I did the same tests mentioned in the previous post using Safe-T-Poxy, fiberglass and urethane foam, and vinyl ester resin, fiber glass and urethane foam. Fuels used were Shell 93 octane purchased in February and the same Shell 93 octane purchased in July from the same pump, Exxon 100LL obtained at 2W6 and gasohol containing ten percent alcohol. The July vintage Shell 93 octane and the 100 LL showed no degradation on the test lay-ups after one year. The February Shell 93 octane specimen was tacky after a one-year exposure. The gasohol had dissolved the epoxy resin after one year. The urethane foam was not affected in those samples. The vinyl ester resin was not affected by any of these fuels. You may have taken my post out of context. It is not the gasoline that does the damage to the epoxy. The alcohol and aromatic additives in the automotive gasoline seem to be the source of the chemical attack. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD USA sidney.w...@titan.com
At 08:08 AM 8/10/2004, you wrote: > For best chemical resistance, recommend that you use vinyl ester resin > for the fuel tank construction. Epoxy will work ok as long as you only > use aviation grade 100 octane LL fuel. Automotive fuels may contain > alcohol and aromatic additives that will attack the epoxy. Vinyl ester > resin is not susceptible to chemical attack by automotive fuels. It is a common misconception that autofuel will degrade epoxy resin. This is not necessarily so. I prepared two sample coupons of Last-A-Foam and EZ-Poxy. One coupon was saved as a control. One half of the test coupon was fully submerged in autogas and the other half was not. This coupon remained in a sealed container for over four years with absolutely no degradation. There was no loss of strength, there was no sediment, and there was no discoloration of the gasoline. After the coupon was removed and dried off, it was impossible to tell the difference between it and its control coupon. The two things that must be done to ensure a chemically resistant gas tank is to have the mixture ratio correct and completely mixed. If your resin/hardener ratio is off, there will be an uncured component in the final epoxy matrix. It can dissolve in an solvent. The same is true if you do not mix the components sufficiently. Epoxy will work with autogas but your quality control is important. Don Reid - donreid "at" erols.com Bumpass, Va Visit my web sites at: AeroFoil, a 2-D Airfoil Design And Analysis Computer Program: http://www.eaa231.org/AeroFoil/index.htm KR2XL construction: http://users.erols.com/donreid/kr_page.htm Aviation Surplus: http://users.erols.com/donreid/Airparts.htm EAA Chapter 231: http://eaa231.org Ultralights: http://usua250.org VA EAA State Fly-in: http://vaeaa.org
