US3168490A - Foundry core binder and process for preparation thereof - Google Patents

Description

United States Patent s 168 4% rouunnr Conn Brianna AND Pnocnss non rnnrsnarron 'rrmnnor Lloyd H. Brown, Qrystal Lake, and David D. Watson,

Barrington, 111., assignors to The Quaker Guts Company, (Ihicago, Ill, a corporation of New Jersey No Drawing. Filed July 11, 1960, Ser. No. 41,728 2 Claims. (Cl. 260-294) part of a metal casting. A foundry core binder may be defined as that part of the foundry core which causes adhesion among the sand particles. To a large extent the properties of a foundry core are determined by the properties imparted to it by the particular binder employed. There are certain required properties for a foundry core. It must resist the washing and burning action of a stream of hot metal; it must admit of the free escape of gases; it must impart its internal contour to the metal casting; it must have sutficient tensile strength so that it is not ruptured while being handled or worked; and finally it must collapse and shakeout after the metal casting has hardened.

Various binders have been used in the foundries with varying degrees of success. One of the oldest known binders is the cereal-core oil binder. The main disadvantage of this system is the long curing time required. With the use of high speed automatic equipment a rapid curing binder is very desirable.

Another type of core binder is made from phenolic resins. Because of the high cost of such resins, the binder is used to merely bond a shell instead of acting as a binder throughout the core. The use of phenolic resin type binders results in cores that have a tendency to resist shakeout after the metal casting has hardened, especially with the casting of low melting point non-ferrous alloys. Other disadvantages of the phenolic resin binders are extended curing times for the cores and less than satisfactory tensile strengths.

A third type of core binder is the urea-formaldehyde cereal binder. The core made from this binder collapses too readily on contact with high temperature melting metals and loses strength in a high humidity atmosphere. In the preparation of this binder a solvent is required in order to prevent crystallization or gelling. Water has been employed as this solvent, but its use incurs certain undesirable elfects, such as an extended curing time and excessive shrinkage of the foundry core upon curing. In addition, since the water is not a reactive solvent, it does not in any way improve any of the inherent weaknesses of the urea-formaldehyde resin.

It is an object of this invention to employ a reactive solvent in the preparation of a urea-formaldehyde resin core binder which will substantially improve the properties of the urea-formaldehyde resin core binder and in addition will not give the disadvantages of an aqueous solvent. I

Another object of this invention is to produce a foundry sand binder that imparts to the foundry core an improved tensile strength.

Still another object of this invention is to produce a binder that when mixed with foundry sand cures rapidly so that the sand-binder mixture may be used with highspeed automatic machinery.

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A further object of this invention is to produce a liquid foundry core binder that when mixed with sand, cures at room temperature to form a foundry core which will produce a metal casting free from blowholes produced by the gas evolution from the core.

A still further object of this invention is to produce a liquid binder that gives a foundry core that can withstand the heat from a high melting point metal and yet can be readily shaken out after the metal casting has hardened.

Still another object of this invention is to produce a stable, liquid foundry binder from materials that are relatively inexpensive as compared to many presently used materials.

A further object of this invention is to produce a foundry core binder which gives foundry cores that do not lose strength in a high humidity atmosphere.

A still further object of this invention is to provide a liquid, resinous, foundry core binder that has sufficient stability for storage and shipment in commerce.

in accordance with the invention the above objects are accomplished by a process in which urea, furfuryl alcohol, and a non-polymerized aqueous mixture of formaldehyde, urea, and equilibrium reaction products thereof about 15% by weight water. The resulting solution from the above components is adjusted to a pH in the range of 5.0 to 6.5; however, the preferred range is a pH of 5.5 to 6.0. The said solution is then refluxed at to C. until the solution has a viscosity in the range of 350 to 3000 centipoises if measured at 25 C. A preferred viscosity range for this end point is 400 to 1500 centipoises. In the final step the pH of the solution is adjusted to a range 6.5 to 8.5.

Aqueous UP. mixtures (non-polymerized) are sold in commerce. One example is UP. Concentrate85. Another aqueous U.F. mixture is marketed as Urea-Formaldehyde 25-60. The formaldehyde, urea and equilibrium reaction products thereof, present in aqueous U.F. mixtures are believed to exist in equilibria. as follows:

NH CONH HCHO:NH CONHCH OH NH CONHCH OH-l-HCHO :HOCH NHCONHCH OH HOCH NHcONHCl-l OH-l-HCHO :HOCH NHCON(CH OH) 2 HGCH NHCON CH OH) HCHO (HOCH NCON (CH OH) 2 The above equilibria illustrate What is meant by the phrase a non-polymerized aqueous mixture of formaldehyde, urea, and equilibrium reaction products thereof. Those urea molecules in the equilibria shown above that have more than one methylol radical attached are sometimes referred to as polymethylol ureas. There is difficulty encountered in distinguishing between different polymethylol ureas in aqueous UJF. mixtures. .For this reason the composition of the aqueous U.F. solution is best reported in terms of the weight percent urea and formaldehyde. A typical analysis of aqueous U.F. mixture (U.F. Concentrate-85") shows 59% by weight form- 3 aldehyde, 26% by Weight urea, and at most by weight water.

The total amount of urea and formaldehyde present in the aforementioned solution of this invention is stated in terms of a molar ratio. The amount of urea added separately (as opposed to that urea included in the aqueous UJF. mixture) will vary with the analysis of the particular aqueous U.F. mixture that is employed. Thus the amount of urea to be added separately can be determined from the aforementioned molar ratio and the analysis of the particular aqueous U15. mixture that is employed.

The term available urea refers to free urea as well as urea combined with the methylol group in the equilibria shown above. The term available formaldehyde refers to free formaldehyde as well as formaldehyde combined with urea in the equilibria shown above.

The refluxing end point may be determined by either measuring the refractive index or by measuring the viscosity of the solution. However, measuring the viscosity is the preferred method to determine the refluxing end point. Both the refractive index and viscosity are indicators of the solutions stage of resinification. The stage of resinification is critical because if there is not sufficient resinification the binder solution will be unstable. If the stage of resinification becomes too advanced then the binder solutions high viscosity will prevent proper mixing of the binder with the sand at the foundry.

The invention will be further illustrated but is not limited by the following examples in which the quantities stated in parts are parts by weight unless otherwise indicated. When the percent of binder is stated, it is percent by weight based on the weight of the foundry sand. When the percent of any of the components of the binder (e.g., furfuryl alcohol, catalyst, water) are stated it is percent by weight based on the total weight of the binder, unless otherwise indicated. All tensile strengths are stated in pounds per square inch (p.s.i.).

Example 1 Into 2710 parts of UP. Concentrate-85 were admixed 2025 parts of furfuryl alcohol and 654 parts of urea. The pH of the resulting solution was adjusted to 5.7 by the addition of 58% aqueous phosphoric acid. This solution was then charged into a 3-necked vessel equipped with a stirrer, thermometer and reflux condenser. The solution was heated to 100 C. over a period of one hour, and then refluxed at about that temperature for an additional two hours. The degree of rcsinification was observed by checking the viscosity at regular time intervals. When a withdrawn sample of the solution had a viscosity of 380 centipoises at 25 C. as measured by a Brooklield viscometer, the refluxing was discontinued and 28 parts of sodium phosphate (in 125 parts of water) were admixed to give a pH of 8.08. Upon cooling the resulting binder composition was a slightly cloudy, light-amber liquid.

Example 2 The procedure of Example 1 was repeated except that only 983 parts furfuryl alcohol were admixed with the U.F. Concentrate-85, and the pH of the solution was adjusted to 5.9 by the addition of 50% aqueous phosphoric acid. The progress of the resiniiication during the refluxing was observed by determining the time required for a sample of the hot solution to drain from a standard consistency cup with a orifice. When there was sixty second draining time, the refluxing Was discontinned andthe solution was neutralized to a pH of 8 with 13 parts of NaOH in parts of water. Upon cooling the resulting binder composition was a slightly cloudy, light-amber liquid.

Example 3 To show the importance of the addition of furfuryl alcohol to the aqueous UP. mixture, binders were prepared essentially as described in Example 1 but with varying amounts of furfuryl alcohol. Foundry cores were then produced employing these binders. To produce the foundry cores, the binders were mixed with sand and catalyst in the proportions shown below and the resulting mixtures rammed into 1% x 2" core boxes. The resulting cores were removed from the core boxes and cured in an oven at 425 F. for 5 minutes. The cured cores were then placed in a Dietert Thermolab Dilatometer at 1590 F. and 2500" F. for 5 minutes. A compressive load was applied. I-lot strength at failure in pounds per square inch was determined. The following results were obtained for three cores employing 1.5% binder:

Percent Hot Strength Core Furfuryl Alcohol in Binder 1,500 F. 2,500 F.

The following results were obtained for three cores employing 2.0% binder:

Percent Hot Strength Core Furfuryl Alcohol in Binder 1,500 F. 2,500 F.

From the above results it is seen that the addition of furfuryl alcohol to the binder appreciably increases the hot strength.

Example 4 The procedure of Example 3 Was repeated except that the cores were A" x 2 and were cured on a hot plate at 237 C. At specified intervals while on the hot plate the foundry cores were tapped lightly with a spatula. The curing time was determined from the beginning of the baking period to that time when an indentation was no longer made by the spatula. The following results were obtained. The term solids refers to all ingredients other than water in the binder before resinification. All percentages given are by weight and based on the binder.

Percent Cure Core Furfuryl Percent Percent Time Alcohol in Solids Catalyst (seconds) Binder The above results show that if the solids content of the binder is lowered, a greater curing time is required.

Example 5 Percent Core Furfuryl Tensile Alcohol in Strength Binder H V E3 The following results were obtained for Thus the addition of furfuryl alcohol to the core binder increases the tensile strength of the core.

Example 6 If there is excessive gas evolution from a foundry core While hot metal is being poured around the core, blow holes may result in the metal casting. To test for gas evolution the procedure of Example 3 was essentially repeated except that the cores were cured at room temperature. The cores were crushed and ten gram samples of the crushed material were placed in porcelain boats which were inserted in a combustion tube maintained at 1800 F. This test simulated the conditions obtained when hot molten metal is poured around a foundry core. The gas evolved was collected in a burette at 120 C. over silicone oil. The total volume of gas collected at 125 C. was measured in milliliters. The pressure was equalized to atmospheric pressure. From cores made with binders having 1.8% by weight solids (based on sand), 25% furfuryl alcohol, and with varying percentages of water (percent by weight of binder) the following results were obtained:

Core Percent Volume Water of Gas The above results show considerably less gas evolution for high solids binder (low water content) when the foundry cores are cured at room temperature.

Example 7 Room temperature curing and oven curing are two separate methods of curing foundry cores. Oven curing is desirable for some uses because the foundry cores moisture content is lowered during the heating. Foundry 0 fromthis invention. The procedure for determining gas evolution from the foundry cores was repeated as in Example 6. The total volume of gas (in milliliters and percent collected at 120 C.) evolved was measured at succes- Core mx Tensile sive time intervals from the time the core was initially Alcohol in Strength a Bi exposed to the 1800 F. temperature. The results were as follows:

r Time (Minutes) Core 1 Core 2 Core 3 The following results were obtained for 3 cores employg9 33 i 162 110 95 Hg 3% bmder 163 115 100 172 gs 198 Percent 176 0 5 Core Furturyl Tensile Algcpigfm Strength 187 142 132 7 0 350 The tensile strength of core 1 was only 300 p.s.i.; while 2 e 258 90 cores 2 and 3 had a tensile strength of 500 p.s.i. To

raise the tensile strength of core 1 to the level of the cores 2 and 3 would require an inrcease in the percent of binder. Since the amount of gas evolved is directly proportional to the amount of binder employed in the core, core 1 would evolve an even greater volume of gas if sufiicient additional binder were employed to give a tensile strength equivalent to that of cores 2 and 3. The amount of gas evolved during the first few minutes of exposure to the molten metal is especially critical. During the first few minutes of exposure before there has been an appre ciable amount of solidification of the molten metal, the gas evolved can cause more blowhole damage, than later evolved gas. The superiority of the cores produced by the binders of this invention is apparent from the aboveresults which show that there is considerably less gas evolution from cores produced by the binders of this invention, particularly during the first few minutes of heat exposure.

We claim: v

1. A process for the preparation of a stable, liquid,

resinous, foundry core binder comprising the steps of,

(a) forming a solution from an aqueous mixture of formaldehyde, urea and methylol ureas, said aqueous mixture containing at most about by weight of water; and furfuryl alcohol; the molar ratio of total available urea to available formaldehyde in said solution being in the range of about 1:1.75 to 1:30, said furfuryl alcohol being present in said solution in such amount that it constitutes about 15 to by weight of said solution;

(b) adjusting said solution to a pH in the range of about 5.0 to 6.5;

(c) then refluxing the adjusted solution at about to C. until the adjusted solution has a viscosity in the range of about 350 to 3000 centipoises if measured at 25 C.; and

(d) then adjusting the refluxed solution to a pH in the range of about 6.5 to 8.5.

2. A foundry core binder prepared according to the process of claim 1.

FOREIGN PATENTS Canada Aug. 14, 1956

Claims (1)

1. A PROCESS FOR THE PREPARATION OF A STABLE, LIQUID, RESINOUS, FOUNDRY CORE BINDER COMPRISING THE STEPS OF, (A) FORMING A SOLUTION FROM AN AQUEOUS MIXTURE OF FORMALDEHYDE, UREA AND METHYOL UREAS, SAID AQUEOUS MIXTURE CONTAINING AT MOST ABOUT 15% BY WEIGHT OF WATER; AND FURFURYL ALCOHOL; THE MOLAR RATIO OF TOTAL AVAILABLE UREA TO AVAILABLE FORMALDEHYDE IN SAID SOLUTION BEING IN THE RANGE OF ABOUT 1:1.75 TO 1:3.0, SAID FURFURYL ALCOHOL BEING PRESENT IN SAID SOLUTION IN SUCH AMOUNT THAT IT CONSTITUTES ABOUT 15 TO 50% BY WEIGHT OF SAID SOLUTION; (B) ADJUSTING SAID SOLUTION TO A PH IN THE RANGE OF ABOUT 5.0 TO 6.5; (C) THEN REFLUXING THE ADJUSTED SOLUTON AT ABOUT 95* TO 105*C. UNTIL THE ADJUSTED SOLUTION HAS A VISCOSITY IN THE RANGE OF ABOUT 350 TO 3000 CENTIPOISES IF MEASURED AT 25*C.; AND (D) THEN ADJUSTING THE REFLUXED SOLUTION TO A PH IN THE RANGE OF ABOUT 6.5 TO 8.5.