Ceramic mold casting, also known ambiguously as
ceramic molding
The ceramic molding process is a production method which guarantees the precision required, and also gives a good surface finish, using a high temperature method to better structure and shape parts. This process also gives a low grade of toleration ...
,
is a group of
metal casting
In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold (usually by a crucible) that contains a negative impression (i.e., a three-dimensional negative image) of the intended shape. The metal is ...
processes that use
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
s as the
mold
A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...
material. It is a combination of
plaster mold casting Plaster mold casting is a metalworking casting process similar to sand casting except the molding material is plaster of Paris instead of sand. Like sand casting, plaster mold casting is an expendable mold process, however it can only be used with n ...
and
investment casting
Investment casting is an industrial process based on lost-wax casting, one of the oldest known metal-forming techniques. The term "lost-wax casting" can also refer to modern investment casting processes.
Investment casting has been used in var ...
.
There are two types of ceramic mold casting: the ''Shaw process'' and the ''Unicast process''.
These casting processes are commonly used to make
tooling
Tooling may refer to:
* Machine tools and the tooling, such as cutting tools, fixtures, and accessories, that is used on them
** Cutting tool (machining), any of hundreds of kinds of cutters
** Fixture (tool), a fixed workholding or support devic ...
, especially
drop forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...
dies, but also
injection molding
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...
dies,
die casting
Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly t ...
dies,
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
molds,
stamping dies, and
extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...
dies.
Shaw process
The ', also known as the ', uses a mixture of
refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
aggregate,
hydrolyzed
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
ethyl silicate
Tetraethyl orthosilicate, formally named tetraethoxysilane (TEOS), ethyl silicate is the organic chemical compound with the formula Si(OC2H5)4. TEOS is a colorless liquid. It degrades in water. TEOS is the of orthosilicic acid, Si(OH)4. It ...
,
alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
, and a
gel
A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...
ling agent to create a mold. This slurry mixture is poured into a slightly tapered
flask
Flask may refer to:
Container
* Hip flask, a small container used to carry a small amount of liquid
* Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes
** Erlenmeyer flask, a common laboratory flask wit ...
and a reusable pattern (''i.e.'' the item used to create the shape of the mold) is used. The slurry hardens almost immediately to a rubbery state (the consistency of
vulcanized rubber
Vulcanization (British: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to includ ...
). The flask and pattern is then removed. Then a torch is used to ignite the mold, which causes most of the volatiles to burn-off and the formation of ceramic
microcrazes (microscopic cracks). These cracks are important, because they allow gases to escape while preventing the metal from flowing through; they also ease
thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
and contraction during
solidification and shrinkage. After the burn-off, the mold is baked at to remove any remaining volatiles. Prior to pouring metal, the mold is pre-warmed to control shrinkage.
Unicast process
The ''Unicast process'' is very similar to the Shaw process, except it does not require the mold to be ignited 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 approximately . If a metal with a low melting point is cast then the firing can be skipped, because the mold has enough strength in the "green state" (un-fired).
Characteristics
The main advantages of ceramic molds are: a reusable
pattern
A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated l ...
(the item used to create the shape of the mold), excellent
surface finish
Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a surface from the perf ...
, close dimensional
tolerances, thin
cross-sections, and intricate shapes can be cast. For
undercuts and other difficult to cast features, part of the pattern can be made from wax in conjunction with a standard pattern; essentially using investment and ceramic mold casting techniques together. The main disadvantages are: it is only cost effective for small- to medium-sized production runs and the ceramic is not reusable. Ferrous and high-temperature non-ferrous are most commonly cast with these processes; other materials cast include: aluminum, copper, magnesium, titanium, and zinc alloys.
Weight limits are 100 grams to several thousand kilograms (3.5 oz to several tons). Cross-sections as thin as are possible, with no upper limit. Typical tolerances are 0.1 mm for the first 25 mm (0.005 in for the first inch) and 0.003 mm per additional mm (0.003 in per each additional in). A
draft
Draft, The Draft, or Draught may refer to:
Watercraft dimensions
* Draft (hull), the distance from waterline to keel of a vessel
* Draft (sail), degree of curvature in a sail
* Air draft, distance from waterline to the highest point on a vessel ...
of 1° is typically required. The typical surface finish is 2–4 um (75–150 uin) RMS.
See also
*
Ceramic forming techniques Ceramic forming techniques are ways of forming ceramics, which are used to make everything from tableware such as teapots to engineering ceramics such as computer parts. Pottery techniques include the potter's wheel, slip casting and many others. ...
References
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Casting (manufacturing)