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Encyclopedia > Casting
Engineering Portal
Casting may be used to create artistic sculptures

Casting is a manufacturing process by which a liquid material such as a suspension of minerals as used in ceramics or molten metal or plastic is introduced into a mould, allowed to solidify within the mould, and then ejected or broken out to make a fabricated part. Casting is used for making parts of complex shape that would be difficult or uneconomical to make by other methods, such as cutting from solid material. Image File history File links No higher resolution available. ... Casting can refer to: in manufacturing, casting is a manufacturing process in entertainment, casting is a pre-production process for selecting a cast of actors and other talent for a live or recorded performance in computer science, casting is explicit type conversion in sport, casting is the placing of the... Download high resolution version (1078x1437, 473 KB)Arnoldo Pomodoros Rotante Dal Foro Centrale in the Sculpture Garden of the Hirshhorn Museum in Washington, DC. Uploaded by photographer. ... Download high resolution version (1078x1437, 473 KB)Arnoldo Pomodoros Rotante Dal Foro Centrale in the Sculpture Garden of the Hirshhorn Museum in Washington, DC. Uploaded by photographer. ... Sculptor redirects here. ... Minerals are natural compounds formed through geological processes. ... Ceramics can refer to: Ceramic, a type of material Ceramics (art), a fine art. ...


Casting may be used to form hot, liquid metals or meltable plastics (called thermoplastics), or various materials that cold set after mixing of components such as certain plastic resins such as epoxy, water setting materials such as concrete or plaster, and materials that become liquid or paste when moist such as clay, which when dry enough to be rigid is removed from the mold, further dried, and fired in a kiln or furnace. In chemistry, epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in... This article is about the construction material. ... This article is about the building material. ... Charcoal Kilns, California Gold Kiln, Victoria, Australia Hop kiln. ... A furnace is a device for heating air or any other fluid. ...


Substitution is always a factor in deciding whether other techniques should be used instead of casting. Alternatives include parts that can be stamped out on a punch press or deep-drawn, forged, items that can be manufactured by extrusion or by cold-bending, and parts that can be made from highly active metals. A Punch Press is a machine that has a set of punches and dies, a male (punch) and female (die), which when pressed together put a hole into the material used that is the same geometry as the punch that is being used. ...


The casting process is subdivided into two distinct subgroups: expendable and nonexpendable mold casting:

Casting iron in a sand mold

Contents

Sand mold casting with iron. ... Sand mold casting with iron. ...

Expendable mould casting

Expendable mould casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mould casting involves the use of temporary, nonreusable moulds.


Waste molding of plaster

A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand the expensive work of bronze casting or stone carving may be deferred until a prosperous patron is found, and as such work is considered to be a technical, rather than artistic processes it may even be deferred beyond the lifetime of the artist.


In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay. When cured it is then remove from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this "plaster" may be further refined and may be painted and waxed to resemble a finished bronze casting.


Sand casting

Main article: Sand casting

Sand casting requires a lead time of days for production at high output rates (1-20 pieces/hr-mold), and is unsurpassed for large-part production. Green (moist) sand has almost no part weight limit, whereas dry sand has a practical part mass limit of 2300-2700 kg. Minimum part weight ranges from 0.075-0.1 kg. The sand is bonded together using clays (as in green sand) or chemical binders, or polymerized oils (such as motor oil.) Sand in most operations can be recycled many times and requires little additional input. Casting is the process of production of objects by pouring molten material into a cavity called a mould which is the negative of the object, and allowing it to cool and solidify. ... For other uses, see Sand (disambiguation). ...


Preparation of the sand mold is fast and requires a pattern which can "stamp" out the casting template. Typically, sand casting is used for processing low-temperature metals, such as iron, copper, aluminum, magnesium, and nickel alloys. Sand casting can also be used for high temperature metals where other means would be unpractical. It is said to be the oldest and best understood of all techniques. Consequently, automation may easily be adapted to the production process, somewhat less easily to the design and preparation of forms. These forms must satisfy exacting standards as they are the heart of the sand casting process - creating the most obvious necessity for human control. The top and bottom halves of a sand casting mould showing the cavity prepared by patterns. ... For other uses, see Iron (disambiguation). ... For other uses, see Copper (disambiguation). ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... For other uses, see Nickel (disambiguation). ... An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ...


Plaster casting (of metals)

Plaster casting is similar to sand molding except that plaster is substituted for sand. Plaster compound is actually composed of 70-80% gypsum and 20-30% strengthener and water. Generally, the form takes less than a week to prepare, after which a production rate of 1-10 units/hr-mold is achieved with items as massive as 45 kg and as small as 30 g with very high surface resolution and fine tolerances. This article is about the building material. ... It has been suggested that Selenite be merged into this article or section. ...


Once used and cracked away, normal plaster cannot easily be recast. Plaster casting is normally used for nonferrous metals such as aluminium-, zinc-, or copper-based alloys. It cannot be used to cast ferrous material because sulfur in gypsum slowly reacts with iron. Prior to mold preparation the pattern is sprayed with a thin film of parting compound to prevent the mold from sticking to the pattern. The unit is shaken so plaster fills the small cavities around the pattern. The form is removed after the plaster sets. General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... For other uses, see Copper (disambiguation). ... This article is about the chemical element. ...


Plaster casting represents a step up in sophistication and requires skill. The automatic functions easily are handed over to robots, yet the higher-precision pattern designs required demand even higher levels of direct human assistance.


Casting of plaster, concrete, or plastic resin

Main article: Resin casting

Plaster itself may be cast, as can other chemical setting materials such as concrete or plastic resin - either using single use waste molds as noted above or multiple use piece molds, or molds made of small ridged pieces or of flexible material such as latex rubber (which is in turn supported by an exterior mold). When casting plaster or concrete the finished product is, unlike marble, relatively unattractive, lacking in transparency, and so is usually painted, often in ways that give the appearance of metal or stone. Alternatively, the first layers cast may contain colored sand so as to give an appearance of stone. By casting concrete, rather than plaster, it is possible to create sculptures, fountains, or seating for outdoor use. A simulation of high quality marble may be made using certain chemically set plastic resins (for example epoxy or polyester) with powdered stone added for coloration, often with multiple colors worked in. The later is a common means of making attractive washstands, washstand tops and shower stalls, with the skilled working of multiple colors resulting in simulated staining patterns as is often found in natural marble or travertine. There are very few or no other articles that link to this one. ... In chemistry, epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in... SEM picture of a bend in a high surface area polyester fiber with a seven-lobed cross section Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. ... For other uses, see Marble (disambiguation). ... Travertine Travertine terraces at Mammoth Hot Springs, Yellowstone National Park A carving in travertine Travertine is a sedimentary rock. ...


Shell moulding

Shell molding is also similar to sand molding except that a mixture of sand and 3-6% resin holds the grains together. Set-up and production of shell mold patterns takes weeks, after which an output of 5-50 pieces/hr-mold is attainable. Aluminium and magnesium products average about 13.5 kg as a normal limit, but it is possible to cast items in the 45-90 kg range. Shell mold walling varies from 3-10 mm thick, depending on the forming time of the resin. This article does not cite any references or sources. ...


There are a dozen different stages in shell mold processing that include:

  1. initially preparing a metal-matched plate
  2. mixing resin and sand
  3. heating pattern, usually to between 505-550 K
  4. inverting the pattern (the sand is at one end of a box and the pattern at the other, and the box is inverted for a time determined by the desired thickness of the mill)
  5. curing shell and baking it
  6. removing investment
  7. inserting cores
  8. repeating for other half
  9. assembling mold
  10. pouring mold
  11. removing casting
  12. cleaning and trimming.

The sand-resin mix can be recycled by burning off the resin at high temperatures.


Investment Casting

Main article: Investment Casting
Valve for Nuclear Power Station produced using investment casting

Investment casting (lost-wax casting) is a process that has been practised for thousands of years, with lost wax process being one of the oldest known metal forming techniques. From 5000 years ago, when bees wax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity. The lost wax process is a method that requires the metallurgist to build a wax replica of the item that is desired to be replicated, followed by the coating of the wax sculpted article in a heat resistant yet durable exterior, typically a ceramic, which is then fired to permit... Image File history File linksMetadata No higher resolution available. ... Casting is a process by which a material is introduced into a mold while it is liquid, allowed to solidify in the shape inside the mold, and then removed producing a fabricated object, part, or casing. ...


The process is suitable for repeatable production of net shape components, from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast. For other uses, see Steel (disambiguation). ... Aluminum redirects here. ... This article is about the manufacturing process. ... Casting is the process of production of objects by pouring molten material into a cavity called a mould which is the negative of the object, and allowing it to cool and solidify. ... Near net shape is an industrial production technique. ...


Nonexpendable mold casting

Tin soldiers being cast in German molds from the early 20th century. The two mold halves are clamped together, and the metal (an alloy of tin and lead, heated to approx. 300°C) is poured into the mold. When the metal has solidified, the mold is cracked open. Sprues (pouring channels) and extraneous flash (metal that has penetrated cracks and air channels in the mold) are seen in the third image, and have been removed from the castings in the last image.

Nonexpendable mold casting differs from expendable processes in that the mold need not be reformed after each production cycle. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting. Image File history File links Size of this preview: 169 × 597 pixelsFull resolution (800 × 2827 pixel, file size: 1. ... Image File history File links Size of this preview: 169 × 597 pixelsFull resolution (800 × 2827 pixel, file size: 1. ... A rare, complete set of Nazi S.A. tin soldiers, from the 1940s. ... Bronze casting showing sprue and risers In foundry work, a Sprue is the passage through which metal is poured into a mold. ... Molding flash is excess material attached to a molded product, which must be removed. ...


Permanent mold casting

Permanent mould casting (typically for non-ferrous metals) requires a set-up time on the order of weeks to prepare a steel tool, after which production rates of 5-50 pieces/hr-mold are achieved with an upper mass limit of 9 kg per iron alloy item (cf., up to 135 kg for many nonferrous metal parts) and a lower limit of about 0.1 kg. Steel cavities are coated with refractory wash of acetylene soot before processing to allow easy removal of the workpiece and promote longer tool life. Permanent molds have a life which varies depending on maintenance of after which they require refinishing or replacement. Cast parts from a permanent mold generally show 20% increase in tensile strength and 30% increase in elongation as compared to the products of sand casting. Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. ... Soot, also called lampblack, Pigment Black 7, carbon black or black carbon, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the...


The only necessary input is the coating applied regularly. Typically, permanent mold casting is used in forming iron-, aluminium-, magnesium-, and copper-based alloys. The process is highly automated.


Die casting

Main article: Die casting

Die casting is the process of forcing molten metal under high pressure into the cavities of steel moulds. The moulds are called dies. Dies range in complexity to produce any non-ferrous metal parts (that need not be as strong, hard or heat-resistant as steel) from sink faucets to engine blocks (including hardware, component parts of machinery, toy cars, etc). In fact, the process lends itself to making any metal part that: This article is about the manufacturing process. ... This article is about the manufacturing process. ...

  • must be precise (dimensions plus or minus as little as 50 µm--over short distances),
  • must have a very smooth surface that can be bright plated without prior polishing and buffing,
  • has very thin sections (like sheet metal--as little as 1.2 mm),
  • must be produced much more economically than parts primarily machined (multicavity die casting moulds operating at high speed are much more productive than machine tools or even stamping presses),
  • must be very flexible in design; a single die casting may have all the features of a complex assembly.

If several machining operations would be required or assembly of several parts would be required (to make a finished part), die casting is probably far more economical. This level of versatility has placed die castings among the highest volume products made in the metalworking industry.


Common metals used in die casting include zinc and aluminum. These are usually not pure metals; rather are alloys which have better physical characteristics.


In recent years, injection-molded plastic parts have replaced some die castings because they are usually cheaper (and lighter--important especially for automotive parts since the fuel-economy standards). Plastic parts are practical (particularly now that plating of plastics has become possible) if hardness is not required and if parts can be redesigned to have the necessary strength.


Centrifugal casting

Main article: Centrifugal casting

Centrifugal casting is both gravity- and pressure-independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 90 g (882.9 kg m/s²). Lead time varies with the application. Semi- and true-centrifugal processing permit 30-50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3-4.5 kg. Centrifugal casting or rotocasting is a casting technique which has application across a wide range of industrial and artistic applications: It is used as a means of casting small, detailed parts or jewelry. ...


Industrially, the centrifugal casting of railway wheels was an early application of the method developed by German industrial company Krupp and this capability enabled the rapid growth of the enterprise. For the U.S. town, see Krupp, Washington. ...


Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting. Vacuum casting is a means of casting small metal parts or jewelry that have fine detail or for casting various plastic materials. ...


Continuous casting

Main article: Continuous casting

Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Molten metal is poured into an open-ended, water-cooled copper mould, which allows a 'skin' of solid metal to form over the still-liquid centre. The strand, as it is now called, is withdrawn from the mould and passed into a chamber of rollers and water sprays; the rollers support the thin skin of the strand while the sprays remove heat from the strand, gradually solidifying the strand from the outside in. After solidification, predetermined lengths of the strand are cut off by either mechanical shears or travelling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimetres thick by about five metres wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut. Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. ... Hot rolling is a metallurgical process in which the metal is passed through a pair of rolls and the temperature of the metal is above its recrystallization temperature, as opposed to cold rolling, which takes place below it. ...


Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increases the quality of the final product. Metals such as steel, copper and aluminium are continuously cast, with steel being the metal with the greatest tonnages cast using this method. For other uses, see Steel (disambiguation). ... For other uses, see Copper (disambiguation). ... Aluminum redirects here. ...


Cooling rate

The rate at which a casting cools affects its microstructure, quality, and properties.


The cooling rate is largely controlled by the molding media used for making the mold. When the molten metal is poured into the mold, the cooling down begins. This happens because the heat within the molten metal flows into the relatively cooler parts of the mold. Molding materials transfer heat from the casting into the mold at different rates. For example, some molds made of plaster may transfer heat very slowly, while a mold made entirely of steel would transfer the heat very fast. This cooling down ends with (solidification) where the liquid metal turns to solid metal. In physics and chemistry, freezing is the process of cooling a liquid to the temperature (called freezing point) where it turns into a solid. ...

Intermediate cooling rates from melt result in a dendritic microsturcture. Primary and secondary dendrites can be seen in this image.

At its basic level a foundry may pour a casting without regard to controlling how the casting cools down and the metal freezes within the mold. However, if proper planning is not done the result can be gas porosities and shrink porosities within the casting. To improve the quality of a casting and engineer how it is made, the foundry engineer studies the geometry of the part and plans how the heat removal should be controlled. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...


Where heat should be removed quickly, the engineer will plan the mold to include special heat sinks to the mold, called chills. Fins may also be designed on a casting to extract heat, which are later removed in the cleaning (also called fettling) procees. Both methods may be used at local spots in a mold where the heat will be extracted quickly.


Where heat should be removed slowly, a riser or some padding may be added to a casting. A riser is an additional larger cast piece which will cool more slowly than the place where is it attached to the casting. A riser is a reservoir built into a metal-casting mold to prevent cavities due to shrinkage. ...


Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure.


Shrinkage

Castings shrink when they cool. Like nearly all materials, metals are less dense as a liquid than a solid. During solidification (freezing), the metal density dramatically increases. This results in a volume decrease for the metal in a mold. Solidification shrinkage is the term used for this contraction. Cooling from the freezing temperature to room temperature also involves a contraction. The easiest way to explain this contraction is that is the reverse of thermal expansion. Compensation for this natural phenomenon must be considered in two ways. In physics, thermal expansion is the tendency of matter to increase in volume or pressure when heated. ...


Solidification Shrinkage

The shrinkage caused by solidification can leave cavities in a casting, weakening it. Risers provide additional material to the casting as it solidifies. The riser (sometimes called a "feeder") is designed to solidify later than the part of the casting to which it is attached. Thus the liquid metal in the riser will flow into the solidifying casting and feed it until the casting is completely solid. In the riser itself there will be a cavity showing where the metal was fed. Risers add cost because some of their material must be removed, by cutting away from the casting which will be shipped to the customer. They are often necessary to produce parts which are free of internal shrinkage voids. A riser is a reservoir built into a metal-casting mold to prevent cavities due to shrinkage. ...


Sometimes, to promote directional solidification, chills must be used in the mold. A chill is any material which will conduct heat away from the casting more rapidly that the material used for molding. Thus if silica sand is used for molding, a chill may be made of copper, iron, aluminum, graphite, zircon sand, chromite or any other material with the ability to remove heat faster locally from the casting. All castings solidify with progressive solidification but in some designs a chill is used to control the rate and sequence of solidification of the casting. Directional solidification is a series of measures applied to control the feeding of castings. ... Look up chill in Wiktionary, the free dictionary. ...


Patternmaker's Shrink (Thermal Contraction)

Shrinkage after solidification can be dealt with by using an oversized pattern designed for the relevant alloy. Pattern makers use special "contraction rulers" (also called "shrink rules") to make the patterns used by the foundry to make castings to the design size required. These rulers are 1 - 6% oversize, depending on the material to be cast. These rulers are mainly referred to by their actual changes to the size. For example a 1/100 ruler would add 1 mm to 100 mm if measured by a "standard ruler" (hence being called a 1/100 contraction ruler). Using such a ruler during pattern making will ensure an oversize pattern. Thus, the mold is larger also, and when the molten metal solidifies it will shrink and the casting will be the size required by the design, if measured by a standard ruler. A pattern made to match an existing part would be made as follows: First, the existing part would be measured using a standard ruler, then when constructing the pattern, the pattern maker would use a contraction ruler, ensuring that the casting would contract to the correct size.


See also

Wikimedia Commons has media related to:
Casting

Image File history File links Commons-logo. ... Rare, water preserved Greek Athlete 310. ... 5 different types of flexible mold compounds in significant use today. ... Hollow casting is a casting process in which molten liquid metal is poured into a two part mold, and then poured out again to leave a hollow shell. ... Injection moulding is a manufacturing technique for making parts from thermoplastic material in production. ... The lost wax process is a method that requires the metallurgist to build a wax replica of the item that is desired to be replicated, followed by the coating of the wax sculpted article in a heat resistant yet durable exterior, typically a ceramic, which is then fired to permit... This article is about the manufacturing process. ... Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as the investment. ... Casting is the process of production of objects by pouring molten material into a cavity called a mould which is the negative of the object, and allowing it to cool and solidify. ... Sculptor redirects here. ... Spin casting or Centrifugal Rubber Mold Casting (CRMC) is a method of utilizing centrifugal force to produce castings from a rubber mold. ...

External links


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