Industrial gas springs help in fight against COVID-19

Gas springs, also called gas dampers, tension springs, gas-pressure springs depending on the setup and context, are compressed-air or oil cylinders that install in motion designs to damp forces and return kinematic linkages and more complicated assemblies to default positions. Gas springs work through a piston on the end of a rod that protrudes from a steel cylinder body; usually compressed gas (often nitrogen) within the cylinder exerts force on this piston to reassume and maintain set positions. Nitrogen is common here because it’s inert and nonflammable. In such designs, oil or grease between the piston and other contacting parts minimize friction.

In fact, the small amount of oil in these gas springs serves another function — to further damp and gently decelerate gas springs during full extension or compression. Some setups even include a fine hole in the piston for damping that’s still slower than with other designs; such slow-damper springs are common on safety gates and doors.

This is an ACE Controls pull-type gas spring.

In contrast, extended-reach gas springs usually leverage telescoping mechanisms pairing multiple cylinders on one rod; then the smaller cylinder extends from within the larger cylinder. Consider one particularly long-stroke application: Passive heave compensators — systems on ships or offshore oil-rig systems that reduce the effect of waves on engineered structures — use gas springs with strokes to many meters long.

Still other gas-spring applications include those for medical beds and hoists; industrial equipment such as machine-tool presses; off-highway and automotive equipment for hatches, hoods, and covers; office equipment and furniture; and general strut and support applications. Fast-acting gas springs find use in weaponry and aerospace design. Specific variations include gas springs with standard or fixed-height cylinders; spindle-only designs; and cable, return, adjustable auto-return, nonrotating, stage, and multi-mode cylinders.

No matter the iteration, gas-spring extension force — a value that usually ranges from 1 to 5,000 N — depends on piston-rod crosssection multiplied by fill pressure. Manufacturers commonly express extension force with two values — for rod extension and rod retraction — at normal ambient temperature and with the piston rod pointing downward. (Note that typical ranges are only those most common; some gas- spring applications in heavy industries use gas springs delivering several hundred-thousand Newtons.) Other gas-spring definitions include two pull-in forces — at rod extension and rod retraction — and overall friction force. These values depend on the gas spring’s gas and damping-oil volumes. Various nozzle orifices and oil quantity allow control of push-out and push-in speed.

Consider one example application of gas springs: As Wuhan, China became the first metropolis to confront COVID-19, crisis managers relied on mobile X-ray machines to quickly supply intensive-care physicians with imaging of patients’ lungs. Medicalimaging machine builder Beijing Wandong Medical Technology Co. supplied these machines.

This is Wandong’s mobile X-ray machine.

The mobile X-ray machine has a beam arm that’s adjustable to patient anatomy. The arm in turn uses a gas spring to hold its position without dropping on technologists or patients.

When COVID-19 struck, Beijing Wandong suddenly needed a large quantity of springs to complete a rush order of the X-ray machines … so they turned to ACE Controls.

The mobile X-ray machine is 66.1 lb including its 22-lb beam arm. So in addition to the total weight, ACE Controls engineers had to account for the starting point (0°) and opening angle (130°) when choosing the specific gas spring.

Ultimately the engineering team chose GZ-28-450 pull-type gas springs — part of the component maker’s industrial gas-spring family. GZ-28-450 gas springs have a 1.10-in. OD, maximum force to 2,700 lb, at a stroke length of 17.72 in. — making them suitable for the mobile X-ray unit’s requirements.

The ACE Controls’ GS-28-450 pull-type gas spring provided a 270-lb traction force and low progression rate to hold the mobile X-ray beam arm in position and support raising and lowering motion.

The gas springs reliably hold the beam arm in position and provide assistance when imaging technologists raise and lower the arm … in contrast with push-type gas springs. More specifically, the gas pressure in the cylinder draws the piston rod in and supports the manual force needed for controlled motion when moving the arm. No matter the stroke length, the GZ-28-450’s traction force is adjustable thanks to a built-in relief valve.

Ultimately, ACE Controls industrial gas springs boost the safety and user-friendliness of Wandong mobile X-ray units.