US2610372A - Apparatus for reducing the porosity of castings - Google Patents

Description

Sept. 16, 1952 H. F. SCHROEDER 2,610,372

APPARATUS FOR REDUCING THE POROSITY 0F CASTINGS Filed April 20, 1949 L (III/1111111111111; :E\X

" jji/ilvrole. BY I m mmwm metal is usually forced into the die cavity The air and gases in- Patented Sept. 16, 1952 UNITED STATES PATENT: OFFICEAEQJ'VITT-Q Henry F. Schroeder, Milwaukee, 'WisQ: Application A'bril'zo, 1949, Serial No. 88,546

1 Claim. 1

This invention relates to improvements in the apparatus for reducing the porosity of castings.

In the manufacture of 1 die castings molten under relatively high pressures. the die are greatly compressedby the molten metal and make it difficult for the molten metal to enter the cavity to form a solid casting. In addition, this entrapped air and gas causesporosity in the resultant casting.

Porosity reduces the strength of castings and tends to, cause leakage when the castings are used for containing fluids under pressure. Porosity is particularly undesirable in castings which are to be plated. .Platers demand castings with such perfect surfaces that only one polishing operation thereon is required, the parting line. All pressure die castings have a chilled surface or skin which is several thousandths of an inch thick. At times, in order to shape a casting or to remove an imperfection,

it is necessary to polish a portion of the surface other than at the parting line; Should porosity be encountered when the polishing wheelabrea'ks and it must be scrapped. In addition to the scrap which results from during the polishingoperation, many castings are scrapped because of porosity encountered when the castings are sawed or broken from the gate.

One of the methods heretofore used in an at tempt to alleviate this porous condition and to produce sound castings was the cuttingof vents in the face of the die from the cavity to the outer edge thereof. This expedient, however, only partially remedied the situation, because all'of the entrapped airand gas could, not escape through the vents, since the vents had to be kept very small. If the vents were made too wide or too deep, the molten metal was iorced from thedie therethrough and endangered the workers in the. vicinity of the casting machine. In addition, metal flowing into the vents produced fiash on the finished casting which increased trimming costs. a 1

Another expedient tried in an attempt to reduce porosity in castings and to achieve soundness and dense grain structure therein was the use of higher pressures for injecting the molten metal into the die. Some of the machines'now in use exert up to 30,000 pounds per square inch injection pressure. These machines require an extremely high. die locking pressure in the 'neighborhood of .600 tons.

namely the removal of porosity encountered,

The cost of very high pressure machines is extremely high as compared to the earlier lower pressure models, and therefore the cost of the finished castings is accordingly increased. In addition, the use of extremely'high pressures" forces molten metal into minute cracksinthe die and into the joint between meetin'g-'"surfaces of the die blocks to a much greater extent than do the lower pressures.

For example, in many cases high pressures on a' given 'die produce a pronounced casting substantially free of a parting line in the'same die.

parting line, whereas re1ativelylow=- pressures will produce 1 a With the above :in mind, it is a general'objec'ti ratus for manufacturing castings whereby the of the invention to provide an improved appa porosity of the finished casting is reduced by the creationjof a vacuum in the die cavity sir'n'ul-f taneously with the injection of molten metal therein.

Another object of the invention is to' provide an improved method of and apparatus for man ufacting castings wherein the trimming costs" 25 through this skin, the casting cannot be plated,

die.

are reduced by the elimination of-vents in" the A further object or the inventionis to provide an apparatus of the class described' whichf produces sound castings havingdense 'grain'structurewithout requiring the useof 'high'injec-l tion pressures.

A further object of the inventionis toprovide an apparatus of'the class described which produces castings in which the parting line is substantially eliminated, thereby reducing the costof polishing and also enhancing the appearance" of the finished casting.

A further object of the invention is to provide an improved die construction having incorpdrated therein an evacuating cylinder prdvid'edj withan evacuating piston; said cylinderb'eingin communication with a die cavity througha restricted aperture. v

A further object of the invention'i's-to provide an improved die constructioniot the'clas'sdescribed wherein the evacuating cylindenas' well as the aperture communicating between said'cylinder and the cavity, is formed in the die in such a manner that any metal which flows therein and solidifies forms an integral part of thegate and can beeasily ejected with said gate.

A furtherobject of the invention is to provide a die constructionof the class described wherein the evacuational movement of the evacuating piston is synchronized with the injectionoper ation'. A further-object of the invention is to provide a die construction of the class described wherein the operative displacement of the evacuating piston is greater than the combined volume of the sprue hole, the runners and the cavities of said die, thereby insuring that the highest possible vacuum is created by operation of the evacuating piston.

A further object or: the invention is to provide:- an improved apparatus for reducing the porosity of castings which is applicable to multiple cavity 16 dies as Well as to single cavity dies, and which is applicable to side gated dies as .well as tocenter gated dies.

A further object of the invention is to provide a multiple cavity die construction-of=theclass described wherein more than one -evacuat-. ing piston may be incorporated therein and operated simultaneously with the injection of-the molten metal to insure complete evacuation of all.ol ,theicavities-of said die.-

A-illrthor:objectioftheinvention is to provide; ardies construction of; the class described which; isgsimple which is relatively easy to 'manufacure,-;and--which isotherwise well adapted .forthe purposes;described.-

Withthe; above and other. objects in: ,view, the inventionconsistsof the improved a aratus for reduoingflhe.porosity of castings and; all of :the pattsandgcombinations.incident thereto, as set: forth yin the claim. and i all equivalents thereof 3O the:drawing;. accompanying; andv forming a part of this specification wherein are shown. threaombodiments: of the:invention-andwherein the-ssmereierence charac ersrindicatc the same parts-l all of theviewsz: 7

Riel :Llssairagmentary vertical sectional View t konvthroueh a, cold ;chambendie ,casting. machine quipped with. a. n r eated die. con-i structed in accordance with the invention;

171g. :2: isragyertical sectionalvicw takenialong 40 thcrline -2-.2 orflig. land looking at..the;face iitht pothalia fg he imp idi t 11%{3 ism-view. similar to Fig. 2, of a side gated; die having multiple cavities and constructed .in ccor ance withgthe invention, said; die .being 45 provid d .with-.;three 5 evacuatin plunsers: and i Rig s;is:asviewsimilartoFigs. .2 and '3 showing aemultiple cavityzcenter gated die constructed in accordance with the invention, and: having two evacuati g. ;p1ungers..

- Referring more: particula y to-fig. 11.0: .the drawing -wherein is shown, a fragmentary .-verioal sectional vi w: et; a; modern; i cold chamber ynesorydie casting machine, the numeral it indicates the die plate whichgis. aporturedto; 55 receive atubular-cold chamber;l I-.' Thechamber l l ia preferably;madeeof :heat-treated-steel and s-provided with :a. sleeve liner I2 ofrany uitable heat resistant i alloy; suchzias; vfor examp e, that kno m.-as;;Nitrallov-? The cold hamber I I and co the liner l2 are formed with alined-pouring :slots. Brand; I4 neantheir outerends. An injection Plun er; I5.- -,is.-.positi ned.-in he hereof the liner IL: -In-1iis-v 1; the plun er is in. retracte position; being; positioned. with; its tip I6 outwardly adjaa e5 centr hi -slot- I4 in the liner I2; The plun er I5 issuitablyufixed to:ap unger-pis on red; I l which. isa o ne t d; tor-a; suitableactuating pi ton. (no shown).

'Moun ed-on1thesdieplat I 11s a zdie. I litwh h 7 0' is. conventionally. formed ofi a cover porti n; r. (Retina-iii lfir'fixed to;-the die plate ID. an ian lector portionlor fejector half? Zll'which is movable into and out of engagement with the cover portion. lit. The; movable. mounting: for. the 75' 4 ejector portion 20 is conventional and is not shown. The halves of the die are apertured adjacent the corners thereof to receive dowel pins 2| which insure alinement of said halves.

The die I8, shown in Fig. 1, is of the center gated type having a sprue hole 22 in the cover portion I9 and a biscuit well 23 in the ejector portion 20,1. the-sprue hole and. the biscuit well being coaxial withthe boreof theliner I2. The cover portion I9 of the die I8 is formed with a cavity 24 and with a runner 25 communicating betweenthecavity zd and the sprue hole 22.

The die I8"is formed with an elongated cylindrical bore 26, extending inwardly from a side 1 thereof, the. axis. of said bore preferably lying in-the plane ofthemeeting faces of the die halves I9 and 20; Each die half, therefore, is formed with asemi-cylindrical recess in the face thereof which forms a part of the bore 26.

A relatively; shallow groove 21 I is formed in the face ofgthecoverportion I9? of the die I8 communicating with the inner end of the'bore.- 26 and with :the cavity. 24, preferably ata- .point opposite-the-runner;25; asshown inFigv 2, or.

saidgroove .-may-bc;in theblock 20 or inv'both die -ha1-ves,,I9-and.20..depending on the type of.

casting. A. cylindrical evacuating plunger, or

piston-28.15 slidably positioned-dnthe bore 26..

Adiacentits outer end the plunger 28;-is formed with an annular shouldenportionlfl. andwith.

a; portion 30 of reduced adiameter, Abutting the outer endof-the plunger281s a plunger piston. rod- 3 I .which is. formedadiacent its. abuttineend. Asplit. sleeve 33 is formed to fixedly connectthe. plunger: 28,.with the piston. rodl3 l and is held together. by. suitable. bolt.s.,iul..v A guide, sleeve 35 is-ifixed with ,a portion-32.0freduced. diameter to the coverportion fl 9 necting sleeve .3' 3 in operated-ram.

The ,e'vacuating'plung'er 28 ismovable out wardly: from: its innermostposition,shown in.

Fig, 2.. Thesize' of thebore 26= and the distance travelled by -the piston 28.,is preferablysuch. that the cubic displacementv ofthe, plunger 28 is. greater than thecombined volume of. the die;

cavity 24, the runner 25, the groove 21, the biscuit well 23, andeat least aportionofthe-sprue hole 2.2-. It, is. preferable tohave a relativelylong stroke iortheplunger 28 withacorrespondingly relatively smalLdiameter, ratherthan .to.,have a short stroke. and relatively. large, diameterhereforia p The operation of the improved apparatus .will

now be discussed) With.theparts,of, the die; casting machine disposed asshown in-Figs. 1 and.

2, a charge. of molten metal I 31 -is-. poured from a ladle 38 into the sleeve-Hahead of the -injection plunger; I 5 through thegpouringslots 13 land- The injection; plunger,

erablybase rate ofrcubic displacement greater than that-.of;thezinjection. plunger. I5. Hence, the air ,-is;; withdrawn from, the..-clie.. cavity: I at a volume rate which is greater 'than the tithe-die... I 8,- as. bylsuite able bolts, 36, and ,said, sleeve surrounds the. 0011-. a manner .to permit axial. sliding; movement or the latter. therein. .The. plun er.- piston rod :3I is connected .to a suitable actuating .-means suchlasrfor example, a fluid.

volume" p ros mol en ,m IQ- using low pressure machines the rate of iniection' o'f the-"molten metal", thereby creatinga vacuum in the ,cavity 24 h smgv iii- 2 wi hdrawi -:-si bst n rr ll. o nsi as sth reirem- .I mQ aIQf ea andsa s -t awiitygZKlpermits the molten metalto flow freely into said cavity. "I'he absence of any substantial m unt o i or s si ihei av t mits the molt n meta o term s n sit ree-iron pin he-ca i 24 and a certain.amount .of ..ili malflow into the groove 21. Some ofthis "metal may even be drawnizinto the bore plunger. Themol ejector; portion 2E of the from the cover portion IS. The gate is then ejected in the usual manner. Since the bore 26 and the groove 21 are formed in the, die faces, the metal which flowed into the groove 21 and the bore 26 is removed from the die with the rest of the casting because it is an integral part of said casting or gate.

tens metal .then' solidifies, ithe die-l8 is moved away Any suitable means may be used for actuating the evacuating plunger 28, but it is important that its withdrawal movement be synchronized with the inward movement of the injection plunger l so that the former is moving'outwardly at the instant the latter seals off the pouring slot is, so that the vacuum is built up at the proper time.

Experience has shown that with die it is possible to make castings of definitely higher density than were previously made on the same machines using conventional dies. It was noted that in the castings made in the improved dies porosity had been substantially eliminated.

Experience has also shown that, when the improved dies are used, extremely high injection pressures are of no substantial advantage. The castings produced in the improved dies used on relatively low pressure machines are of substantially the same quality as those made on the improved dies on high pressure machines.

It is apparent that, not only does the improved apparatus result in sound castings having substantially no porosity, but that high quality castings having these characteristics can be made on relatively low pressure machines. By parting line, which is formed by the extremely high injection pressures of the high pressure machines, is appreciably reduced. In addition, since the improved die does not have conventional vents, there is no flash resulting from metal forced out thereof.

Elimination of porosity greatly reduces'the amount of material scrapped, not only because of leakage (where the castings are to be used to contain fluids under pressure), but also because of poor polishing qualities. The elimination of the parting line and of the flash which results when die vents are used, greatly reduces the trimming cost of the finished casting. In addition to the above features, the elimination of the need for extremely high injection pressures permits the use of relatively inexpensive die casting machines having relatively low die locking pressures. This greatly reduces the investment in equipment which must be made by a manufacturer and reduces the cost of the castings accordingly.

Fig. 3 is a view similar to Fig. 2 looking at the face of one half I9 of a multiple cavity sidegated die I8 constructed in accordance with the through ,the

' y: the evacuatin the improved is provided withfthree evacuating positioned in suitably placed-r bores 26'; which which communicates with through four runners .25; tions extending into the cavities 24.

communicate with the cavities 24. by means .of The numeral 38 indi-y: cates-the nozzle of aconventional metal 'cham-: theair or the plunger passages 21'; as shown...

ber or gooseneck of either Fig. 4 is a view similar to Figs. 2 and 3 docking at the face of-Tone half'fiB." hf a multiple cavity center-gated die constructed in accordance with the invention. The-die l8"- h'as a'sprue hole 22" mli c ns t vities 1 4" t ou h munners 25''. A pair of oppositelydisposed evacuat ing plungers 28 are slidably positioned in the bores 26" which communicate with the cavities 24" through grooves 21" and the interposed enlargement thereof 38. The latter is for the purpose of equalizing the suction effect of the evacuating plungers among all of the cavities communicating therewith.

Any type of die can be constructed in accordance with this invention, and any suitable number of evacuation plungers may be employed depending upon the number and positioning of the cavities, the number and positioning of movable cores and slides used, and upon the interference with parts of the die casting machine. An important feature common to all dies constructed in accordance with the invention is that each evacuating plunger and the passage or passages connecting it with one or more cavities be formed in the die faces, so that any molten metal which might follow a plunger can be ejected as an integral part of the gate. Any suitable and practical means may be employed for efiecting a seal as between the two die blocks.

Generally speaking the passages or grooves 21, 21' and 21" should be large enough to allow air and gases to readily flow therethrough but they should be small enough to somewhat restrict the flow of molten metal therethrough.

While the invention has been shown and described with respect to the art of die casting, the concept of the invention is applicable to principles of permanent mold casting, tothe molding of plastic articles, and to sand mold casting.

Various other changes and modifications may be made without departing from the spirit of the invention and all of such changes are contemplated as may come within the scope of the claim.

What I claim is:

In combination: a die formed with a cavity and with a molten metal inlet passage opening into said cavity, said die being separable into two sections along a plane through the die, and said die being formed with a socket remote from said cavity and said inlet passage which socket is positioned with its axis in the plane of separation of said die, said socket extending inwardly from one side of the die and having a closed end, and said die being formed in one of its meeting faces with a single air evacuating passage remote from said inlet passage and extending between the closed end of the socket and said cavity, said pair of passages being the only passages leading to and from said cavity, said air evacuating passage being of considerably less cross-sectional area than said socket; an airevacuating piston 'slidably positioned in said socket for withdrawing air from said cavity via ingi'a, cubic misplacennent atzleast'ias:great as flie' coinbin'ed wolum'e ot saicl idie :cavity and" the :pair. of paiss'a'g'es within kth'e :die communicating with said cavity; pressure-means aco'ope'liable 'withsd'lhe molten r'xital zinlet lipassage for injectirifg molter mtaUintb the qavity; :an'd :me'ans (for moving said pisfion' iaway :from the nlosed end of "said socket inftimed srelationship with the injection.

of molten Imetal into theadie 1:0 'thereby create a vacuum in said. cavity during an injection oh'eraitirin.

lI-IENRY SCHROEDER.

REFERENCES CITED. "ill-1i? fdlioifiing rferences are 6f 'iixecdrd m the 'fileqififiliis iia'T-fefit:

Number 8"? 45mm Rams

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