DuPont Zytel HTN for coil encapsulation

A wound and terminated coil (left) before it is fully encapsulated (right) in DuPont Zytel HTN.

DuPont Zytel HTN high-performance polyamide resin is being used to encapsulate a coil designed for Eaton Corp. six-speed automatic transmissions. The coil, manufactured by Tri-Tech, LLC actuates an inertia brake that slows engine speed during shifting. It is exposed to synthetic transmission oil at typical operating temperatures of 275°F (135°C), with peaks up to 350°F (177°C).

The coil's design underscores the benefits of thermoplastic encapsulation over thermoset technology, according to DuPont. Integrally molded lugs around the perimeter of the part snap into a groove in a metal clutch plate housing. This approach both simplifies assembly and provides secure, vibration-tolerant mounting, said Bill Everett, Director-Engineering and Sales at Tri-Tech. He added that the toughness and resilience of Zytel HTN are "crucial" for snap-fit assembly.

The coil is manufactured in three steps. A bobbin using a 35% glass-reinforced grade of Zytel HTN is injection-molded. Magnet wire is then wound around the bobbin, and terminations and lead wires are installed. The wound, terminated unit is then placed in a mold and a 15% glass-reinforced grade of Zytel HTN is injected to fully encapsulate it. The coil comes out of the mold ready to use.

The bobbin's flanges have thin, feathered edges, which, during overmolding, soften and bond with the encapsulation material.

- Patrick Ponticel

New magnetorheological fluids from Lord

MR material from Lord Corp. changes from liquid to solid form under a magnetic field.

Lord Corp. has been developing magnetorheological (MR) fluid technology for commercial applications for more than a decade. It is now introducing two new fluids to its standard product line. The new formulations were developed in response to improvements in MR technology driven by high-volume production.

Hydrocarbon oil-based MR fluid MRF-132AD replaces MRF 132LD, which, Lord says, had been the industry product standard for the past five years. MRF-132AD has enhanced stability and durability for use in demanding shock absorber applications. Replacing water-based MRF-240BS is MRF-241ES, which features improved stability and durability for applications requiring natural rubber seals. The two materials being replaced will be available through 2002.

When exposed to a magnetic field, MR material within milliseconds change consistency from a fluid state to a near-solid state. In a rotary brake, MR fluid produces variable shear forces in direct proportion to the applied controlled current to the electromagnet in the piston. The system is simple in design and requires little power. Commercial applications of brakes include pneumatic control and steer-by-wire tactile feedback devices.

MR technology is also used to control shock, vibration, and motion in primary automobile suspension systems and seat suspension systems.

- Patrick Ponticel

Ames seeks big results on "small effects" research

Napolitano (left) and Trivedi place an aluminum alloy single crystal into a furnace to selectively melt certain microscopic regions, forming and trapping a dispersion of tiny liquid droplets within the solid. While this melting proceeds rapidly, stabilization of the droplet dispersion may require several weeks. Morris, the theorist, watches the procedure.

To gain a better understanding of how microstructures develop in materials, scientists at the U.S. Department of Energy's Ames Laboratory at Iowa State University are examining certain properties that exist in metals at the interface between the liquid and solid phases during solidification. The research may one day enable scientists to tailor microstructural development, providing the basis for new and improved materials.

Researchers at Ames have shown that there are many subtle variations in microscopic properties near the liquid-solid interface as the solid is "freezing out." The small variations depend on which crystal face is in contact with the liquid. Difference faces (orientation) give slightly different values for properties such as free energy, mobility, and stiffness (surface tension); these properties play a crucial role in how the microstructure of a metal evolves during solidification.

"There are some properties that are very small," said Rohit Trivedi, an Ames physical metallurgist and an Iowa State University distinguished professor. "For example, the way a snowflake forms depends on very small factors. It turns out that some of these small factors are really the essential ones in determining shape. The same thing is true not only for materials, but for humans, animals, plants—anything that grows."

Innovative experimental techniques developed by Trivedi and Ralph Napolitano, a physical metallurgist and ISU assistant professor, have provided the first reliable measurements of the minuscule variations in free energy at the liquid-solid interface in metallic systems. Computer simulations developed by Ames theoretical physicist James Morris calculate these same quantities and show how the atoms behave at the interface. The combined efforts provide both a direct check between the experiment and the simulation and the opportunity to put forth new solidification theories that may lead to the ability to predict the development of microstructures.

"We're investigating some very specific quantities, such as the variation of interfacial free energy with crystallographic orientation," said Napolitano. "By revealing the essential physical behavior of liqid-solid interfaces, these critical experiments are facilitating significant advancement in the theoretical prediction of microstructures."

The two-phase structures that form within the droplets during rapid quenching from the liquid state reveal the overall pre-quench equilibrium shapes of the droplets. Trivedi and Napolitano use such cross sections to quantify the deviation from sphericality in the quenched droplets. The deviation is extremely small, but enough to effect big changes in microstructural development.

In experiments designed to measure small effects on the property of interfacial free energy, Trivedi and Napolitano have developed a technique to selectively melt certain microscopic regions within an aluminum alloy single crystal, forming a dispersion of tiny liquid droplets trapped within the solid. (A single crystal is one in which all the atoms are oriented in a specific direction. The orientation is uniform throughout the material, creating a simple, symmetric structure.) The material is then heated to bring the droplets structures to equilibrium (the condition at which no change occurs in the state of a system unless its surroundings are altered). After rapid quenching, the droplet shapes are measured carefully and their equilibrium shapes determined, providing the necessary link to interfacial properties.

"Thermodynamics tells us how the equilibrium droplet shape is related to the interfacial free energy," Napolitano said. "These measurements provide a direct means for quantifying the subtle variation of this property with respect to crystallographic orientation. The challenge is to accurately measure the degree to which the droplet shapes deviate from being spherical, and they deviate only by a percent or so."

It's the job of Morris to determine the size of the deviation. If the droplet is not perfectly spherical, "We want to measure that," he said. "We don't want it to be influenced by dirt in the system or anything else. The deviation is a very small number, but it's very important—and that's where doing the calculations and modeling the atomic fluctuations of the liquid-solid interface have come in."

- Patrick Ponticel

Elliott Group acrylic for Communiport display

Delphi's Communiport Integrated Navigation Radio uses a polymethyl methacrylate coating for the display.

Delphi Corp. is using Clarex AR coat filter material from Elliott Group International for the visual display of the Tier 1 supplier's Communiport Integrated Navigation Radio. Specificed by Delphi, the antireflective, acrylic material for the 5.8-in diagonal, full-color display is a 2 in (50 mm) thick polymethyl methacrylate with scratch-resistant, anti-reflective, and anti-smudge coatings.

Clarex, available in various sizes, thicknesses, and transmissive properties, allows flexibility to maximize image quality and visibility. Cast in lightweight acrylic and available in light transmissions from 45-98%, it offers reflection prevention of under 0.5% at 550 nm (22 µin).

Standard AR coat filter material is available in clear, neutral-density gray, green, and red with respect to light transmission and thickness. Five nonglare matte surfaces are available. Thickness range is 0.008-0.197 in (0.2-5 mm).

The Communiport radio system has a full-map, turn-by-turn navigation system with voice prompts.

- Patrick Ponticel