What is vacuum impregnation?

Vacuum impregnation seals porosity and leak paths that form during the casting or molding process. The process is the preferred method to seal porosity in order to prevent fluids or gases from leaking under pressure.

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What are the types of porosity?

There are three types of porosity:

•  Blind Porosity: From one surface only and therefore not forming a continuous passage for liquid

•  Through Porosity: Stretching from one inner face to another thereby causing a leakage path

•  Fully Enclosed Porosity: This cannot be reached by impregnation.

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How long will a sealed part last?

As long as the casting itself.

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What size porosity can be sealed?

Vacuum impregnation can seal porosity of any size. While vacuum impregnation can seal porosity of any size, it is important to realize that the leak path is the key characteristic to evaluate and not pore size. Instead of asking “What size of porosity can vacuum impregnation seal?” one should ask “Can vacuum impregnation seal the leak path?

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What materials can be impregnated?

All ferrous and non-ferrous metals, whether sand cast, gravity die, pressure die castings or forgings can be impregnated to eliminate porosity. Iron, graphite, bronze, aluminum, zinc, magnesium, steel, sintered metals and plastics, as well as alloys of these metals can be impregnated.

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What is the vacuum impregnation process?

In a nutshell, the impregnation sealant is introduced into the voids within the wall thickness of the casting through vacuum and/or pressure methods. Subsequent processing solidifies the sealant. 

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What temperature will the sealant withstand?

For most sealants, 400°F is the highest temperature generally recommended for continuous usage.

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Can vacuum impregnation seal surface flaws?

No. This is because impregnation is within the part and not a surface treatment.  

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Can cracks be fixed with vacuum impregnation?

No. Impregnation will not increase the strength of a casting. The cracks will reopen when the casting is under pressure.

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Should vacuum impregnation be done before or after finishing?

Vacuum impregnation should be done before any surface finishes. This will seal the porosity and eliminate any failure mode that could develop from outgassing, chemical compatibility or bleed out of pretreatments. 

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Should vacuum impregnation be done before or after machining?

Impregnation occurs after a casting is machined.  This is because machining may potentially uncover additional porosity.

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