1. Sep 19, 2010

### soltice_9

Hi,

I'm having trouble producing 22 AWG polypropylene cable. I keep on getting "missing insulation" and "reduced insulation".

The Extruder Head I'm using is quite old and I'm not sure that it is "centered". But a mechanical engineer told me not to worry, it doesn't mater if the Head is positioned to the side a bit, the conductor going into it will "self-center" itself! He was very adamant that the concept of self-centering works. I'm not sure how that works, because I'm not a mechanical engineer.

I'm thinking about getting a preheater, but I'm hoping for a lower cost solution (I was told the preheater is $30k). Thanks 2. Sep 19, 2010 ### Danger I must admit that from an engineering standpoint, I have no idea what the hell you're talking about. Going strictly by the English language, it makes sense, but I might not be grasping the finer details that an engineer would.$30,000 for a pre-heater??!! WTF?! You don't have to bathe the bloody thing in liquid gold just to warm it up.
I have no idea of what scale is involved, so I'm just going to toss out an idea or 3. Microwave or ultrasonic heating on-station. Deposit the cable in a steel tube and run it through an induction coil. Maybe high-intensity IR lamps.
I can probably think of some other stuff in the future, but that's it for now. I am currently on my 31st, 32nd, and 33rd shots of Scotch (I like to car-pool), so my analytical abilities are somewhat stifled.

3. Sep 21, 2010

### jpckmg

soltice_9:

Self-centering is a phenomenon in cable jacket extrusion in which the melted plastic envelopes the conductor and forces it to the middle of the extrusion. The injection pressure allows the plastic to provide inward forces on all sides of the extrusion which are greater than the forces which move the conductor to the sides.

The problem with "missing insulation" or "reduced insulation" is one of variation in injection pressure, melt temperature, or conductor pull speed. There is no need to add another heater as the heating elements of your extrusion machine should be more than adequate to get a consistent flow.

"Missing insulation" and "reduced insulation" are the same problems of different degrees. The conductor is moving faster than the plastic melt. Therefore, find the sources of variation. As a last resort, slow down the pull so you are less susceptible to narrowing.

BTW, I'd like to be in Danger's carpool.