US2974050A - Core binder - Google Patents

Description

nited States Patent 2,974,050 CORE BINDER Thomas E. Barlow, McHenry,'lll., assignor to International Minerals & Chemical Corporation, a corporation of New York t No Drawing. Filed June 27, 1958, Ser. No. 744,917

5 Claims. (Cl. 106-385) The present inventionrelates to foundry cores. More particularly, it relates to an improved foundry core of high hot strength, containing a binder having superior properties. 1 1

In foundry practice, it is frequently necessary to incorporate cores in the molds to produce'void spaces in the metal castings. Such cores are ordinarily prepared by compacting sand in the desired shape. In order for thecore to have sufiicient mechanical strength to withstand the impact of the hot metal, it is customary to incorporate one or more substances in the coremixture and thereafter to bake the core at elevated temperature before assembling it into the mold. A wide range of substances have been employed for this purpose, including cereal products, water glass, drying oils, resins, sulfite liquor,

proteinaoeous materials,-molasses, clays, wood fiour, gelatinized starches, dextrinized starches, and the like. The present invention involves a novel combination of substances for use as a core binder, whereby cores of superior strength at casting temperaures are obtained.

One object of the present invention is to prepare starch or starch fraction comprising gelatinized amylo' pectin, and a phosphate salt ofv an alkali metal or an alkaline -earthamet-al. The resulting mixture is formed into the desired shape. and is thereafter baked under conventional conditions. The core obtained thereby has excellent baked tensile strength and outstanding hot properties.

' In preparing a foundry core according to ,one embodimer t of the present invention, sand is mulled with between about 3 and about 6% by Weight ofi'water, optimallyaround 4 to 5%. added in a proportion between about-0.5 and about 2.5% by weight of the sand, dry basis, and is mulledin. Finally, the phosphate salt is added in a proportion between aboutS and about 25% by-weight offthe. amylopectin,

lg drybasis, and the entiretmixture is mulled until homogenews. The mulling steps ordinarily require-periods of' about 1, 1, and 6 minutes, respectively, for completion. Other materials of the types commonlyemployed as core binders may also be incorporated the core mixture if desired.

Gelatinizedamylopectin is then v The cores produced in accordance with the present invention are baked under conventional conditions.' The required temperature and'tirne will vary considerably, as theprior art recognizes, according to the size of the core,

the surface-to-volume ratio, the water content, and the Laboratory reasinglylonger baking times, particularly cores'iwhich 1,

:of thebaked cores was measured interms cfitlieirteiisile strength atroom temperature. (baked strength) and in have lower surfacerto-volume ratios. Higher tempera.- tures may'in many cases be employed, but are generally not preferred, owing to a tendency of the cores to become I overbaked and case-hardened. V I

Other procedures may be employed satisfactorily in the preparation of the core mixture. For example, the sand the gelatinized amylopectin, the phosphate'salt, and any other dry ingredients can first be mulled together, followed by the water and any other wet ingerdients. In another method, the phosphate salt can be dissolved in the water, then mulled with the sand, followed by the gelatinizcd amylopectin. The method and sequence of admixing the various components can be varied at will while still producing-improved results in the resulting cores; The mulling times employed are not critical, so long as a homogeneous mixturelof the materials is achieved. For this purpose, it is ordinarily sufficient to mull the initial admixtures, if any, for only about 1 minute, and to mullthmcompleted, mixture for about 5 to -l() minutes,ppreferably around 6 minutes.

Starch generally comprises two primary fractions- -viz., amylopectin and amylase, the proportions varying, markedly. from one starch to another. The present invention can suitably employ either amylopectin, or whole starch, or a starch fraction comprising arnylopectin, so long as the said-materials have been subjected to gel,- atinization. In this respect it should be noted that amylo pectin, as ordinarily marketed, is in gelatinized form owing to the method by which it is separated from .the original starch. It should further be noted that the so.- called'foundry cereals are invariably gelatinized starch of one type or. another, always comprising arnylopectin', land aresatisfactory for use in the present invention." 'Suitable salts forusetin the present invention are the Water-soluble orthophosphate, pyrophosphate,.1metaphos, phate, and polyphosphateisalts of the alkali metals and of the alkaline-earth ess, or mixtures thereof, which have a composition yielding a; saturated aqueous solution of a pHbetween about4' and-about 7 at 25 C. such salts :or saltinixtures can conveniently be prepared byi reacting a phosphoric acidw-ith a basic alkali metal'or' alkaline earthmetal-compound in aqueous solution while adjusting'the proportions to reach thedesiredpI-I level. A preferred type of salt is 'a mixture of monosodiurii 'or'th'ophosphate and disodium orthoprosphate having a 'pH of about 6. Another preferred salt is sodium metaphosphate. Other suitable salts include mixtures-of monopotassium and dipotassiurn orthophosph ates jmixtures of monocalciurn dicalcium ortho-phosphates, and the like, within the broad definitionsetl forth above. The following specific examples will more clearlyillustrate the invention. All of the tests describedtherein were carried out according" to stand'ard methods defined ill: the Foundry Sand Handbook, '6tl'i' edition #1952) published by the American Foundrymens Societyj'fChicago. Except as noted below, all of the testsieinployed fineness of 62 '(.AGI 62). Measurements were based upon tthet'dry weight of, sand-..empl yfiirtbil ll ll sllh carried out in a laboratory-size Simpson muller.. After mulling was completed tlie coreimixture was discharged from the muller and stored'in 'a'sealed can-until used tb make cores? "The cores werebaked'ar 425 "F'."for' 15 minutes, then cooled toj roomltemperature. The strength terms of the time jrequiredfor them to collapse'at 800 the reported results are thelaverag e J Gelstlntzed corn starch Example 1 The following example illustrates the effectiveness of gelatinized amylopectin in combination with mixed sodium orthophosphates as a core binder. The phosphate salt mixture was a blend of disodium orthophosphate dihydrate and monosodium orthophosphate monohydrate in 2.54:1 ratio by weight. The composition and preparation of the core mixtures were as follows:

% water 0.15% phosphate salts 0.85% gelatinized amylopectin Remainder sand The sand and water were mulled 1 minute; the phosphate salt mixture was added and mulled for 1 minute; and the gelatinized amylopectin was added and mulling was continued for 6 minutes. The completed mixture retained 5.1% water. Cores prepared therefrom had a baked strength of 200 p.s.i. and a breakdown time of 11.33 minutes.

For comparison, a core mixture was prepared in a similar manner, omitting the phosphate salts. The resulting cores had a high baked strength, 290 p.s.i., but the breakdown time was only 3.07 minutes.

For further comparison, two core mixtures were prepared with 0.25 and 0.5% of phosphate salts, omitting the gelatinized amylopectin. Cores prepared therefrom had baked strengths of only and p.s.i., respectively, and were not tested for breakdown time.

Example 2 Mixed sodium orthophosphates were dissolved in water and mulled with sand for 1 minute. Gelatinized amylopectin was then added, and mulling was continued for 6 minutes. The materials, proportions, and procedure were otherwise the same as described in Example 1. The cores prepared therefrom had a baked strength of 225 p.s.i. and a breakdown time of 9.90 minutes.

Example 3 The following example illustrates the use of gelatinized whole corn starch in combination with phosphate salts as a core binder. The starch was prepared by wetting it with water and passing it downward between rotating drums heated with steam under pressure. By this means, the starch was simultaneously gelatinized and dried in the form of a thin film. Before use, the starch was ground to a fine state of subdivision. Cores were prepared according to the procedure of Example 1, substituting the gelatinized corn starch for gelatinized amylopectin. The resulting cores had a baked strength of 190 p.s.i. and a breakdown time of 9.57 minutes.

For comparison, three additional groups of cores were prepared in an analogous manner using ungelatinized whole corn starch alone as the core binder, ungelatinized whole corn starch plus the sodium orthophosphate salt mixture referred to above, and gelatinized whole corn starch alone. Cores prepared therefrom were far inferior in breakdown time:

Breakdown Time, min.

Baked Ungelattnized corn starch Same, plus phosphates Example 4 A core mixture was prepared according to the. procedure described in Example 1, using 0.25% of the sodium orthophosphate salt mixture and 0.1% of a standard foundry cereal (i.e., a gelatinized starch preparation). Cores prepared therefrom had a baked strength of 165 p.s.i. and breakdown times of 7.37 minutes at 800- F. and 5.82 minutes at 1000" F.

For comparison, a core mixture was prepared according to the procedure of Example 1, employing only a foundry cereal at the 1.0%. level as the core binder. Cores prepared therefrom had a baked strength of only p.s.i. and a breakdown time of only 1.45 minutes at 100 F.

Example 5 A core mixture was prepared as in Example 1, replacing the sodium orthophosphate mixture with 0.2% of sodium metaphosphate. Cores prepared therefrom had a baked strength of p.s.i. and a breakdown time of 10.64 minutes at 800 F.

The foregoing description refers to numerous details of core mixture composition, preparation techniques, and the like, for the purpose of illustrating and clarifying the invention, but in no respect by way of limitation. It will be apparent that numerous modifications and equivalents of the invention will be suggested thereby to those skilled in the art.

The following claims particularly point out and distinctly claim the subject matter of the invention:

I claim:

1. In a method for producing a foundry core, which method comprises commingling sand, water, and binder, forming the resulting mixture into the desired shape, and baking the shaped mixture at a temperature between about 350 and about 450 F., the improvement which comprises employing as said binder, in combination, at least about 0.5% by weight of gelatinized amylopectin, based on the 'dry weight of sand contained in the core mixture, and a phosphate salt selected from the group consisting of the water-soluble alkali-metal and alkaline-earthmetal phosphates and mixtures thereof which produce a pH between about 4 and 7 in saturated aqueous solution at about 25 C., the proportion of said phosphate salt :being between about 5 and about 25% by weight, based upon said gelatinized amylopectin.

2. The method of claim 1 wherein said gelatinized amylopectin is employed in a proportion between about 0.5 and about 2.5% by weight, based upon the dry weight of sand contained in the core mixture.

3. The method of claim 1 wherein said phosphate salt is an alkali-metal orthophosphate.

4. The method of claim 1 wherein said phosphate salt is a metaphosphate.

5. In the method for producing a foundry core, which method comprises commingling sand, water, and binder, forming the resulting mixture into the desired shape, and baking the shaped mixture at a temperature between about 350 and about 450 F., the improvement which comprises employing as said binder, in combination, gelatinized Whole starch containing between about 0.5 and about 2.5% by weight of gelatinized amylopectin, based upon the dry weight of sand contained in the core mixture, and a sodium orthophosphate of a composition which produces a pH between about 4 and about 7 in saturated aqueous solution at about 25 C., the proportion of said sodium orthophosphate being between about 5 and about 25% by weight based upon said gelatinized amylopectin.

References Cited in the file of this patent UNITED STATES PATENTS 1,531,871 Nagel Mar. 31, 1925 1,974,915 Giesecke Sept. 25, 1934 2,779,693 Pacsu et al Jan. 29, 1957 2,884,412 Neukom Apr. 28, 1959 FOREIGN PATENTS 515,470 Great Britain Dec. 6, 1939 543,202 Great Britain Feb. 13, 1942 7 770,561 Great Britain Mar. 20, 1957 879,150 Germany June 11, 1953 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent. No. 2 974,o5o March '2 1961 I Thomas E. Barlow It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 4 line 6 for "100 F," read 1000 F. V column 4 line 35 for about 4 and '1" read about 4 and about 7 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 A METHOD FOR PRODUCING A FOUNDRY CORE, WHICH METHOD COMPRISES COMMINGLING SAND, WATER, AND BINDER, FORMING THE RESULTING MIXTURE INTO THE DESIRED SHAPE, AND BAKING THE SHAPED MIXTURE AT A TEMPERATURE BETWEEN ABOUT 350 AND ABOUT 450*F., THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS SAID BINDER, IN COMBINATION, AT LEAST ABOUT 0.5% BY WEIGHT OF GELATINIZED AMYLOPECTIN, BASED ON THE DRY WEIGHT OF SAND CONTAINED IN THE CORE MIXTURE, AND A PHOSPHATE SALT SELECTED FROM THE GROUP CONSISTING OF THE WATER-SOLUBLE ALKALI-METAL AND ALKALINE-EARTHMETAL PHOSPHATES AND MIXTURES THEREOF WHICH PRODUCE A PH BETWEEN ABOUT 4 AND 7 IN SATURATED AQUEOUS SOLUTION AT ABOUT 25*C., THE PROPORTION OF SAID PHOSPHATE SALT BEING BETWEEN ABOUT 5 AND ABOUT 25% BY WEIGHT, BASED UPON SAID GELATINIZED AMYLOPECTIN.