Published On: Thu, Oct 18th, 2012

Gentle and powerful: planetary roller extruder for EVA sheet

Enormous outputs of up to 2 t/h can be achieved in the production of EVA sheet for solar panels with the PWE 250 planetary roller extruder from battenfeld-cincinnati, Bad Oeynhausen/Vienna. In addition to high performance, this machine concept stands out by its extremely gentle treatment of the materials processed. This is why some 15 extrusion lines are already in operation worldwide in this growth market.

Gentle and powerful: planetary roller extruder for EVA sheet

Gentle and powerful: planetary roller extruder for EVA sheet

Today, solar cells for photovoltaic modules are regularly embedded in EVA sheet. This sheet protects the sensitive silicon cells, which transform sunlight into electrical energy, from environmental damage such as corrosion or impact. For this purpose, the sheet must be electrically insulating, very tough and simultaneously highly transparent and UV-resistant. Each m2 of panel requires 500 g of EVA per layer, i.e. a total of 1 kg. Thanks to its excellent processing and long-term stability properties, EVA has a market share of about 90% in the steadily growing solar energy market.

For the production of EVA sheet, the plastic granulate must be plasticized gently at no more than 150° C and mixed with several additives. A planetary roller extruder is the ideal machine for this purpose, since it already achieves a highly effective dispersion and homogenization performance at low processing temperatures. This is due to its special process technology design. A planetary roller extruder consists of a conventional single screw as feed section and a planetary gear section. The latter consists of a fixed roller cylinder with internal gear teeth, a teethed main spindle driven by a motor, and the revolving planetary spindles.

All components of the planetary roller extruder are fitted with helical gears cut at an angle of 45°, with the teething of the planetary spindles being ar-ranged at a counter-pitch to the other components. The machine concept of planetary roller extruders is well known from calender feeding in PVC processing, since, here also, gentle plasticizing at pre-defined low temperatures is a vital prerequisite.

Thanks to its high output, the planetary roller extruder is the optimal equipment for PVC processing as well as numerous alternative processes, such as EVA sheet production. While single screw extruders of comparable size reach up to 800 kg/h and twin screw extruders up to 1,200 kg/h in output, the planetary roller extruder achieves a performance of up to 2,000 kg/h. Apart from perfect transparency, optimal mechanical key values and low shrinkage are also important criteria for EVA sheet used in photovoltaic modules. The innovative Multi-Touch roll stack from the complete line supplier battenfeld-cincinnati meets these re-quirements to perfection.

The concept consists of a two-roll roll stack for preliminary calibration and up to seven post-cooling rolls. This ensures even sheet tolerances, a uniform thickness profile, as well as optimal transparency, excellent flatness with only few orientations, and perfect mechanical properties.