Epoxy Mold Making - Flanges vs. Clay Layup - Pics of my molds inside!

General Composites Discussions Composites Talk
#1

Ok, so hopefully some experts can jump in here and give advise.

I have been having trouble getting a perfect vacuum on my molds. I have made 4 molds so far and I can only pull a perfect vacuum on 1 of them. I was starting to think that maybe I am building the molds incorrectly and they are not “tight”.

I have attached some pictures of my molds. The process I use is to lay the part up with clay so the part extends down to a flat surface, and then I brush on an epoxy gel coat. After that I lay fiberglass on the back side for strength. I do this in a pre made box as shown in the picturess.

Since none of the pieces I am making molds from will lay flat I have to build them up with clay, you can see in the pictures that the clay leaves rough edge. It is nice because you can see the part outline.

In the pictures the mold that I get a perfect vacuum on each time is the smooth one.




So here are my questions:

  1. Is how I am making the molds correct? How can I ensure they are tight?

  2. Since these parts need so much clay should I just use a thin wood to make flanges?

  3. Any additional advise?

#2

Where are you placing your tape when you vac down on your mould? are you applying the tape on the gel coat or on the wooden box. If its on the box then you most likely will struggle to vac down due to leakage at the interface between the gel coat and the box. If you are tapeing onto the flat gel coated area then i see no reason why the mould should leak.

If your mould does leak however you can apply flow coat onto the backside of the mould and this will help reduce any leakage that you do have because it seals the back side of the mould

#3

Thanks, I am taping on the surface coat. Thanks for the advise, I’ll look into that stuff!

#4

are there any techniques used to find if the epoxy is the leak? could you for instance spray the mould with a mist of soapy water, bag it and vac it down to find if this is the case? or do you just coat it with a product like matvd said and forget about it?

#5

Are you waxing the area where your bagging adhesive sits? I usually clean any wax from the area where the bag adhesive sit’s. Other than that I would be suspicious of your entire setup(hoses, connections and etc.)
The mold itself being an issue seems odd. It’s easy to get carried away on one little tangent thought and loose site of the rest of the potentials.

I’ve built some quick molds in a jiffy that I wouldn’t show in public (…lol) and never had one “leak” under infusion. I’m refering to flange surfaces that are nothing short of crap and they do just fine as long as they are cleaned of wax or pva where the “tape” sit’s.

#6

I do wax the entire mold and have thought about that. Ill try cleaning off where to tape site in the mold flange.