Application Digest

December 16, 1996

Conductive elastomers add versatility to EMI shielding

Todd Sousa, Applications Engineer, Chomerics,
Division of Parker Hannifin Corp., Woburn, MA

Design engineers face more EMI concerns than ever before, from tighter packaging and added openings to faster clock speeds and stricter global standards. Many shielding gasket materials are available to fix EMI problem spots, such as enclosure seams, cables, displays, and cross-talking components.

The most versatile EMI gasket choices are conductive elastomers. Nearly any shape that can be drawn can be produced in these materials. Thousands of standard extruded and molded shapes are available, and new technologies have cut the time and cost of making custom gaskets.

For decades, conductive elastomer gaskets have shielded military electronics. During the past 10 years, however, manufacturing efficiencies have made them attractive to commercial markets. Recent developments include high-speed extruding and molding, robotic gasket dispensing, and finite element analysis of proposed gasket shapes.

Fundamentally, the formula for conductive elastomers remains unchanged. The base material is typically silicone, with fluorosilicone, fluorocarbon, and EPDM used for special needs. The elastomer binder is loaded with electrically conductive fillers. Common filler choices include silver- or nickel-plated particles. Binders and fillers can be matched to specific needs, e.g. shielding level, corrosion resistance, or flame retardancy.

To speak with a Chomerics applications engineer, call 617-935-4850.

How to optimize zinc-component design

Scott Phillips, Manager-Marketing Services, Fishercast
Peterborough, Ontario, Canada

To help engineers optimize small-component design for function, castability, and economy, Fishercast has prepared a Design Guide for Zinc Die Cast Components. Outlined in the guide are the many engineering services and technical capabilities offered, beginning with the initial concept through actual component design.

Fishercast's team of application engineers has more than 50 years of diecasting experience. They utilize finite element analysis (FEA) as a part of this customer service. By measuring stresses, deflections, and temperatures for critical areas of the component, FEA allows the designer to accurately predict the part's performance level in its operating environment.

Also, prototyping services are offered. They include: selecting zinc alloy bar stock that, when machined, closely resembles the properties of the die-cast component; soft tooling that provides a pre-production quantity of components for testing purposes; spin casting; and stereolithograpy.

Fishercast uses Pro/ENGINEER exclusively to design the diecasting tools. As a leading-edge CAD technology software based on solid modeling, Pro/ENGINEER accurately models the component, providing a software prototype that guarantees more accurate design results.

With Fishercast's small-component zinc alloy diecast process, the customer can maintain precise part-to-part consistency and dimensional stability over large production volumes. Components are cast flash-free and ready to use.

To speak with a Fishercast applications engineer, call 705-748-9522.

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