LCM and SMC share top billing at SPI composites conference.

LCM and SMC Share Top Billing At SPI Composites Conference

Automated RTM/SRIM preforming and improved SMC surface finish with shorter cycle times will lead the news in reinforced-plastics/composites manufacturing at the annual conference and exhibit of SPI's Composites Institute in Washington, D.C., February 12-15. A total of four sessions will be devoted to SMC/BMC (including one specifically on quality optimization), two to RTM/SRIM (which are coming to be known jointly as Liquid Composite Molding, or LCM), and two sessions to pultrusion. As a sign of what's currently hot in this field, there will also be two sessions on thermoplastic composites, one on process modeling and simulation, and one on low-flame/smoke phenolic composites.

AUTOMATED PREFORMING FOR LCM

The newest thing in preforming is an automated "Compform" process to be unveiled by C.A. Lawton Co., De-Pere, Wis., and Freeman Chemical Co., Port Washington, Wis. (see schematic). Previous preforming methods limit the ability to specifically engineer a preform with various types, thicknesses and configurations of reinforcements in high-stress areas of the part, without increasing thickness and weight of the preform overall. Compform allows the addition of ribs, closed sections, cores, and encapsulation of metal, foam, wood, or other materials. The process is also said to be relatively simple and energy-efficient, and to optimize usage of material with the lowest possible waste.

Although patent applications limit the companies' freedom to discuss details, the process starts with broadgoods reinforcement--usually mat. It is cut to predetermined patterns and permeated with a Freeman binder resin by spraying, rolling or calendering. Then single or multiple plies of reinforcement are mechanically placed on one half of a matched mold. The forming press closes, and "directed energy" is applied in the mold by a proprietary method (possibly radio-frequency or microwave energy) that heats the binder with minimal heating of the reinforcement itself or the mold surface. After initial preforming, additional sections of precut reinforcement can be attached to portions of the preform outside the press by robotic application of a "chemical stitching" process using directed energy as before. The robotic applicator holds the reinforcement in place with the same head used to apply the "stitching" energy. (CIRCLE 38)

PPG Industries, Pittsburgh, will discuss a new directed-fiber preforming technique that's in early stages of development. It uses a large-filament-diameter, single-end roving to produce a highly filamentized preform. With the exception of notched Izod impact energy, mechanical properties are comparable to those produced with PPG's standard 5540/5542 roving or continuous-strand mat preforms. The company says the technique offers significant cost savings over multi-end roving. (CIRCLE 40)

The company will also present data on a head-to-head comparison of directed-fiber and thermoformable-mat preforms in an automotive bumper-beam application. (CIRCLE 41)

LCM PROCESS SOPHISTICATION 

RTM Systems, Indianapolis, a new subsidiary of Glas-Craft Inc. set up to supply RTM equipment and technology, will describe a way to automate mold filling with less resin waste than occurs with simple timing mechanisms. A new type of dielectric sensor provides precise indication of the moment of mold fill by sensing resin arrival at the extremities of the mold, and also provides indication of the progress of curing in the mold. Called the Arrival, Gel and Cure (AGC) resin sensor, it can also provide a signature of the gel, exotherm and cure profile of the resin.

Its function is based on the fact that thermosetting resins act to a small degree as an electrolyte in the ungelled and curing condition. The AGC sensor shows a voltage peak when resin arrives, and the voltage decays as the resin cures. A second voltage peak occurs as the resin curing reaction produces an exotherm. (CIRCLE 42)

A number of other papers will indicate growing sophistication in understanding LCM processes. Experimental studies and computer models for predicting injection times, pressures, and flow patterns through specific types and amounts of reinforcements will be presented by researchers from the University of Minnesota in Minneapolis, Ohio State University Engineering Research Center for Net Shape Manufacturing in Columbus, and the Ecole Polytechnique de Montreal, Quebec. And GenCorp Research, Akron, Ohio, will present examples of flow simulation to aid in properly locating injection ports and vents to avoid air entrapment during LCM.

Contributing to the widely sought goal of high-speed RTM, Dainippon Ink and Chemicals, Chiba, Japan (parent of Reichhold Chemicals, Inc.), will describe a new low-viscosity vinyl ester RTM resin (Polylite SRM-100) that can produce 10,000 parts per month per mold with total cycle times of a little over 4 min. (CIRCLE 43)

FOCUS ON SMC QUALITY

Major news at the last two SPI Composites meetings were the introductions of new surface-quality measuring instruments--the LORIA device from Ashland Chemical Co., Columbus, Ohio; and the D-Sight from Diffracto Ltd., Windsor, Ontario. This year, Owens-Corning Fiberglas Corp.'s Technical Center in Granville, Ohio, will report on tests to quantify the repeatability and sensitivity to test variables of the LORIA device. And Commercial Composites, St. Charles, Ill., will discuss use of the LORIA surface analyzer to quantify improvements in molding, bonding, and topcoating of an automotive exterior panel that was produced in a 58-sec cycle time with no preheating.

Diffracto Ltd. will describe expanded applications for the D-sight surface-quality instrument, which has enhanced software for rib read-though analysis, and can also be used for mold or tooling surface inspection. Since D-sight is a real-time technique, areas needing rework can be directly marked on the tool. Images can be stored as data or produced as hard copy to be marked up and given to tool reworkers. (CIRCLE 44)

This year's conference will see the introduction of an SMC test instrument of a different type. A device for evaluating flow of SMC and BMC under "real-world" conditions was developed jointly by Premix Inc., N. Kingsville, Ohio, and the University of Akron. The Premix Processability Tester, or PPT-100, is a squeeze-flow rheometer consisting of a small laboratory press with servovalve-controlled hydraulics, pressure and position sensors, and an IBM-compatible personal-computer interface, mounted on a wheeled cart. It compresses a material sample at a preset velocity and measures pressure from the compound's flow resistance. Rugged enough for use on the production floor, the PPT-100 can also be used for formulation R&D.

Software leads the user through an automated standard flow test. A SMC sample is placed on the 3-in.-diam., electrically heated platen (no mold is required), and the press closes to a preset position and halts for a specified time.

The instrument's screen displays a graph of pressure vs. time (see illustration), together with stored curves of minimum and maximum allowable pressures. Once the test is over, a curve of calculated viscosity vs. shear rate is also displayed. All data can be stored in a spreadsheet format for SPC analysis. For research use, multi-step speed profiles and other customized functions can be programmed.

A commercial version of the instrument is available from Interlaken Technology Corp., Eden Prairie, Minn., for around $40,000-45,000. A second-generation version, to become available in perhaps a year, will integrate dielectric cure monitoring with flow testing. The device will be displayed at Premix's booth at the SPI meeting. (CIRCLE 45)

In other SMC news, Dainippon Ink & Chemicals (DIC) of Japan (parent of Reichhold Chemicals) will announce a fast-cure SMC formulation with a special low-profile additive (LPA) that's said to reduce pinholes and yield a Class A surface. The formulation is already being used for the production of the Daihatsu Applause rear spoiler. The proprietary LPA is said to deliver the surface quality of polyvinyl acetate and the toughness of polyurethane. (CIRCLE 46)

DIC's W. German subsidiary, Reichhold Chemie GesmbH, will describe new phenolic SMC/BMC resins with controlled thickening performance and a non-acid catalyst, capable of providing heat- and flame-resistant, low-smoke products. (CIRCLE 47)

Rockwell International Plastics Products' Business Process Development Center in Centralia, Ill., will describe its computer-controlled press operation and automated SMC mixing and compaction. The company says it has achieved a 57-sec cycle time for an uncoated Ford Aerostar liftgate panel and an 87-sec cycle time for a Mack truck hood panel with in-mold coating. Rock-well says that proposed new catalyst systems, more reactive resin systems, and improvements in coating techniques should enable significant improvement upon both cycle times by the time of the conference.

International Copper Association, N.Y.C., and Isorca Associates, Granville, Ohio, will discuss advantages of aluminum bronze tooling for composites. A combination of high thermal conductivity and strength is reportedly unique to aluminum bronze and certain other copper alloys. Cast aluminum bronze tools have been used in autoclave molding of aircraft composites. More recently, this alloy has proved useful in certain SMC applications, where aluminum bronze cavities are inserted in a steel master die. (CIRCLE 48)

PULTRUSION NEWS

American Composite Technology, Boston, will soon form a separate company to sell its new disposable sensor for direct measurement of pressure inside a pultrusion die. This thin, low-cost ($20-25) sensor can be fed into the die embedded in the laminate. If used at intervals during production, it would provide advance warning of internal die buildup that would eventually lead to a jam.

The sensor can also monitor vacuum pressure in an autoclave when placed between the tool face and part or between the vacuum bag and the part. Other possible applications include hot-press molding, RTM, and filament winding. Current models operate at up to 500 F; one is in development for up to 800 F, which will cost $50. (CIRCLE 49)

Research at the University of Minnesota, Minneapolis, describes heat-transfer analysis for optimizing heater-band placement on a pultrusion die. Future work may allow the optimization of preheater power, initiator concentration, and die insulation.

Shell Chemical Co., Houston, will introduce two new, non-MDA epoxy resin systems for pultrusion. Epon 9405 and 9420, were developed in response to proposed health regulations on MDA handling. Epon 9420 has shorter gel time and lower viscosity than Epon 9405. Both use the same curing agent, Epon 9470, and can be adjusted by the Epon curing agent accelerator 537. They're said to produce composite properties "essentially equivalent" to those from a high-performance epoxy pultrusion system with MDA (Epon 9310/9360/537), with similar performance retention in hot and hot/wet environments. (CIRCLE 50)

THERMOPLASTIC COMPOSITES

In the fast-developing area of thermoplastic composites, researchers from NASA's Langley Research Center, Hampton, Va., will present one of four papers on thermoplastic pultrusion. Two more, from the Dept. of Macromolecular Science at Case Western Reserve University, Cleveland, will present work on "RIM-pultrusion" of nylon 6 composites from caprolactam with rubber toughener added, and on RIM-pultrusion of epoxy, with continuous impingement mixing of resin components just prior to the die. The fourth paper provides an unusual close-up look at a continuous impregnation process for producing thermoplastic prepregs. It will be presented jointly by McGill Univeristy's Dept. of Engineering, Montreal, and Vetrotex International, Chambery, France (which licenses fiberglass technology to Certainteed Corp., Valley Forge, Pa.). As shown in the accompanying schematic, these researchers have developed a sequence of concave and convex rollers, to open up the fiber bundles for thermoplastic impregnation within an extrusion crosshead.

Owens-Corning Fiberglas, Toledo, will describe new glass fibers for thermoplastic pultrusion to produce long chopped-fiber compounds for injection molding. Thermoplastic impregnation of continuous fiberglass requires lubricity, ease of strand opening, and low fuzz generation at strand contact points. The company ahs developed fibers for 1) engineering polymers (nylons, polyesters, polycarbonate, and styrenics); 2) polypropylene, and 3) high-temperature polymers like PPS. (CIRCLE 51)

A developmental "cocoon-shaped" glass fiber that is said to give improved flow and mechanical properties in thermoplastics will be presented by Nittobo Co., Ltd. of Japan. The company says all glass fibers tend to reach a saturation loading level in individual resins, above which properties improve little and rather tend to decline. Nittobo's new fiber with elongated cross-section (see schematic) reportedly reaches such saturation at higher loadings, permitting better properties to be attained. This is shown for PBT in figure. Nittobo also reports easier flow at equal fiber loadings, and better retention of average fiber length in injection molding. Besides PBT, these advantages have been observed in SAN, nylon, ABS, PPS and other resins. (CIRCLE 52)

Nippon Electric Glass, Notogawa, Japan, and Manville Sales corp., Toledo Ohio, have developed a new glass fiber for acetal. They say the Star Stran 751 fiber eliminates the need to add adhesion-promoting additives such as isocyanate and aminosilane to increase molded part strength. Many of these additives are known to cause discoloration, restrict flow properties and create decomposition gases during molding. (CIRCLE 53)

OTHER NEW RESINS, ADDITIVES

Vinyl esters will get a lot of attention at the conference. Dow Chemical Co., Midland, Mich., has designed vinyl ester resins for reduced styrene emissions. One successful approach has been to modify the epoxy backbone of a bisphenol-A resin to lower the viscosity and permit less styrene monomer diluent to be used. Another approach was to substitute less volatile vinyl toluene monomer for styrene. (CIRCLE 54)

Akzo Chemicals, Inc., Chicago, will discuss a new cumene hydroperoxide-based catalyst formulation (R-239A), which reportedly eliminates gassing and other problems associated with MEKP, BPO, and TBPO. (CIRCLE 55)

Interplastic Corp., Minneapolis, recently developed vinyl ester laminating resins and gel coasts specifically for use with non-foaming, room-temperature TBPO/cobalt/DMA catalyst systems in place of MEKP. Because these bubble-free systems cure faster and better than with MEKP, they reportedly have proven commercially successful in marine tooling as an alternative to isophthalic polyesters, which opens up other tooling applications--RIM, RTM and thermoforming--typically dominated by epoxies. (CIRCLE 56)

J.M. Huber Corp.'s Chemicals Div., Havre de Grace, Md., will show that its unique precipitated silica, together with "bridging agents" such as ethylene glycol or glycerine, gives better thixotropy in vinyl esters than fumed silica, and at a 28% cost saving. (CIRCLE 57)

Great Lakes Chemical Corp., W. Lafayette, Ind., will describe a new intumescent, low-smoke flame retardant for polyester, vinyl ester and epoxy composites. CN-1197 is a phosphorus-based, white crystalline material that reportedly yields Class I tunnel-test flame and smoke performance at 20-25% use levels. (CIRCLE 58)