Machine Design

Everything you wanted to know about seals, almost

Sizing O-rings and grooves used to involve a lot of calculator work because it required precise tolerances and surface finishes. It still does, but software such as Total InPHorm replaces the calculator with several easy-to-use programs that assist selecting O-rings and seals, specifying thermal conductors, and sizing support geometry.

Typing nominal geometry for an O-ring into Total inPHorm brings up information such as this.

To design a Chomerics product, users first choose one of two product classes. Each selection presents different image cues as explanations for where the components work best.

After selecting a hydraulic rather than pneumatic application from the packing section, users are presented with a cross section detailing further possibilities.

The software has sections devoted to Chomerics (electrically conductive compounds), composite-sealing systems, glands from a division of Parker Hannifin Corp., O-rings, packings, Web links and, of course, an order pad. Each section has its own software and reference library. Chomerics, for example, includes 12 documents such as the EMI Shielding Engineering Handbook and related topics. Hypertext links connect most topics.

The CD could be subtitled, "Almost everything you wanted to know about seals," thanks to the bounty of information. The learning curve is short because each section works similarly. For instance, users choose a category --one of the five products -- describe the application by menu selections, specify a product line, and choose a type, material, and size. With each selection, pictures and sketches pop up to make sure the selection is what the user is expecting.

Chomerics, for example, are used as resilient grounding contacts and for attenuating radiated emissions. Seals from this section are used to create Faraday-cage enclosures and shield apertures in enclosures. Each section and subproduct grouping includes detailed descriptions so novices know what they are selecting.

The main Chomerics menu lets users select EMI shielding and thermal-interface products. These later items are thermally conductive materials, generally in the form of elastomers, tapes, liquid compounds, and insulated foils. They improve heat conduction from one surface to another by replacing air gaps with a more thermally conductive medium. They also insulate power semiconductor packages and attach heat sinks to hot devices.

And for composite seals, the software contains data on Gask-o-seals, flange integral seals, fastener and fitting seals, metal gaskets, and V-seals. Gask-o-seal molds an elastomer directly into grooves of metal or plastic retainers. A special section covers a range of unusual design considerations, such as contact with acids and bases, fuels, high pressure, medical, and temperature considerations.

Sizing some seals require more information than the software provides. Seals in food-service applications, for instance, must comply with FDA regulations. But the list of approved seals is not included, so users have to contact the developer for more data. Metal seals, for instance, are so specialized they also require a call to the developer's engineering office.

The section titled JBL deals with glands, which are seals with rectangular cross sections. After selecting one of three styles, users select a material, and familiarize themselves with special considerations, such as the FDA White List compounds. Each material includes compound information and a material report. Typing dimensions into the size selector serves as a design check. If the hardware is incorrectly sized, the software recognizes disparities and flashes warnings such as, "Radial clearance between the mating parts is excessive. Tighten tolerances or change nominal dimensions." It also provides dimension limits to guide users.

The packings section is a bit more involved because of the wide range of cylinders that could be encountered. For instance, the Describe Application window asks for temperature range, whether the design reciprocates, oscillates, or rotates, a stroke length, and pressures. An onboard database holds hundreds of packing designs and part numbers. A version of the software can be run online from the company Web site.

The software comes from Parker Hannifin Corp., Seal Group, 14300 Alton Pkwy., Irvine, CA 92618, (949) 833-3000,

TAGS: Fasteners
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