BS 12254:2010 pdf download – Screens for laser working places — Safety requirements and testing
5.4 Stability to UV radiation and stability at elevated temperature
5.4.1 Stability to UV radiation
Testing shall be done according to Clause 6 of EN 1 68:2001 with an exposure time of (50 ± 0,2) h.
5.4.2 Stability at elevated temperature
Screens shall be stored for at least 7 h in a climatic cabinet at a temperature of (55 ± 2) °C and a relative humidity of > 60 %, and then stored for at least 2 h at room temperature (23 ± 5) °C.
5.5 Mechanical strength
5.5.1 Flexible screens
188.8.131.52 Testing machine
The tensile testing machine shall be power-driven and capable of maintaining the appropriate rate of grip separation as specified in 5.5.1 .3. The testing machine shall be equipped with the following devices.
Grips for holding the test sample, one being fixed and the other movable.
The grips shall be self-aligning in that they are attached to the machine in such a way that they move freely into alignment as soon as any load is applied so that the long axis of the test sample coincides with the direction of pull through the centre line of the grip assembly. The test sample shall be held in such a way that slip relative to the grip is prevented as far as possible and this shall preferably be effected with the type of grip which maintains or increases pressure on the test sample as the force applied to the test sample increases. The clamping system shall not cause premature fracture at the grips.
Load indicator incorporating a suitable load-indicating mechanism capable of showing the total tensile load carried by the test sample when held by the grips. 184.108.40.206 Test samples Test samples 7 to 9 (1 0 mm wide and 1 50 mm long) are cut from the screen.
Test samples 1 0 to 1 2 (1 0 mm wide and 1 50 mm long) are cut from the screen, the longer dimension being perpendicular to the longer dimension of samples 7 to 9 when cutting them from the screen. Determine the mean width and mean thickness of the test samples. Gauge marks (50,0 ± 0,5) mm apart shall be marked on the centre portion of the test samples using ink or other medium that does not affect the material being tested. Gauge marks shall not be punched, scratched or impressed upon the test samples. Before testing for resistance to tear, the 6 samples shall be tested according to 5.4 for resistance to UV radiation. During this testing, at least the zone between the gauge marks shall be irradiated.
220.127.116.11 Procedure Mount the test sample in the grips of the testing machine so that the axial alignment coincides with the direction of pull. Tighten the grips uniformly and firmly to prevent the sample from slipping, but not to the extent that the test sample is damaged. Clamp the test sample so that the distance between the grips of the testing machine is (1 00 ± 1 ) mm and the gauge marks are centrally disposed between the grips. Separate the grips of the testing machine with a speed of (250 ± 25) mm/min until a tensile stress of (1 5,0 ± 1 ,5) N/mm ² is reached. 1 0 s after the maximum tensile stress has been reached, it is noted if any of the samples did tear. Some materials have a very high elongation, which may bring them outside the stretching capacity of the testing machine. In such cases, it is permissible to reduce the initial distance between the grips to (50 ± 0,5) mm. The test with reduced distance shall be performed with a new sample.
5.5.2 Inflexible screens Robustness shall be tested according to 3.1 of EN 1 68:2001 .
5.5.3 Resistance to ignition Testing of flexible screens shall be done in accordance with EN 1 598:1 997 and EN 1 598:1 997/A1 :2001 . Testing of inflexible screens shall be done in accordance with Clause 7 of EN 1 68:2001 .