Insulation of Co-axial Cables

Dear All,

For Solid HDPE Insulation over Solid Copper Conductor do we need to use special grades of HDPE Compound as the thickness of Insulation is very high (0.8mm to 1.3mm). Or is there any other means to maintain the concentricity of Insulation with such high thickness during extrusion.

Thanks

Hello Once more Shekhar

First, I am very surprised to hear you want to use solid HDPE for the dielectric in coaxial cables because the closer you get to a theoretical air core dielectric, the better the transmission characteristics.

Secondly you will also have to preheat the copper conductor and use gradient cooling to improve adhesion to the conductor and reduce shrink back.

Are you sure you are not talking about foam polyethylene?

Anyway, the following is appropriate to solid HDPE extrusion in your case.

(1) Electrically preheat the conductor
(2) Use a high accuracy fixed center cross head and tooling.
(3) Fast cool with hot water once the insulated wire exits the cross head.
(4) Gradient cool for as long as practical.
(5) Use an accurate X-Y laser diameter monitor to check for insulation sag or ovality once the wire is cold and dry. Modify gradient cooling to achieve optimum results.
(7) Check the center (Concentricity) after every reel.
(Use an extrusion recipe for repeatability.


Regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com