating treating solutions for general purpose application have a surface tension less than 24 dynes per centimeter at 20C.

While it is desired to employ organic liquids having as low a surface tension possible in order to formulate a mixture which can be used to wet a large number of different pattern material compositions, it is to be understood that liquids having surface tension values greater than the indicated preferred minimum values can be used in particular situations. ln the case of liquids which are not significantly more volatile than water, the ability to wet a pattern material can be easily determined by dipping a piece of the material into the liquid and observing whether the liquid withdraws or recedes from areas of the piece when it is withdrawn from the liquid. In the case of more volatile liquids, the wetting ability is determined by treating a specimen of pattern mate rial with a mixture formulated with the liquid, drying the specimen, applying a water-base refractory slurry, and then observing whether the slurry recedes from areas of the treated specimen.

In addition to the required property of being able to wet the particular .pattern material to be treated, the organic liquids which are useful in formulating the mixture of this invention are at least partially soluble in water, and are preferably soluble in water in all proportions. This characteristic assures that the organic liquids can be mixed with the aqueous sols to form single phase mixtures with the colloidal refractory dispersed throughout. The most preferred liquids are further characterized by being more volatile than water. Mixtures formulated with organic liquids which are more volatile than water are fast drying and are therefore advantageous to use.

Examples of useful water soluble, organic liquids which are more volatile than water and have surface tension values less than 24 dynes per centimeter at 20C include methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone and the like. Of these liquids, isopropyl alcohol is especially preferred for a number of reasons. Mixtures based on isopropyl alcohol are particularly effective in wetting practically all of the commercially available pattern materials, and this property is maintained over a wide concentration range. In addition, isopropyl alcohol is very compatible with aqueous, acidic colloidal silica sols, is not hazardous to use, and is economical. Examples of water soluble organic liquids which are less volatile then water but are nevertheless useful because of their low surface tension values include n-propyl alcohol, diacetone alcohol, and the like. Examples of useful organic liquids which are characterized by being partially soluble in water and by surface tension values less than 281 dynes per centimeter at 20C. include methyl acetate, methyl ethyl ketone and the like. Organic liquids, such as methyl ethyl ketone, which are capable of wetting many of the organic pattern materials but which have limited solubility in water or poor compatibility with the preferred acidic, aqueous colloidal refractory sols, may be used in the presence of a small amount of a third liquid, such as isopropyl alcohol, which will make the overall composition compatible.

As has been indicated above, the amount of the organic liquid is at least sufficient to cause the mixture to wet the surface of the patterns to which the mixture is applied. In most instances, the organic liquid should be present in an amount of at least 6 percent by weight of the mixture, but a much larger amount, for example, percent or more, is preferred. An amount of the organic liquid exceeding the usable minimum is desired, since the preferred organic liquids are more volatile than water and therefore cause the mixture to dry faster on the patterns. A fast drying rate is advantageous, since it reduces the waiting time after dipping and prevents excessive drainage of the treating mixture which tends to cause uneven coverage. The maximum amount of the organic liquid that can be used, assuming complete compatibility with the sol, is the amount that dilutes the refractory content of the sol to the minimum amount required to render the pattern surfaces hydrophilic.

An example of an especially preferred mixture formulated in accordance with the invention consists of the following:

93.75 parts by weight isopropyl alcohol 6.25 parts by weight of an aqueous, acidic colloidal silica sol having a pH of about 3.1, an average of particle size in the'range of from 16 to 22 millimicrons, and containing 34 percent by weight SiO and less than 0.01 percent by weight Na O.

The medium or vehicle with which the aqueous sols are mixed may include other liquids in addition to one or more of the organic liquids described above. It is possible, for example to add a certain amount of water to the mixture to reduce its cost and yet maintain the useful properties. Water diluted mixtures are somewhat more limited in the range of pattern materials which the mixtures will wet satisfactorily and have the further disadvantage of being slower drying than mixtures in which the medium consists entirely of one or more of the preferred organic liquids, such as isopropyl alcohol. Normally, the only water in the mixture is that which enters with the sol, although diluted solutions containing water in an amount as high as 62 percent by weight have been used successfully in some instances.

The liquid medium also may contain a solvent for the purpose of removing excessive amounts of lubricant from the pattern surfaces. Lubricants of various types, for example, silicone fluids such as dimethyl silioxane polymers, are commonly sprayed on the surfaces of pattern injection dies to facilitate release of the patterns. A certain amount of this lubricant may remain on the pattern surfaces after injection. When the amount of the lubricant is not excessive, no particular problems are encountered, but on some occasions the pattern may have such a heavy layer of lubricant that the preferred compositions of the invention will not wet the patterns satisfactorily. In such cases, a solvent for the lubricant can be added to the pattern coating mixture. The solvent used for this purpose should not be one which will dissolve the pattern, since such solvents can cause loss of pattern detail and can cause the refractory particles to be covered with a layer of the wax or other pattern material so as to prevent the mixture from functioning in its intended manner. Suitable solvents for use in the mixture include 1, l, l-trichloroethane and the like.

The liquid compositions of this invention can be applied to patterns in any expeditious manner. For example, the patterns can be dipped into a quantity of the liquid and then allowed to dry, whereby the colloidal refractory is deposited over the pattern surfaces. The dipping time is not critical, although it will be understood that the pattern should not be immersed and withdrawn so fast that the liquid does not have a chance to displace the air film around the pattern.

The invention is further illustrated by the following examples:

Example I Silica Sol lsopropyl Alcohol (Parts by Volume) (Parts by Volume) -Continued Silica Sol lsopropyl Alcohol (Parts by Volume) (Parts by Volume) 1 l5 1 20 l 25 l 40 Specimens of commercially available dental wax were dipped in each mixture and were allowed to dry. Another specimen of the same dental wax was dipped in straight isopropyl alcohol and allowed to dry. Each of the treated specimens was then dipped in distilled water and one additional specimen which had no treatment was also dipped in distilled water. The water wetted each of the specimens treated with the silica sol/isopropylalcohol mixtures and formed a thin film over the surfaces. It was found that the water did not wet the untreated specimen and the specimen which had been dipped in straight isopropyl alcohol. In the latter two instances, the water formed beads on the wax surfaces.

The specimens were then dried and dipped in a refractory slurry consisting essentially of 15% pounds of refractory material and 5 pounds of an alkaline, aqueous colloidal silica sol. The refractory material used in the slurry was composed of percent zircon powder and 40 percent fused silica powder. The silica sol had a pH of 9.7, an approximate particle diameter of 7 millimicrons, and contained 30 percent by weight SiO and approximately 0.43 percent by weight Na O.

All of the wax specimens which had been treated with the silica sol/isopropyl alcohol mixtures were wetted and coated by the slurry. The coverage of the specimen which had been dipped in straight isopropyl alcohol was incomplete and large areas were bare. The untreated specimen evidenced no substantial wetting so that almost the entire surfaces were bare.

The foregoing tests demonstrate that the liquid mixtures of acidic colloidal silica sol and isopropyl alcohol are effective over a wide range of composition. The tests further demonstrate that the wetting by the slurry is a result of the silica which is deposited on the pattern surfaces by drying of the coating mixtures, since merely dipping the specimens in isopropyl alcohol was not effective. It is also shown that the mixtures prepared according to the invention are effective to cause uniform coverage of organic pattern materials by refractory slurries even though the conventionally used wetting agents are omitted entirely from the slurries.

Example ll Wax patterns were injected in dies that had been heavily lubricated with a 350 centistokes silicone fluid. It was found that isopropyl alcohol would not completely wet these patterns because of the presence of the lubricant on their surfaces.

A pattern treating mixture was then following composition:

3 parts by volume l,l,l-trichloroethane,

7 parts by volume isopropyl alcohol,

1 part by volume of an alcohol water-base, acidic colloidal silica sol having a pH of 3.5 i 0.5, an average particle diameter in the range of from 16 to 25 millimicrons, and containing in amounts by weight 28 percent SiO 32 percent water, 40 percent alcohol, and less than 0.005 percent Na O.

prepared of the One of the patterns was dipped for 30 seconds in the foregoing mixture, dried, and then dipped in a slurry consisting of 6 pounds, 12 ounces of refractory material and 2 pounds, ounces of an alkaline stabilized, aqueous colloidal silica sol. The refractory material used in the slurry was composed of 60 percent zircon powder and 40 percent fused silica powder. The silica sol had a pH of 8.6, an average particle size in the range of from 16 to 22 millimicrons, and contained in amounts by weight 35 percent SiO and 0.10 percent Na O.

The pattern to which the treating mixture had been applied was coated satisfactorily by the slurry. Another pattern was treated simply with a trichloroethylene/isopropyl alcohol solution and was dipped into the same slurry. The latter pattern was wetted very poorly by the dipcoat slurry and an incomplete coating was obtained.

Example III A liquid, pattern coating mixture was prepared according to the invention using an alkali stabilized colloidal silica sol. The sol was an alkaline, aqueous, fine particle size sol having a pH of about 9.7, an approximate particle diameter of 7 millimicrons, and consisted of about 30 percent by weight SiO and about 0.43 percent by weight Na O. The sol was acidified and mixed with isopropyl alcohol, according to the following formula:

2 parts by volume sulfuric acid 100 parts by volume silica so! 1000 parts by volume isopropyl alcohol The acid was added to the sol with rapid stirring to avoid localized gelling or precipitation of the silica, and the solution was then added to the isopropyl alcohol. Wax patterns were coated with the resulting mixture and the treated patterns were satisfactorily wetted with a water-base slurry of the type described in the previous examples. It was found that the mixture formulated with alkali stabilized silica sol was still usable after storing in a closed container for a period of three weeks.

Example IV Patterns were injection molded from the composition of Example I of US. Pat. No. 3,296,006. One pattern was dipped for seconds in straight methyl alcohol and another pattern was dipped for 15 seconds in a coating mixture containing 100 parts by volume methyl alcohol and 10 parts by volume of the same aqueous,

I acidic colloidal silica so] used in preparing the coating mixtures of Example I.

After drying the treated patterns together with a pattern which was given no treatment were dipped in a slurry prepared as described in Example II. The slurry readily wetted and coated the patterns which had been dipped in the silica sol-methyl alcohol treating mixture. The same slurry did not satisfactorily coat either the patterns treated with straight methyl alcohol or the pattern which had been given no treatment.

Example V Specimens were cut from pattern wax to reveal all fresh surfaces. One specimen was dipped for 5 seconds in straight diacetone alcohol and another was dipped for 5 seconds in a liquid mixture including I00 parts by volume diacetone alcohol and 10 parts by volume of the same acidic colloidal silica sol used in the coating mixture formulations of Example I.

The specimens were dried and were then dipped in a dipcoat slurry consisting of refractory material and the same aqueous colloidal silica sol'used in formulating the coating mixture. The slurry composition was as follows:

2 pounds, 12 ounces colloidal silica sol 7 pounds refractory material consisting of 60 percent zircon powder and 40 percent fused silica powder The specimens treated in the silica sol/diacetone alcohol mixture were wetted and coated satisfactorily by the dipcoat slurry. The specimen which had been treated only with diacetone alcohol was only partially wetted by the slurry and the slurry coating was unsatisfactory.

Example VI Specimens were cut from pattern wax to reveal all fresh surfaces. One specimen was dipped for IS seconds in straight acetone and a second specimen was dipped for 15 seconds in a pattern treating mixture containing parts by volume acetone and 10 parts by volume of the aqueous colloidal silica sol used in formulating the coating mixtures of Example I.

After drying both specimens were dipped in the slurry of Example V. The specimen which had been dipped in the pattern treating mixture was wetted and coated perfectly by the slurry. The specimen which had been treated only with acetone was wetted poorly by the slurry and large areas of the wax surfaces were left uncoated.

Example VIII A pattern wax specimen was dipped in a treating mixture containing 100 parts by volume denatured ethyl alcohol and 20 parts by volume of the aqueous colloidal silica sol used in formulating the coating mixtures of Example I. A second specimen of the same wax was dipped in straight denatured ethyl alcohol.

Both specimens were dried and dipped in distilled water. The specimen treated with the silica sol/- denatured ethyl alcohol mixture was wetted completely by the water. The other specimen which had been dipped in straight denatured alcohol was wetted poorly and the water film receded to leave areas of the specimen bare.

Example IX A pattern treating mixture was prepared by first mixing 1.5 parts by volume of isopropyl alcohol with one part by volume of the aqueous colloidal silica sol used in formulating the mixtures of Example I. The resulting mixture was added to 15 parts by volume of methyl ethyl ketone to obtain a single phase mixture. In the absence of isopropyl alcohol, methyl ethyl ketone was found to be incompatible with the sol. When the sol was added to methyl ethyl ketone in quantities of 1:10 parts by volume of 1:20 parts by volume, the combinations were not completely miscible and two phases resulted in each instance.

Specimens were cut from pattern material wax to reveal all fresh surfaces. One specimen was dipped for 5 seconds in straight methyl ethyl ketone and a second specimen was dipped for 5 seconds in the above pattern mixture containing methyl ethyl ketone, silica sol and isopropyl alcohol. The patterns were dried and were then dipped in the dipcoat slurry used in Example V. The slurry wetted and coated the specimen which had been dipped in the pattern treating mixture. The slurry did not wet the specimen which had been dipped in straight methyl ethyl ketone.

Example X Specimens of a pattern material wax were treated with a mixture consisting of one part by volume isopropyl alcohol and parts by volume of the same colloidal silica sol used in formulating the coating mixtures of Example I. The specimens were wetted satisfactorily by the mixture and, after drying, were wetted and coated satisfactorily by a dipcoat slurry of the type described in Example 1. Although the described treating mixture was found satisfactory for use, mixtures prepared using a large amount of silica so] in relation to the organic liquid are not preferred for the reasons previously discussed. Such mixtures are expensive because of the large amount of colloidal silica sol and have certain disadvantages, including a slower drying rate and the difficulty of obtaining uniform coverage due to the excessive silica concentration.

Example XI Specimens of pattern wax were dipped in a treating mixture consisting of 2 parts by volume of the same colloidal silica sol used in formulating the mixtures of Example l, 10 parts by volume water and parts by volume isopropyl alcohol. The mixture wetted the patterns and, after drying, the treated patterns were satisfactorily coated with a dipcoat slurry. As explained above, mixtures as used in this example which have been diluted with water are somewhat limited in the pattern materials which they will wet and also have the disadvantage of being slower drying relative to the mixtures in which the medium consists entirely of the required organic liquid, such as isopropyl alcohol.

Example Xll A liquid mixture was prepared using an aqueous colloidal zirconia sol containing about 20.69 percent by weight ZrO and having an estimated particle size of from 5 to millimicrons and a pH in the range of from 0.5 to L0. The sol was mixed with isopropyl alcohol in an amount of 10 parts by volume colloidal zirconia sol to 50 parts by volume isopropyl alcohol. A specimen of the same wax used in Example I was treated with the solution and dried. A second specimen was treated with isopropyl alcohol and dried, and a third specimen was untreated. All three specimens were dipped in distilled water and it was found that the water completely wetted the specimen treated with colloidal zirconia The other two specimens were not wetted by the water.

Example Xlll A liquid treating composition was prepared using an aqueous colloidal aluminosilicate sol containing about percent by weight solids and having a pH in the range of from 4.0 to 4.6. The average particle size diameter was estimated to be 16 millimicrons. One part by volume HCl was added to 10 parts by volume of the sol to prevent precipitation of the solids, and the mixture was added while stirring to 89 parts by volume isopropyl alcohol. A wax specimen treated with this composition was wetted satisfactorily by distilled water. An

untreated specimen of the same wax and another specimen treated only with isopropyl alcohol were not wetted by distilled water.

Example XIV A liquid treating composition was prepared by mixing 26 parts by volume methyl acetate with parts by volume of the acid stabilized silica sol used in the mixtures of Example I. A wax specimen treated with this composition was wetted by distilled water, while an untreated specimen of the same wax was not wetted by the water.

Many modifications and variations'of the invention will be apparent to those skilled in the art in the light of the foregoing detailed disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically described.

What is claimed is:

1. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a waterbase refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: v

a. coating the pattern with a liquid mixture consisting essentially of discrete, individual, colloidal refractory particles in a liquid medium comprised of at least one organic liquid characterized by the capability of wetting the pattern,

the colloidal refractory being present in an amount of at least about 0.5 percent by weight of the mixture and the organic liquid being present in an amount sufficient to cause the mixture to wet the pattern, and

b. drying the coated pattern to deposit the colloidal refractory particles on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsequently applied water-base refractory slurry.

2. A method as claimed in claim 1 in which the organic liquid is characterized by a surface tension less than 28 dynes per centimeter at 20C.

3. A method as claimed in claim 1 in which the organic liquid is present in an amount of at least 6 percent by weight of the mixture.

4. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a waterbase refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of:

a. coating the pattern with a liquid consisting essentially of a water-base sol containing discrete, individual colloidal refractory particles admixed with a liquid medium comprised of at least one organic liquid characterized by the capability of wetting the pattern, the colloidal refractory content of the mixture being at least 0.5 percent by weight and the organic liquid being present in an amount to cause the mixture to wet the pattern, and

b. drying the coated pattern to deposit the colloidal refractory on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsequently applied water-base refractory slurry.

5. A method as claimed in claim 4} in which the sol is acidic.

6. A method as claimed in claim 4 in which the organic liquid has a surface tension of less than 28 dynes per centimeter at 20C.

7. A method as claimed in claim 1 in which the organic liquid is present in an amount of at least 6 percent by weight of the mixture.

8. A method as claimed in claim 4 in which the colloidal refractory content of the mixture is in the range of from 1.5 to 5 percent by weight of the mixture.

9. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a waterbase refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of:

a. coating the pattern with a liquid mixture consisting essentially of an acidic, water-base sol containing discrete, individual, colloidal refractory particles and a liquid medium containing at least one organic liquid characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20C. the colloidal refractory content of the mixture being at least 0.5 percent by weight and the organic liquid being present in an amount of at least 6 percent by weight of the mixture, and

10. A method as claimed in claim 9 in which the colloidal refractory content is in the range of from 1.5 to 5 percent by weight of the mixture.

111. A method as claimed in claim 9 in which the organic liquid is present in an amount of at least 90 percent by weight of the mixture.

l2. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of:

a. coating the pattern with a liquid mixture consisting essentially of an acidic, water-base sol containing discrete, individual, colloidal refractory particles and a liquid medium containing at least one organic liquid characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20C. the colloidal refractory content of the liquid mixture being in the range of from 1.5 to 5 percent by weight of the mixture, and the organic liquid being present in an amount of at least about 90 percent by weight of the mixture, and

b. drying the coated pattern to deposit the colloidal refractory on the pattern surfaces to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsquently applied 5 water-base refractory slurry.

13. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of:

a. coating the pattern with a liquid mixture consisting essentially of:

discrete, individual, colloidal particles of at least one refractory selected from the class consisting of silicic and zirconic materials, said particles having a size of from about 2 to 70 millimicrons, and

a liquid medium comprised of at least one organic liquid having the capability of wetting the pattern and selected from the class consisting of alcohols, ketones and esters, and

b. drying the coated pattern to deposit the colloidal refractory particles on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by subsequently applied water-base refractory slurry.

14 A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of:

a. coating the pattern with a liquid mixture consisting essentially of:

an acidic, water-base sol containing discrete, individual, colloidal particles of at least one refractory selected from the class consisting of silicic and zirconic materials, said particles having a size from about 2 to 70 millimicrons, and

a liquid medium comprised of at least one organic liquid selected from the class consisting of alcohols, ketones and esters and characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20C. and

b. drying the coated pattern to deposit the colloidal refractory particles on the pattern surfaces to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by subsequently applied water-base refractory slurry.

15. A method as claimed in claim 14- in which the col loidal refractory content of the liquid mixture is in the range of from about 1.5 to percent by weight of the total weight of the mixture, and in which the organic liquid is present in a minimum amount of about 90 percent by weight of the total weight of the mixture.

Claims

2. A method as claimed in claim 1 in which the organic liquid is characterized by a surface tension less than 28 dynes per centimeter at 20*C.
3. A method as claimed in claim 1 in which the organic liquid is present in an amount of at least 6 percent by weight of the mixture.
4. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: a. coating the pattern with a liquid consisting essentially of a water-base sol containing discrete, individual colloidal refractory particles admixed with a liquid medium comprised of at least one organic liquid characterized by the capability of wetting the pattern, the colloidal refractory content of the mixture being at least 0.5 percent by weight and the organic liquid being present in an amount to cause the mixture to wet the pattern, and b. drying the coated pattern to deposit the colloidal refractory on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsequently applied water-base refractory slurry.
5. A method as claimed in claim 4 in which the sol is acidic.
6. A method as claimed in claim 4 in which the organic liquid has a surface tension of less than 28 dynes per centimeter at 20*C.
7. A method as claimed in claim 4 in which the organic liquid is present in an amount of at least 6 percent by weight of the mixture.
8. A method as claimed in claim 4 in which the colloidal refractory content of the mixture is in the range of from 1.5 to 5 percent by weight of the mixture.
9. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: a. coating the pattern with a liquid mixture consisting essentially of an acidic, water-base sol containing discrete, individual, colloidal refractory particles and a liquid medium containing at least one organic liquid characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20*C. the colloidal refractory content of the mixture being at least 0.5 percent by weight and the organic liquid being present in an amount of at least 6 percent by weight of the mixture, and b. drying the coated pattern to deposit the colloidal refractory on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsequently applied water-base refractory slurry.
10. A method as claimed in claim 9 in which the colloidal refractory content is in the range of from 1.5 to 5 percent by weight of the mixture.
11. A method as claimed in claim 9 in which the organic liquid is present in an amount of at least 90 percent by weight of the mixture.
12. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: a. coating the pattern with a liquid mixture consisting essentially of an acidic, water-base sol containing discrete, individual, colloidal refractory particles and a liquid medium containing at least one organic liquid characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20*C. the colloidal refractory content of the liquid mixture being in the range of from 1.5 to 5 percent by weight of the mixture, and the organic liquid being present in an amount of at least about 90 percent by weight of the mixture, and b. drying the coated pattern to deposit the colloidal refractory on the pattern surfaces to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by a subsquently applied water-base refractory slurry.
13. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: a. coating the pattern with a liquid mixture consisting essentially of: discrete, individual, colloidal particles of at least one refractory selected from the class consisting of silicic and zirconic materials, said particles having a size of from about 2 to 70 millimicrons, and a liquid medium comprised of at least one organic liquid having the capability of wetting the pattern and selected from the class consisting of alcohols, ketones and esters, and b. drying the coated pattern to deposit the colloidal refractory particles on the pattern surfaces in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by subsequently applied water-base refractory slurry.
14. A process of preparing a disposable casting pattern composed primarily of organic material for use in the production of an investment mold made with a water-base refractory slurry, said process being carried out prior to the formation of the investment mold and comprising the steps of: a. coating the pattern with a liquid mixture consisting essentially of: an acidic, water-base sol containing discrete, individual, colloidal particles of at least one refractory selected from the class consisting of silicic and zirconic materials, said particles having a size from about 2 to 70 millimicrons, and a liquid medium comprised of at least one organic liquid selected from the class consisting of alcohols, ketones and esters and characterized by the capability of wetting the pattern and by a surface tension of less than 28 dynes per centimeter at 20*C. and b. drying the coated pattern to deposit the colloidal refractory particles on the pattern surfaces to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by subsequently applied water-base refractory slurry.
15. A method as claimed in claim 14 in which the colloidal refractory content of the liquid mixture is in the range of from about 1.5 to 5 percent by weight of the total weight of the mixture, and in which the organic liquid is present in a minimum amount of about 90 percent by weight of the total weight of the mixture.