US3212156A - Mold and core construction - Google Patents

Description

Oct. 19, i965 F. DERROR MOLD AND CORE CONSTRUCTION Filed July 1, 1965 3 Sheets-Sheet 1 I6 II y y I? z Z \L x fivzyfi 22/ 7 \22 \24 INVENTOR Fl 2 FRED L. DERROR ATTORNEYS Oct. 19, 1965 F. DERROR 3,212,156

MOLD AND CORE CONSTRUCTION Filed July 1, 1963 3 Sheets-Sheet 2 IO f 3 INVENTOR. FRED L. DERROR ATTORNEYS Oct. 19, 1965 F. DERROR 3,212,156

MO LD AND CORE CONSTRUCTION Filed July 1, 1965 5 Sheets-Sheet 3 j INVENTOR.

////// FREDLDERROR ATTORNEYS United States Patent 3,212,156 MOLD AND CORE CONSTRUCTION Fred L. Derror, Lucas, Ohio, assignor to Mansfield Sanitary, Inc., Perrysville, Ohio, a corporation of Ohio Filed July 1, 1963, Ser- No. 291,671 6 Claims. (Cl. 129) The present invention relates generally to molds and cores. More particularly, the present invention relates to molds and cores for slip casting hollow ceramic shapes. Specifically, the present invention relates to molds and cores for slip casting hollow ceramic shapes with coreformed passages therethrough and without air entrainment or internal tensile fractures.

The use of a mold and an interfitting core for slip casting hollow ceramic shapes is well known to the art. However, considerable difficulty has always been experienced when it was required to provide the cast item with through passages. For example, toilet tanks have been slip cast for years and these items require passages through the bottom for the water flow pipe as well as for the bolts which secure the tank to the member on which it is carried. Heretofiore, it has been the accepted practice to cast the tank between a mold and core to provide the desired wall thickness. After the slip has cast up, the core is removed, leaving the cast,i.e., initially set and partially cured, tank within the mold. A workman then inserts a template into the casting and using this as a guide, takes various sized cutting punches and removes those portions of the casings through which passageways are desired. This, however, is a tedious and time consuming task which has occasioned many attempts to mold the passages directly into the casting.

Primarily'these attempts have utilized a resilient subcore attached beneath the primary core. A resilient subcore was thought to be the solution since it is well known that the tolerances in the dimensions of the mold and core would not permit a sub-core to seat against the mold at the same time the primary core seated therein. It'was reasoned that a flexible sub-core would expand radially when seating against the bottom of the mold and then correspondingly contract to facilitate withdrawal. However, resilient materials are inherently wettable and slip, as it casts, will adhere to a wettable surface. Therefore, when the sub-core contracted upon withdrawal, the casting adhered to the sub-core and would tear, or fracture, around the passage. I The lack of close dimensional tolerance between the mold and the core, which suggested flexible sub-cores, also creates'another cause of damage to the castings which frequently relegates them to the scrap pile.

.When the liquid slip is poured into the mold a flash of the slip will form at the parting line between the top of the mold and that portion of the core which does not exactly seat on the mold. After the cast, and as the moisture is further withdrawn from the slip, there is a large amount of shrinkage present. During the course of this shrinkage cracks often appear in the casting in the proximity to the flash. I have discovered that green cured casting material has relatively high shear strength but comparatively low tensile and bending strength, and that this undesirable cracking was occasioned because of these differential strengths, as will be hereinatfer more fully described. Furthermore, when the slip is poured into the cavity between the mold and the interfitted core through funnels, as is the standard prior art practice, the slip flowing through the funnel creates a vortex which entrains air into the slip. This air does not have the opportunity to escape before the slip casts and thus deleterious air bubbles are caused in the final ceramic item.

3,212,156 Patented Oct. 19, 1965 It is therefore an object of the present invention to provide an improved mold and core for slip casting hollow ceramic shapes with cored passageways therethrough.

It is another object of the present invention to provide an improved mold and core, as above, having sub-cores for producing passages in said casting without tearing or cracking the casting upon withdrawal of the core.

It is another object of the present invention to provide an improved mold and core having sub-cores for producing passages through the castings which will be effective irrespective of the dimensional variations existent in standard molds and cores.

It is another object of the present invention to provide an improved mold and core which eliminates cracks in the casting in proximity to the flash by preventing the high shear strength of the green casting from acting deleteriously upon itself.

It is a further object of the present invention to provide an improved mold and core wherein the flash formation is oriented such that the stresses between the flash and the green casting act as bending forces rather than shear forces.

It is a still further object of the present invention to provide an improved mold and core, as above, which eliminates the entrainment of air into the slip as it is being poured into the cavity between the mold and the core to provide a deaerated casting. These and other objects of the invention, as well as the advantages thereof over existing and prior art forms, will be apparent in view of the following detailed tie-- scription and the attached drawings and are accomplished by means hereinafter described and claimed.

One preferred embodiment is shown by way of example in the accompanying drawings and hereinafter described in detail without attempting to show all the various forms and modifications in which the invention might be embodied; the invention being measured by the appended claims and not by the details of the specification.

' In the drawings: FIG. 1 is a top plan of a mold and core according to the present invention;

FIG. 2 is a cross section taken substantially on line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary area of FIG. 2 showing the green casting with the flash attached thereto;

FIG. 4 is a view similar to FIG. 3 with the core removed;

FIG. 5 is a view similar to FIG. 4 depicting the casting after a sutficient amount of the moisture has been removed to cause the casting to shrink and showing the flashing having been severed therefrom by the shrinkage;

FIG. 6 is a view similar to FIG. 3 depicting the prior art construction;

FIG. 7 is an enlarged cross section taken substantially on line 7-7 of FIG. 2;

FIG. 8 is a view similar to FIG. 7 depicting the casting removed from the mold and core; and,

' FIG. 9 is a view similar to FIG. 8 showing the finished casting.

In general, a mold and core according to the present invention comprises a hollow mold for receiving an interfitting core so as to form a cavity therebetween in the shape of the article to be cast. A seat is provided on the rim of the hollowed mold for abutting a similar seat on the support shoulder of the core when the core is received within the mold. The abutting seats are angularly inclined, preferably at 49 from horizontal, in order to reduce the shear stress between the flash and the main portion of the casting to an optimum amount and sub stitute a bending stress therebetween.

A series of one or more sub-cores depend from the primary score to form the necessary passageways through the casting. These sub-cores are of such dimension that they do not ordinarily contact the mold but are designed to be preferably spaced apart from the mold approximately 4,

The cap portion of the core is provided with two wells, each of which communicates with the cavity formed between the mold and the interfitting core. One of the wells functions as a filling well with an offset exit porch to reduce vortex and the other well acts as a shrinkage well. Both wells may be similarly constructed so that either may be the fill or shrinkage well.

Referring more particularly to the drawings, the mold, indicated generally by the numeral 10, is hollow to receive the primary portion 11 of the core, indicated generally by the numeral 12. The primary portion 11 of the core 12 and the mold into which the primary portion 11 fits, form a cavity 13 therebetween in the shape of the article to be cast, a toilet tank being disclosed, although the concept of the present invention is readily adaptable to many other cast shapes.

The core 12 also has a cap portion 14 which extends transversely of the primary portion 11 and forms a support shoulder 15 which rests against the upper edge of the vertical mold walls 16 to position the primary portion 11 of the core 12 properly within the mold 10.

A seat 18 is formed on the undersurface shoulder 15 around the periphery of the primary portion 11. The seat 18 engages a similar seat 19 formed on the upper edge of the mold walls 16. The abuttingly engaged seats 18 and 19 are both inclined with respect to a horizontal reference for a particular purpose.

The particular inclination, preferably 49", with respect to horizontal, obviates the undesirable cracking or fracturing of cast shapes which often occur in proximity to the flash on the upper edge of the cast shape.

As shown in FIG. 6, the prior art mold had a substantially horizontal seat 19A on the top edge of the mold wall 16A which was engaged by a similar substantially horizontal seat 18A on the shoulder 15A of the core 12A. At places around the periphery of the mold the liquid slip enters into the crack between the seats 18A and 19A. This slip casts with the article, forming a flash 20A. As the article loses moisture it begins to shrink. A portion of this shrinkage decreases the vertical dimension of wall 21A causing the top thereof to move vertically in the direction indicated by the line marked with the letter X. The flash 20A, however, is prevented from moving downwardly with the wall 20A by the fixed position of 19A. These opposing vertical forces react as a shear stress along the vertical plane Y marking the jointer of the flash 20A with the casting wall 21A. At the same time the downward force acts internally of the wall 21A as a tensile stress.

I have found that the shear strength of green slip cast ceramic material is far in excess of the tensile strength. Accordingly, the wall 21A often cracks or separates, as a result of the internal tensile stress along a line such as marked with the letter Z in FIG. 6 before the shear stress was suflicient to separate the flash 20A from the wall 21A along the vertical plane Y.

A mold and core according to the present concept obviates this difficulty. As shown in FIG. 3, the slip will also invade any cracks between the seats 18 and 19 of the subject mold and core to form a flash 20 as the slip casts. At this point it should be understood that molds and cores alike are made from a water absorbing material such as plaster of Paris and it would not be practically or economically feasible to machine fit the seats 18 and 19.

As depicted in FIG. 4, the core may be removed after the slip has cast. Here too, as the moisture is withdrawn, the wall 21 will shrink, a portion of this shrinkage tending to cause the top of the wall 21 to move vertically downwardly in the direction indicated by the arrow X. The flash 20 is pl'eve lwd from moving with this vertical shrinkage of wall 21 by the fixed position of seat 19.

The angular inclination of seat 19 provides both vertical and horizontal reaction forces against the slip 20, the resultant of which acts perpendicularly to the plane of seat 19, creating a bending moment about the point Y. The extremely low bending strength of green cured, slip cast ceramic material causes the flash 20 to break away from the wall 21 through point Y, as shown in FIG. 5, well prior to the time that the vertical components of the force acting on the flash 20 creates excessive shear between the flash and the casting wall 21 or the internal forces of the wall 21 exceed the tensile strength thereof. Thus the cracking and fracturing of the wall of the casting has been eliminated. It has been found that when seat 19 is inclined at an angle of approximately 49 from horizontal the most satisfactory results are obtained. See FIG. 5.

Referring again to FIG. 2, one or more sub-cores 22 are dependingly supported from the underside of the primary portion 11 of the core 12. These sub-cores 22 are preferably of the same material as the primary portion of the core and may be integrally formed therewith.

As has been previously discussed, it is impractical to machine set seats 18 and 19. Accordingly, it is impossible to gauge the vertical dimension of the sub-cores 22 such that their unde-rsurface 23 engages the bottom surface 24 of the mold cavity just as the seats 18 and 19 engage.

For this reason, the prior art attempted to manufacture the sub-cores 22 of an expansible material so that when the sub-cores contacted the mold before the seats 18 and 19 engaged, the sub-core would yield by lateral expansion until the seats 18 and 19 were engaged. It was further theorized that such cores would contract when the core 11 was removed after the slip had cast, supposedly facilitating removal of the sub-cores. However, the wettable, expansible materials provide surfaces to which the slip adheres as it casts so that the green casting would crack in the vicinity of the subcores as the core was removed.

The present concept obviates this difficulty. The subcores 22 have the same characteristics as the primary portion 11 of the core. That is, they are moisture absorbent and not wettable so the cast ceramic material will not adhere to them, and the sub-cores 22 are constructed so that their vertical dimension brings them no closer to the bottom surface 24 of the mold cavity than approximately & By this construction, the Sub-core never engages the mold before the seats 18 and 19 are engaged. Furthermore, the surface tension of the slip is such that it will not flow into a crack of A or less. On the other hand, when the variation of the mold dimension tends to the large size the spacing between the undersurface 23 of sub-cores 22 and the bottom surface 24 of the mold exceeds only a small flash 25 will be formed around the periphery of the passageway 26 through the casting 27, as shown in FIGS. 7 and 8, and this can easily be removed by the workmans finger or other suitable tool when the green casting is removed from the mold, in order to assure a satisfactorily uniform passageway 26, as shown in FIG. 9.

Finally, two slip wells 30 and 31 are provided in the upper surface 32 of the cap portion 14 of the core 12. As best shown in FIGS. 1 and 2, each well 30 and 31 is substantially oblong in shape with a tapered floor 33 intersecting a horizontal flow channel 34 at the base of each well. A vertical port 35 is positioned laterally adjacent one end of the flow channel 34 in a recess 36 in cap portion 14 which is laterally adjacent to and communicates with, the well. Port 35 provides flow communication between the base of the well and the cavity formed between the mold 10 and the interfitted core 12. The relatively horizontal flow channel 34 and the laterally offset vertical port 35 assures that the slip can flow laterally into the port 35 in order to prevent the formation of a vortex as the slip leaves the well and flows into the cavity.

The elimination of vortical flow when filling the mold is especially necessary in slip casting ceramic material because of the undesirable air entrainment incident to vortical flow. Entrainment of air in the slip is especially undesirable since the cast, or initial setting, of the slip material will often occur before the air bubbles can rise through the slip and exhaust. Larger air bubbles can cause destructive faults in the casting, and particularly lower the internal tensile strength to induce cracking along line Z. Smaller bubbles create what is known as pin points or minute craters, in the finished glaze. The present construction obviates the entrainment of air during the mold filling process by the elimination of vortical flow into the mold cavity.

A mold and core constructed according to the concept of the present invention readily and economically produces a slip cast ceramic shape with core formed passageways therethrough without the cracks which occur in proximity to the flash and without entrainment of destructive air pockets within the casing.

Accordingly, such a mold and core accomplish the objects of the invention.

What is claimed is:

1. Mold and core construction of water absorbing material for slip casting hollow, deaerated, ceramic shapes with at least one passageway therethorugh comprising, a hollow mold having a bottom surface and side walls terminating at an upper edge, a seat on the upper edge of said walls, a core having a primary portion and a cap portion, said primary portion inserted within said mold to form a cavity between the mold and said primary portion, said cap portion forming a shoulder extending laterally of said primary portion, a seat on the under side of said shoulder, said seats being inclined with respect to horizontal, at least one sub-core carried on the primary portion of said core, said sub-cor being also formed of a water absorbing material and extending to within approximately of an inch to the bottom surface of said mold, at least one slip well in said cap portion adapted to receive slip from an external source, a horizontally oriented flow channel at the bottom of said well, a port communicating between said well and said cavity, said port communicating with said well at one end of and laterally offset from said flow channel to prevent air entraining vortical flow between said well and said cavity.

2. Mold and core construction of Water absorbing material for slip casting hollow, deaerated, ceramic shapes with at least one passageway therethrough comprising, a hollow mold having generally vertical side walls and a bottom surface, said side walls terminating at an upper edge, a seat on the upper edge of said side walls, a core having a primary portion and a cap portion, said primary portion inserted within said mold to form a cavity between the mold and said primary portion, said cap portion forming a shoulder extending laterally of said primary portion, a seat on the under side of said shoulder, said seats being substantially engaged when said core primary portion is inserted within said mold, said seats being inclined at approximately 49 from horizontal, at least one sub-core dependingly mounted from the primary portion of said core, said sub-core being also formed of a water absorbing material and extending to within approximately of an inch of the bottom surface of said mold, at least one slip well in said cap portion adapted to receive slip from an external source, a horizontially oriented flow channel at the bottom of said well, a recess in said cap portion, said recess located laterally of and in communication with said slip well, a port in said recess laterally of said flow channel, said port communicating between said recess and said cavity.

Mold and core construction of water absorbent material for slip casting hollow ceramic shapes with at least one passageway therethrough comprising, a hollow mold having side walls and a bottom surface, a core having a primary portion and a cap portion, said primary portion inserted within said hollow mold to form a cavity between said mold and core primary portion, at least one sub-core carried on the primary portion of said core, said sub-core being also formed of a water absorbing material and extending to within approximately of an inch of the bottom surface of said mold.

4. Mold and core construction of water absorbing material for slip casting hollow, deaerated, ceramic shapes comprising, a hollow mold, a core having a vertically oriented primary portion and a cap portion, said core primary portion inserted within said mold to form a cavity between said mold and core primary portion, at least one slip well in said cap portion adapted to receive slip from an external source, said slip well being elongate along at least one horizontal axis, a recess in said cap portion, a port communicating between said recess and said cavity, said recess being positioned laterally of the elongate axis of said well and communicating with said well to prevent air entraining vortical flow between said well and said cavity.

5. Mold and core construction of water absorbing material for slip casting hollow, deaerated, ceramic shapes comprising, a hollow mold, a core having a vertically oriented primary portion and a cap portion, said core primary portion inserted within said mold to form a cavity between said mold and core primary portion, at least one slip well in said cap portion adapted to receive slip from an external source, a horizontally oriented flow channel at the bottom of said well, a port at one end of and laterally offset from said flow channel, said port communicating between said Well and said cavity.

6. Mold and core construction of water absorbing material for slip casting hollow ceramic shapes with at least one passageway therethrough comprising, a hollow mold having a bottom surface and side walls terminating at an upper edge, a first flash removing seat on the upper edge of said mold walls, a core having a primary portion and a cap portion, said cap portion forming a shoulder extending laterally of said primary portion, said shoulder resting upon the upper edge of said mold to support said core therein, a second flash removing seat on the under side of said shoulder adjacent said core primary portion, said core primary portion vertically and removably inserted within said hollow mold to form a mold cavity therebetween, said first and second flash removing seats being opposed when said core is inserted in said mold to allow formation of a flash therebetween, said first and second seats being inclined at approximately 49 from horizontal, said inclination subjecting the flash to a bending stress as the ceramic shape green cures within said mold, and at least one sub-core dependingly mounted from beneath the primary portion of said core, said sub-core being also formed of a water absorbing material and extending to within approximately of the bottom surface of said mold.

References Cited by the Examiner UNITED STATES PATENTS 1,375,950 4/21 Bewley 25-29 1,852,332 4/32 Perry 2529 1,921,240 8/ 33 Porter 22-209 2,311,358 2/43 Baily 25130 2,683,298 7/54- Fadden 25-128 2,838,816 6/58 Strom 22-134 3,136,024 6/64 La Monica 25-124 FOREIGN PATENTS 3,544 8/06 Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner.

MICHAEL V. BRINDISI, Examiner.

Claims (1)

1. MOLD AND CORE CONSTRUCTION OF WATER ABSORBING MATERIAL FOR SLIP CASTING HOLLOW, DEAERATED, CERAMIC SHAPES WITH AT LEAST ONE PASSAGEWAY THERETHROUGH COMPRISING, A HOLLOW MOLD HAVING A BOTTOM SURFACE AND SIDE WALLS TERMINATING AT AN UPPER EDGE, A SEAT ON THE UPPER EDGE OF SAID WALLS, A CORE HAVING A PRIMARY PORTION AND A CAP PORTION, SAID PRIMARY PORTION INSERTED WITHIN SAID MOLD TO FORM A CAVITY BETWEEN THE MOLD AND SAID PRIMARY PORTION, SAID CAP PORTION FORMING A SHOULDER EXTENDING LATERALLY OF SAID PRIMARY PORTION, A SEAT ON THE UNDER SIDE OF SAID SHOULDER, SAID SEATS BEING INCLINED WITH RESPECT TO HORIZONTAL, AT LEAST ONE SUB-CORE CARRIED ON THE PRIMARY PORTION OF SAID CORE, SAID SUB-CORE BEING ALSO FORMED OF A WATER ABSORBING MATERIAL AND EXTENDING TO WITHIN APPROXIMATELY 1/32 OF AN INCH TO THE BOTTOMSURFACE OF SAID MOLD, AT LEAST ONE SLIP WELL IN SAID CAP PORTION ADAPTED TO RECEIVE SLIP FROM AN EXTERNAL SOURCE, A HORIZONTALLY ORIENTED FLOW CHANNEL AT THE BOTTOM OF SAID WELL, A PORT COMMUNICATING BETWEEN SAID WELL AND SAID CAVITY, SAID PORT COMMUNICATING WITH SAID WELL AT ONE END OF AND LATERALLY OFFSET FROM SAID FLOW CHANNEL TO PREVENT AIR ENTRAINING VORTICAL FLOW BETWEEN SAID WELL AND SAID CAVITY.

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