FEATURE SPRINGS & SHOCK ABSORBERS
It’s all in the construction S
What is a gas spring? How is it constructed? And what applications can it be used in? Camloc Motion Control explains
uitable for use in a wide range of applications, gas spring and damper solutions can be found anywhere there is a need for assistance with lowering and/or counterbalancing weights, through to lift assistance. Principally, a gas spring is the same as a mechanical coil spring: a device for storing energy. However, a gas spring stores energy by compressing the gas contained inside, rather than straining material, which makes up a coil spring. A gas spring is a closed system which
requires no further gas to be introduced once charged and manufactured. The pressure on either side of the piston (reference point one) remains equal no matter where it is positioned, due to the small cross-sectional area of the rod (reference point two) where the gas is unable to exert any pressure. As the rod is pushed into the tube, the gas contained in the spring is compressed, increasing the pressure and creating the spring-like behaviour. The piston attached to the rod allows the flow of gas across the piston and provides the means of controlling the flow of gas as the rod is depressed and extended.
GAS SPRING CONSTRUCTION The rod: This comes as either precision ground, polished carbon or stainless steel and the surface is treated to improve wear and increase corrosion resistance. Generally, the rod will always be longer than the stroke of the spring and shorter than the length of the tube. Carbon Steel can be treated in several
ways such as chrome-plating, salt-bath nitriding and using a Nitrotec surface layer treatment. For Camloc’s carbon steel rods, a layer of Nitrotec surfacing is used as this offers: better wear resistance; lower frictional characteristics; and a corrosion resistance equivalent to stainless steel. Tube: The next component is a
Gas spring operation
in position. The gas springs are charged to their maximum force during manufacture, but the gas can be gradually released via the Vari-Lift valve. This is done by inserting the Allen key provided into the Vari-Lift valve found at the end of the tube and making a quarter-turn. Once gas can be heard, make a quarter-turn back to close the valve prior to checking whether the application is running smoothly. If not, repeat the process. Release of gas must be carried out on a gradual basis to ensure too much is not released.
THE APPLICATIONS Thanks to the benefits, gas springs are used in many applications, with some examples including: • Car boot – lift assist and controlled rate of movement, with damping.
high-integrity, powder coated, carbon or stainless steel seamless welded tube. The internal surface finish and tensile strength of this tube are critical for the gas spring’s longevity and burst pressure performance. Guide and seal package: Manufactured
from plastic composite, this provides a bearing surface for the rod and prevents the escape of gas and ingress of contamination. In addition to plastic composite, the guides used in Camloc’s gas springs can also be manufactured from zinc, brass or other materials, with a suitable bearing sleeve incorporated. Rubber is used as standard for seals. Piston assembly: This is manufactured
from zinc, aluminium or plastic. For factors involving safety and preventing the rod being expelled from the spring, the integrity of the piston to rod attachment is critical. The piston assembly controls the rate at which the gas spring extends and compresses. End Plug: This is used to seal the tube end of the gas spring, with this also attaching to the tube end fitting. Camloc’s Vari-Lift can be incorporated here where required, allowing for the release of Nitrogen gas and subsequent reduction in force of the spring. Nitrogen Gas Charge: Nitrogen is used inside gas springs as it is inert and non-flammable.
DE-GASSING Camloc’s Vari-Lift can be de-gassed while
• Access panel doors • Lid applications • Hospital beds – positioning leg rests in multiple positions and providing smooth control and operation of the descent of back rests; hydraulic height adjustment systems, etc.
• Monitor arms – Camloc’s stop and stay and stop and stay+ range counterbalance the weight of the screen, through ‘stick-lip’ friction to the rod being applied by adjusting the lock-nut, allowing finger-tip movement to any position. The in-house design team at Camloc
has the ability to design bespoke gas spring solutions to suit application needs.
Camloc Motion Control
www.camloc.com
GAS SPRING TERMINOLOGY Stroke - The maximum amount of distance the rod can
travel from closed length to extended length. Extended length – The total length of the gas spring
measured from the centre of one end fit to the centre of the next end fit. Closed Length – The total closed length measured
from the centre of one end fit to the centre of the next end fit. There may be times when no end fits have been specified, so this measurement will refer to the length from rod end to tube end (excluding threads). Beadroll – The grooved section of the tube. This is used to retain the guide and seal package and prevent the piston from damaging the seal package during extension.
Nitrogen gas Rod
Guide and seal 8 APRIL 2019 | DESIGN SOLUTIONS
Tube
Piston assembly
End plug
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