US1886252A - Casting freely oxidizable metal - Google Patents

Description

Patented Nov. 1, 1932 UNITED STATES PATENT OFFICE JOHN A. GANN AND MANLEY E; BROOKS, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN CASTING; FREELY OXIDIZAIBLE METAL No Drawing.

' only is there a pronounced tendency for the metal to burn in the sprue, but the surface of the casting formed by contact with the complementary surface of the mold tends to become oxidized, pitted, or both, due to the formation of a powder (presumably an oxide or a nitride of metal). Where the casting poured in this manner is a relatively heavy section it either completely burns up or is .badly damaged due presumably to the term,

perature of the metal c'ast remaining in the rapid oxidation range for a longer period of time than is the case with a thin section casting which chills promptly. Even if the im- .pairment of the surface of such castings as can be made is not serious enough to prevent the cast article from being used or finished when removed from the mold, the casting has an unsightly'appearance and a certain loss of metal isinvolved. It is to be noted, of course,

80 that the cleaner the casting the more easily may the subsequent finishing operations be carried out.

It has heretofore been" proposed to over,-

come these difliculties, specifically in casting magnesium and alloys containing same in dry sand molds, by dusting the mold prior to casting the metal with sulphur which is capable of giving off in contact with the molten metal a vapor which is more easily oxidizable than magnesium. This procedure, however, has the objection that it is obviously difficult to correctly gauge the amount of sulphur thus used and particularly if an excess is applied to the surface either of the mold proper or the mold core so much vapor may be generated that some of it becomes entrapped during the period-in which the metal is solidifying, the result being blow holes or surface shrinks in the casting.

Application filed July 30, 1931. Serial No. 554,148.

More recently it has been proposed to avoid the difliculties encountered in casting magwhich is commercially sold as a fine powder,

is not only unnecessary but detrimental since it makes the moldless porous and thus tends to prevent the ready escape of gases generated during casting. This in itself is undesirable since it causes pitting, surface shrinks, and general surface injury to the casting. We have further found that the use of magnesium oxide in contact with hot magnesium and its alloys accelerates or promotes oxidation of the metal.

. While Working with pulverized carbon base molding compositions, we have discovered that not only can we omit the use of magnesium oxide to advantage, but that the relatively expensive mineral oil used as above noted can be omitted so that the use of any relatively expensive oil can be entirely avoided. Our improved composition consists of a mixture of pulverized carbon, a plasticizer, a relatively .small amount of an oxi- 1 dation inhibitor, and suflicient water to render the composition moldable.

Accordingly, among the objects of the present invention is the production of a water bound carbon base molding composition suitable for use in casting readily oxidizable metals such as magnesium and its alloys, the useof such composition further permitting the production of sound castings having av good surface appearance. Other objects and advantages will appear as the description proceed To the accomplishment of the foregoing and related ends, the invention, then, consists of the method and product hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail means and modes of carrying out the invention, such disclosed means and modes illustrating, however, but several of the various ways in which the principle of the invention may be used. I

Where pulverized or finely divided carbon is used instead of sand for formingla mold, such mold will have a much higher eat conductivity than a similar sand mold. This increased heat conductivity causes the readily oxidizable metal bein'gupoured into the mold to chill promptly w 'ch not only decreases the period wherein rapid oxidation can take place, but 'produces a fine grain structure casting which exhibits superior properties as compared with a like cast-' ing made in sand. We have further found that where such carbon base mold is rendered moist or moldable b water instead of .oil that the chilling e' ect is still further increased and accumulatively aids in -producing a casting having exceptionally good pro erties. In this connection it is to be noted t at carbon is chemically and physically not an equivalent to sand since it is not an oxide, it is combustible, and has a much higher heat conductivity than sand. We are aware that gra hite, powdered coal, and lamp black have een used as facings and washes for molds used in the casting of iron and steel; however, the problem encountered there is in no way comparable with that encountered in the casting of an extremelyreadily oxidizable metal, such as magnesium and its alloys, which has to be handled and oured at a temperature wherein it readily ignites and burns.

Our improved molding composition, consisting of pulverized carbon, a plasticizer,

and an oxidation inhibitor, moistened or made moldable with water, may be used to form a mold to produce a casting of any desired shape or s1ze, e. g. a crank case for an mternal combustion engine or like article and such mold, if desired, may have incorporated therein cores or metal parts, as is well known to the art.

If-with the carbon base molding composition used inmaln'ng such mold approximately 2 to 10 per cent of boric acid, ammonium compounds, sulphur, or a combination. of these or other like oxidation inhibitors be intermixed, a very satisfactory result in the 1 way of'a casting is obtained upon pouring the metal into the mold in the usual manner, it being noted, of course, that ordinarily unless the castingsection is very thin an amount .of the above noted agents greater than the notedi should be used}.

For general casting service with such comitions, we have found that 4 per cent of one acid, or! per cent ammonium chloride,

'or 5per cent of sulphur admixed'therewith,

.will produce castings of readily. oxidizable "metals thatare substantially free from burn ing and exhibit, upon pickling or otherwise cleaning accordingto commonp'ractice, an. exceptionally good surface finish. The use. 55 5 of our present invention is concerned broads: phur,-or a mixture of them) ly with the treatment of a water bound or moistened green molding com osition wherein pulverized or finely divide carbon is a major constituent. As a specific example of such a mixture may be noted the pulverized carbon, bentonite,'oxidation inhibitor, water composition, wherein the proporof course, normally depends uponthe bond strength and permeability desired when the composition is formed into a mold. While we have given percentage ranges and prefeired amounts of oxidation inhibiting agents to be added to the pulverized carbon molding composition, we do not wish to be strictly limited to those specific ranges since we have found that as high as 20 per cent by Weight of the oxidation inhibiting agent or agents can be used with satisfactory results. We have further noted that where sulphur is used according to the method described that as the percentage approaches 10 the casting produced takes on a dark appearance and that, however, when the percentage of sulphur is increased to 20 the "dark appearance almost completely disapcastings, however, when pickled or cleaned according to common practice exhibit sound castings having an exceptionally good surface. The following examples show in detail two preferred formulae of our improved molding composition.

Example 1 When .using a freshly made mixture of pulverized carbon, bentonite, and an oxidation inhibitor,'rendered .green or moldable with water, we have found that verygood castings can be made by using thefollowing hand-mixed co p f' 10% water v i 10% bentonite --r 3 4% of oxidation inhibitor (boric acid, ammonium chloride, ammonium sulphate, sul

I 76% carbon (pulverized coke) having the following sieve'analysis I,

Percent 886 Mesh 33 -100 47 100-200 -20 Through 200 E wample 2 into intimate contact, a relatively small percentage of plasticizer is necessary to form a satisfactory molding composition. A preferred composition when mixed in this manner is as follows 7% water 3% bentonite 4% oxidation inhibitor (boric acid, am-

monium chloride, ammonium sulphate, sulphur, or a mixture of them) 86% carbon (pulverized coke) having the following sieve analysis 7 Percentage f 30400 43 100-200 12 Through 200 In using the above compositions we have found that the. castings produced present a very good surface which is substantially free from oxidation, pitting, and surface shrinks, and further we have found that the tensile properties, Brinell hardness, and fatigue endurance and toughness of such castings are above the average of like articles cast in sand according to current practice and are somewhat better than like articles cast in oil bound pulverized carbon composition molds.

overcomes or greatly mitigatesthis difliculty and moreover does not act as an active oxidation accelerator. Specifically, 4 per cent of calcium chloride is satisfactory for the purpose at hand.

In using our improved water boundmolding compositionfo'r casting, a small amount of the oxidation inhibitor is driven off or otherwise lost due to the heat given off by the hot metal during the casting operation.

There is, however, none of the relatively expensive oil present to be driven off and re-.

quire replenishment. After the so poured casting has cooled to a point where it will not ignite or rapidly oxidize when exposed to air, it can be shaken out and the molding composition reconditioned by adding thereto sufiicient of the oxidation inhibitor and water to overcome the losses and place the composition in shape for reuse, it being noted that the other ingredients of the composition will be substantially unaffected by casting conditions. The use of water for making our improved moldin composition moldable is without the bad effects ordinarily encountered since the oxidation inhibitor in some way prevents the water or steam in the mold from giving up oxygen to oxidize the metal. While we have mentioned pulverized coke as the carbon material used in our improved molding composition, we do not wish to be limited to that material since we have found that pulverized gas carbon, coal, and other similar hard high carbon compounds can be used in l1ke' manner. The term carbon will, accordingly, be understood to broadly cover this class of materials unless otherwise specified. Further, we have found that the sieve analysis of the pulverized carbon may vary considerably'from that specifically noted in the foregoing examples, the analysis used depending largely upon the permeability and bond strength desired.

The present application is a continuation "in part of our copending application filed July 7, 1930, Serial No. 466,031.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the method and product herein disclosed pro vided the method and product stated by any of the following claims or the equivalent thereof be employed.

We therefore particularly point out and distinctly claim as our invention l 1. The process of casting a freely oxidiza ble metal which consists informing a mold from pulverized carbon, a plasticizer and an oxidation inhibitor rendered moldable by the addition of water, and casting said metal in said mold.

'2. In a process of casting a freely oxidizable metal to eliminate excessive burning thereof, the step which consists of pouring the molten freely oxidizable metal into a water bound carbonaceous mold containing a plasticizer and at least one of the materials boric acid, ammonium salt, sulphur.

3. Ina method of casting a freely oxidizable metal such as magnesium and its alloys to eliminate excessive burning thereof, which comprises forming a water bound carbona ceous mold havingboric acid in surface exposure, and casting the molten freely oxidiza- 4. In a method of casting a freely oxidizable-metal such as magnesium-and its alloys to eliminate excessive burning thereof, which comprises for'minga water bound carbonaceous mold having ammonium chloride in surface exposure, and casting the molten freely oxidizable metal in said mold in con-M tact with such surfaces.

mold being formed from a water readily oxidizable metal such as magnesium and its alloys which consists of a' thorough mixture of pulverized carbon (86%), finely divided bentonite (3%) ammonium chloride (4%), and water (7%).

16. As an article of manufacture a mold for casting readily oxidizable metalsb, so?

oun

the molten freely oxidizable metal in said mold in contact with such surfaces.

7. A molding composition for casting readily oxidizable metals which comprises a mixture of pulverized carbon, a plasticizer, an

oxidation inhibitor, and water.

8. A molding composition for casting readily oxidizable metals which comprises a Water bound mixture of pulverized carbon, a plasticizer and at least one of the oxidation. inhibitors, b oric acid, ammonium salt, sulphur.

9. A molding composition for casting read- 7 ily oxidizable metals which comprises a water bound mixture of pulverized carbon, a plasticizer and at least one, of the oxidation inhibitors, boric acid, ammonium chloride, sulphur. A

10. A molding composition for casting readily oxidizable metals which comprises a water-bound mixture of pulverized carbon, a plasticizer and boric acid.

11. A molding composition for casting readily oxidizable metals which comprises a water bound mixture of pulverized carbon, a plasticizer and ammonium chloride.

moldable mixture containing chiefly pulverized carbon having admixed therewith finely divided bentonite, and an oxidation inhibitor.

17. As an article of manufacture a mold for casting readily oxidizable metals, such mold being formed from a mixture of pulverized carbon and finely divided bentonite moistened with water and having incorporated in the surface thereof an oxidation inhibitor.

18. As an article of manufacture a mold for casting readily oxidizable metals, such mold being formed from a mixture of pulverized carbon (7 6%), finely divided bentonite (10%), boric acid (4%), and water (10%).

19. A molding composition for casting readily oxidizable metals comprising a waterbound mixture of pulverized carbon, a plasticizer, per cent of a hygroscopic halogen salt, and per. cent of an oxidation inhibitor.

20. A molding. composition for casting readily oxidizable metals which consists of a water bound mixture of pulverized carbon, a plasticizer, calcium chloride, and at least one of the oxidation inhibitors boric acid, ammonium chloride, sulphur.

Signed by us this 28th day. of July 1931.

- JOHN A. GANN.

MANLEY E. BROOKS.

12. A molding composition for casting.

readily oxidizable metals which comprises a water bound mixture of pulverized carbon,

a plasticizer and sulphur.

13. A molding composition for casting readily oxidizable metals comprising a m1x ture of 63 to per cent of pulverize carbon,

2 to 15 per cent of plasticizer, 2 to 10 per cent of oxidation inhibitor, and 6to 12 per cent of water.

p 14. A molding composition for casting a readily oxidizable metal such as magnesium and its alloys which consists of a mixture of tonite pulverized carbon (76%) finely divided ben- (10%), boric acid (4%), and water 15. A molding composition for casting a of Correction November 1,1932. JQHN A. Gmm ET AL. It is hereby certified that error appears in the Erinted specification of the abovenumbered atent requiring-correction as follows: the ed wprd ffcerbonaceous; read carbonaceous; line 18, claim 6, for

jiele' ninatev read gal/immune 92; claim 19, for 1 read 11 0,and' line 93, for W read 2-20; and that the said Letters Pat en't should be read with these corrections therein that the same may conform .to the record of the casein the Patent Oflice.

. Signed and s'eaied this 10th day of January, A. D. 1933.

, sun. M. J; MOO l: i of %ents,

age 4, lines 12, and 13, claim 5, for