Encapsulated%20Wirejoints

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 gt .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)

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
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