US2389540A - Foundry composition - Google Patents

Description

Patented Nov. 20, 1945 I UNIT STATES fPATENT OFFICE Arnold Edward Pavlish and Chester Ronald Austimcolumb'us, Ohio, assignors, by memo assignments, to

Peerpatco,

Incorporated,

Indiana, Pa., a corporation ofDelaware No Drawing. Application July 23, 1943,

- Serial No. 495,900

Claims. (01. 22-217) Our invention relates to compositions for use in foundries and the like.

Among the objects of our invention is the provision of a foundry composition, together with the art of preparing the same, which composition displays marked enhancement of green strength,

controlled dry strength, improved permeance, and the like, all with a minimum of added operational steps; which composition is produced readily and in simple, inexpensive manner with the use of a minimum of inexpensive and easily handled ingredients readily available on the market, according to a practice in which; the

operational steps are. in large measure automatic and which require but a minimum of skilled labor and a minimum of attendance on the part of the operator; which composition flows readily and is easily rammed about the pattern, which is free from mold-hardening and does not cake" readily, which does not burn onto the casting,

which collapses easily in interior sections following casting, which shakes out of the molding flask easily, and which displays a high degree of recovery after use, with substantial absence of lumpy particles, and which composition produces good, sound castings wherein are faithfully reproduced the exact details of the pattern and which are characterized by freedom from cracks,

checks or other surface defects. Other objects will inpart be obviousand in part pointed out hereinafter.

Our invention accordingly consists in the coinbinationof elements, mixture of materials, and composition of ingredients, and in the several operational steps, and in the relation of each of the same to one or more of the others, all as described herein, thescope of the application of which is indicated in the following claims.

It is advantageous at this point, to facilitate more thorough comprehension of our invention,

prevented. Improved'workability of in the upper half of the mold, is imparted to'the' sand by the clay. Dropping, breaking or disintegration of the mold while drawing the pattern or during subsequent handling is eflectively the composition is also imparted by the clay.

Notwithstanding these desirable qualities attributable to the added clay, the presence of a large amount of clay in the composition is not desired. The bonding agent is found to decrease the porosity or permeability of-the composition. This permeability, however, is essential in the mold to ensure that the gas evolved when the hot metal contacts the walls of the mold is properly eliminated.

. The quantity of clay which must be added, according to the practices heretofore employed, depends upon a number of factors. To illustrate,

( large work requires a strong, self -sustaining mold.

Small light-work, on the other hand, can be made with a comparatively weak mold. The type of sand, too, is a factor which must be'considered. Sand having smooth, rounded grains quire more binder than, do'sands having fine grains. Where part of the sand comprises burnt or used sand, then less clay is necessary, since requires more bonding material than do sands of rough, irregular grains. Coarse sands resome clay is already present in the used material. In general, the amount of bonding agent employed ranges from 5% to 30% by weight of Y the foundry composition.

to note that it has heretofore been common prac-.

tice, in the casting of metals and alloys, asin forming a mold, for example, to add asuitable bonding clay to silica sand. Water added in moderation thereupon produces a moist, workable mass. Where desired, it has been customany to use acertain amount of burnt or bonded sand in place of a corresponding quantity of clean sand.

The composition thus prepared is suitable for -general foundry use. when employed as a mold composition, it is rammed compactly and tight-:

ly'. about a desired pattern which has first been positioned in a molding flask. When so employed, the-high strength which is required. particularly their use is attended by only a comparatively limited increase in the strength of the resulting mold. Accordingly, appreciable increase in strength. can be accomplished only by the addition of a substantial quantity of clay to the composition. This substantial proportion of clay, however, is inclined to curtail severely the permeability of the mold. Compromise has heretofore been, required between the factors of together with being entirely'satisfactory from either standpoint.

It-has also been found that western bentonlte is well suited as a bonding agent for many types of foundry compositions. High permeability accompanies the use of this clay. Certain disadvantages attend upon its use, however, among which are included its water-swelling propensity andits high dry strength. It rams about the pattern only with difliculty, and has a tendency to swell, cut and scab. Loss of sand in the discarded molds is observed, while cracked castings frequently-occur.

In the United States Patent No, 2,180,897, issued November 21, 1939, to Norman J. Dunbeck, southern bentonlte is proposedas the binder. Southern bentonlte is there described as a nonswelling, colloidal montmorillonite, found in numerous parts of the United States, particularly in the South Central States. Colloidal clay, as the term is there used, indicates a clay'largely 'consisting of fine particles of one micron or less.

This southern bentonlte, when employed .as a foundry binder, gives a mold composition displaying high green strength and a quite moderate dry strength. For this reason, this montmorillonite clay ,is admirably suited for the binder in molds for making castings 'ofconsiderable detail. Moreover, the low dry strength permits the castings to contract during cooling without appreciable restraint. sult.

Now foundrymen desire the highest possible green strength in the mold composition, other factors, particularly mold permeance, .remalning unimpaired. High green strength ensures faithful reproduction of the detail of the pattern. Moreover, increased green strength permits the use of smaller quantities of bonding agent, thus increasing the permeance of the composition, and resulting in less dead clay and fines in the sand, as well as other advantages which will be apparent to those skilled in the art.

An important object of our invention, therefore, is the production of a foundry composition, the art of preparing the same, in which the quantity of bonding agent is appreciablyreduced, which composition has high green strength and but moderate dry strength, and which produces good, sound castings of faithful adherence to detail and free from surface defects. I

In our co-pending application serial No.

illed July 23, 1943, and entitled Foundry composition, we have disclosed treating southern bentonlte or suitable refractory clays with boric acid; while in our co-pending application Serial No. 495,899, filed July 23, 1943, and entitled l'oundry composition, we have disclosed blending'southern. bentonlte or suitable refractory clays with one or more of the sulphates of calcium.- In each instance, the objectives were achieved of increasing appreciably the 'green strength .of a foundry composition in which the new binder was employed, and of enabling the useof a smaller proportion of binder. thus increasing the mold permeance.

, We have now made the surprising and important discovery, during the course of our experlments directed to that end, that foundry compositions display even further important increw in green strength when the bonding agent a subjected to appreciable superatmospheric temperaturea and pressures, as by autoclaving. over a considerable period of' time. Material improvement in green strength over that prior to such treatment is observed both for untreated bonding agents, such as southern bentonite, and for treated binders, such as those described in our two said co-pending applications.

We are by no means certain as to the correct explanation of this advantageous phenomenon.

Perhaps some structural change is worked in the clay by the prolonged high pressure and high temperature treatment, due, possibly, to a change in the combined water.

our invention, we first subject a bond clay, such' as southern bentonlte, to autoclaving for about sixty minutes at a pressure of about 300 pounds per square inch. Then to a heap of sand we add about 5% by weight of the autoclaved bond clay,

Good, sound castings reof Paris, or gypsum. In our lications. we have disclosed characterized by together -'with a desired amount of water, in

this instance 2 by weight. This water con- I tent conveniently may be varied from 2% to 5%, and we have obtained quite good results with a water content ranging between these limits, mixing results in a uniform mix. The mix is then ready for use in preparing a sand mold or for other foundry use, methods.

The. new mold composition thus produced is easy .to handle. It rams firmly .and tightly about a pattern and flows freely. The resulting smooth surface of the mold accurately follows the details of the pattern. A durable mold is produced which has a surprisingly high green strength.

Consequently, the mold remains firmlyin the cope when the pattern is drawn. This mold is its smooth, unbroken surface and freedom from defects. Required preliminary repair work is reduced to a minimum. Moreover, since only a small quantity of binding agent'is required, the mold display high permeability to the fumes and gases arising when the molten metal is poured into the mold.

Where desirable, we employ as a bonding agent a clay which has been preliminarily treated with from 5% to 39% of boric acid or one or more of the materials selected from the group consisting of anhydrous calcium sulphate, plaster said co-pending apthat these treated bondingagents greatly improve the green strength of the resulting composition, as compared with the admixture of southern bentonlte alone, and that when boric acid is employed as the additive, of thedry strength. The clays, treated as noted, then are subjected to autoclaving.

The superior qualities of our novel foundry composition are best illustrated in the following Where treating agents also are present, possibly dehydration occurs of in accordance with well-known there is likewise a marked increase were prepared Foundrymens Association. Conveniently, the test data for a bonding agent of southernv bentonite are exhibited in the following table:

Table I Green com- Dry com- Cornposition (95% silica sand, wiih) pression pression strength strength V Pounds r Pounds er sq. inc sq. inc 5% southern bentomtc. 9.8 46.00 5% south. bent., autociaved at 50#,'sq.

in. pressure for sixty minutes ll. 46 46. south. bent, autoclaved at l00f/sq.

in. pressure for sixty minutes 13. 20 41. 40 5% south. bent, autoclaved at Z00l/sq.

in. for sixty minutes ll. 95 ii. 40 5% south. bent., autoclaved at 300# sq. in. pressure for sixty minutes 13. 91 39. 00

It will be observed from the foregoing that with southern bentonite alone as the bonding agent the composition subjected to autoclaving displays a substantial increase in green strength over a similar composition in which the treatment has been omitted, together with a notable decrease in dry strength. Permeance is not adversely affected.

, Superior qualities, even without special autoclaving, are had 'with the treated binder of our co-pending application referred toas seen from the following table showing comparative tests on Additionally superior results are had from foundry compositions employing the treated andautoclaved binders. The sample mixes are made and tested ,according to procedure given above in connection with the tests of Tables I and II.

The test reports are as follows:

TableIII 5% mixture: 85% south. b'ent., 5% boric acid 5% mixture: 85% south. bent., 15% gypsum 5% mixture: 85% south. bent,

15% boric acid, autoclaved at 50#/sq. in. pressure for sixty minutes 5% mixture: 85% south. b'ent., 15% boric acid, autoclaved at 1001i /sq. in. pressure-for sixty minutes 5% mixture: 85% south. b'ent., 15% boric acid, autoclavedat 200#/sq. in. pressure for sixty minutes 5% mixture: 85% south. b'ent.. 15% boric acid, autoclaved at 300#/sq. in. pressure for sixty minutes 5% mixture: 85% south. bent.. 15% gypsum, autoclaved at 300#/sq. in. pressure for sixty minutes inch have been employed. Conversely, no upper limit has been observed as to the pressure whichcan effectively be employed.

,In connection with all compositions, it is note worthy that increased green strength is accompanied by no decrease in permeability. This is in marked and important contrast-with the action of most bonding agents, when increase in dry strength is attended by proportional decrease in permeability. Also, the important advantages are observed that the composition can be mixed faster, and with lower water content. When it s considered that as already stated, the water content is largely responsible for'the evolution of gas incident upon pouring the molten metal, the. value of diminishing the water content will be appreciated.

When our new .composition is employed in the construction of a foundry mold, that mold displays a minor contraction at high temperatureshas illustratively been given as 5%, wehave obtained satisfactory'results with from about 2% to about 8% of the binder. Where part of the sand comprises burnt sand, which already contains some clay, and since this clay is reversible in character and can be used over again, we can advantageously extend this lower range to about /2 of bonding agent.

Although southern bentonite either treated or untreated preliminarily in accordance with the may be employed with advantageous results. Thus we have achieved satisfactory performance where the bonding agent is western bentonite or refractory clays, either untreated or treated with boric acid or sulphates of calcium and thereupon subjected to autoclaving, in accordance with the practice of our invention.

We have described the practice of our invention, for purposes of illustration, largely in connection with a green sand mold. It is particularly to be understood, however, that it is equally applicable to dry sand molds, or green or dry sand cores, or similar foundry constructions. Also we find it to be applicable to like compositions for other foundry uses. To illustrate, we have prepared. facing sands embodying our new composition and consisting of variouscombinations of new or burnt silica sand, new or burnt molding sand, lake or bank sand, together with the bonding clay, either treated or untreated. and, thereafter, subjected to autoclaving. Additionally, where desired, auxiliary binders have been added insmall quantities without departing from the purview of our invention, such as cereal binders, cement,. goulac- (sulfite lye), pitch or rosin. Materials tending to clean casting have been added, such as sea coal, wood flour or oils.

Thus it willbe seen that our new invention provides a new composition, in which the various in a limiting sense;

objects hereinbeiore noted are all achieved, to.

We claim:

1. In preparing a composition or matter for ioundry 'uses, the .art which comprises autoclavlng clay (or an appreciable time interval at elevated pressures, and mixing with about 99%% to about 92% by weight of silica sand about to about 8% by weight 01' the autociaved clay.

- 2. In preparing a composition for foundry purposes, the art which comprises treating s am southern mamas with boric acid. autoolaving the treated bentonite for an appreciable time interval at elevated and mixing with pressures about 55% to 92% by weight silica sand about '/z% to about 8% by weight of the treated and autoclaved bentonite.

8. In preparing a foundry binder, the art which comprises subjecting a bonding clay to autoclaving at superatmospheric pressures for an appreciable interval of time. a

4. In preparing a foundry binder, the art which comprises subjecting a bentonite clay to autoclavink at a pressure between about 50 pounds per square inch and 300 pounds per square inch 7 tor approximately one hour or more.

5. In preparing a foundry hinder, the art which comprises subjecting a-bonding clay treated with about 5% to 30% by weight or boric acidto autoclaving at superatmospheric pressures for an ap- I 20 preciabie interval or time.

ARNOLD EDWARD PAVLI8H. CHESTER RONALD AUSTIN.