Microseal for porous Al castings
Microseal for porous Al castings
(OP)
Has anyone here tried Microseal sealant for porosities in cast aluminum? I'm ordering some for a test drive, just curious if any of you have used it, what sort of results you obtained, and if so what tips you might offer in the application of it. The porosities I'm trying to seal are sponge-like formations with pores about .005" to .015" that are allowing slow lubricating oil leakage in bearing housings for rotory lobe dewatering pumps. The link to the Microseal website is below.
Thanks -John
http://www.microleak.com
Thanks -John
http://www.microleak.com





RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
Our use was both for pressure containment and prevent adsorption of oil onto a surface.
The base material Bakelite is a very chemical resistant material that can take a little temperature.
RE: Microseal for porous Al castings
The vacuum impregnation resin monomers are rinsed from the surface before heat curing, so it is possible to anodize or chemfilm the impregnated aluminum castings. Info on one resin:
http://www.nealuminum.com/loctite.htm
RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
On a regular basis if you are looking into salvaging some of the leaked castings, vacuum impregnation techniques are successful at low temperatures.
Hipping is a good tool,provided costs permit such an operation.
RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
I have raised the same issue. Especially for a bearing housing a simple static component if it has sponginess the foundry should accept responsibility and replace a defect free one.
I have visited a few aluminium die casting units and no where was vacuum impregnation offered as a solution.
Early in my career I had made steel valve body castings and I was new to the trade. The castings leaked in hydro test. Someone advised me to use this technique of vacuum impregnation. I was elated. They cleared the test bench but in the field they failed. The fluid temperature was high and all the resin impregnated melted.
RE: Microseal for porous Al castings
RE: Microseal for porous Al castings
The material is 356 alloy as cast, the process is green sand with a wooden pattern.
RE: Microseal for porous Al castings
It is perhaps the moisture in the sand or the volatile matter that are creating the problem
RE: Microseal for porous Al castings
I'm new to the forum and appreciate all of the experience and knowledge.
It is difficult some times achieving defect free Al casting when using sand, perm. mold, or HPDC, however it is doable. A356 lends itself well to not only these processes but also squeeze and my favorite, semi solid casting. I agree with BillPSU, swall, and arunmrao that a well controlled process should achieve the desired absence of defects. Removal of hydrogen and oxides from the melt is key at the beginning, then making sure there are no other factors such as excessive die lubes or in the is case volatile binders in the sand etc. I believe the best way to plug holes is not to have any to start with.
Mike
RE: Microseal for porous Al castings
356 castings in green sand can be cast to have shrinkage defect free castings(sponginess ) as mentioned by arunmrao.
In moulding have sufficeint vents and ensure a sand to metal ratio of at least 4:1.
In Melting use min 1.5 to 2% Sodium modification.
You can see detailed notes on my thread "356 sand castings."
Have a very clean melt.
Also use ceramic foam filters 20 ppi to ensure clean metal into the castings.
Preferred gating ratio when using filters just after downsprue to runner is 1:1.1:1.2.
Gate your thick sections through open ,hot risers and use antipiping compound for topping the riser .
THese are preventive actions.
Microseal is a corrective action and any porosity which is more than 0.4mm cannot be sealed by any selant.
Also porosities which are continuous and open up to a surface on machining will not be served by any sealing action before machining.
Hope these provide you with good inputs for a lasting solution.