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Method - connector repair and body overmoulding

Problem

Cables tend to suffer wear, often catastrophical. A cable damage is the most common fault that leads to decommissioning of an otherwise perfectly functional device. The most common points of failure are the spots where the cable is exiting a rigid plastic overmould of the connector body.

Solution

The repair is fairly simple. The original connector body has to be removed, the damaged section trimmed from the cable, and a new overmoulding formed on the connector.

The advantage of self-forming of the overmoulds is less reliance on the shapes and sizes of commercial offerings; the resulting connector can be much more compact and better fitting to the application, whether it desires straight or angled cable exit.

The alternative for hot-glue overmould is using e.g. Sugru. For some, the advantage may be easier processing and different mechanical properties. The disadvantage is the fairly long time it takes to set (typically 24 hours). For extra-tough connector bodies, polycaprolactone moulding can be used.

Overmoulding removal

The first step is removal of the old overmoulding. The materials are deposited in layers that often do not perfectly adhere and can be separated with the aid of longitudal cuts, by a blade or wire cutters.


Original connector

Original overmolding stripped

Second overmolding layer stripped

Insulation stripping and solder coating

The wires in the cable are often strands of thin enameled wires. These are somewhat difficult to strip. Two methods are working; gentle scraping with a blade, or flame-burning.

As the wire strands often contain plastic fibers, or the enamel itself is flammable, a flame barrier has to be placed along the wire; holding the wire in tweezers or pliers does the job well. A flame from a small torch (a little blue-flame cigarette lighter is sufficient) is blown at the wires until the insulation burns off (but not until the copper melts, that's too much). Aggressive flux is recommended here due to the presence of copper oxide coating; it can be washed off later.

Some cables use plastic insulation sleeves and no enameling. These are easier to solder as only conventional mechanical stripping of the plastic layer is needed. Sometimes an aggressive flux is also required, as some plastics corrode the copper over long time.

The connectors then get soldered back to the wires. At this stage an electrical test is strongly suggested to be performed.


Wire ends

Wire ends, held and insulation flame-burned

Solder-coated wire ends

Connectors resoldered to wires

Overmoulding forming

The last operation is crucial for sustained reliability. A new connector body, including strain relief, is formed from a suitable material.

Good materials for this purpose are hot-melt adhesives. They come in a range of properties, with different rigidity, tack, melting point, and time they stay molten ("open time").

Three different glues are ideal for the purpose of overmoulding. A higher-strength, more rigid glue, for the internal structural support, to hold the wire and the connector together so they would not be torn apart. A lower-strength, more rubbery glue, for making the gradually tapering-off strain relief, which spreads the curvature of the cable over larger area and smaller angles, dramatically reducing the wear (this is crucial to get right). And an optional colored glue, to provide a color code for the connector (e.g. green for headphones, red for microphone). The colored glue used in this example has the advantage of having more waxy surface, less tacky and dust-attracting than the second layer.

For the first layer, a Steinel-brand high-strength glue was used. For the second layer, a generic transparent-ish soft polyvinyl-alcohol-based glue stick was employed. The third layer was made again from Steinel brand, a colored glue for crafts purposes.

The deposition is done using a torch (or a small hot-air gun). The end of the glue stick is melted and glue is rubbed onto the places where it should be. A quick blast of hot air or flame then remelts the outside layer and lets it flow into a smooth, pretty surface. This has to be repeated multiple times until satisfying result is obtained, layer by layer. Care has to be taken with flame to not damage the wire insulation just next to the strain relief, as weakening of it there would negate the strain relief's purpose and concentrate deformations and stress to the weakened spot.


Hot-glue overmolding, first layer

Hot-glue overmolding, first layer

Hot-glue overmolding, first layer

Hot glue overmolding, second layer

Hot glue overmolding, second layer

Hot glue overmolding, second layer

Hot glue overmolding, third colored layer

Hot glue overmolding, third colored layer

Hot glue overmolding, third colored layer

Hot glue overmolding, third colored layer

Hot glue overmolding, third colored layer

Hot glue overmolding, third colored layer

Hot glue packs

TODO


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