Vacuum Degassing System Used by NONA Composites to Create Part for NASA
LACO Technologies has provided a vacuum degassing system used by NONA Composites to create a part for NASA’s space program reports this blog posting by Composites World magazine. Once again, LACO Technologies is proud to provide vacuum systems used by leading manufacturers to produce or test parts bound for future space missions.
When epoxies or silicones are mixed with the required additives, accelerator, filler etc., air bubbles become trapped within the mixture. Vacuum degassing is the process of using vacuum to remove gases from compounds which become entrapped in the mixture when mixing the components. If not removed before the material cures then the air bubbles will cause defects such as nodules, cavities, hollows in the finished cast. Sometimes such defects remain out of sight just below the surface only to appear after a period of use. Alternate methods can be used to remove or minimize the quantity of air bubbles, but vacuum used in degassing applications can improve the quality of products and shorten processing.
A vacuum degassing system comprises of two main items; a vacuum chamber and pump. To select a vacuum chamber for your purpose, ensure that your container will fit into the chamber and that there is sufficient space in your container to allow for expansion of the liquid to be degassed. When this mixture is put into the vacuum degassing chamber and the air pressure above it reduced, i.e., evacuated, then the air bubbles which were formed now expand and rise to the surface where they burst. In practice, vacuum degassing causes the whole mixture to expand to about two to six times its original volume before expansion decreases. This process can take from one to several minutes depending upon the nature of the mixture, the volume of the vacuum chamber and the speed of the vacuum pump used with it. Mixing can be done by hand or an electric mixer before degassing, depending upon the quantities involved. Mixing of the product can also be performed in the vacuum chamber to enhance and speed up the degassing process. If degassing is too slow, then you may need to either increase the evacuation speed by changing the pump or decreasing chamber size to reduce the pump down time, or decrease the accelerator.
“NONA Composites (Dayton, OH, US) was spun off from Cornerstone Research Group (CRG, Dayton, OH) to commercialize two-part epoxy resin technology that enables room-temperature infused composites within hours using no additional heat source beyond the resin’s exotherm during cure. NASA is interested in this technology as one of a variety of materials and manufacturing methods for potential use in manufacturing large composite tools and structures for the Space Launch System (SLS) and other programs. NASA wants to take advantage of the weight and cost benefits of single-piece composite structures, but must remove the size restrictions and cost penalties of current processing to make these structures affordable.
Through Phase I and Phase II Small Business Innovative Research (SBIR) programs, Cornerstone Research Group and NONA Composites have been able to mature No Oven, No Autoclave composite processing to a Technology and Manufacturing Readiness Level (TRL/MRL) of 9. The latest demonstration reviewed at CAMX was a tool for fabricating a 1/10th scale petal (ogive and upper barrel) for a NASA SLS payload fairing. (Note: CWreported on a 1/6th scale tool made out of autoclave by Janicki in the Sep 2013 issue of HPC). The scaled fairing part made using NONA composites is approximately 192 cm long, 81 cm wide, and 41 cm high.
A master model for the tool was made by General Plastics (Tacoma, WA, US) using its FR-4718 high temperature polyurethane foam due to its low thermal conductivity and high temperature resistance. The machined foam was coated with Duratec vinyl ester primer and finished by hand. Airtech International (Huntington Beach, CA, US) Tooltec CS5 adhesive backed Teflon film was applied during the second tool facesheet fabrication described below.
The tool was built from the master model using NONA RT-177 two-part infusion resin. The resin was mixed by hand, degassed in a Laco Technologies (Salt Lake City, UT, US) degassing unit to an absolute pressure of 13.3 Pa (0.1 torr) over 10 minutes, and kept below 30 °C throughout the infusion. Simply stirring the resin maintains adequate temperature control for batches less than 1 kg. However, the larger batch size used for this tool fabrication required use of a static cold water bath and occasional stirring. Absolute pressure less than 133 Pa (1 torr) was maintained within the vacuum bag during infusion to increase fiber compaction and decrease laminate porosity.”