W. Ebenstein Duke University Encapsulated Wirejoints Motivation: To use existing “proven” glass...

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 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




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

W. Ebenstein Duke University Encapsulated Wirejoints Motivation: To use existing “proven” glass...

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