Rough XLPE Insulation

This was sent by to me by Mr Mohammad Zaree

"We started extruding XLPE on LV cables and we have problem with it. It occurs in most of the sizes.

The outside surface of the insulation becomes rough after coming out of the cooling water in all the colors..

We tried to adjust most things but nothing worked. We changed the temperature zones, exchanging the master batch extruders with the insulation extruders,but no improvement.

The problem still remains. If some one could help us we would be really appreciative."

Thank you.

We assume that you are manufacturing a one-shot, three component, saline-grafted, moisture cross-linkable polyethylene system consisting of a proper (Density Please!) XLPE base compound rated for the appropriate voltage, a catalyst master batch approved for use with the base compound and a color concentrate fully compatible with the two other components..

We are however unclear on your statement "masterbatch extruders" as this tends to conflict with a one-shot.extrusion process.

If you are getting a rough surface after extrusion, make sure of the following points: (This is most appropriate for a "one-shot" XLPE colored insulation.)

1) That the components were properly sealed before use and that all the components are completely dry.
2) That all components are within their shelf lives,and that all have been stored in accordance with the directions on the packages and on the materials sheets.
3) That all components are all dried before extrusion n accordance with the directions on the packages and the material data sheets.
4) A gravimetric mixer must be used at the extruder hopper so that all components are precisely mixed by weight. Do this at the extruder hopper so there is no random compound segregation by the hopper loading system. Properly seal unmixed material that was not used in the run (left over) and discard any left over mixed material. At the end, properly wipe out the hopper with a clean rag..
5) The die must have a land or bearing appropriate to the density of the base XLPE material you are using and if high or medium density may require gradient cooling.

These items should resolve your Vinyl Silane XLPE extrusion problem.

First of all I say thanks to you Mr. Stewart-Hay for your answer.

i want to complete my question and write my experience with this problem.

Two days ago I took a sample from the line which i spoke about. The size of wire was 1 mm^2, the color was white but surface was awful with lost of rough and very ragged i couldn't send you the picture.

I did the hot set test on the sample that that would not cure in vapor room and the result was incredible, The result was 55 percent, and acceptable to the standard. i mean the sample was pre-cured in the extruder barrel. There was the answer to my rough and ragged insulation.

Thank you for the time you awarded to me.....