Talk Composites - The Forum for Advanced Composites

Epoxy Mould problems

http://www.talkcomposites.com/Topic4010.aspx

By fgayford - 12/30/2012 2:19:08 PM

Hi Guys
I have run into some problems in making my first epoxy molds.
I prepared my mock up as usual and brushed on an epoxy surface coat (not Easy composites product) and let it get to the almost tack free state and then applied a second coat then let that go to the almost tack free state and then proceeded to build up the thickness. All looked good when I split the mold.
I then proceeded to apply my release system (also not Easy Composites product, but similar).
I infused an carbon part with 2 layers of twill 6k and had a perfectly sealed bag. When I demoulded the part next day I found that the fibers had pushed imprints into the surface coat as if into wax. I could wet sand them out with 1200 paper but could not buff the finish up to a high finish.
So what happened?
My first thought is that the surface coats were still soft.
If so how long do you need to wait for the epoxy to cure fully?
Your thoughts.
Fred
 
   
By fgayford - 12/31/2012 1:55:32 AM

Kevin-Lee (30/12/2012)
Hi Fred,

Could you tell us what your mould was made from, ie. surface coat and chopped strand or surface layer and woven cloth?

How long did you let the mould cure?

Was the surface layer a filled on unfilled resin system?

Kev.


Mould is made of two layers of surface coat designed for this purpose 3 layers of 10 oz . Followed by 1/2 inch thick layer of Freemans mould builder putty and 3 more layers of 10 oz. Cured at 80 f for a day or so.
I suspect soft surface coat and will contact the company that sold it to me tomorrow.(note it is not Easy Composites stuff)
I am going to design an instrument to check surface hardness. A simple arm arrangement with a pressure point shaped like the eraser of a pencil. I will measure the pressure it exerts on a scale when adding a known weight. I will then place samples under it for a duration of say 12 hours and see if the surface is imprinted. I will then compare it to known hard moulds. With some experimenting I will get a reference to know when a surface coat has reached hardness.
So does anyone have experience with epoxy moulds that can tell me how long it usually takes for epoxy surface coat to reach full hardness? 
Thanks
Fred