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Hanaldo - 8/11/2018 2:27:20 AM

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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Hanaldo - 8/12/2018 2:40:40 AM

Dont worry about the gauge, they are all going to be inaccurate in one way or another. Some may be better calibrated than others, but at the end of the day the number they point to really doesn't matter. Keep in mind that elevation above sea level and atmospheric conditions will change the reading the gauge gives you as well. So one day it might read 26", the next day it could be 30mm past the 30" mark - and I promise you wont be pulling 32" of vacuum! 

Stick with what you've got. Your pump should be perfectly capable of pulling full vacuum, so if it goes quiet and stops emitting oil vapour when the gauge says you are at full vacuum then you are likely at full vacuum. If you're really worried about it, do some playing around and infuse some flat sheet. You'll learn a lot, and you'll also be able to look at the flat sheet and diagnose any problems - pump related problems are going to be obvious.

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Hanaldo - 8/12/2018 2:40:40 AM

Dont worry about the gauge, they are all going to be inaccurate in one way or another. Some may be better calibrated than others, but at the end of the day the number they point to really doesn't matter. Keep in mind that elevation above sea level and atmospheric conditions will change the reading the gauge gives you as well. So one day it might read 26", the next day it could be 30mm past the 30" mark - and I promise you wont be pulling 32" of vacuum! 

Stick with what you've got. Your pump should be perfectly capable of pulling full vacuum, so if it goes quiet and stops emitting oil vapour when the gauge says you are at full vacuum then you are likely at full vacuum. If you're really worried about it, do some playing around and infuse some flat sheet. You'll learn a lot, and you'll also be able to look at the flat sheet and diagnose any problems - pump related problems are going to be obvious.

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Hanaldo - 8/16/2018 1:27:52 PM

Depends on if you're using a brush or spray viscosity tooling gelcoat. If you're using Unimould then its brush viscosity and it wont spray through a regular gun with a 2.5mm tip, you'd need a 5 or 6mm tip on a gelcoat cup gun.

But yeh as you said, it doesnt matter. The only benefit to spraying over brushing is application speed, so it's great for big parts that will take a long time to brush up because you can spray it in 5 minutes. It's also slightly easier to get a consistent thickness, but if you've got a brush viscosity gelcoat then that shouldn't be a concern either. In any case, you shouldn't need to spray it for these pieces, it'll take 5 minutes to brush on.

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Hanaldo - 8/17/2018 5:38:13 AM

Ok, if its spray viscosity then it should spray through a 2.5mm. Might be a little slow. You can brush, but it's harder to get a consistent finish, so catalyze it slightly higher and keep an eye out for alligatoring.