US2676371A - Piston molding core - Google Patents

Description

April 27 1954 w. M. VENNER l-:TAI` 2,676,371

PIsToN MoLDING CORE original Filed Jan. 2. 1947 37 FIG FIG@ Patented Apr. 27, 1954 UNITED STATES oFFIcr:v

Bowser, Jr.,

Continuation of application January 2, 1947. T 1950, Serial No. 161,20

7 Claims.

This invention relates to piston mold cores, and particularly of the type disclosed in United States Patents Nos. 1,551,193, issued August 25, 1925; 1,952,199, issued March 27, 1934; and 1,993,439, issued March 5, 1935. This application is a continuation of application Ser. No. 719,844, filed January 2, 1947, now abandoned.

In the piston molding machine of the character described, a core is provided conforming to the inside of the piston, such as a trunk piston, particularly adapted for internal combustion 'engines and provided with a head and a skirt. Where there are internally projecting parts, such as Wrist-pin bosses, which prevent the withdrawal of the core, this core cannot be of a single piece, but supplementary or side sections must be provided, all as described in the patents referred to. In some cases there may beinternal projections or ledges which may be in regions at right angles to the bosses, such as balancing lugs or ire-enforcements in those regions, or there may be an annulus inside the piston for a ringland. In such a case it is diilicult and in some cases impossible to withdraw the center core section.

A trunk piston which nowadays is constructed of an aluminum alloy, has a, construction which renders its production by a permanent molding process dimcult. Such a piston comprises a head and a skirt, the latter provided with inwardly extending wrist pin bosses. The head is rather thick, and such thickness extends down the sides in order to provide for ring grooves. The'skirt itself, however, is made thin 'in order to reduce the weight, there being usually ribs extending from the head to the bosses inside the piston. In casting the piston, the core as well as the mold must be kept ata temperature of S25-900 F., for otherwise a good casting will not be produced. An aluminum Yalloy itself has not only high crystallization shrinkage, but a high cceiicient of expansion and contraction several times that of cast iron or steel of which the coreV is almost universally constructed. After the metal has been poured, there will be nrst compensation for crystallization shrinkage and thereafter solidiication, both `of which are indicated by a drop in the center of the' gate and colora-v tion of the gate by which the melder can deterf mine when shrinkage has been compensated for and when the metal has solidified around the core. The problem of opening the mold, that is the outside mold parts, is not of moment; for the metal will simplyshrink away from the outside inold parts, which" 'are usuallyin halves as shown in the patents referred to. The problein University City, Mo.

Serial No. 719,844,

his application May 10,

of releasing the core is, however, critical; for if the core be withdrawn too early and before the metal has set, the piston will be ruined; if, however, the release of the core be delayed too long, the metal will shrink on the core, which may re sult not only in the development of hairline cracks in the thin skirt, but even seizure of the casting on the core. The release ofthe side sections of a core is again not a serious problem,l provided the middle section is released in time, for if that is done, the side sections Vwill simply move in upon further contraction of the casting. The release of the middle core is, however, a problem, because it must be done not'too soon and not too late. yThe casting of a piston is, therefore, something very special, and it involves a special problem and a special solution.

One of the objects of this invention, therefore, is to provide a piston core of the character described, which will meet the above-described re'- quirements and which will have distinct advantages.

In the machines of the patents, -the piston is cast with the head up and core is withdrawn from the bottom, leaving the piston casting setting on the machine. y

Another object of this invention, therefora'is to provide a collapsible core capable of forming a casting of the character described, but which may be withdrawn as a whole from the casting, as distinguished from picking the core-parts out piece-meal.

Further objects will appear from the detail description taken in connection with the accompanying drawing, in which will be set forthl an illustrative embodiment of this invention.` It is understood, however, that this invention is susceptible of various embodiments Within the scope of the appended claims.

In accordance with an illustrative 'embodiment of this invention as in the piston holding machine of the character described in the above patents, the core comprises a middle section and a pair or pairs of side sections movable into the space occupied by the middle section when the latter is withdrawn. The middle section is composed of an inner section and one or more lateral sections slidably engaging the inner section and means is provided adapted to collapse the lateral section or sections against the inner section upon relative sliding thereof. In the piston core of Patent 1,993,493, while the engaging faces of the inner and-lateral sections are inclined, thisinclnation is not abru'ptbut vslig'htvin order tosimply avoid dragging oi the core along the cast inner surface of the casting.

In accordance with an illustrative embodiment or this invention, the piston core assembly is de signed to provide for the formation of an inwardly projecting ledge on the inside oi the casting. ln order to eilectuate that purpose the core exterior has a recess for molding that ledge with a projection above, i .e. toward the end of the core, and the core assembly has means between the inner and lateral sections adapted upon relative sliding thereoi to permit retraction oi that projection inwardly to clear the ledge. Where the ledge is in the region of a side section or sections, then the movement oi the latt r into the space occupied by the former will retract the recess from the ledge. in the embodiment described, the inner and lateral sections are permanently held in assembled relation to slide relatively while so held but to remain parallel, and a series of sets of cooperating elements on the inter-engaging sections and spaced therealong are adapted upon sliding of the inner section with 1espect to the lateral section, and while the lateral section is held by the casting to move the lateral section parallel to and against the inner section. It is, however, important in the molding of pistons to avoid dubbing or rounding of the head-forming ends of the sections; for otherwise an objectionable :dn will be formed. Means is provided to avoid such dubbing or rounding. lt is understood that the expressions abo-ve, below, innen side and lateral are used ior convenience in connection with the drawing showing the core with the top up.

In the accompanying drawing:

Figure l is an elevation, partly in section, oi a piston core illustrating an embodiment of this invention, one of the side cores being shown in elevation, the parts being shown assembled ready for pouring of the metal and the casting being shown in sections;

Figure 2 is a top View oi the entire core but with the casting and core parts in sections on line 2 2, Figure l;

Figure 3 is a view similar to Figure 1,out showing the middle core collapsed; and

Figure s is a view similar to Figure 2, but showing the middle core collapsed, partly in section on line fil-Ji, Figure 3.

Referring to the accompanying drawing, iii designates the inner section of the middle sec tion oi the core assembly, while ii designates lateral sections which, together with the side sections i2 form the inside oi the piston. The side sections have recesses 3B which form the wrist-pin bosses and the outside mold halves (not shown) may have cores to form holes in the bosses as in Patent 1,952,199. rlhese side sections have lugs do provided with extensions 5% and guided on a base 5l on the molding machine and connected by rods 62 to handles (not shown) whereby these side sections may be moved into the space left by the center core when the latter is withdrawn, all as shown in Patent 1,952,199.

rllne core section lo is provided with a threaded recess is for attachment to the withdrawing piston rod @t of a molding machine as also illustrated in the patent referred to. The inner section lo of the middle core has lateral extensions 54 which engage with lateral extensions 2li on the lateral sections ii, which in turn are adapted to engage base parts 5I on the machine when the center core is moved to pouring position generally as shown in the patents referred to.

As shown, the external surface of the core as'- sembly has a recess I4 with a projection i2 there above, in order to provide on the inside of the piston a ledge such as an inward annulus, Fifi, Figure 3. The lower part of the projection ft2 is inclined to present a cam face and to form a complementary cam face on the upper part of the ledge cast on the piston. It will be apparent that in such a construction, the center core, including sections I and H cannot be withdrawn 'from the piston unless a special construction is However, when the middle core assembly is withdrawn, then the side sections iii may 'oc moved into the space occupied by the middle core, in a manner as described in the patents.

As shown, the inner core section iii has assembled therewith the pair of lateral sections i i, each or which is adapted to slide relatively alt the inner section. The engaging faces may also be inclined upwardly towards the center of inner section as in Patent 1,993fl39. section iii, however, has spaced therealon,v series oi sets of recesses 2i and projections providing abrupt cam faces 22, and each lateral section il has spaced therealong a corresponding series of sets oi recesses 23 and like projections 415, providing abrupt cam faces 2d. The recesses and projections on the lateral sections il are thus complementary and mesh with the recesses and projections on the inner sections it when the sections are slid relatively to move the lateral section parallel to and against the inner section.

The core shaped to the interior or" the piston therefore comprises an inner section and a lateral section permanently held in assembled relation to slide relatively while so held, but to remain parallel. The lateral section has an inwardly extending recess for molding an inwardly projecting ledge on the piston, which section has a projection extending outwardly above the recess. The inner and lateral sections have series of sets oi cooperating meshing cam ele ments on their inner engaging faces, and which are spaced therealong. These elements, however, project laterally to extend corresponding to said projection and cooperate when said sections are relatively extended to hold said lateral section extended laterally, but adapted upon sliding ci said inner section with respect to said lateral secion, and while the lateral section is held against longitudinal movment, to move said lateral section toward and against said inner section in order to retract said projection inwardly to clear said ledge.

The bottom of the section i6, i. e. its extensions M is arranged to abut against the extensions 2c on each section Iii at 25, and short cam faces 26 are provided at the bottom of each section i i for cooperation with like carn faces 5% cn section ill as shown. In order to hold the sections iii and il in assembled relation, a screw threaded into each section li is provided with fiat head 28 adapted to lie in a slot 2s, undercut laterally to provide an inside shoulder iii? extending along the inclined outer iace oi the section lo. In order to permit insertion of the head in the slot, the head may be narrow on one dimension to permit such insertion, so that when the head is in the slot and the head turned, it will extend behind the shoulder 3E. That is a well known construction in mechanics in general, the insertion of the head in the slot being aecomplished while the sections are held at right angles.

When. partsare in the positionshowniin Figures 1 and 2, vthe core sections. will form a construction conforming tothe; inside of the piston.. At'this time complementaryA projections 44 .an 45 will be in engagement to hold. the lateral sections I I extended on the inner section as shown, while the cam recesses between the inner and lateral sections will be closed at their ends by the side sections I2 and the side sections will complete the core structure. Assuming now that the outer mold halves are in position to form the outside of the piston 58y and its gate. 5S, the casting metal such as aluminum is cast in the mold and over the core as described, Yfor instance, in Patent No. 1,952,199.

Assume now, Figure 1, that the piston metal has been cast over the core and solidified with the metal filling .the recess i4 to form the ledge l inthe piston, and assuming that the metal has set. Upon withdrawal of the middle section from the piston casting. the lateral sections Il will rst be held against movement by the 4ledge i3 in the casting lling the recess, causing the inner section Iii to slide with respect to the lateral sections II. Upon the first movement of the .middle section I il with reference to the lateral sections lI, the engagement of the inside faces of the shoulder 3G with the head 28 will initially move the side sections in but only to an extent determined by the inclination of the shoulder 39 as in Patent No. 1,993,439. Such action will, however, be to simply break the middle core away from the inside of the casting, for the actual release of the core and particularly from the iedge :i3 will be accomplished as follows:

The downward movement of the inner section with respect to the lateral sections I! will con tinue while the projections 44 and 45 move into their respective recesses`2I and 23 asshown in Figure 3. During that time the lateral sections will move towards and collapse against the inner section, caused by the cam action of the complementary cam faces on ledge or annulus 43 on the casting, on the projection e2 on the lateral section, while the head 28 simply moves further laterally into the slot 29 and away from the shoulder' 30. After the ledge annulus 43 is cleared by the projection 42, the entire middle core assembly will move down below the side section l2 so as to permit the side sections to move into the space left by the middle section. The piston casting will then be left standing on the side core sections I2 and canthenbe picked off; for the side sections l2 will move in sufciently to clear even an annular projection like d3 inside of the casting. By reversal of these movements the core sections are again placed in assembledrelation as shown in Figure 1.

In order to further explain the above operation, it will be noted that after the metal has been cast upon the core, `as shown in Figure l, the casting will, after solidication, begin to shrink on the core so as to not only adhere to lateral sections II, but to force these lateral sections against the inner section Ill, as well as to force the side sections I2 against the lateral sections.v There will, therefore, be frictionalldrag between the inner section I and, the lateral sections i I, so that upon downward movement of the inner section I0, it will tend to drag the lateral sections I i with it. While upon the initial downward movement of the inner section IS, the inclination of thelshoulders will tendto move the lateralsections inwardly, suchv movement will be sughtbecause .orthezslightiinclinatoo; .howe- A 5f. ever, 'there willagainbe`- rictional :drag between the .heads of v.the screws 211 andl the shoulders 39. The slight inclination-will simply be tobreak the adhesion or the incipient `weld between the casting and the'lateral sections. The frictional drag between the lateral sections and the inner section will continue, tendingto drag the lateral sections down until the .projections M and 45 move intothe respective recesses 2i and 23. How ever, thenthe cooperation'of the cam face on the projection 42 on the .lateral sections with cam faceof the ledge 43 on the casting will keep up the frictional drag between the lateral sections and the inner section, .while cam faces 22 and 2.4 on the sectionspermit inward movement of the lateral sectionsgas the cam faces .of 42 and :i3 move the lateral sections'inwardly. It will be understood, of course, 'that the inner section I9 is moved downwardly rapidly because such movement is accomplished hydraulically as-in Patent No. 1,952,199, so that frictional drag effectively comes into play to 'secure the above described operation. The nal result will be thatthe parts will reach the position shown in Figure 3 where the projections 42 will have cleared the ledge d3. Thereafter, the entire core .will move further down from the position shown in Figure 3 with the projections 42 passing the ledge 43. Thereafter, the entire middle section IO-Il can move down entirely clear of the casting, because any tendency for the lateralsections to again move outwardly is prevented when the projections 132 f the lateral sections come opposite the ledge 43 on the casting.v However, vas will be seen from Figure 3, the projections 44 and45 are somewhat shorter than the recesses v2l and 23 so that some idle mcvementis providedfor.

1n order to prevent dubbingfor damage to the upperfcorner 350i the inner section by the cam surface 36, the top cam projections 3l' are made shorter than the remaining cam projections de and- 45, and the recesses E1. inthe sections are longer than 2l and 22 therebelow. Accordingly, the cam surface Bti-Will have cleared the corner 35, while the other cam parts 4d and 45 are still in full engagement. As shown, this construction causes the engaging sections to ride upon the intermediate projections 44 and "i5 while the projection 3'! is still free at the top of the core. Likewise, the projection 38, at the bottom of the inner section I@ is made shorter than are the intermediate projections 44 and 135 and the cam surfaces 25 and are provided. Itwill thus be seen that the upper `corner is never engaged by the face 36; when the lateral section Il is moved from Figure 1 toFigure Spositions, for the cam faces 22 and 24 below 36 will engage to move the side sections out before the face 35 reaches the corner; thereafter the faces at si will simply slide relatively. Upon Vreverse movement of the sections I and I i, from Figure 3 to Figure 1 positions, the-cam sections 44 vand 5 will engage and will remain inv engagement until the cam faces 35 have passed the-corners 35 at the top of the `core so as toagain avoiddubbing. Wearing f the core corners at the top, and the formation of vobjec'tionable castngins `is therefore avoided.

After the inside'core Eil-5I! .has moved below the side section I2, after the side sections have moved into the space left by the inside core and after the outer mold sides are moved away from the casting, the piston casting maybe picked off in the manner described in Patent No. 1,952,199. .The machineis thenplacedlncondition for an other pouring by.,movingzthepsidecores out Aand by raising the middle core, causing the parts to resume the position shown in Figure 1. During that movement, the projections 44 and i5 will move out of the recesses 2l and 23 by the interengagement of the cam faces 22 on the projections.

This invention enables a casting having inside recesses to be produced in an expeditious manner. It is not necessary to provide an inner core assembly of pieces which must be picked out separately after the casting has solidified. The sections of the inner core are always maintained in assembled relation, so that by simply moving the middle core assembly out of the casting, and moving the side sections into the space vacated by that assembly, the casting can be picked oil. Again after the side sections have been separated, the middle core assembly can be moved therebetween and extended. This enables the casting operations to be performed in a machine as in the patents referred to.` Moreover, as noted above aluminum castings have a high crystallization shrinkage and a high expansion and conn traction. If the core be withdrawn too early, the crystallization is not compensated for and a sound and clean casting will not be secured. Gn the other hand, if the withdrawal oi the core be delayed, the casting will seize the core and will crack and be ruined. 'Ihat is avoided by this invention. While after the withdrawal of the middle core the side core sections are left standing for subsequent movement into space leit by the middle core, even if these side sections should not be moved in, shrinkage will simply move them in to the extent that the casting contracts; for as shown in Patent No. 1,952,199, these side sections simply rest on the base and inward movement is not impeded by such contraction.

Having thus described the invention, what is claimed and desired to be secured by Letters Patentis:

l. In an apparatus for moldcasting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and ccmprising, an inner section `and a lateral section held in assembled relation to slide relatively, said lateral section having a recess i'or molding said ledge and having a projection above the recess, the lower part of said projection having a cam tace to form a cam face on the upper part of the ledge, and meshing projections on the in erengaging faces of the sections adapted to hold them extended laterally and meshing with recesses therein adapted upon relative sliding movement oi said sections and by engagement of said cam races to collapse said lateral section against said inner section.

2. In an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and comprising, an inner section and a lateral section held in assembled relation to slide relatively, said lateral section having a recess for molding said ledge and having a projection above the recess, the lower part of said projection having a cam face to form a cam face on the upper part of the ledge, and meshing projections engaging faces of the sections adapted to hold them extended laterally and meshing with recesses therein adapted upon relative sliding movement of said sections and by engagement of said cam faces to collapse said lateral sections against said inner section, the top meshing projection being formed to clear the top of the core betere the sections are extended or collapsed.

3. In an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and comprising, an inner section and a lateral section held in assembled relation to slide relatively, said lateral section having a recess for molding said ledge and having a projection above the recess, the lower part of said projection having a cam tace to form a cam face on the upper part of the ledge, and meshing projections on the interengaging faces of the sections ladapted to hold them extended laterally and meshing with recesses therein adapted upon relative sliding movement of said sections and by engagement of said cam faces to collapse said lateral section against said inner section, the meshing prcjecn tion at the top of the core being shorter than the meshing projection therebelow.

4. In an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston comprising, an inner section and a lateral section held in assembled relation to slide relatively, said lateral section having a recess for molding said ledge `and having a projection above the recess, the lower part of said projection having a cam race to form a cam face on the upper part of the ledge, meshing projections on the interengaging faces oi the sections adapted to hold them extended laterally and meshing with recesses therein adapted upon relative sliding movement of said sections and by engagement or cam 'laces to collapse said lateral section against said inner section, and side sections cooperating with said inner and lateral sections to complete the core and movable into the space vacated by sections.

5. ln an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and con pricing, an inner section and a lateral section permanently held in assembled relation to slide relatively while so held but to remain parallel, said lateral section having an inwardly extending recess for molding said ledge and having a jection extending outwardly above the rece s, and a series of sets oi cooperating meshing elements on the interengaging sections and spaced therealong, said elements projecting lat erally to extents corresponding to said projection and cooperating when said sections are relatively extended to hold said lateral section extended laterally, but adapted upon sliding oi said inner section with respect to said lateral section and while the late-ral section is held against l gitudinal movement, to move said lateral secti. toward and against said inner section in ord to retract said projection inwardly to clear said ledge.

6. In an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and comprising, an inner section and a lateral sec i permanently held in assembled relation to relatively while so held but to remain pa said lateral section having an inwardly ing recess for molding said ledge and hat projection extending outwardly above the and a series of sets o cooperating meshi elements on the interengaging ssctio.u spaced therealong, said elements projecting laterally to extents corresponding to said projection and cooperating when said sections are rela tively extended to hold said lateral section tended laterally, but adapted by engagement or said projection with the ledge of the casting, upon sliding of said inner section with respect to said lateral section and While the lateral section is held against longitudinal movement by the casting to move said lateral section toward and against said inner section in order to retract said projection inwardly to clear said ledge.

7. In an apparatus for mold-casting a piston having an inwardly projecting ledge, a core shaped to the interior of such a piston and comprising an inner section, and a lateral section permanently held in assembled relation to slide relativelyr While so held but to remain parallel, said lateral section having an inwardly extending recess for molding said ledge and having a projection extending outwardly above the recess, the lower part of said projection having 4a carn face to form a cam face on the upper part of the ledge of the casting, and cooperating meshing cam elements on the interengaging sections and spaced therealong, said elements projecting laterally to extents corresponding to said projection and cooperating when said sections are relatively extended to hold said lateral section extended laterally, but adapted upon sliding of said inner section with respect to said lateral section and while the lateral section is held against longitudinal movement by the casting and by engagement of said cam faces to move said lateral section toward and against said inner section in order to retract said projection inwardly to clear said ledge.

References Cited in the file 0f this patent UNITED STATES PATENTS Number Name Date 613,524 Morris Nov. 1, 1898 1,408,980 Bruce et al Mar. '7, 1922 1,645,729 Vaughan Oct. 8, 1927 1,959,648 vTandy May 22, 1934 1,975,038 Glazner Sept. 25, 1934 1,993,439 Flammang Mar. 5, 1935 2,286,994. Nocar June 16, 1942

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