A FREQUENTLY requested item in the testing of laminated plastics is the Gelbo flex tester from IDM Instruments . Flex failure is determined by measuring the pinholes formed in a barrier structure after being subjected to the Gelbo flex test.
Pinholes are determined by use of coloured turpentine and allowing it to stain through the pinholes onto a white backing.
Depending on the test specimen, conditions, severity and number of test strokes can vary. The flexing is done at a rate of 45cpm with a twisting motion repeatedly twisting and crushing the film.
The IDM Gelbo tester consists essentially of a 90mm diameter stationary mandrel and a 90mm diameter moveable mandrel spaced at a distance of 180mm apart from face to face at the starting position (that is maximum distance) of the full stroke.
The mandrels contain vents to prevent pressurisation of the samples. The motion of the moveable mandrel is controlled by a grooved shaft, to which it is attached.
The groove is designed to give a twisting motion of 440° in the first 90mm of the stroke of the moveable mandrel, followed by a straight horizontal motion of 65mm, so that at the closed position the mandrels are 25mm apart.
The motion of the Gelbo flex tester is reciprocal with a full cycle consisting of the forward and return strokes.
For the partial flex test cycle, the moveable mandrel is set up to travel only 80mm of the 180mm spacing. Therefore, only 90 per cent of the twisting stroke is utilised giving a twisting motion of only 400°, and none of the horizontal stroke is utilised.
A stainless steel template 200mm x 280mm is supplied for ease of preparing test sample size.
Flexible, double sided, pressure sensitive tape no more than 13mm wide, is used to hold the sample on to the mandrels, which will need to be supplied by the user along with a paint brush, absorbent tissue paper, white paper and coloured, water free, turpentine.