Epoxies are strong, durable, and highly resistant to heat and chemicals. As a result, epoxies are used in a wide variety of demanding applications, such as automotive and aerospace assemblies.
Problem is, epoxies can also take a long time to fully cure. Cure times measured in hours or even days are not uncommon. Moreover, curing time can vary considerably, depending on the temperature, mix ratio and amount of epoxy.
Long, variable cure times translate into work-in-process inventory, and assemblies that are sitting around curing aren’t making money for the manufacturer. To get bonded assemblies out the door as quickly as possible, researchers at NASA’s Langley Research Center (Hampton, VA) have developed a noninvasive system for monitoring the cure status of epoxies and other resins.
The system works by monitoring one or more compounds in the vapors emitted by epoxies as they cure. The concentration of these compounds in the air surrounding the epoxy is approximately proportional to the degree of cure. In other words, a high concentration of the compounds would indicate the epoxy is far from being fully cured. Conversely, a low concentration would indicate the epoxy is nearly done.
Developed by engineers K. Elliott Cramer, Daniel F. Perey and William T. Yost, the system promises to reduce the cost of the curing process, since assemblies would spend the least amount of time necessary to achieve a complete cure. Manufacturers would not need to provide excess curing time “just to be safe.” Manufacturers could also use the system to control the curing process to optimize the properties of the epoxy.
The heart of the system is a sensor for measuring the compounds in the vapors. Manufacturers have various options for the sensor, ranging from general-purpose, full-size laboratory instruments capable of detecting many different compounds, to microelectromechanical systems designed to detect compounds specific to one epoxy. Depending on the curing process, the sampling could occur at room temperature, at elevated temperature, under vacuum, or at atmospheric pressure.
During the curing process, the system can alert the operator when the concentration of a particular vapor compound reaches a predetermined level. Alternatively, the system can be integrated into a control loop that would turn off the curing apparatus upon completion of the cure. It could also be configured to control the rate of cure by automatically adjusting the pressure or temperature in response to certain levels of chemicals.
For more information, call 751-864-1000 or visit www.nasa.gov/centers/langley.