W. Ebenstein Duke University Encapsulated Wirejoints Motivation: To use existing “proven” glass joints but protect them from chemical attack Design: start with standard joint surround with Mylar heatshrink tubing not protective, just to contain glue fill with Stycast 1266 (potting glue) covers whole joint with extra at ends glue must be low viscosity

W. Ebenstein Duke University Encapsulated Wirejoints  Procedure: 1.set up wires with joints on racks 2.Mylar tube already on wire near joint 3.capillary action fills tube with glue 4.slide filled tube over joint, center it 5.apply heat (~120 ºC) to shrink tube, force out some glue at ends 6.wipe off excess glue 7.inspection 8.allow glue to cure overnight 9.string directly out of storage rack

W. Ebenstein Duke University Encapsulated Wirejoints  Prototype setup: have encapsulated ~ 100 joints camera Heated copper block wires

W. Ebenstein Duke University Encapsulated Wirejoints  Closeup of heater block and joints air 6 mm above block ~120 ºC tube shrinks in ~ 3 seconds too hot for too long hardens glue

W. Ebenstein Duke University Encapsulated Wirejoints Tubing is.46 mm i.d. x.013 mm wall x 10 mm long before shrinking 1 mm

W. Ebenstein Duke University Encapsulated Wirejoints  After heat shrinking: finished length ~ 8 mm finished diameter ~.4 mm Quality control: ends of glass must have >.3 mm glue no air channels tubing fully shrunk no protruding glue on outer surface glass joint ends glue barrierGlue barrier excess glue gets wiped off air

W. Ebenstein Duke University Encapsulated Wirejoints  Example of quality inspection: u (all in mm) Wire #Left tubingLeft glueRight glueRight tubing

W. Ebenstein Duke University Encapsulated Wirejoints  Wire # 3 from table – rejected: “6.0”

W. Ebenstein Duke University Encapsulated Wirejoints  Quality problems: asymmetry of tube position glue beads left on wire – will this section be inside center wire support? Stringing implications: joints are longer and fatter – more friction through twisters not stringing from continuous spool – cleaning implications?

W. Ebenstein Duke University Encapsulated Wirejoints  Advantages: uses strong glass-to-wire bond protection by approved glue uses existing inventory of joints relatively “low-tech” encapsulation is “batch” process could be done at stringing sites  Disadvantages: larger size of finished joint extra dead region from glue beads? cost, time add to existing budget for glass joints, not instead of shipping/storage/cleaning/stringing uses rack system instead of spools

W. Ebenstein Duke University Encapsulated Wirejoints  Estimate of cost / time: new tooling: setup racks for wires, with auto. tensioning inspection microscopy glue application system, centering jigs heating system to evenly shrink whole batch shrink tubing: ~ $0.20 each labor (add to existing joints) ~ 1 hour for batch of 30 wires: slightly slower glass joint production to add tubes on wires possible slower stringing if joints get stuck in twisters  Continuing work: trying different tubing (.36 mm diam) trying to develop tooling to cure asymmetry / high rejection rate