US3167854A - Method and coring for casting and manufacturing cylinder heads and the like - Google Patents

Description

2, .965 v. E. SCHAFER, JR 3,167,854

METHOD AND CORING FOR CASTING ANDMANUFACTURING CYLINDER HEADS AND THE LIKE Original Filed April 2, 1957 3 Sheets-Sheet 1 INVENTOR. 2

ATTOzP/VEV 196:) v. E. SCHAFER, JR 6 METHOD AND CURING FOR CASTING AND MANUFACTURING CYLINDER HEADS AND THE LIKE Original Filed April 2, 1957 3 Sheets-Sheet 2 A TTOANf V- Feb 2, 1965 Original Filed v. E. SCHAFER, JR\ 3,167,854 METHOD AND CORING FOR CASTING AND MANUFACTURING CYLINDER HEADS momma LIKE April 2, 1957 3 Sheets-Sheet '3 INVENTOR ATTORNEY United States Patent METHGD AND (IQRING FOR (IASTING AND MANUFACTURING CYLINDER HEADS AND THE LIKE Vernon E. Schafer, .lr., Livonia, Mich assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Original application Apr. 2, 1957, Ser. No. 650,249, new Patent No. 2,893,371, dated July 7, 1959. Divided and this application Oct. 30, 1958, Ser. No. 770,704

17 Claims. (Cl. 29-4564) This invention relates to a method of forming an expansion joint in a member of a thermal device having a limited surface portion thereon subjected to rapid and extreme cyclic changes of surface temperature thereby subjecting said surface portion to severe cyclic thermal expansive and contractive conditions relative to the other surface and interior portions of the member and has particular application to internal combustion engines and the like. This is a division of my copending United States patent application S.N. 650,249, filed April 2, 1957, and entitled Expansion Joint, now Patent No. 2,893,371, issued July 7, 1959.

The various surfaces defining a combustion chamber or cylinder of an internal combustion engine are subjected to rather severe cyclic thermal conditions due to the extremely rapid changes in temperature alternately imposed on these surfaces by the heats "of compression and combustion and by the flow of relatively cool gaseous charges into the cylinders during the engine operating cycle. These changes in surface temperature result in the cyclic imposition of expansive compressive and contractive tensive stresses on these surfaces and the immediately adjacent layers of the various cylinder-defining members. In time these cyclic stresses result in fatigue cracking of these surfaces. Such cracking generally occurs intermediate and adjacent ports or openings in such members where the surface layer subjected to such cyclic stressing is of reduced dimension. Such cracking is also particularly prevalent in those applications where the engine is subjected to excessive fluctuations in load and speed; factors which result in sudden applications of relatively cool incoming air onto overheated cylinder-defining surfaces.

This invention contemplates providing the combustion chamber surfaces of a thermal device of the type described with expansion joints similar in function to those provided by the shallow grooves shown and described in United States Patent No. 2,791,989 issued to John Dickson and entitled Internal Combustion Engine. In accordance with the invention, such expansion joints are formed by casting inserts of nonfusible material into the cylinderdefining members adjacent critical areas. The resultant castings are machined so that these inserts intersect the combustion chamber surface and extend through the layer of the member normally subjected to such cyclic expansive and contractive thermal conditions. Under engine operating conditions the initial expansive compression imposed on this surface layer stresses this layer beyond its compressive yield point for the temperatures involved and effects the formation of grooves immediately adjacent to and including the opposite sides of the insert. These grooves serve to accommodate and isolate subsequent expansion and contraction of the surface layer from the adjacent FIGURE 1 is a fragmentary view of a cylinder for an internal combustion engine of the unifiow Diesel type with par-ts thereof broken away and in longitudinal section to show a cylinder head such as may be formed in accordance with the invention;

FIGURE 2 is a fragmentary view taken substantially on the line 22 of FIGURE 1 and shows a portion of the underside of the cylinder head in elevation;

FIGURE 3 is an enlarged fragmentary sectional view taken substantially on the line 3-3 of FIGURE 2;

FIGURE 4 is a view similar to FIGURE 3 and taken substantially on the line 44 of FIGURE 2;

FIGURE 5 is a perspective view of one form of insert shown in the embodiment of the invention of FIGURES 2-4;

FIGURE 6 is a perspective view of a second form of insert as used in the embodiment of the invention of FIGURES 24;

FIGURE 7 is a perspective view of a modified form of insert adapted for use in place of the insert shown by FIGURE 6; and

FIGURES 8, 9 and 10 are views showing the method of casting and machining a cylinder head to include expansion joint inserts in accordance with the invention.

Referring more particularly to the drawings, FIGURE 1 shows a portion of a uniflow, two-cycle diesel engine in which a cylinder bore 10 in an egine block 12 reciprocably mounts a piston 14. The piston forms an expansible combustion chamber 16 with a cylinder head 18 secured to the engine block and closing the cylinder bore at its upper end. The cylinder head is cored to provide coolant passages 20 and two exhaust passages 22. The exhaust passages 22 terminate in two ports 24 opening on the combustion chamber or fire deck surface of the head in diametrically flanking relation to an opening 2s provided therein for the nozzle of a fuel injector 28. The exhaust ports 24 are counterbored to receive annular inserts which are beveled to seat the heads of two exhaust valves 32 reciproca-bly mounted in the head.

As indicated above, the combustion chamber or fire deck surface of the cylinder head of such an engine is particularly susceptible to surface cracking intermediate and adjacent the valve ports and injector nozzle opening. The cracking which occurs intermediate the injector opening and the exhaust ports is generally in a diametrical plane common to the several openings. The expansion and contraction of the fire deck surface parallel to this common diametrical plane also tends to develop sunburst type cracking of the fire deck surface radially out wardly from the exhaust ports transversely of this common diametrical plane. After such cracks are initiated in the fire deck, they tend to progress through the fire deck and in time may result in the leakage of coolant into the combustion chamber. Such cracking and the subsequent cyclic expansion and contraction of the adjacent combustion chamber surfaces also result in the oval izing of the injector and valve seating surfaces with attendant Wear and malfunctioning of the injector and valves.

As shown in FIGURES 2-4, inserts 34 and are cast into the cylinder head in accordance with the invention and serve to isolate the cyclic expansion and contraction of the combustion chamber surface from the critical areas intermediate and adjacent to the injector opening, the valve ports and other openings through the fire deck of the cylinder head. These inserts are of a material or are coated to prevent fusion with the molten metal during the casting process. They are also of limited mass to prevent chilling of the adjacent portions of the casting. It has been found that these inserts can be of either a metal or ceramic-type material having a high fusion temperature or may be of a metal and coated with an oxide, ceramic or metallic material providing such fusion-resisting char- '2 m9 acteristics. In the illustrative embodiments these inserts are first stamped from rolled sheet steel and are then coated by dipping in a molten aluminum bath which is followed by a diffusion heat treating process in the manner shown and described in the United States Patent 2,569,097. This provides a coating of a highly temperature resistant iron-aluminum compound.

In the illustrative embodiments the inserts 34 and 40 are arranged in pairs in parallel spaced relation flanking the critical areas intermediate and adjacent to the injector and valve port openings thereby serving to isolate the cycle expansion and contraction of the remainder of the combustion chamber surface from these critical areas. The inserts 34 and 4% each have corrugated portions and 41, respectively, normal to and intersecting the surface layer of the fire deck which defines the combustion chamber and is subjected to the cyclic thermal conditions. The corrugations in the inserts extend parallel to the combustion chamber surface and interlock with the adjacent surfaces of the cylinder head. By using such corrugations it has been found that such inserts can be used without increasing the thickness of the fire deck inasmuch as the interlocking serrated surfaces carry the compression and combustion loads imposed on the adjacent portions of the fire deck.

The inserts 34 and 40 are terminated inwardly of the fire deck from their corrugated portions by rounded or cylindrically looped portions. These looped portions are open lengthwise to permit the free flow of molten metal within the loop during the casting process and serve to terminate the cracks formed in the head by the use of such inserts. The inserts 34 each have a single looped portion 36 which extends in parallel spaced relation to the combustion chamber surface and intersects the counterbores for the valve seat inserts at its opposite ends. The inserts 4t? are each rounded to provide two cylindrical or looped portions 42 and 43 formed at right angles to each other. The looped portion 42 is normal to and intersects the combustion chamber surface at one end and the looped portion 43 extends in parallel spaced relation to the combustion chamber surface and intersects the adjacent valve seat insert counterbore at its end opposite the looped portion 42.

Under normal engine operating conditions, the cyclic expansion of the surface layer of the head adjacent the combustion chamber effects the formation of grooves 37- and 44 immediately adjacent the inserts 34 and 40, respectively. Since the compressive stresses resulting from such cyclic expansion exceeds the yield points of the insert and head materials at the temperatures involved, these grooves are formed in part by the outward extrusion of a portion of the insert and in part by the permanent upsetting of the adjacent surface layer. The grooves 37 and 44 are thus formed during the initial or breakingin period of engine operation to the depth of this surface layer subjected to cyclic thermal conditions and are adapted to accommodate subsequent expansive and contractive plastic flow of this surface layer without imposing further compressive and .tensive stresses on. the critical areas of the head intermediate the inserts.

While the illustrative embodiments of the invention show the use of paired inserts in flanking relation to the critical the deck surfaces, satisfactory results have also been obtained using single inserts biseeting such critical surfaces. In certain engines and particularly those of larger size, additional inserts have also proven advantageous in preventing cylinder head cracking. In certain engines and particularly smaller engines where radial suburst type cracking from the exhaust port openings is not a problem, inserts in the fire deck transverse to the diametrical plane of the valve axes may not be necessary. Other forms of nonfusible inserts also are contemplated withinthe scope of'the invention and may be highly desirablein certain engines since the design and location the inserts within the head castingproper.

of the inserts should be related necessarilyto the prob lems deriving from the cyclic thermal conditions imposed on the surfaces of the various engine members.

A third form of insert 45 is shown in FIGURE 7. This insert is triangular in shape and particularly'designed for use in applications similar to that for which the inserts at) are used in the above-described embodiment. As shown, the insert 45 has a portion 46'correspending to the portion 41 of insert 49 and having corrugations intended to provide interlocking surfaces parallel to the combustion chamber surface of the fire deck. A round bead 47 is formed arcuately and diagonally of the corrugations and is adapted to terminate the insertcreated crack; intersecting the exhaust port at one end and the surface of the combustion chamber at its other end. The insert 45 may be made of a pressure and heatformed asbestos or other suitable nonmetallic material, as shown, or may be of a suitably coated metallic sheet material similar to that used in the above-described embodiment.

A preferred method of casting and forming a cylinder head to include such inserts is shown in FIGURES 8, 9 and 10. Referring to FIGURE 8, the various members of the head mold are formed separately and include a slab 5t) of baked core sand which forms the lower half of the head mold. The upper face 52 of this core slab is adapted to mount and reference cores for water, gas and other passages within the head. Such scores for exhaust gas and .water passages are indicated at 54 and 55,-

respectively. A plurality of grooves 56 are formed in the core slab and open on its upper face, being arranged in appropriate patterns with relation to the various core mounting positions. These grooves are beveled, as. indicated at 58, adjacent the upper face of the core slab and are adapted to mount the various inserts to be cast into the cylinder head. Prior to their insertion in the mounting grooves, the portion of each insert intended to extend within its mounting groove is coated with a suitable mounting paste. Upon insertion in the groove'any excess of this paste which is designated by the referencenumeral 6b is retained within the beveled portion of the groove thus preventing any blow-hole inclusions of the paste within the head casting proper. .This beveled portion of the groove also serves to insure thatthe molten metal, having convex meniscus characteristics with relation to the nonfusi'ble insert, will not leave any pockets adjacent When the inserts have been mounted-in their. respective grooves, the various cores are mounted on the slab core in their proper positions. An upper mold half, not shown, is then clamped to the slab core to complete thehead mold. After the mold has been thus assembled, the head 18 is cast by pouring molten metal in the mold. After the casting operation, the mold members are removed in a conventional manner, leaving the resultant head casting as shown in FIGURE 9. The casting is then cleaned and subsequently machined in the usual manner to' the finished fire deck surfaces and valve seat insert counterbores as shown in FIGURE l0g'the metal removed being indicated by phantom lines. These machining operations, of course, insure that these inserts intersect these finished surfaces of the head.

From the foregoing description it will be obvious to those skilled in the art that various changes might be made in the'preferred method of casting and forming the thermal device member to include non-fusible expansion joint'inserts, in the materials and shapes of the inserts and in the core mounting location, spacing and number of inserts utilized without departing from the spirit of steps-of forming mold members including aicore slab adapted to form combustion chamber end wall portions and to mount and reference core assemblies for providing passages and contours Within said head and having a plurality of grooves therein adapted to mount said inserts in predetermined spaced relation to said core assemblies, the side walls of each of said grooves being chamfered adjacent the mold face of said slab; mounting oneend of each of said inserts within one of said grooves and projecting outwardly therefrom, mounting said core assemblies with reference to said slab core and said inserts; assembling said mold members to form a mold; casting said head by pouring molten metal into said mold with convex meniscus flowing of the molten metal around the inserts within the chamfered portions of said grooves; removing the mold members from the resulting head casting; and subsequently machining said casting to provide finished combustion chamber surfaces by removing a portion of the metal formed adjacent said slab core and including the portions of said inserts projecting Within the mounting grooves during the casting process.

2. A method of manufacturing cylinder heads as defined in claim 1 including the further step of subjecting the finished surfaces of said head intersected by said inserts to cyclic thermal conditions thereby effecting the formation of grooves immediately adjacent the several inserts by the compressive upsetting of the layer adjacent said surface subjected to such cyclic thermal conditions.

3. A method of manufacturing a cylinder head for an internal combustion engine having a plurality of nonfusible inserts cast therein comprising the steps of forming mold members including a slab adapted to form combustion chamber end wall portions of the head and to mount and reference core assemblies for a plurality of passages and contours within the head and having a plurality of grooves therein adapted to mount said inserts adjacent certain of said core assemblies, the side walls of each of said grooves being chamfered adjacent the mold face of said slab the immersion of each insert in a mounting paste to a depth substantially equal to the unchamfered depth of said grooves; inserting the paste immersed end of each insert into one of said grooves; the referencing and mounting of said core assemblies with respect to said slab and inserts; assembling the mold; casting said head by pouring molten metal into said mold with convex meniscus flowing of the molten metal around the inserts Within the chamfered portions of said insert mounting grooves; removing said mold members and said core assemblies from the casting; and subsequently machining said casting to provide finished surfaces by removing a limited portion of the metal formed adjacent said slab and the portions of said inserts projecting within the mounting grooves during the casting process.

4. A method of manufacturing cylinder heads as defined in claim 3 including the further step of subjecting the finished surfaces ofsaid head intersected by said inserts to cyclic thermal conditions thereby effecting the formation of grooves immediately adjacent the several inserts by the compressive upsetting of the layer adjacent said surface subjected .to such cyclic thermal conditions.

5. A member of a mold for casting a cylinder head for an internal combustion engine comprising a slab having one face thereon adapted to mount and reference core assemblies for water, gas and other passages and cooperative therewith to form the combustion chamber end Wall portions of the head casting, said slab having a plurality of grooves opening on said one face and having a desired predetermined orientation with respect to the core mounting locations associated With said one face and said grooves being adapted to mount inserts of nonfusible sheet material to be cast into said cylinder head and being beveled adjacent said one face to receive a convex meniscus flowing of molten metal around said groove mounted nonfusible inserts.

6. A member of a mold for casting a cylinder head for an internal combustion engine comprising a slab having one face thereon adapted to mount and reference core assemblies cooperative therewith to form the combustion chamber end wall portions of the head casting and Water, gas and other passages Within said head, said slab further having a plurality of grooves opening on said one face and arranged in spaced relation to the core mounting locations provided on said one face and thereby to the passages to be formed by said core assemblies, said grooves being dimensioned to receive and support projecting inserts of sheet material adapted to be nonfusibly cast into the cylinder head and said grooves being of an increased opening width adjacent said one face, the increased opening Width of said grooves being adapted to receive limited fiow of molten metal Within each groove opening around the nonfusible insert mounted in each groove.

7. A mold assembly for casting a cylinder defining member for an internal combustion engine including a first mold member of baked core sand, said first mold member mounting and referencing a plurality of secondary core sand members cooperative therewith to form combustion chamber end Wall portions and to define Water, gas and other passages within said cylinder defining member, said first mold member further having a plurality of grooves opening on at least one face thereof in predetermined spaced relation to the passages to be defined by said core assemblies and to each other, said grooves being dimensioned to removably mount inserts of sheet material adapted to be nonfusibly cast into said cylinder defining member and the openings of said grooves to said one face of substantially greater width than said inserts and adapted to receive molten metal flow into said grooves during casting and around the groove mounted inserts.

8. A mold for casting a member having a surface thereon adapted to be subjected to extreme thermal conditions capable of inducing plastic flow therein adjacent said surface, said mold including a mold member having a face thereon adapted to define said surface, said mold member having a plurality of grooves therein opening on said one face in spaced relation to each other and adapted to mount inserts of nonfusible sheet material to be cast into said member to intersect and limit the thermally induced plastic flow of said surface between said inserts, and said grooves being beveled adjacent said one face to receive a convex meniscus flow of molten metal around said surface intersecting nonfusible inserts during the casting of said member.

9. A mold for casting a member having a surface thereon adapted to be subjected to extreme plastic flow inducing thermal conditions, said mold including a mold memher having a face thereon adapted to define said surface, said mold member having a first plurality of grooves therein opening on said one face in spaced parallel relation to each other, said mold member having a second plurality of grooves therein opening on said one face in space parallel relation to each other and extending transversely of said first grooves, and said first and second grooves being beveled adjacent said one face, the nonbeveled portions of said grooves being adapted to paste mount inserts of nonfusible sheet material to be cast into said member to intersect said surface and limit the thermally induced plastic flow thereof between said inserts, and the beveled portions of said grooves being adapted to receive excess insert mounting paste and convex meniscus flow of metal around said inserts during the casting of said member.

10. A method of manufacturing a cylinder head for an internal combustion engine comprising the steps of first casting said head to include at least one insert of nonfusible sheet material intersecting a combustion chamber defining surface of said head; subsequently machining said casting to remove a portion of the cast surface metal and of each insert to provide a finished combustion chamber surface; and the further step of subjecting the finished sur-

Claims (1)

13. A METHOD OF MANUFACTURING A MEMBER HAVING A SURFACE THEREON ADAPTED TO BE SUBJECTED TO EXTREME THERMAL CONDITIONS, SAID METHOD INCLUDING THE STEPS OF FIRST CASTING SAID MEMBER TO INCLUDE AT LEAST ONE INSERT NONFUSIBLE THEREIN AND INTERSECTING SAID SURFACE AND THE FURTHER STEP OF SUBJECTING SAID FINISHED SURFACE TO CYCLIC THERMAL CONDITIONS THEREBY IMMEDIATELY ADJACENT EACH INSERT BY THE COMPRESSIVE UPSETTING OF A LAYER OF SAID MEMBER ADJACENT SAID SURFACE AGAINST EACH INSERT TO PREVENT THE EXTREME THERMAL STRESSES WHICH WOULD OTHERWISE RESULT IN SAID MEMBER ADJACENT TO AND INCLUDING SAID SURFACE FROM THE EXTREME THERMAL CONDITIONS NORMALLY APPLIED TO SAID SURFACE DURING OPERATIONAL USE OF SAID MEMBER.

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