Casting sands

Casting is the simplest and most direct way of producing a finished shape from metal. Casting shapes from liquid metals can be done by a variety of processes, the simplest ofwhuch is sand casting. 

For the production of small castings, a method known as box moulding is employed. The box is made up of two frames with lugs at each end into which pins are fitted to ensure accurate alignment when the frames are placed together. The top frame is referred to as the cope and the bottom frame as the drag. 

A removable pattern is used to create the required shape of cavity within the mould. The pattern is made in two parts, split at a convenient position for ease of removal from the mould - this position being known as the parting line. The two parts of the pattern are accurately aligned with each other using pins or dowels. 

The cope is then carefully lifted off and turned over. Both halves of the pattern are carefully removed. Small channels known as gates are then cut from the bottom of the runner and riser to enable metal to fill the mould cavity. Any loose sand is blown away to leave a clean cavity in the mould. The core is placed in position in the bottom half of the mould 

The mould is now ready for pouring. When the metal has solidified, the mould is broken up to release the casting. The runner and riser are broken off, and the rough edges are removed by fettling (Le. hand grinding). 

The drag is then turned over and the second half pattern is located by means of the dowels. 

The cope is then carefully lifted off and turned over. Both halves of the pattern are carefully removed. Small channels known as gates are then cut from the bottom of the runner and riser to enable metal to fill the mould cavity. Any loose sand is blown away to leave a clean cavity in the mould. The core is placed in position in the bottom half of the mould box (the drag) and the top mould box (the cope) is carefully replaced in position with the aid of the locating pins and is clamped to prevent lifting when the metal is poured. Fig. 16.2(c). The core which is necessary to provide a hollow section, in this case the bore of the gear blank, is made separately. 

Green sand casting the most common and the cheapest. Associated problems are that the mold has low strength and high moisture content. 

Dry sand core boxes are used instead of patterns, and an oven is used to cure the mold. Expensive and time consuming. 

Skin-dried sand the mold is dried to a certain depth. Used in the casting of steels. 

Patterns one-piece solid patterns are the cheapest to make split patterns for moderate quantities match plate patterns for high volume production. 

High degree of shape complexity possible. Limited only by the pattern. 

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Sandarac [9000-57-1] Sandblasting Sand casting Sand cores Sander Cramer test Sandimmun(e) Sand-lime brick Sand mills Sandofan... 

S, sand cast P, permanent mold cast D, pressure die cast. Aluminum and impurities constitute remainder. Table 22. Mechanical Properties of Aluminum Foundry Alloys ... 

Property AHoy No. 8, Sand Cast Permanent-Mold Sand Cast Sand Cast, H.T. 

Sand Casting. Sand casting is the most popular method of molding for cast copper alloys. It is the least expensive near net shape process, and pattern costs are low. Dimensional tolerance capabiUties vary widely and are the least accurate when compared with other methods of casting. 

Aluminum bron2e alloys have been successfully cast ia the centrifugal, continuous, permanent, plaster, and sand molding methods. Depending on the alloy, the minimum tensile strengths of sand-cast test bars are 448—620 MPa (65,000—90,000 psi). 

S = sand-cast P = permanent-mold-cast other = temper designations. 

Fig. 14.4. Sand casting. When the casting has solidified it is removed by destroying the sand mould. The casting is then "fettled" by cutting off the ingate and the feeder head.

SAND CASTING PROCESS CAPABILITY MAP FOR ALUMINIUM AND MAGNESIUM ALLOYS... 

SAND CASTING PROCESS CAPABILITY I MAP FOR COPPER ALLOYS ... 

As sand castings. The new heat treatment designations and their former equivalents I M... 

Ni-hard type 2 r 2.7 Si 0 6 Sand-cast — 55 5.50 Strength, wiih heat- and... 

Mg 10.0 /VI bal. Sand-cast hcal-tieated-T4 26 48 16 75 Strength with shock... 

S" Monel Ni 60.0 Cii 29.0 Sand-casting 80-115 110-14.> 2 270-350 High-strength ca.siing alloy ... 

Clark, AZ91E Magnesium Sand, Casting Alloy. The Standard for Excellent Corrosion Performance, Proc. IMA World Magnesium Conference, Los Angeles, June (1983)... 

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