Encapsulated Wirejoints

W. EbensteinDuke University

Title: (AIATL_LOGO2.eps)Creator: Adobe Illustrator(r) 6.0CreationDate: (4/3/97) (11:26 AM)

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




Procedure:1. set up wires with joints on racks2. Mylar tube already on wire near joint3. capillary action fills tube with glue4. slide filled tube over joint, center it5. apply heat (~120 ºC) to shrink tube,

force out some glue at ends6. wipe off excess glue7. inspection8. allow glue to cure overnight9. string directly out of storage rack




Prototype setup:• have encapsulated ~ 100 joints

camera

Heated copper block

wires




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




• Tubing is .46 mm i.d. x .013 mm wall x 10 mm long before shrinking

1 mm




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 barrier Glue barrier

excess glue gets wiped off

air




Example of quality inspection: (all in mm)Wire # Left tubing Left glue Right glue Right tubing

1 3.2 1.6 -0.4 -0.4

2 0.0 0.0 3.2 3.6

3 2.8 2.0 0.1 0.4

4 2.0 1.6 2.0 2.0

5 2.4 1.6 0.4 0.4

6 1.6 0.8 0.4 0.4

7 2.4 2.0 1.2 1.2

8 2.4 1.2 2.4 2.8

9 2.0 2.0 1.6 2.8

10 2.8 2.0 0.8 1.2

11 0.0 0.0 4.0 4.4




Wire # 3 from table – rejected:

“6.0”




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?




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




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

Encapsulated Wirejoints

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