Krauss Maffei: Double-strand core extrusion for lower capital investment

In profile manufacture, coextrusion can cut costs substantially. For example, producing a profile with a regrind core covered with virgin material in all visible areas sharply reduces material costs.

Schüco International KG has recently invested in a profile system using core extrusion technology. Schüco International is a global player, developing and marketing complete systems using plastic, aluminium and steel. One current project combines double-strand extrusion with core technology. Double-strand extrusion produces two profiles simultaneously. This reduces both the capital investment and the required floorspace for the extrusion line.

Schüco embarked on a cooperative project with Greiner Extrusion and KraussMaffei Berstorff to develop a double-strand extrusion solution for producing its 5-chamber main window profiles. The big challenges were to design the die, to split up and manage the melt streams, and to come up with a cost-effective extruder concept. The combined know-how of the three partners made it possible to meet these challenges in a remarkably short time.

Pressure-optimized channel system
The material ratios in Schüco’s main window profiles are around 60% virgin PVC and 40% regrind. The new system uses two extruders, both of which supply both strands. The melt streams are split via a pressure-optimized channel system so that they reach the dies in the required pattern. The two extruders need to be positioned very close together in order to feed the channel system effectively.

The concept uses two separate KMD 90-36/P profile extruders from KraussMaffei Berstorff, each on its own base frame. The main control cabinets are positioned at a distance from the extrusion line. Two extra compact control units, positioned close to the extruder output zone, house the die control circuits and the operator panels. Both operator panels (one for each extruder) are on the operator side. Each extruder can be operated separately, or the two extruders can be operated in synchrony. This gives Schüco maximum flexibility to respond to future requirements.

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