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7/1/1999 | 7 MINUTE READ

Pultrusion Starred At SPI Composites Expo

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This small but fast-growing processing sector scored most of the prizes for innovative parts, and also accounted for much of the news in equipment and materials.

Driven by expanding opportunities in construction and infrastructure, pultrusion is growing by 8% a year, or 60-100% faster than composites as a whole. That vitality was evident at the the recent International Composites Expo in Cincinnati. Although pultrusion will probably amount to around 260 million lb this year--only 7% of total poundage for composites--it accounted for a disproportional share of the news at the ICE. Pultruded parts won seven of the 11 Product Showcase awards, including the grand prize for Innovation Design of Excellence.

Although this ICE turned out to be the last ICE ever (because the sponsor, SPI's Composites Institute, went out of business soon thereafter), the show still yielded a healthy crop of news in resins, reinforcements, additives, and machinery. Although pultrusion accounted for many of these developments, there was also news in filament winding, RTM, and open molding.

Pultrusion advances

A fundamental study that should be important to many pultrusion processors is being conducted by Dow Chemical Co., Freeport, Texas, in conjunction with Ohio State University, Columbus, Ohio. They are seeking to remedy the general lack of design guidelines for resin-injection dies, which are becoming more common. These dies may even be required by the EPA's new MACT (Maximum Achievable Control Technology) air-emissions standards, expected to come out next year.

Herbert Engelen of Dow and Shoujie Li of OSU are comparing the results of pultruding the same profiles via a large-cavity, low-pressure die, three types of high-pressure dies, and two chevron-channel designs, as well as an open resin bath. They are seeking to compare the merits and limitations of each system in terms of pulling speed, allowable thickness, and acceptable reinforcement package. They are examining processing behavior along with microstructure and mechanical properties of finished parts.

Within the next year, pultruders may be introduced to a new material for this process: polyurethane. It offers inherently fast reaction, almost no VOCs, and adjustable viscosity of 400-500 cp. It produces parts with 5-10% elongation, good impact strength and HDT, low CLTE, low voids (2-3%), and glossy surfaces. ICI Polyurethanes has been developing materials and processing technology for two years in Europe. It developed a special resin-injection die that has a static mixer attached to the feed port. Liquid polyol and MDI prepolymer streams are pumped to the static mixer, where they are combined without entraining air. Because of the resin's high reactivity, the injection section of the die must be water-cooled and then followed by a heated curing section.

ICI sources note that most polyurethane metering machines are not designed for continuous operation and so may need modification for pultrusion use. These sources add that pultrudable urethane will be a specialty material priced in the range of a high-performance vinyl ester.

Another new pultrusion material is a carboxy-toughened epoxy/vinyl ester hybrid from MAS Epoxies. Designated 45103, it reportedly has a 9-14 hr pot life but cures in 11.5 sec at 335 F to give a glossy finish. Viscosity is 2500 cp. The cured resin's ultimate elongation is 8%, tensile modulus is 390,000 psi, and Tg without post-cure is 135 C. Price is $3/lb. The product has been used to pultrude a 4 x 3 in., carbon fiber top-hat structure for ship stringers at 18-22 in./min.

In pultrusion machinery, Martin Pultrusion Group says it has overcome the limitations in power, speed, and profile size that have plagued laboratory pultruders until now. "The market needs an economical and capable lab machine," says president Jeff Martin. His new Durapul 5000 Labstar has 5000 lb of pulling power to make profiles as large as 8 x 3 in. at up to 6 ft/min. Unusual for a lab machine, it has reciprocating pullers plus 10,000 lb of adjustable clamping pressure, four heat zones, and transducer readout of pulling load. Price is $64,900.

Also new from Martin Pultrusion is a so-called "die recycling program." Called Retool, the program encourages pultruders to contribute obsolete dies to the program inventory. Martin would then machine a die to a new shape for any participating company. Since there is no cost for the steel, and the die would already have an acceptable bolt pattern and alignment system, the die could be readied for a new application much faster and at much lower cost than a brand-new die. Martin will periodically publish a list of available die-block sizes for program participants.

News in filament winding

Entec had several new developments to report. One is a new winding system for making self-contained breathing apparatus for firemen. To obtain a smooth outside surface, the operator rolls on a layer of Loctite uv-cure resin after winding is finished. The part then indexes into a built-in uv oven that cures the surface resin layer in 3 min.

Entec has upgraded its controls with the new Windows version of its FiberGrafix winding software. Also new is data-acquisition software that collects QC data on products using barcode readers and then forwards that information to a central computer. Data include part number, operator, date, customer, fiber and resin lot numbers, curing times and temperatures, and finished weight and diameter.

New fibers and fabrics

A new line of 90° (weft) unidirectional fabrics has been launched by Fiber Glass Industries. The first products of this type from FGI come in standard weights of 9, 12, and 15 oz.

"Woven quadraxial" fabric is another new FGI product. It consists of woven roving and double-bias (±45°) fabric stitched together with mat to yield a reinforcement for RTM, hand lay-up, and marine manufacturing. It's reportedly more conformable than typical stitch-bonded quadraxial fabric without mat. A typical version is product SXQ410808, which is a sandwich of 24-oz woven roving, 0.75-oz mat, 17-oz double-bias fabric, and another 0.75-oz mat--for a total weight of 54.5 oz. FGI says many boat builders lay up this combination by hand but now can buy it in one handy package.

"Enhanced Nexus" is a developmental polyester veil from Precision Fabrics Group (PFG). It gives laminates a better appearance and 20% better color yield. Higher gloss, richer color, improved fiber hiding, and a thicker resin-rich layer are claimed. It competes with spunbonded nylon and polyester, which also give good surface characteristics but are less weatherable, PFG says. The trade-off for the improved appearance of Enhanced Nexus is that the veil does not show up under uv light--an important QC test for corrosion-resistant products. That may restrict it to non-critical applications.

Brunswick Technologies has new Black Steel heavyweight biaxial knitted carbon-fiber fabrics. They are based on large-tow commercial grades of carbon fiber and are available in weights of 60-100 oz with or without glass. BTI also now offers heavy woven carbon and carbon/glass fabrics.

Lighter-weight carbon tows are new from Fortafil Fibers, which has come out with 40K tows at 680 ft/lb yield. The company says these are comparable in weight to 30K tows of thicker aerospace-grade carbon fibers. The new tows are aimed at lighter prepregs and stitched fabrics, small pultrusions, and thin-wall filament winding.

Glass fiber from Saudi Arabia is now available in the U.S. at competitive prices. Fibertech Fiberglass Reinforcements represents Gulf Glass Fiber Technological Industries Co. It offers direct-draw rovings for epoxies and polyesters, spray-up rovings, mats, woven rovings, yarn, and yarn fabrics.

E-CR glass rovings are now available from Fiberex Glass Corp. in Canada, which opened a 16.5-million-lb/yr plant last October. E-CR glass is more corrosion and heat resistant than standard E-glass. It has slightly higher tensile strength, modulus, and elongation as well, which can allow higher line speeds with fewer breaks, Fiberex says. Although E-CR glass used to be premium-priced, Fiberex charges the same as for E-glass.

News in additives

A reportedly unique epoxy hardener suitable for filament winding, pultrusion, and high-voltage electrical potting/encapsulation is new from Lonza. "MTHPA-EG" (methyl tetrahydro phthalic anhydride) is said to give optimum electrical-insulation properties together with higher glass-transition temperatures, lower moisture permeability, and improved thermal-shock resistance. It is also low-viscosity, non-crystallizing, and nearly colorless. Price is around $1/lb.

Two new pigment pastes in "safety orange" and "safety yellow" are available from Ferro Corp. These heavy-metal-free formulations are based on blends of bismuth vanadate and organic pigments. They are said to provide better heat and light stability than low-cost all-organic pigment formulations.

Molders of RTM auto parts can save downtime for mold cleaning with a non-scumming, semi-permanent release agent from Axel Plastics Research Laboratories. Extend 19W is the newest addition to Axel's Extend line of reactive resin solutions that crosslink and cure on the mold surface. This product is said to eliminate the need for mold sealers and to give clean releases with polyester, DCPD vinyl ester, epoxy, and even hard-to-release Modar acrylic vinyl esters from Ashland Chemical.