Sand Casting - PART TWO with Philip White and Jenny Dunseath
Part two of the Sand Casting Process with Philip White and Jenny Dunseath in the foundry at Camberwell college of Art London. Video by Chris Follows part of the Process Arts Project.
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NOTE: Because the sand is used in a damp condition there is minimal sand dust,and this occurs at the mould face immediately arround the hot metal casting ,clearly visible when the casting is knocked out. At this stage a small watering can or spray will help to stableize this dry material.A standard dust mask could be worn.It is always worth taking sensible precautions with all processes.With sand casting on the scale immagined here keep a water spray handy and use it when cleanig away any dry material.
Text Information supplied by Jenny Dunseath:
The Pattern is a full size model of the part that makes an impression in the sand mold, with dimensional allocation for shrinkage and finishing.
If the casting is hollow, additional patterns called cores are used to create these cavities in the finished product.
Patterns are usually made of wood, plastic, metal, or plaster; however, other materials or combinations of materials are used if there are additional specific properties required of the pattern.
Every Pattern must have a draft angle of approximately 2° - 3° to all walls parallel to the parting direction to facilitate removing the part from the mold.
Paint the surface of the Pattern with Varnish or Shellac to make it water tight and to ensure that the sand does not stick.
For a Flat back pattern- put screw holes in the back to aid its removal from the sand.
Molding is the multi-step process in which molds are created.
In horizontal casting, the mold is contained in a two piece frame, called a Flask. The upper portion of the flask is called a Cope and the lower portion is a Drag.
First, molding sand is packed into a Flask around the pattern. After the pattern is removed, Gating and Runner arrangements are positioned in the drag half of the mold cavity and the Sprue is placed in the cope portion.
Gating systems are necessary for the molten metal to flow into the mold cavity.
Cores are also placed in the drag portion of the mold if they are needed. To finish the mold, the Cope (top) section is placed on the Drag (bottom) section, and the mold is closed and clamped together.
Two main routes are used for bonding the sand moulds:
The "green sand" consists of mixtures of sand, clay (Bentonite) and moisture. If the sand can be squeezed together and hold its shape, it is suitable for use.
The "dry sand" consists of sand and synthetic binders cured thermally or chemically.
The sand cores used for forming the inside shape of hollow parts of the casting are made using dry sand components.
Between uses, the sand is rejuvenated by adding water and mulling (mixing and smashing). If you do not let the sand dry out all the way, you do not have to mull, just add water. Sand grit is determined just like sandpaper. 150 is very fine and 50 grit is coarse. Fine sand will give good detail, coarse sand will give a pebbly or rough texture.
Aluminum alloys1220 °F (660 °C)
Brass alloys1980 °F (1082 °C)
Cast iron1990-2300 °F (1088-1260 °C)
Cast steel2500 °F (1371 °C)
The Complete Handbook of Sand Casting - by CW Ammen
Metal Casting: A Sand Casting Manual for the ... - by Steve Chastain