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Author Topic: Cyano Glue - Does It Dry Lighter  (Read 712 times)
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Laminar001
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« on: April 03, 2017, 10:02:35 PM »

Hello

Does anyone know if Cyano glue (Super Glue) dries out lighter than when applied?

My query here is due to the fact that many paints and some glues do so by about 35% apparently.  This is because as they dry they give up water or solvent or both. Eg. Two-pack polyurethane.

I know that Cyano is a little water soluble and will break down over time.  Some years ago an experienced aero-modeller told me to always consider the weight of the glue going into rubber models, not just the balsa.  So if a rubber model has more balsa than usual the glue will add even more weight.  I have noticed that even cyano does add some weight.

Any chemical engineers reading this forum?

Kind Regards

Marc.
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ZK-AUD
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« Reply #1 on: April 03, 2017, 11:02:31 PM »

Cyano fumes off when it cures so I would guess that it does lighten a little but probably imperceptibly - pretty much what comes out of the bottle and goes on the model stays there. 

Aliphatic is my personal first choice for light models as it is essentially water based and lightens to almost nothing once dry.  There are some areas where cyano is useful because of its quick drying qualities and ability to bond dissimilar materials,  but I use it really sparingly and usually applied with 2 pins pushed through a block of balsa to form a spring-bow type tool
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aardvark_bill
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« Reply #2 on: April 03, 2017, 11:13:36 PM »

CA's don't dry like solvent-based glues so the change in mass will be very small if any.  Small amounts vaporize before it cures but once polymerization takes place whats there is there.  Cyanoacrylate adhesives polymerize in the presence of moisture - check out this article for a good explanation.

http://www.chenso.com/instant_adhesives.pdf
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Laminar001
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« Reply #3 on: April 03, 2017, 11:43:23 PM »

Hello ZK and Bill

Thanks for the information.

Regards

Marc.
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tom arnold
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« Reply #4 on: April 04, 2017, 08:43:24 AM »

The question of what glue is "lightest" can be answered by "It depends". You want the glue to be as strong as the balsa and anything more than that is just extra weight no matter what the glue is. CA glue is so strong it needs only literally a drop off a needle to fix a joint and it is still over-strong. The problem is that most builders soak joints or glob on piles of gap-filling CA. In that case there is a LOT of excess weight. Just because a glue has a solvent that evaporates does not make it lighter than a correct CA joint. The hardened glue left behind can easily be far heavier. Some builders dilute water based glues like carpenters glue and of course that is "lighter" than the full strength after evaporation but continued dilution will soon weaken a glue joint such that it pops apart on the first hard landing and then "lighter" is meaningless. So how much can you dilute a water based glue? The only way to decide is to run some lab tests on your bench and then come up with your own dilution. Same thing with cellulose based glues only you are using acetone instead. It is the technique that gives you a light joint and technique means very close and good fitting joints and glue (of any type) ONLY where the wood touches. As you can imagine, that is pretty hard to do for most of us but it saves a ton of weight.
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pedwards2932
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« Reply #5 on: April 04, 2017, 09:29:20 AM »

On that subject.....when you use cellulose based glue thinned how do you avoid it coming apart when you use dope on the framework?  Or is it unnecessary to dope the framework before covering?  I went back to carpenter glue because my last project required a lot of regluing after putting dope on.
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danberry
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« Reply #6 on: April 04, 2017, 10:13:17 AM »

It does not.
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tom arnold
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« Reply #7 on: April 04, 2017, 10:44:53 AM »

The only reason you would want to dope the framework is if you lay tissue over the framework and stick it by soaking thinner through the tissue---an old classic way of covering. You have to put numerous coats of dope on too. Other than that there is no reason to dope the framework if you stick the tissue on with glue stick or dilute white glue. All it does is add weight. Thinned cellulose-based joints are a lot more susceptible to dope fumes than the full strength joints in any case so your carpenter glue solution is the best.
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USch
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« Reply #8 on: April 04, 2017, 01:42:05 PM »

.... how do you avoid it coming apart when you use dope on the framework? 

Most of my balsa wood joints are made with thinned UHU Hart. If, before covering, you like to seal the wood dont "flood" the structure but just pass over it with a soft brush. The thinner, normally acetone, evaporates before softening the glue joints.
Personally I prefer to seal lightly the frame on outdoor models to be less affected by early morning humidity. I actually seal all the wood, not only where the covering touches the frame. As Tom said, this will add weight. But on a typical wing with 10-15dm2 it is only about 1 g, hardly noticeable. Trouble with glue stick covering is if you have to redo the covering. Near to impossible to take off the old paper, just my 2-pence worth. And I redo often the covering  Cheesy

Urs
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cavelamb
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« Reply #9 on: August 17, 2017, 01:55:58 AM »

In the "It depends" category...

Using CA (superglue), one can blot off quite a bit of excess glue with Kleenex.

Just don't linger on the joint!

A small bit of Kleenex held in forceps can reach inside joints.

 
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pburress
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« Reply #10 on: September 09, 2017, 01:03:21 AM »

CA glue is relatively heavy, its similar to solid acrylic when try.   The lightest glue would be cullulose such as Duco, Sigment or testors wood model cement.  I use Duco thinned 50% with acetone. Cellulose glue also sands well and you can undo a joint easily using acetone.
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