A raw cast impeller is an impeller (the rotating component of a pump, compressor, or turbine) in its initial state immediately after being formed in a foundry mold. At this stage, it has the general shape of the final product but is rough, oversized, and completely non-functional.
Here is a breakdown of what characterizes a raw cast impeller and what happens next to make it usable:
Characteristics of a Raw Cast Impeller
Rough Surface Finish: The texture depends on the casting method. Sand-cast impellers will have a gritty texture, while investment-cast (lost wax) impellers are smoother but still unpolished.
Extra Material (Machining Allowance): It is purposely cast slightly larger than the final required dimensions. This extra metal will be machined away to achieve precise tolerances.
Risers, Gates, and Flash: It often still features the remnants of the channels where molten metal was poured into the mold (gates/sprues) and excess metal that leaked between mold halves (flash).
Internal Material Stress: The rapid cooling of molten metal creates internal structural stresses that must be relieved.
Common Casting Methods
Depending on the application, size, and material (such as stainless steel, bronze, or aluminum), impellers are usually cast using one of two methods:
| Method | Best For | Description |
| Investment Casting | Complex, high-efficiency impellers | Uses a wax pattern coated in ceramic. It provides excellent detail, tighter tolerances, and smoother internal vanes. |
| Sand Casting | Large, heavy-duty impellers | Uses sand molds. It is cost-effective for massive industrial pumps but leaves a rougher finish and requires more machining. |