US2287153A - Foundry facing - Google Patents

Description

Patented June 23, 1942 FOUNDIYI'ACING Burgess P. Wallace, Brooklyn, N. Y.

No Dr-lng. Application May 11, me,

, Serial Na sums 3 Claims. (Ci. zs-rso) This invention relatesto the casting of metals in ordinary sand molds and has for its particular objects the provision of a facing of the carbonaceous type which is peculiarly adapted to be suspended in water and delivered to the mold in the form of a spray, thus admitting of such facing being effectively applied as a substantial coating to all of the mold surfaces and particularly the vertical surfaces thereof with the result that the castings obtained in a subsequent casting operation are characterized by their smooth, fine, clean surfaces which are free from pits, pin holes, blow holes, as well as from burnt-in-sand or fused silica skins and from which castings the adhering sand is readily peeled, thus minimizing the brushing, tumbling or milling and pickling operations thereof. Further objects will hereinafter appear.

In the production of so-called pattern-true castings, it has been customary, heretofore, to emplo facing materials such as graphite, for example to fill up or slick over the surface voids in the mold surface in such a manner as to avoid the sealing of' such surfaces so as to prevent the escape of the steam and gases evolved from the molten metal when the same is poured thereinto, which facing serves as a refractory protective layer against the fusing or cutting action of the molten metal on the sand surface of the mold' surface, thereby facilitating the peeling of the sand from the casting and thus minimizing the amount of brushing, tumbling or milling and pickling operations in order to remove extraneous silicious material from the surfaces of the casting. Such facing was usually either applied from a dust bag or by means of a so-called slicka spray. Furthermore, such improved product is peculiarly adapted for me in such spraying operations, since the same remains suspended in the liquid vehicle for relatively long periods of time, there being a minimum tendency for the same to settle out and thus it is possible to apply a substantially uniform layer of the facing to the vertical and other surfaces of the mold con-.1 I

tinually throughout the spraying operation and also all possibility of the nozzles becoming clogged. during the spraying operations is avoided. I

My improved carbonaceous facing is preferably prepared as follows:

A mixture of finely pulverized coke, karaya gum, dextrine and bentonite is introduced into a mixer equipped with suitable agitating devices and therein the same are intimately mixed together, the proportions thereof preferably comprising Parts Coke of say 200 mesh or finer 200 Karaya gum 1.1 Dextrine 4.5 Bentonite 9.0

Total 214.8

Preferably a very small percentage of a preservative such as one tenth of one per cent of either copper sulphate, beta naphthol, bensoate of soda or like common preservatives are added to the foregoing mixture to prevent fermentation of the gum and dextrine in storage.

In the application of the aforesaid facing composition to green sand molds, the same is intimately admixed with a relatively limited quanvert cal surfaces. excessive brushing, tumbling,

pickling and milling operations have been reouired. These operations were not only expen-, sive and laborious but in many cases, because of the tendency to obliterate fine designs on the mold surfaces, they were decidedly objectionable.

My investigations have led to the discovery that it is possible to produce castings wherein all of the surfaces, inchiding the vertical surfaces therecf,rare pattern-true and essentially free from burnt-in-sand and dimcult removable silica skins by applying the herein described facing composition to the mold surfaces in the form of tity of water, preferably about 5% to 8 lbs. of the aforesaid facing. product is admixed with 8 lbs. of water.

The aforesaid bentonite, as i well known, is

a natural clay that contains a large percentage of aluminumhydrate and silicic acid (hydrated silica), together with impurities such as the the water and thereby not only facilitates the Yrhixed with water as being stirred and application to to add sumcient water such as herein described on surface than bonaceous facing is applied to the mold surfaces insofar as it tends to assist in binding the particles of the facing composition to the sand particles of the mold surface,yet primarily functions as a colloidal coke-suspending agent and materially as,- sists the bentonite in that respect. However, of itself and without the presence of bentonite in the mixture, such gum is incapable of effecting as suitable a suspension of the facing cmp0si' tion in the water. ciailyassist in effecting the suspensibility of the coke in the water of thespray mixture, but acts primarily as a cementing agent to cause the fac ing composition the mold surface to to adhere .to the sand particles of which .the spray mixture is applied. I

. My improved facing composition when adaforesaid, may be stored fora week or two and still be susceptible of forming a satisfactory mixture for spraying whereas if the coke alone were. dmixed with'water in the same proportions but without there being any gum, any bentonite or dextrine present, the same would tend to settle to a hard residue if the mixture were allowed to stand overnightwhich could be stirred with great difiiculty if at all.

1 The aforesaid facing composition, following its the mold, does not promptly dry to a dry skin but remains damp and for a considerable period of time thereafter will stick to the fingers if lightly touched.

In the event in the preparation of the facing composition it is desired to prevent any tendency I of the bentonite to clump or cluster and thereby I interfere with the uniform admixture of the bentonite with the coke, it is merely necessary to the bentonite, before admixing the same with the coke, to form a thin slurry which latter is then admixed with the coke, um and dextrine and then the resultant mixture is dried and comminuted.

'Thecastings obtained from applying a spray the vertical or other surfaces of the mold, possess an even'smoother that obtained when a: dry cari'rom a dust bag because of the fact that the manner of application results in the facing com position being compacted under pressure in the cavities of the sand surface of the mold. Preferably, the air pressure employed to spraying the liquid composition onto a mold ranges from 7 about 25 to 45 lbs. depending on the viscosity of the mixture.

7 While karaya gum is preferred as the gum ingredicnt of my improved facing composition because of its ability to absorb several times its bulk of water and form a gel, other gums having a somewhat similar property but to a lesser degree such as tragacanth gum, may be substituted therefor. Likewise, goulac, a by-product from the, manufacture of sulphite paper pulp or molasses, or like products having generally similar adhesive qualities capable ofcementing the carbonaceous particles of the facing to the The dextrine does not espesand particles in the mold surface may be sub,- stituted for the dextrine.

The proportions of the gum, dextrine and bentonite with respect to the coke are not highly critical but may vary substantially, for example the amount of bentonite should not be sufficient to render the spray mixture too viscous to be freeflowing through the spray nozzle and the amount of dextrine or its equivalent should preferably not be less than about 2 parts nor more than about 10 parts while the karaya gum or its equivalent should be present in an amount sufficient to materially assist in the suspension of the coke but not in a sufficient amount to render the spray mixture too viscous to be freeflowing so as to interfere with the application of the same as a spray to the mold surface.

The amount of water which is employed is preferably not more than twice the amount by weight of the amount of the facing composition and desirably the amount thereof is but-some to %:greater than the amount of the facing composition. If too much water is added to the facing composition when preparing the spray mixture the facing applied to the mold surface will be toosloppy and consequently an insufficientamountof facing will adhere to the mold surface and furthermore, the same night tend to dislodge the sand particles of ,the mold surface and thereby prevent the production of a pattern-true casting.

My improved facing composition not only produces castings all of whose faces including the vertical walls are pattern-true andfromwhich castingsthe adhering sand layer can be readily peeled but because of'the characteristic properties of the water suspension of the facing composition, as hereinbefore set forth, the same is suitable for application in the form of a water spray to thesand surfaces of a mold with the consequence that the cost of applicationminimized and'also the costs of finishing-the casting are materially reduced as compared with castings prepared with otherfacing compositions.

The characteristic viscidity or stickiness of the karaya or equivalent gum, as well as its ability to swell and thicken the mixture, produces a suspension of the coke dust when the facing composition is admixed with water-in' the manner aforesaid, which cannot be accomplished with bentonite alone owing to the absence of such viscidity or stickiness characteristic in bentonite and as a consequence, my improved facing composition containingsuch a gum, remains in suspension for much longer periods of time and can, on settling, be far more easily re-suspended with slight stirring than is possible were bentonite alone employed as such suspending agent. However, such karaya gum :alone even in the absence of any bentonite is capable of accomplishing the suspension of the coke dust if the proportions of such gum are substantially increased beyond that employed in the aforesaid example of my improved facing composition, nevertheless, the excessive amount of karaya gum required to effect such suspension imparts anobjectionable viscidity or stickiness to the-mixture which not only interferes with the proper spraying thereof but also materially increases the tendency of the spray mixture to clog the fine aperture in the spray mzzle employed to apply the same.

Applicant is well aware of the Patent No. 1,787,964 of Jan. 6, 1931, which discloses a facing containing coke, bentonite and dextrine and also 2,287,153 Patent No. 1,845,371 of Feb. 16, 1932, which discloses a facing composition wherein various gums are suggested as the equivalent of dextrine for the purposes of that patent and the claims of this application are therefore confined to the improvement on such compositions which is specifically set forth therein since neither of the foregoing patented compositions are susceptible of forming a water suspension possessing the characteristics of applicants improved product as herein set forth.

Various modifications may be made in the hereindescribed facing composition without in any way departing from the spirit of my invention as embraced within the scope of the appended claims.

Having thus described my invention, what I claim and desire to obtain by United States Letters Patent is:

1. An intermediate product for use in a spray composition for metal casting sand molds comprising a dry mixture consisting principally of a carbonaceous dust, the particles or which are coated with an adhesive agent consisting of dextrine and are intimately admixed with at least 2% and not more than ofbentonite and said mixture containing not less than and not exceeding 3% of a thickening agent beonging to the group consisting of karaya gum and tragacanth gum, said dry product being characterized by the fact that when admixed with one to two volumes by weight of water, then a water suspension of the composition canbe obtained which is susceptible of being continually which suspension the composition remains suspended for long periods of time without the solidsof the mixture becoming compacted in such a manner that they can not be readily rc-sus pended by merely manually stirring the mixture.

2. In a spray composition for metal-casting sand molds, comprising a water suspension containing at least 50% of water by volume and the solid content of which suspension contains a major percentage of coke dust, the particles of which are coated with an adhesive agent consisting of dextrine, also in excess of 2% and less than 10% of bentonite and from A;% and not exceeding 3% of a gummy thickening agent belonging to the group consisting of karaya gum and tragacanth gum and the said spray composition'being highly stable, capable of remaining in prolonged suspension on standing and being especially adapted .for application to a mold surface by spraying through a spray' nozzle.

3. In a spray composition for metal-casting sand molds, comprising a water suspension containing at least 50% of water by volume and the solid content of which suspension contains .at least 90% of coke dust, the particles of which are coated with an adhesive agent consisting of dextrine, also in excess of 2% and less than 10% of bentonite and from 4% and not exceeding 3% of a. gummy thickening agent belong to the group consisting of karaya gum and the said spray composition being highly stable, capable of remaining in prolonged suspension on standing and being especially adapted for application to a mold surface by spraying through a spray sprayed from a spray nozzle as a uniform coating nozzle.

upon the surface of a green sand mold and in BURGESS P. WALLACE.