Thomas Jefferson National Accelerator Facility Page 1 Clear Mold VPI Visualization D. Kashy S. Christo May 14, 2014

Thomas Jefferson National Accelerator Facility Page 2 Test Objectives Test system proposed by JLab to study the process and components on a small scale test Learn about gravity feed to the molds Learn more about resin distribution through tight spaces (vacuum loaded glass cloth) Show that peel ply in mold does not impede progress of the resin

Thomas Jefferson National Accelerator Facility Page 3 Setup Mixing/Degassing vessel Secondary Degassing/Reheating Vessel 2 Molds with same space for materials Same materials in each mold –2 layer of e-glass cloth 0.005” thick –1 layer of nylon peel ply 0.005” thick Tygon tube ¾”ID and ¼”ID Clamps for tubes to act as valves

Thomas Jefferson National Accelerator Facility Page 4 Schematic

Thomas Jefferson National Accelerator Facility Page 5 Process Summary #1 Assembly system Pump overnight to degas with molds and tanks at 60C Start a Logbook and note all actions (click HERE to view logbook)HERE Leak test with helium (not good for RTV) Do Rate of Rise tests on system –Full system –Molds independently –System w/o molds Pre-heat Parts A and B overnight in over set at 60C Mix 1liter batch of resin in bucket first

Thomas Jefferson National Accelerator Facility Page 6 Process Summary #2 Pour resin into mixing/degassing vessel and degas approximately 1 hour Complete 3 ROR on resin as it degasses –Resin continues to degass during ROR because stirring brings resin from below the surface (at high pressure) to the top (at low pressure) –Evidence is that when pumped on the minimum pressure is quickly achieved

Thomas Jefferson National Accelerator Facility Page 7 Process Summary #3 Transfer resin to secondary vessel –At start of transfer the resin did not flow from first Mixing vessel –A plug was found in the bottom of the vessel (source may have been a used fitting plugged with other type epoxy from previous use) –Plug was broken by breaking vacuum and pushing rod through the bottom tube –Because the plug created an orifice that was small and the resin flowed down hill into a low pressure tank it further (boiled/outgassed) To view the transfer and bubbles in the tube click HERE HERE

Thomas Jefferson National Accelerator Facility Page 8 Process Summary #4 Start transfer to Molds –Control mold pressure by closing the valve to the pump opening it once in a while to re-pump as needed to keep the pressure between 3 and 8 torr during filling –Molds a few inches below the Secondary vessel –Resin flow slowly but steadily in ¼”ID tube –Resin race tracked though perimeter groove –Adjust relative height between 4 and 24” below tank to adjust flow rate into molds To View start of resin transfer click HEREHERE

Thomas Jefferson National Accelerator Facility Page 9 Process Summary #5 Slow resin flow to allow wicking –A characteristic dimension was noted that the width of the wicking was the same for both the slotted mold and the plain mold –Flow to molds start at 12:02 from logbook 12:11 (9 minutes) 12:28 (26 minutes)

Thomas Jefferson National Accelerator Facility Page 10 Process Summary #6 After much time both molds fully race-tracked 13:08 (1 hr 6 minutes) 12:48 (46 minutes)

Thomas Jefferson National Accelerator Facility Page 11 Process #7 Before backfilling we took fill rate of the plain mold We got a flow of ¾” height in ¾” ID tube in 3 minutes thus 2cc/minute If the flow to the second mold were the same then the total would be 4cc/minute This is for a ¼” ID tube 6 ft long with 2 ft of head Scaling to a ¾” ID tube 6 ft long with 2 ft of head we get 3 to the 4 th power so 81 x more flow thus 324 cc/minute – NO PROBLEM with gravity filling from degassing vessel to mold

Thomas Jefferson National Accelerator Facility Page 12 Process Summary #8 Collapse the dry void with resin from the outlet tubes To see the first pressurization cycle click HEREHERE

Thomas Jefferson National Accelerator Facility Page 13 Summary ROR tests were more sensitive to determine leaks and Outgassing level Mold at 3 to 8 Torr was sufficiently HIGH pressure to keep resin from boiling in molds and sufficiently LOW to allow full collapse of dry sections of coil Grooves in mold worked well to distribute resin much more quickly throughout the coil (90 degree bevel groove 3mm wide and 1.5mm deep is sufficient spacing between groove should be ~2.5”) Wicking with mold covers collapsing on the fiberglass cloth is very slow and gets slower as the mold fills Overnight the Polycarbonate covers popped off the aluminum and the molds drained

Thomas Jefferson National Accelerator Facility Page 14 Lessons learned Flow test through the inlet and outlet tubes to be sure lines are not blocked during setup Do not count on RTV to mechanically restrain the clear mold cover Install catch pan below molds just incase there is a leak

Thomas Jefferson National Accelerator Facility Page 15 Possible Future work in small molds Add sight glass tube at center of molds to see how they fill with and w/o channels ** –This would be a way to see the resin progress through the coil at center turns since the coil mold plates are steel ( Use ¼”ID tygon to limit the amount of epoxy needed to fill tube since its source will be limited by wicking and or during the backfilling process) –Put in strips of 0.003” glass to see if that works like the channels * Tests could be done with soap to save time ** One could even pump on just those tubes to draw resin in to coil center if needed

Thomas Jefferson National Accelerator Facility Page 16 Addendum We decided that we must be able to add flow distribution channels to the molding process and that we needed to be able to visually inspect the coil impregnation. So how to do this. VPI in vacuum bagging often uses media that increases flow path for resin. For our application we need a “stiff” material that allows flow. Industrial Netting produces an extruded polypropylene mesh Samples were obtained and visualization tests confirmed it as an easy way to add flow channels to the process and to take up the extra space in the mold since the copper was being removed. Test with resin and heat confirmed its acceptability. It was tested with 70cm molds and finally when Bleeder B was used it showed to be an acceptable matial in all aspects