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Plastic peel ply method


John Slade

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The following are my recent posts to the CA-mail list concerning plastic peel ply. Some of the text below "didn't make it" to the public posting.

 

> Unless there is something else being used that is new, better or

> different, the term "plastic" in this dialogue, may simply be a generic

> term. I suspect it's still Dacron or some other similar material.

No. What Bulent and I are talking about here is the use of clear 6 ml plastic sheeting, as found in home depot, on top of the finished layup and any standard cloth peel ply. The technique has been described as "poor mans vacuum bagging". The plastic sticks to the wet epoxy and shows up bubbles very well. Squeege over the plastic with a little help from a hair dryer and you can watch the bubbles run along in front of you're squeege and out the edge. Wet the squeege with epoxy for a better slide over the plastic. The air can't get back in because of the seal caused by the plastic. Lots of excess epoxy can be removed this way for a very tight, compact and lightweight result. Do not press too hard because air can be sucked back into the layup through the foam - you'll see this when it happens because the area goes dark when you squeege it, then goes white again. If this happens lift the plastic and add more epoxy. After cure the plastic comes off in an instant and you have a very smooth, almost moldlike finish. I describe this in detail in my web page "tips and tricks" section. http://kgarden.com/cozy I first saw this at Bulent's shop 3 years ago after finishing my fuselage sides. I've used it ever since. The airframe is now finished and in gloss. The only place I saw pin holes was in the parts I did BP (before plastic).

Try it once. You'll never go back.

 

> I'm sure John Slade would jump in but... The technique is to use

> your basic

> peel ply and then cover that with a plastic sheet - 3mil plastic

> drop sheets

> at Agent Orange (Builders Depot) or equiv. (see

> http://kgarden.com/cozy for a

> more in depth explanation).

 

Actually, I find the 3mil too thin. 6 Mil works better. Doesnt wrinkle up as much.

The 15% reduction was in the weight of the layup. I subtracted the weight of the foam in each case.

 

> (created by getting all of the air out) would actually pull the

> layup off of the foam.

Hmmm. I never heard of (or saw) anything like that.

 

> so do some test layups and destroy them with a spring guage

> in shear, torsion and tension (I couldn't find a difference).

Wouldnt hurt, just to make you feel better.

 

> I suspect I am missing something that makes your process worthwhile. Can

> you explain it again for me please? Thanks

Yes, Art. What I think you are missing is that significant compression DOES take place. With the squeege sliding on plastic the fibers are squeezed. Air can't get back in, so they stay squeezed. Its hard to get a dry layup this way, and its very obvious when you do. The color change from light to dark as the squeege passes tells you everything. Air bubbles are being displaced. The gloss finish is very easily scuffed up for bond since there is no weave to deal with. I think we had the best suggestion earlier - try it on some test pieces and do structural tests. Prove (or disprove) the technique with practical experiment rather than theoretical science.

 

> You are the one who has been quoted as having reduced your part weight by

> 15% using this method, not me.

 

Wrong. I said:

"The 15% reduction was in the weight of the LAYUP."

 

You said:

"Vacuum Bagging ...they consistently reduce the weight of PARTS

made that way by 25%."

 

Apples and oranges, even at grade school level.

 

>I am telling you that if you use those parts in your airplane, you are

>risking creating a great deal of pain and sadness for those who love you!

 

Ahha! the old scare tactic, commonly used to assert the status quo when innovation rears its ugly head. Usually indicates the end of a discussion.

 

The plane is almost finished, Art. I'll "drop in" and give you a demo one day.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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