We posted a blog in May about the common frequently asked questions about vacuum impregnation. With the complexity of the subject, these questions and answers do not fully address all porosity and vacuum impregnation questions. The following are additional answers to commonly asked questions about porosity and vacuum impregnation.
How much does impregnation cost?
This question should read "How much can you save?". It is important to remember that impregnation costs are a small fraction of remelting, recasting, remachining and overruns. Vacuum impregnation seals the inherent problem of porosity, thus allowing parts once deemed as scrap to be useable. The cost of impregnation depends upon several factors including (but not limited to) the size and complexity of the casting, the amount of castings to be impregnated, and the type of material used to impregnate.
What size porosity can be sealed?
Micro-porosity causing "weepers" is usually easy to seal. For larger micro-porosity and macro-porosity sealing depends on wall thickness and the type of porosity present. Straight through porosity in thin walls is difficult to seal. Sponge like porosity of any type can usually be sealed. 100% solid resin will seal porosity many times larger than other impregnants.
Will impregnated sealant vibrate loose or fall out?
No. When sealing porosity within the wall thickness of a casting, the sealant is locked in and will remain so for the life of the casting.
What temperatures will the impregnant withstand?
For most sealants, 400°F is the highest temperature generally recommended for continuous usage, but will withstand 500°F
temperatures for short intermittent periods. Higher surface temperatures, up to 1400°F, can be withstood without resin failure
when parts are water-jacked or forced air-cooled. This is because sealant remains strong and solid in the porous areas of the cool side. The sealant may char next to the hot side, it never melts and is protected by the thermal conductivity of the metal.
Examples of this are automotive cylinder heads and blocks.
How long will the impregnant last?
As long as the casting itself.
What else will impregnation do?
In addition to sealing for pressure tightness, impregnation is used to seal sintered components and other parts to avoid corrosion. It is also used prior to electro-plating to prevent bleedout from acid etches and electrolytes absorbed into porous areas which are sealed in by subsequent plating. Where bleedout and blistering due to porosity is a problem on other types of finishes,
such as lacquers and baked enamels, impregnation before finishing eliminates out-gassing and blistering.
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