Learning a New Technique

Vacuum bagging is a skill I have yet to master, as was proven when we attempted bagging the old design upper tool cowl. so why not take it one step further and try to learn vacuum bagging and vacuum resin infusion all at the same time? I like to take big bites of the elephant, so why not.

There are some advantages to resin infusion. 1) it’s less messy and sticky. 2) it is more repeatable. 3) you have all the time in the world to arrange, cut, and straighten the plies of the layup schedule before going on the clock when you mix the epoxy. 4) you test the vacuum bag before mixing epoxy and if it doesn’t seal, you can replace the bag or start over with little lost but some bagging film. 5) you don’t have to wet each layer out individually.

There are also some drawbacks, the biggest of which to me is the steeper learning curve. Infusion also requires an infusion resin which is very watery and not suitable for a wet layup. So you will need another resin system/kit. Also you need some additional consumables like flow media to make it work.

Those pros and cons being said, I am hoping to infuse my final cowl parts and get a really good surface finish. Therefore I need to learn this new technique. I also was getting a little bored of working on the cowl plugs so I decided to spend the morning yesterday taking my first shot at resin infusion with my induction inlet mold.

Prep was the same as for any layup. Five coats of wax, five coats of PVA, cut cloth, cut consumables the consumables were peel ply, flow media, and bagging film.

For the cloth, I wanted one ply glass, two carbon, and a ply of glass. With the circular nature of the part, it is hard to get flat cloth to lay into the mold nicely. So I ordered some glass and carbon fiber sleeve. It is really neat stuff, almost like a Chinese finger trap. It is woven in such a way that you can expand or shrink its diameter within certain ranges. It really makes slick work of tubular or circular parts like this. You can find it at composites supply shops online such as Composite Envisions.

I then stuffed the mold with the glass, carbon, glass, peel ply, and flow media. From there it was tacky tape around the perimeter and make, pleat, and seal the bagging film. On one side there is a vacuum line, and on the other is the resin supply line clamped off.

To my surprise, it actually pulled pretty good vacuum. About 26” HG. I was pretty satisfied. So we mixed the Proset INF resin. We dropped the supply tube into the cup of epoxy and opened the valve. Low and behold the resin started traveling up and infusing the part. It was very fun to see.

Of course about that time we also started having leaks in the stretchelon bagging film. I think the cut ends of the flow media was puncturing the bag. It took me about an hour, and half a roll of tacky tape to find the leaks, but eventually I got the bag to seal again. It looked horrendous and I don’t suggest resealing this way.

By the end of my workshop session, the resin was cured and I de-bagged and released the part. Which wasn’t easy, especially with all the tacky tape on the bag itself.

There is certainly room for improvement in the part and my technique. The surface finish is not very good with one small area where the cloth bridged and many pin holes. I know it can be better, and I will keep practicing until I get it there. This part would be useable with a few hours sanding time and some finishing work. It is a strong and light part. But I should be able to make them where they come out of the mold with little to no requirement to do any secondary processing to use them. If I am going to infuse the cowls, I certainly need to be capable of better surface finish too.

All in all, it was a very educational day in the Garaggio, and taking the first steps in the infusion learning curve will get us that much closer to being able to use it as part of our regular bag of tricks.

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