LOW PRESSURE A CASE FOR
SAND CASTING OF ALUMINUM
Less common than gravity sand casting and low pressure permanent mold casting, low pressure sand molding holds a distinct combination of advantages for large aluminum castings.
FRANCO CHIESA, CENTRE DE MÉTALLURGIE DU QUÉBEC, TROIS-RIVIÈRES, QUÉBEC, CANADA, AND JOCELYN BARIL, TECHNOLOGY MAGNESIUM & ALUMINIUM, TROIS-RIVIÈRES, QUÉBEC, CANADA
A
a common process producing high qual- ity castings due to tranquil fi lling of the mold and the applica- tion of pressure to fi ll the mold effi ciently and cleanly. T e two main
characteristics of the LPPM process are: 1. The filling
from the bottom of the mold is perfectly controlled compared to the turbulent flow associated with grav- ity casting. Also, the
majority of aluminum castings are produced via sand or permanent mold casting, but for large precision components, another viable option is low pressure sand casting, which uses principles from both low pressure permanent mold (LPPM) and gravity pour sand casting. Low pressure sand casting marries the use of
bottom pouring for tranquil fi lling of the mold (which avoids metal oxidation) with the fl exibility
to make larger parts. T e capable process can be ideal when producing large “top quality” aluminum castings. T e process also can be considered when walls are too thin (such as 0.1 in. [2.5 mm]) to be obtained by gravity casting. LPPM casting is
liquid metal is drawn from under the melt surface, preventing dross entrainment into the mold cavity. 2. Effi cient feeding from the
bottom injection pipe occurs through pressure applied to the melt during solidifi cation, elimi- nating the need for risers. T e resulting yield is high: typically 80-90% versus 50-60% for gravity permanent mold casting. How- ever, not all casting geometries are
Fig. 1. The principle of the low pressure process is illustrated. 36 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2016
Fig. 2. Shown is a low pressure poured sand mold.
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