US2284729A - Method of casting finned cylinder heads - Google Patents

Description

June 2, 1942. J. vvDusk-:vom

METHOD OF CASTING FINNED CYLINDER HEADS D Filed Oct. 6, 1941 (gem y '-14421 INVENTOR r JZZz'z/s Zyl/eyoz' r.'

A Y TORNE YS.

latented June 2, 19.42

UNITED STATE S PAT ENT OFFICE METHOD O F CASTING FINNED -CYLINDER HEADS Julius Dusevoir, Dearborn, Mich., assigner to Century Motors Corporation, DcarbornM1ch.,

a. corporation of Michigan Application October 6, 1941, Serial No. 413,739

' (c1. ca -126) 16 Claims.

This invention relates to the casting of finned..

cylinder heads for internal combustion engines of the air cooled' type and has for its principal object the provision of such method by the practice of which more perfect castings may be obtained than heretofore possible, as well as to a mold for use in connection therewith.

Objects of the invention include a method of casting a nned cylinder head comprising forming a mold part for the finned portion of the head from ,a refractory heat insulating material and forming another mold part for the combustion chamber portion of the head from a heat conducting material, casting the molten metal into the mold andl circulating a cooling medium in contact with the heat conducting portion of the mold before the metal has had an opportunity to completely set, whereby to accelerate the cooling of that portion of the metal defining the combustionchamber of the head; the provisionI of a method as above described in which the.l`

iin forming portion of the mold is formed principally from sand; the provision of a method as above described in which that portion of the mold defining the combustion chamber of the head is formed from metal and provided lwith hollow walls through which a cooling medium is cir'- culated; and the provision of a method as above culated; and the provision of a mold as above described that is capable of yielding under the contracting pressure of the surrounding casting during cooling thereof.

parts in both the views,

described in which the heat conducting portion` i of the Imold is heated prior to the placing of the moltenmetal in the mold and is cooled intermediate the time the molten metal is poured and 4is completely solidified.

Other objects of the invention include the pro? '.vision of a mold for casting finned cylinder heads for internal combustion engines of the air cooled type for non-hardening metal comprising a .mold portion for forming the iinned surface of the cylinder head presenting a refractory surface of low heat conductivity for contact with the molten metal poured into the mold, and a mold `portion for forming the combustion chamber portion ofthe head including a bare metal surface for contact withthe molten metal; the provision of a mold as above described having means for heating the bare metal surface preliminary to the casting operation; the provision of a mold as above described having means for cooling" the bare metal surface; the provision of a mold as above `described having means -for first heating. and

then cooling the bare metal surface; the provision of a mold as above described in which the bare metal portion`forms a part of a metallic mold part having hollow'walls through which a heat exchange 'medium is adapted to be cir- The above being among lthe objects of the preslent invention the same consists incertain novel features of construction, combination of parts and steps of operation to be hereinafter described with' reference to the accompanying drawing, and then claimedfhaving the above and other objects in view.

In the accompanying drawing which illustrates a suitable embodiment of a cylinder head and of apparatus which may be employed in the casting of the same in accordance with the present invention, and in which like numerals refer to like Fig. 1 is a fragmentary side elevational View of a cylinder for an internal combustion engine of the air cooled type illustrating the same as being provided with a finned cylinder head;

' Fig. 2 is a more or less diagrammatic ver-l the head to the cylinder must be relatively heavy inorder to withstand the explosion pressures oc curring within the combustion chamber and to permit the head to be secured to the cylinder with required security and sealing effect. On the other hand the fins, in order to be as eincient as possible in the dissipation of heatirom. thel head to the surrounding air, must be relatively thin. As a result of the relatively thick body and the relatively thin ns, regardless of the metal employed, certain foundry problems arise in the casting of such heads due to unequal cooling' and, therefore, unequal shrinkage of the metal in changing from the molten to the solid state. Aluminum is the metal most commonlyf'used in forming such cylinder heads and its coeicient of contraction in solidifying is higher than most metals,` thus causing the above described problems to be present toa greater extent. For this vreason reference herein will, for' the purpose of Simplicity in explanation, be limited to the explanation ofthe present invention in connection with casting of aluminum cylinder heads only, it being understood that the problems involved and the method of overcoming them are likewise applicable. to the casting of such headsfrom other methls and particularly those light metals or alloys thereof having a relatively high coeili cient of -contraction when changing from the molten to the solid state,

From the standpoint of foundry practice, if unequal sections of metal are cast in one piece in accordance with conventional practice; heat is dissipated from the thin sectioned part faster than the other, causingd such thin part to solidify before the thicker part and in solidifying to pull some of the molten metal away from the thicker part, thus causing shrinkages which ."'cause a change in the grain of the metal, gas

holes, core disturbances and other defects which make such a problem a serious one in the foundry. Particularly where such parts being cast are cylinder .heads of the type above described and are formed from aluminum or other light metal having a high coeiiicient/of contraction when changing from the liquid to the solid state the problem becomes so serious that a material percentage of the castings have to be scrapped when cast` in accordance with conven` tional practices. Fine cracks or checks appear lin the surface of the combustion chamber side of the head which appear to be caused by cracks in the sand core. Inasmuch as., the combustion chamber surface of the head isl required to be of solid metal free from al1 defects, the presence of such cracks or checks form defects which require the scrapping of many of such castings. Heretofore in attempting to overcome such defects in cylinder heads cast in accordance with conventional practice the combustion chamber side of the casting has been thickened and the excess metal machined away in an endeavor to cut away the checked surface and present clean solid metal in the final product. ha's been my experience that such procedure only aggravates the conditions initially forming such checks or other imperfections in that it still further aggravafes` the difference in thicknessbetween the main portion of the head and the fins, besides involving a material amount of additional cost in the excessive machining operations necessarily resulting to bring the-head to its nished condition.

The present invention, which is designed to overcome the defects above described resulting from conventional methods of casting such cylfrom the thickened portion of the head which now occurs in the practicev of the conventional, casting methods. Such Withdrawal of heat from However, it y.

-the thickened portion will occur at a time when,

in the practice of convention methods, the metal in the ns is solidified and the metal in the thicker portion of the head still remains in molten or partially molten condition. f It is, therefore, based upon the assumption that if in the casting operation this withdrawal of the heat by the fins from the thick portion ofthe head can be stopped completely, or to a major extent, 75

ically from metal, and after the pouring operation is completed this metal is quickly cooled so as to abstract heat from the combustion chamber side of the thick metal portion of the head. This cooling may be accomplished in the broader aspects of the invention in any suitable way, but

`in order to abstract the heat as fast as possible note that such metal portion is not-used as a y chill in the ordinary sense in that no attempt is made to harden the metal coming in contact with it, this being impossible because of the character of the metal being cast. Its purpose is solely .to cause solidification of thefmetal for the thick portion of the casting at a rate com- H mensurate with the solidiiication of the metal for the fins.

Where the shape of the combustion chamber is such that the metallic part of the mold is substantially surrounded by the molten metal during the casting operation, then with certain designs of combustion chambers and particularly.

in the larger sizes, unless some provisions are Amade to remedy it, the cast metal in solidifying and cooling may shrink to such an extent about the unyielding metallic part of the mold as to actually cause portions of the casting to be split. To overcome this ditlicultmin a more limited sense the present invention provides a construction which will permit theI metal portion ofthe mold thus surrounded by thecasting being made to yield under the contracting pressure of the cooling casting so as to minimize the strains thus setup in the casting. This is preferably accomplishedv by slotting or otherwise forming the metal portion so as to provide a plurality of parts or segments yieldably connected together.

Referring now to the accompanying drawingv cylinder head includes a relatively heavy main ilanged edge l5 and body portion I 6 of substantially the same thickness provided with a pair of hollow bosses lserving as inlet and outletborts n 2,284,729 for the associated cylinder. Fins 20 are formed integrallywith the main body portion I6 and lbosses I8. As indicated in Fig. 2 the cylinder head is interiorly formed to provide' a combustion chamber space 22, and while this may be of any desired size, shape and contour, as a matterof illustration it is shown in the present case as being partially spherical.

Referring now' to Fig. 2 the mold for forming the cylinder head shown in Fig. 1 is illustrated, the mold cavity being shown lled with metal in the condition it assumes after the pouring operation. It. will be understood that the showing in Fig. 2 is more or less diagrammatic particularly inview of the fact that it will be appreciated that in connection with the particular cylinder head shown the copewill ordi narily have to be formed in separate parts to permit the removal of the pattern in view of the differently directed fins 20 in the nal product. In any event, however, the mold will include a drag 30 and cope 32. Dependingupon the particular foundry practice. followed, the cope 32 may be green sand or it may be of baked sand such as is conventionally employed for forming cores; and the cavity therein is complementary in shape to the exterior surfaces of the cylinder head with the exception that two cores 34 are mounted therein for forming the hollow interior of the bosses I8. On the other hand thecope 32 may be of a permanent character such as is conventionally employed in so-called permanent molds. That is, it mayl be made up of one or more metallic parts in which case' the surfaces forming the mold cavity therein will be coated i with a suitable thickness of refractory material to insulate it against too rapid an absorption of heat from the molten metal cast therein. VIn

any event and regardless of the construction of the cope 32 it will, of course; be appreciated that it will be provided with a sprue hole 36 and a gate 38 connecting the sprue hole 36 with some suitable part of the cavity therein as for instance ,that portionthereof in which the flange I5 is formed and as indicated.

The drag 30 may be of any suitable character and construction as long as lit incorporates the features of the present invention. In other words, it may be of a permanent character as above described, it may be formed of green sand with the metallic combustion chamber forming `portion hereinafter described included as an insertion therein, or it may be formed of baked sand with such insertion therein. For the purpose of illustration it may b'e assumed in the case shown f that the drag 30 includes a main body portion 40 formed from baked sand and formed about an insert indicated generally at 42 which is imbedded in the main body portion 40. -The insert 42 is formed from metal and while the particular metal employed for this purpose is `more or less unimportant as long as `its melting point tem` perature is not such that the molten metal introduced .into the mold cavities will tend tofuse thereto, where the cylinder head being cast is to be formed from aluminum it may be conveniently formed from cast iron. The upper surface of the insert 42 is formed as a part of a spherical surface in-the particular case shown and complementary at least in part to the size and shape of the combustion chamber cavity 22 "desired in the cylinder head, due allowance, of

course, being made for shrinkage during the 'solidifying of the metal in the mold Aand machining stock where desired. In other words, the

upper portion of the insert 42 is complementary in size, shape and contour, with required allowances for contraction of the metal and machining stock where desired, to the combustion cavity 22. In Vthe particular case shown the partially spherical upper surface `of the insert 42 is extended downwardly into' the main portion 40 of the drag 30 and is there reduced to form a cylindrical collar 44. shown the insert 42 not only is hollow but it is provided with hollow Walls forming a passage 46 therein for the circulationy of heating and/or 'cooling mediums therethrough. Such heating and/or cooling medium may be introduced into the passage 46 in any suitable manner as, for' instance, by means of -a pipe 48 extending up through the hollow interior of the insert 42 and threaded through one-half of the hollow wall thereof so as to ldischarge its contents centrally of the hollow walls of the insert. Such heating and/or cooling medium may be discharged from -such hollow walls by means of one orv more discharge pipes 50 which, in the particular vcase shown, are threaded into the lower edge of the collar 44 and into communication with the passage 46 therein.

In the particular construction shown,because of the fact that the insert 42 is substantially semi-spherical it is possible that difficulty might arise due to the yshrinkage of the metal in cool- .ing during the cooling of the casting about it. In other words if ,the insert 42 was solid and unyielding it would present van uncompressible part about which the molten metal would attempt to shrink, and this occurring at a time when the metal of the casting is at an elevated temperal ture and, therefore, of low tensile strength might cause the casting to be split under the shrinkage strains. Where such a condition exists it is preferable to so design the insert as to render it capable of yielding under this contracting pressure in order to prevent the possibility above mentioned. This is preferably accomplished by forming the insertas a plurality of yieldably connected parts capable of yielding under the contracting pressure of the casting during shrinkage. In the particular case shown this is accomplished by forming four slots 6.0 in the insert 42, such slots being located in two planes perpendicular to each other and with their line of intersection coincident with the axis of the insert 42. These slots extend from the lower edge of the insert 42 to a point adjacent to butl spaced from the center of the insert 42 at its upper end, as shown, to thus provide four equally angularly disposed segments connected to each other over a limited area at thetop of the insert. The slots E0 do not, of course, cut into the passages 43 but are ments of the insert lare squeezed 'toward each other as the metal contracts about the insert and, of course, resistant to the heatof the molten metal. On the upper Vface of the insert 42 the 75' materialfilling the slots 60 is brought into flusn In fthe particular case,V

when the casting contracts about the insert the various segments will yield inwardly about their areas of connection with the central portion of the insert, the green sand in the slots 66 simply being squeezed out into the center of the linsert under the contracting force applied to the insert. l

It will be understood that the exposed surface of insert 42 in the mold is not covered by any refractory material which would materially reduce its heat absorbing capacity when in contact with the molten menu, but at the most it will 16 be merely given a light coating of lamp black or other dry lubricant to prevent possibility of the molten metal sticking to its surface.

In some cases it may be satisfactory to pour the molten metal into the mold without pre` 20 'heating the insert 42 and before cooling of the samehas been started, but in most instances it Will be preferable if the insert42 is heated immediately prior to the pouring operation so as not to materially chill the molten metal coming.

. through the pipe 46 to the hollow walls of the in contact with it before the mold has had an opportunity to become completely filled with molten metal. Where such preliminary heating is desired the same circulating passage employed for circulating the cooling uid may be employed 3,0

for circulating a heating medium. In such case the pipe 48 may be provided with a three-way valve 52 to which is connected a pipe 54 connected to a suitable source of cooling medium under pressure and' a pipe 56 connected to a 35 suitable source of heating medium under pres- -Y sure. 'I'he source of cooling medium towhich the pipe 54 may be connected may be suitablyv cooled air or other gaseous medium or may be a suitably cooled liquid medium. Preferably a 4U cold brine under pressure is employed as a cooling medium. Likewise the pipe 56 maybe connected to any suitable source of heating medium and while this-'may be either in a gaseous or liquid form it is preferably in a gaseous form, as

-for instance highly heated air, so that there will be no problem in the separation of the heating and cooling Amediums which may= momentarily intermingle upon 'shifting of the valve 52, this 'being particularly desirable where one of such 50 mediums is to be re-cirulated. f

Where no preliminary heating o f the insert 42 is to be done, the valve connecting the pipe 48 with. a source of cooling medium is closed, a

suitable charge of molten metal is poured into b5 the sprue hole 36 to charge the mold until the mold is completelyfilled, the metal is allowed to partially set or solidify and then the valve is.

turned on to cause a rush lof the cooling fluid through the hollow walls of the insert, thus with- 60 drawing heat from thecombustion chamber surblow holes, 'and the like particularly in the sur- 76 face 22 of the cylinder head. By employing an insert such as )42 of relatively high heat conducting capacity and forcinga cooling medium through the hollow walls thereofrthe metal of the mainbody portion I6 is caused to solidify at a rate'commensurate with the rate of solidifi-v cation of the metal in the ns 20, the result being that the casting is solidified more or less uniformly throughout during its transition from the molten to the solid state. Tests have indicated that by -following out the above described procedure thefdefects occurring in cylinder heads ofthe type described cast in accordance with conventional methods are substantially entirely eliminated, and the percentage of scrap heads resulting from casting in accordance with thev present invention is a fraction only of the heads scrapped because of defects occurring when cast -by conventional methods. l

Where cylinder heads cast as above described indicate freezing of the metal in contact with the insert 42 prior to com-plete filling of the mold, then preliminary heating of the insert 42 may be resorted to by means of introducing a suitable heating medium through the pipe 56 and then insert 42. In such case theheating medium is, of course, introduced into the insert 42 before the metal is poured and may be discontinued immediately prior to the pouring operation, immetact with the insert r42 prior to completing the pouring-of the mold, and that in .any case after the molten metal has been given an opportunity to partially set, the valve 52 is turned to cause an- `immediate forced circulationof the cooling medium through the insert thereby to quickly abstract the casting. 'A

Having thus described my invention what I claim by Letters P atent is: 5

1. The method of forming a cast light metal cylinder head having a rela'tively thick body provided with a multiplicity of relatively thin coolingviins on one, side thereof-and formed to pro, vide a combustion chamber cavity von the opposite side thereof, comprising the steps of casting molten metal to substantiallythe size, shape and contour of said head, protecting said finned side of said molten metal casting against rapid loss of heat from the surface thereof, and onlyafter said molten metal has partially set but is still in partially molten condition rapidly withdrawingheat from saidv opposite-side thereof.

2. The method 0f forming a cast light metal cylinder head having a relatively thick body provided with a multiplicity of relatively thin 5 cooling fins on one side thereof and formed to provide a combustion /chamber cavity on the opposite side thereof, comprisingv the steps of casting molten metal to substantially the size, shape and contour of said head, protecting said finned side of said molten metal casting against rapid loss of heat from the surface thereof, and only after said molten metal has partially set but -is still in partially molten condition rapidly Withdrawing heat from said opposite side-thereof by the circulation of a cooling medium in heat conheat from the surface 22 `of thev Y ducting relation with respect thereto, whereby to effect approximately uniform solidification of said molten metal throughout said casting.

3. The method of forming a cast light metalV cylinder head having a relatively thick body pro; vided with a multiplicity of relatively thin cooling fins on one side thereof and formed to provide a. combustion chamber cavity on the oplposite side thereof, comprising the steps of casting molten metal to substantially the size,shape and contourof said head, protecting. said finned, side of said molten metal casting against rapid loss of. heat from the.surface thereofjdelaying solidiflcation of said molten metal on said opposite side by retarding the loss of heat `therefrom until a part onlyV of said molten metal has` solidified, and thenj rapidly withdrawing heat from said opposite side commencing' while said molten metal is in partly moltencondition to acceleratevthe solidification of said molten metal on said opposite side.

4. The method of forming a cast lightvmetal cylinder head having a relatively thick body provided with a. multiplicity of relatively thin cooling fins on one side thereof and formed to pro vide a combustion chamber `cavity on the opposite side thereof, comprising the steps of cast-A ing molten metal to substantiallythe size, shape and contour' of said head, protecting said finned y side of said molten metal casting against rapid loss of heat from the surfacevthereof, delaying ducting relation thferewith after saidmold cavity 'has been fllled'with said` molten mctal but beginning at a time before said molten metal in said mold Ycavity has become completely solidified. 7. A mold for forming a cast light metal cylin-l der head having a relatively thick'body portion provided with a multiplicity of relatively thin size, shape and contour to said nned side of said A I Y head, and a mold portion presenting an unin- Sula-ted surface of bare metal complementary in size, shape and contour to said combustion chamber cavity, said uninsulated metal surface being arranged in metallic heat conducting relation-y ship with respect to a fluid circulation passage.

- 8. A mold for forming a cast light metal cylinder head having a relatively thick body portion provided withv a multiplicity of relatively thin cooling fins projecting outwardly from one sidel thereof and formed to present a combustion solidification of said molten metal on said opposite side by retarding the loss of heat therefrom until 'a part only of said molten metal has solidified, and then rapidly withdrawing heat from said opposite side commencing while said molten metal is in partly molten condition bythe forced circulation of a cooling medium in metallic heat conductingk relation with respect thereto to accelerate the solidication .of said molten metal on said opposite side.

5. The method of forming 'a cast light metal cylinder hea'dl having a relatively thick body provided with a multiplicity of relatively thin cooling fins on one surface thereof and formed to present a combustion chamber cavity on the other side thereof comprising, in combination, forming a mold with a cavity substantially complementary in size, shape andv contour to the desired cast head and with that surface comple mentary to said surface having said fins of a refractory material and that surface comple-4 provided with a multiplicity of 'j relatively thinmentary to said combustion 'chamber cavity of completely solidified in said mold cavity.

6. Themethod of casting a cylinder head having a multiplicity of relatively thin external cooling fins and a combustion chamber cavity on the side thereof opposite said fins, comprising the steps of forming a mold having a cavityc'ome plementary to said cylinder head and with that surface of said mold cavity complementary Ato said 'finned surface of vsaid cylinder head formed 9. A mold for forming a cast light metal cylinder head having a relatively thick body portion fprovided with a multiplicity of Vrelatively thin cooling fins projectingv outwardly from one side thereof and formed to present--a combustion chamber cavity on the opposite side thereof com- I prising, in combination, a mold portion'presenting a refractory surface complementary in size,

.shape and contour to said finnedside of said head, and a metallic, hollow walled mold portion presenting a substantially bare metal surface complementary in size, shape andA contour to said combustion chamber cavity.

10. A mold for forming a cast light metalcylinder head having a relatively thick body portion cooling fins projecting outwardly from one side thereof and formed to' present a combustion chamber cavity on the opposite side thereof comprising, in combination, a mold portion presenting a refractory surface complementary in size, shape and contour to said finned side of said head, a metallic, hollowwalled mold portion presenting a substantially bare Vmetal surface complementaryin size, shape and contour to said combustion chamber cavity, and meansfcr circulating a heating medium through said hollow of a refractory material of low heat conductivity and that surface of said mold cavity comple` mentary to said combustion vchamber cavity of substantially uninsulated metal, filling said mold cavity with molten metal, and abstracting heat from said metal` surface of said` mold cavity by 'the circulation of a cooling fluid in heat conl1. A mold for forming a cast light metal cylinder head having a relatively thick body portion provided with a mmtipiicity of relatively thin cooling fins projecting outwardly from one4 side thereof and formed to present a combustion chamber cavity on the opposite side thereof comprising, incombination, a mold portion present- `shape and contour to said finned side of said head, a metallic, hollow walled mold portion" presenting a substantially bare metal surface.

complementary in size, shape and contour to said combustion chamber cavity, and` means for circulating a cooling'medium through said hollow walls. f'

12. A mold for forming a cast light metal cylinder head having a relatively thick body portion provided with a multiplicity of relatively thin cooling fins projecting -outwardly from one side thereof and formed to present a combustion chamber cavity on the opposite side thereof comprising, in combination,la inold portionpresenting a refractory surface complementary in. size, shape and contour to said finned side of said head, a metallic, hollow walled mold portio'n presenting a substantially bare metal surface complementary in sizeshape and contour to said combustion chamber cavity, means for circulating a heating medium through said hollow walls,

senting an uninsulated surface'J of bare metal l complementary in size, shape and contour to said combustion chamber cavity, said uninsulated metal surface being-arranged `in metallic heat and means for circulating a cooling medium said combustion chamber cavity, means for circonducting relationship with respect tb a fluid circulation passage.

15. A niold for forming a cast light metal cylinder head having a relatively thick body portion provided with a multiplicity of relativelyv thin cooling fins projecting outwardly from one side thereof and formed to present a combustion chamber cavity on the opposite side thereof comprising,y in combination, a mold portion presenting alrefractory surface complementary in size, shape and contour to said finned: side of said head, and a mold portion presenting an uninsulated surface of bare metal complementary in size, shape and contour to said combustion chamber cavity, said uninsulated metal surface comprising a part of a hollow walled element the Walls of which are provided with a iiuid Y circulation inlet and outlet passage and including a plurality of portions each directly xed Y16. A mold for forming a cast light metal cyl- 'I inder head having a relatively thick body porside thereof and formed to present a combustion.

l chamber cavity on the opposite side thereof comwalls, means for circulating a cooling medium through said hollow walls, and control means for said mediums operable to permit ow of one of said mediums only atkone time through said hollow walls.

14. A mold for forming a cast light metal cylinder head having a relatively thick body portion provided with a multiplicity of relativelyl thin cooling ns projecting outwardly from one side thereof and formed to present a combustion chamber cavity on the opposite side thereof prising, in combination, Ia mold portion presenting a refractory surface-.complementary in size, shape and contour to saidl finned side of said head, a mold portion presenting an uninsulated 'surface of bare metal complementary in size,

shape and contour to said combustion chamber cavity, said uninsulated metall surface comprisp ing a part; of a hollow walled element the walls lof which are provided with a iiuid circulation y inlet and outlet passage, said hollow walled element including a plurality of segments generally spaced from each other but yieldably connected comprising, in combination, a mold portion together, and yieldable heat resisting [means A presenting a 'refractory surface4 complementaryY in size, shape and contour to said iinned side of,f

said head, and a contractible mold portion prebridging the space between said segmentsg J ULIUS DUSEVOIR.

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