US3278316A - Foundry sand composition - Google Patents

Description

United States Patent of Maryland No Drawing. Filed Mar. 21, 1960, Ser. No. 16,117

7 Claims. (Cl. 106--38.6)

The [present invention relates to molding sands of the type used in casting nonferrous metals and alloys. The invention relates especially to improved waterless molding sands.

Green molding sands are made by binding sand grains with clay, usually a bentonitic clay, and tempering the composition with water. In recent years so-calle-d waterless molding sands have come into Widespread use. These sands .are produced by binding the sand grains with a small quantity of a hydrocarbon oil-thickening agent, with oil being used as the tempering agent. An important advantage of the waterless molding sands is that casting flaws caused by steam generated when the molten metal contacts the mold are obviated. Oil, unlike water, does not produce large quantities of gaseous decomposition products which become occluded in the mold during casting and thereby produce flawed castings.

One of the hydrocarbon oil-thickening agents that has been suggested is an onium clay, such as dimethyldioctadecyl-ammonium bent-onite. Onium clays may be produced by stoichiometrically replacing inorganic cations of a clay having a high base'exchange capacity with the long chain radical of an amine containing nitrogen in pentavalent state. Usually bentonite clay is employed in the production of onium clays because it has a higher base-exchange capacity than other clays. In making up waterless foundry sands with oil and onium clays, a methanol catalyst is required in order to obtain a molding sand of good green strength. Also, relatively long mulling times, such as minutes, must be employed to obtain sands of satisfactory green strength.

It has been found that these disadvantages, among others, may be obviated by employing as the thickening agent colloidal attapulgite clay together with an oleophilic surface active agent. The resultant molding sands have exceptionally high green strength as well as good permeability and, especially when high viscosity oils are employed, produce castings of exceptionally fine finish. In producing this type of waterless sand, the surface active agent may be mulled with the oil, sand, and attapulgite clay. Preferably, the surface active agent is uniformly adsorbed or coated on the clay particles before the clay is introduced into the muller. This simplifies material handling and assures reproducible result-s.

In addition to the advantages mentioned above, attapulgite clay waterless sands formulated with an appropriate surface active agent have exceptionally high green compressive strength, typically within the range of 8.0 to 14.0 p.s.i.

Although the use of attapulgite clay together with an oleophilic surface active agent permits the formulation of relatively inexpensive waterless molding sands with short mulling periods and without the use of methanol catalyst, certain difliculties are experienced in the foundry when waterless sands of this nature are utilized. These difliculties are .most pronounced when the sands are formulated with oils of relatively low viscosity, such as oils having viscosity less than 2000 S.S.U. at 100 F. Attapulgite waterless sands made up with these relatively low viscosity oils have been found to require heavy ra-mming in order to make up a mold which will not require patching when the pattern is withdrawn. On the other hand, the nature of waterless sands formulated with onium bentonite clay-s is such that softer ramming may be used 3,278,316 Patented Oct. 11, 1966 successfully. It is known that many commercial foundries do not have the equipment for heavy ramming and consequently have to ram less hard with a resultant loss of detail in the cast piece and the necessity of undesirable patching of the mold. The ease of making up a mold with a green sand is usually referred to as the moldability of the sand. The relatively poor moldability of attapulgite waterless sands formulated with oils of low viscosity restricts the use of this type of product to formulations utilizing high viscosity oils or to foundries in which heavy ramming can be accomplished.

Still another disadvantage of attapulgite clay waterless sands is their relatively poor patching properties. During the preparation of a mold, portions of the molding sand are sometimes broken off or cracked. When this happen-s, the operator can either repair the cast metal piece to remedy the defect caused by the broken mold or he can repair or patch the mold. Patching is accomplished by pressing out a crack or, in the case that a portion of the molding sand is broken off, a fresh portion of molding sand is inserted and pressed into place. Obviously, patching is the simpler remedy and is preferred. When attapulgite clay waterless green sands are use-d, the foundryman can resort to mold patching only with difficulty.

Accordingly, a principal object of the present invention is the provision of means for obviating the abovementioned difiiculties and disadvantages of attapulgite clay waterless green sands.

A 'more particular object of the invention is the provision of attapulgite clay Waterless green molding sands which have improved moldability and patching properties without appreciable sacrifice in the high green strength and other desirable properties normally characteristic of molding sands of this type.

A further object of this invention is the provision of a simple, inexpensive method for realizing the above-mentioned improvements in attapulgite clay waterless sands.

Still another object of my invention is the provision of attapulgite clay waterless molding sands in which higher quality castings may be produced.

These and further objects and advantages of my invention will be readily apparent to those skilled in the art.

I have discovered a simple and inexpensive method of attaining exceptional improvements in the moldability and patching properties of waterless foundry sands made up with attapulgite clay.

Briefly stated, in accordance with the present invention, a small quantity of finely divided particles of the phenolic, petroleum hydrocarbon-insoluble fraction of wood rosin is incoporated in a molding sand made up by binding sand with a nondrying hydrocarbon oil, colloidal attapulgite clay and an oleophilic surface active agent. The surface active agent may be uniformly coated on the clay particles before the clay is mulled With the sand or the clay and the surface active agent may be incorporated separately.

Molding sands of my invention are useful in making up molds employed in the casting of nonferrous metals or alloys, such as aluminum, bronze and copper. If desired, the novel molding sands may be employed only as the facing sand. The moldability and patching qualities of sands of this invention represent a substantial improvement over those of prior art waterless sands containing attapulgite clay and suitable surfactant. These improvements are reflected in the superiority of metals cast in molds made up from the sands, especially the substantial freedom of such castings from pinholing, washing and inclusion of sand grains and rough surface.

More specifically, the resinous additive I employ is usually known by its trade name Vinsol. Vinsol resin is an extract from southern pine wood. The resin ob- Q tained from the aged virgin pine stump by a procedure involving the step of extracting dried wood chips with an aromatic solvent. The production of the resin is described in US. Patent No. 2,193,026 to L. C. Hall. Vinssol resin is a hard, brittle, high-melting thermoplastic material which is a complex mixture of various chemical components including acidic materials derived from rosin acids and oxidized rosin acids, neutral high-molecular weight compounds and acidic phenolics such as substituted phenolic ethers, polyphenols and other high-molecular weight phenolic compounds. The phenolic constituents account for an appreciable fraction of the Vinsol. Some of the properties of a typical Vinsol resin are:

Acid number 94 Methoxy content (ASTM), percent 5.3 Molecular weight (average) 470 Oxygen absorption (300 p.s.i., 7 days), percent 0.25 Saponification number 165 Unsaponified matter (ASTM D1065), percent 7.7 pH of a water-alcohol solution 4.4 Softening point, hercules drop method, C 115 Color dark Density at 20 C 1.218 Gasoline-soluble matter, percent 12 Toluene-insoluble matter, percent 20 I employ the resin in finely divided form and find the commercially available pulverized grade of Vinsol to be eminently satisfactory. This grade has a particle size distribution such that 100 percent by weight is finer than 20 mesh, 85 percent is finer than 80 mesh and 50 percent is finer than 200 mesh. Finer and somewhat coarser grades of the resin may be used.

The Vinsol is insoluble in the type of oil I employ in the practice of my invention. Apparently the fine Vinsol particles are present in my improved molding sand as a dispersion in the oil.

Vinsol is very inexpensive and adds little to the cost of the molding sand. When incorporated in the sand, the Vinsol effects a very marked change in the consistency and texture of the sand. By way of illustration, attapulgite clay waterless molding sands containing a suit-able quantity of powdered Vinsol resin have a spongy feel to the hand, whereas in the absence of Vinsol, the molding sands are grainy and lack resiliency.

The sand I usually employ is silica sand which may consist of new sand, burnt sand, or mixtures thereof. Zircon and olivine 'sandsmay be used for specific applications. Normally, the sand I employ has an AFS Grain Fineness Number within the range of 80 to 160, although coarser or finer sand may be used.

The oil I employ is a nondrying petroleum hydrocarbon oil which has a flash point greater than about 350 F. A wide variety of naphthenic, aromatic or parafiin petroleum stocks or mixtures thereof are useful for the purpose. Oils of a wide range of viscosity, for example, 100 to 3000 S.S.U. at 100 F., are suitable. A conventional petroleum lubricating oil or mineral oil is recommended. The beneficial effect of the Vinsol is most apparent when oils having a relatively low viscosity are employed in making up the molding sand.

The attapulgite clay I employ is a colloidal grade, by which is meant attapulgite clay which is dispersible in water into its ultimate colloidally dimensioned lath-like particles. I may employ the raw clay which has merely been crushed and, if desired, degritted to remove coarse particles and agglomerates. The raw clay as mined has a volatile matter content of about 48 percent and a free moisture content of about 35 percent. The term volatile matter (V.M.) refers to the weight percentage of a material eliminated by heating it substantially to constant weight at 1800 F. The term free moisture (F.M.) as used herein refers to the Weight percentage of a material eliminated by heating the material substantially to constant weight at 250 F. In the case of pure clay, volatile matter and free moisture are chiefly water. I prefer to employ attapulgite clay which has been dried somewhat, as to a V.M. of 20 to 25 percent and a EM. of about 10 to 15 percent. Clays which have been dried to a V.M. as low as about 10 to 13 percent may be used. Clay which has been dried to a V.M. lower than 10 percent has its colloidal properties irreversibly impaired or lost and is not useful in the practice of the present invention.

A typical analysis of attapulgite clay on a volatile free (V.F.) clay basis, is as follows:

SiO 67.0

A1 0 12.5 F6 0 4.0 MgO 11.0 CaO 2.5 Others 3.0

Any oleophilic surface active agent may be employed in the production of my improved molding sand provided it is one which enables colloidal attapulgite clay to gel the hydrocarbon oil when the clay is dispersed in the oil in the presence of the surface active agent. I have found that the beneficial effects of the Vinsol are apparent in oil tempered sands formulated with attapulgite clay and oleophilic surfactants of diverse chemical and ionic nature.

The preferred surfactant is an oleophilic Water-dispersible, nonionic fatty acid amide. Many surface active agents have been evaluated for the purpose and the fatty acid amides, especially fatty acid alkanolamides (and fatty acid dialkanolamides) have been found superior because they result in the production of molding sands of exceptional green compressive strength at very low cost. This class of amides is less toxic than many surface active agents which facilitate the dispersion of attapulgite clay in hydrocarbon oils. Another important advantage of members of this class of surface active agents is that they are water-dispersible and therefore they can be readily coated on the clay by replacing native free moisture of the clay in a manner hereafter described. The fatty acid amide surface active agent .I employ is one which may be represented by the following structural formula:

wherein: R is selected from the group consisting of alkyl and alkenyl groups having from 7 to 17 carbon atoms; R is an alkylene group having from 2 to 4 carbon atoms; R is selected from the group consisting of hydrogen, alkyl and alkanol groups having from 2 to 4 carbon atoms; and X is selected from the group consisting of hydrogen and hydroxyl.

Mixtures of amides may be used. As examples of the preferred alkanolamides may be cited oleic acid diethanolamide, coconut fatty acid monoethanolamide, stearic acid diethanolamide, stearic acid monoethanolamide, and lauric acid monoethanolamide.

Another class of surface active agents which is useful in carrying out the present invention are N-aliphatic alkylene diamines of the formula:

wherein: R is an aliphatic hydrocarbon radical having from 12 to 22 carbon atoms and x is an integer of from 2 to 10.

N-aliphatic trimethylene diamines of this type are commercially available under the trade name Duomeen. These polyamines are useful also in the form of salts with higher aliphatic fatty acids (e.g., C and N-aliphatic aminoaliphatic carboxylic acids. The latter acids are formed by reacting a long chain amine and an unsaturated acid or ester such as crotonic, acrylic, etc.

Still another class of surface active agents which are useful in producing molding sands of the present invention are imidazolines of the following structural formula:

wherein: R is a member of the group consisting of saturated and unsaturated aliphatic groups containing from 7 to 17 carbon atoms; and R is a member of the group consisting of hydrogen, alkyl groups containing 1 to 3 carbon atoms, hydroxy-substituted alkyl groups containing 1 to 3 carbon atoms and amine-substituted alkyl groups containing l to 3 carbon atoms.

The imidazoline supplied under the trade name Amine 0 and consisting chiefly of 1-beta-hydroxyethyl-Z-heptadecenyl glyoxalidine is representative of this class of surface active agents.

Although several types of suitable surface active agents have been mentioned, it will be apparent to those skilled in the art that others may be employed.

The approximate proportions of essential ingredients I employ in producing my improved waterless green sands are as follows:

Parts by weight Sand 100.

Hydrocarbon oil 3-7.

Colloidal attapulgite clay 2-5 (as is clay basis).

Surface active agent 15 to 50% (based on V.F.

clay weight).

Powdered Vinsol A to 2 (preferably to As mentioned, in accordance with a preferred embodiment of my invention I employ attapulgite clay which has been previously uniformly coated with the surface active agent. Using the precoated clay, I employ the surface active agent in amount from 15 percent to 40 percent, based on V.F. clay weight.

I have found that when the powdered Vinsol is employed in amount less than about A percent, based on the weight of the sand, the improvement in the moldability and patching properties of the sand is not appreciable. The green strength of the sand is decreased to an undesirable level when Vinsol is employed in amount in excess of about 2 percent of the sand weight. The optimum quantity of Vinsol for any system can readily be found by simple experimentation.

It will be readily apparent to those skilled in the art of making clay-bodied greases, that the quantity of clay I employ is considerably greater than that required to gel the oil when it is dispersed therein in the presence of the surface active agent.

It has been mentioned that I preferably employ colloidal attapulgite clay which is uniformly coated with a surface active agent. Suitable coated clays are commercially available under the trade names Britecast 0 and Britecast 0-1. Waterless foundry sands formulated with onium bentonites do not appear to be benefited by incorporation of the Vinsol resin. The clay may be coated with the surface active agent by spraying, impregnation or by dry milling the surface active agent (or solution thereof) with the clay. When the surface active agent is Water-dispersible, as is the case of the preferred alkanolamides, a recommended coating procedure inv-olve-s mixing attapulgite clay having a RM. content of at least 25 percent to apparent uniformity with the surface active agent. The mixture is dried (at a product temperature not to exceed about 250 F.) to a F.M. content not less than about percent, and preferably about 12 percent to about 20 percent. The dried product is then ground to particles substantially all finer than 325 mesh. In carrying out this procedure, some but not all of the native free moisture of the attapulgite clay is replaced with the water-dispersible surfactant. As a result, a high degree of uniformity of coating is obtained.

In making up molding sands of the invention, mullers of the type used in foundries for making up conventional water-tempered sands will be useful. The usual procedure will be to add the sand to the muller and incorporate the Vinsol and colloidal attapulgite (coated with surface active agent or uncoated). The dry mixture is mulled for a short time, such as /2 to 2 minutes. The oil (and surface active agent, in the case uncoated clay is employed) is then added to the mixture and the whole mulled for about 3 to 5 minutes.

Although the molding sands of the instant invention comprise as essential components, sand, and small quantities of attapulgite clay, nondrying oil, surface active agent and powdered Vinsol, it will be distinctly understood that the compositions as described and claimed may contain also such additional ingredients as are sometimes incorporated in waterless foundry sand-s such as, for example, finely divided iron oxide, silica flour, oil inhibitors, metal deactivators, boric acid and sulfur. Also, in addition to the small but finite quantity of water inherently present in the colloidal attapulgite clay com ponent of the sand composition, for some applications I may incorporate very small additional quantities of water in the molding sand, such as /2 percent of the sand weight.

The following example is given to illustrate my invention more fully.

Tests were conducted to illustrate the beneficial effect of Vinsol resin on strength, moldability, and patching characteristics of oil tempered molding sands containing attapulgite clay coated with various surface active agents. Tests were also conducted to correlate the effect of incorporating Vinsol resin in such sands on the properties of alloys cast in the sands. Various ratios of oil and surfactant-coated clay were employed in the study and oils ranging from high viscosity to low viscosity were used.

Imidazoline-coated attapulgite clay and fatty acid alkanolarnide-coated attapulgite clay were used in making up the test sands. In producing the coated attapulgite clays, attapulgite clay from a deposit near Attapulgus, Georgia was used. Four hundred parts by weight of the raw clay, crushed to 2/ 4 mesh and having a V.M. of about 50 percent and a F.M. of about 44 percent, was mixed in a pug mill with 66% parts by weight of the tallow fatty acid amide of diethanolamine. Four parts by weight of water was added to make the mix extrudable and the mixture was extruded in an auger extruder. The extrud-ate was dried to a free moisture content of about 25 percent in a kiln under conditions such that the product temperature did not exceed 250 F. The dried material was ground through a hammer mill and reground through a micropulversizer to a fineness of percent minus 325 mesh. The V.M. of the ground product (Coated Clay A) was about 20 percent. The same procedure and relative proportion of ingredients were employed in producing colloidal attapulgite clay uniformly coated with 1- beta hydroxyethyl 2-heptadecenyl-glyoxalidine (Coated Clay B). The compositions of these two coated clays are as follows:

The physical properties of the petroleum hydrocarbon oils used in the study are listed below.

The sand was #120 silica sand. The Vinsol used in experimental molding sands was a pulverized grade, 100 percent minus 20 mesh.

In making up the molding sands, dry solid ingredients were mulled in a Simpson Intensive Muller for a minute, the oil added and the whole mulled for 5 minutes.

Green compressive strength and green surface hardness of all molding sands were determined by the procedure described in Foundry Sand Handbook, published by American Foundrymens Society, Sixth Edition (1952). Test specimens were prepared in accordance with the method described in this reference.

The various test molding sands were used in making up molds for producing test castings from both aluminum and a bronze alloy. The test casting was a box having concave and convex curved interior sections.

The sands were rated for moldability and patching characteristics as follows:

Moldability rating Poor (p)Major breaks in sand on pattern withdrawal. F air (f)-Minor breaks in sand on pattern withdrawal. Excellent (e)Virtually no breaks in sand on pattern withdrawal.

Patching characteristics Very poor (vp)Practically unpatchable. Poor (p)--Difficult to patch.

Fair (f)Reasonably easy to patch. Good (g)Patches easily.

In evaluating castings produced in molds of the various test sands, sprues and runners on finished castings were examined for breakdown and erosion which had occurred during metal pouring. Each cast piece was also examined for evidence of sand inclusion, pinholing or any traces of thermal instability of the molding mixture. The following criteria were used in evaluating the castings: Poor (p)Extensive pinholing, washing and inclusion of sand grains. Generally rough surface (indicative of poor moldability).

Fair (flfiSlight pinholing and washing. No sand inclusion. Smoother surface than castings rated poor. Good (g)-No pinholing, Washing or inclusion of sand.

Better surf-ace than castings rated fair.

Excellent (e)Very smooth surface with no defects.

Molding sand formulations, corresponding physical properties and results of castings in molds produced from the test sand compositions are given in the accompanying table.

The results reported in the accompanying table show that in every instance the use of the Vinsol resin improved the moldability and patching characteristics of the oil tempered green sand formulated with surfactant coated a t tapulgite clay. This effect was particularly pronounced in the case of molding sands formulated with the lower viscosity oils, i.e., the 150 Coastal oil and 85B oil. The data show that the Vinsol tended to lower the green compressive strength of the molding sand; however, the green compressive strength of sands containing the resin were above 8.0 and well within the range acceptable to foundry operators. The resin improved the surface hardness of all sands in which it was incorporated.

The data show also the correlation between moldability and patchability of green sands with quality of cast metals. The result of improving the moldability and patchability of the green sand by incorporation of the resin in the sand was a corresponding improvement in the quality of the casting.

EFFECT OF VINSOL RESIN ON PROPERTIES OF WATERLESS GREEN MOLDING SANDS PRODUCED WI'III SURFACE ACTIVE AGENT-COATED ATTAPULGITE CLAY Green Sand Composition Green Sand Characteristics Casting Results Coated Coated Vinsol resin, Green eom- Green Patching Oil parts Oil type clay 13 Clay A parts by pressive surface Moldcharacter- Aluminum Bronze alloy by wt. parts by parts by wt. strength, hardness ability istics alloy (85 5-55) wt. wt.

6 150 Coastal 6 12.0 55 P VP F (Some P (Consider- Washing). able Washzi g). 6 0.5 11.0 ome 6 Washing). 6 6 1. 0 9. 2 4 6 12.8 4 6 1. 0 10. 4 4 6 13.3 F (Some Washing). 4 6 1. 0 13. 3 G. 4. 25 6 1. 0 11. 5 5 6 13.3 4. 5 6 1.0 8. 3 3. 5 d0 6 12. 5 4. 5 Procoil 2500A. 6 14. 8 4. 5 do 6 1.0 14.7 6 150 CoastaL... 10.0 6 1. 0 8. 5 4. 5 11. 5 4. 5 1.0 8.7

1 For 100 pounds #120 silica sand.

2 Attapulgite clay coated with 33%% (V.F. Clay basis) of l-beta-hydroxyethyl-2-heptadeeenylglyoxalidine. 3 Attapulgite clay coated with Bil 5% (V.F. clay basis) 01' tallow fatty acid amide oi diethanolannne.

I claim:

1. An improved molding sand useful in the precision casting of metals which consists essentially of a mixture of sand, and small quantities of a nondrying hydrocarbon oil, colloidal attapulgite clay, .an oleophilic surface active agent which enables said attapulgite clay to gel said oil and from A to 2 parts by weight per 100 parts by weight of sand of finely divided particles of a petroleum hydrocarbon-insoluble fraction of wood rosin.

2. An improved molding sand useful in the precision casting of metals which consists essentially of 100 parts by weight of sand, 3 to 7 parts by weight of a nondrying hydrocarbon oil, 2 to 5 parts by weight of colloidal attapulgite clay, 15 to 50 percent, based on the volatile free weight of said clay, of an oleophilic surface active agent which enables said attapulgite clay to gel said oil and from A to 2 parts by weight of finely divided particles of a petroleum hydrocarbon-insoluble fraction of wood rosin.

3. An improved molding sand composition which con sists essentially of 100 parts by Weight of sand, 3 to 7 parts by weight of a nondrying hydrocarbon oil, about 2 to 5 parts by weight of colloidal attapulgite clay, the particles of said clay being uniformly coated with from 15 to 40 percent, based on the volatile free weight of said clay, of an oleophilic surface active agent which enables said attapulgite clay to gel said oil and from A to 2 parts by weight of finely divided particles of a petroleum hydrocarbon-insoluble fraction of wood rosin.

4. In the preparation of a waterless molding sand involving mulling sand with small quantities of nondrying hydrocarbon oil, colloidal attapulgite clay, and an oleophilic surface active agent which enables said attapulgite clay to gel said oil, the method of improving the moldability and patching properties of said molding sand which comprises mulling with said sand from A to 2 percent, based on the weight of said sand, of finely divided particles of a petroleum hydrocarbon-insoluble fraction of wood rosin.

5. The composition of claim 2 wherein said particles of petroleum hydrocarbon-insoluble fraction of wood rosin are present in a mount of to 1% parts by weight.

6. The composition of claim 3 wherein said particles of petroleum hydrocarbon-insoluble fraction of wood rosin are present in amount of /1 to 1% parts by weight.

7. The method of claim 4 wherein said particles of petroleum hydrocarbon-insoluble fraction of wood rosin are present in amount of to 1% percent.

References Cited by the Examiner UNITED STATES PATENTS 2,813,035 11/1957 Sauter et a1 106-38.7 2.834,741 5/1958 Bleuenstein 10638.6- XR 2,885,360 5/1959 Haden et a1 10638.7

I R. SPECK, Primary Examiner.

H. M. MCCARTHY, Assistant Examiner.

Claims (1)

1. AN IMPROVED MOLDING SAND USEFUL IN THE PRECISION CASTING OF METALS WHICH CONSISTS ESSENTIALLY OF A MIXTURE OF SAND, AND SMALL QUANTITIES OF A NONDRYING HYDROCARBON OIL, COLLOIDAL ATTAPULGITE CLAY, AND OLEOPHILIC SURFACE ACTIVE AGENT WHICH ENABLES SAID ATTAPULGITE CLAY TO GEL SAID OIL AND FROM 1/4 TO 2 PARTS BY WEIGHT PER 1O0 PARTS BY WEIGHT OF SAND OF FINELY DIVIDED PARTICLES OF A PETROLEUM HYDROCARBON-INSOLUBLE FRACTION OF WOOD ROSIN.