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Dry Micro layering

Freemasm

Well Known Member
Trying to aerodynamically fair my inlet. The lip is sharp on the backside. Any issues with layering dry micro? The shape is rough filled but will take some more iterations to get a good pressure recovery type flow path.

Let me know your experiences, please. Much thx.
 
Trying to aerodynamically fair my inlet. The lip is sharp on the backside. Any issues with layering dry micro? The shape is rough filled but will take some more iterations to get a good pressure recovery type flow path.

Let me know your experiences, please. Much thx.

No experience with that exact area but I did layup inlets for my plenum. No scientific flow design but they are low pressure stock inlets so hopefully it will be ok.

I'm sure you'll get answers from far more experienced but I would make a mold and layup fiberglass. Micro isn't very strong. Time spent on a mold pays dividends. Foam is easy to shape. If it's disposable, apply some packing tape over it before the layup then just carve it out.
 
Layering up any composite requires the first layer to be well roughed up with 60 grit (or more coarse) for good adhesion. But, do you really want to take a large lump of filler (any filler) flying? Perhaps remodel with polyester filler (easier to sand), cover with glass and grind out the filler. Whatever you do I would apply glass over the filler to keep it all together in the long term.
 
The area in need of "smoothing" is upstream of the filter. It will get glassed over. It will be impractical, almost impossible to grind out any foam once glassed over. I am also leery (probably needlessly) of having cavity vent holes in an area that could see bulk water
 
Trying to aerodynamically fair my inlet. The lip is sharp on the backside. Any issues with layering dry micro?

None except the possibility of exotherm. If using a very slow hardener to counteract exotherm, micro can even be cast.

Micro is weak in contrast with flox or fiber, but it's not a problem for fill...and it is stronger than many imagine. Next time you have excess dry micro, cure a few random blobs, then hit 'em with a hammer.

As a general rule, do not apply micro in layers. Much better to apply the full thickness, plus some, all in one mix. The reason is sanding density; it is challenging to get the exact same ratio of bubbles to epoxy each time you mix, and layers tend to be a little wet at the surface, i.e. cure with a hard skin. A layered surface can be difficult to sand optically flat because hardness can be variable.

Photos...casting inlet rings. Wet out a layer of fabric in the mold, pour wet micro, slow cure.
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Attachments

  • Intake Ring Layup.jpg
    Intake Ring Layup.jpg
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  • Inlet Ring Core.jpg
    Inlet Ring Core.jpg
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