Vacuum bagging updates

I recently mentioned that I was working on vacuum bagging as a method of molding parts. I’ve done some work with this and I think it is viable, but there are some significant challenges I have to overcome first.

The first challenge is very basic, and that is that my vacuum chamber isn’t able to get to a low enough vacuum. It only gets down to 26.5 in-Hg, which is not enough to remove all the air bubbles in the epoxy. I’m not sure where the problem in my system is. It might be that the vacuum pump itself simply cannot pull a low enough vacuum because it is a cheap harbor freight pump. Or it might be that there is a leak in the chamber. Both of these situations are very likely and it might be that there is a tiny leak and the pump can keep up with it all the way up to 26.5 in-Hg. I’m going to have to work on narrowing down the problem, but so far I’m having a hard time figuring out the problem. I tried replacing the oil in the pump, but that didn’t help much at all.

The next challenge is getting a ziplock bag that is actually airtight. So far I’ve tried a few different bags and brands and all of them, even the one designed specifically for vacuum bagging food, don’t stay sealed at high vacuum. When I seal them they seem to work very well, but then after about a day they have air in them. A few hours after sealing, they’ve lost all negative pressure, making them useless for compression molding. Maybe I just need to find a different brand or type that works perfectly, but it doesn’t seem like any ziplock bags are going to work for this. I was really excited about this method of vacuum bagging because the sealing method was working really well, but if these bags can’t hold a vacuum then they’re useless for this.

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