Extrusion.

New developments in die technology hogged the spotlight at K '95. In particular, two flat-die makers unveiled designs that promise either better flow control or virtually no hang-up. In blown film, a new die permits LDPE or LLDPE extrusion with small die gaps, no process aids, and no melt fracture. New multilayer blown film dies premiered - including one for quick changeovers - as well as new tooling for pipe, profile, and wire coating.

Not to be outdone, controls makers announced some firsts in film and web gauge control (see PT, Sept. '95, p. 59). One company even brought out computerized air-ring controls.

FLAT-DIE INNOVATIONS

Extrusion Dies Inc. (EDI) offered a glimpse into what the firm sees as the next step in flat dies: fixed die lips with flexible manifolds. Its new AutoBar automated restrictor-bar technology adjusts flow distribution through the manifold, eliminating die-gap adjustments, which can create stresses in the film or sheet. Fixed lips aid in producing uniformly oriented film or sheet, says EDI manager of product development Harry Lippert. Compatible with automatic die-lip adjustment software, AutoBar technology employs computer-controlled, thermally actuated restrictor-bar bolts and an elongated, teardrop-shaped manifold of a clamshell design. Field testing of the new die is scheduled to start this month.

Breyer GmbH of Germany unveiled a unique flat-die technology that uses a membrane in place of a restrictor bar to adjust melt flow within the die. The design leaves no gap in the flow channel that can become a source of hang-up, degradation, and gel formation. The membrane (still being tested) covers the top surface of the flow channel within the manifold and is adjusted with small bolts inserted vertically through the die. Breyer sales manager Reinhart Melzer says the membrane permits problem-free processing of temperature-sensitive materials and may also help reduce the frequency of die cleanings.

Cloeren Co. rolled out its new fixed-geometry (FG) feedblock for cast film, in which portions of the flow geometry can be changed to optimize material flow by switching selector plugs. Removable inserts can change plug geometries.

Klockner ER-WE-PA introduced its first flat die with internal deckling and an edge-bead reduction system. Series 500 die options include manual or automatic adjustment of the diebolts. Single- or two-manifold designs are available.

A versatile new line that can produce film or sheet from 80 microns up to 2 mm was introduced by Klockner ER-WE-PA. Klockner also combined a casting section with a three-roll stack that can be adjusted quickly for thin to thick film. The system has a coex feedblock with exchangeable inserts for different structures. Klockner also developed a winder for both thin and thick films.

SMOOTHER BLOWN FILM

As reported last month (p. 12), Brampton Engineering claims its new "No Frac" die technology can run LDPE or LLDPE using narrow die gaps without process aids and without experiencing melt fracture. The die will be field tested for the next six or seven months. Brampton R&D engineer John Perdikoulias says in-house tests ran 100% LLDPE with a narrow 0.65-mm die gap at 9 lb/hr/in. of die circumference. No melt fracture was observed, even though shear stress at this rate was equivalent to running the material with a more common 1-mm die gap at 22 lb/hr/in. "We are running at rates of three times the stress where melt fracture is documented to occur on conventional dies," Perdikoulias says. Shear stress levels during one test went above 50 psi, he says, without melt fracture, which typically occurs at 25-30 psi.

Future Design introduced new retrofittable remote-control capability for all its Saturn dual-lip air rings (PT, July '95, p. 72). The RCA (remote-control air ring) system positions the dual lips for optimum air flow. Separate dial-in controls govern positioning of each lip. Readings are shown on an LCD and settings are repeatable to 25 microns. The system also records ambient air temperature and relative humidity for more complete operating data.

Italian equipment manufacturer Macchi S.r.1 (represented here by Warner Sales Associates) developed a new five-layer blown film die that reportedly can change from LLDPE to EVOH or from EVOH to nylon in less than 30 min without cleaning the die head. The die incorporates a concentric spiral design and feedblock based on Macchi's three-layer dies. Die diameters from 250 to 600 mm are available with outputs from 440 to 1300 lb/hr.

Windmoeller & Hoelscher introduced two new pieces of equipment for better processing of tacky blown films. One is said to be an industry first: a noncontact oscillating capacitance gauge. The new on-line gauge uses the principle of a contact gauge but operates at a distance from the bubble, so that tacky films - such as EVA or metallocene plastomers/elastomers - aren't marked by the gauge. The gauge is reportedly accurate to [+ or -]0.03 microns.

W&H also developed a new oscillating haul-off for tacky films, which features a specially designed non-contact air turning bar.

Kiefel has added flexibility to its Compex 100 SA blown film line with a new barrier screw (26:1 L/D) that runs HDPE, LDPE, or LLDPE at around 900 lb/hr. Different resins require only a change of die-lip inserts and adjustment of the air ring. An optional 31:1 screw increases output.

Kiefel also displayed a new grooved stabilizing cone for high-stalk extrusion. Whereas previous designs used a grooveless aluminum cone with a cotton sock covering, the new one is of a proprietary plastic, which reduces the need for cleaning. Kiefel also incorporated the proprietary plastic into its vertical oscillating haul-offs. The plastic eliminates the need for air turning bars, making possible a two-bar design. The bars are staggered to minimize surface contact.

A NEW LOOK FOR PVC PIPE HEADS

As previously reported, the biggest news in pipe dies was the first-ever spiral design for PVC. Cincinnati Milacron offers it in sizes from 32 to 180 mm (PT, Aug. '95, p. 11).

In addition, American Maplan has a new PVC pipe head with concentric double spiders. It accommodates more flow volume in a smaller area, says v.p. of technology Mike Wallen. Initial tests on an 8-in. head yielded a 30% drop in pressure and 50% drop in wall-thickness variation. Tests of a 4-in. head showed good wall-thickness control and improved pipe impact strength. The die offsets the legs of the inner and outer spiders, which is said to result in reduced knit lines and improved impact strength. Maplan intends to develop double-spider head sizes from 0.5 to 18 in.

QUICK-CHANGE WIRE HEADS

A new fixed-head device for single-screw extruders, developed by Mapre of Belgium, (represented in the U.S. by its Gauder Group subsidiary) promises quicker head changes. Two heads can be mounted on a swivel base that is part of the extruder body. Heads can be changed by turning the desired head to the extruder front. Mapre added a clamp mounting on the extruder for quick head connection and disconnection. The company also moved all of the electronics under the machine for compactness.

Mapre, which recently added single-screw extruders to its established twin-screw line, brought to the show a new "Micro" series single screw for low outputs. A 15-mm, 25:1 model for outputs of 6.5-9 lb/hr will be available in about six months.