US2381242A - Molding sand and method of controlling flowability of same - Google Patents

Description

Patented Aug. 7, 1945 TIDILING FLOWABIIJ'I'Y 01'' 1mm in Wood, Cleveland, on, ma Alu- America,

minum Company of corpora tion of Pennsylvania u h. Pa a No Drawing. Application November :1, 1941,

' sel'lll No. new:

s Claims. (oi. 22-10:)

I This invention relates to the art of casting metal members in sand molds, and is more particularLv concerned with the provision of a method or controlling, increasing, and maintaining the flowability of used green sands.

. In present sand foundry practice, green sands areemployed for the casting ct a variety of metals, including the light metals aluminum, magnesium, and their alloys. The constituents of such sands vary somewhat, depending on the use to which they are put, but most of them contains clay bonding material. Sands used for ma'singmolds in which magnesium is cast are usually bonded with bentonite and contain certain additional substances toinhibit oxidation of the molten metal. For example, relatively small amounts of various inhibiting agents such as boric acid and sulfur are introduced into the sand. Such substances as glycerine, ethylene I glycol, diethylene glycol, or otherpo yhydric alcohols which are disclosed in U..S.' Patent No. Q 1,888,453 are frequently employed, usually in combination with the boric acid and sulfur. The" use of small amounts of certain fluorides that 25 of substances which control the flowability and will decompose or vaporize has been proposed asanother-means of inhibiting oxidation of molten magnesium in sand molds.

Itis important-that molding sand possess ir- 1 'so its shape during handling and operations.

taln desired p ysical characteristics. It should be relatively strong so that the mold will retain However, while the sand should have-the requisite strength, it should not possess this property in such high degree as to be regarded as tough The sand should also be relatively flowable, that is',-take the shape of the pattern easily when the moldis being made. This property of flowability Y permits the sand, when rammed, to conform to every portion or the pattern, and thus enables the production of castings having sharply deflned contours and smooth surfaces.

In ordinary foundry practice, the molding sand is used over and over again, and it is de-' sirable that the sand retain its initial P11181011 properties throughout the period of use. Ithas been found; however. that with continued usage sands bentonite'or other-similar bonding materials have a tendency to become somewhat toughersnd less flowable. .Buch bonding materials are herein referred to as argillaceous bonding substances; This tendency seems tobe '4 cent sulfur, Ito-2 per cent'boric acid, with orwinioui about 1.5 to 2.5 per cent by weight orglycol or other suitable inhibiting agent.

makes is ramming of the molds much more diflicult. It is not fully understood why this decrease in flowability should occur, but it is" thought to relate, to-the polymerization and colloidal suspension or various constituents in the It is, therefore, an object of this invention to overcome the foregoing deficiency of used molding sands. More particularly, it is an object toprovide a means of restoring the initial flowability of a used molding sand and to control the same throughout the subsequent period of use of the sand. Astiil further object-is to attain such results inmolding sands used in the casting of light metals, particularly magnesium.

I have discovered that potassium fluoride, or sodium fluoride, or both, when introduced into tough sand in suitable amount, reduce the toughness and increase the flowability. 'I'hroughuse of these compounds, it is possible not only to attain these results but also to control them throughout the subuquent period of use of the sand. I'brthepurpose of my invention, these fluorides are considered as constituting a group toughness of molding sands containing bentonite or similar argillaceous bonding material. While 1 either of the fluorides, or mixtures of them, may be employed, I prefer to use potassium fluoride since this material 'seems to give somewhat superior results. In general, the type of molding sands to which I propose to add sodium or potassium fluoride may'be either natural or synthetic. Synthetic ll sands generally contain a mixture of about 90 to! percentsharpsillcasand andaboutflt'o 5 per cent bentonite or other similar bonding mawhereas. natural molding sands usually contain an even larger per cent of a bonding medium. To either y e of sand I add about 0.10 to 2.0 per cent of either sodium fluoride or potassium fluoride, and where a mixture is employed, the total amount should not exceed about iper cent nor should the minimum amount or each fluoride be less than 0.1 per cent, though,

as stated above. I prefer to employ only potassium fluoride. when this latter substance is employed;

it is iserably added within the limits of 0.25

to 0.5 per cent. These flgures represent "by weight of his in addition to .the above named substances, a suitable magnesiumnioldingeandwillalsocontainltoiiper The sodiumand potassium fluoride addition has very little, it any, oxidation inhibiting eflect in magnesium molding sands, and therefore cannot be considered as belonging to the group of oxidation inhibitors used in such sands.

It has been noted that with the continued usage of the sand to which sodium or potassium fluoride has been added, some small loss oi the added fluoride may occur. In such instances it is very important that the fluoride content of the sand be maintained within the approximate limits indicated above by suitable additions from time to time. The fluorides of sodium and potassium are nevertheless relatively stable substances in comparison with organic compounds or other substances which are added to molding sands, especially magnesium. molding sand, that decompose or vaporize and escape irom the sand.

Having thus described my invention,

1 claim:

1. The method of controlling the flowability of used molding sands containing an argillaceous bonding material which comprises adding thereto, and maintaining therein, from about 0.1'to 2 per cent of at least one fluoride oi the group consisting of sodium fluoride and potassium fluoride.

2. The method of controlling the flowability of a used synthetic molding sand containing from about 2 to 5 per cent bentonite, which comprises adding thereto and maintaining therein, from about 0.1 to '2 per cent oi at least one fluoride of the group consisting of sodium fluoride and potassium fluoride.

3. The method of improving the flowability of a used esium molding said containing trom about 2 to 5 per cent bentonite, l to 2 per cent sulfur, and 1 to 2 per cent boric acid, which comprises adding thereto and maintaining therein, from about 0.1 to 2 per cent of at least one fluoride selected irom the group so cisodi fluoride and-potassium fluoride.

4. The method of improu 1:; the flowabiiity at a used magnesi rim-1;; d con i about2to5pereentbentonite,1to2percent sulfur, 1 to 2 per cent boric acid, and 1.5 to 2.5 per cent of a polyhydric alcohol, which comprises adding thereto and maintaining therein, irom about 0.1 to 2 per cent oi at least one fluoride selected from the group consisting 01. sodium fluoride and potassium fluoride.

5. A used molding sand containing an argil-, laceous bonding material and from about 0.1 to 2 per cent of at least one fluoride selected from the group consisting of potassium fluoride and sodium fluoride, said sand being characterized by a flowability substantially equivalent to that of the orig inal sand prior 'to use and the addition of said fluoride constituent.

8. A used molding sand (or casting magnesium containing about 2 to 5 per cent bentonite, 1 to 2 per cent sulfur, l to 2 per cent boric acid, and 0.1 to 2 per cent of at least one fluoride ircm the group consisting of potassium fluoride and sodium fluoride, said sand being characterized by a flowability substantially equivalent to that of the ori inal sand prior to use and the addition of said fluoride constituent.

7. A used molding sand for casting magnesium containing about 2 to 5 per cent of an argillaceous bonding material, 1 to 2 per cent sulfur, l to 2 per cent boric acid, 0.25 to 0.5per cent pot fluoride, and about 1.5 to 2.5 per cent of a polyhydric alcohol, said sand being characterised by a flowability substantially equivalent to that of the original sand prior to use and the addition of said fluoride constituent.

8. A used molding sand for casting magnesium containing about 2 to 5 per cent bentonite, 1 to 2 per cent sulfur, 1' to 2 per cent boric acid, 0.25 to 0.5 per cent potassium fluoride, and, about 1.5 to 2.5 per cent of a nolyhydric alcohoi, said sand being characterized by a flowability substantially equivalent to that oi. the original d prior to use and the addition oi said fluoride constituent.

ET T. W630.-