I saw a video where they turned off the vacuum and clamped the vacuum line after the epoxy fully wet the material during an infusion. They then let it stand to cure. I understand that the vacuum bag needs to be 100% sealed, but in my mind, I would think leaving the pump running “just in case” would be a good idea.
Is there any reason to do this? Why not just let the vacuum pump run until the epoxy is cured?
A number of reasons, the main one being that infusion needs a 100% seal anyway. There shouldn’t be a ‘just in case’, because it needs to be sealed. If it’s sealed, the pump is doing nothing. So you’re just putting wear and tear on your pump for no reason. It also isn’t going to save the part if a leak does develop, so it’s just totally pointless.
You also run the risk of drawing too much resin out of the part. A solid resin break ‘should’ slow this down enough that you don’t draw a large amount before the resin gels, but it’s still a risk.
I also hate having vacuum hoses dangling off my parts for people to trip on and cause a vacuum leak. I clamp the hoses off just above the breach and then actually chop them off so there’s no chance they get pulled or move and cause a leak.
The only time I ever leave my pump running is on the odd occasion I have a part that requires double bagging, and then has a small leak in the outer bag. In that case, I clamp off the inner bag after the infusion has finished and leave the pump running to allow it to keep the outer bag at full vacuum. This works because even if the outer bag has a tiny amount of air in it, only an irrelevant percentage makes it into the inner bag.
Thank you for your reply Hanaldo. It is very helpful.
I would assume that the same stands true for layup’s where the resin is spread by hand. If there is a tiny leak, you stand to draw out too much resin. I guess the difference is that you can’t test the vacuum seal on a hand layup like you can on an infusion, so you take your chances on the hand layup.
Is a digital gauge really necessary for infusion? They are expensive. I was thinking about an analog gauge and letting the layup sit for 2 or 3 hours before infusion to test. I would think that this would be enough time for any tiny leaks to show on the analog gauge.
Another quick question, my vacuum pump pulls the gauge down to 26 inches of mercury. Do I need a a better pump for infusion? I see beginners pumps that will pull 29.9" of mercury. That is a big difference.
Thanks again for your help.
Generally with hand laminating you are using a higher viscosity resin, so it doesn’t flow under vacuum as quickly and hence you don’t really get a lot of movement in there. The breather also helps to choke flow, so it just isn’t much of a concern.
Digital gauges aren’t necessary at all. They can certainly make things a bit easier for you, as they will tell you if there is any leak. When you’re doing this professionally, it’s better to be able to pull vacuum, check the gauge and then infuse straight away. Having to wait for a few hours just slows your production process. When doing it as a hobby, you can leave it as long as you like to be certain, and honestly if you are holding vacuum for 2-3 hours and you get no change in tone from your pump, then that’s as good an indication as a digital gauge will give you.
And yes, you need a pump that can pull at least 29in/Hg. 26 is not enough.
Thanks Hanaldo. Order is going in tonight for new pump and supplies.
Does the amount vacuum pertain to your area? We have a huge vacuum tank which usually only pulls 26.5 at best.
No, volume only affects how quickly the pump can draw down to full vacuum. The actual vacuum level should not be affected by size.