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quinn
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+x+x+x+xAnother question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right? I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks. If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it. Ok, what would you recommend as a chemical release? Preferably something affordable in very small quantity. The canopy surface is about square 0.2 meter and I'll only do a couple so no need to spend a bunch of money on expensive release that will expire. I imagine maybe I want to season my mold with a few runs using pva? I could just do a few single layer lay ups with fiberglass cloth just to help deactivate the mold surface before doing a canopy with no pva if that would help. EasyComposites offers Easy-Lease at £6.80 for 100ml I didn't look at the shipping, but I assume it's similar to when I tried to buy s120 sealer. Like 60 bucks shipping for a 10 dollar item. Really sucks that I can't use the products from easy composites. Wish I could, but shipping chemicals from UK to US is just too expensive. Do you know of another product this would be similar to? Maybe similar to frekote? I looked into that a bit. Some guys swear by it, other prefer wax and pva
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quinn
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Group: Forum Members
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Pump showed up today. It pulls 26 inches. Will this be enough for a good infusion? Not sure what most pumps are capable of
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Hanaldo
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No, you really need a minimum of 29.95".
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Steve Broad
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quinn
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+xNo, you really need a minimum of 29.95". Ok, yeah definately a faulty pump. Advertised to hit 150micron, obviously not even close at 26 inches. Getting it replaced. Just out of curiosity, why is it so important to get like 99.9% vacuum? There's only 14.7 psi pushing on the lay up at full vacuum, so let's say you only hit 29 inches, that's 14.2 psi instead of 14.7. why is it so important to get that last tiny bit of vacuum?
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Hanaldo
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How are you measuring the vacuum level though, just an analogue gauge? Or do you have a digital gauge?
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quinn
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+xHow are you measuring the vacuum level though, just an analogue gauge? Or do you have a digital gauge? Analog gauge, but with it reading only 26 inches, there's obviously an issue right? Could analog gauge be that far off?
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Hanaldo
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Absolutely, analogue gauges are extremely inaccurate. That number will change with the weather as well. They are really only useful as a relative indicator of your vacuum dropping, so you can pull full vacuum and ignore the specific number the gauge tells you, but just see if it is moving at all - if the needle moves then you have a leak. They aren't any good for anything more than that. Fairly sure the analogue gauge I have also reads 26", or somewhere thereabouts.
If your pump is specified to 150 micron then it's almost certainly achieving it and the gauge is telling you lies. It's very unlikely its a faulty pump, and if it were then I'd be sure you would hear it in the pumps operation - the pump would sound like it is struggling.
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quinn
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Group: Forum Members
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+xAbsolutely, analogue gauges are extremely inaccurate. That number will change with the weather as well. They are really only useful as a relative indicator of your vacuum dropping, so you can pull full vacuum and ignore the specific number the gauge tells you, but just see if it is moving at all - if the needle moves then you have a leak. They aren't any good for anything more than that. Fairly sure the analogue gauge I have also reads 26", or somewhere thereabouts. If your pump is specified to 150 micron then it's almost certainly achieving it and the gauge is telling you lies. It's very unlikely its a faulty pump, and if it were then I'd be sure you would hear it in the pumps operation - the pump would sound like it is struggling. well it is a somewhat cheap 80 dollar pump. It had good reviews on amazon, but there was one review out of about 50 where a guy stated it only pulled 25 or 26 inches. when i looked up the gauge specs it says within 3% accuracy so shouldnt be off more than an inch but who knows. how would i know if its actually hitting near full vacuum without a very expensive gauge? is there some kind of cheap test that can be done? so lets say it really was only pulling 26 or so inches, proportionally that would mean im getting 12.74psi pushing on the lay up instead of 14.7psi right? would it really make that much difference? why is it so important to get that close to full vacuum?
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Hanaldo
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Likely to be somebody else using an analogue vacuum gauge to judge the pumps performance. Analogue vacuum gauges are too relative to be accurate, they dont know what your atmospheric conditions are, they dont know what your elevation above sea level is. They're an indicator but that's it. You need an absolute pressure gauge to have an accurate representation of vacuum level.
What sort of pump did you buy, can you show us? If it is a rotary vane pump, it should be able to achieve 99.99% vacuum, even if it is a cheap one.
As for why infusion needs full vacuum; the mechanical force behind the process is the atmospheric pressure driving the resin through your laminate. 1 bar isn't a lot of pressure to begin with, and this actually drops as the resin enters the laminate and the pressure differential balances back out. So when the infusion is completed, you don't actually have 14.7psi of pressure on the bag anymore. If you're starting lower, then not only does your resin have less force driving it into your laminate (which increases the likelihood of poor wet-out) but you also have a lower consolidation pressure as a result, which in turn means that you have more space between fibres which must fill with resin so you end up with a resin rich and heavier laminate.
There's also air inclusion. The two main benefits of resin infusion from a performance perspective are lower resin content from higher consolidation pressure, and very low void content due to the fact that all air has been evacuated from the laminate before any resin is introduced. If you dont have full vacuum, then you have air inside the laminate which will present itself as voids. Not only will this give you a weaker part, but there's a good chance it will present itself as pinholes on the surface of the part.
The difference between 14.7psi and 12.7psi may not sound like much, but every micron counts. Ask anyone that has made a mistake and let just a tiny bit of air into the bag during infusion - it shows up. Even a 0.1% drop in vacuum pressure will cause defects, let alone 15%. This may not mean you end up with a completely unusable part, it depends what you consider acceptable. You will have voids, you will have a heavier part. You basically lose all the performance benefits of having done resin infusion over a wet-layup.
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