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Old 03-09-2017, 12:32 PM   #1
peter95

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Default Gel coat repair for high-temp CFRP tool

Hello everyone,

This is my first time posting here, so please forgive me if this is not the normal route for asking for help, this is a duplicate post, or if I am missing information. I have a bit of a predicament though...

I recently laminated two tools for making a prepreg part. The tool is CFRP using a high temperature epoxy resin and graphite filled gel coat. The tools have aluminum guides for placing hardpoints in the final part. I covered the surface of the plug with gel coat, let it out-gas and tack, then began the CFRP wet layup on the surface of the gel coat.

The problem areas in the final part are where the bag did not conform well to the plug surface. As a consequence, the gel coat seems to have pulled up off of the plug leaving a concave recess, especially where there were many guides grouped in one area or at the edges of the core material (see images "1" through "3"). I suspect the pull from the vacuum contributed to this.

The final part is for a structural application, so it is important that the surface is relatively flat and without waves.

My initial thoughts were to use the gel coat that I had originally used on the part to patch these areas, then sand down to the surface. However, I have some concerns about proper adhesion between the new and old gel coat since the preliminary cure has already been completed on the initially applied gel coat. I am preparing a test part on an old tool to see if this is a viable option.

Additionally, some regions of the gel coat do not appear to be cured. They are still tacky, even though the cure cycle was completed. I had a few inexperienced hands helping me with the process, so it is possible that the gel coat was not fully mixed or done so in the right proportions (see image "4"). I may try to locally heat them in case our oven was just that uneven in its heat distribution, but if that doesn't work, I am kind of at a loss.

I'm kicking myself because these seem to be some real rookie mistakes. I believe that taking a bit more care to the above during the layup would resolve these issues, however, due to time constraints and cost, I would like to explore other options if at all possible.

Does anybody have any recommendations?

Thank you in advance,
Pete
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Old 03-09-2017, 08:44 PM   #2
hojo

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Hi, I cant tell the scale of the damage to the moulds. However you should still be able to get a good bond if you rough up the surface with 80 grit and clean well. This is a pretty common repair process for damaged gel coat.

If the damage is on a large scale, you might find it easier to start fresh. Thats a judgement call.

When you mix resins, and especially gel coat, you should always double cup. This means you mix well in one cup, then transfer to a second cup and mix longer. If you dont do this, you will have unmixed gel coat on the side walls of the cup. And as you get low on gel coat you will start scrapping the walls, transferring unmixed gel coat to the pattern. This is a very common mistake. Lessons learned though. Good luck on your project
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Old 03-10-2017, 10:04 AM   #3
Kma4444

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The gel might not have cured because it wasn't in contact with the plug. You could try covering the area with PVA to seal it and if that was the reason it will cure quickly.

I have used, and am today using, http://www.spartite.com/p-42-esg-215...ng-series.aspx It is an excellent high temp repair compound for mold repair. It sand nicely, fairs out well and polishes quickly. Not sure how much area you are dealing with but your gel might work just fine. But you will have to seal it with PVA or similar to get it to completely cure.
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Old 03-10-2017, 05:57 PM   #4
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Quote:
Originally Posted by Kma4444 View Post
The gel might not have cured because it wasn't in contact with the plug. You could try covering the area with PVA to seal it and if that was the reason it will cure quickly.

I have used, and am today using, http://www.spartite.com/p-42-esg-215...ng-series.aspx It is an excellent high temp repair compound for mold repair. It sand nicely, fairs out well and polishes quickly. Not sure how much area you are dealing with but your gel might work just fine. But you will have to seal it with PVA or similar to get it to completely cure.
If I understand him correctly, he is using a epoxy surface coat, not PE/VE
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Old 03-11-2017, 04:38 AM   #5
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You are right, nevermind....... I'd have to go with the epoxy not being well mixed to have spots of uncured material. I'd also have to consider making another mold if it was me.
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