Manufacturers can significantly reduce feedstock costs for PVC pipe by increasing filler content. The engineering challenge is to guarantee a stable process and consistently good product quality even for highly filled pipe.
Krauss-Maffei’s 36D twin-screw extruders have proved outstandingly successful in processing highly-filled formulations. For PVC wastewater pipe, filler content of up to 65 parts (approx. 40%) chalk (CaCO3) is feasible. The highly filled pipes with diameters between 50 to 500 mm are used for transporting wastewater.
To facilitate processing of highly filled formulations, the extruders have special material feed, weighing and metering systems. The PVC dryblend and the CaCO3 are transported from the storage container to the hopper of the gravimetric metering unit with the help of a spiral feed screw. The hopper is fitted with shakers and agitators to prevent bridging.
In addition, all metering unit surfaces in contact with the material have a special coating to guarantee unimpeded material flow. From the metering unit, the material is transported via an agitator and a special twin-screw feed into the stuffing unit above the extruder feed throat.
The parallel twin-screw extruders in Krauss-Maffei’s 36D range are designed for optimal processing of PVC. They are capable of combining high output with maximum protection for the mechanical properties of the product.
In addition, these extruders deliver constant high pipe quality. The 36D extruders have internally heated screws and air-cooled barrels. Krauss-Maffei offers these extruders in four sizes: KMD 75-36, KMD 90-36, KMD 114-36 and KMD 133-36. The rheological design of Krauss-Maffei’s spider-type pipeheads ensures a homogenous melt and ensures perfect fusing of the melt downstream of the spider legs.
Hakan Plastik A.S. in Turkey specialises in manufacturing highly-filled PVC pipe and already operates five Krauss-Maffei extrusion lines for this application. Satisfied with the outstanding pipe quality, Hakan Plastik has now ordered two more lines for highly filled pipe. The systems are due to go into operation between March and June 2007.
Krauss-Maffei is represented in Oceania by HBM Plastics Technologies.