Why should you eliminate porosity?
1. To prevent leakage of fluids and gases
2. To reduce scrap and increase profits
3. To prevent plating defects
4. To increase machinability
Proper processed castings are clean and have no change in appearance or dimensions. Castings can be impregnated in the rough, or fully machined. The physical seal on an impregnated casting is permanent. The seal will withstand pressure equal to the bursting point of the component. The sealants are impervious to all but the most aggressive acids and caustics. In almost all cases, the parent metal will deteriorate long before the impregnant is affected. Porosity can be caused by numerous factors in the design, tooling or pouring of castings and forming of P/M parts. Cold shuts, enclosed gas bubbles and poor metal flow will all cause porosity in metal.
What are the advantages of impregnation?
Porosity in powdered metal causes chatter, resulting in reduced tool life. When porosity is filled through impregnation, chatter is eliminated and tool life is extended.
The porosity in powdered metal will absorb oils, deburring fluids, preplating cleaners, and acids that can later cause spotting on the plated surface. Impregnation fills voids and eliminates spotting.
Interconnected porosity can cause leakage of gases, fuels, hydraulic oils, etc., through the wall section of the part. Impregnation fills this porosity, eliminating leakage.