Architectural Metalwork

Sand Casting

Sand Casting is ideal for low volume items and one off's. We have the facilities to cast items up to 5m in length, 2m wide and 1.5m deep, with weights upto 200kg.

Sand Casting requires a pattern which is commonly made from wood. Patterns can be made by hand or routed using CNC technology for exacting dimensions. Items can also be cast from originals.

Sand cast items are generally fractionally smaller than their pattern due to shrinkage, a consideration which should be taken into account during the design phase. However, for many architectural applications this shrinkage is negligable and within tolerances. Bronze actually expands on cooling, it is only aluminium, lead and copper that shrink.

Air Set

We offer air set casting. The air set method uses dry sand bonded to materials other than clay, using a fast curing adhesive and is permanent and must be discarded after use. Air set casting offers a more reliable and accurate method but is a little more expensive. The surface finish of a casting produced using green sand is fairly rough, whilst the Air-set molds can produce castings with much smoother surfaces.

Cores

Cores can be used for more complex castings where internal cavities are rquired. These cores are premanufactured from sand and placed within the surrounding mould.

Sand Casting Standard Tolerances

Castings should be within linear tolerances of ±1.0 upto 150mm and ±0.20 upto 25mm thereafter.

The draft or amount of taper given to the pattern to facilitate withdrawing from the mould depends somewhat on the size and shape of the pattern. A general guide would be 1 to 2 degrees of taper per side.

Shrinkage allowances are approximate values only, since the exact allowance depends upon the size and shape of the casting and resistance of the mould. It is, therefore, possible that more than one shrinkage allowance will be required for different parts of the same pattern / casting. A general guide for aluminium alloy castings would be 1.3%.