The conventional way of handling tubing made from plastics with colorants, radio-opaque materials, or other additives, has been to compound the plastic first, usually in a twin-screw extruder, and then put it in a single screw tubing extruder to make the tube. This is very cost ineffective. Further, it means running the plastic through an extruder twice, and this can be very detrimental for PVC or other heat-degradable plastics.
Some processors have tried combining the compounding process with the tubing extrusion using twin screw extruders. But twin screw extruders are very expensive, both in initial cost and in maintenance.
Now for the first time it is possible to do both the compounding of the plastic and the tubing extrusion in a single pass with a single screw extruder, and at a cost negligibly higher than that of the tubing line alone.
The key is the use of the Harrel MIXTRUDER, which, for the first time, is able to offer mixing as good as a twin screw extruder, but in a single screw machine. If you need to introduce a colorant, a radio-opaque additive, a foaming agent, or any other additive to the plastic, you can do a rough tumble-mix at room temperature, and then put the mixture in the hopper. Or, a more sophisticated method is to use a multi-component weigh feeder to introduce the appropriate proportions of each component into the hopper. Either way, it represents a real breakthrough in extrusion technology!
The key to the performance of the MIXTRUDER is, of course, the new Rauwendaal CRD mixing screw. This screw introduces two elements missing from standard mixing screws -- elongational mixing, and reentrant flow. The result has been demonstrated in repeated tests to be equal to or better than the mixing heretofore only available in twin screw machines of two or three times the cost of the MIXTRUDER.
With suitable modifications to the barrel and to the hopper arrangement, the MIXTRUDER can also handle powder feed stock. This holds out the promise of even further reductions in cost over present methods.
Harrel SINGLEPASS techniques are available in any TUBETROL extrusion lines, whether for straight tubing, for multi-lumen tubing, or bump tubing. They can also be used in the new Harrel ALTERNATE POLYMER extrusion system. It is also possible to retrofit existing Harrel tubing extrusion lines.
You can't buy a finer tubing extrusion line than a Harrel SINGLEPASS TUBETROL line!