US2283611A - Composition - Google Patents

Description

May 19,1942. NEIMAN 2,283,611

COMPOSITION Filed March 4, 1941 T/IE/ZM/IL EXPANSION IN PER CENT o 300 400 1300 800 I000 I200 I400 I600 I600 TEMPERATURE m DEGREES F.

Tql

SETTING EXPANSION lN PER CENT 0 0 4o-eo-z 4 8 16 32 64 TIMEJN MINUTES TIME IN HOURS.

- l I INVENTOR.

ROBERT NE/MA N,

Mamie Attorney Patented May 19, 1942 UNlTED STATES PATENT oFFm a 2,283,611 a coMrosrnoN- Robert Neiman, Louisville, Ky., assignor to Edmund A. Steinbeck, l iouisvllle, Ky.

Application March 4, 1941, Serial No. 381,709

' Claims. (Cl. 22- 188) This invention relates to compositions that become plastic when gaged with aqueous solutions, and may be formed into a desired shape and size and thence set to av hard cementitious mass suitable for dies, counter-dies, patterns, molds for casting metals, etc., all of which must conformwith great exactness to a predetermined size,

- shape, and detail.

Thisinvention will be described in detail with regard to its application in making dental castings, such as inlays. This is an example of a type of casting which must be very accurately made as far as size and shape are concerned,,

After the investment sets the 'mold is heated to a temperature of 800 F. to 1800 F., in order to melt and burn out the wax, and also to prepare the mold for casting. Any suitable or desirable casting method may then be employed.

Usually, use is made of some machine which forces the molten metal, under pressure, into, the I cavity formerly occupied by the wax. The mold is then usually cooled by plunging it into water, it is then broken apart to recover the casting.

The casting is then cleaned, sprues removed,-

and polished for use.

o It is the general practice in most industries to enlarge the original pattern so as to take care of the casting'shrinkage of the metal. Since this is practically impossible or very 'diflicult when using a wax pattern another method must be used. Inthis instance and in order to make the castingconform to .a predetermined siz'e and shape, that is, to the original pattern,.lthe mold is caused to expand sumciently, prior to the casting operation, to counteract the shrinkage of the metal or alloythat takes'place when the lattercools and solidifies during the casting process. This shrinka e'to be counteractedgenerallyvaries from- 'about 1% to. somewhat over 12%, depending ion the size and shape of the casting, and especially onthe type of casting alloy used. For dental castings, using precious alloys, it varies from about 1% to 1.5 generally There are a number of iactors which control the exact amount of expanslonnecessary'. The

shrinkages in the process are incurred-.whenthe wax pattern is removed from the human-mouth at 95 F. and taken'in a room of varying-temperature, but generally cooler than the mouth.

gagin water.

The metal upon casting shrinks, and a'precious dental alloy gives a uniform casting shrinkage of 1.25%. To counteract these shrinkages, one

which is uniform and the other which varies due to diiferent conditions, it is necessary to vary the expansion of the mold. The principal expansion is achieved through the thermal expansion of the investment mold upon heating from room temperature to casting temperature, generally about 1300 F. Furthermore, the investment expands during the setting reaction of the binder. The following is a list of the important features and properties which the dental profession heretofore especially has desired in a commercial investment and mold produced therefrom.

1. The thermal expansion of .the mold from room temperature to casting temperature (of the mold) should be as nearly as possible equal to the total shrinkage encountered and preferably be attained by an investment mix of painting or pouring consistency.

2. Practically all of the expansion should have taken place at 1150 F. with no radical change thereafter up to at least 1300 F.

3. There should be little variat-ionin expansion due to the usual slight variation in amount of 4. The thermal expansion curve,.throughout the entire heating range, should approximate a straight line and preferably should never rise above the practically straight line curve of the encircling metallic ring or container-of approximately equal total expansion.

'5. The investment should incorporate readily with water and mix to a smooth, creamy consistency which can readily be applied to the intricate sections, of a wax pattern and should have a good adherence to the waxpatt'ern.

'6. Should have enough setting expansion to make an accurate reproduction which is usually about 0.1%. l I

- 7. Should setrapidly to a hard mass that will withstand rapid heating to the casting' -temp'eratures without cracking or distorting.

' 8. Whenonce set, the mold should not change "chemically or physically or distortappreciablyin any deleterious way.

9. Should pos'sessenoughjstrength when at the casting temperature to safely resist the inrush of molten alloy under casting pressure and not-too strong to prevent its being easily removed from the casting after quenching inwater and without leavinga tenaciously'adhering film on the casting. I

' 1 10. The mold should be very'smooth and of. such chemical makeup as to prevent undue oxidation and'sulfurization of the casting, and preferably should produce the cleanest possible smooth and dense casting.

' binder.

aaeaen surface so as to produce the smoothest, densest,

and least contaminated, castings possible. Such materials include accelerators, retarders, reducing agents (such as carbon or graphite) flne clay, powdered metals, and oxides, as well as other modifying agents to reduce the amount of gaging .water necessary, such as polysaccharides and alhas a testing or pouring consistency of 60 parts of water to 100 parts .of plaster by weight. An-

other form of hemihydrate, known as alpha gypsum, (United States Patent Number 1,901,051) and commercially known as I-Lvdrocal," general- 1y has a testing or pouring consistency of approximately 40 parts of water to 100 parts of alpha gypsum. This lower consistency is ad-. vantageous in increasing-the expansion and also the strength 'of the mold. There are several other forms of calcium sulfate, such as, for example, dehydrated-hemil'iydrate and Keenes cement, both hydrated and dehydrated, that set when gaged with water, and may also act as a The term calcium sulphate or calcium sulphate binder will be used hereinafter to cover high thermal expansion, it is obvious that refractory fillers with inherent high expansion properties are to be preferred. Silica, in its three principal modifications, quartz, tridymite,

and cristobalite, possesses high thermal expansion along with good refractory properties and in addition is fairly inexpensive. The Quartz form is tlfe'least expensive and most generally used. Of the three forms, cristobalite has the greatest inherent thermal expansion and when used to replace an'equal amount of. quartz will impart a greater expansion to the mold in direct proportion to the amount used.

Many other types of refractories may be used to replace all or part of the silica and include, for example, such common and widely used, inexpensive refractory materials as magnesia, alumina, chromium oxide, refractory clays, and many other silicates and oxides. Other common silicates and oxides have high expansions due to change of phase or inversion. They may be used advantageouslyas partor all of the refractory filler. l e

' The term refractory filler when used here- V inafter shall be construed to include any of the above mentioned refractories alone or in any mixture thereof, or any similar materials having substantially the same property of being fairly inert chemically and withstanding the temperatures encountered in the casting process and which are compatible withthe other ingredients present.

In addition to the binder and refractory filler, it is desirable to add one or more of the following agents to adjust the setting or hardening characteristics, improve the smoothness or permeability of the mold or otherwise to impart desirable physical or chemical action to the mold with the accompanying drawing, forming a part pattern method that will attain the desired kali.

ample, a mixture of 30 parts Hydrocal, 69

parts powdered quartz, and 1 part modifying agent and being gaged with 32 parts of water will showvn expansion of .74% at 1300 F, A number of .materials are known that will increase the thermal expansion of such a mixture when added thereto or used in replacing part of the quartz or filler. Materials of this nature include boric acid, cristobalite, chlorides, (such as sodium, potassium, and lithium) also organic carboxylic and polycarboxylic acids. Each of these, or combinations thereof, are of particular value in increasing the expansionsupon heating, but each of them fails to meet one or more of the eleven desired properties or meets them but partially. All of the eleven desirable qualities are met by investment compositions made in accordance with the disclosure in prior patent application filed February '7, 1936, Serial No. 62,801 for Investments, but these compositions do not always successfully operate at, so called, high heats, that is, above 1350" F.

Dueto the difficulty of getting high thermal expansion in an amount suiiicient to counteract the metal casting shrinkage plus wax pattern shrinkage it has been believed desirable to provide investments with additional considerable setting expansion. Also, no means. was known to reduce the setting expansion when found unnecessary. This practice resulted in mold distortion due to unequal radial and vertical expansion in a partially confining mold forming member, such as the usual metallic ring..-

All of the foregoing difliculties have been overcome by the investment of this invention.

It is therefore the principal objective of this invention to provide a composition for m I refractories and an investment composition for use in casting. principally by the disappearing wax tures described above.

in an investment composition for making molds an expansion control whereby other desirable features will be attained, as will be hereinafter more fully described, above the already mentioned eleven features.

Other objects and advantages of this invention should be readily apparent by reference to the following specification, considered in conjunction thereof, and it is understood that any modifications may be made in the exact proportions set forth within the scope of the appended claims and without departing from or exceeding the spirit of the invention.

In thedrawing: Fig. 1 is a graph illustrating the thermal ex pansion of three investment compositions each of different constituents when heated under identical conditions.

Fig. 2 is-a graph illustrating the setting'expension ofthree investment compositions each The above simple type of investment compothese ingredientsas just set forth may be varied beyond these limits, depending upon the exact technic used in producing castings.

In Fig. 1 of the drawing the reference numeral l indicates the thermal expansion curve of a mixture of 30% alpha gypsum, 69% quartz and approximately 1% of modifying agents as generally used in the art, and indicates the thermal expansion of 124% between room temperature and 1300 F- This investment was made with a water to powder ratio (W/P) of .32, that is, 32

parts of water to 100 parts of powder mixture on a weight basis. An increase of the W/P ratio causes an appreciable decrease in the thermal expansion of this type of mixture. It should be vestments containing the last named expansion improving agents have a failing in that they show considerable shrinkage at'temperatures in excess of approximately 1350 F.

It will be noted, therefore, the curve ll begins to show a shrinkage at approximately 1350 F.

and which shrinkage becomes quite pronounced.

' above 1400" F. It has been found that all other noted, however, that, while the converse'is true and also while the W/P ratio could be lowered, from a commercial standpoint this particular .W/P ratio is very excellent for a painting composition or mixture, that is, the consistency-is very suitable for painting onto the wax pattern.

In Fig. 1 of the drawing, the curve indicated by reference numeral II, shows the thermal expansion resulting from a modificationof the simple investment composition (curve 10) by adding to said simple investment composition 1.75%, by weight, of barium chloride for a similar amount of quartz. In this composition, the W/P ratio was held the same as above, that is, .32. As is readily apparent this resulted in a thermal expansion of 1.20% between room temperature and 1300 F. By comparison of the curves l0 and II it will be noted that the barium chloride produced an investment composition that was, throughout the heating range from room temperature to 1300 F., expanding regularly while the simple investment composition expanded, contracted slightly and then re-expanded. In commercial practice, especially on comparatively large molds, there is often a temperature differential of several hundred degrees between different parts of the molds. Ob-. viously, if one-part is expanding and another standing still or contracting slightly, distortion and cracking often takes place. Such distortion, etc.,' often occurs when using the simple investment composition, while, in the modified comsoluble chlorides, as have been clearly disclosed v and described in the co-pending application above identified, act similarly. These chlorides, similar to barium chloride, have the tendency of breaking or shrinking at temperatures comparative to that of said barium chloride. It is the property of these chlorides, however, to give very clean castings of precious alloys when cast at the usual casting temperature of 1200 to 1300" F.

As was noted above, other thermal expanding improving agents have been employed but none of these have s'ofar been as successful for inlay castings as the one whose curve is'shown in curve H and which investment has best met the requirements in practical use and is the only one I that meets all of the eleven desirable features to the greatest extent.

It has beenv found that the shrinkage which occurs in the composition that gave curve ll may best be overcome by the use of cadmia cadmium oxide), Curve l2 in Fig. 1 illustrates the position, such danger is practically eliminated.

It should be noted'that precious alloys, as used in dentistry and when cast in a mold at 1300 F., have a casting shrinkage of 1.25%. The barium chloride investment, as shown in curve H, has

an expansion of 1.20% at this casting temperature. This is practically sufiicient for counteracting the casting shrinkage of the metal.

Thermal expansion improving agents such as disclosed in co-pending patent application, above identified, with barium chloride as'the best example, enable investments to be made that will meet all of the eleven above named heretofore desirable features. Due, however, to the in-, creasing use of electrically heated furnaces, many of which have nomeans for accurately controlling the 'upper temperature limit, as a means for heating investments, the above mentioned inshrinkage occurs.

tremendous advantage to be gained by the addition of as little as 1% of cadmia. It must also be noted that as little as 0.1% will be quite helpful and, in fact, any appreciable addition of cadmia increases the thermal expansion range seemingly out of proportion to the small amounts used and cadmia has been found to be the most powerful such agent known on a weight basis. To give an equal amount of increased thermal expansion above 1350 F. and prevent the breakdown, the best heretofore known agent has beenpowdered metallic-copper, but it willtake approximately 5% of it to equal the improvement given by 1% of cadmia.

It also seems that where air is passed over the mold and a slightly oxidizing condition is present that copper loses some of its effectiveness, whereas under similar conditions cadmia is substan tially unimpaired.

It seems that, perhaps, the most effective amount of cadmia to be added to the composition giving curve II is 1%*=thereof.

not appreciably further raise the thermal expansion curve. As a matter of fact, increased raise the temperature at which even slight Amounts in excess of about 2% of cadmia gives a practically straight line curvefrom 1200 F. to 1800 F. and even higher.

Upon running a thermal expansion test of'the composition giving curve II the iron-constantan thermocouple wires used were completely deteriorated by the decomposition gases, which very likely includes those of chlorine and sulphur at about1350 F., the temperature at'w'hich shrinkage began. With the addition .of 1% of cadmia forming the investment giving curve 12 a number of expansion tests were made with the same size and grade of thermocouple wires which did not deteriorate until a temperature'of 1500 to 1550 F.'was reached. It thus seems that the decomposition products are absorbed or adsorbed by the cadmia. This is further accentuated by the fact that deleterious fumes are noticeable in Increased amounts of cadmia above approximately1% do .present conditions to the best advantage.

the laboratory at the respective temperatures at aase'p'n g most'desirable type ofsmoothcleanpastings and which the thermocouple wires are destroyed by the compositions with and without the addition of cadmia. It is known that cadmia will form a very stable sulphide and, perhaps, this explains whythe expansion properties are improved and the shrinkage range extended to higher tempera-e tures. This is probably due to the reaction 01.

the cadmia with the decomposing sulphur prodagents. They do however, shrink at the higher temperatures. In general the soluble bromides give greater expansion and are useful at higher temperatures than the corresponding chlorides,

see co-pending application Serial No. 293,448, filed September 9, 1939. In turn the soluble iodides give greater'expansion and are useful at higher temperatures than thebromides, see 00- pending application Serial No. 293,449, filed September 9, 1939. All soluble nitrates also considerably improve the thermal expansion properties,

some of them, for example, ammonium nitrate are even more effective than the iodides at. the higher temperatures, see co-pending application, Serial No. 297,723, filed October 3, 1939. It has also been found that solublech'romates, chlorates,

bromates, iodates, borates, phosphates, sulphates, and also the ites of all these, and even organic salts, acids and alkalies, which is also trueof the inorganic group, will also improve the thermal expansion properties at some temperature or The advantages of one over the other often depend upon the desired features and upon the technicused. The chlorides, for example, generally achieve the full thermal expansion at about 1150 Band then remain constant untilabout 1300 tog 1400 F., depending upon the nature of the filler, etc., and then begin to shrink some slightly, for example, sodium chloride, but most "of them give curves similar to curve ii.

The bromides increase the temperature at which shrinkage begins, the iodides further raise 1% or cadmia. does not interfere with" this already highly desirable property? There is reason to believe that castings made above 1325"" F. in

the presence or cadm ia are somewhat better than those-made in the-compositions without it, such as curve ll composition and this is probably explained by the removal of at least some of thedeleterious decomposition produced by the cadmia.

Soluble chlorides, when added in amounts of. 1 to 2% to the basic composition (as shown in Fig. 1), will providecurves of greater expansion than the latter, but. show shrinkage at higher temperatures. with thesesoluble chlorides the addition of about 1% of cadmia will give an investment whose thermal expansion curve is of the type as shown in curve l2 and which curve is, perhaps, the most desirable possible for an invention to be used in the casting of precious metal dentalrestorations. It reaches the most desirable figure of 1.25% thermal expansion at the most desirable casting temperature of approximately 1300 F, and, in fact, castings may be made in this composition that will be extremely accurate whether they be made at 1150" F. or at any temperature up to-1800' F. Thus the only detriment of the composition, which developed curve H to prevent its exceeding all of the eleven desirable characteristics is efi ectively overcome.

Cadmia lends similar improvement to other chlorides, for example, ammonium, copper, cadmium and nickel. Allof th'ese, especially copper,

'give a curve showing tremendous shrinkage between 1325" F. and higher temperatures and.

of cadmia is less pronounced in raising the shrinkage temperature, but has been found of at least some advantage.

it and the nitrates, especially ammonium, seen: u

to raise it the most, that is, give the steepest rise in curve from 1100 F. up to approximateiyv 1800 F. The latter type giving a steep rise enables the user to achieve the desired expansion by controlling the casting temperature and choosing that temperature at which the invest- 1200 F. and under such conditions the chlorides,

especially the one shown in curve ii, meets 0bviously; where the casting temperature cannot be controlled, and there are numerousi'urnaces'that arein this category, such as the uncontrolled electric, type furnaces, above indicated, the

- shrinkage that takes place, and which begins at approximately 1350 F. for the particular composition shown, is detrimental and is. perhaps, the only detrimental feature found when compared with other present-day investments.

As mentioned heretofore, chlorides give the As already explained, cadmia isespecially effective in raising the decomposition temperature,

or temperature at which shrinkage begins, in

compositions containing soluble chlorides. In

addition, cadmia seems to absorb a considerableamount of the decomposition products given ed in investments due to the heating and containing soluble chloride. With those expansion improving agents that in themselves cause expansion to take place to-temperatures approaching 1800 F.- the improving eiTect of cadmia is less pronounced. The more effective the thermal expansion improving agent is in maintaining a rising curve above 1200 F. the less pronounced the efiectiveness of cadmia in improving this effect. It still seems, however, to be efiective in, absorbing deleterious decomposition products, even though these do, not cause shrinkage to take place.

To help counteract shrinkages, in addition to that of casting shrinkage, especially that of the wax pattern, the setting expansion of investments have heretofore been believed to be of advantage. The-usual setting expansion of an investment is about 3% and all of the important investment compositionson the market show M 2,288,611 found and desired, it has been the consensus of experts that the effective setting expansion is as unpredictable as its cause is unexplainable.

Most inlay castings are made by investing the wax pattern on a sprue former while held inside a confining metallic ring. Theoretically, the setting expansion of an investment cannot take place radially, since the metallic confining ring will resist such an attempt. Assuming that all of the setting expansion takes place, it must, therefore, take place vertically, that is, in a-direction perpendicular to the radial confining ring. Obviously, this will cause an appreciable and, perhaps, even greater setting expansion vertically with practically no expansion radially. Distortion is bound to take place under such circumstances. Furthermore, evenwhen the setting expansion is permitted to take place evenly by the cushioning effect of a strip of asbestos inside the ring, there will still be distortion when the investment pushes against the inside surfaces of patterns such as M. O. D.s. It is now known that investments show a slight rise in temperature upon setting and composition shown in curve I 2 under practical conditions will show a rise in temperature of about 7 F. This will naturally expand the wax pattern and will do so to the extent of approximately 0.1%. Obviously, if the setting expansion was .l% there could be no possible distortion. This would be true to the utmost extent if the setting expansion and heat rise took place simultaneously and caused the wax to expand by heating exactly as much as the investment expanded on setting.

Curve l3 shows the setting expansion of the in vestment base used to develop thermal expansion curve i0. This addition of 1.75% barium chloride to this base composition decreased the setting expansion slightly as shown in curve It of Fig. 2. The addition of 1% of cadmia to the latter composition then gives setting expansion curve I5 and it will be seen that-this setting expansion seems to be ideal as explained above, since it is' very approximately 0.1%.

It thus seems that the ideal investment from all standpoints is obtained in the composition utilizing barium chloride and cadmia as added to a simple investment composition base.

Since the reason for setting expansion taking place when a calcium sulfate binder is used is still unexplainable, it is impossible to reconcile the effectiveness of cadmia on investment compositions. .It is believed that the setting expansion is due to the growth of crystals upon setting and also possibly upon somecolloidal phenomenon.

'ingly a logarithmic function rather than tory or glass and clay and towhich an electrolyte has been added. It is probable that adsorption plays an important part in this condition. The effect on dispersion of the solids, interfacial tension and particle adherence are undoubtedly related to this phenomenon. Cadmia seems to raise the yield value and also somewhat the mobility as referred to in ceramics. To maintain the same consistency the W/P ratio must generally be raised about .01, that is, it takes another cc. of water per 100 grams of powder. Since "the setting andthermal expansions are unaffected in compositions such as shown by curve H due to this slight, raising of the W/P ratio, the only adverse effect is the-slight loss in compressive strength but this is generally overcome by the added increase in permeability.

The finer the particle size of cadmia the more viscous the investment mix becomes and also the settingexpansion is additionally generally decreased. In other words, the setting expansion canalso be'controlled by the particle size of the cadmia. The finer particle size does not seem to affect the thermal expansion so appreciably and a given weight of cadmia, regardless of particle size seems fairly equally effective. This indicates a straight chemical or' physico-chemical reaction and is controlled by the actual weight or weight percentage of cadmia present.

In both setting and thermal expansion effects, cadmia is most powerful when used in smaller amounts. The first increment is more powerful than the second increment, etc. This is seema straight line arithmetic function.

Cadmia is generally a brown crystalline material that melts above 2550 F.- although some authorities claim that it begins tochange com It is known that many salts will decrease the setting expansion of calcium sulfate compositions, but so far no water insoluble and comparatively inert material such as cadmia has been found that will have such a powerful effect; This or is especially advantageous in compositions where an excess of soluble salts areundesirable. Soluble salts often cause surface efilorescence and under most conditions change the setting time considerably. Cadmia does not show eitherof these disadvantages ,to any comparable extent and furthermore it will resist'heating to high temperature where many salts, or perhaps most of them, will decompose.

When cadmia is mixed with investments, even' in small proportions, there is a fairly marked change in consistency and working properties.

The mixture at the same W/P ratio will be stiller and resembles an aqueous suspension of refracposition slightly in the neighborhood of 1800 F. It is available commercially as an extremely fine powder that may be amorphous or crystalline,

or a mixture of the two. It is used as a pigment in ceramics because of its abilityto withstand high temperatures. It may be secured in the crystalline form My heating the carbonate or nitrate, and can be well crystallized by long heating above a red heatwith or without a catalyst. Itmay'also be secured in comparatively large crystals by heating in the electric furnace where the crystals will sublime. A fairly well crystallized material does not seem to change the setting time of many mixtures of investments appreciably, but the finest divided form may show an appreciable change. Again, this may be due to colloidal phenomena. Cadmia is reduced to the metal in the presence of carbon at a red heat and this is sometimes undesirable, but may be controlled by the proper ingredients and heating conditions.

Cadmia is a fairly inert material but on oc-" casion seems'to show some slight reaction with boric acid investments and also will liberate a noticeable amount of ammonia from investments containing ammonium chloride and ammonium nitrate, for example. This is explained by the fact that it is somewhat soluble. in ammonium salts and acids. It is insoluble in alkalis. Since every material 'is at least minutely soluble in water, cadmia will perhaps give a slightly alkaline reaction, and this. is why it changes theconsistency of the mix since alkalis, such as lime},

will generally act ina s'imilarfashion. f

It has been found that some of these properties of cadmia, that;is,' its effects on-"the consistency and other properties may be changed this further to about .1% more.

solution and then heated to give a homogeneous product. Cadmia and iron oxide will form a cadmium ferrite of the formula CdFezO4 .(CdOFeaOs). These mixtures sometimes slightly enhance the effectiveness of a given percent age of cadmia by possibly increasing the surface area of.the same weight of'cadmia. These mixed oxides may also prevent reducing action of other ingredients upon the cadmia, itself, or otherwise modify the apparent colloidal phenomena.

It has been-found that some salt's will decrease the setting expansion of investments, some are apparently neutral in effect, and others actually raise the setting expansions, some considerably. As specific examples, the base compositions, as shown in curve l3, has a settingexpansion of 375%, 1% of cadmia will lower this to .14% and 5% of cadmia will give a setting expansion of only .055%. Two percent of borlc acid will lower the expansion of the base to 215% and the addition of 1% of cadmia will give an expansion of -.02%. This is one of the few, and perhaps the first combination that will actually give a negative expansion in investments. With the same base, 1% of potassium iodide will give a setting expansion of 22% and when a further addition of 1% of cadmia is made the setting expansion is reduced to .05%. Ammonium chloride, when added in the amount of 1% reduces the setting expansion of the base to 28%, and an additional 1% of cadmia reduces it to .2%.

setting expansion is desired, such composition is possible by adding 1% of cadmium chloride and 1% of cadmia to the same base.

One per cent ofcupric chloride will raise the settingexpansion of the base to over 1.0% and the addition of 1% of cadmiaeven increases Five per cent does not appreciably affect thesetting expansion of the base, but the addition of 1% of cadmia lowers it to.2%. It is thus seen that there v is almost unlimited field forc'ontrol of setting expansion with the use of cadmia. If a composition having a low setting expansion and even a negative one is desired, cadmia-is perhaps the only material that will do this in the small amounts of 1%, and of course, large amounts will even decrease'lthe setting expansion further. Where unafiected orhigh setting expansions are desired, cadmia, when it has tov be used to help the thermal expansion, etc., will nothinder the setting expansion, and thus the range of setj ting expansion between a shrinkage and apositive expansion of over 1% is possible.

As a general rule, the alkali salts reduce the setting expansion, and cadmia enhances this effect. The alkaline earth salts do not reduce the setting expansion so much, but cadmia is still effective in reducing the setting expansion. The other metallic salts, especially those that I are of fairly heavy specific gravity, with cadmium .If the cadmia of an extremely fine grade parand copper as examples, the setting expansion is not appreciably reduced, or actually increased, and cadmia is not so: effective in changing this sometimes desirable property. No strict rule can as yet be set down, since, as. mentioned above, the

As remarked above, with barium chloride as an example, cadmia greatly enhances the thermal expansion and materially lowers the setting expansion and thus compositions with high thermal and low setting expansion are made possible for the first time, and of course the ranges and combinationsof thermal expansiomand setting expansion are increased many fold and without impairing other desirable properties, such as set-- ting time, contamination of castings, strength,

etc.

In order to improve the surface of the castings it is possible to incorporate materials into the investment that will reduce the surface tension and thus permit the investment to makeperfect contact with the wax pattern. Alkyl- 'sulphates, etc., are examples of such materials.

Also they may be painted on the pattern and the investment painted on soon thereafter. Likeof cadmia will begin to show its usual eflect, and

setting expansionof the base to .2% and the further addition of cadmia lowers it to .075%. One per cent of ammonium nitrate reduces the setting expansion' of the base to 34% and the addition of 1% of-cadmia lowers this considerably to .065%. r

One per cent of cupric nitrate, for example, again increases the setting expansion of the base to .5% and 1% cadmia does not affect this figure.

One per cent of nickel chloride, for exampl as replacing all or wise, they may be added to the powdered portion of the investment or to the water with which the investment is gaged. This is, of course, true of all the materials used and described. They may be added to the water or to the powder or divided among the two so able results. Strongly hygroscopic materials should preferably be added to the gaging water.

,Some finely divided solids and refractories aid somewhat in improving the surface of the mold, for example, titanium dioxide. Extremely finely divided quartz and zircon are also advantageous for this purpose. The use of these finely divided materials generally raises the WI? ratio somewhat and also affects the permeability. In this connection it might be'stated that an even grind of refractory will give greater. permeability than a particularly selected group of very fine, fines. and coarser materials, the latter combination, however, increases the strength.

Wherever it is desired to have expansions in excess of 1.25% at the usual casting temperature of 1300 F., it is advantageousto use cristobalite part of the quartz. Using 69% of cristobalite instead of 69% of quartz, curve l2, could be raised to 2% or possibly above This will vary depending upon the exact grade as to give most desir-- or cristobalite used. It seems that cristobalite made at higher temperatures and held for a longer period of time will give greater expansion and is generally preferable, although in some cases the use of catalysts, such as sodiumsilicate will lower the temperature of cristobalite formation andthus enhance its expansion properties.

It is, of ,course, possible to substitute only a portion of cristobalite and secure investments that will expand between 1.25% and 1.5%, for example.

Spodumene may be added .as all or part of the filler and will give unusually high expansions, even approaching and higher, but this will take place generally around 1800 F. unless proper catalysts are added thereto, as disclosed in copending application, Serial No. 309,784 flled De-' cember 18, 1939.

It has been found that fora chloride investment, such as that which developed curve ll, powdered metallic copper will enhance the thermal expansion properties when used in sufficient amounts. The copper, however, will not notice ably change the setting expansion and thus has onlyone of the two desirable features, cadmia having both of them. Of course, mixtures ofup to about 1%. Between 1 and 5% the effect .is also considerable but begins to diminish after that. The other cadmia compounds, as mentioned above, are also most effective in smaller amounts although not as strong as cadmia and their upper limits are also,-perhaps, lower, since the metal, for example, would melt and vaporize unless held under oxidizing conditions and other compounds may also be somewhat disadvantageous due to the inherent qualities of the com'-' pound. I r

Some expansion improving agents will enable the production of investments with comparatively high thermal expansions and with a' very minicadmia and copper can be used wherever desirable.

. increased setting expansion due to the hygroscopic expansion is now no longer so deleterious Under conditions wherein more setting expanto the pattern and will take place both radially and vertically to the same extent, since the asbestos acts as a cushion.

As mentioned above, hundreds of experiments have shown that every soluble salt tested increased the thermal expansion at least to some degree and hereinafter the term expansion improving agents will be used and shall be construed to include any and all of the soluble salts that will increase the thermal expansion of an form or another as thebinder.

-In many cases, cadmia will cause the setting expansion to reach its final value in a minimum time. For example, curve 15 reached its upper example, is to carve the wax pattern either on -investment containing calcium sulphate in one mum of filler and, in fact, the nitratesand iodides will permit the use ofv straight alpha-gypsum,

' also boric acid has some advantageflinthese compositions. -By adding cadmia to these, the material may be used as a die and-castings may be' made directly into or onto them. Obviously, for die-making purposes low setting expansion is desirable and with cadmia and boric acid, for examples, neutral or zero setting expansion is possible.

These compositions will be known as die casting compositions.

The die casting composition may be used to form a section of the mold and the balance of the mold may be made of another and softer composition, such as one of the investment compositions described herein. Furthermore, when using this type of die casting composition, the wax pattern need not necessarily be removed by heating themold to high temperatures sufficient to carbonize and vaporize.the wax. The wax may be removed at .low temperatures by melting it or dissolving it out with a suitable solvent. The metal or alloy may be cast into these compositions while the mold is at a comparatively low temperature.

The general procedure for casting inlays, for

the tooth in the mouth or on a die, reproduced into an impression taken from the tooth. In either case, the wax pattern is removed and encased in an investment. It would speed up the process if it.were possible. to take an impression of the tooth cavity in wax, and without carving the outer contour, remove it from the tooth and form a die in the inner surface to the inner setting expansion limit in an hour whereas the same composition without the cadmia showed a slight setting expansion increase even after. 24 hours and a considerable increase between one and two hours. Obviously, this means that a mold will not change dimensions after about an hour with the composition as shown in curve l5 and, therefore, no distortion can take place thereafter, also castings made at any time after one hour will be the same in dimensions. Some few materials, for example, boric acid, are powerful fluxes and will cause a shrinkage in an investment at temperatures such as 1400 F. or above due to-their chemical reaction or fluxing with the other ingredients. In this case cadmia will not prevent this inherent type of decomposition.

Other cadmium compounds such as the metal itself, the carbonate, etc., that decompose or oxidize to leave the oxide at the casting temperature will also generally, however, affect the setting expansion,

give much of the desirable properties imparted by cadmia itself. They will not cavity, and thence carvethe outer contour of the -wax pattern while still on the die and, thence,

withoutv removing it, enclose the outer side with investment and cast same. This would eliminate removal of the wax pattern from the die and the necessity of lubrication, and possible distortion, upon removal. Heretofore, investment compositions were too soft, especially on the surface, to permit accurate margin carving. a

Such die casting compositions, asthey will be called; may be made by considerably increasing the binder or calcium sulfate and thus produce harder dies. The difficulty .lies in-securing adequate thermal expansion and preferably without unduly high setting expansion. These difiiculties'may beovercome by using the proper expansion improving agentjsuch as, for example, chlorides, bromides, iodides, andnitrates. These increase the, thermal expansion considerably and make it possible to use from to approximately 99% .binder, and still get expansions in the neighborhood of 1.0 to 1.25%. Cristobalite is perhaps preferable when it is desired to get the most expansion with the least amount of By using such compositions and adding theretosome cadmia, it is possible to enhance the' refractoriness, that is, ability to withstand higher temperatures without shrinking and especially to lower the setting expansion to .1% which otherwise, in some cases, would be in the neighborhood of .5% to .6% and would easily distort the wax pattern.

By using practically pure calcium sulfate and 0.1% to 5.% of boric acid in addition to such expansion reducing agents as Rochelle salts and potassium sulfate, or mixtures thereof, it is possible to produce very hard die compositions of excellent surface hardness, and with setting expansions in the neighborhood of .05% to .l%. Such compositions do not withstand high heating but form excellent dies and counter-dies at room temperature and may be heated to about 500 to 600 F. and are therefore useful for casting such metals as low fusing alloys, etc., that form very valuable and extremely accurate dies and sectional dies for producing intricate wax patterns from which castings are later made. By adding approximately 1% or a fraction of a percent of cadmia, it is possible to lower the setting expansion to a neutral or zero value and even to give negative setting expansion properties wherever such are desirable.

These latter die compositions thus have such useful properties as to enable them to serve many other and obvious purposes. They. may be useful for holding such materials as plate glass when polishing the latter. Also, the unusually high compressive strength surface hardness, combined with a substantially neutral or zero setting expansion', make them advantageous as patterns, in conjunction with the die sinking machine.

The above mentioned compositions may also be used to hold objects in. place or to'cement materials of a brittle or fragile nature and where an intervening layer of expanding cement would crack same.

By using neutral soluble salts along with cadmia, it is possible to reduce the setting expansion to practically a neutral value and yet produce objects .which are difficult of production now,

may be reduced to 10% and, in rare cases, somewhat lower, the upper value is about 55%, possibly 60%. By using additional amounts of calcium sulfate, it becomes a difierent type of composition, much stronger, and serves additional purposes. The calcium sulfate contents of these die casting compositions varies from about 60% to approximately 95%. Dies for lower temperature work, especially, consist practically entirely of calcium sulfate and, with proper additions of soluble salts and cadmia, these compositions have their properties enhanced and become more useful. These die compositions refer to those compositions having approximately 95% or more of caiciiiln sulfate.

In all of these compositions, which may be called molds and/or dies, the refractoriness is generally increased by increasing the amount of refractory filler, and the strength is increased by the increased amount of calcium sulfate and binder. With the soluble salts mentioned as particularly good examples and with cadmia, the range of useful die and mold compositions containing calcium sulfate is widened considerably.

All of the cementitious compositions herein mentioned may be referred to as molds and dies and contain as the binder, calcium sulfate which,

in turn, has its properties improved by the addition of soluble salts and further improved and a wide range of control given thereto by caldmia.

What is claimed is:

1. A composition comprising 20 to 50% calciuin sulfate binder, 50 to filler, and .05 to 10% of cadmia.

2. A composition for making molds or dies for use in forming or casting metals, alloys and other materials and containing a calcium sulfate binder, and having present in the composition a cadmia compound such as metal, carbonate and organic salts and being capable of forming .05

to 10% cadmium oxide upon heating.

3. A composition for making molds or dies for use in forming or casting metals, alloys and other materials, said'composition. including acalcium sulfate binder, .1 to 5% of a solublesalt as an expansion improving agent, and .05 to 10% of cadmia.

4. A composition for making molds or dies for use in forming or casting metals, alloys and other materials, said composition including a calcium sulfate binder, 1.0% of a soluble salt as an expansion improving agent, and .05 to 10% ofcadmia.

5. A composition for making molds or dies for use in forming or casting metals, alloys and other materials and comprising 50 to 80% filler, 20 to 50% calcium sulfate binder, .1 to 5% of a soluble salt as an expansion improving agent, and .05 to 10% of cadmia.

6. A composition suitable for making molds or dies for use in forming or casting metals, alloys and other materials which has a calcium sulfate binder, .1 to 5% of soluble chloride, and .05 to 10% of cadmia. I

v 7. A composition suitable for making molds or dies for use in forming or casting metals, alloys and. other materials which has a calcium sulfate binder, .1 to 5% of barium chloride, and .05 to 10% of cadmia.

8. A composition suitable for making molds or dies for use in forming or casting metals, alloys and other'materials which has a calcium sulfate binder, .1 to 5% of barium chloride, and 1% of cadmia.

9. A composition suitable for making molds or dies for use in forming or casting metals, alloys and other materials which has a calcium sulfate binder, .1 to 5% of boric acid, and .05 to 10% of cadmia.

10. A composition suitable for making molds or dies for use in forming or casting metalsr alloys and other materials which has a calcium of cadmia. 5

ROBERT NEIMAN.

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