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Extrusion scrap reduction
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TOPIC: Extrusion scrap reduction

Extrusion scrap reduction 2 years, 3 months ago #145

Hello dear colleagues

Kindly advise of possible methods that can be applied to reduce scrap on XLPE extrusion processes (reducing bleeding, material mixing defect & usage of catalysts)

Mostly, bleeding should be controlled to reduce the amount that is used while on start up & changeover

Thanks for any comment.

Re: Extrusion scrap reduction 2 years, 3 months ago #146

Hi eraser,

Can you please be a little more specific about your XLPE process (Horizontal steam, catenary dry cure, vertical dry cure or moisture cure) and the size of the conductor. Thank you

Peter Stewart-Hay
Stewart-Hay Associates

Re: Extrusion scrap reduction 2 years, 3 months ago #147

Hi Peter

Actually my question was in general but can be specific to the following:
Steam curing after horizontal normal single screw extrusion process.
The conductors mostly are Cu with sizes 300mm2 & 240 mm2

Thanks in advance

Re: Extrusion scrap reduction 2 years, 3 months ago #148

Hello Again Eraser,

That is good size conductor for a single extrusion line so suspect that you are manufacturing service entrance low voltage cable (No shields.). Likewise I imagine you have a large extruder, say a 24:1 with a 120 mm barrel.The most important method of reducing is to make a quick start with very little bleeding. This means:
- That the extruder, screw and crosshead be in like new condition.
- That the preheater is working perfectly.
- That the line controls are working perfectly.
- That the thermal controls and screw water cooling system are all working perfectly
- That the crosshead be equipped with mechanical read-out centering bolts so that the proper set-up can be made before any plastic is introduced. (Recipe parameters.)
- That operator training must be top of the line so that they always run to the minimum wall thickness.
- That scrap is measured after every shift and plotted by machine and shift so that more corrective action can be instituted.
- That all length measurement equipment be calibrated once per month so that extra length is not going out the door gratis.
- That the unabsorbed material variance be plotted in kilograms per week so that all know what is going out the door essentially as over-sized cable.
- That all instruments be re-calibrated and a proper check schedule be instituted.
Peter Stewart-Hay
Stewart-Hay Associates

Re: Extrusion scrap reduction 2 years, 3 months ago #149

Good day!

We have already conducted a study regarding the scrap extrusion reduction on change over.
- the machine must have an auxiliary extruder because it is much smaller.
- the set-up time on pay-off must not be more than 5 minutes.
- Run the screw at 1-2 RPM during the set-up.
Now we are on the process of studying extrusion scrap on XLPE CB
I have some questions regarding XLPE CB:
1. Why is it that when we are using XLPE CB, it burns easily when the machine stops for a minimum of 20 seconds.
2. Can we use the auxiliary extruder for OHL?
3. Can we use tube tooling rather than pressure tooling? It tube tooling we can bleed while setting up the pay-off drum but in pressure we don't bleed because the plastic might get inside the tooling.
Thanks for the help.

Re: Extrusion scrap reduction 2 years, 3 months ago #150

Hello jprs_ie,

Are you the same person as "eraser"? We did note that you are in the same city.

As I understand it, you have two separate, permanently mounted extruders so that you can extrude an XLPE (CB){carbon black} inner semi-conducting shield in tandem with the XLPE insulation extruder. Likewise, I expect you can bypass the inner shield extruder by removing the crosshead and run the CV line with insulation only. (Not XLPE CB (carbon black} but just XLPE). Is this correct?

To answer your questions:
1. Presumably your inner shield extruder is very small (Say a 2 1/2 inch or a 60 mm machine.) If your inner shield extruder is too large, running too hot or if there is no controlled water cooling on the screw, you will burn the XLPE CB when the screw is stopped. In other words you are running on the thermodynamic edge. This of course presumes you are NOT compounding your own XLPE CB and purchasing same from a reliable source like Borealis.

2. If the extruder configuration is as I described and assuming your line wire has insulation only, you cannot use the axillary extruder because there is no way to contain the steam in the CV tube. (Extremely dangerous with a rigged set up and something we do not recommend at all.) Moreover the axillary extruder would be far too small to economically manufacture the line wire. (Slow line speed.)

3 You cannot use tube tooling because the wall thickness cannot contain the steam (Very dangerous)! What some companies do however is to move the tip forward (If possible.) before start up and then slowly run the extruder to check and adjust the center before running the line. After adjustment, they stop the extruder and move the tip back to its proper position, close the splice box and start the line.
Peter Stewart-Hay
Stewart-Hay Associates
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