GOTEBORG, SWEDEN — An inventor and several companies with Finnish roots have teamed up to create a radical new coextrusion technology.
The technology appropriately is called Conex, and uses a series of nested, hollow, cone-shaped screws to produce extruded products with an almost unlimited number of layers. A gearbox connects the rims of each screw to the base of the machines.
The concept, which inventor Kari Kirjavainen started developing about a decade ago, first was revealed at Plastics Pipe X, a trade and technical conference held Sept. 14-17 in Goteborg. Further demonstrations are planned for the K'98 plastics industry show in Dusseldorf, Germany, which opens Oct. 22.
While the Conex system can be used to produce multilayered pipe, films and other typical extruded products, it first was developed as a way to coat wires without leaving weld lines, Kyosti Valta, a senior research scientist with VTT Chemical Technology in Tampere, Finland, said Sept. 14 during his presentation to the conference.
In typical pipe and wire-coating extrusion processes, molten plastic is forced over a mandrel to give the products their hollow shape. But the melt also must pass over thin ``spider legs'' that support the mandrel. While the separate melt flows weld back together after passing the supports, weaknesses still can exist along those lines.
The Conex process avoids that problem because the melt flow never is separated in the first place, Valta said. The mandrel is built into the back end of the machine, and does not need spider-leg supports.
The basic design of the conical screw also allows additional layers to be extruded together, simply by adding more of the compact units together in a line. Holes in the back end of the screws allow resin to be conveyed to both the inside and outside of cones. That helps balance the axial pressure against the screw, Valta said.
Valta said other basic advantages of the Conex system include:
A compact size facilitated by the ``nesting'' of screw units.
An ability to orient reinforcement fibers along the hoop direction of a pipe, instead of the usual machine direction.
Lower extrusion pressures and temperatures.
Shorter residence time of the plastic melt in the extruder.
Lower power consumption.
``So far everything is in product development,'' Valta said after his presentation, adding that there are about six Conex machines now operating.
Pipe company Uponor Oy of Espoo, Finland, helped develop the technology, and has exclusive rights to use it to make multilayered pipes.
``We will be better able to develop customized products to meet the needs of our clients,'' Jyri Jarvenkyla, a research manager at Uponor, said in a news release. ``Now we can make so-called functional pipes, which have several layers and in which each layer performs its own task precisely in the desired manner.''
Also involved in the development of Conex is NK Cables Oy, of Helsinki, Finland, which is looking into wire-coating applications for the technology, and Nextrom SA of Ecublens, Switzerland.
``The prospects are very wide,'' said Richard Phillips, a process engineer with Nextrom. ``We haven't seen the limits of the technology yet, although we are looking for them. So far it's just the tip of the iceberg.''
Nextrom Technologies, a machinery company based in Lausanne, Switzerland, is concentrating on blown film and blow molding applications. The Swiss company also will have the exclusive right to manufacture Conex machines. One such machine will be running at K'98.
Those machines initially will not be for sale, but will be made available to partners, Phillips said.
Dow Chemical Co. of Midland, Mich., is interested in the technology, Phillips said. The unique processing properties of the Conex machine would suit metallocene-type resins, which offer better physical properties than conventional polyolefins, but are trickier to process.