thomas jefferson national accelerator facility page 1 clear mold vpi visualization d. kashy s....

Thomas Jefferson National Accelerator Facility

Clear Mold VPI Visualization

D. Kashy

S. Christo

May 14, 2014


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


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


Schematic


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)• 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


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


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


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 HERE


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)


Process Summary #6

• After much time both molds fully race-tracked

13:08 (1 hr 6 minutes)

12:48 (46 minutes)


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 4th power so 81 x more flow thus 324 cc/minute – NO PROBLEM with gravity filling from degassing vessel to mold


Process Summary #8

• Collapse the dry void with resin from the outlet tubes• To see the first pressurization cycle click HERE


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


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


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


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

thomas jefferson national accelerator facility page 1 clear mold vpi visualization d. kashy s....

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