Fast, high-precision extrusion systems

The wide variety of extrusion systems available in the market today has given manufacturers of plastics products an edge in terms of efficiency and cost control.

The five-layer pipe extrusion line, developed and produced by Extrudex GmbH from Mühlacker, Germany, is characterised by high production speed and precision. The line has been delivered to customer in August and was started production within two days. Now it is used to produce pipes for floor heating systems. These consist of a core pipe layer, an adhesive tie layer, an EVOH barrier layer, a further adhesive tie layer, a protective layer in PE, as well as three stripes.

“It began with monolayer pipes earlier, later on 3-layer pipes were introduced into the market, consisting of a core pipe layer, an adhesive tie layer and the EVOH barrier layer. As the outer EVOH barrier layer dissolves easily in water and is very sensitive to mechanical damage, the EVOH barrier layer was moved to the interior of the pipe, and this is how the 5-layer pipe arose”, according to Mr. Helmut Wahl, Extrudex’s Managing Director.

The newer pipes even have internal protection for the EVOH barrier layer: this makes them even more secure and better sealed, so that no osmosis is possible. Mr. Wahl adds: “the five-layer pipe produced with our line meets the specific needs of the industry and is used as a high grade product for heating or cooling systems. It also finds use for wall heating”.

RT 2344, 2388 or DX800 grades of PE materials form the basis for the pipes. Six extruders in the line produce the final finished pipes in diameters from 16 to 25 mm. “We have to respect layer thicknesses and tolerances on a micrometre scale”, Mr. Wahl stresses. The extruder applies and evenly distributes finest layers. The 16x1 and 17x1 mm [16 mm & 17 mm diameter, 1 mm wall thickness] pipes are produced with a speed of 30 m per minute in the required dimensions and tolerances. An ultrasonic measurement head measures the overall wall thickness inline, while an X/Y laser head controls the outer diameter. The fully automatic VR-3 vacuum calibration control unit ensures constant vacuum in the calibration bath. “The line is efficient, because it is so precise and fast”, says Managing Director Wahl.

During last three years, the company has delivered seven similar lines to its customers. Extrudex has been developing its own programme of multilayer tool heads for the past seven years and using them very successfully in various application areas.Tools are made out of highly alloyed steels.

Until product corresponds with prescribed dimensions such as outer diameter, layer thicknesses, ovality etc., line has to be started up manually. During the next step, production speed is synchronised within the line control system, which then ramps up the entire line to the required extrusion speed. Monitoring and regulation of the entire line takes place in a central control system.

“Each single extruder can be controlled individually, which is very important, especially, as explained, during start-up of the line. Production only commences when the pipe has been shown optimal performance following measurement after the last cooling bath”, Mr. Wahl explains. With six extruders, the calibration and the three spray cooling baths six metres each, the entire line measures 35 metres. Individual components of such a line, such as e.g. a multilayer die head, the control system, a vacuum calibration bath, a Helibar extruder, the VR-3 controlRunning Shoes, Trainers, Shorts, Spikes and Clothing