First of all this process is a little labor intensive and probably not much economical benefit for one-off parts production. The benefit is your hands never touch the epoxy! The process is also wasteful. There are a lot of consumables involved, the resin flow media, peel ply, bag, spiral wrap, t-fittings, the butyl tape and the bag. I also wasted 25' of plastic line (forgot to cut it shorter) and a small resin trap I tried (too small).
The tooling surface is a 2x4' piece of malamine. 10 coats of release wax later you test it for adhesion with a piece of masking tape. If it sticks at all, more wax. This was the first time for this piece so I gave it a couple extra coats. There are other mold
release agents available but I didn't try them.
It is vital to ensure that your layup
will maintain a perfect vacuum after you shut off the pump. The clamping pressure is what maintains the ultimate shape of the part you're trying to produce. I'll explain later on what happens when you don't.
The location of your resin inlets and vacuum outlets are also critical to the success of the part. Seen here the panel is not infusing well. The resin was able to circumnavigate the part and reach the vacuum outlet too soon. This meant either pumping a lot more resin in (as I now know is wrong) or stopping the process and adjusting the flow media etc. (which is an extremely messy proposition.
I eventually got the entire part infused after about 32 minutes. About twice as long as it should have taken and using twice as much epoxy as required.
The epoxy I used is specially formulated for resin infusion. It has an ultra low viscosity and a very long working time (+5 hrs). For small parts like this the longer working time is more of a PITA than a benefit.
The completed part came out of the stack fairly easily. The peel ply did it's job perfectly. The resin flow media (nylon screen
mesh) did stick to the tooling surface. There are some areas along the edges of the part that didn't stick due to loosing vacuum on the stack. What happened is the excess resin that was being pulled off the part kicked off in the vacuum line just ahead of the resin trap. This in essence shut off the vacuum to the stack. After that there was no way to get the whole layup
back under vacuum. I had planned to trim the edges anyways.
The larger flat surfaces of the part are perfectly infused. There are absolutely no bubbles or areas where there shows any resin starvation or delamination
. Both sides of the part were infused at the same time and I was a little worried about the backside (laying on the tooling surface) not getting resin. No worries there. The flow media looks after that.
The biaxial fabric
is 1708. Amazing product! A little awkward to handle such heavy fabrics and it takes some getting used to. A little 3M Super77 adhesive
was req'd to keep things from moving around too much when setting up the stack. The peel ply a fine weave nylon fabric
left a very smooth surface. It would probably need some light sanding
for a secondary bond. I'm just guessing until I cut into the part but I figure there's 40% resin and 60% fabric. Maybe a little less resin but not much.
So the things I learned are:
Proper location of the resin inlet and vacuum outlets are critical. Experience necessary I think so that you can judge when/how the resin will reach the outlet AFTER the part is fully infused (Ideally).
Having a perfect vacuum seal on the layup is also critical to the complete success of the final part. Any leak, no matter how small is unacceptible. An ultrasonic leak detector, such as those used in the refrigeration
repair industry would be a big benefit.
A bigger resin trap is required. Mine was only about 5 oz, sort of an inline filter thingy. I have my eye on an old paint
pot at the local flea market that'll work. Shorten your vacuum lines so you don't waste them if you suck in some resin.
Heat lamps and hair dryers are good to help control the flow of resin. As soon as the part is fully infused we lit the exit area with lamps to help the resin kick off quicker. This helped a little bit in restricting the flow of resin, as it will with a sustained vacuum applied. Downside is it prevented us from reapplying vacuum when we needed it. Two vacuum outlets, a primary and a backup is maybe a good idea.
I'll probably do the other half next week. Need to acquire a few more materials. Hopefully it'll go better. Will post the results as well.
I'm thinking all this tinkering with this process might lead to being able to produce some smaller parts for our project, hatch
covers, etc. We'll see. I don't think I have the stones to try this on the whole hull
of a TW28!!! That's risky beyond belief (for me anyways). I've seen it done on the Internet
but without professional guidance I don't think I'd even attempt it (feel free to remind me of that)!