the ceramic shell mold process

8/9/2019 The Ceramic Shell Mold Process

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The Ceramic Shell Mold Process

This process has largely replaced the original block or solid moldprocess except for some smaller high volume parts and for somealuminum casting where the mold is plaster bonded.

The ceramic shell mold technique involves dipping the entire clusterinto a ceramic slurry, draining it, then coating it with ne ceramicsand. After drying, this process is repeated again and again, usingprogressively coarser grades of ceramic material, until a self-supporting shell has been formed. The shell may be from !"# to $!%in. thick.

The coated cluster is then placed in a high temperature furnace orsteam autoclave where the pattern melts and runs out through the

gates, runners and pouring cup. This leaves a ceramic shellcontaining cavities of the casting shape desired together with asuitable running and feeding system.

Ceramic mold castingFrom Wikipedia, the free encyclopedia

Ceramic mold casting, also known ambiguously asceramic molding,[1]is a group of metalcastingprocesses that use ceramicsas the moldmaterial. It is a combination ofplaster moldcastingand investment casting.[][!]"here are two types of ceramic mold casting# the Shaw

processand the Unicast process.[$]

"hese casting processes are commonly used to make tooling, especially drop forgingdies, butalso in%ection moldingdies,die castingdies,glassmolds, stampingdies, ande&trusiondies.[!]

'ontents

[hide]

1 (haw process

)nicast process

! 'haracteristics

$ *eferences
http://en.wikipedia.org/wiki/Ceramic_moldinghttp://en.wikipedia.org/wiki/Ceramic_moldinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Mold_(manufacturing)http://en.wikipedia.org/wiki/Plaster_mold_castinghttp://en.wikipedia.org/wiki/Plaster_mold_castinghttp://en.wikipedia.org/wiki/Plaster_mold_castinghttp://en.wikipedia.org/wiki/Investment_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-blair-4http://en.wikipedia.org/wiki/Machine_toolinghttp://en.wikipedia.org/wiki/Drop_forginghttp://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/wiki/Injection_moldinghttp://en.wikipedia.org/wiki/Injection_moldinghttp://en.wikipedia.org/wiki/Die_castinghttp://en.wikipedia.org/wiki/Die_castinghttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Stamping_(metalworking)http://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/wiki/Ceramic_mold_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Shaw_processhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Unicast_processhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Characteristicshttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Referenceshttp://en.wikipedia.org/wiki/Ceramic_moldinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Mold_(manufacturing)http://en.wikipedia.org/wiki/Plaster_mold_castinghttp://en.wikipedia.org/wiki/Plaster_mold_castinghttp://en.wikipedia.org/wiki/Investment_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-blair-4http://en.wikipedia.org/wiki/Machine_toolinghttp://en.wikipedia.org/wiki/Drop_forginghttp://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/wiki/Injection_moldinghttp://en.wikipedia.org/wiki/Die_castinghttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Stamping_(metalworking)http://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/wiki/Ceramic_mold_castinghttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Shaw_processhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Unicast_processhttp://en.wikipedia.org/wiki/Ceramic_mold_casting#Characteristicshttp://en.wikipedia.org/wiki/Ceramic_mold_casting#References


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Shaw process[edit]

"he Shaw process, also known as the Osborn-Shaw process, uses a mi&tureof refractoryaggregate, hydroly+edethyl silicate, alcohol, and a gellingagent to create a mold. "hisslurry mi&ture is poured into a slightly tapered flaskand a reusable pattern i.e.the item used tocreate the shape of the mold- is used. "he slurry hardens almost immediately to a rubbery state the

consistency ofvulcani+ed rubber-. "he flask and pattern is then removed. "hen a torch is used toignite the mold, which causes most of the volatiles to burnoff and the formation ofceramic microcra+esmicroscopic cracks-. "hese cracks are important, because they allow gases toescape while preventing the metal from flowing through/ they also easethermal e&pansionandcontraction duringsolidification and shrinkage. 0fter the burnoff, the mold is baked at 1,22 3F42 3'- to remove any remaining volatiles. 5rior to pouring metal, the mold is prewarmed to controlshrinkage.[][!]

Unicast process[edit]

"he Unicast processis very similar to the (haw process, e&cept it does not re6uire the mold to beignited and then be cured in a furnace. Instead, the mold is partially cured so the pattern can be

removed and it is then completely cured by firing it at appro&imately 1,422 3F 1,2$2 3'-. If a metalwith a low melting point is cast then the firing can be skipped, because the mold has enoughstrength in the 7green state7 unfired-. [8]

Characteristics[edit]

"he main advantages of ceramic molds are# a reusable patternthe item used to create the shape ofthe mold-, e&cellent surface finish, close dimensional tolerances, thin crosssections,and intricateshapes can be cast. For undercutsand other difficult to cast features, part of the pattern can bemade from wa& in con%unction with a standard pattern/ essentially using investment and ceramicmold casting techni6ues together. "he main disadvantages are# it is only cost effective for small tomediumsi+ed production runs and the ceramic is not reusable. Ferrous and hightemperature nonferrous are most commonly cast with these processes/ other materials cast include# aluminum,

copper, magnesium, titanium, and +inc alloys. [1][][$]

Weight limits are 122 grams to several thousand kilograms !.8 o+ to several tons-. 'rosssectionsas thin as 1.! mm 2.281 in- are possible, with no upper limit. "ypical tolerances are 2.1 mm for thefirst 8 mm 2.228 in for the first inch- and 2.22! mm per additional mm 2.22! in per each additionalin-. 0 draftof 13 is typically re6uired. "he typical surface finish is 9$ um :89182 uin- *;(.[]

Ceramic Mold Casting
http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=1http://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/Hydrolyzedhttp://en.wikipedia.org/wiki/Ethyl_silicatehttp://en.wikipedia.org/wiki/Alcoholhttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Flask_(casting)http://en.wikipedia.org/wiki/Vulcanized_rubberhttp://en.wikipedia.org/wiki/Vulcanized_rubberhttp://en.wikipedia.org/wiki/Microcrazinghttp://en.wikipedia.org/wiki/Microcrazinghttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Shrinkage_(casting)http://en.wikipedia.org/wiki/Shrinkage_(casting)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-5http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=3http://en.wikipedia.org/wiki/Pattern_(casting)http://en.wikipedia.org/wiki/Surface_finishhttp://en.wikipedia.org/wiki/Engineering_tolerancehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Undercut_(manufacturing)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-blair-4http://en.wikipedia.org/wiki/Draft_(engineering)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=1http://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/Hydrolyzedhttp://en.wikipedia.org/wiki/Ethyl_silicatehttp://en.wikipedia.org/wiki/Alcoholhttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Flask_(casting)http://en.wikipedia.org/wiki/Vulcanized_rubberhttp://en.wikipedia.org/wiki/Microcrazinghttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Shrinkage_(casting)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-mt-3http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-5http://en.wikipedia.org/w/index.php?title=Ceramic_mold_casting&action=edit&section=3http://en.wikipedia.org/wiki/Pattern_(casting)http://en.wikipedia.org/wiki/Surface_finishhttp://en.wikipedia.org/wiki/Engineering_tolerancehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Undercut_(manufacturing)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-eh-1http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-blair-4http://en.wikipedia.org/wiki/Draft_(engineering)http://en.wikipedia.org/wiki/Ceramic_mold_casting#cite_note-degarmo-2


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The manufacturing process of ceramic mold casting is like the process of plaster mold

casting but can cast materials at much higher temperatures. Instead of using plaster to create

the mold for the metal casting, ceramic casting uses refractory ceramics for a mold material.

In industry, parts such as machining cutters, dies for metalworking, metal molds, and

impellers may be manufactured by this process.

The &rocessThe rst step in manufacture by ceramic mold casting is to combinethe material for the mold. A mixture of ne grain 'ircon ()r*i+,aluminum oxide, fused silica, bonding agents, and water, creates aceramic slurry . This slurry is poured over the casting pattern and let

set. The pattern is then removed and the mold is left to dry. Themold is then fred.

The firing will burn off any unwanted material and make the mold hardened and rigid.

The mold may also need to be baked in a furnace as well. The firing of the mold

produces a network of microscopic cracks in the mold material. These cracks give the

ceramic mold both good permeability and collapsibility for the metal casting process.

Figure:29


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Once prepared, the two halves of the mold are assembled for the pouring of the metal

casting. The two halves,(cope and drag section), may be backed up with fireclay

material for additional mold strength. Often in manufacturing industry, the ceramic

mold will be preheated prior to pouring the molten metal. The metal casting is poured,

and let solidify. In ceramic mold casting, like in other expendable mold processes, the

ceramic mold is destroyed in the removal of the metal casting.

&roperties And onsiderations +f /anufacturing 0yeramic /old asting

/anufacturing by ceramic mold casting is similar to plaster

mold casting in that it can produce parts with thin sections,excellent surface nish, and high dimensional accuracy./anufacturing tolerances between .112 and .1"1 inches arepossible with this process.


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To be able to cast parts with high dimensional accuracyeliminates the need for machining, and the scrap that would beproduced by machining. Therefore precision metal castingprocesses like this are e3cient to cast precious metals, ormaterials that would be di3cult to machine.

4nlike the mold material in the plaster metal castingprocess,the refractory mold material in ceramic casting can withstandextremely elevated temperatures. 5ue to this heat tolerance,the ceramic casting process can be used to manufactureferrous and other high melting point metal casting materials.*tainless steels and tool steels can be cast with this process.

eramic mold casting is relatively expensive.

The long preparation time of the mold makes manufacturingproduction rates for this process slow.

4nlike in plaster mold casting, the ceramic mold has excellentpermeability due to the microcra'ing, (production of

microscopic cracks, that occurs in the ring of the ceramicmold.
http://thelibraryofmanufacturing.com/plaster_metalcasting.htmlhttp://thelibraryofmanufacturing.com/plaster_metalcasting.html


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Shell Mold Casting

hell mold casting or shell molding is a metal casting process in manufacturing industry in

which the mold is a thin hardened shell of sand and thermosetting resin binder, backed up by

some other material. hell molding was developed as a manufacturing process during the

mid!"#th century in $ermany. hell mold casting is particularly suitable for steel castings

under "# lbs% however almost any metal that can be cast in sand can be cast with the shellmolding process. &lso much larger parts have been manufactured with shell molding. Typical

parts manufactured in industry using the shell mold casting process include cylinder heads,

gears, bushings, connecting rods, camshafts and valve bodies.

The &rocess

The rst step in the shell mold casting process is to manufacture theshell mold. The sand we use for the shell molding process is of amuch smaller grain si'e than the typical green sand mold. This negrained sand is mixed with a thermosetting resin binder. A specialmetal pattern is coated with a parting agent, (typically silicone,which will latter facilitate in the removal of the shell. The metalpattern is then heated to a temperature of $16-7116 degrees,


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("7$-71.

Figure:30

The sand mixture is then poured or blown over the hot casting pattern. 'ue to the

reaction of the thermosetting resin with the hot metal pattern, a thin shell forms on the

surface of the pattern. The desired thickness of the shell is dependent upon the

strength reuirements of the mold for the particular metal casting application. &

typical industrial manufacturing mold for a shell molding casting process could be .

in (*.+mm) thick. The thickness of the mold can be controlled by the length of time

the sand mixture is in contact with the metal casting pattern.

Figure:31


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The excess loose sand is then removed, leaving the shell and pattern.

Figure:32


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The shell and pattern are then placed in an oven for a short period of time, (minutes),

which causes the shell to harden onto the casting pattern.

Figure:33


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Once the baking phase of the manufacturing process is complete, the hardened shell is

separated from the casting pattern by way of e-ector pins built into the pattern. It is of

note that this manufacturing techniue used to create the mold in the shell molding

process can also be employed to produced highly accurate fine grained mold cores for

other metal casting processes.

Figure:34


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Two of these hardened shells, each representing half the mold for the casting, are

assembled together either by gluing or clamping.

Figure:35


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The manufacture of the shell mold is now complete and ready for the pouring of the

metal casting. In many shell molding processes, the shell mold is supported by sand or

metal shot during the casting process.

Figure:36


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&roperties and onsiderations of /anufacturing by*hell /old asting

The internal surface of the shell mold is very smooth and rigid.This allows for an easy 8ow of the liquid metal through themold cavity during the pouring of the casting, giving castings avery good surface nish. *hell mold casting enables themanufacture of complex parts with thin sections and smallerpro9ections than green sand mold casting.

/anufacturing with the shell mold process also imparts highdimensional accuracy. Tolerances of .1"1 inches (.2$mm arepossible. 6urther machining is usually unnecessary when

casting by this process.

*hell sand molds are less permeable than green sand moldsand binder may produce a large volume of gas as it contactsthe molten metal being poured for the casting. 6or thesereasons, shell molds should be well ventilated.


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The expense of shell mold casting is increased by the cost ofthe thermosetting resin binder, but decreased by the fact thatonly a small percentage of sand is used compared to othersand casting processes.

*hell mold casting processes are easily automated.

The special metal patterns needed for shell mold casting areexpensive, making it a less desirable process for short runs.:owever, manufacturing by shell casting may be economicalfor large batch production.

Ceramic Shell Molds

Introduction:A process that can be fully automated, ceramic shell molding

is the most rapidly used technique for mold and core making. Also known a

croning process, this casting technique was invented and patented by

J.Croning durign World War II. Also know as the C process, shell molding; ;

technique is used for making thin sections and for acquiring surface finish and

dimensional accuracy.

Process:In the first stage of ceramic shell molding, a metal pattern is made

which is resistant to high temperature and can withstand abrasion due to

contact with sand. he sand and resin mi!ture for the shell mold is brought in contact with the pattern.

he mold is placed in an oven where the resin is cured. his process causes the formation of a thin shell

around the pattern. he thickness of the mold can be "#$%#mm as compared to the heavy mold made

for sand castings. When fully cured the skin is removed from the pattern, which is the shell mold.

&or each ceramic shell moldsthere are two halves know as the cope and drag section. he two

sections are 'oined by resin to form a complete shell mold. If an interior design is required, the cores are

placed inside the mold before sealing the two parts.

&or heavy castings, ceramic shell molds are held together by metals or other materials. (ow, the molten

metal is poured into the mold, and once it solidifies, the shell is broken toremove the casting. his process is highly useful for near net shape castings.

Another advantage is that shell molding can be automated.

Automated Ceramic Shell Molding Machines and Robots:)hell molding

machines like the cold shell molding machines helps in making castings with

little molding material. In a cold shell molding machine the molds are made

using cold binding materials. In it patterns made of wood, metal or plaster


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can be used. And the greatest benefit is that the mold can be kept hori*ontally or vertically.

Robotizing: +sing robots for ceramic shell molding is a milestone for the old molding technology.

obots which are multi functional and re programmable are used in some foundries. obots are used for

a number of activities like robotic gate and sprue removal, robotic cutting of wedges for gate valves,; ;

robotic core setting, etc. he robots are reliable, consistent, more productive, provides better surfacefinish, and less machining etc.

Applications:A si*able amount of the casting in the steel industry are made by shell molding process,

that ensures better profitability. Carbon steel, alloy steel, stainless steel, low alloys, aluminum alloys,

copper, are all cast using shell molding process. Casting that require thin section and e!cellent

dimensional accuracy are cast using this process. -ody panes, truck hoods, small si*e boats, bath tubs,

shells of drums, connecting rods, gear housings, lever arms, etc. are cast using croning process.

Advantages:

hin sections, comple! parts and intricate designs can be cast

!cellent surface finish and good si*e tolerances

/ess machining required for the castings

(ear net shape castings, almost 0as cast0 quality

)implified process that can be handled by semi skilled operators

&ull mechani*ed and automated casting process

/ess foundry space required.

*:


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with the other methods > have used (resin-bonded-sand and traditional investment. researched the method ofceramic shell mold making to determine if it was a superior method than the others> have used. / learned was resin-bonded-sand. >n thismethod, a pattern is taken and a mold is created out of silica sand and sodiumsilicate, a resin that hardens the sand and allows it to retain a shape. *and moldsare often done in two or more parts so that the mold can be opened in order toremove the pattern. +nce the pattern is removed, channels for pouring metal andventing gasses, called sprues, are carved into the hardened sand. The sand mold isthen bound back together, and the metal is poured in. The sand mold took abouttwo days to make and weighed approximately $$ lbs. The next mold method >learned was traditional investment. This method involves a wax pattern with thesprues for pouring and venting created in wax and attached to the pattern. A"2B=4


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of the rst things > learned was that the slurry had to be maintained. >t had toconstantly be mixed and the amount of moisture had to be constant. > hadnFtproperly maintained the slurry and evaporation took place. This caused the interiorsof one of the shell molds to weaken and the nal castingFs surface had a chipped orbroken texture. Another problem > faced was proper venting. had with the shell method were great. The spruesystems were less intricate, and therefore they required less time and eEort toremove and clean up than the investment mold. Also there was less 8ashing in theshell than in the sand and investment molds. 6lashing is when molten metal llsinto tiny cracks along the surface of the moldFs interior pattern. The 8ashing has tobe chiseled oE of the casting and is slightly detectable in *:

the ceramic shell mold process

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