mylar heat treatment under tension

[malthuse]

A lot has been written about how quad 'bakes' their panels under tension which locks in the tension and prevents creep over time. I believe that the baking in affect does to the mylar what heating with a heat gun does when repeated to the point that the mylar no longer shrinks. At this point there is no more ability for the material to creep.

I am going to try a method where I stretch the mylar on a regular jig to my required tension. Then I'll heat with a gun to relax the mylar. Retension. Heat. Retension etc.. until the mylar has lost all of it's ability to heat shrink and I'm at my desired tension. I think this might go a long way to stabilizing the mylar over longer periods. Although how I measure that without waiting ten years I don't know.

 

[geraldfryjr]

That is the basic process of Tensilizing.

This is why it has been suggested to only use Tesilized Mylar, but it seems that it is hard to come by anymore, even when it is stated that the stock you buy is already supposed to be, many have stated that it is not.

The stuff I got way back in the 90's is and I really haven't had any issues with it.

Cheers!!!

jer

 

[malthuse]

I didn't realize that was what they meant by tensilized.

I looked up my tensilized mylar and found that it will still shrink 2% with heat which in my mind means it can continue to creep over time. If you mechanically stretch and remove that shrinkage with heat it should be more stable I would think. In any case it can't hurt, unless I end up melting the membrane!

 

[Penguin87]

Hi Malthuse,

Did this process work out? Interested in the results before I start a new project.

 

[malthuse]

It did work, it produced stable membranes. I alternated heating and tightening to get to the desired tension. Some trial and error was needed to work out how much heating was needed to completely get rid of the membranes creep.

 

[Penguin87]

Ok, great! Something like 1 min. then wait, stretch, then 1 min.? How many times did you do that process?

Also, was there a problem of even heating, or does reasonable movement across the membrane seem to work out fine?

Thanks so much. I am pumped about this possibility. I know some DIY electrostats that stretched pretty quickly after being built, so this relieves a fear of having that happen.

 

[malthuse]

Even heating was an issue. I just manually watched the height and did lots of hot passes. You run the risk of burning the membrane but with some practice you can get it. I think it’s better than just stretching as you relief any problems that can occur in the corners with under tensioning.

 

[bentoronto]

My panels are made from Dayton-Wright cells (6 to a side) that are about 45 yrs old. The old ones with the good treble. 30 years in storage in the middle of their life.

Maybe once every two years (except while in storage), I give them a vacuuming and a run with a hair dryer. The dryer I keep in motion, about two inches a second.

I have no idea if it helps in the least or if I am over- or under-heating or why I bother.

Of course, they are working as good as ever, at least to my ears.

Anybody want to comment on the right way to heat or not?

B.