ADHESIVES UPDATE
Urea Formaldehyde glue came into use just prior to World War II in the aircraft industry. It was used to laminate wood structures and fabrics in air-frame applications.
For the rod maker, urea formaldehyde offer a combination of strength, water resistance, and adequate open time, so that straightening can be done before drying. UF's are available in a variety of formulations which possess flexibility in storage, working temperature, drying and open times.
There are at least two makers of urea formaldehyde resins and catalysts in the United States: Borden and American Cyanamid. Borden owns the Casco Resin trademark and American Cyanamid owns the "Urac" apellation. The following are addresses where each of these products may be obtained. Borden of Canada can provide dealers with "CR5H" . As far as I can determine, CR5H is L-100 resin.
Casco Resin Custom-Pak Adhesives 11047 Lambs Lane Newark Ohio 43055
URAC Nelson Paint Company P.O. Box 907 Iron Mountain MI
Mr. Kent Pitcher, of Custom-Pak Adhesives has been most generous on sharing his expertise in adhesives and catalysts for this article. He has formulated a mixture using Borden's L-100 resin. This mixture is fairly thin, yet it delivers more than enough resin to create a maximum strength bond. Borden recommends a 40% delivery of resin to the joint for all edge gluing (our type) applications. Since L-100 liquid resin is 65% resins, it is obvious that there is a considerable leeway in the catalyst-resin mixture. Actually, S-120 and S-125(summer) catalysts can vary from 10% to 24% of a mixture and still deliver enough resin to the joint to insure a maximum strength bond at the edge. This fact allows the user to vary both viscosity and reactivity. Up to 24% of mixture (catalyst), the cross linking process procedes faster as more catalyst is used. At contrations of hardener of more than 24%, the reaction slows down because of a buffering effect. Here is a bench-mark mixture that works. This can be varied according the needs of open time, temperature and viscosity. 100 pts resin 20 pts catalyst(S-100 or S-120) 10 pts Water 7.5 pts GF-10 wetting solution You may ask what GF-10 is. It is a wetting agent that makes the mixture flow better.This already exists as a percentage of the liquid resin (especially URAC). However, up to 10% more is allowable. Five to eight percent is considered optimal.
Urea formaldehyde also comes in dry form. It has a much longer shelf life than the liquid form. But, in all other respects, it is the same as the L-100 resin. It just lacks the water. Borden's version is called Cascamite.
Urea formaldehyde mixtures cure completely in about four days at temperatures between 75 and 90 F. They can be heat cured very rapidly. I suggest you do some experimenting here. Both American Cyanamid and Borden will provide the user with information on heat curing. In any case, I always allow my glued sections to rest a while after gluing. I'm not sure that one needs to do this- I do it.
OTHER ADHESIVES
Resorcinol is probably the best glue ever formulated for cane. It is the strongest, most craze resistant, and most water-proof of the non- epoxy formulations. Its big draw-back is its purple color. But, thanks to Hoagy Carmichael, that problem can be mitigated. Check out page 94 of the latest edition of "the Book". This should work on UF glues. Especially, if on wanted white URAC.
Casein glues are protein based glues of great strength and pretty-good water resistance. Anyone who has tried to remove milk paint should know. However, its craze resistance and shear resistance is not so good. Its open time is short too. But, a lot of old timers used it and it worked.
Hide glues are strong. As long as the joints are dry, no problem. Just think about a 250 year old violin built for gut strings holding itself together ( strung now with steel) with hide glue. And, if you've ever witnessed the string players at an outdoor concert run like hell when it starts to rain, you'll know why hide glue might not be so good for fly rods.
Acid catalyzed PVA's are being used by at least one will-known rod maker to very good effect. However, make sure that you get one that cross-links at an 85% ,of more, rate. Without a high rate of polymerization, you may experience joint- creep ( movement under the clamps) or you might find that you had a relatively low water resistance. The good thing about this class of adhesives is that, given the correct formulation, the bond is thermoplastic. The glue softens when heat is applied. Rod sections bonded with this class of glues should be easy to straighten. Much more so than other glues.
Melamine bonds to slick surfaces- like other melimines. In other respects, it seems to be a good prospect for cane makers. I know that there is an old Leonard formula kicking around for a urea formaldehyde/melamine mixture. I think I could exhume it if anyone were interested.
And lastly, there are the Epoxy resins. They exist in such a plethora of brands and formulations that it is nearly impossible to comment of all but a few that might available to the rodmaker. Epoxy offers the maker great strength and absolute resistance to moisture. But, you had better have your rod straight before you allow the resin to cure. Epoxy glued rods seem to have a greater resistance to heat straightening than any other rod that I know. In fact, it is quite possible to apply enough heat while straightening to produce a catastrophic failure of the glued seams. All that being said, if you're good with your binder and can straighten before the glue cures, epoxy resins offer the strongest and most durable bond available. Of late, Bill Fink has been using a blend of epoxies that respond well to heat straightening after the curing process has occurred. Bill has been using a 50/50 mix of Shell Epon 829 and Versimid V-40 to very good effect. I suggest that you make contact with Bill if you wish to pursue this possibility
J. C. Zimny