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CURING JB WELD FASTER QUESTION

davehour

Elite Veteran

Guayama, Puerto Rico 00785

Hi:

"JB Weld" high strength epoxy cure time is about 24 hours. Placing the glued piece in an oven under 200 degrees Fahrenheit cures it in 30 minutes or even less. I haven't seen any problem using this fast curing method but I would like to know if the strength is affected in any way.

Thank you very much.

David

04-21-2004 Over year old.
shootist

Senior Heliman

New York State, East Coast US

Fast forced cure at 200 degrees may weaken the bond to the base materials a bit, but I believe that the strength of an epoxy bond is still more than we need in most applications. I keep forced cures down to about 140 degrees.
On the other hand, post-cure heat treatment of epoxies almost always increases the strength and heat resistance of the bond. 140- 170 degrees, after the cure has completed, is beneficial, but may be overkill.
The biggest things to check are that the surfaces are roughened and chemically cleaned before epoxy is applied.

04-21-2004 Over year old.
rcnuts

Veteran

Millersville, Penna

Dude, I wouldnt do it. The only person who could tell you for sure how strenth would be affected would be a chemical engineer. Tests would have to be performed, like tensile breakage and compression distortion (etc) with identical glued parts, some baked and some not. The odds are already NOT in out favor flying these helis, why push the envelope by rushing things?
Harris,

Hooligan, at large

04-21-2004 Over year old.
davehour

Elite Veteran

Guayama, Puerto Rico 00785

I believe the only one which is machinable and high heat widstanding is the long cure time formula.

04-21-2004 Over year old.
shootist

Senior Heliman

New York State, East Coast US

dave,
The 5 minute is not as strong as the 24 hour subjected to a fast cure.
We use the 24 hour stuff in high power rocketry a lot, because of its heat resistance. We were finding that "normal" high strength epoxies were subject to thermal breakdown after repeated exposure to heat, and became soft during each exposure.
Here's the website:
http://www.jbweld.net/

It has the properties of both JB weld and JB quik. The accompanying instruction sheets talk about the curing process. Heating it to 200 degrees is not mentioned. A little heat with a heat lamp is mentioned for certain conditions.

Either way, the shear strength of JB Weld is 3,900 psi. If you calculate the surface area to be glued, you can get a good idea of the bond's shear strength (if everything is done right):

Let's look at a .25 inch torque tube glued .75 inch into an end fitting:

pi times diameter times cylinder length gives the square inches at 3,900 pounds per square inch:

3.1417 x. 25 x .75 equals about .59 square inches of surface area
x 3900 psi= 2,297 pounds of rated shear strength.

Can you twist your torque tube with 2,300 pounds of force without breaking everything else?

04-21-2004 Over year old.
davehour

Elite Veteran

Guayama, Puerto Rico 00785

Hmmm, looking there I found that Marine JB Weld has all the properties of the original JB Weld, but the curing and setting times are the same as for the Kwik one. That should be the best bet.

Thanks you very much.

04-21-2004 Over year old.
rcnuts

Veteran

Millersville, Penna

Hey Shootist, how could I disagree with your info? However, you forgot one thing, Tensile strenth or tortional rigidity isnt the big question. Its adhesion- thats what I would be worried about. Differant products / materials expand / contract at differant rates. (coefficiant I think) My concern would be the rod and JB weld going their seperate ways when they cooled down. I definately like the long cure JB weld. Some guys at the field have used the 5 minuet product for emergency repairs, I would too if the need arised
Harris,

Hooligan, at large

04-21-2004 Over year old.
rcnuts

Veteran

Millersville, Penna

Wingtip, I couldnt aggree more!
Harris,

Hooligan, at large

04-22-2004 Over year old.
davehour

Elite Veteran

Guayama, Puerto Rico 00785

But we are missing a point here...

Ok, ok. All the facts about the fast cure JB Weld are true. But, we may be missing an important point here. What if you need the magic of JB Weld but at the same time need more time to work the parts you want to glue? Many times 5 minutes is just too short.

There you have the reason why of this thread.

David

04-22-2004 Over year old.
shootist

Senior Heliman

New York State, East Coast US

dave,
My point in the 'high school geometry' post above, was to show how strong the glue line is. While boosted slow cure is stronger than fast cure, they're both plenty strong (in my opinion).
There is one good way to test a glue application that is not endorsed by the manufacturer: Glue up a set of spare parts, and treat it similarly to your real part. Then try to pull it, push it, or twist in apart. You'll have to use some mechancal help.
If the glue line breaks first, you lose and have to use different techniques. I'd bet 10 cents (or more!) that the base materials will fail first.

04-22-2004 Over year old.
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CURING JB WELD FASTER QUESTION

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