New machines & processes at SPE ANTEC.

New ways of extrusion blow molding APET, in-mold orientation of injection molded parts, and continuous forming of programmable shapes in-line with extrusion were just some of the new concepts introduced at the recent SPE Annual Technical Conference in San Francisco. Only a sampling can be reported here from the huge ream of technical papers--three volumes encompassing 3700 pages. The following selection includes processing tips for extruding films with post-consumer reclaim and optimizing injection molding processes. The accompanying exhibits also showcased several new extrusion hardware developments.

NOVEL APET BLOW MOLDER

Sabel Plastechs Inc., Cincinnati, in association with the Sterling Div. of Davis-Standard, Edison, N.J., has developed a novel, patented approach to extrusion blow molding unoriented amorphous PET (APET) bottles. A continuous tube of APET is extruded into an in-line traveling mold carrier, producing a continuous chain of linked bottles--like sausage links--which are subsequently cut apart. The "hand-over-hand" dual-mold transport system produces bottles up to 89-oz size at rates of 1800-3600 parts/hr, says Sabel president Sam Belcher. The machine uses only electric and pneumatic drives (no hydraulics), suiting it to clean-room production of medical/pharmaceutical containers.

The machine, designed by Sabel, will be built and marketed by Sterling Davis-Standard and is priced around $250,000, with tooling costs ranging from $3000 to $16,000. Sabel will provide tooling and processing support for users. The system is designed for 30-min mold-changing capability and can be adapted for coextrusion. The first machine is slated to be on-line next month at an unnamed processor in New Jersey that will be making white 8-oz pharmaceutical bottles.

Belcher lists two limitations of the machine: It requires use of needle blowing, which may not provide the cosmetic level of neck finish required by some customers. And the system generates a moderate amount of trim scrap between bottles in the chains, though this scrap can be automatically recycled back to the drying hopper.

Sabel is developing a second-generation machine, which will employ stretch-blow molding to make bioriented bottles from 6 oz to 1 liter and will incorporate multiple parisons and handleware capability.

NEW PROCESSES

A couple of other new twists on familiar processes turned up in the technical presentations. One was injection spin molding, in which the mold cores are motor-driven to produce orientation in cylindrical parts. The other is a continuous forming process that works in-line with extrusion. Continuous Three-Dimensional Forming from Continuous Molding Inc. (CMI) of Daly City, Calif., fits into both production and rapid-prototyping applications. Ted Jacobson, who developed the process, describes it as "flexible tooling." To produce easily variable 3D shapes from flat extruded sheet or other extruded shapes, the process uses a series of computer-controlled, rod-like actuators to deform the still-hot extrudate shortly after it leaves the die. The part geometry is taken from a CAD file, from which the system creates a "dynamic model" or sequential series of profiles that together define the 3D part.

For now, the system's most promising application is making parts normally produced by thermoforming--except in this case there is no dedicated tooling. But CMI may soon branch out to automated fabrication of composites. Jacobson reports that work is under way to integrate the sheet-forming system with a prepreg tape-laying system to produce composite shells. This developmental tapelaying system uses neural-network software to control how the plies are applied to the formed sheet.

NEW RESIN DEVELOPMENT

The Packaging & Industrial Polymers unit of DuPont Co., Wilmington, Del., has commercially released its "Fusabond" family of maleic anhydride-grafted polyolefins, which serve as compatibilizing and coupling agents. Prior to this introduction, the Fusabond resins had been available only for internal use at DuPont and in small-scale quantities for select compounders.

Priced at $1.50-1.70/lb tl, the resins are available in eight grades based on modified PP, PE, or EVA. In addition, DuPont offers two experimental grades of modified EPDM and ethylene acrylate copolymer in test-sample quantities.

Fusabond resins are designed for use as coupling agents in glass-filled PP compounds and as compatibilizers for PP/nylon alloys and recycle streams of mixed plastics. They also have applications in hot-melt adhesives and sealants and as a flame-retardant additive for wire and cable.

PCR FILMS

Many a blown-film processor knows that using post-consumer reclaim can introduce a source of variability in film strength. For those times when the reclaim has to be added anyway--for regulatory or "green-marketing" reasons--a paper from Mobil Chemical Co. of Edison, N.J., spelled out a way to predict the strength of virgin-LLDPE/PCR films without any trial-and-error blending of various types and levels of PCR. This new model predicts film strength from the density and melt flow of the final virgin/PCR blend. The films used for the study were made by blending a 0.918 g/cc, 1-MI LLDPE with 10%, 20%, and 30% PCR consisting of mixed HDPE, LDPE, and LLDPE from a variety of sources. Using equations originally intended to predict film strength for virgin LLDPE from the resin's density and melt flow, a close match emerged in all the PCR/virgin films between predicted and actual values for the MD Elmendorf tear, dart impact, and MD secant modulus.

Another paper from Mobil described property enhancements to virgin-LLDPE/PCR films obtained by using recycled stretch film in place of a more common reclaim material--milk-jug homopolymer HDPE. The stretch film waste is collected mainly from warehouses and retail establishments. For the past year, Mobil has been selling a 100%-PCR stretch-film resin called PCX-610 for dryblending with virgin grades. The PCR typically shows a 0.919 density and a 1.5 MI, though both numbers can vary with the feedstock.

Jill Paul, one of the paper's authors and Mobil's recycling program manager, notes that stretch film made from high-strength octene or hexene copolymers intrinsically provides a better fit with LLDPE than does HDPE homopolymer. "Our goal here is to offer a versatile reclaimed material that upholds the original functionality of the virgin material," says Paul. Indeed, the paper demonstrates that films made from the company's Super Strength LLDPE with 25% stretch-film PCR content exhibit more than twice the dart impact strength and more than five times the MD tear resistance of LLDPE films containing the same amount of HDPE PCR.

In the next six months, Mobil hopes to develop recommendations for appropriate virgin materials to blend with stretch-film PCR for injection and blow molding. Pricing of PCX-610 hovers a few cents above virgin prices.

EXTRUSION MACHINERY NEWS

Maag Pump Systems Inc. of Charlotte, N.C., announced plans to offer screw designs optimized for use with a gear pump. General manager Jorge Guzman explains that the Pump Optimized Screw (POS) will have deeper-than-usual flights and will emphasize melting and mixing while letting the gear pump take care of maximizing output. Introduction of the screw is expected this fall.

In other extrusion news, Normag Corp., Hickory, N.C., showed a new medical extrusion gear pump that was scheduled to debut at NPE. Unlike some other small pumps, this one features a straight bore despite its small size. Output range is 0.1 to 1.2 cc/rev.

Randcastle Extrusion Systems, Inc., Cedar Grove, N.J., has several developments in its lab-sized cast-film lines, including a new interchangeable manifold and a double chill roll that allows higher output rates and thicker films. For cast films under 0.010-in. thick, another new line can now make films 20 in. wide, up from a previous maximum of 6 in.

OPTIMIZING MOLDING SETUP

For injection molders, Denes Hunkar of Hunkar Laboratories Inc., Cincinnati, delivered a paper detailing a comparatively quick and easy alternative to standard Design-of-Experiments (DOE) methodology. The objective is to determine the control limits or processing windows for key process variables. According to Hunkar, the Molding Area Diagram (MAD) method achieves nearly the same precision as DOE procedures but more quickly--in about 2 hr or so--and at minimal expense. It does not require a machine to be taken out of production and it generates minimal waste in scrap parts.

The MAD method determines processing windows through a series of molding experiments on those parameters critical to making an on-spec part. The sequence of experiments is commensurate with the degree of influence, or relative "weight," that each processing parameter has on part quality. Hunkar says the "weights" of such variables as hold pressure, backpressure, boost pressure, injection speed, hold time, plastication time, and mold temperature have already been determined through statistical analysis of millions of shots on hundreds of production molding machines. That statistical knowledge has been incorporated into Hunkar's SPC-Pro machine-monitoring software for the last six years and it makes the rigors of DOE unnecessary in many cases.

The parameter weights and sequence of experiments would depend on whether a filling- or packing-related problem is being investigated. Once the sequence has been identified for a given part, the molder incrementally varies each parameter in both directions until a part drifts out of dimensional specifications. Machine control holds all but the subject parameter constant until the experiment reveals upper and lower control limits--that is, the point where the part goes out of spec.

Off-press data gathering consists of "hot gauging" molded parts rather than waiting for them to cool. Dunking hot parts in cold water temporarily slows shrinkage enough to permit accurate measurement. Hunkar found that hot and cold dimensions correlate well and that part weight also correlates with dimensions. Waste can be minimized through hot gauging, since an experiment can be terminated as soon as part dimensions are found to exceed allowable ranges.

Although MAD can be performed without the aid of a computer, Hunkar says his new Smart Box machine monitor can make the process faster and easier. The unit automatically collects machine data and calculates control limits. It also analyzes how changes in the seven primary variables tested affect other variables not being tested and thereby finds the molding window of those secondary variables, too.

CAE AND OTHER SOFTWARE

AC Technology of Louisville, Ky., rolled out new C-Mold modules for two more processes: structural RIM (SRIM) and coinjection molding. Though similar to the analysis of RIM, the SRIM module also considers the flow and reaction-rate changes linked to the reinforcing fiber preform.

The new coinjection module once existed as a feature of the basic C-Mold injection mold-filling module but has now been "unbundled" into its own $20,000 module. It analyzes the spatial distribution of the two material components during molding--illustrating, for example, how gate placement affects the encapsulation of one melt stream by the other.

Marketing manager Jim Spann says the creation of a separate module reflects his firm's "new internal commitment to coinjection molding." More resources are now being directed at developing added capabilities such as the ability to switch between tracing the primary and secondary materials during flow analysis; users will be able to look at the skin material first, then at the core material, and finally at the skin again as the cycle nears completion. That feature will likely be part of C-Mold Release 4.1, Spann says.

The Polymer Processing Institute in Hoboken, N.J., has developed a new expert system for extrusion process design. Called the Designer's Assistant (DA), it offers recommendations on material selection, screw configuration, and operating conditions. According to Ron Rakos, PPI's computations manager and author of a paper on the product, a "rule base" lies at the heart of DA. To come up with the design variables for a given set of processing goals, the rule base combines data-driven reasoning with the sort of sequential problem-solving knowledge employed by human extrusion experts. Rakos reports interviewing experts and surveying recent processing literature to capture the most recent extrusion knowledge in DA's rule base. The DA's other sources of information are a Resin Processing Database and a Materials Database, which together form a "knowledge base" of strictly empirical information.

Beyond coming up with design variables, the DA addresses a common difficulty with computerized extrusion modeling by helping users interpret the simulation results. In one example, Rakos explains how the DA, working from graphical simulation information, can tell whether an extruder can develop enough head pressure to process a material at a given temperature.

Another example of an expert system for extrusion came from Witt Plastics, which recently implemented a program called the Extrusion Adviser in the company's Greenville, Ohio, facility. The system provides "diagnostic assistance" for 19 quality-related product defects. Twenty-four hours a day, the Extrusion Adviser now dispenses on-line assistance, replacing slower, more costly consultations with in-house experts who may or may not be on duty when trouble strikes. The system's "smarts" come from two of Witt's most experienced operators, whose collective knowledge has been embodied in the PC-based system.

Chemineer-Kenics of North Andover, Mass., talked about its new Computational Fluid Dynamics (CFD) software, which simulates flow inside a static mixer. CFD was developed jointly with analysis-software vendor Fluent Inc., Lebanon, N.H., and supercomputer-maker Cray Research, Eagan, Minn. So far, CFD has been used to customize mixing elements for given applications, says Steve Willis, senior applications engineer. For example, Chemineer used it to come up with a new 90 [degrees]-pitch element that does a better job of mixing than the older 180 [degrees] model it replaces.

IDES Inc. of Laramie, Wyo., announced the release of a Windows version of Prospector, a materials database with over 17,000 resins. In addition to property- and name-based search methods, the system lets users look for appropriate materials by simply entering an end-use. Price of the Windows version is $495, or $895 with quarterly updates.

IDES also has a new version of its cost-estimating software, CostMate 3.0. The package now includes graphing capabilities and ability to incorporate regrind into cost calculations. The new version also allows single quotes to deal with mixed-unit systems--for example, part weight in grams and material cost in dollars per pound. CostMate sells for $395.