US2437177A - Method of casting and apparatus therefor - Google Patents

Description

March 2, 1948. T. o. THEOBALD 2,437,177

Patented Mar. 2,1948

EMETHDD 'onossmehmn nrmrwws imam-on 7 "Dhomas' -OS Theobald, ltoyaliioabliwch. AriplicationLOctoher'ZS,1944;ISerlaI15705550384 3' Claims; (01322-1584) This invention :"relates "to a. .new "method "of metal castmg, the "specific; improvement being the provision of means whereby the risers "and runners associated with such *casting "may be more conveniently "removed, therefrom; It "is usual 'ifoundry practice to provide at "least one gate-"tin 'eacnmoldinto which "gaterthe molten metal is poured, and which gate is connected to the article cavity by "means of runners. Risers "extend "upwardly from'the mold cavi'tiv' into which a relatively large. amount of metal can .rise -to feed the casting "proper as'the metal in the'east-ing shrinks as it solidifies. The'num bar and size 'of risers; require'dior any particular "casting "varies with theshape of the'casting andwith theitype of, metal used. For example, comparatively tfew risers are .requiredtWhenthe casting is "to bemade 'of iron; whereas, when casting or aluminum, T01 magnesium/many risers" ofiarge 'crosssectioniare' required'to com- 2 "pensate""for"shrinkage in thecasting. -.Eurthermore, few risers are required wl ierethecasting is of uniform wall thickness; whereas, a riser must be "placed 'OppOSite-"a'thick bosso'rthe' like, as *such'boss cools slower "than "the "walls and must be fed 'by taliquid .SOUICGfflSitCOUIS. V

A riser to ir-unction satisfactoriiymust 'ice design-ed with suflicient cross "sectional-area, so that *the'metal in the casting will have completely "solidified *before solidification or "the metal intheriser. If the riser'solidifles hefore any portion or the casting,'thenshrinkage :;defects inevitably occurrin the casting fFromthe foregoing, it will be apparent that when forming casting having "comparatively thick bosses or sections,"the"risers musthavea-fairlyiarge cross sectional 'areaotherwise the riser will solidify before the thick section of the casting.

One "disadvantage of providing risers of large cross section isthat the riser must-be sawed or cut from 'thecasting in cleaning up the casting prior to :the anacl-rine operations' 'preper. This requires monsidera-ble "labor. Furthermore, where :the riser :is :positioned benea'th -a flange ;or :the ilike 'great diificu lty is usually experienced in :removing :the B1561, 1a saw :i earmot be serted rat :the ijbase :ofthe iriser.

The subject oizt'his :invention is "to provide a method :ercasting whereby :the "riser may designed "with :a relatively large erosssectionai area, :butistill may be reanilyremoved rromthe casting by striking'iitsa sharpflalow.

A further object of my'inventionis to'provide :readi'ly Paccomplished. 7

:With these and other'iobjects :in view, :my -J-in- -vention consists in thewarious steps of m'y proved-process "and "in m improved ar'ticle Y as *descrlbed in this specification, -=claimed in ft'fl :zrelatively zeimple isnag ing rwasher which is sea-st in :the riser whereby :thefabove lebieets are (I "Figure i is' a, plan-view of asnagging plate or washer adapted to -be cast in the base-of the'riser, an'd Figure 5 is a i'frag mentary sectional view,

similar to iF'igure hg butshows a modified form of my snagging washer.

"Referring *to the =-accompanying drawings, I have usedthevnumerai "I 0 to indicate a cylin' cler heeid ea-sting propenifrom which a riser H extends,"the arisefibeingconnected thereto by a means of a pair of necks 12'. In the construction shown, the wiser I I is connected '1 to the casting proper byztwoizneckssflgiont this is :done only for conveniencetiias :iin most fcases'ra "single neck is "ample. @However, iniomiing the :casting' shown,

itis rnecessaryiitoqoiace a'rriser :directly above each otthe closelyespacedi .valve guide bosses i3. These bosses have flarge-icross asectional areas, and :a riser :is required iiior seach'iiboss to supply s'metal *astttheycool. -iin .tliis'scase the'individua'l risers are i so Lclose :together ithat iior iconvenience each twozadjacentirisersaretcombined toform a single riser 'casting. fHowever; due to the provision of theitwo'mecks 51.2, :the single riser feeds both of thezadiaceiit bosses the same as it would two separate risers.

It may benoted f-romFigure 3 that each of the inecks I? is provided with an annular shoulder ll, '=spaced"just-above the casting proper.

"The diameter-of the riser neck must be made sufiieiently iarge so thatthe metal in the boss 13 wili haveisolidiiied bfore the metal in the neck' portionsolidifles, otherwise the molten metal -inthe'riser-wlll not feed down into the casting. when the neck '12 is designed with a sumeiently 'laitge-diameter to accorriplisl'i the above mentionedt jipurpose, "it usually happen-s that the 'neck' has isuoh structural strength that it 'eannot 'be' broken from the eastin g without de- "-stroyin-githe*eiddacentmartof thecasting. If an attemptistmade to break'theriser oiT by striking it 'ablow, it oftenhappens that the casting is broken instead, "thereby-destroying the entire casting.-n*t"nis invention, I provided means Tfor'reducingthecross'sectional area of each neck 12 *as'tar asits structuralstrength is concerned, While maintainingits initially large-cross sectional area *for the'trans'fer ofheat therethrough. It should be kept'-'in**niind thatya riser neck of to the adjacent mold as fast as does the casting,

but the liquid metal in the riser supplies heat to the neck to cause it to cool slower than the adjacent portion of the casting.

The unique feature of this invention is that the means provided for reducingthe cross sectional area of the riser does not retard the transfer of heat to the neck and does not absorb any" appreciable heat itself, so that no chilling effect is produced thereby. I accomplished this by providing a washer l formed of very thin metal as illustrated in Figure 4. The outside diameter of the washer is just large enough to be easily inserted into the neck l2 .and to rest upon the shoulder 14. The opening IS in the washer is considerably smaller than the diameter of the neck l2. Each washer I5 is provided with four tongues 16, which are stamped from the material .4 are in lace, metal is poured therein, which metal flows up through the casting cavity proper and then through the necks l2 to fill the risers ll. As the casting gradually solidifies, metal from the riser I1 is drawn down through the necks I I2 to compensate for shrinkage in the bosses l3.

Due to the fact that the heat radiation from the neck portion [2 is proportional to the area of the washer and which project from the periphery about one 32nd of an inch. The tongues normally lie in the same plane as the washer, but

when it is inserted into position upon the shoulder H, the tongues projecting beyond the periphery of the Washer are sprung upwardly to some extent, as shown in Figure 3. The washer is thus prevented from becoming loose in the mold and possibly being dislocated, as the metal is poured. The tongues extend about two thirds of the way through the washer so that they may be sprun upwardly by the comparatively soft core sand walls of the mold.

It is essential in carrying out this invention that the washer l5 be formed of material having a relatively high heat transfer coefiicient and that it be constructed of relatively thin material, so that the restriction to the transfer of heat from the riser will be a minimum. I have found that in pouring aluminum or magnesium castings, it is preferable to make the washers I5 from a relatively thin sheet steel stock of a thickness of about .010". This stock is known as shim stock. The opening in the washer IS in the casting shown is about one-quarter of an inch smaller than the diameter of the neck l2. It has'been calculated that a minimum riser neck area of 1%" diameter is necessary to maintain fluidity in the riser during the solidification of" the casting bosses shown. The opening in the washer [5, however, is only 1 in diameter. This reduction in the effective structural cross section of the riser directly reduces the strength of the riser by How-ever, the greatest gain resultsfrom the localizing of the stresses along the bottom of the narrow groove formed by the thin washer. This acts as a crack in the riser and causes the riser to break off by an impact force of only a fraction of that required to break off a riser of 1%" uniform diameter. In production, the force required to break off the riser in the casting shown, is only about one third that required to break off a riser formed without the washer I5.

In carrying out my improved method of casting, a mold is formed having cavities therein corresponding to the pouring gate, runners, casting proper and-the risers. This mold is constructed in the conventional manner and forms a part of my invention only in combination with my snagging washer 15. The mold proper has not, therefore, been illustrated in the drawings.

After the mold is formed and the washers l5 of the neck and that heat is added to the neck from the metal in the riser, the metal therein will stay fluid until the casting is completely solidified. Subsequently, the neck I 2 and the riser will'solidify, at which time casting can be removed from the sand. The risers are then removed from the casting proper by simply striking the riser a sharp blow with a hammer. The washers I5 do not form a bond with the metal of the casting, so that it is only necessary to break the portion of the riser within the opening I1. Furthermore, inasmuch as the washer forms a sharp crevice in the riser, the impact force supplied to the riser receiving the blow is localized at this point, so that the riser breaks off with only a fraction of the force otherwise required.

It will be noted that the casting shown has a flange forming a part thereof so spaced that the juncture of the riser with the casting is obstructed by this flange. The riser in this case could not, therefore, be conveniently removed by sawing through the necks I! with the usual snagging band saw. This example illustrates an important feature of my invention, as the riser may be broken as disclosed herein very close to the casting without interference from associated parts of the casting.

I- have heretofore referred only to the casting of aluminum, magnesium, and the like. However, iron may be cast with my improved method, but the washer must be formed so that it will not melt when in contact with the hot metal. This can be accomplished, as shown in Figure 5, by coating the washer herein numbered I! with a ceramic material l8, which fuses at a temperature above that of the metal being poured. In some cases, the washer may be formed. from a higher melting alloy with good results.

It should be kept in mind that while I have shown my invention as applied to a riser, the invention may be equally advantageous for use in removing gates, sprues, runners, etc., from the associated casting. In the attached claims the term riser is thereforev meant to include any part of the rough casting which is added thereto for the purpose of pouring the casting proper.

Some changes may be made in the shape of the washer l5, without departing from this invention, as it may in some cases only be necessary to insert a thin strip of shim stock along one edge oi. a square riser. Furthermore, some changes may be made in the mold structure and in the several steps comprising my improved method, without departing from the spirit of my invention, and it is my intention to cover by my claims such changes as may reasonably be included within the scope thereof.

I claim as my invention:

1. A snagging washer to be inserted in a riser of a casting mold comprising, a flat thin sheet metal stamping formed of shim stock having an opening therein, said opening proportioned to reduce the cross sectional area of the riser to about two-thirds, and a plurality of tongues stamped from the material of said washer, said tongues projecting slightly beyond the periphery of the 5. washer and extending back into the body of the washer a major portion of the distance therethrough, for the purpose described.

2. A snagging member to be inserted in a riser of a casting mold, comprising, a. flat thin sheet metal stamping formed of shim stock proportioned to reduce the cross sectional area of a riser to about two-thirds, and a plurality of tongues stamped from the material of said memher, said tongues projecting slightly beyond the periphery of the member and extending back into the body of the member a major portion of the distance therethrough, for the purpose described.

3. A method of casting articles of nonferrous metals comprising forming a. mold having cavities therein corresponding to the casting proper and to a riser, respectively, and inserting in the passageway connecting the casting proper and the riser a snagging washer made of a flat, thin,

sheet metal stamping having an opening therein, go 2,33

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 388,336 Boulton Aug. 21, 1888 855,396 Foreman May 28, 1907 900,970 Washburn Oct. 13, 1908 Hone Nov. 23, 1943

Images