Riser (casting)

A riser or feeder is a built into a metal-casting mold to prevent due to shrinkage. Because metals are less dense as liquids than as solids (with some exceptions), castings shrink as they cool. This can leave a void, generally at the last point to solidify. Risers prevent this by providing molten metal at the point of likely shrinkage, so that the cavity forms in the riser, not the casting.

This only works if the riser cools after the rest of the casting. Chvorinov's rule states that the solidification time t of molten metal is related to the constant C (which depends on the thermal properties of the mold and the material) and the local volume (V) and surface area (A) of the material, according to the relationship



Therefore, to ensure that the casting solidifies before the riser, the ratio of the volume to the surface area of the riser should be greater than that of the casting. The riser must satisfy two requirements: it must be large enough so that it solidifies after the casting (i.e. satisfies Chvorinovs rule) and it must contain a sufficient volume of metal to supply the shrinkage contraction which occurs on cooling from the casting temperature to the completion of solidification. This latter requirement will be more important for platelike shapes; the former will be more important for chunky shapes.

Hence the casting should be designed to produce directional solidification which sweeps from the extremities of the mold cavity toward the riser. In this way, the riser can feed molten metal continuously and will compensate for the solidification shrinkage of the entire mold cavity. If this type of solidification is not possible, multiple risers may be necessary with various sections of the casting solidifying toward their respective risers.

The activity of planning of how a casting will gated and risered is called 'Foundry Methoding' or 'Foundry Engineering'. The efficiency of Methoding the risering plan can be expressed in terms of percentage, by dividing the weight of the casting shipped to the customer by the total pouring weight used to make the casting. Because risers exist only to ensure the integrity of the casting, they are removed after the part has cooled, and their metal is remelted to be used again. As a result, riser size, number, and placement should be carefully planned to reduce waste while filling all the shrinkage in the casting. The Methoding engineer normally aims for the highest efficiency in riser design while making a part quality with minimal or no rejections from shrink defects.


Bronze casting showing sprue and risers (side view)

Bronze casting showing shrinkage in sprue (top view)

References

  • Kalpakjian, Serope, et al. (2001). Manufacturing Engineering and Technology. Published by Pearson Education.

Metalworking:
    [ e]

:
Casting Terminology | Flask | Sprue | Riser | Cope and drag | Draft angle | Dross | Green sand | Molding sand | Chill | Ingot | Pattern | Slag

Metalworking topics:   Casting | CNC | Cutting tools | Drilling and threading | Fabrication | Finishing | Grinding | Jewellery | Lathe (tool) | Machining | Machine tooling | Measuring | Metalworking | Hand tools | Metallurgy | Milling | Occupations | Press tools | Smithing | Terminology | Welding
The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
..... Click the link for more information.
Molding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a mold.

A mold or mould is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials.
..... Click the link for more information.
Chvorinov's Rule is a mathematical relationship first expressed by Nicolas Chvorinov in 1940, that relates the solidification time for a simple casting to the volume and surface area of the casting.
..... Click the link for more information.
Directional solidification is a series of measures applied to control the feeding of castings. As most metals and alloys solidify, changing from the liquid state to the solid state they will undergo an appreciable volume contraction.
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
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.
..... Click the link for more information.
Sand casting is a means of producing rough metal castings using a mold usually made from sand formed around a replica of the object to be cast (called a pattern) that is removed once the sand has been compacted.
..... Click the link for more information.
Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as the investment. The method takes advantage of the properties of foam to simply and cheaply form castings that would be difficult or impossible, using normal "cope and drag" techniques.
..... Click the link for more information.
Investment casting, also called lost-wax casting, is one of the oldest known metal forming techniques. From 5,000 years ago, when bees wax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the production of
..... Click the link for more information.
Die casting is the process of forcing molten metal under high pressure into the cavities of steel molds. The molds 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
..... Click the link for more information.
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.

..... Click the link for more information.
Vacuum casting is a means of casting small metal parts or jewelry that have fine detail or for casting various plastic materials. A porous or vented mold is used and is placed on a table or container where vacuum is applied.
..... Click the link for more information.
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. It allows lower-cost production of metal sections with better quality, due to finer control through automation of the casting
..... Click the link for more information.
For other uses, see Billet (disambiguation).
Billet is a term used in manufacturing to refer to a cast product. A cast product is defined as either as ingot or a billet, depending on whether the cross-sectional diameter is greater than, or less than
..... Click the link for more information.
furnace is a device used for heating.

In American English, the term furnace on its own is generally used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English), and sometimes as a synonym for kiln,
..... Click the link for more information.
A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases.
..... Click the link for more information.
Puddling was an Industrial Revolution means of making iron and steel. In the original puddling technique, molten iron in a reverberatory furnace was stirred with rods, which were consumed in the process.
..... Click the link for more information.
The Bessemer process was the first inexpensive industrial process for the mass-production of steel from a molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855.
..... Click the link for more information.
Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other impurities are burnt out of pig iron to produce steel. Since steel is difficult to manufacture due to its high melting point, normal fuels and furnaces were insufficient and the open hearth
..... Click the link for more information.
An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc.

Arc furnaces range in size from small units of approximately one ton capacity (used in foundries for producing cast iron products) up to about 400 ton units used for secondary
..... Click the link for more information.
induction furnace is an electrical furnace in which the heat is applied by induction heating of a conductive medium (usually a metal) in a crucible around which water-cooled magnetic coils are wound.
..... Click the link for more information.
A casting flask is a wooden or metal frame, used in a foundry to contain molding sand used to make a mold. A simple flask has two parts, the cope and the drag, and more elaborate flasks may have three or even four parts.
..... Click the link for more information.
Sprue is the passage through which metal is poured into a mold. The term can also refer to the excess metal on a rough casting, which solidified in the sprue hole. The term has the identical usage in the plastic injection-molding industry.
..... Click the link for more information.
In foundry work, the terms Cope and Drag refer to the upper and lower parts of a two-part casting flask, used in sand casting. The flask is a wood or metal frame, which contains the molding sand, providing support to the sand as the metal is poured into the mold.
..... Click the link for more information.
A draft angle describes the amount of taper for molded or cast parts perpendicular to the parting line.

Consider the fabrication of a hollow plastic box, without lid. Once the plastic has hardened around the mold, the mold must be removed.
..... Click the link for more information.
Dross is a mass of solid impurities floating on a molten metal bath. It appears usually on the melting of low melting point metals or alloys such as tin, lead, zinc or aluminium, or by oxidation of the metal(s).
..... Click the link for more information.
Green Sand is an aggregate of sand, bentonite clay, pulverized coal and water. Its principal use is in making molds for the casting of metals. The largest portion of the aggregate is always sand.
..... Click the link for more information.
Molding Sand, Foundry sand, or Green sand is sand that when moistened or oiled tends to pack well and hold its shape. It is used in the process of sand casting.

Metalworking:

..... Click the link for more information.
A Chill is an object used in making metal castings.

Molten metal when poured into a sand mold will cool at a certain rate, depending upon the thickness of the casting.
..... Click the link for more information.
Ingot is a metal that is solid moulded into simple shape, similar to the final product. It requires a second procedure of shaping, by means of cold/hot working to produce the final product. They involve relatively simple procedures.
..... Click the link for more information.


This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.