Investment Moulding Material:

The expandable pattern materials utilized with the investment casting procedure are wax and foam polystyrene. The latter is a thermoplastic material that vaporizes at molten metal temperatures. Both materials are said to be expandable, or consumable, because the pattern is utilized up, or lost, while forming the mould cavity where the part is shaped. For these materials, the similar basic properties are necessary as with any pattern material. They are low good fluidity to reproduce detail, ash content, low contraction and expansion characteristics, reproducibility, stability, and compatibility with other procedure materials. In addition, pattern materials also must be easy to join and assemble, economical, nontoxic and easily available.

Of these two main pattern materials, waxes are the most broadly utilized. Numerous wax formulas, natural and synthetic both, have been developed to meet the needs of the investment casting industry. Therefore, inexpensive waxes along a variety of properties are available for utilization. One of the primary considerations in choosing wax is that it be removable through heat without leaving a residue in the mould cavity. Soot, ash or a waste left in the investment could contaminate the last casting. Complete burn-out of the wax must occur between 427 to 538º C (800 to 1000º F).

The ability of wax to achieved the intended shape throughout the pattern making and investing process is another significance material property requirement. A wax that is too soft is probable to distort under the weight of the investment material. Various waxes with varying degrees of strength might be utilized in the production of one casting. For instance, in the areas of intricate detail of the part, this might be necessary to use wax that is pliable and soft. Sometimes, a viscous wax is wanted for dipping, pouring, or brushing. In general, overall wax economy is important, because much of the wax is lost in the burn-out and typically not available for reuse.