• The refractory compound will provide a smoother surface on the pattern and to improve its high temperature resistance.
• Moulding sands usually include bonding agents.
• This process is also called as Lost-Foam process (or) Lost Pattern Process (or) Evaporative-Foam Process.
• The foam pattern includes risers, sprue, gating system, internal core.
• Parting lines and draft considerations are reduced.
In this process, a sand mold is held together by vacuum pressure and not by a chemical binder.
The term vacuum in this process refers to the making of the mould, rather than the casting operation. Casting operation is same as any other process.
Advantages :
(1) No binders are used and hence sand is readily recovered in vacuum molding.
(2) Mechanical ramming is not required.
(3) Since no water is mixed with the sand, moisture related defects are absent from the product.
Disadvantages :
(1) Relatively slow and not readily adaptable to mechanization.
