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.
In most cases the savings is realized from the longevity of the wire rope isolator. Elastomeric mounts are replaced by wire rope isolators when they fail in order to prevent future downtime and replacement costs. The wire rope isolators are sized to operate below the fatigue limit of the stainless steel cable, providing theoretically infinite fatigue life. This, along with the corrosion resistance of the unit provides superior endurance in many applications.
Thanks for the article, Greg. I had always thought of dampening with elastomer, or hydraulic/pneumatic absorbers. Learning some thought provoking ideas today. I can think of a number of application where these could be useful.
Rob, I am sure that elasomer isolators arena lot cheaper than the wire rope versions, but that is if only the purchase price is considered. But where the cost of failure is high the wire rope devices suddenly seem to be a far better choice. In addition, they can survive under a leaky hydraulic power unit, while an elastomeric isolator has the elastomer become a very sticky and messy mush, which does not isolate vibration or even hold the power unit in the correct position. At that point the cable isolator became a much less expensive choice.
Another benefit not mentioned is that the wire rope isolators are quite resistant to most petroleum products, although I suspect that oil immersion would reduce the damping a bit. But after seeing some rubber shock mounts just sort of melt away, the wire ones look good.
These wire rope isolators are an excellent idea when you have the space to use them, although they do make them small enough to hold on your finger-tip. If you are working on relatively small products, and size (and weight) matters, elastomers are always considered first, to isolate a small PCB, for instance. Another option is Lodengraf damping, to absorb higher frequency vibrations. Vibration isolation is a big business, and there are many options. It will depend on the application. Thank you for bringing this option to the forefront.
@JimT: Fortunately, before beginning my 30 years as a design engineer in earnest, I served on a Navy command & control ship full of receivers and transmitters. We had a pair of 5kW AM transmitters that were mounted on these, and those cabinets (IIRC) were really big: about 4 feet by 4 feet at the base and probably 6-7 feet tall.
(Check out the link to ITT Enidine at the end of the article - they make these things.)
I'm kind of embarrassed to say, after 30 years as a design engineer, I've never seen one of these. Great idea, for all the points listed by Greg. Yes, I have had elastomers fail for various reasons (primarily vibration cycling, and extreme low temperatures – even exposure to UV), but these rope isolators really look like a clever way to create a strong, flexible, long-lasting solutions. Been around for 30 years-? I didn't notice a fabricator's name mentioned ,,,,,
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