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Encapsulated Wirejoints

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)

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Encapsulated Wirejoints

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  1. 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

  2. Encapsulated Wirejoints • Procedure: • set up wires with joints on racks • Mylar tube already on wire near joint • capillary action fills tube with glue • slide filled tube over joint, center it • apply heat (~120 ºC) to shrink tube, force out some glue at ends • wipe off excess glue • inspection • allow glue to cure overnight • string directly out of storage rack

  3. Encapsulated Wirejoints • Prototype setup: • have encapsulated ~ 100 joints camera wires Heated copper block

  4. 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

  5. Encapsulated Wirejoints • Tubing is .46 mm i.d. x .013 mm wall x 10 mm long before shrinking 1 mm

  6. 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 glue barrier Glue barrier air glass joint ends excess glue gets wiped off

  7. Encapsulated Wirejoints • Example of quality inspection: • (all in mm)

  8. Encapsulated Wirejoints • Wire # 3 from table – rejected: “6.0”

  9. 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?

  10. 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

  11. 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

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