Rapid Cure, Environmentally Acceptable Liquid Shim

During aircraft assembly, a liquid shim is applied before joints are mechanically fastened to make the joined surfaces fit tightly and to strengthen the joints. Current liquid shims provide excellent physical properties but typically require 8 hours or more to cure and 5-7 days to develop full strength. Unfortunately, this long cure time results in a bottleneck in the aircraft assembly flow. To remove the bottleneck, the U.S. Air Force is looking for a new liquid shim that cures in 1 hour and can be machined in less than 4 hours. Further, it is looking for a more environmentally friendly formulation. During previous work TDA Research, Inc. (TDA) developed a new shim curing chemistry that allows for a reasonably long application time (60 minutes), but short times to machinability (4 hours). The objective of this project is to use TDA’s chemistry to develop a formulation that meet Air Force requirements in terms of curing kinetics and physical-mechanical properties of the cure material. TDA’s formulation will contain no crystalline silica and no VOCs.