Krauss-Maffei: New Developments for Pipe-, Foil-, Sheet- and Profile-Extrusion

Krauss-Maffei: New Developments for Pipe-, Foil-, Sheet- and Profile-Extrusion

Coextruded pipe:
New adapter simplifies two-layer pipe production
The new two-layer adapter for coextrusion of a coating layer on polyolefin pipe guarantees an extremely uniform melt spread and can be retrofitted to pipeheads already in service. This make it a cost-effective choice for increasing production flexibility.
There is growing demand for polyethylene and polypropylene pipe manufactured with various types of coating layer for specific functions, eg, protection against soiling, and environmental influences or as colour coding. Conventional pipeheads for two layer extrusion are complex devices. The most common method of spreading the two melts over the whole pipe circumference is to use concentrically nested spiral distributor systems. In a spiral distributor, the melt stream from the extruder is first split into multiple streams. The primary distributor directs the melt into channels that spiral around the mandrel. The cross-section (width and depth) of these spiral channels decreases in the direction of flow, while the clearance between the mandrel and the wall of the die increases progressively, so that radial flow of the melt in the distributor reverts to an axial flow. The design and manufacture of distributor systems is challenging, partly because it involves leading a number of supply lines and cables for heating, temperature control, etc. through the primary distributor component. The inner and outer spiral distributors must also be exactly aligned. Even very small differences result in a non-uniform gap and non-uniform layer thicknesses. The result is unsatisfactory product quality. A further disadvantage of conventional systems is the lack of flexibility and the additional cost- separate pipeheads are required for single- and for two-layer pipe.

Krauss-Maffei's newly developed adapter for two-layer pipe eliminates these disadvantages. The adapter consists basically of two plates in which the distributor channels are integrated. The melt flows via a ring-shaped primary distributor to a number of coathanger distributors, spaced around the circumference. The flow channels in the adapter have been optimized using a modified resistance network calculation method. This approach, developed in cooperation with the University of Paderborn, makes it possible to analyse and optimize flow processes and results in a design that guarantees highly uniform melt distribution. The new adapter is very compact and can be connected beside the stripe adapter. The flow channels for the main component need not be modified. The adapter can operate with variously positioned coextruders, so that these can be located to suit the available space - to the side of the main extruder or piggybacked above it. In brief, Krauss-Maffei's new two-layer adapter offers a clear increase in production flexibility at an affordable cost and with excellent product quality.

Optimizing sheet extrusion:
Software simulation of cooling processes
Krauss-Maffei is using new simulation software as a tool in designing and planning downstream equipment for sheet and flat film extrusion lines. The innovative SCooP (Simulation of the Cooling Process) software was developed by the Institut fur Kunststofftechnik at the University of Paderborn/Germany. The software simulates temperature changes in an extruded polymer with a high degree of accuracy. In addition to using SCooP in planning all new sheet extrusion lines, Krauss-Maffei also offers customers the option of optimizing existing lines with the aid of the new software.
Cooling processes have a decisive influence on the quality of thermoplastic products. This is especially true of extruded film and intermediates, where the thermal history of the extrudate during the cooling process strongly influences quality-critical morphological parameters (degree of crystallinity, structure of partially crystalline materials and internal strain). This is why it is important for machine manufacturers and for plastics processors to analyse and understand exactly how the material cools down as it moves through the cooling zone.

SCooP uses a one-dimensional finite differences model as the basis for calculation. Input for the simulation consists of data for the material (density, thermal conductivity and specific heat capacity) and temperature data that describe the existing or planned cooling zone (eg, temperature of cooling roll surfaces, heat transfer coefficient). Running the simulation with this input, gives detailed information on the cooling process for up to three layers of extrudate. The results can be used to optimize the cooling zone and/or the material being used. Other applications include analysis of foam-core extrudate (rigid outer and inner layers, foamed core) and situations where the extrudate enters the cooling zone with a temperature distribution (cold surfaces, hot core). The SCooP software can also be used to optimize laminating processes, because it enables the cooling process in each separate layer of a laminate to be clearly understood. By varying thickness coordinates, it is possible to compare cooling profiles at the extrudate surfaces and in the core. The software includes a database in which material data, machine configurations and product details are stored.

The SCooP simulation software makes the cooling process in extruded sheet and film both transparent and predictable. It clarifies the effect of individual processing parameters, machine settings and environmental factors (eg, cooling roll temperature and position, heat transfer, ambient temperature) on the cooling process. In conjunction with the practical experience of users and machine manufacturers, it enables accurate conclusions to be drawn about the development of structures and stress states within the extrudate. Cooling zone design and choice of materials can then be optimized for cost, quality and efficiency.

Extrusion displaces calendering: Attractive alternative for flexible PVC and PO film
Krauss-Maffei has modified its proven 30 UD extruders for a new task - flat film extrusion. A new, special purpose mixing-head screw offers outstanding product quality and lower costs. The redeveloped chill roll unit with extra cooling rolls ensures adequate film relaxation. Faster cooling reduces internal stresses, eliminating the risk of wrinkling .
The first of the new flat film extrusion lines, installed with a customer in Denmark, is producing a 3-layer medical film from flexible PVC. Compared with conventional calendering systems, the Krauss-Maffei extrusion line has the advantage of more flexibility and far lower costs. The initial investment is around 50 % less than for a calendering system. Operating costs drop sharply because fewer operators are required and energy costs are around 70 % lower.

Contributing to flexibility is the fact that layers can be differently coloured and the option of using recyclate for the middle layer. The throughput of the three extruders (type 1 125-30B) is around 1500 kg/h. Films produced in the new system have a thickness variation of no more than plus/minus 4 ,µm over a width of 1.5 m. With excellent print and welding capability, they lend themselves to post production processing, eg, into heavy-duty lining for waste disposal sites, or for many applications in advertising and packaging. Furthermore, the Krauss-Maffei extruders have been engineered to make an easy switch from PVC to PO film by simply adapting the processing unit.

Extruding wood-filled profiles - Throughput doubled:
successful debut for a new extruder generation
Krauss-Maffei has launched a new generation of counter-rotating, twin-screw extruders. The powerful 36 UD machines are ideal - among other things - for extruding wood filled polymers.
Wood extrusion has been under discussion for at least 25 years, but the technology has never really taken off, largely for lack of market demand. In recent years, for various reasons, this situation has changed and there is now a growing demand for wood-filled polymer products in several important economic regions. Extruded wood-filled products give users the positive qualities of wood combined with the lower production cost of plastics. Wood-filled polymer products can be veneered, painted, powder-coated or otherwise enhanced, and the material can be worked like wood nailed or screwed, drilled and planed. The cost advantage comes from cutting out many production steps by extruding a semi-finished profile. In recent weeks, Krauss-Maffei engineers have experimented with a range of different formulations in the company's test lab in Munich. They ran systematic trials under realistic production conditions using formulations for indoor and outdoor use with up to 85 % wood content (by weight) and 15 % PP. The tests demonstrated conclusively that the new-generation 36 UD extruders, developed primarily for high-throughput PVC extrusion, were also ideal for processing wood-filled polymers. The long prewarming zone and double venting barrel offer decisive process benefits. Double venting supports precise adjustment of the moisture content, an important variable in processing different types of material. The long prewarming zone and optimized screw design guarantee a high quality, homogeneous melt.. Using a KMD 90 - 36D extruder, test lab trials achieved steady throughput of 420 kg/h with very good product quality.