Sprue (manufacturing)

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Bronze casting showing sprue and risers BronzeSprueRisersSideView.jpg
Bronze casting showing sprue and risers

A sprue is the vertical passage through which liquid material is introduced into a mold and it is a large diameter channel through which the material enters the mold. It connects the pouring basin to the runner. In many cases it controls the flow of material into the mold. During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered downwards to minimize turbulence and formation of air bubbles.

Contents

Casting

In casting, a sprue is the passage through which a molten material is introduced into a mold, and the term also refers to the excess material which solidifies in the sprue passage.

Function

Sprues can serve as filters, as heat sinks, and as feeders. Bronze, in particular, has a high shrinkage rate as it is cooling. A sprue is tapered with its bigger end at the top to receive the liquid metal, the smaller end is connected to the runner.

Sprue design

The design of the sprue gating and runner is also essential for casting. The design can incorporate either bottom or vertical gating.

For bottom gating

where:

= Time for filling
= Area of mold
= Area of gate
= Acceleration due to gravity
= Total height
= Height of mold cavity

This equation may change if the height of gating is equal to height of casting material.

Then the equation will be:

or, simplified,

where:

= Time for filling
= Area of mold
= Area of gate
= Acceleration due to gravity
= Total height (Height of gating + height of mold cavity)
= Height of mold cavity

Injection molding

Plastic sprue Sprue.JPG
Plastic sprue

In injection molding, sprue refers to the passage through which a liquid material (such as polystyrene or polyvinyl chloride) flows into a die, where the material solidifies to form parts. Sprue also refers to the material that solidifies in these passages, forming a framework that attaches the parts in a roughly planar arrangement.

Sprues, runners, and gates

Some moldmakers distinguish the sprue, the gate, and the runner. The sprue is a large-diameter channel through which plastic flows, usually around the edges of the part or along straight lines. The runner is a smaller channel from the sprue to the individual part. An analogy may be found in a water system that employs a water main (sprue) and smaller pipes (runners) to individual houses. The gate is the location at which the molten plastic enters the mold cavity and is often evidenced by a small nub or projection (the "gate mark") on the molded piece.

Many scale-model kits are made from injection-molded plastic. Hobbyists typically remove the parts of a model kit from the runner using a sharp craft knife or razor saw. The sprues usually form a rectangle with the runners and parts inside which makes them easier to box.

Model makers sometimes use sprues or runners as raw material to fabricate additional parts, such as railings on model ships, antenna wires on airplanes, or greebles on fictional spacecraft.

Sprues in model kits often include engravings to identify the parts by number.

See also

Related Research Articles

<span class="mw-page-title-main">Metal casting</span> Pouring liquid metal into a mold

In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold that contains a negative impression of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

<span class="mw-page-title-main">Injection moulding</span> Manufacturing process for producing parts by injecting molten material into a mould, or mold

Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed, and injected into a mould cavity, where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mould-maker from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower-temperature thermoplastics, can be used for some simple injection moulds.

<span class="mw-page-title-main">Molding (process)</span> Shaping a liquid or plastic material by making it conform to a more rigid mold

Molding or moulding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. This itself may have been made using a pattern or model of the final object.

<span class="mw-page-title-main">Die casting</span> Metal casting process

Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.

<span class="mw-page-title-main">Sand casting</span> Metal casting process using sand as the mold material

Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 60% of all metal castings are produced via sand casting process.

<span class="mw-page-title-main">Cope and drag</span>

In foundry work, the terms cope and drag refer respectively to the top and bottom 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. In flaskless molding, the same terms are used, cope for the top or upper piece and drag for the bottom or lower piece.

<span class="mw-page-title-main">Riser (casting)</span>

A riser, also known as a feeder, is a reservoir built into a metal casting mold to prevent cavities due to shrinkage. Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify. Risers prevent this by providing molten metal to the casting as it solidifies, so that the cavity forms in the riser and not the casting. Risers are not effective on materials that have a large freezing range, because directional solidification is not possible. They are also not needed for casting processes that utilized pressure to fill the mold cavity.

<span class="mw-page-title-main">Rotational molding</span> Making hollow plastic objects in a heated mold

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Spin casting, also known as centrifugal rubber mold casting (CRMC), is a method of utilizing inertia to produce castings from a rubber mold. Typically, a disc-shaped mold is spun along its central axis at a set speed. The casting material, usually molten metal or liquid thermoset plastic, is then poured in through an opening at the top-center of the mold. The filled mold then continues to spin as the metal solidifies.

<span class="mw-page-title-main">Foundry</span> Factory that produces metal castings

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<span class="mw-page-title-main">Hot runner</span>

A hot runner system is an assembly of heated components used in plastic injection molds that inject molten plastic into the cavities of the mold.

Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume.

<span class="mw-page-title-main">Pattern (casting)</span>

In casting, a pattern is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.

<span class="mw-page-title-main">Injection molding machine</span> Machine for manufacturing plastic products

An injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.

Permanent mold casting is a metal casting process that employs reusable molds, usually made from metal. The most common process uses gravity to fill the mold, however gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminium, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds.

<span class="mw-page-title-main">Casting</span> Manufacturing process in which a liquid is poured into a mold to solidify

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various time setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the required size, rather than fabricating by joining several small pieces. Casting is a 7,000-year-old process. The oldest surviving casting is a copper frog from 3200 BC.

Resin casting is a method of plastic casting where a mold is filled with a liquid synthetic resin, which then hardens. It is primarily used for small-scale production like industrial prototypes and dentistry. It can be done by amateur hobbyists with little initial investment, and is used in the production of collectible toys, models and figures, as well as small-scale jewellery production.

Gundam models, or Gunpla, are model kits depicting the vehicles and characters of the fictional Gundam multiverse by Bandai.

Injection mold construction is the process of creating molds that are used to perform injection molding operations using an injection molding machine. These are generally used to produce plastic parts using a core and a cavity.

Transfer molding is a manufacturing process in which casting material is forced into a mold. Transfer molding is different from compression molding in that the mold is enclosed rather than open to the fill plunger resulting in higher dimensional tolerances and less environmental impact. Compared to injection molding, transfer molding uses higher pressures to uniformly fill the mold cavity. This allows thicker reinforcing fiber matrices to be more completely saturated by resin. Furthermore, unlike injection molding the transfer mold casting material may start the process as a solid. This can reduce equipment costs and time dependency. The transfer process may have a slower fill rate than an equivalent injection molding process.

References