Poor Adhesion to conductor on Teflon Wire

First of all, my company is the end user of the wire and not a manufacturer.

We use various copper with silver coating wires with Teflon insulation. Lately, our production people have been complaining on how easy the insulation is slipping on the conductor due to poor adhesion. They also complain on the pull back of insulation after stripping. Please provide inputs on the possible root cause of these problems.

Your input is much appreciated.

Hello vudoan,

First of all I guess you know that polytetrafluoroethylene (PTFE, TFE or Teflon, a Dupont registered tradename) is not formed around a wire with a normal extrusion screw but rather with a ram extruder followed by a sintering process. (At least this is my 36 year old experience.)

Likewise, the copper wire must be exceptionally clean before the silver electroplating process and we assume it is still exceptionally clean and smooth after the electroplating process.

The Teflon is very inert and, after the sintering process, it has an exceptionally low coefficient of friction. This, combined with a very smooth conductor surface, make it really difficult to obtain any real adhesion between the insulation and the conductor itself. A stranded conductor however will exhibit better "apparent" adhesion because the outer helical grooves between the individual conductor strands provide a spot for the insulation to "key" into.

The "pull back of the insulation after stripping" is called shrinkback and it relates to "polymer memory" or inbred stress in the insulation. This can be from shock cooling of the insulation after ram extrusion or more probably after sintering, or by improper or lack of conductor preheating prior to extrusion. You must also be sure when stripping the insulation, your employees do not stretch the insulation remaining on the wire. In this case all you would see is the "memory" effect because of the inbred stress your employees actually placed in the remaining insulation during the stripping process.

The cleanliness of the conductor in this case does not enter the equation because we assume that the conductor is very clean after the silver plating process.

We recommend that you discuss this with your wire supplier's engineering staff very carefully to see if their process engineers can actually tweak their process a bit to give at least a little better adhesion of the insulation to the conductor.

I trust you appreciate the difficulty they will have in doing this.

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

vudoan,
Iam curious of what awg wire you are using.
There is alot of miconceptions about PTFE coating. First of all, PTFE is nothing but a "waxy" soft polymer.It is not a harder more robust coating untill a binder has been added. If the company that is supplying you're PTFE coating is blending their own formulation, they may not be blending correctly.I only ask what awg wire it is because Iam interested to understand if the coating process is extrusion,electro static, or dip process.Also, the silver plating process can cause a horrible surface to coat in regards to adhesion if the wire has not been fully cleaned from the silver plating process. It takes alot of cleaning to fully remove some of the chemicals left on the conductor after a silver plating process.

We have the most problems with the smaller gauge wires. Especially 22 AWG. The problem is intermitten from spool to spool.

Thanks for the reply.

Twxh 1,

Isn't if funny when one says the smaller sizes such as 22 awg.

Richard

tech1 & spectre,

It is good to hear from the two of you. I thought you both had become bored with it all and thus I have been struggling along without your much appreciated input.

Richard, I really enjoy that fine wire perspective.


Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com