7. Test Methods

7.1 Dimensions and Appearance

• 7.1.1 Dimensions shall be inspected using special or universal measuring tools with a scale division value of not more than 0.5mm.
• 7.1.2 Appearance quality shall be inspected by visual observation.

7.2 Force Characteristicsd

• 7.2.1 Test Conditions: The test shall be carried out in an environment of . Before the test, the gas spring shall be kept in the extended state, and the piston rod shall not be pressed. The sample shall be placed in an environment of  for more than 2 hours. The test measurement speed is 400mm/min, and the force – measuring accuracy is not lower than 1%.
• 7.2.2 Test Methods: The test methods for force characteristics include dynamic tests and static tests. Dynamic test methods shall be used as much as possible.
  • 7.2.2.1 Dynamic Testing: Vertically clamp the piston rod of the gas spring upward on the testing machine. In the first cycle of starting the machine, record the unlocking force and start – up force. In the second cycle (when the gas spring has been stored for a long time, the number of cycles can be increased to three to five), record the extension and compression forces , , ,  at the force – taking point C, calculate the nominal force, dynamic friction force, and force ratio, and draw the force – displacement curve. At the same time, observe whether there is any jamming of the piston rod of the gas spring.
  • 7.2.2.2 Static Testing: Vertically clamp the piston rod of the gas spring upward on the testing machine. In the first cycle of starting the machine, record the unlocking force and start – up force. In the second cycle (when the gas spring has been stored for a long time, the number of cycles can be increased to three to five), record the extension and compression forces , , ,  at the force – taking point C, calculate the nominal force and force ratio, and draw the force – displacement curve. The residence time at the force – taking point C during static testing is [a certain time]. At the same time, observe whether there is any jamming of the piston rod of the gas spring.
  • 7.2.2.3 Detection of Locking Force:

a) Rigid Compression Locking Force: Vertically clamp the piston rod of the gas spring, which is locked in the fully extended state, downward on the testing machine. Compress the gas spring at a speed of 2 mm/min to make the piston rod displace 2 mm, and record the compression locking force value (applicable to the locking of Curve II). Or, vertically clamp the piston rod of the gas spring, which is locked in the fully extended state, downward on the testing machine. Start the testing machine, compress the gas spring at a speed of 2 mm/min, and when the locking force value reaches the agreed value, record the displacement of the piston rod (applicable to the locking of Curve I).
b) Rigid Tensile Locking Force: Vertically clamp the piston rod of the gas spring, which is locked in the fully compressed state, downward on the testing machine. Stretch the gas spring at a speed of 2 mm/min to make the piston rod displace 2 mm, and record the tensile locking force value (applicable to the locking of Curve II). Or, vertically clamp the piston rod of the gas spring, which is locked in the fully compressed state, downward on the testing machine. Start the testing machine, stretch the gas spring at a speed of 2 mm/min, and when the locking force value reaches the agreed value, record the displacement of the piston rod (applicable to the locking of Curve I).
c) Elastic Locking Force: To be agreed upon by the supplier and the demander.

7.3 Extension Speed

7.3.1 Test Conditions

The test is carried out in an environment of 20°C ± 2°C. Before the test, the sample should be placed in an environment of 20°C ± 2°C for more than 2 hours, and the scale division value of the timer should not be greater than 1/100 s.

7.3.2 Test Method

Vertically clamp the piston rod of the gas spring downward on the testing machine. Start the testing machine, lock the gas spring in the fully compressed position, and then quickly open the control valve to allow the piston rod to extend freely. Measure the extension time t and the extended stroke S, and calculate the extension speed (average speed)  according to the following formula:

where:

• S is the stroke, with the unit of millimeter (mm);
• t is the extension time, with the unit of second (s).

7.4 Sealing Performance

Lock the gas spring in the compressed state, measure the extended length of the piston rod, store it at room temperature for 24 hours, and then measure the extended length of the piston rod again.

7.5 High and Low Temperature Resistance Performance

Put the gas spring into a low – temperature test chamber at -30°C ± 2°C and keep it for 48 hours. After taking it out, place it in a high – temperature test chamber at 60°C ± 5°C and keep it for 48 hours. Take out the gas spring, test its force characteristics according to 7.2, and calculate the attenuation of the nominal force  and the locking force .

7.6 Cycle Life

Clamp the piston rod of the gas spring, which has passed the high and low temperature test, downward on a testing machine equipped with an oil – collecting device. Conduct a cycle life test at a frequency of 6 times/min to 12 times/min. During the entire test process, the temperature of the gas spring cylinder barrel should not be higher than 50°C. After 40,000 cycles, test the force characteristics and the locking force  according to 7.2, and calculate the attenuation of the nominal force , the dynamic friction force , and the locking force . Test the stroke of the piston rod according to 7.1.1 and calculate its variation. Weigh the amount of oil leakage on an electronic scale with an accuracy of not less than 0.01 g.

7.7 Tensile Resistance Performance

Fix the gas spring in the extended state on the testing machine, load it at a speed of 1 mm/min to 2 mm/min according to the values specified in Table 3, keep it for 3 minutes, and after unloading, test the force characteristics according to 7.2 or make observations.

7.8 Corrosion Resistance Test

The corrosion resistance test of the gas spring is carried out in accordance with the provisions of GB/T 1771 or GB/T 10125.

Technical Specification for Lockable Gas Springs (English version of national strandard, initiated by LeiYan Gas Springs), proposed and prepared by SAC/TC 235 (National Technical Committee 235 on Spring of Standardization Administration of China).