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quinn
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+x+xAnother question before I start the post cure. My mold came out great and the gloss is as good as what I got on the duratec which is pretty good, but out of curiosity I tried hand polishing a small area up in the top and it was immediately obvious that this high temp surface coat will go to a brighter gloss than the duratec did. Is there any downside to polishing my mold now? Or should I just leave it alone? It's possible there's voids under the surface but I'm sure I wouldn't expose them just by polishing. If I do go ahead and polish the mold, should I do it before or after the post cure? I imagine it will polish easier now since the hardness will go up during cure, but will i lose some gloss during the cure? Should I polish afterwards? No problem polishing. I would do it after the post cure. Hardness difference is minimal, might even be lower on some resins (some resins get tougher but the hardness drops a tiny bit). I usually do the final finishing only in the mold. You can kinda rush through the grits on the plug, as remaining scratches are going to be a ridge in the negave mould and much easier to get rid of. Ah, good point. Didn't consider the mold has protruding scratches. I'll probably be good enough with just a polish though. I did put a lot of time in the plug. Do you use anything special for polishing the surface coat? I have aquabuff 1000 and 2000. Just use that?
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Lester Populaire
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+x+x+xAnother question before I start the post cure. My mold came out great and the gloss is as good as what I got on the duratec which is pretty good, but out of curiosity I tried hand polishing a small area up in the top and it was immediately obvious that this high temp surface coat will go to a brighter gloss than the duratec did. Is there any downside to polishing my mold now? Or should I just leave it alone? It's possible there's voids under the surface but I'm sure I wouldn't expose them just by polishing. If I do go ahead and polish the mold, should I do it before or after the post cure? I imagine it will polish easier now since the hardness will go up during cure, but will i lose some gloss during the cure? Should I polish afterwards? No problem polishing. I would do it after the post cure. Hardness difference is minimal, might even be lower on some resins (some resins get tougher but the hardness drops a tiny bit). I usually do the final finishing only in the mold. You can kinda rush through the grits on the plug, as remaining scratches are going to be a ridge in the negave mould and much easier to get rid of. Ah, good point. Didn't consider the mold has protruding scratches. I'll probably be good enough with just a polish though. I did put a lot of time in the plug. Do you use anything special for polishing the surface coat? I have aquabuff 1000 and 2000. Just use that? My composites supply has a polish for plastics that works well. But it's branded by them no idea what it is.
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quinn
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Finished the post cure. Looked good afterwards other than some slight dimple looking shapes in the light. Looks like the surface coat softened and moved around a bit. Went super slow on the cure, less than 0.1 degree per minute. Started sanding with some 1000 grit, the texture went away pretty quickly so no big deal there. Then I hit it with some polish and a bunch of little microscopic voids were highlighted by the white polish. Not sure what to do now, pretty bummed. I have a feeling sanding deeper isnt going to get rid of them. Not sure where I went wrong. Even if I started over, not sure what I would do differently. This isn't one or 2 significant voids, this is probably a few hundred little tiny ones. Big enough that I can catch the tip of a razor on.
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Lester Populaire
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Maybe try a mould sealer?
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KLComposites
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I make wet-laid molds out of fiberglass, compensating for the reduced stiffness with extra thickness. The glass, being translucent when saturated, allows me to see any voids between the surface coat and the first several layers of reinforcement that need to be rolled out. Any air, no matter how small the bubble, will expand as its heated in the post-cure cycle and pop through the surface coat, leading to what you've described - burst pinholes and/or blisters.
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quinn
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+xMaybe try a mould sealer? I think I'm just gonna have to try again. Aside from the little voids, the slightly wavy dimpled surface isn't great either. It does sand out, but it's not gonna be the perfectly flat surface like I started with on my plug. The little voids were only in a couple patches and obviously from trapped air. It was in areas where I first started trying to brush the coat on thin and it wasn't liking it, brush was dragging. might order the slower hardenener, maybe degass after mixing, and then not try putting a thin coat on. So anyway, I think I have some ideas on how to avoid the trapped air, but not sure what to do about the slightly wavy dimpled surface. I'm guessing this is from post curing off the tool so the surface coat got soft enough to start moving. Any suggestions on how to improve on this? Like I mentioned, I went no faster than 0.1 degree per minute, at times slower, and about a half hour soak every 10 degrees or so. Do I need to go even slower? Longer soaks? Maybe go up and back down a few times, starting at lower temps? Like maybe cure to 90c, back down to 20, then all the way up to 120? Or is it just gonna be really hard to avoid this surface distortion no matter what when curing off the plug? I'll also contact the manufacturer of the coat, see if they have recommendations. Open to suggestions though. Just looked at the specs again for this surface coat. They recommend a post cure of 2 degrees per minute, which is like 20 times faster than what was recommended here, but I don't know if they are assumining you are curing on a tool. Maybe I went too slow?
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quinn
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Group: Forum Members
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+xI make wet-laid molds out of fiberglass, compensating for the reduced stiffness with extra thickness. The glass, being translucent when saturated, allows me to see any voids between the surface coat and the first several layers of reinforcement that need to be rolled out. Any air, no matter how small the bubble, will expand as its heated in the post-cure cycle and pop through the surface coat, leading to what you've described - burst pinholes and/or blisters. Ah, that makes sense. The waviness/dimples I saw did appear to be positive bumps when sanding. Would make sense that expanding air would push these out. I remember thinking when I was doing wet lay that I can't tell if there's air in the laminate, definitely easier to see with fg. I always thought the issue with a fg mold for cf parts was the difference in expansion rate? Is this not a concern? Anyway, I think that makes sense as a reason for the dimple shapes, but not so sure about the couple patches of little micro air pockets. I kind of doubt the surface coat got soft enough for little bubbles to actually flow through it from the laminate. I'm thinking those micro voids were more likely in the surface coat to begin with.
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quinn
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On another note, do you guys think it's possible to save the first mold? Figured i might as well try if I'm making another anyway. With more sanding, I think I can flatten the surface well enough, but what about the tiny voids? Was thinking maybe plop some surface coat on the patches of tiny voids and squeegee it in with a piece of plastic. My concern is the little bits of cured surface coat stayimg in the voids. Unfortunately I didn't see the voids until I hit it with polish, so getting it cleaned back out might be hard. Maybe acetone and high pressure air to try and blow it out. I guess even if the bond in those voids isn't great, it will still be better than the bond between the filled areas and prepreg part, so I doubt they would pull out. Also the way the part comes out of the mold, it kind of slides out so those filler pieces should stay. Any chance that could hold up?
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KLComposites
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You can sand the bumps from the expanded voids flat, but they'll just bow out again during the cure cycle. Been there, done that. The only way to solve that is to hog the blistered areas out and re-fill with resin. I think you're better off abandoning it and doing another mold. Sorry : (
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quinn
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Group: Forum Members
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+xYou can sand the bumps from the expanded voids flat, but they'll just bow out again during the cure cycle. Been there, done that. The only way to solve that is to hog the blistered areas out and re-fill with resin. I think you're better off abandoning it and doing another mold. Sorry : ( Figured that might be the case. Not a huge deal, I have enough surface coat and epoxy leftover. Just hope it goes better next time. I'll use fg so air is easier to see in the laminate. Here's another thing I noticed when laying up, the 3212 epoxy turns into a thin jelly like substance within a couple minutes of mixing even though it has 1 hour pot life. Is this normal? I've never had epoxy do that until it's about to kick off. This does it right away and stays in that state for about an hour. I guess you could call it more of a raw egg white texture. I feel like it would wet out better and be less likely to have air in the laminate if it didn't turn to jelly like that. Just seems odd
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