Complex part. Bag option problem....

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#1

Over the past week Ive been working on a part that looks like a 2 foot high top hat with about 10 degrees of draft and then tapers off to a square top. Both sides are equally important in terms of finish quality.

Ive bagged it 6 times (2 times per complete part). Each finished part has failed to meet expectations. The bag is 100% the problem. And each time Ive altered the bag according to my bosses demands. My most recent attempt has also failed. Its under vacuum as I type, but just from a visual I can tell that there are major ribs being formed.

Stretchlon bags we’ve used: small square bag with pleats. HUGE square with ribs (figuring it will stretch the pleats out), and circular. I didnt want anything to do with these bags mostly becuase I could tell that it just wouldnt work without creating several low vacuum areas and resin pools.

Heres what I think. Resin infusion would absolutely work perfect on this part. As of yet, we do no infusion, and my boss is probably sick of hearing me say it (because it wasnt his idea). So, the only option I have would be to make a silicone, or, latex bag. Problem solved, and ridging goes away. Plus Ive mentioned this about 4 to 5 times. As in “hey, a silicone bag would work great” type comments. He’s turned a def ear.

So, am I off base? How would you bag a top hat (like those in old movies) with a square top?

#2

If its causing so much problems, wouldnt it be easier and quicker to laminate by hand, rather than waste lots of time and money trying to vacuum something which may be extremely difficult to do in this way?

#3

JRL…it seems to me someone has been studying here and taking it in! You get an A+ for your semester grade!:stuck_out_tongue:

#4

I agree. And I wish it was my decision. The part would have been done last week.

Were copying an old part for a low production run. It needs to be EXACTLY the same as what was sent to us. The tolerances have to be exact. So bagging is our only option.

Ive been successful on its 2 smaller counter parts. The parts are out, they fit, and our customer is happy. They look very pre-preg in finish, and we have the ok to move forward.

This big one is a real pita. My only option, as I see it, is a custom bag (and yes were getting paid well enough to justify the extra cost). Just curious what other ideas you guys may have. And like I said, my boss is very close minded towards infusion…so no option there.

#5

LOL! Yeah, you guys have helped me a ton over the past 7 months.

#6

If parts have to be exactly the same, then I would think a 2 piece male and female mould, would realistically be the only way to achieve this.

#7

It has to be a 1 piece female.

So far I have managed to pull a nice and clean part from our mold, other than the resin ridges. There about 1/8 inch high, which would normally be fine. But in this case I still have to bag it for a second time to build thickness…which means the ridges will grow.

#8

I am assuming that you probally using yellow or green nylon bag, have you tried the orange stretching bag?it stretches 300%

#9

Green polyurethane film 500% elongation.

Our last bag was a 48" diameter circle…it had more ribs in it than the square bag. And not to my suprise it didnt work.

My bosses newest idea is to elevate the part off the table. His thinking is that it will cause the bag to pull harder, thus pulling the ribs out of the bag.

#10

:eek::rolleyes::smiley: does someone want a new job? LOL!

#11

I like my job. I just hate mediocrity. Thats where I feel this whole experience is leading me.

And the “you cant teach an old dog new tricks” saying is looking like its pretty true in this case.

#12

can you get pictures of this part that your trying to bag?

#13

:D…

I’m 52 years young or old…and I used to tell my Plastics & Composites classes many times to “never stop learning” and I’ll probally will learn things this semester along with them. No more as I have retired from babysitting these HS kids these days!:frowning: They wouldn’t even try to do things and just wanted to sit around, listen to their Ipod and play text or video games on their cell phones…:mad:

That is why I use the same signature at the bottom on most every forum I’m on!

#14

I can take partial pics of it. Ill try and post them tomorrow.

Werks: Your sig is great advice.

#15

Heres about as much as I can show. As you can see I havent cleaned it (lots of peel ply stands on it). And the overlapping layers are that big because I litterally am copying the part we were given to a “T”. If I had to guess I would say its about 18" high.

The rest of it is cylendrical (sp?) with a large flange area. And thats where the resin ridges are building. All of them are where the large bridged pleats formed.

Funny story: Boss number 2 walks by me today and I say…“hey, we really need to make a silicone bag for this thing”. “Were going to waste a lot of money on this”. He says…“Great where do we buy one?”.

Boss number 1 is the one Im having problems with. He thinks he needs to solve EVERY problem.

Edit: I deleted the pic.

#16

ok, so what I gather is happening is your bag pleats are creating resin build up in all the pleats at the bottom? if so I would try a couple things, first have you tryed non stretching bag(nylon bag)? You actually might get a better result, I never liked the stretchy bag so much, it has its applications, but it teaches bad habbits. second, when you start bagging take a rubber squeegy and push on top of the bag in the corners to help form it, it sounds like your bag is bridging a little and causing the resin to fill these cavitys, one thing I notice when most people bag is that they never try to form the bag, they just apply vacuum and try sealing the bag before they get the bag formed well. Not to say that is what you are doing, but am just trying to guess with out seeing the problem. all so make sure your peel ply gets cut in all corners. hope that helps

#17

Yep. Your exactly right on whats happening.

We currently only have Stretchlon in stock. I agree stretchy bags do teach bad habbits, but, if you had to bag parts with some of my co-workers you would fall in love with the stuff.

I really like the squeegee thing. Ill have to try it. Applying vacuum slowly is good when I work by myself, as I did on this part. Normally though I bag with atleast one co-worker who is rarely on the same page as me. Most of this extra detail would never happen.

By the way the part is finished and getting shipped tomorrow. Turned out ok. Started on a latex bag today. Looks good so far.

#18

yea, its defenitly woth using a rubber squeegie, I always do. I just started a new job and every looks at me weird when I was using it, but no more bridging in corners. If you pm me your mailing address, I can send you a squeegie, I have a few extra. They are definetly a most for any composite shop doing bagging.

#19

JRL…all you can do is use his failures as freebies to learn from.

Let him fail miserably you know that you can do things differently.

Anyone not willing to work outside the lines or think outside of the box is doomed to failure.

#20

Change your Boss, bring another one:D.
Anyway, you said is 100% vacuum bag, tell me something, is your construction of your mould good and give to the bag to cover all the curves? Maybe is a silly question but who knows. In the past my first moulds it was not construct it very well and the bag was not cover all the mould and of course the part was disaster. Tomorrow I will post one mould and the part from it just to take an idea. The first mould it was not schedule it nice so I try 4 times to make the part but with no results. So I re-build my mold and this time was fun.