Porosity Sealing

Porosity sealing can be defined as the process of filling a porous substrate to make it air tight. Porosity is also referred with various names such as vacuum impregnating, metal impregnating, polymer metal sealing and porous metal sealing. Porosity sealing consist of four step process such as air within the pores is expanded under reduced pressure, pressure reversal adding pressure outside the part which saturates pores with monomer, excess monomer is rinsed from the exterior surfaces of the part and the liquid monomer within the porosity is polymerized into a solid to seal the passage.

Common applications of porosity sealing

Some of the common applications include die castings and permanent mold castings which comprise internal porosity. The porosity is usually confined to the deepest cross sections of the part and does not extend to the outer skin. Nevertheless, if the part is also machined, the internal porosity will be exposed and the part will leak if pressurized. Machined die castings that require clutching fluids like intake manifolds, coolant connectors, transmission cases, pump housings and fluid power components that are regularly sealed for life using acrylic resins. Due to the sealant that is internal to the part, the exterior dimensions and appearance of the part remain stable.

Powder metallurgy components

Powder metallurgy elements are sealed before plating and to decrease internal corrosion. Plating functions distinctively include submerging the parts in acid solutions. Once is plating is performed, residual acid internal to the part can uphold corrosion or preclude an acceptable plating finish. The solution to this problem is said to seal the internal voids before plating. Then the porosity is saturated with monomer and is then rinsed fully clear of the surface. The resin treats to a durable polymer and consequently the exposed surface metal is free to be plated while the interior spaces are sealed dry.

Enhancement of machines’ capacity

The porosity in powder metal parts turns into a liability when the part must defy a distinctive pressure. Powder metallurgy applications for compressed air, fuel dealing or hydraulic housings are usual and useful. Nevertheless, they have to be sealed primarily. The polymer does not add structural strength to the physical part, but it will hold high pressures without creeping.

Powder metal is also impregnated to improve the capacity of the machines. Powder metallurgy parts are usually complex to machine and certain compositions may not be turned without ruining the cutting cool. Porosity sealing enhances the life of cutting tools by ten to one-hundred times. And resin impregnation is very useful than compacting additives and can be selectively applied for near net pressed parts.

Questions:

• What is porosity sealing?
• What are the uses of porosity sealing?