This porosity can range in size, from sub-micron to voids greater than 10 mm, depending on the casting.
Casting defects caused by porosity can affect the part’s structural integrity, creating a failure point.
[2] Vacuum impregnation is governed by Military Standard MIL-I-17563C and MIL-STD-276A as well as numerous proprietary and customer specifications.
In the course of sealing castings against porosity, the parts would be processed through the following four stations: Vacuum impregnation should be done prior to final assembly.
Porosity is only considered a defect if it is interconnected and creates a leak path can affect the part's structural integrity and performance.
This is the main reason why vacuum impregnation is used on any material-die cast, powder metal, plastic, wire harnesses.
Vacuum impregnation stabilizes and supports the individual powdered metal granules during machining.
Sealing the leak paths before secondary finishes will eliminate any failure mode that could develop from outgassing, chemical compatibility, or bleed out of pretreatments.
As the vacuum impregnation sealant cures within the perforations, it creates a bond between the part layers.
When the parts experience heat during manufacturing or normal use, the plastic and metal expand at different rates.
PM applications for compressed air, fuel handling or hydraulic housings are common and effective; however, they must be sealed first.
Thus, the exposed surface metal is free to be plated while the interior spaces are sealed dry.
Vacuum impregnation stabilizes and supports the individual powdered metal granules during machining.
Sealing the porosity before secondary finishes will eliminate any failure mode that could develop from bleed out of pretreatments.