US3149090A - Shell mold formulations - Google Patents

Description

United States Patent ()ffice ILMQWQ Patented Sept. 15, 1964 3,149,090 SEELL M013) FORMULATIQNS Wesley L. Archer, Midland, James B. Louch, Coleman,

and Robert S. Montgomery, Midland, Mich, assignors to The Dow Chemical Company, Midland, Mich, a

corporation of Delaware No Drawing. Filed Jan. 6, 1960, Ser. No. 691 4 Claims. (Cl. 26tl37) This invention relates to binder-filler compositions used in preparing refractory structures and more particularly relates to compositions of cross-linkable resin-producing mixtures of coal acids adducts and inert siliceous fillers useful in foundry practices for the preparation of shell molds, hot top devices and similar constructions.

The use of shell molds in foundry practice is becoming more and more widespread since this technique is economical, facilitates metal casting operation, and gives cleaner, sounder and more accurate castings than can be obtained by conventional sand casting techniques. Conventionally, shell molds for use in casting ferrous metals are prepared from compositions of a fine grained siliceous material, e.g. sand, precoated with a thermo-setting phenolic resin binder. Satisfactory shell molds are prepared from these compositions. However, ordinarily to insure homogeneous precoating of the grains, the phenolic binder is applied to the grains in the form of a relatively expensive alcoholic solution and the solvent then is removed during the mixing and drying of the resin coated sand composition. Also, since many of these phenolic resins contain readily flammable substances it is not uncommon that shell molds prepared with these resins as binders many times start burning during fabrication which makes these resins somewhat hazardous to use.

Recently, it has been shown that refractory structures prepared using as a binder thermosetting, resin-providing cross-linkable coal acids polyfunctionalamine compound adducts (U.S. Patent 2,895,936) or coal acids alcamine compound adducts (U.S. Patent 2,895,934) can result in structures which are not readily flammable during fabrication, but which still give proper resin burn-out during casting operations. Furthermore, these coal acids adducts can be applied to the siliceous filler materials in the form of an inexpensive water solution.

The cured refractory structures, e.g. shell molds and hot top devices obtained using the coal acid adducts resins as a binder for the siliceous fillers generally are strong and rigid products. They have desirable high gas permeabilities because of their excellent porosity characteristics. These cured structures also have good surface smoothness and dimension stability. In addition, they have little tendency to adhere to the surface of the hot metal after it has solidified and may be easily stripped or removed therefrom. Furthermore, the structures usually disintegrate easily and cleanly upon sharp impact or other means conventionally used for their removal from the solidified metal casting.

Now, unexpectedly, it has been found that still better shell molds result if, instead of a single coal acids adduct certain mixtures of the coal acids adducts are used as binders for the sand in such molds.

It is the principal object of this invention, therefore, to provide compositions of an inert siliceous material and a mixture of resin-providing, thermosetting coal acids adducts suitable for the production of shell molds. An object of these compositions is to provide a mixture of coal acids adducts which when used as a binder with an inert filler gives useable shell molds at lower total adducts concentrations than is used for the individual coal acids adducts members alone. A further object of the invention is to provide mixtures of the coal acids adducts which exhibit better flow characteristics than do the individual members during the forming of the shell mold, and thereby give more uniform molds than can be obtained with the individual coal acids adducts. Additionally, with certain of the mixtures, lower pattern temperatures can be used during the forming. Another object of the mixtures is to provide cured shells having increased surface hardness and sharpened pattern surface detail when these mixtures are used as binders. Still other objects and advantages will be apparent from the following detailed description of the invention presented hereinafter.

According to the invention, a siliceous filler is coated with from about 1.5 to about 12 percent on the weight of the filler with a binary or ternary mixture containing from about 20 to about 70 percent of coal acids polyfunctional aliphatic amine cross-linkable adducts and from about 30 to about 80 percent of coal acids alcamine cross-linkable adducts. Aliphatic polyfunctional amine coal acids adducts useful in these compositions are those wherein the polyfunctional amine members are of the formulae H NRNH and NH --(RN) RNH where R is a hydrocarbon alkyl radical of from 2 to about 5 carbon atoms and n is a whole integer having a maximum value of 2. Alcamine coal acids adducts useful in these compositions are those wherein the alcarnine members are of the formulae H N-R-OH and HO-RNHROH where R is a hydrocarbon alkyl radical of from 2 to about 4 carbon atoms.

The free coal acids product is a hygroscopic, usually yellowish, essentially Water-soluble material thatis believed to be comprised substantially of various aromatic polycarboxylic acids. The average molecular Weight of the coal acids that are ordinarily obtained is frequently in the neighborhood of 250. Their average equivalent weight is generally about 80 and seldom less than or more than 90. They ordinarily appear to have an average of 2.5 to 5 carboxylic groups per molecule with an apparent average of 3 to 4 being common. While their exact chemical nature and constitution may be somewhat conjectural, they evidently contain considerable quantities of triand tetra-carboxylic benzene acids as well as aromatic acids having more complex nuclei. Frequently, for example, the greatly preponderant proportion of aromatic nuclei obtained in coal acids prepared in the described fashion have been found to consist of methylnaphthalene, benzene, biphenyl, naphthalene, phenanthrene, alkyl benzene, benzophenone and toluene nuclei.

In a. preferred embodiment of the invention for preparation of refractory structures such as shell cores, the binder composition will be comprised of a ternary mixture of about 60 percent of coal acids diethanolamine adduct, about 20 percent coal acids diethylenetriamine adduct, and about 20 percent coal acids ethylenediamine adduct blended with sand at about 2 to about 4 percent of resin mixture on the weight of the sand.

It is generally advantageous to utilize only as little 2. quantity of the resin binder in the composition for refractory structures as may be necessary in order to obtain suitable strong structures. In this way the refractory structures can be readily obtained with the desired adequate porosity.

The individual coal acids polyfunctional amine adducts may be prepared according to the process described in US. Patent 2,895,936. The coal acids alcamine adducts may be prepared according to the process described in US. Patent 2,985,934.

Preferably, according to the processes described in these patents, stoichiometrically equivalent amounts of the amine or alcamine and the polycarboxylic coal acids (taking the polyfunctionality of each ofthe reactant ingredients into account) are reacted in a suitable solvent medium, such as water, low molecular weight alcohols, e.g. methanol, ethanol and the like and in many instances even a surplus of the polyfunctional amine or alcamine compounds. The reaction of the compounds provides an adduct of coal acids polyfunctional amine or coal acids alcamine having an optimum maximum potential for cross-linking and interreaction upon being subsequently thermoset and exposed to heat at elevated curing temperatures. Although preferably stoichiometrically equivalent amounts of both polyfunctional reactants are used in preparing the adducts, proportions of either polyfunctional reactant in excess of strictly equivalent stoichiometry requirements and less than about a 2:1 equivalent parts ratio can be utilized in preparation of the adducts.

In the instant application unless specifically stated otherwise, it is understood that the coal acids polyfunctional amine adducts and coal acids alcamine adducts are all prepared using substantially stoichiometrically equivalent amounts of the reaction components.

The sand/ coal acid adducts compositions useful for refractory structures may be formulated by thoroughly intermixing sand with the powdered coal acids adducts mixture. Alternatively, with usually greater advantage, the compositions may be prepared by intimately intermixing with the sand by continuous or batch mulling or intensive mixing procedures, a relatively strong solution, such as an aqueous solution that contains at least about 50 and preferably in the neighborhood of 70 percent or more by weight, based on the weight of the solution, of the dissolved adducts. The mixture of coal acids adducts/sand compositions may either be fabricated as a wet mix into desired shapes prior to being thermoset or, alternatively, may be dried at a non-thermosetting temperature of between about room temperature and 225 F. in order to form a particulate, coated sand composition into desired structures prior to being completely thermoset.

While in the process of drying an adducts mixture coated sand, it may often be beneficial to subject the sand to continued agitation in order to facilitate its being obtained in a suitable granular condition. It may also be beneficial to screen the dried, thermosetting coated sand formulation to obtain a desired particle size. In order to prepare shell molds in accordance with typical dump box techniques, it is usually preferred to first dry the sand composition if it has been prepared using a solution of the cross-linkable coal acids adducts. The free-flowing, dry, coated sand then is granulated by any desired granulation procedure to give average particle size characteristics such that the preponderance of the formulation, usually at least about 70 percent by weight, it is not larger than 70 mesh in the US. Standard Sieve Series.

Addition of a small amount, less than one percent of a lubricant, e.g. a modified fatty acid ester wax such as Acrawax, a product of Glyco Products Co., Inc., to the sand/adducts mixture during blending can further facilitate the granulation of the coated sand. Use of the lubricant also has been found to improve back side detail in the cured shell mold.

The sand/ coal acids adducts compositions, when they are prepared as dry, free-flowing, coated sand mixtures, may generally be pre-formed into a desired structure, such as a shell mold, by placing them in contact while in a suitably thick layer with or against a heated pattern for a period of time (investment time) from about 5 to 40 seconds at pattern temperatures between about 400 and 700 F. Wet mixtures may generally be pre-formed into desired structures such as hot top devices or shell molds by compacting or compressing them against a suitable pattern or in a suitable mold form under pressures, for example, from about 80 to about 120 pounds per square inch as may be developed with a hydraulic or pneumatic ram or the like. Core blowing techniques may also be employed to distribute a Wet mixture against pattern surfaces or in mold forms. Regardless of whether dry or wet mixtures are used, the pre-formed integral composite structures may be suitably thermoset and cured by exposing them to temperatures between from about 350 to 4 about 750 F. for a period of time from about 10 seconds to about 2 minutes or more, depending again upon the particular configuration and composition that is involved in the structure being cured.

Any ordinary sand (or other inert refractory material) that, advantageously, has a fineness in the numerical range between about 25 and 180, American Foundrymens Society (APS) fineness rating, may be utilized as filler for the preparation of refractory structures bound together with the thermoset, cross-linked coal acids adducts resin mixtures of this invention. Such sands, for example, as the types known as Berkeley Float Sand, Juniata Sand, Lake Sand, Vassar Sand, Wedron Sand, Gratiot Bank Sand, Portage 40-60 Sand and the like may be beneficially employed. It is desirable that the sand be clean and substantially free from foreign metal oxides, clay, moisture and organic matter. In many cases, it may be advantageous to employ a granular refractory material for compositions intended for shell mold fabrication having an AFS fineness number from about 50 to 125. Very frequently, sands having an AFS fineness number in the neighborhood of may be preferable for shell mold purposes. Relatively coarse sands that have an AFS fineness number between about 25 and 75 are ordinarily more desirable for utilization in formulations with the coal acids adducts of the invention that are intended for fabrication into hot top devices and the like.

The following examples will serve to further illustrate the invention but are not meant to limit it thereto.

EXAMPLE 1 A solution of a coal acids adducts mixture was prepared from the following components; 310 grams of coal acids diethanolamine adduct, 103 grams of coal acids diethylenetriamine adduct, 103 grams of coal acids etbylenediamine adduct and 224 grams water. The individual adducts were prepared by reacting substantially stoichiometrically equivalent amounts of the alkanolamine, or polyfunctionalamine with the coal acids. This solution was added to about 14,000 grams of Wedron AB 114 white silica sand contained in at Simpson Muller mixer. The adduct sand coating concentration based on reacted resin solids was about 3.0 percent on the total composition weight.

The sand/adducts mixture was mulled for about 10 minutes during which mixing the sand particles became coated with adducts and agglomerated into a damp, plastic-like mass. At this stage 14.5 grams (about 0.1 percent) of Acrowax lubricant were added to the mass. Mulling then was continued for an additional 10 minutes during which time a hot air supply from a small, portable electric blower was directed onto the mixture. The use of the hot air assisted drying of the blend and along with the lubricant facilitated the break-down of the plastic mass into the desired granular product. The resultant free flowing coated sand was mulled for an additional 15 minutes and finally screened through a 40 mesh screen.

One quarter inch thick briquettes formed from a portion of this dry coated sand and cured at 650 F. for 2 minutes gave tensile strengths in the range of about 240 pounds per square inch. These briquettes had a surface hardness of about 75 as measured using a conventional 'Dietert Hardness Tester.

Good shell molds with excellent surface detail were obtained from the so-coated sand using a conventional dump box shell mold machine at a pattern temperature of about 600 R, an investment time of about 15-20 seconds and cure time of about 90 seconds.

A second portion of the above described sand/adducts composition was also used to prepare commercial shell cores on a commercial Shalco core-blowing machine. The fabrication of the shell cores in this device was accomplished in a conventional manner. The integral unit of core box, heater and sand reservoir assembly was rotated 180 degrees, the coated sand blown into the core J box, at about 27 pounds per square inch air pressure for about a 2 second period, and the unit then returned to its normal position. Investment times of 2.5-5.0 seconds at a pattern temperature of about 600 F. and curing from about 4.5 to about 6.0 minutes also at 600 F. gave shell cores of excellent surface detail, hardness ratings of from about 80 to about 95, and good tensile strengths.

Shell cores prepared using commercially precoated phenolic sand required an investment time of about 15 seconds and a cure time of from about 2.5 to about 3.0 minutes cure also at a temperature of about 600 F.

EXAMPLE 2 A number of tests were run to evaluate the effect of various binder formulations in the preparation of commercial shell molds using a dump box shell mold machine. In carrying out these tests, Wedron AFS 116 white silica sand was precoated with various coal acid adducts compositions according to the procedure described in EX- ample 1.

Shell molds then were prepared in a conventional dump box shell mold machine using a commercial shell core pattern. In actual operation, the dump box method of shell mold fabriction involved the following steps: The dry adduct-coated sand was dropped onto a preheated metal pattern (550650 F.) and allowed to remain in contact with the pattern for a fixed length of time from about 5 to about 20 seconds. This time period known as the investment, or dwell, time determines the thickness of the shell. At the end of the proper dwell time, the entire pattern was inverted 180 degrees allowing all the excess, unbonded, coated sand to fall back into the dump box. A dough-like shell of adduct-bonded sand was left adhering to the metal pattern. The tendency of the uncured, dough-like pattern to peel away from the pattern (peel back) was noted. The metal pattern and partially cured shell then were placed in an electric furnace at about 600 F. for a period of time from about 25 to about 90 seconds to cure the mold. The cured shell mold then was finally ejected from the metal pattern by hydraulically operated ejection pins. These molds hold molten iron with ease and are readily strippable from the solidified metal upon cooling.

Table I, which follows, presents test data and results obtained from a number of sand/ coal acids adducts compositions.

For purposes of comparison, the results of tests 6 through 11 of Table I using individual coal acids adduct members as shell mold core binders are included. These indicate that with the individual members greater quantities of binder are needed to give molds having properties substantially equal to that shown by low concentrations of adduct mixtures of the instant application.

In a manner similar to that described for the foregoing examples, it is understood shell molds also can be prepared using as a binder for the sand from about 1.5 to about 12 percent of the following cross-linkable, thermosetting coal acids adducts mixtures; (1) binary mixtures having from about 40 to about percent coal acids dipropylenetriamine adduct and about 30 to about 60 percent coal acids monoisobutanolamine adduct, (2) a binary mixture having about 20 percent coal acids amylenediamine adduct and about percent coal acids diisopropanolamine adduct, (3) mixtures having from about 0 to about 40 percent coal acids triethylenetetramine adduct, from about 40 to about 80 percent coal acids monobutanolamine adducts and about 20 percent coal acids propylenediamine adduct, (4) ternary mixtures having from about 35 percent to about 45 percent coal acids diamylenetriarnine adduct, from about 35 percent to about 45 percent coal acids dibutanolamine adduct, and from about 10 to about 30 percent coal acids monopropanolamine adduct, and (5) mixtures having from about 0 to about 40 percent coal acids triamylenetetramine adduct, from about 40 to about 80 percent coal acids diisobutanolamine adduct and about 20 percent coal acids butylenediamine adduct.

Any of the suggested aliphatic polyfunctional amines can be substituted for any of the aliphatic polyfunctional amines mentioned in the above listed compositions and any of the suggested alkanolamines can be substituted for any of the alkanolamines mentioned in the above listed compositions according to this invention and these mixtures then blended with siliceous materials to give refractory structures.

Various modifications may be made in the present invention Without departing from the spirit or scope thereof, for it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. Thermosetting mass for forming integral composite structures characterized in being thermosetting when Table I SHELL MOLDS CORES PREPARED USING COAL ACIDS ADDUCTS COATED SAND Coal acid resin composition Mold Preparation Mold Properties Test No. Pattern, Invest- Cure Comments Classification Per- Temp. ment, time Surface Shell Peel of adduct cent F.) (time) (See) hardness strength back see.

3ODEA,7ODETA. 3.5 550 10 60 Fair Average-.- Yes--- Shfieflll gas of about correct C ness. 50DEA,50DETA 3.5 650 20 60 Fair Fair No.--. Do. 40DEA,4ODETA, 3.5 600 8 40 Average.. Average... No.- Do.

20MEA. 5ODEA,25DETA 3.5 600 15 .do -r10....- Some- D0.

25EDA. 60DEA,20DETA, 3.5 600 15 60 Good Good No.... Do.

8 650 20 50 .do .do No. Surface shell thicker than necessary. 8 650 12 40 .do .do No...- Surface shell of about correct thielmess. 6 650 20 40 .do Average... Some.. Do. 4 650 30 25 Average.-. .do Yes-.. Very thin shell. 8 650 12 55 Poor Poor Yes--. Poorssshell. Not thermoset in sec. 8 650 12 40 Good Good Half of shell-broke when released from pattern. Thin shell.

nolamine.

2 0n weight of sand. 3 Cure temperature about 600 F.

1 DEA--dietha.nolamine, DETAdiethlylenetriamlne, MEA-monoethanolamine, EDA-ethylenediainine, TEA-triethaheated to a temperature between about 350 F. and about 750 F. comprising an inert siliceous filler substance blended with from about 2 to about 4 percent on the weight of the siliceous filler of a resinproducing mixture consisting essentially of from about 40 to about 70 percent of coal acids diethylenetriamine adduct and from about 30 to about 60 percent of coal acids diethanolarnine adduct, said coal acids being hygroscopic, essentially Water soluble, aromatic polycarboxylic acids having an average molecular weight of about 250, an average equivalent weight of from about 75 to about 90 and containing an average of from 2.5 to 5 carboxylic groups per molecule.

2. A thermosetting shell mold composition which comprises; sand in combination with from about 2 to about 4 percent on the Weight of the sand of a resin-producing ternary mixture comprised of about 60 percent coal acids diethanolamine adduct, about percent coal acids diethylenetriarnine adduct and about 20 percent coal acids ethylenediamine adduct, said coal acids being hygroscopic, essentially water soluble, aromatic polycarboxylic acids having an average molecular weight of about 250, an average equivalent weight of from about 75 to about 90 and containing an average of from 2.5 to 5 carboxylic groups per molecule.

3. Thermosetting mass for forming integral composite structures characterized in being thermosetting when heated to a temperature between about 350 F. and about 750 F. comprising an inert siliceous filler substance blended with from about 2 to about 4 percent on the weight of the siliceous filler of a resin-producing mixture consisting essentially of from about 0 to about percent of coal acids diethylenetriamine adduct, from about 40 to about 80 percent of coal acids diethanolamine adduct and about 20 percent of coal acids ethylenediarnine adduct, said coal acids being hygroscopic, essentially water soluble, aromatic polycarboxylic acids having an average molecular weight of about 250, an average equivalent weight of from about 75 to about 90 and containing an average of from 2.5 to 5 carboxylic groups per molecule.

4. Thermosetting mass for forming integral composite structures characterized in being thermosetting when heated to a temperature between about 350 F. and about 750 F. comprising an inert siliceous filler substance blended with from about 2 to about 4 percent on the weight of the siliceous filler of a resin-producing mixture consisting essentially of from about 35 to about percent of coal acids diethylenetriamine adduct, from about 35 to about 45 percent of coal acids diethanolamine adduct and from about 10 to about 30 percent of coal acids monoethanolamine adduct, said coal acids being hygroscopic, essentially Water soluble, aromatic polycarboxylic acids having an average molecular weight of about 250, an average equivalent weight of from about to about and containing an average of from 2.5 to 5 carboxylic groups per molecule.

References Cited in the file of this patent UNITED STATES PATENTS 2,471,631 Lebach May 31, 1949 2,683,296 Drumrn et a1 July 13, 1954 2,895,934 Archer et a1. July 21, 1959 2,895,935 Archer et al July 21, 1959 2,895,936 Archer et al July 21, 1959 2,923,989 Thomson Feb. 9, 1960

Claims (1)

1. THERMOSETTING MASS FOR FORMING INTEGRAL COMPOSITE STRUCTURES CHARACTERIZED IN BEING THERMOSETTING WHEN HEATED TO A TEMPERATURE BETWEEN ABOUT 350*F. AND ABOUT 750*F. COMPRISING AN INERT SILICEOUS FILLER SUBSTANCE BLENDED WITH FROM ABOUT 2 TO ABOUT 4 PERCENT ON THE WEIGHT OF THE SILICEOUS FILLER OF A RESIN-PRODUCING MIXTURE CONSISTING ESSENTIALLY OF FROM ABOUT 40 TO ABOUT 70 PERCENT OF COAL ACIDS DIETHYLENETRIAMINE ADDUCT AND FROM ABOUT 30 TO ABOUT 60 PERCENT OF COAL ACIDS DIETHANOLAMINE ADDUCT, SAID COAL ACIDS BEING HYGROSCOPIC, ESSENTIALLY WATER SOLUBLE, AROMATIC POLYCARBOXYLIC ACIDS HAVING AN AVERAGE MOLECULAR WEIGHT OF ABOUT 250, AN AVERAGE EQUIVALENT WEIGHT OF FROM ABOUT 75 TO ABOUT 90 AND CONTAINING AN AVERAGE OF FROM 2.5 TO 5 CARBOXYLIC GROUPS PER MOLECULE.