Pultrusion's promise.

Huge new markets beckon. Part sizes seem to know no limits. And new technology in resins, reinforcements, and equipment sets the stage for growth.

Pultrusion is already one of the fastest growing sectors of composites processing, but it seems poised for even more rapid acceleration in the next decade as construction and infrastructure applications generate major new opportunities.

The 100-120 pultrusion processors in North America produced an estimated 200 million lb of profiles in 1994. Based on industry forecasts of 10-15% annual growth for pultrusion in the next five years, profile shipments could easily pass the 300-million-lb mark by the year 2000. The most optimistic projections push that market volume over 400 million lb by the end of the decade.

Pultrusion appears ready to graduate to a larger scale of part sizes as well. Much of today's R&D excitement focuses on thick-walled, structural components for novel marine, power-transmission, civil-engineering, and high-rise construction projects. These profiles range up to 4 in. thick and weigh 20 to 55 lb per lineal foot. They will require new technologies for materials handling, resin delivery, and wetout of massive stitched fabrics and multilayer fiber preforms.

At the same time, pultrusion process technology is evolving from reliance on "black art" and trial and error to a more scientific understanding of cure dynamics inside the die. Advances in electronic process control, resin injection, and tool design are helping to optimize quality and productivity. And sophisticated new tooling concepts could make possible nonuniform profiles that would never have been considered possible for the pultrusion process.

"The pultrusion industry is going through several transitions at one time," observes W. Brandt Goldsworthy of Goldsworthy & Associates. Goldsworthy pioneered pultrusion technology in 1950. "The potential in areas such as infrastructure represents a new ballgame for pultrusion, with the opportunity for production volumes that far exceed anything we've seen so far. Today we have the technology in place that not only makes composites price-competitive with traditional materials like metal and concrete, but actually makes composites even less expensive to manufacture and assemble," he declares.

BETTER PROCESS KNOWLEDGE

More thorough understanding of the cure process inside the die presents a major opportunity to upgrade pultrusion processing technology, according to Joseph Sumerak, president of Pultrusion Dynamics Inc. Using finite-element analysis as a predictive tool, Sumerak creates a computer model of die-temperature distribution based on part geometry and a die's energy-input profile (see cover illustration). This computer simulation makes it possible to identify and correct temperature imbalances that impede cure and result in part-tolerance problems.

Temperature is a major determining influence, Sumerak explains. "The coldest region of a part is the primary constraining element of pultrusion line speed," he says. That region will be the last to cure and consequently the last area to release from the die cavity - often the cause of "sloughing," which results in surface defects and fiber breakage.

Sumerak offers a proprietary design and analysis service, known as "TopDie" (Thermally Optimized Pultrusion Die), which uses FEA data to position die-heating elements and establish a balanced heat profile.

More sophisticated microprocessor controls are also helping to get a tighter grip on the process. PTI div. of MMFG Co. last year introduced its Pulstar Series 2000, which offers enhanced closed-loop, touchscreen control and SPC data (see PT, Oct. '94, p. 12).

"SPC is and will be important for pultrusion," says Thomas E. Deller, president and CEO of Omega Pultrusions Inc. in Aurora, Ohio (formerly Dexter Pultrusions). "As we improve our understanding of the process, we'll know when and how it deviates. Much of the technology to monitor processing conditions already exists; it's more a matter of capital investment and commitment on the part of manufacturers to continue to improve."

Some processors are developing their own SPC software. In the last two years, DFI Pultruded Composites Inc. in Erlanger, Ky., developed PC-based software programs for data acquisition and production control. President Lee Burch says the on-line SPC system is monitoring process parameters on two of DFI's six pultrusion lines, with the remaining four lines slated for integration by year end. Burch says the DFI control system includes thermocouples and pressure transducers in the die, and real-time laser-guided gauging and inspection of parts coming out of the die.

Most pultruders say one area of process technology that will require improvement is streamlining the collimation of mat, roving, and veil reinforcements upstream of the die. The goal is to reduce scrap, improve line speeds, and shorten changeover times. These challenges resist standardized solutions because each application requires a different package of reinforcements to be gathered and shaped to enter a specific die. So, for now, each processor is relying on its own home-grown approaches.

Processors are also the main source of innovation in operations downstream of the die. For example, Shakespeare Co. in Newberry, S.C., has developed a proprietary in-line coating process to be used on window/door lineals and light poles. Joe Prochak, composite product manager, says it will impart 20-yr uv and weather protection. This "modified painting process" will go line in the second quarter. Shakespeare also is using automated in-line machining and assembly systems that were developed in-house.

Other processors that are developing in-line coating or finishing systems include Owens-Corning Fiberglas Corp. Its Fibron window and door lineal operation in Hazelton, Pa., is employing a proprietary in-line painting process (PT, March '94, p. 27).

And Omega developed a technique for in-line coating or overcapping a thermoset pultrusion with an extruded thermoplastic (PT, May '92, p. 61). Besides weather, scratch, and stain protection, the thermoplastic offers the ability to add 3-D surface detail.

Integrated painting systems are offered on turnkey pultrusion lines newly available from window-lineal producer and technology licensor Omniglass International. This year, Omniglass will launch its new line of DuraPul machines, which will employ new die technology developed by Pultrusion Dynamics, according to Omniglass president Jeff Martin.

MOVING TO RESIN INJECTION

Better methods of resin delivery and fiber wetout are other R&D goals, especially for pultrusion of larger parts. One evident trend is toward injecting resin into the die, rather than pulling reinforcements through a traditional open resin bath. Lee Green, president of Composite Process Equipment (CPE), says most pultruders still utilize the open-bath method, but a growing number of his new equipment orders specify a "closed" resin-injection system. The key advantages are reduced emissions and better control of glass placement and integration, since the reinforcements enter the die in a dry state. "You can have a higher glass content with an injection system than with a resin bath, which is an advantage in structural parts," Green says.

The disadvantage of injection systems is generally 10-20% lower line speeds. However, Green notes that line speeds with injection systems have improved significantly during the last five years. Before then, most injection systems averaged more than 50% slower than a comparable bath process, he says.

The Werner Co., Franklin Park, Ill., recently developed a "high-pressure" resin-injection system, which it uses for producing ladder rails. Without revealing specifics, vice chairman Robert I. Werner says the injection tooling - which was developed jointly with Owens-Corning - reduces styrene emissions by 64% while maintaining or surpassing line speeds obtained with the bath process.

Creative Pultrusions Inc., Alum Bank, Pa., reports that it has developed new injection-die technology for improved wetout of thick-walled structural parts. Sean McMullen, director of marketing and sales, says this injection technique will be used in a new multicavity line, built by CPE, for processing parts such as bridge components with a 6 x 2 ft work envelope.

NOVEL DIE TECHNOLOGY

Joe Sumerak is seeking patents on an innovative technology that he calls Selective Interval Pulshaping. It uses articulated tools and stop-and-go pulling to vary the cross section and contour of pultruded parts at regular or varying intervals [ILLUSTRATION OMITTED]. The technology utilizes Sumerak's thermal-analysis know-how and new process-control capability to "manipulate the state of cure" so that the composite remains soft enough to be reshaped in the die. Sumerak's invention lends itself to structural parts that incorporate such features as connection points and interlocking male/female shapes that would otherwise not be possible without machining or secondary bonding.

A patent has been issued to Omni-glass International for an innovation that combines different resins in the same part. The method involves pulling reinforcements through two different resin baths and joining them in the die. In window production, this permits using polyester for the majority of the profile and vinyl ester in selected areas that require higher strength.

MACHINERY TRENDS

Green of CPE says pultrusion machinery is growing larger year by year, with greater working envelopes and higher pull strengths. Two years ago, CPE built what was then believed to be the largest machine in the world - 52 x 18 in. working envelope and 100,000-lb pull force (PT, June '94, p. 47). Now, the firm has just built a machine with comparable pulling force to make 100-in.-wide panels.

Machines are also getting faster. PTI's new Series 2000 reportedly offers a max. line speed of 180 in./min, compared with 120 in./min for the previous generation of Pulstar machines.

Some sources say reciprocating or "hand-over-hand" pullers are gaining favor, owing to faster clamping and line changeover. However, caterpillar-type pullers also remain popular, especially for smaller, high-volume profiles like ladder rails and window lineals.

To handle multiple streams, equipment suppliers are developing more sophisticated cutoff systems. CPE has come out with two- and four-bladed saw systems in which each blade can be programmed for a different cut length. And PTI's new 2000 MX series offers a single saw that can be programmed for two "zones" or cut lengths.

NEWS IN REINFORCEMENTS

The last two years have seen glass-fiber suppliers such as Owens-Corning, PPG Industries, Vetrotex CertainTeed, and GAF focus on optimizing roving and mat products for pultrusion (PT, April '93, p. 101; April '94, p. 19). Several of these products are designed for compatibility with phenolic resins, which are beginning to gain acceptance for this process. An example is brand-new Star Rov 507 phenolic-compatible roving (113 yield) from Schuller International.

Quite recently, PPG joined Owens-Corning, Vetrotex, and Nicofibers as a domestic supplier of continuous-strand mat for pultrusion (PT, Dec. '94, p. 42). PPG also just came out with a new family of low-catenary rovings for pultrusion (Types 715, 2011, and 2788).

As pultrusion markets move toward larger and more highly engineered profiles, processors have had to find ways to achieve greater transverse-directional strength in their products. Continuous-strand mat has been their main tool so far, and suppliers have worked to improve the mat's wet and dry strength. In addition, some processors have begun to explore the potential of more highly engineered multiaxial fabrics produced by braiding or knitting (also called stitch-bonding). Such fabrics can readily be customized to specific applications, allowing higher strength to be provided with less weight of glass than by simply packing in large amounts of mat.

For example, CollinsCraft Composites can make its Cofab knitted fabrics in any weight from 10 to 96 oz and can bond veils and rovings to one or both sides of the fabric, creating a single reinforcement package that saves creel space, according to CEO Ken Collins.

"Some pultruders have used knitted fabrics for five or six years, but more of them need to learn what's possible," says William Dubay, chief operating officer of Brunswick Technologies Inc. (BTI). "Biaxial fabrics offer new design potential." Although they cost more than mats, some knitted-fabric prices have come down recently.

Owens-Corning has established a joint venture with Hexcel Corp. for production of "Knytex" specialty fabrics (PT, March '93, p. 73). Bruce Fawcett, Owens-Corning's North American market manager for composites, terms knitted fabrics "an emerging technology," but also a crucial "enabling technology" for higher-performance composites.

A new factor in knits is Fiber Glass Industries, which is offering 0/90 [degrees] biaxial fabrics in 18-32 oz weights and plans to offer [+ or -]45 [degrees] fabrics by midyear.

Several innovations in polyester surfacing veils for pultrusion are being launched by Precision Fabrics Group (PFG). Nexus MR is a veil impregnated with mold release to provide increased pulling speeds with lower pulling force and less die wear. Nexus UV is impregnated with uv stabilizer, which dissolves into the resin and provides weathering protection on the surface of the profile. PFG also has new Conductive Nexus, which permits electrostatic coating of pultruded profiles. Finally, PFG offers Nexus and Reemay veils with adhesive to permit bonding to mat.

NEW RESINS FOR PULTRUSION

Because of its enhanced mechanical, thermal, and corrosion-resistance properties, vinyl ester is attractive for many of the new large-part pultruded applications. The tradeoff has been lower line speeds compared with polyester. To remedy that limitation, Alpha/Owens-Coming recently unveiled E-711 isophthalic/vinyl ester hybrid resin. It's said to combine polyester processing with properties like those of a vinyl ester.

AOC also has introduced a broad new line of polyesters for pultrusion, including grades tailored for enhanced corrosion resistance, better electrical properties, smoother surfaces, higher filler loadings, higher line speeds, better stain resistance, or higher thermal stability. Also new is Altek 14-70, a polyester containing 14% by weight recycled PET.

AOC is developing new polyesters based on dicyclopentadiene. DCPD reportedly provides improved surface properties without thermoplastic low-profile additives. Reichhold also produces DCPD-based polyesters. Marketing director James Maas sees lower viscosity as their main advantage, which could aid wetout in injection-type dies.

Reichhold recently introduced three resins for pultrusion. One is Dion 31029-02, a polyester with enhanced gloss and low-profile characteristics. It's also a high-solids (73%), high-reactivity grade for low styrene emissions.

Two new urethane vinyl ester hybrids from Reichhold are said to offer enhanced wetout. Dion 31038-00 provides superior mechanical properties and corrosion resistance. Atlac 31632-00 provides improved retention of mechanical properties at elevated temperatures (70% retention at 275 F) .

There is heightened interest in pultruding phenolics for low-smoke, flame-retardant applications. Phenolics' primary drawback are their water content, which is corrosive to tools, retards line speed, and creates surface porosity.

BP Performance Polymers is developing a new low-water phenolic series known as NAPR, which has a water content of 2%, compared with up to 12% for standard phenolics. A spokesman says NAPR replaces water with a proprietary reactive monomer and utilizes a less acidic catalyst, which makes it feasible to use with chrome-plated dies.

Indspec Chemical Corp. is test marketing two new phenolics: Resorciphen 2074-A and 2026-B. Both grades have 6% water content and a non-acid catalyst, along with extended shelf life (up to 12 months in refrigerated storage).

The Durez Div. of Occidental Chemical is developing a new phenolic grade, VNF26, with a neutral-cure chemistry, 1% water content, and six-month shelf life at ambient temperature. Current development work focuses on reducing the high cure temperature (410 F).

Georgia-Pacific Resins is developing a phenolic that contains no organic solvents. It reportedly retains mechanical properties after long-term exposure to temperatures up to 500 F.

RELATED ARTICLE: The Future Is in Larger Parts

Large shapes for civil engineering, building construction, marine, and transportation applications represent the vanguard of pultrusion development. The following five "snapshots" illustrate how some innovators are seizing those opportunities.

* Goldsworthy & Associates Inc., Rolling Hills, Calif., is developing new pultrusion equipment capable of processing structures up to 10 ft wide for two still-secret engineering projects. He reveals only that the programs involve fabricating composite framing structures and fascias for residential, high-rise buildings. Goldsworthy says the program includes new techniques for wetting and curing such large parts. "There's no size limit for pultrusion," he notes.

* Glasforms Inc., San Jose, Calif., recently shipped three windmill blades to a California industrial wind farm. Peter Pfaff, president, says each blade is fabricated with 42 plies of triaxial fabrics, plus rovings and veil and a proprietary vinyl ester blend. The blades are 160 ft long, 27 in. wide, and 3/8 in. thick, weighing 20 lb/ft.

* Stoughton Composites Inc., Brodhead, Wis., is pultruding panels for 48-ft refrigerated cargo containers for truck and rail transport. Rob Sjostedt, president, says the company built its own pultrusion equipment to make 12 different profiles for the containers. They measure up to 48 x 16 in. and have wall thicknesses from 0.065 to 0.75 in. Pulling speeds for the isopolyester/glass panels are greater than 2 ft/min.

* Ebert Composites Corp., San Diego, is in the final stages of a four-year development project to design and produce large pultruded structural parts for high-voltage power-transmission towers in Southern California. Funded by two electric utilities, the project calls for construction of three towers, requiring an initial shipment of over 17,000 lb of pultruded parts.

Finite-element analysis was employed to design parts that weigh 2-8 lb/ft. Each transmission tower - 84 ft high and weighing 5700 lb - is designed to be assembled without the use of adhesives or bolts, relying on mechanical connections in a proprietary joint design.

In a separate research effort, CEO David W. Johnson says his firm recently received a National Institute of Standards & Technology (NIST) grant and a U.S. Navy contract for a program that involves pultruded structural beams and bracing components that measure up to 50 sq. in.

* Heath Techna Aerospace Co., Kent, Wash., recently installed two machines built by CPE Inc., each with a 100,000-lb pulling strength. One unit has a work envelope of 52 x 18 in.; the other is 102 x 15 in. The units will be used for pultruding epoxy/carbon-fiber shapes.