Just joined and wanted to introduce myself. My name is Brian Alley and I operate Carbon Fiber Composites in West Virginia. We specialize in infusion and double bag infusion of carbon fiber parts for experimental aircraft and now manufacture structural assemblies Out of Autoclave with advanced double bag process. I hope I have something to offer the forum from our shop experience and also wish to learn from the group to add quality to what we offer our customers. Looking forward to meeting the membership.

Hi Brian

I am sure you can add to this knowledge base. I heard a guy at Sun N Fun give a seminar on double vacuum bagging. It was very interesting.

I have not tried it yet. So how do you find vacuum infusion compared to double bag infusion? Are the parts much lighter etc.

Thanks

Fred

Fred, I've given seminars at Airventure with Russ Emanis but not at SNF. The double bag process correctly done offers advantages in consistency. Imagine that the compacted laminate stack is stored energy in the form of compaction. As the laminate is infused, everything behind the flow front in a single bag operation has lost vacuum. This allows the compacted laminate to spring back to it's original state increasing the resin uptake of the laminate. This is often evident by resin pooling in the bag or the bag feeling loose. By placing a second bag over the part with a breather layer between the bags, full vacuum pressure can be applied to the second bag retaining the compaction of the laminate stack. Consistant 70/30 fiber resin ratios have been laboratory verified. I recently completed an aircraft project where the fuselage skins were a balanced carbon fiber laminate stack using four layers of 6 oz twill and one 18 oz NCS in between. The completed fuselage skin was checked in several places with dial calipers. The only readings found were .062 and .063. The double bag process allows more vacuum pressure to be applied to the part without exposing the resin to this high level of vacuum. I often hold 29"hg on the second bag for compaction but reduce the vacuum applied to the first bag to 18-20" hg to infuse the part. Take a look at the picture I've attached. This violin body has very tight radius edges and was extremely challenging to fabricate. Double bag vacuum resin infusion allowed me to produce a perfect flawless part first time, and every time.

Hi Brian

Come to think of it it was Oshkosh that I went to one of your seminars I talked to the speaker in length.

I usually go to Sun N Fun and Oshkosh every year so I get them mixed up some times. I am also an ultralight pilot I fly an Earthstar Thundergull JT2 on a rotax 503.

Strange you should post a violin, I just finished my first carbon fiber Strad 1701 copy yesterday. It was a 5 month project. Do you produce violins or is it a hobby?

Could you post some pictures that show what a double vacuum bag set up looks like? I heard some say they open both resin feed lines and vacuum lines in the first bag and allow the second bag to be a t full vacuum. In doing this excess resin is squeezed out the open lines. Is this a good idea?

Have you ever weighed two identical parts? One with normal infusion and the other one with double vacuum bags.

Thanks

Very interesting.

Fred  

I'll look thru my photo's and see if I have a good example. In the mean time here is a link to the article that got me started infusing.