High Speed Extrusion

We have been using Rosendahl high speed extruder for the manufacturing of single core unsheathed flexible multi strand and rigid strand cables.

There is no arrangement for preheating the PVC-compound in the hopper. However, we are preheating the compound in the mixture and feeding this in to the hopper. The problem that we have been encountering through the process is, finished cables have smooth and shiny insulation covered at line speed up to 200 m/s whereas for the higher line speed above this, the extruded insulation is dull and rough. Has this problem occurred due to the poor heating system or due to the PVC-compound that we are using.

The hardness of the PVC-Compound is 88 Sore-A. We have also heard of special PVC-Compound for high speed extrusion.
I have here attached the test report of the PVC-Compound manufacturer.

Please suggest us to overcome this problem.
Your valuable suggestions are highly appreciated.

Hello Amar,

When you preheat PVC pellets you must be very careful to make sure the pellets do stick together in the extruder hopper and bridge the throat of the hopper. Many use vibrators on the outside surface of the hoppers (Air or Electric) to prevent bridging inside the hopper. Experimentation is necessary to prevent pellet compaction that could make the problem worse

It would seem to me that you are at the limits of the extruder to properly extrude this particular PVC compound. You neglected to tell us what kind of extruder screw are you using, the diameter of the extruder and the L/D ratio of the extruder but care must be used there as well as burning by shear is always a potential issue.

We suggest that you start communicating with Rosendahl as follows:

Rosendahl Nextrom GmbH
Schachen 57
8212 Pischelsdorf, Austria

Phone: +43 3113 5100
Fax: +43 3113 510059
www.rosendahlnextrom.com
This email address is being protected from spambots. You need JavaScript enabled to view it.

- Provide them with the model number serial number of the extruder and the information on the screw.
- Provide them with the data sheet for the compound you are using and your speed limitation issues.

Please note that 200 meters per second is 39,370 feet per minute which is inordinately fast and quite unlikely. We therefore think you have made an error in describing the line speed. Please double check.

Rosendahl Nextrom GmbH will have a booth at wire Dusseldorf in April.

Thank you.