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Encapsulated Wire Joints for Glass Joints Protection

Encapsulated Wire Joints use Mylar tubing and Stycast glue to protect glass joints from chemical attack. Procedure involves shrinking tubing over joints. Quality control ensures no protruding glue. Advantages and disadvantages discussed.

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Encapsulated Wire Joints for Glass Joints Protection

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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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