Page 22 - MetalForming-Feb-2018-issue

Gas-Spring Safety
A die-spring malfunction can harm not only production, but life and limb as well. An industry expert weighs in on how to mitigate risks while enhancing spring life.
BY LOUIS A. KREN, SENIOR EDITOR
If we use a hammer correctly, it is not dangerous. But if we use it to hit our hand, suddenly it becomes very dangerous. The same holds true for nitrogen-gas springs. If used cor- rectly, they are safe and effective. Gas springs can withstand all the working stresses for which they were designed. But they cannot sustain overstresses generated by incorrect usage. Gas springs essentially are pressure vessels, with all of the inherent dangers of pres- sure vessels. Fortunately, advance- ments have yielded gas springs that can help prevent dangerous overpres- surization and/or take steps to reduce pressure. That said, users must keep in mind practices that result in safe, effective gas-spring operation.
Like any pressure vessel, care must be taken to make sure that the com- pressed ingredients do not unleash in unintended ways that can produce sometimes catastrophic results. For example, a compromised gas spring can turn a cylinder rod into a projectile,
When employing nitrogen-gas springs, do not use more than 90 percent of the cylinder stroke length. This helps elimi- nate an overstroke condition that can damage a cylinder and cause the release of some components. Under pressure, these components can release at dan- gerously high speeds.
reaching speeds north of 200 mph. Shot straight up, a cylinder could rocket straight over the Empire State Building. Imagine what would happen to any- thing, and anyone, in its path.
To help MetalForming review proper safety practices for the die designers, builders and operators often working with nitrogen-gas springs, we reached out to Jim Glynn, president of Special Springs, LLC North America (www.spe- cialspringsna.com), with U.S. head- quarters in Canton, MI. The company’s website offers a number of safety and design tips. We asked Glynn to identify
Some nitrogen-gas springs feature the ability to vent during overpressurized- cylinder conditions.
common safety and design factors that should stay top of mind when speci- fying, installing and using nitrogen- gas springs, and here they are.
Allow for 10-Percent Stroke Reserve
All nitrogen-gas springs have a rec- ommended maximum stroke length. It’s recommended that this maximum length not be approached.
“When designing a tool or specify- ing a nitrogen-gas spring, make sure to factor in a stroke reserve so that stamping forces do not drive a cylinder to the endpoint of its stroke,” says Glynn. “Do not use more than 90 per- cent of a cylinder’s stroke length. Fol- lowing this rule helps eliminate an
20 MetalForming/February 2018
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