4307867 molds for slip casting and simil

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United States Patent [19]Shannon

[11][45]

4,307,867Dec. 29, 1981

[54] MOLDS FOR SLIPCASTING AND SI~ILARPROCESSES[75] Inventor: Richard F. Shannon, Lancaster, Ohio[73] Assignee: Owens-Corning FiberglasCorporation, Toledo, Ohio[21] Appl. No.: 176,164[22] Filed: Aug. 7, 1980

Related U.S. Application Data[63] Continuation of Ser. No. 100,799, Dec. 6, 1979, aban-

doned, which is a continuation of Ser. No. 913,419,Jun. 7, 1978, abandoned.[51] Int. OJ B28B 1/26; C04B 21/00[52] U.S.O....................................49/134; 106/383;

106/38.9; 249/141; 425/84[58] Field of Search 425/84; 249/113, 134,249/141; 106/38.27, 38.3, 38.9, 50, 109, 110[56] References Cited

U.S. PATENT DOCUMENTS2,681,863 6/1954 Croce et al. 106/1092,754,220 7/1956 Gardner 106/38.32,871,134 1/1959 Loech1 106/1103,062,670 11/1962 Marzocchi et al. 106/109

3,147,127 9/1964 Shannon 106/993,289,371 12/1966 Pearson et al. 52/3383,616,173 10/1971 Green et al. 106/1103,885,980 5/1975 Noone 106/1093,887,386 6/1975 Majumdar , 106/503,948,673 4/1976 Chase et al. 106/994,072,534 211978 Ryder , 106/1094,185,138 1/1980 Graham 428/3914,187,275 211980 Bracalielly et al 264/764,200,487 4/1980 Bondoc 162/135

Primary Examiner-James B. LoweAttorney, Agent, orFirm-Ronald C. Hudgens; RobertF. Rywalski; William P. Hickey[57] ABSTRActA mold for slip-casting and the like comprising: a gyp-sum or other water pervious body having a three-di-mensional network of chopped glass fiber filamentshaving a water wettable surface thereon and in anamount of more than 924 lineal inches of filament percubic inch of the water pervious body. The preferredmold is a gypsum mold having from 4,621 lineal inchesof filament to 46,210 lineal inches of filament per cubicinch of gypsum.

10 Claims, 3 Drawing Figures


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u.s. Patent Dec. 29, 1981 4,307,867

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1 4,307,867MOLDS FOR SLIP-CASTING AND SIMILARPROCESSESThis is a continuation, of application Ser. No. 5

100,799, filed Dec. 6, 1979 now abandoned, which inturn is a continuation of application Ser. No. 913,419filed June 7, 1978 now abandoned.The present invention relates to new and improvedmolds for producing ceramic slip-cast ware, as for ex- 10ample, ceramic sanitary ware.The slip-cast process for producing ceramic ware is avery old process and has been used to produce substan-tially all of the ceramic sanitary ware since the start ofthis industry. Sanitary ware are of complicated shapes 15and have hidden passageways, so that the slip-castingprocess is ideally suited for producing these compli-cated structures.In the slip-casting process, an aqueous suspension ofclay materials is let stand against a surface of desired 20contour which is water pervious. As the water of theslurry passes through the pervious surface, a build-up ofthe suspended clay materials is deposited on the surface;and when this build-up reaches a desired thickness, anyexcess slurry is poured off, and the deposited clay is 25removed from the surface for drying and firing. Wherehidden passageways are to be. produced, the clay slip ispoured between opposing water pervious surfaces thatare spaced apart by a distance equal to the thickness ofthe desired passageway plus the thickness of the ce- 30ramie that is desired on both sides of this passageway. Asupply of slip is communicated to between the surfacesin a manner which assures a supply to both surfaces asthe water proceeds out of both surfaces. By keeping theslurry supplied to both surfaces, a substantially equal 35build-up of clay occurs on both surfaces; and when thisbuild-up equals the desired ceramic thickness, any re-maining slurry is poured out from between the surfacesof the mold to leave the desired passageway. It will,therefor", be seen that slip-casting has the very great 40advantage of being able to provide internal passage-ways without the use ofcores, etc. Plaster of Paris, orgypsum hemi-hydrate, is an ideal material for producingthe surfaces of slip-cast molds; since gypsum cementscan be cast into complicated shapes, it hardens into a 45generally water insoluble surface, and the surface ispervious to water. What is more, the clay bodies whichbuild up upon gypsum surfaces do not adhere thereto,and can be stripped therefrom without breaking.For the above reasons, slip-casting molds have been 50

substantially universally made from cast. gypsum. Oneof the principle problems with gypsum molds is that itmay take 8 hours or more from the time that the clayslurry is poured into the mold, before the part that isproduced has then been dewatered to the point where 55the slip-cast material is handleable. Gypsum slip-castmolds are heavy, delicate, and fragile; and constituteone of the major processing expenses of the slip-castingindustry. Gypsum slip-cast molds may produce hun-dreds of parts before chipping and cracking of the gyp- 60sum proceeds to the point where the molds are nolonger economically reparable. This short life occurseven when the gypsum is reinforced by fibrous materi-als including glass fiber strand. Prior to the presentinvention, the benefits which were derived by using 65glass fiber strand has not proven economical to thedegree necessary for general acceptance by the indus-try.

2According to principles of the present invention, it

has been discovered that chopped glass fiber strandhaving a size thereon which solubilized when mixedinto the gypsum cement slurry will produce a moldwhich may have production rate approximately 20%greater than does either a nonreinforced gypsum mold,or a gypsum mold that is reinforced by nonfilamentizedglass strand. This has been a completely unobvious andunexpected result, and is perhaps the first developmentsince the start of the industry to significantly increasethe rate of production that is possible from slip-castingmolds.A principle object of the present invention, therefore,is the provision of a new and improved mold for pro-ducing slip-cast ware which will increase the rate atwhich water passes through the mold.A further object of the present invention is the provi-sion of a new and improved material for producingmolds of the above described type, which have agreater mold life.Further objects and advantages of the invention will

become apparent to those skilled in the art to which. theinvention relates from the following description of thepreferred embodiments hereinafter described.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1s a vertical section through the center line of

a two-piece mold for producing the ceramic lavatoryshown in FIG. 3;FIG. 2 is a vertical sectional view substantially identi-

cal with that of FIG. 1but showing a slip-cast partproduced therein prior to separation of the parts of themold; andFIG. 3 is a plan view of the lavatory that is produced

in the mold shown in FIGS. 1and 2.DESCRIPTION OF THE PREFERREDEMBODIMENTS

As previously mentioned, the new .and improvedmolds of the present invention will have advantages inany slip-casting operation. As exemplary of the type ofmolds with which the invention is concerned, there isshown in the drawings a two-piece mold for producinga clay wash basin having a totally enclosed internaloverflow passage. Itwill be understood, however, thatthe molds of the present invention will have equal ad-vantages in all sanitary ware such as toilets, bidets,tanks, urinals, etc.; as well as other items of ceramicware, as for example, plates, slip-cast tile, etc.The lavatory mold shown in the drawing comprises:

a male mold portion 10 and a female mold portion 12which abut each other on a plane that is generally coex-tensive with the bottom edge of the lip 16 which ex-tends around the lavatory and which sits on top of thesupporting cabinetry. The mold portions 10 and 12 aredesigned to produce a lavatory having a blind overflowpassage leading from the front of the basin to the drain;and accordingly the space or cavity 18 between themold portions 10 and 12 on the centerline where thedrain is to be produced, equals the desired width of theinternal passageway plus the desired thickness of ce-ramic material on opposite sides thereof. The spacebetween those portions of the mold which are intendedto produce a single thickness of material is equal to thedesired thickness of material. An opening 20 is providedin the male mold 10 at the location where the drain holeis desired, and a plastic plug 22 is inserted therein. Oneof the concerns in the design of the mold is that all air


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3 4,307,867is swept free of long thin passageways when the mold isfilled. This is accomplished in the mold shown in thedrawing by providing a filling funnel 24 with its bottomend wedged into an opening 26 which communicateswith the area of the lip 16which will later be cut out to 5form the opening 28 in the lavatory for receiving astopper control rod, not shown. A riser funnel 30 ispositioned in the area of the female mold portion 12where the drain 32 is located; and one or more ventopenings 34 is provided in the area of the female mold 10portion 12 where experience indicates air bubbles maycollect when the mold is filled. The two mold portions10 and 12 may be clamped together at their edges byany suitable means, as for example, by commercial tog-gle clamps; and the slip may be added to the funnel 24 ISby any suitable means, preferably by a slurry recircula-tion system from which slurry isobtained through a sideoutlet tee 36 and shut-off valve 38. The filling funnel 24is filled with slurry to a level well above the top surfaceof the mold cavity 18; so that it rises up in the riser 20funnel 30 by an amount which will assure sufficientsolids to provide the desired thickness of deposit oneach mold portion. The mold portions 10 and 12 are, ofcourse, pervious to water, so that the water of the slurryslowly exudes out of both mold portions 10 and 12to, in 25effect, strain out the slurry solids on all surfaces of thecavity 18. A generally predetermined amount of slurryis added to the funnel 24 initially. When the slurry levelhas drained down to a predetermined level adjacent totop ofthe mold 12, the plastic plug 22 ispulled, to allow 30the excess of liquid in the cavity 12 to drain out, asshown in FIG. 2. The funnels 24 and 30 are removed atthis time, and the mold is let stand for a sufficent periodof time for the desposited clay body, to dry to a condi-tion wherein the clay will retain its shape when the 35mold portions 10 and 12 are separated. The time re-quired for clay separation and build-up on the moldsurfaces, plus the time required for drying of the claybuild-up to a handeable state, may take as much as 8hours and, of course, will depend upon the particular 40molds and configuration being cast.According to principles of the present invention, anew and improved water pervious mold material isprovided which will increase the rate at which waterpasses therethrough by more than approximately 20%. 45According to the present invention, it has been discov-ered that if water wettable fibers are present in an indi-vidually spaced apart condition, rather than in the formof bundles as occurs in strand, an increase in drying rateis had. The same effect is not had, however, if the fila- 50ments are held together in the form of bundles. Thereasons why this is so have not been completely estab-lished. It is believed that for monofilaments on whichthe angle of wetting approaches zero, water applied toone end of the fiber spreads over the surface of the fiber 55to its opposite end. If the opposite end is adjacent an-other fiber, the water transfers to the other fiber and theprocess is repeated. On the other hand, if the fibers arepresent in the form of a bundle, the water isheld withinthe bundle by capillary attraction. Strands have a very 60small exposed surface so that evaporation from the endof a strand occurs at a much slower rate than it doesfrom the exterior surface of a similar number of fila--ments.Conventionally, the molds for slip-casting have been 65made of gypsum. In my efforts to reinforce a gypsummold material with chopped strand, no observable in-crease in drying rate occurred. I discovered, however,

4that if the chopped strand had a size thereon which waswater dispersible, and if I used a mixing procedure ofthe chopped strand with the gypsum slurry whichbroke the chopped strand completely apart into its fila-ments, the filaments were dispersed throughout theslurry and an unexpected increase in drying rate washad. Ithas been found that the dispersed monofilamentsarrange themselves in a three-dimensional networkwhich passes through or adjacent all of the interstitialspaces between crystals of the gypsum mold material.Monofilaments may be thought of as sticks having adiameter less than approximately 0.0010 inches, which,of course, are sufficiently tiny that the zeta potential ofthe water wetted filaments is capable of repelling eachother and dispersing the monofilaments generally uni-formly throughout a gypsum slurry. On the other hand,chopped strands comprise more than 200 filaments, andthe zeta potential around the outside of such a bundle offilaments is not sufficiently strong to uniformly dispersethe bundles.By way of example, a gypsum mold similar to thoseshown in the drawings is produced form a creamy mixof gypsum hemihydrate and water, and to which 0.2%by weight of solids of a filamentizable strand that ischopped into ~ inch lengths is added. This mix is agi-tated for a sufficient period of time to completely breakthe bundles apart and to distribute the filaments gener-ally uniformly throughout the slurry. A suitable strandwill comprise 440 E-glass filaments, each having a di-ameter of 0.00036 inch, and which strand is held to-gether by 0.6% by weight of the following size:

Polyvinyl acetate copolymer 92%containing sufficient poly-vinyl alcohol groups to makethe copolymer water dispersibleCationic lubricant (Fatty acid 2.2%tetraethylene pentamine conden-sate)Glacial acetic acid 1.75%Ammonium chloride 1.5%Nonionic wetting agent (Octyl 1.6%phenoxy polyethoxy ethanol)

The slurry is then cast into the desired shape of themold. The resulting mold will have a rate of drying thatis more than approximately 20% greater than a moldthat is made from gypsum which is devoid of the glassfilaments. This is also true if the mold is made fromgypsum containing 0.2% of a nonfilamentizablechopped strand. It is also true that this improvement indrying isnot had if the filaments of the water dispersiblestrand have a water repellent thereon, such as a non-ionic lubricant, or a silicone solution.In general, it has been found that a detectable increasein drying rate will occur when the mold contains aslittle as 0.01% by weight of solids of water wettabledispersed glass filaments, and that the rate of drying willincrease as the amount of dispersible filaments addedincreases. As a practical matter, no more than approxi-mately 1% of chopped glass fiber filaments can beadded to gypsum slurry without creating mixing prob-lems, and the preferred range of water wettable dis-persed filaments will be between approximately 0.05%and 0.5%. The following is a table which gives thenumber of lineal inches of filament per cubic inch ofnonfoamed product having a density ofO.0838Ib./cubicinch for different weight percentages of glass filamentshaving a diameter of 0.00036 inch.


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Percent By WeightInches of filament per .0838 lb.per cubic inch of product

0.0\0.050.20.5

92 44,62118,48046,210

The network of filaments that is utilized in the method 10and materials of the present invention must be formedby substantially completely filamentized strand. Strandthat is not filamentized has voids between the filamentswhich attract and hold water. On the other hand, indi-vidual filaments retain only a very thin layer of water, 15perhaps several molecules thick, and this water spreadsalmost indefinitely along the surface since the angle ofwetting on nascent glass approaches zero. Since this isnecessary, the surface of the individual filaments mustnot be poisoned by silicones, organic polymers, or other 20nonwetting materials. It is known that nascent glassfibers in water have identical negative- charges whichrepell each other; and this phenomenon is believed nec-essary to disperse the individual filaments and form thethree dimensional criss-crossing fiber network that is 25necessary to pass through or adjacent all interstitialspaces of the gypsum molds. The filaments used in thepresent invention develop a zeta potential of mutuallyrepelling negative charges which causes them to repelleach other and spread throughout the gypsum material. 30The same will be true, however, if the mold is madefrom some other water pervious material, other thangypsum, such as a Portland cement mortar, or an alumi-num silicate cement. The filaments should preferablyhave a length of more than one eighth inch. 35While the invention has been described as embodiedin gypsum molds, wherein the glass ftlaments networkextends from the molding surface to the outside surfaceofthe mold, it isnot so limited. In some instances, it may 40be desirable to provide a water pervious coating overthe portion of the mold which contains the monofila-ment network. In such instances, it will be seen that themonofilament network will still remove water from thewater pervious coating of the mold. Itwill further be 45seen that the manner in which the water spreads alongthe surface of the ftlament network is not dependentupon the pervious material on which the mold itself ismade, and that the monoftlament network of the presentinvention will increase the drying rate of any water 50pervious mold. Gypsum, however, is a low cost andinexpensive mold material that is easily cast into compli-cated shapes. Therefore, it is desired to specificallycover gypsum molds that contain the monofilamentnetwork of the present invention.

6While the invention has been described in consider-able detail, I do not wish to be limited to the particularembodiments shown and described; and it is my inten-tion to cover hereby all novel adaptations, modifica-5 tions, and arrangements thereof which come within thepractice of those skilled in the art to which the inven-tion relates, and which come within the purview of thefollowing claims.I claim:1. A new and improved mold for producing ceramicslip cast ware and the like, comprising: a body having aforming surface of desired shape to which a ceramic slipis communicated, said body having pores which strainout ceramic particles of the slip without having theceramic particles becoming locked therein and whileallowing water from the slip to pass therethrough, saidbody having chopped water' wettable spaced apartmonofilaments embedded therein for conducting wateraway from said forming surface, said monofilamentsbeing at a loading of at least approximately 675 inchesper cubic inch of solid body.2. The new and improved mold of claim 1 whereinthe water wettable monofilaments are glass monofila-ments.3. The new and improved mold of claim 1 whereinsaid monofilaments are in the form of a three dimen-sional network.4. The new and improved mold of claim 1 whereinsaid water transfer portion containing the monofila-ments consists essentially of gypsum.5. A new and improved mold for producing ceramicslip-cast ware and the like comprising: a porous bodyhaving a forming surface of desired shape to which aceramic slip is communicated, said body having poreswhich strain out particles of the slip without having the

ceramic particles becoming locked therein and whileallowing water from the slip to pass therethrough, saidporous body having a three dimensional network ofchopped glass monifilaments spaced apart and embed-ded therein, said monofilaments being at a loading of atleast 3,376 inches per cubic inch of the solids of theporous body.6. The mold of claim 5 wherein the filaments have anegative zeta potential in water.7. The mold of claim 5 wherein the monofilamentshave a diameter less than 0.0010 inch.8. The mold of claim 7 wherein the monofilamentshave a length of more than approximately one eighthinch.9. The mold of claim 5 wherein said water transferportion consists essentially of gypsum.10. The mold of claim 9 wherein said network ofmonofilaments extends between opposite surfaces of themold.55 ' " ' "

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4307867 molds for slip casting and simil

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