Extruding

 

Where's the extruder?" was the comment often heard about the most unusual extrusion exhibit at K'98, a screwless, cone-shaped device that can extrude two or more melt streams. Other attention-grabbing exhibits included three operating seven-layer blown film lines, a water-quenched PP film system, and three double-bubble oriented-film lines (see p. 15). In cast film, simultaneous biaxial orientation took the prize for novelty. There were also several new developments for sheet, pipe, and profiles.

Cone extruder saves space

The new Conex extruder from Nextrom SA (formerly Nokia Maillefer) was making two-layer blown film at K'98. Conex nests one or more hollow spinning cones between stators, allowing each cone to melt and extrude materials on its inside and outside surfaces. Conex has a tiny footprint, almost as if a conical die had become the whole extruder.

The cones are powered by two motors on opposite sides. Feed augers, also located on opposite sides of the cone, can feed the same or different resins to the outside and inside surfaces of the cone. Changing feeder speeds makes the different layers thicker or thinner. Also, clearance between cone and stator is adjustable from 0.3 to 0.8 in. The unit needs no cooling--temperature is also controlled by feeder speed.

Material is fed in at the wide end of the cone, where it melts rapidly because of the high rotational velocity. Spiral melt channels in the cone surface help transport material toward the narrow end of the cone and the attached die. As the cone narrows, rotational velocity decreases, which helps avoid overworking sensitive materials, Nextrom says. Energy use is also reportedly 20% lower than with a standard extruder. Short residence time contributes to quick start-ups and fast color changes, and dies can be changed in 5 min, Nextrom says.

Conex was developed jointly by three large Finnish firms. Uponor Oy has the exclusive right to use the device for pipe manufacture. NK Cable has exclusive rights to cable uses until 2001. Nextrom can develop and sell Conex machines for all other markets, such as blown film and cast film and blow molding.

Nextrom has built eight Conex machines so far: five for pipe, one for cable (the biggest so far, capable of 660 lb/hr), and two lab machines. The pipe model uses three concentric rotors and four feeders. The version for power cable uses three rotors and six feeders. Unlike blown-film models, Conex systems for pipe or cable are arranged horizontally. This novel machine makes possible some entirely new products. By spinning two cones in counter-rotation, for example, it can cross-orient the melt or even criss-cross fiber reinforcements in opposing spiral patterns.

At K'98, a 270-mm O.D. Conex machine with one rotor and four feeders blew a two-layer bubble of 30-micron PE film. The machine has the same output as Nextrom's 60-mm, 24:1 conventional extruder. Nextrom expects to have three Conex blown-film lines operating next year.

Other blown film news

Three impressive seven-layer blown film lines were operated at K'98 by Battenfeld-Gloucester Engineering, Windmoeller & Hoelscher, and Macchi Srl. Battenfeld's was technically the most challenging: It was the first seven-layer coex demonstration using two layers of homopolymer nylon. (Copolymer nylon, which is less challenging, ran in Battenfeld's seven-layer demonstration at NPE '97.) The structure used a blend of metallocene PE (mPE) and LLDPE, followed by a tie layer, nylon, EVOH, nylon, tie, ionomer. Battenfeld used its Optiflow LP die and an NDC Systems oscillating gamma backscatter gauge that was air-lubricated so that it wouldn't damage the ionomer skin on the 50-70 micron film. The company also showed its new "Extrol Anywhere" control system with remote access via modem.

W&H also ran a seven-layer barrier film based on homopolymer nylon, but with only one nylon layer and no EVOH. The structure was mPE, white LDPE, tie, nylon, tie, white LDPE, mPE. Because of the sticky mPE skin layer, the line ran W&H's latest generation NoStic noncontact turning bars on the oscillating haul-off. The company also showed its recently introduced Optifil P-2 multi-cone die, along with new CAN-bus controls and quiet brushless AC vector drives on the seven extruders.

Macchi ran a structure without tie layers. It consisted of mPE, LDPE, EVOH, nylon, EVOH, LDPE, mPE. The line used an oscillating hauloff and motorized A-frame with specially coated rollers, the largest of which were internally cooled.

Hosokawa Alpine demonstrated the flexibility of its technology by running very different types of products on the same basic extruder and die package. One line with a 120-mm extruder ran high-stalk HMW-HDPE at more than 1000 lb/hr. The other ran high-clarity, metallocene-based low-density film in a three-layer configuration. Both lines used grooved-feed extruders and Alpine's new side-fed "K" die.

Several companies showed ingenious small bubbles that economized on space and price. TAM Maschinentechnik GmbH, a German firm whose machines are built in Taiwan, demonstrated downward extrusion of a polypropylene bubble with chilled water flowing over it. The TAM PP-55G system has a 23-in. layflat. The complete line, including an embosser, costs under $200,000.

C.M.G. Construzione-Meccaniche-Galia SrL of Italy showed a compact three-extruder blown-film line that fit neatly into a 130-sq-ft booth. A major space saver was the optional vertical hauloff on the 20-ft tower.

In controls, Octagon Process Technology GmbH from Germany showed its "SCAN" system for the first time. It consists of a single i-r sensor mounted after the nip that can control film width of up to 32 in. This task formerly took two i-r sensors, Octagon says.

Kiefel showed off the versatility of its three-layer blown-film system by running clear film in the morning and colors in the afternoon with a range of resins, including LDPE, hexene LLDPE, PP, and MDPE. The line included a new conical-flow die and a modified barrier screw. A cavity-transfer mixer on the screw, borrowed from PVC extrusion, allowed the line to run both PP and PE.

Kiefel also showed a new segmented dual-lip insert for an air-ring. It provides intensive cooling for automatic gauge control.

News in cast film and sheet

Bruckner Maschinenbau is commercializing DuPont's LISIM technology (linear motor simultaneous stretching). LISIM stretches PET or PP film in two axes at once (see PT, Nov. '98, p. 15), instead of in two steps. The first two production-scale systems have been installed at DuPont in Luxembourg for OPET and at 3M Co. in Greenville, S.C., for OPP film. Though designed by Bruckner, the equipment is built by Luigi Bandera SpA in Italy.

LISIM is intended to use less expensive PP than is required for conventional sequential stretching because MD pulling is gently distributed over the whole 9-meter line, instead of with an abrupt jerk in the first tenth of the line length.

LISIM thus does not require polypropylene with special melt strength and it has less risk of web breaks in case of holes or impurities in the film. Consequently, output is expected to be four times higher with LISIM than it is with sequential stretching.

Adolf Seide Engineering in Germany (which is looking for a U.S. rep) showed an unusual three-roll "planetary" sheet-roll stack for the first time. It accommodates a wide range of sheet thicknesses by changing roll positions along two C-shaped guide tracks in the metal frame. Incidentally, one of Seide's specialties is very thick sheet--up to 2.5 in.!

Hair-thin profiles

Gimac of Italy (represented by Citsco Inc.) showed the prototype of a 6-mm diam. machine for coextruding profiles thinner than a human hair. Model TTV-1-14/24 is driven from the feed end and can use pellets, whereas most lab-sized machines can only use powder. A patented feed zone has three long, tapered channels that wedge pellets into the screw flights, where the pellets are crushed. At K'98, Gimac micro-encapsulated a 25-micron polyethylene strand for a medical application.

Milacron showed a conical twin-screw machine with a new long-wearing tungsten-lined barrel and tungsten-coated screws. Though this treatment doubles the cost, the company reportedly has sold several dozen of these screw/barrel sets in the U.S. since last spring.

Technoplast of Austria, a maker of conical twin-screws, showed its first parallel twin-screw. Model TDE-115 puts out 1100 lb/hr of PVC profiles.

KUAG GmbH in Austria (represented in the U.S. by Plastic Processing Technologies Inc.) showed a relatively new and very high-speed pipe puller. Model Rei 32 pulls at over 300 ft/min, where previously the company's fastest time was 130 ft/min.

Roll out the knobby sheet

Plammer Maschinen GmbH in Austria (now looking for a U.S. rep) showed a patented roller system to emboss sheet with high, wedge-shaped protrusions that are wider at the top than at the base. Sheet with rows of these protuberances is used to repair and protect large concrete culverts. (The rows of bumps anchor the sheet in freshly poured concrete.) The bumps are demolded from the chilled embossing roll by folding the sheet back at a sharp angle, popping the bumps out of the roll cavities.

Take up the slack

Welex has applied for a new patent on a built-in accumulator to take up sheet during roll changes. It stores the excess sheet under the flat conveyor, above the heat exchangers. A 12-ft take-up was shown at K'98 for the first time. It costs roughly a third as much as conventional accumulator rolls, Welex says.

All-digital bubble control

Addex Inc. showed what it calls the first fully digital bubble-width control system. It uses four ultrasonic sensors, of which up to three can be taken out of service without affecting width control. The system actuates alarms for off-spec layflat width, bubble "breathing," repeated instability, or an off-center bubble. Unlike other ultrasonic sensors, Addex says its new ones eliminate drift and are accurate to ±0.003 in. vs. a more typical 0.1 in.

Cool screws for foam sheet

Krauss-Maffei and Battenfeld Gloucester have new systems for solid and foamed sheet that use water-cooled screws and air-cooled barrels.

Simulation aids set-up

Using its built-in resin database, simulation software now embedded in Davis-Standard's Epic III and Exact-S control systems guides operators to set up extrusion lines and calculates expected output rates. The simulation software (available separately) comes from Compuplast.

Dies ride on air

Aerofilm Systems BV from the Netherlands whisked around an 8000-lb die carriage on a cushion of air. With a load space of 4 x 4 ft, the 2.5-ft-high Aircushion Transporter runs on a standard smooth factory floor and uses normal shop air. It has a range of up to 1000 ft on an extension hose and costs $15,000.

No flaw gets through

ConPro GmbH in Germany (seeking a U.S. rep) introduced a new ultrasonic defect detector for pipe of 30 to 225 mm diam. It uses 12 overlapping probes around the pipe to guarantee 100% defect detection.

Large pipe coiler

Nextrom showed its new MWP-2000 automated coiler for pipes of 25-63 mm diam. It's said to be one of the biggest pipe coilers in the world. It has automatic changeover and a special device that holds tube ends after cutting.

Gentler cast-film die

Die maker Verbruggen N.V. has applied for a patent on a dual-flex-lip cast-film die with a half-round restrictor bar. Not yet commercial, it's being tested with temperature-sensitive polymers like polycarbonate and PVC because it has few corners where resin can degrade.