Combating Shock & Vibration Is About More Than Cost

Neither snow, nor rain, nor heat will keep a wire rope isolator from performing its appointed job, which is withstanding shock. In spite of that, engineers often pick elastomer products, like rubber mounts, to deflect shock. That's because elastomers are cheap, as low as $3 apiece, and people don't always consider the benefits of wire rope isolators.

The wire rope isolator, which has been around for at least 30 years, is made of stainless-steel strands of cable threaded through aluminum alloy retaining bars and crimped. When the strands flex from vibration input or shock impulse, they convert kinetic energy into thermal energy, which then dissipates to atmosphere. This protects whatever product the wire rope isolator is cushioning as it acts to decouple the equipment from the vibration or shock source. For example, GPS gear mounted to an agricultural tractor or communications equipment aboard a warship are applications for wire rope isolators.

The increased deflection capability of the wire rope isolator enables the product to withstand shock and protect whatever equipment it's mounted to, deflecting up to an inch or more under a high force shock impulse. Under similar conditions, an elastomeric compound gets very stiff and may deflect only 0.060 inch to 0.100 inch. The larger wire rope isolators can deflect up to 6 inches under extreme input conditions, while supporting up to 5,000 lb (2200 kg) per isolator.

The wire rope isolator also withstands temperatures as high as 500F (260C), chemicals, and ozone without compromising performance. In contrast, heat and weather degrade elastomers. And washdown environments corrode them. But it's easier to mold hundreds or thousands of rubber mounts, and thus cheaper to buy these products than handmade wire rope isolators. Finally, wire rope isolators enhance protection. When sized properly, they can outlast the equipment that they support.

- Greg Herman is the product manager for ITT Enidine, part of ITT Control Technologies.

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