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TOPIC: XLPE curing temperature

XLPE curing temperature 3 years 10 months ago #692

I need some information related to the curing temperature required for XLPE insulation compounds
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Re: XLPE curing temperature 3 years 10 months ago #693

Hi there Bighead,

This is a very interesting question and somewhat difficult to answer as most seemingly straightforward technical questions are. In fact, you really should be discussing this with your chemical laboratory and your XLPE polymer suppliers.

As I recall, the temperature to achieve crosslinking is somewhere around 210C (410F) with a range of 210C (410F) to 215C (419F).

If, in saturated steam, steamcure, the gage pressure is around 18 to 20 bar (260 psi to 290 psi gage).

If you are using an electrically heated tube with an inert gas atmosphere (drycure), you need a gage pressure somewhere between 5 and 10 bar (72.5 and 145 psi gage) to prevent the formation of voids due to organo-peroxide (dicumyl or di-tert-butyl peroxide) decomposition products.

Now, there is one fundamental thing that must be achieved in any CV tube. The inside surface of the polyethylene insulation, immediately adjacent to and in intimate contact with the conductor must get up to that 210C-215C temperature for a period of time. This takes time because the heat comes from the outside of the insulation and that necessary time for the heat transfer controls the line speed against the length of the curing tube. This is why conductor preheaters are used with triple crossheads - anything to reduce the cooling effect of the conductor itself on the inside surface of the insulation. The driving force for the heat transfer is the higher temperature of the outside surface of the insulation and in a dry cure line this is even thermally more complex because of both radiation and convective heating by the CV tube itself.

In drycure lines, the temperature of the outside surface of the XLPE must not get so high for the pressure in question that you are using that the cooling water begins to boil at the cooling section when the polyethylene is quenched. If this happened you would have in effect inadvertently created a steamcure line. This will also give very high high insulation shrinkback and excess organo-peroxide decomposition products in the dry cure atmosphere itself. (Plus on the surface of the cooling water at the gas-water interface.)

I trust this answers your question.

Kindest regards,
Peter J. Stewart-Hay
Stewart-Hay Associates
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