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Hi Mark
I don't know the Hysol adhesive number off the top of my head but they do have a structural equivilent to the old stuff. What is typical is to have a standard base resin and various speeds of "hardener" which react at different rates. For example I have one type of toughened epoxy base resin and have three different hardeners with pot lives between 15 minutes and 3 hours. Open time is different than pot life and they are each something of a loose target since volume of resin and thin film vs concentrated container all change the reaction rate. As a rough estimate, you can predict roughly a doubling of the reaction rate for every 17 degrees F (or about 10 degrees C) of temperature. So if you need to extend the life of your resin, you can out it in a bucket of ice. This will thicken the resin however, making it a bit harder to work with but once warmed, will thin down nicely. Obviously, never laminate in the sun if you are rushed for time. Another trick is to use relatively small batches of adhesive pre-measured and ready to go because once you spread the adhesive out into a film, the hardening time slows down considerably from being in a pot that can develop a lot of exotherm.
Anyway, I will check with a couple of sources I have that deal with Hysol to see what they say. And if I remember correctly, it wasn't that they stopped making the 9339, it's just that they stopped selling it in batches smaller than 5 gallons or so.
Anyway, that is a long way of saying that Hysol may have the same base resin with a slower hardener that will give identical properties.
BTW, I use the "" around hardener and resin since these are really kind of arbitrary designations. Unlike polyester resins which use an MEKP catalyst, epoxies use co-reactants. That is to say the one molecule of "part A" must find one molecule of "part B" to polymerize. So that any excess of one part or the other will weaken the matrix. That is not so of the polyesters/vinylesters -Othopthalic/isopthalic resins and MEKP which are generally very tolerant of various mix ratios of between 1% - 3%.
As to switching adhesives, you are absolutely correct, there is a HUGE difference between laminating and adhesive formulations of epoxy. Jeffco is a fairly ordinary room temperature laminating adhesive with a relatively low HDT (heat distortion temperature). There are many high strength bonding adhesives with much, MUCH higher strength. I would NOT use Jeffco for bonding on the skins. It is probably alright but that is as close as I would say, i.e. "alright" as in "There is a good chance you will survive" but as a general rule, don't go with any material that is weaker than the material called out in the instructions. When in doubt, contact the manufacturer and get a set of their physical properties and compare. If a material exceeds the physical properties in every way, you have a pretty good chance of making it at least as good as the originally called out adhesive, but what if it is not as strong? Why do that? I would also look at the flex strength. I suspect the Jeffco is more brittle but I could be wrong.
Rich Molton at Applied Poleramic has some bonding adhesive that is great and you can specify the amount of thickening you want and the speed of the hardener. Check out his bonding adhesives. I think his thixotropic adhesive was ADH/ADUD but he or Doyle can tell you for certain. I would take his figures and compare them to the Hysol and you can make an informed decision.
One tip, too is that yo can typically improve the cross link density of the matrix by adding some heat. It is time and temperature dependant but basically, if you heat most of these adhesives up to around 200 degrees for 4 hours or so, you will increase the strength. This is often easily done by covering the parts in a black tarp under a hot summer sun. A word of caution though: BE CAREFUL NOT TO EXCEED THE HDT OF THE PARTS< IN PARTICULAR WITHOUT THE PARTS BEING WELL SUPPORTED! That means that if the matrix resin gets heated past HDT, where the resin turns soft, the part can sag and permanently distort. This is evidenced by the instructions in the Lancair manual that tell you to use a heat gun to soften and GENTLY move composite parts that have become distorted.
Anyway, I will check to see what I can find out about the various Hysols. I'll post on the LML if you don't mind because you bring up some excellent points.
Dan Newland
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