Logo
Innovative motion control solutions since 1947

Category: Gas Spring

How to Improve the Life Expectancy of Your Gas Springs, Pt. II

In the first part of this extended article, we talked about how to extend the life expectancy of your gas springs — and here, we continue that conversation. Let’s get right back into it.

Things to Avoid
To keep your gas springs working better, longer, never use the bottom of the spring as the strike surface — the top of the piston rod is the correct option. Rather than using improper or inadequate guidance, which can lead to side loading due to axial misalignment, us guide retainer sets, roller bearings, wear plates, and a hardened strike surface. That will extend spring life as well. Anything more than a single degree of side load on the piston rod is asking for a gas spring that fails years earlier than it could.

Along that same vein, avoid contaminants. Even minor contamination within a die can cause premature failure. Die designers ought to specify drainage holes in the spring pockets so that fluid doesn’t pool around the springs. Gas springs shouldn’t be exposed to caustic draw-die compounds or other contaminants; if your production line makes this a necessity, contact the gas spring’s manufacturer to talk about what protective measures you can take.

Preventative Maintenance
Of course, any discussion of extending the functional lifespan of any piece of equipment, from gas springs to pneumatic cylinders, needs to touch on the cornerstone of equipment care: preventative maintenance. Sound preventative maintenance procedures require users to check the pressure, temperature, and physical condition of the springs for signs of wear.

If a random sample of springs in a die exhibit signs of being overworked, overpressured, or overheated, every other spring should be examined as well. A significant variation in spring pressure or condition could indicate a flaw in the die’s design, build, or operation. If a specific spring’s pressure is low, check for leaks, then recharge and check for leaks again.

The physical condition of a spring should be determined with a visual examination; there should be no need to dismantle the spring. Worn springs that are still viable should be rebuilt. If the rod is damaged, it obviously will need to be replaced as well.

Following these four major areas of care should help any project keep its gas springs lasting as long as their construction allows — good luck!

How to Improve the Life Expectancy of Your Gas Springs, Pt. I

The number one determinant of the life expectancy of a gas spring is, perhaps without much surprise, the manufacturer. Choosing a manufacturer whose representatives will offer you assistance choosing the best design for your job — and then actually listening to the reps — is a great step toward a long-lasting gas spring. Also, talking to your supplier about performance guidelines — specifically, operating temperature, speed, and charging pressure — can help you understand how to stay within a spring’s operating parameters, which will help it last.

The decision of which gas spring to use should be based on several criteria. The spring must match the task it’s intended for, it’s location in the die, and the mounting method most appropriate for the task.

Tool Build and Die Design
Die design is one of the most important parts of optimizing gas spring life. Such springs have standard operating specifications — for example, a spring may be charged to a maximum pressure of 150 bar (2175 psi), and reach a maximum operating temperature of 160 degrees Fahrenheit. Exceeding either of those guidelines will rapidly slash the life expectancy of that spring.

Futhermore, unless there is no other option, you should never use more than 90% of the stroke of a gas spring — and a rod travel of 75% to 80% is even better, as it reduced both in-cylinder pressure rise and the amount of heat produced per stroke. Further, aiming to distribute loads evenly between springs so that no one spring outworks the others and none are approaching full capacity goes a long way toward keeping a spring functioning in the long term.

Accessorizing for Lifespan
Gas spring accessories like nitrogen-gas surge tanks added to a piped system will add volume so as to maintain a lower pressure rise. Piping gas springs together with pneumatic fittings can give you the ability to monitor and control force from outside the die, giving you the ability to manually modify a spring’s operations based on external conditions like load, which further enhances the lifespan.

This is still only scratching the surface — come back next week for part II of our guide to maximize gas spring lifespan.

Extend the Life of Your Gas Springs

Gas springs are pneumatic cylinders of heavy-gauge steel that hold pressurized nitrogen gas. A nitrite- or chrome-coated steel shaft with a seal on one end extends out from the cylinder. If you push on the shaft, it will collapse in on itself, and then the strength of the pressurized air on the inside will push back. If you pull on the shaft, it will extend outward, then pull back in as the vacuum created by your pull fights against the force of your hands. Depending on the cylinder and shaft diameters, the sealed kind of gas springs generally come with initial internal pressures between 5 lbs and 450 lbs.

Some variations (which use natural atmosphere rather than nitrogen) have a small hole on the far end of the cylinder that allows air to flow slowly into or out of the cylinder — thus creating a mechanism by which pressure on the gas spring is first fought by the pressure created inside the cylinder, then slowly released as the pressure inside equalizes with the pressure outside through the small hole.

If you want your gas springs to keep functioning for as long as possible, you want to minimize stroke (the distance the shaft has to travel) and maximize gas volume (the pressure inside the cylinder). You also want the end connectors — generally ball-and-socket joints to protect the gas springs from experiencing torque-induced load — to be strong enough to withstand both tensile and compressive loading. (The cheaper flat connector with a hole that creates a hinge joint is awful for your gas springs’ life as it has no ability to relieve stress from out-of-plane movements.)

The best placement for the gas spring has the shaft pointing down (and correspondingly the cylinder pointed up.) This is because the spring passes through a thin layer of oil at the end of it’s complete stroke to keep it lubricated, and the shaft-down orientation ensures the oil is gathered in one place to present maximum effectiveness at lubricating the spring.

Finally, keep the gas springs within the temperature limits recommended by the manufacturer. Over-hot springs allow gas to escape by increasing the pressure of the gas inside the spring (and remember that we’ve already chosen to maximize the internal pressure in order to improve spring life, so increasing it even more will cause problems), and over-cold springs allow gas to escape by causing shrinkage of the seal that holds the gas in.

Stick with these guidelines, and your gas springs will last for decades.

AirMount Isolators: Better Than Springs For Many Common Industrial Functions

Firestone’s AirMount isolators are a very unique form of gas spring, essentially strong rubberized outer walls capped on either end by metal caps. By filling the inner area with a mass of compressed air and shaping the outer wall correctly, the result is a compact device capable of up to nine inches of static deflection with spring rates lower than a coil spring and an installed height that would be impossibly small with any solid isolator.

The AirMount is also incredibly versatile compared to a coiled spring; by adjusting the pressure of the air within the isolator — which can be done on the fly — the device can easily adapt to loads from dozens to thousands of pounds without needing to be switched out or manually adjusted. No solid spring could hope to achieve the same kind of flexibility.

Furthermore, the ability to adjust the volume of air inside the AirMount on the fly gives you the ability to maintain a level surface: as the load shifts, the air springs can be adjusted to maintain a constant height and thus a level surface for the load. This variability also means the AirMount can be used across a wide variety of loads with constant efficiency — very much the opposite of a coil spring, which loses isolation efficiency if the supported load decreases even by a small amount.

Also, the AirMount is a remarkably compliant with vibratory motion. That means that you don’t need to add inertia mass to your loads. That means no expensive structural aluminum framing to cope with the added mass. The AirMount has a low natural frequency and a large travel range to boot, further reducing the need for inertia mass.

In fact, the already low natural frequency of the AirMount can be reduced even further with the addition of an auxiliary reservoir — below 1 Hz. To accomplish the same frequency with a coil spring, you’d have to have a real static deflection of nine inches; a spring offering that much deflection would have to be so long as to be nearly impossible to stabilize.

You Use Gas Springs All The Time And Probably Never Knew It

Have you ever opened someone’s screen door and had it not slam shut on you when it closed? Congratulations — you’ve used a gas spring. Gas springs range in size and power from the tiny ones that keep screen doors from sliding shut or keep the lid of your hatchback’s trunk up to massive gas springs that act as shock absorbers on cranes and other construction equipment.

Gas springs are steel tubes that hold pressurized gas, usually nitrogen because it’s the cheapest noble (i.e. nonreactive) element. Unlike a pneumatic cylinder, however, the purpose of a gas spring isn’t to push the gas to a new location; it’s to use the physical properties of the gas to cushion impacts.

Because gas compresses when pushed upon, a gas spring acts much like a normal spring, absorbing impacts and then pushing back. Gas springs with fine holes in the cylinder will then proceed to lower the load slowly until it reaches a stopping point — as is the case with the screen doors. Other gas springs have nitrogen on both sides of the airtight seal, and thus provide impact absorption in both directions and settle toward the middle of the spring.

Other variations include locking gas springs, which use a locking shroud to keep the spring fully extended until it’s unlocked; friction-stop springs, which have a locknut that can be positioned anywhere along the spring; and adjustable-force springs that allow the amount of gas inside the spring to be adjusted on-site after installation.

A close cousin to the gas spring is the damper, which is essentially the same mechanism but filled with hydraulic fluid and with a small reservoir into which the fluid flows as pressure is exerted on the piston. A damper slows the load’s progress by forcing the fluid inside through a small hole. Like gas springs, dampers can work in one direction or in both.

If you’re working in any kind of major industry, you may be well aware of the gas springs and dampers that surround you and help you get each day’s work done. If you’re like the rest of us, you may be surprised at just how commonplace these helpful little items actually are.