The longitudinal retraction rate of the plastic pipe (from GB / T 6671-2001) is the percentage change in the distance length before and after heating of the test tube at a predetermined temperature of 1 h. Use this value to indicate the longitudinal retraction rate of the pipe.
The longitudinal retraction test of plastic pipes can be carried out in a constant temperature oven or in a liquid. Here only the pipe in the oven heating temperature test method.
⑴ longitudinal retraction rate test equipment
① hot air circulation oven, the requirements of the oven heating cycle temperature fluctuations allow the value of 2 ℃.
② temperature with a thermometer, temperature accuracy of 0.5 ℃.
③ crossed needle.
⑵ preparation before the test test
① Take the sample tube length (200 ± 20) mm, tube diameter greater than 400mm, the tube along the axial uniform cut into four as a sample.
② at the end of the pipe at not less than 10mm to draw two 100mm away from the circle marking.
③ sample tube in the (23 ± 2) ℃ environment for less than 2h.
⑶ test test operation sequence
① measure the actual distance of the circle mark, accurate to 0.25mm.
② Heat the oven to (140 ± 2) ℃.
③ the test tube hanging or flat on the pad with a layer of talc in the oven on the plate (slice sample should be convex face down), the time is 15min; pipe wall thickness greater than 8mm, the heating time of 30min.
④ Remove the sample from the oven on the plate, cool to room temperature (23 ℃), detection of two round mark distance, accurate to 0.25mm.
The longitudinal retraction ratio RLi = (Lo - Li) / Lo × 100%
Where Lo - put the oven before the sample on the round mark distance, mm;
Li - put the oven on the sample after the round mark distance, mm.