There's a choice to be made when balancing screw performance to processing requirements. A perfect set of screw parameters may translate to energy savings
Several qualities of an extrusion screw help qualify it as being of optimum design. Matching the screw performances to the specific processing requirements may work in favor of sustainability. A perfect balance of screw parameters can bring energy savings while respecting flow homogeneity and production requirements.
Just the right mix
The screw qualities include regular dosing of the material, shear degree, stable pressure, a good mix of the extruded components, homogeneity of the mass temperature, and appropriate flow. The homogenization of the material is obtained thanks to an efficient fusion process coupled with distributive and dispersive mixing elements.
A screw with a high degree of shear and mixing also inputs a greater amount of energy to the extruded material. However, the shear requirement varies according to the composition and the viscosity of the material used. A careful choice of the model of extrusion screw makes it possible to reduce the energy necessary for the transformation of polymer resins, while maintaining a high degree of quality.
Running cool
As a general rule, a screw with a higher specific flow allows the mass temperature to be reduced, provided that the elements are suitable. For the same production speed, it is possible to slightly drop the extruder’s rotational speed and lower the line’s electrical consumption. Our flow simulations and lab trials are proving it.
Savings that range from 5% to 12% have been achieved on our blown fiber microduct lines. Plus a cooler mass temperature, even relatively small, makes it possible to reduce the need of water cooling the extruded product. At Maillefer we run predictive cooling analysis to optimize downstream trough lengths and overall line speeds. Less energy and less cooling both result in substantial savings.
Conversely, for the extrusion of “blends”, multiphase materials with additives such as plasticizers or impact modifiers, it is often desirable to guarantee a high level of shear. We then select screws with a lower specific flow rate and that require a higher rotational speed. These screws often also include dispersive type elements characterized by a higher shear rate.
Sustainability features built-in
The volumetric feed zones used at Maillefer allow precise adjustment of the specific flow to adjust the extrusion process to the materials used and to optimize the final results in terms of quality, performance and energy costs.
We offer a wide range of extrusion screws, each adapted to the specific material, the process and the production requirements at hand. Whether considering an investment in a complete line that includes efficiency features built-in, or responding to the evolving production conditions on an existing line, a properly selected extrusion screw program brings savings and makes a sustainable difference.
Yves Zweifel, PhD
R&D Manager, Pipe & Tube Business Line
yves.zweifel@maillefer.net