Extrusion of Polidan® XLPE and Polidiemme® XLPO - FAQ

Frequently Asked Questions

Can we use any kind of PVC or PE screw for these materials?

No, all kind of screw design can be used; mixing zones, pins, Maddok zones and similar on the screw profile must be avoided; in these zones the material could give place to stagnation that, when released, appears on the cable surface as lumps

Can we expect a similar throughput as PVC or PE from my extruder?

Yes, the throughput of your extruder will be more or less the same; using a standard PVC screw with single or double flight, the maximum line speed will be 80-100% compared to PVC

What is the maximum actual melt temperature that material can reach during processing?

The maximum temperature measured at the exit of the die is 220°C (428°F) and optimal one is 170-180°C (338-356°F)

What happens if we use an extruder longer than 25 L/D?

Due to the longer residence time of the material in the extruder and the increased mixing, normally a reduction to 2/3 of the Catalyst MB will be required without loss of crosslinking rate or ageing performances

What happens if we use an extruder shorter than 25 L/D?

The material could not be plasticized enough (poor mechanical properties) not good homogenization of catalyst and of color master batch. Proper processing temperature profile needs to be set.

What is the impact of screw diameter on processing?

Normally, the smaller the diameter of the screw, the better the control on the melt temperature is. We suggest extruders not larger than 120 mm

Can we use the cooling of the screw to control the melt temperature?

The screw cooling may determine a gradient of temperature and viscosity of the material along the depth of the flight, with possible decrease of mechanicals and increase of friction; cooling of the screw is normally not suggested

Can we run at low screw speed or stop the extruder with material inside?

A too long residence time in the extruder may cause a start of material pre-crosslinking; at the beginning of the extrusion, it is suggested to run slowly (5-8 rpm) just for 5-10 minutes, then speed up over 10-12 rpm; never interrupt the extruder to run for more than 2-3 minutes; in that case, use a by-pass valve on collar to purge continuously the material at low speed

What differences do we observe in processing the material with and without the Catalyst MB?

Adding the Catalyst MB means a decrease in the current load (5-10%) and the backpressure on collar and crosshead (5-10%). It has the effect of fluidizing, easing the material melting and decreasing viscosity and friction

May we grind and recover scraps during extrusion?

No, scraps cannot be recovered at any time