Infrastructure and environment are themes of SPI Composites Expo.

Twenty-six technical sessions with 106 papers, three panel discussions, three live processing demonstration periods, and over 100 show exhibitors will make up the International Composites Expo '97, the annual show and conference of SPI's Composites Institute, to be held later this month in Nashville, Tenn. Despite the variety of topics to be covered, two themes will stand out: civil-engineering or "infrastructure" applications, and controlling styrene and other VOC emissions to meet EPA and OSHA regulations.

COMPOSITE BRIDGE TO THE 21st CENTURY

The excitement surrounding potential opportunities for composites in infrastructure - bridges, highways, dams, piers, and railroads - is reflected in six technical sessions with 28 papers and two panel discussions devoted to repairs, rehabilitation, and new construction. One session is devoted entirely to bridges, another to enhancing concrete's performance with composites, and a third to fire-performance standards in civil engineering.

* A key goal of recent years has been to replace steel I-beams with a design optimized for pultrusion. A phenolic composite solution has been developed by Morrison Molded Fiber Glass Co. (MMFG), Bristol, Va. (see illustration, p. 20). This spring, MMFG plans to pultrude 36-in. beams of this shape. MMFG estimates the job will require development of a pultrusion machine with 120,000 lb of pulling force and 140 kw of heating capacity.

* Over 12 million wood railroad ties are replaced annually in the U.S. at a rough cost of $500 million. Tie life could be improved by overwrapping the wood with a thin FRP laminate to increase its stiffness. According to research spearheaded by the Dept. of Civil and Environmental Engineering at West Virginia University in Morgantown, an optimized design requires only 0.1-0.2 in. of filament-wound glass and epoxy over the wood fie.

* So-called "smart" composites that contain embedded sensors to detect mechanical damage or incorrect processing (voids or misaligned fibers) are of great interest for infrastructure applications and other uses such as pressure vessels. Four papers address smart composites. The most versatile approach appears to be incorporating ferromagnetic particle "tags" whose vibration in an oscillating magnetic field can reveal the "health" of a composite.

* If you have an innovative concept for using composites in highways and bridges, a new nonprofit service center could help you get the product to market at lower cost. In Nashville, learn about the Highway Innovative Technology Evaluation Center (HITEC) in Washington, D.C. It was founded in 1994 to provide a single source of fee-based testing and evaluation and to save entrepreneurs the cost of going through the process repeatedly to satisfy different public and private organizations. HITEC is affiliated with the Civil Engineering Research Foundation (CERF) and the American Society of Civil Engineers (ASCE).

GET THE FACTS ON 'MACT'

Attention to styrene and VOC emissions has become especially urgent because this July OSHA is expected to start enforcing stricter "voluntary" styrene exposure limits (see PT, April '96, p. 91). Meanwhile, EPA is preparing a Maximum Achievable Control Technology (MACT) standard that will take effect May 15, 1999 for processors that emit 10 tons of styrene or other VOCs annually. The first draft of the standard is expected this fall.

The conference will contain two sessions on health, safety, and environmental issues. Besides ample discussion of MACT, the Composites Fabricators Association (CFA) will present results of its latest studies of styrene emissions in open molding (see story on p. 24), and Dow Plastics, Midland, Mich., will discuss a study of emissions from filament winding. There will also be a paper and a demonstration of a brand-new photocatalytic technology that eliminates styrene fumes. Patented by VVK Weege of North America, Inc., Granville, Ohio, the system has no moving parts and boasts extremely low operating costs.

VVK Weege, a new firm offering air-pollution control technology specifically for composites fabricators, will also discuss two other systems, the Wega Bio-Scrubber and Wega Bio-Filter. Both use microbes to digest styrene aerobically into CO2 and water. The scrubber is a closed system that generates no sludge. It can cost from $250,000 for a system to handle 37,000 [ft.sup.3]/hr (615 cfm) to around $950,000 for a system to handle 1.5 million [ft.sup.3]/hr (25,000 cfm). Those prices compare favorably with incineration systems costing $3-5 million. Operating costs are also said to be low: A small system requires 11 kw of power, 200 liters/day of water, and about $13/day worth of additives.

LIGHTER SIDE OF SMC 

The conference this year again addresses hot topics in SMC - low-pressure and low-density formulations. Data showing good moldability, mechanical properties, paintability, and bondability of Class A low-pressure SMC will be presented by Cambridge Industries (formerly GenCorp), Marion, Ind. The company's proprietary 7125 LPSMC for auto and truck parts is conventionally thickened and molds comfortably at 300 psi. Because molds can be less beefy, cost savings of at least 15% are said to be possible.

Not content to stop there, Cambridge has developed pigmentable grades and materials that can be molded at only 100 psi and temperatures as low as 180 F. Such low-temperature/low-pressure SMC allows even greater cost savings through use of "soft" tooling made of epoxy, kirksite, or cast aluminum and heated by hot water. Low-cost tooling could make prototyping in SMC cost-effective.

Solutions to problems of reduced physical properties and increased porosity in low-density SMC are offered by Byk-Chemie U.S.A., Wallingford, Conn. The company recommends using combinations of its wetting and dispersing additives to reduce paste viscosity and prevent filler separation. Byk-W996 is said to work well with hollow microspheres, while Byk-W972 is recommended for mineral fillers like calcium carbonate. With the help of these additives, Class A SMC reportedly can be produced with a 30% density reduction while maintaining 80-90% of the strength and stiffness of standard SMC.

Byk also says you can overcome porosity problems caused by the pulling out of microspheres when parts are sanded prior to painting. Byk's answer is to split the SMC into two batches, one containing most of the microspheres and the other containing most of the calcium carbonate. Mold charges consist of a sandwich with the higher-density compound on the outsides (facing both mold surfaces) and the lower-density compound in the center. This arrangement minimizes microspheres at the part surface.

BETTER-LOOKING SMC

The Madison Group, Madison, Wis., will show how finite-element simulation of flow in the mold provides calculations of fiber orientation, shrinkage, and stress build-up that can be used to predict sink formation over ribs. The company is developing quantitative sink-prediction software as an enhancement to its Cadpress package, which simulates SMC flow and cure. The sink feature is expected to become commercial this year.

RELATED ARTICLE: Sticky Tape Cures Bonding Ills

Adhesive structural bonding of large marine and other structures involves difficulties in clamping the parts while the adhesive cures. Other problems involve controlling bond-line thickness and width and avoiding waste of adhesive that escapes through the edges of the seams (20-50% wastage is reportedly typical in the marine industry). All of these problems are said to be alleviated by a method developed at Structural Composites, Inc., an FRP R&D firm in West Melbourne, Fla.

The trick is to temporarily secure the joint with double-sided adhesive tape. Two or more strips of tape (in this case, from 3M Co., St. Paul, Minn.) are used to create a channel between the parts to be joined. The thickness of the tape determines the thickness of the bond line and the spacing of the strips defines the width of the bond. Adhesive is then pumped into the channel to permanently secure the joint.

This patent-pending approach allows complex structures to be "tacked" together quickly and checked for accuracy before permanent bonding. The tape channel provides consistent bond-line dimensions and seals the joint, preventing adhesive waste. The taping method also increases production flexibility because other fabrication steps can be performed before the adhesive is applied.