US2977236A - Core binder - Google Patents

Description

H. NEUKOM CORE BINDER March 28, 1961 Filed Deo. 50, 1957 2,977,236! Patented Mar. 28, 1961 2,977,236 GQREBNPER Hans Neukom, Erlenbach, Zurich, Switzerland, assigner to International Minerals 8.- Cheniica; Corprtipn, a corporation of New York Filed; Dec-30,-1f957i Ser... No.. 706,1@ 4Glaims. (Si. ltlt-eiiiy 'lfhe present, invention relates to foundry cores. More particularly, it relates to animproved'oundry c't'g're containing a binder having'superiorproperties.i 'Y

A foundry core has been dened as an aggregate of inert matter such as sand, having ar degree, ofporosity and a controlled mechanical` st ngth, sufficient to allow the core to be assembled breakage., as a,l part of a mold and to form molten metal into adesired'; shape. For this purpose, it is necessary to A incorporate in the Sand4 a. material. 0 1: materials, t0. bind. the Saad together and to give it the desired mechanical strength, Numerous materials have been used for this purpose 'in the past, including cereal products, water glass, drying oils, resins, suliite liquor, proteinaceous materials, molasses, clays, wood flour, gelatinized starches, dextrinized starches, and many other substances and combinations thereof. All of these materials have their points of: superiority and inferiority, depending upon the particular type of"v sand employed, the type of metal to be cast, the Size of the casting,`v the precision required, and,V other factors disclosed ia. the@ The ar @at if1.,ve.11ti.011A @v01-ves the use of a novel typev ot core binder, either alone orin conibi,irritiertdY withwothe'rbinding materials, whereby4 cores of Superior Properties area. tasti,

One object of the present invention is to prepare a foundry core having improved.V properties. A Y' Another object is to providean. improved. binding material for foundry cores. t

Another object is to provide a core binding. material of versatile properties, adaptabletouse in the' preparation of cores having special characteristics.`

Other objects of the invention will: be apparent from the present description and, claims In. accordance with the present invention, l employ. as ayfoundry coreb' lk 1' metalphosphate-modified Strchrrreparesas. sienten Tha-Phosphate. modied starch is preferably employed in the',4 form `01E a dry powder., which is suitably. pulled or Qtlerwis Vlended into acore sand in a` proportion between about 0.1 and about 3%by`weight, optimally aroupdftlj to 1.5% based on the dry mixture.V Water is nalso added to the sand and blended therein, preferably before addition ofthe phosphatefmodied starch, theinal proportion of water being. suitably betweenabout 2. andfabout 6% by. weight, preferably. between abouty 3. and about 5%`.

, Alternatively, the. phosphatefmodiedstarch can be. added to sand, it desiredJ in the form of an aqueous dispersion or paste- Othsr materials, of. their cammelli. employed as core binders may also beincorpo'ratednin core mixture as dired.. Thereafter, the mixtureis'formed into cores in the'conventional manner, after whichy the v core is bakedv or cured under conventionalconditions prior to use. 'e

In baking cores, the temperature and time required vary widely according to the size of the core, the' surf face-to-volurne. ratio, the water content, the'type ofsand, andthe nature ofthe core bi'nderf-v Laboratoryicoesare baked at)temperatures'-,` between about 11300V and about 00," F., and bakirigtimes` of aboutV 10 to. about "100. minutes are required @waas-mariana @site strength-5 baking temperature. is preferably. between. abont350v and about-450 F., and@ for small',cores'eontainingrnyhimf proved binder, a bahingtina of around lOtoSO minutes E; ing time may range up to 24 hours, and temperatures up to r600 F. are sometimes used-to speed up to process.

The preparation of alkali-metal phosphate-modified starches suitable for use in my invention is described in my U.S. Patents 2,884,412- (April 28, 1959) and 2,865,762 (December, 23, 1958). In the described method, starch is impregnated with a solution of an aLtali-metal phosphate salt, then dried and heated at a temperature between about 12.0 and-about 175 C., whereby desirable changes are. produced in the properties of the` starch. In one representative example, dried, ungelatinized starch is immersed in` an aqueous solution of an alkali-metal orthophosphate, the liquidA phase is. removed, the impregnated starch is dried to less than about 15% moisture at. a temperature below itsn gelatinization point, and the dried' starchTphosphate mixture is heated for aroundl to l5 hours atabout 130 to? about 170"y C., preferably about 5 hours at` about 160- C., the length of the heating period varying inversely with the temperature. A modiied. starch is obtained thereby having the property ofY dispersing rapidly. in coldy water to produce dispersions having a viscosity' between about 1,000 and about` 5,000 cp., Vmeasured in 5% aqueous solution at room temperature.

As dened in my U.S Patent 2,884,412, the starch phosphat'esv employed. in my invention are substances prepared by impregnatingan ungelatinized starch with at least about 1.0% by weight, calculated as phosphorus, of at least one phosphate salti of an `alkali-metal in an aqueous solution of said salt having a pH between 3.0fand about 7.5, and heating the impregnated starch in the substantial absence oil unabsorbed water at a temperature between about and about-175or C. for a period. Of about 1 to about 1,5 hours.

Preferred phosphate salts are sodium, potassium, and lithium orthophosphates, alone or in suitable combinations to yield; api-lin. aqueous solution between aboutl 4 and about 7, preferablyk around 6, measured at'25" C'. at the concentration employed. For example, monosodium orthophosphate and-disodium orthophosphate are combined inaqueous solution in such proportions as to produce a pH between about 6 and about 7. Or the de` sited salts may be formed in situ, for example, by dissolving. trisodium orthopliosphate or other basic phosphate salt in water and adjusting the pH 'of the solution to the desired level by. adding. orthophosphoric. acid or an acidic orthophosphate salt. Alternatively, orthophosphoric acid oran acidic. phosphate in aqueous solution may. bewadjusted upward tothe desired pH by Aadding an alkaliar'netal hydroxide or a basic alkali-metal orthophosphate, salt. n y befphosphate solution maysuitably. be between about 1. and about 3,l molar` in phosphate and should beV used in a quantity equivalent to at least about 1% by weight of phosphorus, preferably between about 3 and about 5%.; based onthe quantity of-starch to be treated. The quantyand concentration of solution should be chosen soL t the starch. will Vtorrn `a slurry: when commingled therewith. efgquautity of starch will generally be lessV than v1.5; times then/eight ofy the` water contained in the solution, and will. ineferfablyr 1re-less than the Weight .Of

become soaked with the solution; e y r=i"l:1e soed starch granules are separated from the. solul tion by'ltration, centrifugation, or thelilge, and the liquid phase. largely removed, suitably 'by air `drying at a tenipera'tureLbelow th'pointatwhichsfaifch gelatinizes', e.g.,

` -belowiyabout-o to,- SOJC., depending-upon the particular ,is ordinarily. suicient. l.Earl.comnaeircial.-r'cores, the bak-fv 'starch'.f Thezresulting granules, which generally'coniain .l

"1i-Therrien# treated material is a phosphate-modified starch suitable for use as a core binder or a core-binder component in accordance with my invention.

The phosphate-modified starches prepared as described above can be fractionated if desired to separate a material yielding dispersions of higher viscosity according to a technique described by Jacob W, Sietsema and William C. Trotter in copending application Serial No. 637,351, filed January 31, 1957. In accordance with the Sietsema- Trotter technique, a phosphate-modified starch is dispersed in Water in a proportion between about l and about by weight or higher up to the saturation level, based upon the quantity of water employed, and a fraction thereof is precipitated by yadding an oxygen-containing water-miscible organic liquid, such as methanol, acetone, or the like, in a proportion suli'icient to produce a mixed solvent containing between about 35 and about 65% by volume of the added organic liquid. I'he precipitate is separated from the liquid phase, and preferably dried. This material contains a decreased proportion of inorganic phosphates, color bodies, and other impurities, and aqueous dispersions thereof are substantially higher in viscosity than comparable dispersions of the starting material.

Cores prepared according to my invention have normal green strength, breaking at -a tensile strength around 1 p.s.i. Surprisingly, I have found that the green strength can be markedly improved, if desired, by addition of certain inert lines, such as tine sand, silica flour, olivine lour, ironoxide ines, and the like. Such mixtures also exhibit the unusual property of increased baked strength. Moreover, I have further found that my new cores can be improved in both green strength and hot strength by adding certain carbonaceous materials, such as pitch and sea coal. All of these additives, it should be noted, are highly detrimental when used with conventional core binders.

My new type of core exhibits the remarkable property of baking equally fast with either high or low proportions of binder. Thus, overbaking may occur when the cores are made with open sands, which themselves tend to bake faster and to require less moisture. With such sands, it is desirable to reduce the baking time, to increase the moisture content, or to add a humectant such as glycerin or sorbitol; the simplest expedient, however, is to introduce a quantity of ne sand or our. Angular sands bake even more rapidly, and require the closest control. With all open or angular sands, an increased proportion of cereal is desirable, together with a smaller proportion of phosphate-modified starch.

I have observed that cores containing my new binder are more resistant to humid atmospheres than cores made with oil binders. Nevertheless, the bond produced by my binder is water-soluble; and when a core made therewith is immersed in water, it disintegrates. This is seldom a problem in commercial operations; but where it is, the problem can be avoided in a simple manner by incorporating a water-repellent material such as' a silicone or other material known to the art.

The following specific examples will more clearly illustrate my invention. All of the tests described therein were carried out according to standard methods defined in the Foundry Sand Handbook, sixth edition (1952), published by the American Foundrymens Society, Chicago. All measurements are on dry basis. In each case, the cores were prepared and tested in triplicate, and the rel ported results are the average of the three tests.

Example 1 A series of tests were carried out to ycompare cores containing phosphate-modified corn starch alone, phospirate-modified corn starch in'combination with cereal and with a core oil, and a conventional binder comprising cereal, oil, and clay. y The phosphate-modified starch was a high-viscosity material having aviscosity above 100,000 cps. atV 25 C., measured in 5%"aqueo'us dispersion, vand was obtained by methanol precipitation from an aqueous dispersion of phosphate-modified starch according to the technique described above. The sand employed was No. 1 steel sand having an AFS grain neness of 65 (AGF 65). Il-1e core mixtures were prepared as follows:

A. Phosphate-modied starch alone:

' 1% phosphate-modified starch 5.5% water Remainder sand The dry ingredients were mulled l minute in a laboratorysize Simpson muller, the-water was added, mulling was continued for 6 minutes, and the mixture was discharged and stored in a sealed can until used to make cores. The retained water content was 5.1%.

B. Cereal added:

1% phosphate-modified starch 1% corn cereal (I`ruscor) 0.3% southern bentonite 5 .5% water Remainder sand The mixture was mulled as before. The retained water content was 5.5%.

C. Core oil added:

1% phosphate-modified starch 0.25% core oil 0.125% kerosene 0.3% southern bentonite 6% water Remainder sand The dry ingredients were mulled l minute. The water was added and mulled 1 minute. The core oil was added and mulled 5.5 minutes. The kerosene was added and mulled 0.5 minute. The completed mixture was discharged and stored. It retained 5.6% water.

D. Standard cereal-oil binder:

1% corn cereal (Truscor") 1.25% core oil 0.125% kerosene 0.3% southern bentonite 3% water Remainder sand The dry ingredients were mulled 1 minute. The water was added and mulled 3 minutes. The core oil and the kerosene were added together and mulled 3 minutes. The completed mixture was discharged and stored. It retained 3% water.

' The various mixtures were formed into standard test cores and found to have green strengths (tensile strength at break, before baking) as follows:

P.s.i.

A 1.2 B 4.2 C 1.1 D 0.76

. Test cores were then baked at 425 F. over a series of baking periods, and were found to have baked strengths as follows:

'rt-.D511 st th t k Baking Timo, min. e reng a Brea A B o D 190 14o 185 125 9o 155 120 14o 110 155 153 120 105 170 162 V12o 105 180 155 105v 105 175 156 100 165 154 175 The foregoing data are Vplotted inthe attached drawing. From the curves contained therein, it will be observed that phosphate-modified starch, when used alone as a binder (curve A), produced a core which was stronger than the typical prior-art cereal-oil-clay combination (curve D), and reached maximum strength in only 20 minutes, compared with 50 minutes for a similar core containing oil. The phosphate-modiiied starch was compatible with core oil and with cereal, and could be used to improve one or more of the properties thereof. The inclusion of clay in cores containing phosphatemodied starch appears to be contra-indicated.

The core mixtures were then tested for hot strength, measured in terms of the time required by a 1A; dia. x 2" cylindrical test core to collapse under a 100 lb. load at a given oven temperature. In each case the test cores were baked for a time known to give approximately the maximum hot strength. For this purpose, the specimens containing core oil required 70 minutes at 425 F., while the other specimens required only 20 minutes. The test results were as follows:

Time for Collapse at 100 lb. Load, mn.

Oven Temperature, F.

A .B C D These data demonstrate that my new binder imparts satisfactory hot strength to cores.

Example 2 strength was as follows:

Baked Baking time, min.: Y strength, p.s.i.

Hot-strength test cores, baked 20 min.

at 425 F., had the following properties:

Time for Oven temp.: collapse, 800 F. 9.14 1000 F. 5.92

Example 3 The following test illustrates the combination of cereal with my new core binder material. Thevmixed core binder comprised corn our and the technical-grade phosphate-modified starch employed in Example 2.

No. 1 steel sand, AGF V65, was mulled with 5% water for 1 minute; then 1% lof corn flour and 0.25% of the phosphate-moded starch'were added, and the mulling was continued Yfor 6 minutes.` The completed mixture contained 5.1% of water. Standard test cores prepared therefrom had a green vstrength of 1.05 p.s.i. 1 When baked 20 minutes at 425 F., their tensile strength at breakwas 230 p.s.i. n I. f

Hot-strength test cores, baked 20min. at 425 F., collapsed at the end of 2.79V minutes` at an oven temperature of 800 F. f

When baked at 425 F. their an aqueous alkali-metal orthophosphate solution having 6 Example 4 A comparative -test showed that a conventional oilcereal core lost 23% of its baked strength when stored at 100 F. for 16 hours at 100% humidity. A comparable phosphate-modified starch core lost only 8%.

My invention can suitably employ alkali-metal phosphatemoditied starches of a wide variety, including those prepared from potato starch, corn starch, wheat starch, cassava starch, arrowroot starch, and the like. The starchesy should not be subjected to gelatinization, dextrinizing, or other treatment prior to phosphate modilcation which would materially alter or destroy the essential characteristics of the starch molecule. For this reason, after the starch has been soaked in phosphate solution, it should be dried to less than 15% moisture content betore being heated to a temperature above the gelatinization point. If this is not done, the starch undergoes gelatinization and perhaps other forms of degradation during the heat treatment, and a modified starch of inferior properties is obtained.

My cores can be prepared from tine sand with no loss in strength. They bake satisfactorily over a wider range of temperatures than cores containing oil as a binder. They bake in one-half to two-thirds the time of the fastest oil or resin core, or one-third to one-fourth the time of an ordinary oil core. They have Ahigh baked strength, in the range of around 175 to 200 p.s.i. or higher at the 1% level, equivalent to 1.25% linseed oil plus 1% of cereal. They have excellent retention of strength when stored in humid atmospheres. Finally, they exhibit low gas evolution, Vonly about one-third as much as a con- -ventionaloil-cereal mixture of equal strength.

It is to be understood that the various starting materials, manipulative techniques, process condi-tions, and other rexemplary matter disclosed herein-above are intended to'be'illustrative only and not as a limitation upon the scopeof the invention. Numerous modifications andvequivalents of the invention will be `apparent from the foregoing description to those skilled in the art.

VThis application is a continuation-impart of my application Serial No. 378,666, tiled September 4, 1953, which issued as U.S. Pat. 2,884,412 on April 28, 1959.

In accordance with the foregoing description, I claim as my invention:

1. In the preparation of a foundry core, the improvement which comprises commingling sand lwith water in a proportion affording a water content between about 2 and about 6% by weight and between yabout 0.1 'and about 3% by. weight of an yalkali-n'ietal phosphate-modified starch, prepared by soaking dry, ungelatinized starch in a pH between about 4 and about 7 vto incorporate said alkali-metal orthophosphate therein in a proportion equivaient to at least about 1% by weight of phosphorus, dry

basis, removing surface moisture yfrom the starch, dryingv the starch to a moisture content less than `about 15 %l by weight at a'temperature below the gelatinization point thereof, baking the dried starch at a temperature between about and about 175 C. for a period of about 1 to about 15 hours, the length of the baking period varying'inversely with the temperature, forming the resulting v mixture into'the desired shape, and, baking the shaped mixture at a temperature between Iabout 300 and about 600 F. v

2. In .the preparationtof a yfoundry core, the improveinent whichV comprises rnulling sandl with water in a kproportion aiording a water Vcontent between about 2 and'Y about 6% `byweight, adding thereto and mulling therewith betweenabout 0.5 and about 1.5% by weight ofa sodiumphosphate-modiiied starch prepared byirn.`

mei-sing aY dry, ungelatinized starch in an aqueous solution of .a `sodium orthophosphate ihavinga concentration between about 1 and about 3 molar in phosphate land havinga pH between about 4 and about 7 to incorporate V said sodium orthophosph-ate therein in a proportion equivalent to at least about 1% by weight of phosphorus, dry

basis, removing the liquid phase from the starch, drying the starch to a moisture content less than about 15% by weight at a temperature below the gelatinization point thereof, baking the dried starch at a temperature between about 130 and `about 170 C. for a period of about 1 to about 15 hours, the length of the baking period varying inversely with the temperature, forming the resulting mixture into the desired shape, and baking the shaped mixture at a temperature between about 300 and about 600 F.

3. In the preparation of a foundry core, the improvement which comprises mulling sand with water in a proportion affording a water content between about 2 and about 6% by weight, adding thereto and rnulling therewith between about 0.5 and about 1.5% by Weight of a sodium phosphate-modiied starch prepared by irnrnersin-g a dry, ungelatinized starch in an aqueous solution of a sodium orthophosphate having a concentration between about 1 and about 3 molar in phosphate and having a pH around 6 to incorporate said sodium orthophosphate therein in a proportion equivalent to between about 3 and about 5% by weight of phosphorus, dry basis, removing surface moisture from the starch, drying the starch to a moisture content less than about 15% by Weight at a temperature below the gelatinization point thereof, and baking the dried starch for a period of around 5 hours at va temperature around 160 C., forming the resulting mixture into the desired shape, and baking the shaped mixture at a temperature between about 300 and about 600 F.

4. In the preparation of a foundry core, the improvement which comprises commingling sand with Water in a proportion affording a. water content between ,about 2 and `about 6% by weight and with betweenpabout 0.1 and about 3% by weight of an alkali-metal phosphatemodified starch, prepared by impregnatingV an ungelatinized starch with at least about 1.0% by weight, calculated as phosphorus, of at least one phosphate vsalt of an alkali metal in an aqueous solution of said salt having a pH between 3.0 and about 7.5, and heating the impregnated starch in the substantial absence of unabsorbed water at a temperature between about 120 and about 175 C. for a period of about l to about 15 hours, the length of the heating period varying inversely with the temperature, forming the resul-ting mixture intothe desired shape, and baking theV shaped mixture at a temperature between about 300 and about 600 F.

References Cited in the tile of this patent UNITED STATES PATENTS 1,531,871 Nagel Mar. 31, 1925 1,974,915 Giesecke Sept. 25, 1934 2,687,966 Miner et al Aug. 3l, 1954 2,779,693 Pacsu et al. Ian. 29, 1957 2,806,026 Evans Sept. l0, 1957 2,884,412 Neukorn Apr. 28, 1959 FoRnrGN PATENTS 543,202 Great Britain Feb. 13, 1942 879,150 Germany June 11, 1953 OTHER REFERENCES Foundry, February 1950, p. 177.

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No? 2,977,236 March 28 1961 Hans Neukom It is h'ereby certified that error appears n the vabove numbered patent requiring correction and 'that the said Letters Patent should read as corrected below.

Column 2, line 2, for "up to process" read up the process -m column 5, line ll for "I/8" read l l/8 Signed and sealed this 29th day of August 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. IN THE PREPARATION OF A FOUNDRY CORE, THE IMPROVEMENT WHICH COMPRISES COMMINGLING SAND WITH WATER IN A PROPORTION AFFORDING A WATER CONTENT BETWEEN ABOUT 2 AND ABOUT 6% BY WEIGHT AND BETWEEN ABOUT 0.1 AND ABOUT 3% BY WEIGHT OF AN ALKALI-METAL PHOSPHATE-MODIFIED STARCH, PREPARED BY SOAKING DRY, UNGELATINIZED STARCH IN AN AQUEOUS ALKALI-METAL ORTHOPHOSPHATE SOLUTION HAVING A PH BETWEEN ABOUT 4 AND ABOUT 7 TO INCORPORATE SAID ALKALI-METAL ORTHOPHOSPHATE THEREIN IN A PROPORTION EQUIVALENT TO AT LEAST ABOUT 1% BY WEIGHT OF PHOSPHORUS, DRY BASIS, REMOVING SURFACE MOISTURE FROM THE STARCH, DRYING THE STARCH TO A MOISTURE CONTENT LESS THAN ABOUT 15% BY WEIGHT AT A TEMPERATURE BELOW THE GELATINIZATION POINT THEREOF, BAKING THE DRIED STARCH AT A TEMPERATURE BETWEEN ABOUT 120 AND ABOUT 175*C. FOR A PERIOD OF ABOUT 1 TO ABOUT 15 HOURS, THE LENGTH OF THE BAKING PERIOD VARYING INVERSELY WITH THE TEMPERATURE, FORMING THE RESULTING MIXTURE INTO THE DESIRED SHAPE, AND BAKING THE SHAPED MIXTURE AT TEMPERATURE BETWEEN ABOUT 300 AND ABOUT 600*F.

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