Wet-Layup Over Parts

[GregJames]

Hi, I've worked with composites for quite a while, but I've never actually done any wet-layup. I've always made parts (in the motorsports industry) via pre-preg carbon.
So, if someone could please give me a rundown on how to do wet-layup correctly when applying the carbon over an item.

Example: We have a plastic gauge pod, and would like the exterior to be made of carbon fiber for an aesthetic purpose only.

Here are a few questions I'd like to figure out:
1. Which type of resin should I use?
2. Does it need to to be vaccuum bagged, and if so, do I need to use breather material and release film?
3. Will the heat of the resin curring cause plastic to melt? (.040 thick)
4. After the item is curred, how would I go about smoothing out the surface so that it can be clear coated? (wet sand?)
5. What would the cure time be for the type of resin being used?
6. Would 2X2 fabric be the easiest material to use or could I use 4X4?

 

[berkshire]

GregJames (Mechanical)
I take it that you want to lay carbon fiber over an existing gauge pod, using the pod as a male mold.
If you use a room temperature curing epoxy resin, slow cure, you should not have a problem with an exothermic reaction melting your plastic part.
For drape ability over a strongly curved part use a 2 pick basket weave, I think this is what you are referring to as a 4x4 or a twill weave .You should be able to do this without vacuum bagging
Keep the resin to the minimum you can use and do not be tempted to add more if the carbon does not look wet enough.
When using liquid resin ( Epoxy, Vinyl ester, or Polyester.), the carbon tends to float on the resin. It is also difficult to see if it is properly wetted out. If you need to make a smooth surface to clear coat you can paint a layer of clear resin over the molded surface when the resin is almost dry, (hard but just leaves a thumb print in the surface). Some people add a little acetone to this resin for better self leveling.
Depending on the resin and hardener system, room temperature resins can cure hard to the touch in one to two hours to six hours, you get to choose what you want there.
If you are doing this on a production basis you may want to invest in a female mold. lay in the carbon fiber and press in the plastic part as a retainer into the wet resin.
Your only problem then may be porosity in the molded part.
This may require a resin coating in the mold first.
Good luck with your endeavor and feel free to ask more questions.
B.E.

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