https://www.machinedesign.com/mechanical-motion-systems/article/21837752/a-guide-to-gas-spring-design-and-customization

A Guide to Gas Spring Design and Customization

pril 30, 2019
Knowing how gas springs work will help you select the right one for a design.
David Rowland
When a design calls for an industrial gas spring, there’s a wide range of standard, off-the-shelf products available from various manufacturers. But ordering a gas spring from a catalog comes with a lot of risks. Depending on the application, it’s likely that some degree of customization is necessary to ensure just the right gas spring is found.

There is a better way to get the best gas spring: Take an engineering approach to adding gas springs to designs, and use standard industrial gas springs as a starting point.

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Gas springs are self-contained, force generating, maintenance-free cylinders. They are used to move and position lids, chairs, table-tops, and host of other assemblies. body is pre-charged with nitrogen gas to provide a specific output force. Pressure is applied to the piston and diameter area, which provides the output force in push-type gas springs.

Standard Gas Springs
Standard gas springs are quick and easy to order. They’re also relatively inexpensive, provided they don’t need troubleshooting right out of the box to fit the application. However, customers may underestimate how much data they need to specify gas springs. Furthermore, off-the-shelf gas springs commonly offer only one of three choices of output force. Will one of them be exactly right? There’s a good chance designers and customers may get unintended results.

If factory-supplied output forces don’t work, hoods or lids may open unexpectedly, or the spring might not support the load it needs to move. Another concern with off-the-shelf gas springs: customer drawings fail to allow room in the installation for the spring. Or, the spring comes with the wrong end fittings. These situations often force customers to waste time trying different forces and modifying the assembly, and they still may not get the right gas spring for the job. All this trial-and-error inflates labor costs and the project suffers needless delays.

Unlike most standard gas springs, an engineered spring is, in essence, a custom part the manufacturer typically adjusts to an application’s specifications. The added investment usually pays off via saved time and labor costs that come from gas springs working perfectly the first time.

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Gas Spring Basics
To understand the important factors to consider when ordering a custom gas spring, engineers should know the basics behind how they work.

Gas springs are self-contained, force generating, maintenance-free cylinders. The body is filled with pressurized nitrogen gas that generates a specific pressure. The pressure pushes on the piston, which provides the output force in push-type gas springs. As the piston rod is pushed and compressed, the piston generates a constant output force and controls its velocity by metering nitrogen through a hole. A little oil dampens, or cushions, piston movement at the end of travel when the gas spring is mounted with the piston rod facing downward. Some gas springs have a field-accessible vent valve for venting nitrogen to reduce the spring’s force.

Depending on the application, designers can choose from several types of gas springs. Some common gas spring types include:

Push-type to lift and lower loads with easy control and minimal exertion. Push-type gas springs support covers and lids in a broad range of industries.

Pull-type to fit in tight. This type is compact and mounts in any orientation and position. Unlike in standard push-type springs, pressure in the cylinder retracts the piston rod. Pull-types can have low progression rate. Progression is the increase in force exerted by the gas spring over the stroke. Progression rates, which measure the change in progression, can be as low as 11%.

They also can have an adjustment valve to control the traction force. Traction force is the pulling force from the gas pressure that retracts the rod. It can be as low as 11 lb and as high as 1,630 lb, depending on the gas spring. Providing this pulling force is the gas spring’s main function as it helps in lifting and holding up all types of heavy objects in many different applications.

Locking to hold a position. Chairs often need to maintain a certain position to support a patient or someone. In an adjustable desk chair, for example, a person adjusts the height by first pressing a button or lever. This opens a piston valve so the seat can be moved up or down to the desired position. Letting go of the button or lever lets the valve closes and locks the piston so the seat remains at that height.

Two custom-made stainless-steel locking gas springs from Ace Controls lets this hygiene and toileting device for children with disabilities be inclined up to 15 deg. forward or aft and be easy to clean.

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