![SandMoldBronzeAluminium](https://upload.wikimedia.org/wikipedia/commons/8/81/SandMoldBronzeAluminium.jpg)
Sand casting, also known as sand molded casting, is a
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 ...
process characterized by using
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
as the
mold
A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized
factories
A factory, manufacturing plant or a production plant is an industrial facility, often a complex consisting of several buildings filled with machinery, where workers manufacture items or operate machines which process each item into another. T ...
called
foundries
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
. Over 60% of all metal castings are produced via sand casting process.
Molds made of sand are relatively cheap, and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop the strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or
mold boxes known as a
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 ...
. The
mold cavities and
gate system are created by compacting the sand around models called
patterns
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 li ...
, by carving directly into the sand, or by
3D printing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
.
Basic process
There are six steps in this process:
#Place a
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 li ...
in sand to create a mold.
#Incorporate the pattern and sand in a gating system. Remove the pattern.
#Fill the mold cavity with molten metal.
#Allow the metal to cool.
#Break away the sand mold and remove the casting.
Components
Patterns
From the design, provided by a designer, a skilled ''pattern maker'' builds a ''pattern'' of the object to be produced, using wood, metal, or a plastic such as expanded polystyrene. Sand can be ground, swept or
strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as ''contraction allowance''. Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand
cores. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks.
Paths for the entrance of metal into the mold cavity constitute the runner system and include the
sprue, various feeders which maintain a good metal 'feed', and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via
risers, which are added either in the pattern itself, or as separate pieces.
Tools
In addition to patterns, the sand molder could also use tools to create the holes.
Molding box and materials
A multi-part molding box (known as a
casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with a molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically
screeded level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a "green" mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes casting possible without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.
Additive manufacturing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
(AM) can be used in the sand mold preparation, so that instead of the sand mold being formed via packing sand around a pattern, it is 3D-printed. This can reduce lead times for casting by obviating patternmaking.
Besides replacing older methods, additive can also complement them in hybrid models, such as making a variety of AM-printed cores for a cavity derived from a traditional pattern.
Chills
To control the solidification structure of the metal, it is possible to place metal plates, ''
chills'', in the mold. The associated rapid local cooling will form a finer-grained structure and may form a somewhat harder metal at these locations. In ferrous castings, the effect is similar to
quench
In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as p ...
ing metals in
forge work. The inner diameter of an engine cylinder is made hard by a chilling core. In other metals, chills may be used to promote
directional solidification
Directional solidification (DS) and progressive solidification are types of solidification within castings. Directional solidification is solidification that occurs from farthest end of the casting and works its way towards the sprue. Progressiv ...
of the casting. In controlling the way a casting freezes, it is possible to prevent internal voids or porosity inside castings.
Cores
Cores are apparatus used to generate hollow cavities or internal features which cannot be formed using pattern alone in moulding, cores are usually made using sand, but some processes also use permanent cores made of metal.
To produce cavities within the casting—such as for liquid cooling in
engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...
blocks and
cylinder head
In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber.
In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ...
s—negative forms are used to produce ''cores''. Usually sand-molded, cores are inserted into the casting box after removal of the pattern. Whenever possible, designs are made that avoid the use of cores, due to the additional set-up time, mass and thus greater cost.
With a completed mold at the appropriate moisture content, the box containing the sand mold is then positioned for filling with molten metal—typically
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
,
steel,
bronze,
brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...
,
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
alloys, or various
pot metal
Pot metal (or monkey metal) is an alloy of low-melting point metals that manufacturers use to make fast, inexpensive castings. The term "pot metal" came about due to the practice at automobile factories in the early 20th century of gathering up no ...
alloys, which often include
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
,
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
, and
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
. After being filled with liquid metal the box is set aside until the metal is sufficiently cool to be strong. The sand is then removed, revealing a rough casting that, in the case of iron or steel, may still be glowing red. In the case of metals that are significantly heavier than the casting sand, such as iron or lead, the casting flask is often covered with a heavy plate to prevent a problem known as ''floating the mold.'' Floating the mold occurs when the pressure of the metal pushes the sand above the mold cavity out of shape, causing the casting to fail.
![CoreBoxPatternCoreCasting](https://upload.wikimedia.org/wikipedia/commons/4/4c/CoreBoxPatternCoreCasting.jpg)
After casting, the cores are broken up by rods or shot and removed from the casting. The metal from the
sprue and risers is cut from the rough casting. Various
heat treatment
Heat treating (or heat treatment) is a group of industrial process, industrial, thermal and metalworking, metalworking processes used to alter the physical property, physical, and sometimes chemical property, chemical, properties of a material. ...
s may be applied to relieve stresses from the initial cooling and to add hardness—in the case of steel or iron, by quenching in water or oil. The casting may be further strengthened by surface compression treatment—like
shot peening
Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot (round metallic, glass, or ceramic particles) with ...
—that adds resistance to tensile cracking and smooths the rough surface. And when high precision is required, various machining operations (such as milling or boring) are made to finish critical areas of the casting. Examples of this would include the boring of cylinders and milling of the deck on a cast engine block.
Design requirements
The part to be made and its pattern must be designed to accommodate each stage of the process, as it must be possible to remove the pattern without disturbing the molding sand and to have proper locations to receive and position the cores. A slight taper, known as
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 vesse ...
, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mold. This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting. Should a piece of core or mold become dislodged it may be embedded in the final casting, forming a ''sand pit'', which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed. For critical applications, or where the cost of wasted effort is a factor, non-destructive testing methods may be applied before further work is performed.
Processes
In general, we can distinguish between two methods of sand casting; the first one using ''
green sand'' and the second being the ''air set'' method.
Green sand
These castings are made using sand molds formed from "wet" sand which contains water and organic bonding compounds, typically referred to as clay. The name "green sand" comes from the fact that the sand mold is not "set", it is still in the "green" or uncured state even when the metal is poured in the mould. Green sand is not green in color, but "green" in the sense that it is used in a wet state (akin to green wood).
Contrary to what the name suggests, "green sand" is not a type of sand on its own (that is, not
greensand
Greensand or green sand is a sand or sandstone which has a greenish color. This term is specifically applied to shallow marine sediment that contains noticeable quantities of rounded greenish grains. These grains are called ''glauconies'' and co ...
in the geologic sense), but is rather a mixture of:
*
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
sand (SiO
2),
chromite sand (FeCr
2O
4), or
zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
sand (ZrSiO
4), 75 to 85%, sometimes with a proportion of
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
,
staurolite, or
graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
.
*
bentonite
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
(
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
), 5 to 11%
* water, 2 to 4%
* inert
sludge
Sludge is a semi-solid slurry that can be produced from a range of industrial processes, from water treatment, wastewater treatment or on-site sanitation systems. For example, it can be produced as a settled suspension obtained from conventional ...
3 to 5%
*
anthracite (0 to 1%)
There are many recipes for the proportion of clay, but they all strike different balances between moldability, surface finish, and ability of the hot molten metal to
degas
Edgar Degas (, ; born Hilaire-Germain-Edgar De Gas, ; 19 July 183427 September 1917) was a French Impressionist artist famous for his pastel drawings and oil paintings.
Degas also produced bronze sculptures, prints and drawings. Degas is espec ...
. Coal, typically referred to in
foundries
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
as
sea-coal, which is present at a ratio of less than 5%, partially combusts in the presence of the molten metal, leading to offgassing of organic vapors. Green sand casting for non-ferrous metals does not use coal additives, since the
CO created does not prevent oxidation. Green sand for aluminum typically uses
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
sand (a mixture of the minerals
forsterite
Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorh ...
and
fayalite
Fayalite (, commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group ''Pbnm'') with cell parame ...
, which is made by crushing
dunite
Dunite (), also known as olivinite (not to be confused with the mineral olivenite), is an intrusive igneous rock of ultramafic composition and with phaneritic (coarse-grained) texture. The mineral assemblage is greater than 90% olivine, with ...
rock).
The choice of sand has a lot to do with the temperature at which the metal is poured. At the temperatures that copper and iron are poured, the clay is inactivated by the heat, in that the
montmorillonite
Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite gro ...
is converted to
illite
Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina ...
, which is a non-expanding clay. Most foundries do not have the very expensive equipment to remove the burned out clay and substitute new clay, so instead, those that pour iron typically work with silica sand that is inexpensive compared to the other sands. As the clay is burned out, newly mixed sand is added and some of the old sand is discarded or recycled into other uses. Silica is the least desirable of the sands, since metamorphic grains of silica sand have a tendency to explode to form sub-micron sized particles when thermally shocked during pouring of the molds. These particles enter the air of the work area and can lead to
silicosis in the workers. Iron foundries expend considerable effort on aggressive dust collection to capture this fine silica. Various types of respiratory-protective equipment are also used in foundries.
The sand also has the dimensional instability associated with the conversion of
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
from alpha quartz to beta quartz at 680 °C (1250 °F). Often, combustible additives such as wood flour are added to create spaces for the grains to expand without deforming the mold.
Olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
,
chromite, etc. are therefore used because they do not have a
phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...
that causes rapid expansion of the grains. Olivine and chromite also offer greater density, which cools the metal faster, thereby producing finer grain structures in the metal. Since they are not
metamorphic minerals, they do not have the
polycrystals found in
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
, and subsequently they do not form hazardous sub-micron sized particles.
"Air set" method
The ''air set'' method uses dry sand bonded with materials other than clay, using a fast curing
adhesive. The latter may also be referred to as
no bake mold casting. When these are used, they are collectively called "air set" sand castings to distinguish them from "green sand" castings. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand); the latter is generally preferred due to its more consistent composition.
With both methods, the sand mixture is packed around a ''pattern'', forming a mold cavity. If necessary, a temporary plug is placed in the sand and touching the pattern in order to later form a channel into which the casting fluid can be poured. Air-set molds are often formed with the help of a
casting flask having a top and bottom part, termed the
cope and drag. The sand mixture is tamped down as it is added around the pattern, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. Then the pattern is removed along with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process.
The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture to the surface, and this makes them easy to identify. Castings made from fine green sand can shine as cast but are limited by the depth to width ratio of pockets in the pattern. Air-set molds can produce castings with smoother surfaces than coarse green sand but this method is primarily chosen when deep narrow pockets in the pattern are necessary, due to the expense of the plastic used in the process. Air-set castings can typically be easily identified by the burnt color on the surface. The castings are typically shot blasted to remove that burnt color. Surfaces can also be later ground and polished, for example when making a large
bell
A bell is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be made by an inte ...
. After molding, the casting is covered with a residue of oxides, silicates and other compounds. This residue can be removed by various means, such as grinding, or shot blasting.
During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially automated casting processes have been developed for production lines.
Cold box
Cold box uses organic and inorganic binders that strengthen the mold by chemically adhering to the sand. This type of mold gets its name from not being baked in an oven like other sand mold types. This type of mold is more accurate dimensionally than green-sand molds but is more expensive. Thus it is used only in applications that necessitate it.
No-bake molds
No-bake molds are expendable sand molds, similar to typical sand molds, except they also contain a quick-setting liquid
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
and catalyst. Rather than being rammed, the molding sand is poured into the flask and held until the resin solidifies, which occurs at room temperature. This type of molding also produces a better surface finish than other types of sand molds. Because no heat is involved it is called a cold-setting process. Common flask materials that are used are wood, metal, and plastic. Common metals cast into no-bake molds are brass, iron (
ferrous
In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...
), and aluminum alloys.
Vacuum molding
''Vacuum molding'' (''V-process'') is a variation of the sand casting process for most ferrous and non-ferrous metals, in which unbonded sand is held in the flask with a
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...
. The pattern is specially vented so that a vacuum can be pulled through it. A heat-softened thin sheet () of
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
film is draped over the pattern and a vacuum is drawn (). A special vacuum forming flask is placed over the plastic pattern and is filled with a free-flowing sand. The sand is vibrated to compact the sand and a sprue and pouring cup are formed in the cope. Another sheet of plastic is placed over the top of the sand in the flask and a vacuum is drawn through the special flask; this hardens and strengthens the unbonded sand. The vacuum is then released on the pattern and the cope is removed. The drag is made in the same way (without the sprue and pouring cup). Any cores are set in place and the mold is closed. The molten metal is poured while the cope and drag are still under a vacuum, because the plastic vaporizes but the vacuum keeps the shape of the sand while the metal solidifies. When the metal has solidified, the vacuum is turned off and the sand runs out freely, releasing the casting.
[.]
The V-process is known for not requiring a draft because the plastic film has a certain degree of lubricity and it expands slightly when the vacuum is drawn in the flask. The process has high dimensional accuracy, with a tolerance of ±0.010 in for the first inch and ±0.002 in/in thereafter. Cross-sections as small as are possible. The surface finish is very good, usually between 150 and 125
rms. Other advantages include no moisture related defects, no cost for binders, excellent sand permeability, and no toxic fumes from burning the binders. Finally, the pattern does not wear out because the sand does not touch it. The main disadvantage is that the process is slower than traditional sand casting so it is only suitable for low to medium production volumes; approximately 10 to 15,000 pieces a year. However, this makes it perfect for prototype work, because the pattern can be easily modified as it is made from plastic.
Fast mold making processes
With the fast development of the car and machine building industry the casting consuming areas called for steady higher
productivity
Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...
. The basic process stages of the mechanical molding and casting process are similar to those described under the manual sand casting process. The technical and mental development however was so rapid and profound that the character of the sand casting process changed radically.
Mechanized sand molding
The first mechanized molding lines consisted of
sand slingers and/or jolt-squeeze devices that compacted the sand in the flasks. Subsequent mold handling was mechanical using cranes, hoists and straps. After core setting the copes and drags were coupled using guide pins and clamped for closer accuracy. The molds were manually pushed off on a roller
conveyor
A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transport of heavy or bulky materials. Conveyor systems allow ...
for casting and cooling.
Automatic high pressure sand molding lines
Increasing quality requirements made it necessary to increase the mold stability by applying steadily higher squeeze pressure and modern compaction methods for the sand in the flasks. In early fifties the
high pressure
In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By ''high pressure'' is usually meant pressures of th ...
molding was developed and applied in mechanical and later automatic flask lines. The first lines were using jolting and vibrations to pre-compact the sand in the flasks and
compressed air powered pistons to compact the molds.
=Horizontal sand flask molding
=
In the first automatic horizontal flask lines the sand was shot or slung down on the pattern in a flask and squeezed with hydraulic pressure of up to 140
bars. The subsequent mold handling including turn-over, assembling, pushing-out on a conveyor were accomplished either manually or automatically. In the late fifties
hydraulically
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...
powered pistons or multi-piston systems were used for the sand compaction in the flasks. This method produced much more stable and accurate molds than it was possible manually or
pneumatically
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air.
Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and e ...
. In the late sixties mold compaction by fast air pressure or
gas pressure drop over the pre-compacted sand mold was developed (sand-impulse and gas-impact). The general working principle for most of the horizontal flask line systems is shown on the sketch below.
Today there are many manufacturers of the automatic horizontal flask molding lines. The major disadvantages of these systems is high spare parts consumption due to multitude of movable parts, need of storing, transporting and maintaining the flasks and productivity limited to approximately 90–120 molds per hour.
=Vertical sand flaskless molding
=
In 1962, Dansk Industri Syndikat A/S (DISA-
DISAMATIC) invented a flask-less molding process by using vertically parted and poured molds. The first line could produce up to 240 complete sand molds per hour. Today molding lines can achieve a molding rate of 550 sand molds per hour and requires only one monitoring operator. Maximum mismatch of two mold halves is . Although very fast, vertically parted molds are not typically used by jobbing foundries due to the specialized tooling needed to run on these machines. Cores need to be set with a core mask as opposed to by hand and must hang in the mold as opposed to being set on parting surface.
=Matchplate sand molding
=
The principle of the matchplate, meaning pattern plates with two patterns on each side of the same plate, was developed and patented in 1910, fostering the perspectives for future sand molding improvements. However, first in the early sixties the American company Hunter Automated Machinery Corporation launched its first automatic flaskless, horizontal molding line applying the matchplate technology.
The method alike to the DISA's (DISAMATIC) vertical molding is flaskless, however horizontal. The matchplate molding technology is today used widely. Its great advantage is inexpensive pattern tooling, easiness of changing the molding tooling, thus suitability for manufacturing castings in short series so typical for the jobbing foundries. Modern matchplate molding machine is capable of high molding quality, less casting shift due to machine-mold mismatch (in some cases less than ), consistently stable molds for less grinding and improved parting line definition. In addition, the machines are enclosed for a cleaner, quieter working environment with reduced operator exposure to safety risks or service-related problems.
=Safety standards
=
With automated mold manufacturing came additional workplace safety requirements. Different
voluntary technical standards apply depending on the geopolitical jurisdiction where the machinery is to be used.
Canada
Canada does not have a machine-specific voluntary technical standard for sand-mold making machinery. This type of machinery is covered by:
Safeguarding of machinery, CSA Z432. Canadian Standards Association. 2016.
In addition, the electrical safety requirements are covered by:
Industrial Electrical Machinery, CSA C22.2 No. 301. 2016.
European Union
The primary standard for sand-mold manufacturing equipment in the EU is
Safety requirements for foundry moulding and coremaking machinery and plant associated equipment, EN 710. European Committee for Standardization (CEN).
EN 710 will need to be used in conjunction wit
EN 60204-1for electrical safety, an
EN ISO 13849-1an
EN ISO 13849-2o
EN 62061for functional safety. Additional type C standards may also be necessary for conveyors, robotics or other equipment that may be needed to support the operation of the mold-making equipment.
United States
There is no machine-specific standard for sand-mold manufacturing equipment. The ANSI B11 family of standards includes some generic machine-tool standards that could be applied to this type of machinery, including:
* Safety of Machinery, ANSI B11.0. American National Standards Institute (ANSI). 2020.
* Performance Requirements for Risk Reduction Measures: Safeguarding and other Means of Reducing Risk, ANSI B11.19. American National Standards Institute (ANSI). 2019.
* Safety Requirements for the Integration of Machinery into a System, ANSI B11.20. American National Standards Institute (ANSI). 2017.
* Safety Requirements for Transfer Machines, ANSI B11.24. American National Standards Institute (ANSI). 2002 (R2020).
* Functional Safety for Equipment (Electrical/Fluid Power Control Systems) General Principles for the Design of Safety Control Systems Using ISO 13849-1, ANSI B11.26. American National Standards Institute (ANSI). 2018.
* Sound Level Measurement Guidelines, ANSI B11.TR5. American National Standards Institute (ANSI). 2006 (R2017).
Mold materials
There are four main components for making a sand casting mold: ''base sand'', a ''binder'', ''additives'', and a ''parting compound''.
Molding sands
''Molding sands'', also known as ''foundry sands'', are defined by eight characteristics: refractoriness, chemical inertness, permeability, surface finish, cohesiveness, flowability, collapsibility, and availability/cost.
[.]
Refractoriness — This refers to the sand's ability to withstand the temperature of the liquid metal being cast without breaking down. For example, some sands only need to withstand if casting aluminum alloys, whereas steel needs a sand that will withstand . Sand with too low refractoriness will melt and fuse to the casting.
Chemical inertness — The sand must not react with the metal being cast. This is especially important with highly reactive metals, such as
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
and
titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
.
Permeability — This refers to the sand's ability to exhaust gases. This is important because during the pouring process many gases are produced, such as
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
, and
steam, which must leave the mold otherwise
casting defects, such as blow holes and gas holes, occur in the casting. Note that for each cubic centimeter (cc) of water added to the mold 1600 cc of steam is produced.
Surface finish — The size and shape of the sand particles defines the best surface finish achievable, with finer particles producing a better finish. However, as the particles become finer (and surface finish improves) the permeability becomes worse.
Cohesiveness (or bond) — This is the ability of the sand to retain a given shape after the pattern is removed.
Flowability – The ability for the sand to flow into intricate details and tight corners without special processes or equipment.
[.]
Collapsibility — This is the ability of the sand to be easily stripped off the casting after it has solidified. Sands with poor collapsibility will adhere strongly to the casting. When casting metals that contract a lot during cooling or with long freezing temperature ranges a sand with poor collapsibility will cause cracking and
hot tear
Hot or the acronym HOT may refer to:
Food and drink
*Pungency, in food, a spicy or hot quality
*Hot, a wine tasting descriptor
Places
* Hot district, a district of Chiang Mai province, Thailand
**Hot subdistrict, a sub-district of Hot Distric ...
s in the casting. Special additives can be used to improve collapsibility.
Availability/cost — The availability and cost of the sand is very important because for every ton of metal poured, three to six tons of sand is required.
Although sand can be screened and reused, the particles eventually become too fine and require periodic replacement with fresh sand.
In large castings it is economical to use two different sands, because the majority of the sand will not be in contact with the casting, so it does not need any special properties. The sand that is in contact with the casting is called ''facing sand'', and is designed for the casting on hand. This sand will be built up around the pattern to a thickness of . The sand that fills in around the facing sand is called ''backing sand''. This sand is simply silica sand with only a small amount of binder and no special additives.
[.]
Types of base sands
''Base sand'' is the type used to make the mold or core without any binder. Because it does not have a binder it will not bond together and is not usable in this state.
=Silica sand
=
Silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
(SiO
2) sand is the sand found on a beach and is also the most commonly used sand. It is either made by crushing
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
or taken from natural occurring locations, such as beaches and river beds. The
fusion point of pure silica is , however the sands used have a lower melting point due to impurities. For high melting point casting, such as steels, a minimum of 98% pure silica sand must be used; however for lower melting point metals, such as
cast iron
Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impur ...
and
non-ferrous
In metallurgy, non-ferrous metals are metals or alloys that do not contain iron (allotropes of iron, ferrite, and so on) in appreciable amounts.
Generally more costly than ferrous metals, non-ferrous metals are used because of desirable proper ...
metals, a lower purity sand can be used (between 94 and 98% pure).
Silica sand is the most commonly used sand because of its great abundance, and, thus, low cost (therein being its greatest advantage). Its disadvantages are high
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 ...
, which can cause casting defects with high melting point metals, and low
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
, which can lead to unsound casting. It also cannot be used with certain
basic metals because it will chemically interact with the metal, forming surface defects. Finally, it releases silica particulates during the pour, risking
silicosis in foundry workers.
[.]
=Olivine sand
=
Olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
is a mixture of
orthosilicate
In chemistry, orthosilicate is the anion , or any of its salts and esters. It is one of the silicate anions. It is occasionally called the silicon tetroxide anion or group.C. A. Kumins, and A. E. Gessler (1953), "Short-Cycle Syntheses of Ultram ...
s of iron and magnesium from the mineral
dunite
Dunite (), also known as olivinite (not to be confused with the mineral olivenite), is an intrusive igneous rock of ultramafic composition and with phaneritic (coarse-grained) texture. The mineral assemblage is greater than 90% olivine, with ...
. Its main advantage is that it is free from silica, therefore it can be used with basic metals, such as manganese steels. Other advantages include a low thermal expansion, high thermal conductivity, and high fusion point. Finally, it is safer to use than silica, therefore it is popular in Europe.
=Chromite sand
=
Chromite sand is a
solid solution
A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...
of
spinels. Its advantages are a low percentage of silica, a very high fusion point (), and a very high thermal conductivity. Its disadvantage is its costliness, therefore it is only used with expensive
alloy steel
Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The differe ...
casting and to make cores.
=Zircon sand
=
Zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
sand is a compound of approximately two-thirds
zirconium oxide
Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...
(Zr
2O) and one-third silica. It has the highest fusion point of all the base sands at , a very low thermal expansion, and a high thermal conductivity. Because of these good properties it is commonly used when casting alloy steels and other expensive alloys. It is also used as a
mold wash (a coating applied to the molding cavity) to improve surface finish. However, it is expensive and not readily available.
=Chamotte sand
=
Chamotte is made by
calcining
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
fire clay
Fire clay is a range of refractory clays used in the manufacture of ceramics, especially fire brick. The United States Environmental Protection Agency defines fire clay very generally as a "mineral aggregate composed of hydrous silicates of alumi ...
(Al
2O
3-SiO
2) above . Its fusion point is and has low thermal expansion. It is the second cheapest sand, however it is still twice as expensive as silica. Its disadvantages are very coarse grains, which result in a poor surface finish, and it is limited to
dry sand molding. Mold washes are used to overcome the surface finish problems. This sand is usually used when casting large steel workpieces.
Other materials
Modern casting production methods can manufacture thin and accurate molds—of a material superficially resembling papier-mâché, such as is used in egg cartons, but that is refractory in nature—that are then supported by some means, such as dry sand surrounded by a box, during the casting process. Due to the higher accuracy it is possible to make thinner and hence lighter castings, because extra metal need not be present to allow for variations in the molds. These thin-mold casting methods have been used since the 1960s in the manufacture of cast-iron engine blocks and cylinder heads for automotive applications.
Binders
''Binders'' are added to a base sand to bond the sand particles together (i.e. it is the glue that holds the mold together).
Clay and water
A mixture of
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
and water is the most commonly used binder. There are two types of clay commonly used:
bentonite
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
and
kaolinite, with the former being the most common.
Oil
Oils, such as
linseed oil, other
vegetable oil
Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or f ...
s and
marine oil
Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the body a ...
s, used to be used as a binder, however due to their increasing cost, they have been mostly phased out. The oil also required careful baking at to cure (if overheated, the oil becomes brittle, wasting the mold).
[.]
Resin
Resin binders are natural or synthetic high melting point
gums. The two common types used are
urea formaldehyde (UF) and
phenol formaldehyde
Phenol formaldehyde resins (PF) or phenolic resins (also infrequently called phenoplasts) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commerc ...
(PF) resins. PF resins have a higher heat resistance than UF resins and cost less. There are also cold-set resins, which use a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
instead of a heat to cure the binder. Resin binders are quite popular because different properties can be achieved by mixing with various additives. Other advantages include good collapsibility, low gassing, and they leave a good surface finish on the casting.
MDI (methylene diphenyl diisocyanate) is also a commonly used binder resin in the foundry core process.
Sodium silicate
Water glass (
sodium silicate 2SiO3 or (Na2O)(SiO2)">a2SiO3 or (Na2O)(SiO2)) is a high strength binder used with silica molding sand both for cores and molds.
To cure a mixture of finely ground
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
(e.g. by using a sand muller) and 3 to 4% of sodium silicate the binder,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(CO
2) gas is used.
The mixture is exposed to the gas at ambient temperature reacting as following:
:
+ CO2 <=> + + Heat
The advantage to this binder is that it can be used at room temperature and is fast. The disadvantage is that its high strength leads to shakeout difficulties and possibly hot tears in the casting.
The mixed sodium silicate and sand may also be heated by a
heat gun
A heat gun is a device used to emit a stream of hot air, usually at temperatures between 100 °C and 550 °C (200-1000 °F), with some hotter models running around 760 °C (1400 °F), which can be held by hand. Heat ...
to achieve better rigideness.
Additives
Additives are added to the molding components to improve: surface finish, dry strength, refractoriness, and "cushioning properties".
Up to 5% of ''reducing agents'', such as coal powder,
pitch,
creosote
Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics.
Some creosote types were ...
, and
fuel oil, may be added to the molding material to prevent wetting (prevention of liquid metal sticking to sand particles, thus leaving them on the casting surface), improve surface finish, decrease metal penetration, and
burn-on defects. These additives achieve this by creating gases at the surface of the mold cavity, which prevent the liquid metal from adhering to the sand. Reducing agents are not used with steel casting, because they can
carburize the metal during casting.
[.]
Up to 3% of "cushioning material", such as wood flour,
sawdust
Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machine ...
, powdered
husks,
peat
Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficient ...
, and
straw, can be added to reduce
scabbing,
hot tear
Hot or the acronym HOT may refer to:
Food and drink
*Pungency, in food, a spicy or hot quality
*Hot, a wine tasting descriptor
Places
* Hot district, a district of Chiang Mai province, Thailand
**Hot subdistrict, a sub-district of Hot Distric ...
, and
hot crack casting defects when casting high temperature metals. These materials are beneficial because burn-off when the metal is poured creates tiny voids in the mold, allowing the sand particles to expand. They also increase collapsibility and reduce shakeout time.
Up to 2% of ''cereal binders'', such as
dextrin
Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch and glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosidic bonds.
Dextrins can be produced from ...
,
starch,
sulphite lye
A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali which is highly soluble in water producing caustic basic solutions. "Lye" most commonly refers to sodium hydroxide (NaOH), but historically has been u ...
, and
molasses, can be used to increase dry strength (the strength of the mold after curing) and improve surface finish. Cereal binders also improve collapsibility and reduce shakeout time because they burn off when the metal is poured. The disadvantage to cereal binders is that they are expensive.
Up to 2% of
iron oxide powder can be used to prevent mold cracking and metal penetration, essentially improving refractoriness. Silica flour (fine silica) and zircon flour also improve refractoriness, especially in ferrous castings. The disadvantages to these additives is that they greatly reduce permeability.
Parting compounds
To get the pattern out of the mold, prior to casting, a parting compound is applied to the pattern to ease removal. They can be a liquid or a fine powder (particle diameters between ). Common powders include
talc
Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...
,
graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
, and dry silica; common liquids include
mineral oil
Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils.
The name 'mineral oil' by itself is imprecise, ...
and water-based silicon solutions. The latter are more commonly used with metal and large wooden patterns.
[.]
History
Clay molds were used in ancient China since the
Shang Dynasty
The Shang dynasty (), also known as the Yin dynasty (), was a Chinese royal dynasty founded by Tang of Shang (Cheng Tang) that ruled in the Yellow River valley in the second millennium BC, traditionally succeeding the Xia dynasty and ...
(c. 1600 to 1046 BC). The famous
Houmuwu ding (c. 1300 BC) was made using clay molding.
The
Assyria
Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the ...
n king
Sennacherib
Sennacherib ( Neo-Assyrian cuneiform: or , meaning " Sîn has replaced the brothers") was the king of the Neo-Assyrian Empire from the death of his father Sargon II in 705BC to his own death in 681BC. The second king of the Sargonid dynas ...
(704–681 BC) cast massive bronzes of up to 30 tonnes, and claims to have been the first to have used clay molds rather than the "lost-wax" method:
[ Stephanie Dalley, ''The Mystery of the Hanging Garden of Babylon: An Elusive World Wonder Traced'', Oxford University Press (2013). . Translation by the author, reproduced by permission of Oxford University Press.]
Whereas in former times the kings my forefathers had created bronze statues imitating real-life forms to put on display inside their temples, but in their method of work they had exhausted all the craftsmen, for lack of skill and failure to understand the principles they needed so much oil, wax and tallow for the work that they caused a shortage in their own countries—I, Sennacherib, leader of all princes, knowledgeable in all kinds of work, took much advice and deep thought over doing that work. Great pillars of bronze, colossal striding lions, such as no previous king had ever constructed before me, with the technical skill that Ninushki brought to perfection in me, and at the prompting of my intelligence and the desire of my heart I invented a technique for bronze and made it skillfully. I created clay moulds as if by divine intelligence....twelve fierce lion-colossi together with twelve mighty bull-colossi which were perfect castings... I poured copper into them over and over again; I made the castings as skillfully as if they had only weighed half a shekel each
Sand casting molding method was recorded by
Vannoccio Biringuccio
Vannoccio Biringuccio, sometimes spelled Vannocio Biringuccio (c. 1480 – c. 1539), was an Italian metallurgist. He is best known for his manual on metalworking, '' De la pirotechnia'', published posthumously in 1540.
20th Century translation by ...
in his book published around 1540.
In 1924, the
Ford Motor Company
Ford Motor Company (commonly known as Ford) is an American multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. The company sells automobi ...
set a record by producing 1 million cars, in the process consuming one-third of the total casting production in the U.S. As the automobile industry grew the need for increased casting efficiency grew. The increasing demand for castings in the growing
car and machine building industry during and after World War I and World War II, stimulated new inventions in
mechanization
Mechanization is the process of changing from working largely or exclusively by hand or with animals to doing that work with machinery. In an early engineering text a machine is defined as follows:
In some fields, mechanization includes the ...
and later
automation
Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...
of the sand casting process technology.
There was not one
bottleneck
Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...
to faster casting production but rather several. Improvements were made in molding speed, molding sand preparation, sand
mixing,
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
manufacturing processes, and the slow metal
melting
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which inc ...
rate in
cupola furnace
A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made almost any practical size. The size of a cupola is expressed in diameters and can range ...
s. In 1912, the sand slinger was invented by the
American company Beardsley & Piper. In 1912, the first sand mixer with individually mounted revolving
plows was marketed by the Simpson Company. In 1915, the first experiments started with
bentonite
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
clay instead of simple fire clay as the bonding additive to the molding sand. This increased tremendously the green and dry strength of the molds. In 1918, the first fully automated foundry for fabricating hand
grenades for the
U.S. Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cl ...
went into production. In the 1930s the first high-frequency coreless electric
furnace was installed in the U.S. In 1943,
ductile iron
Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis. While most varieties of cast iron are ...
was invented by adding magnesium to the widely used
grey iron
Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed ...
. In 1940, thermal sand reclamation was applied for molding and core sands. In 1952, the "D-process" was developed for making shell molds with fine, pre-coated sand. In 1953, the hotbox core sand process in which the cores are thermally cured was invented. In 1954, a new core binder—
water glass
Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate , sodium orthosilicate , and sodium pyrosilicate . The anions are often polymeric. These compounds are generally colorless transparent ...
(sodium silicate), hardened with
CO2 from ambient air, came out
In the 2010s,
additive manufacturing began to be applied to sand mold preparation in commercial production; instead of the sand mold being formed via packing sand around a pattern, it is 3D-printed.
See also
*
* , common sand casting defect
*
*
*
* (
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
), est. 1881, specialized in sand casting
* (
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
),
3D printing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
,
References
Notes
Bibliography
*
*
*
External links
Sand Molding at Hopewell Furnace (18th-19th century techniques) - U.S. National Park Service (YouTube video)Different Types of Metal Casting Processes
{{DEFAULTSORT:Sand Casting
Casting (manufacturing)
es:Fundición
es:Moldeo en arena verde