TM 1004:2010
DETERMINATION OF THE DIMENSIONAL STABILITY (DS) OF POLYURETHANE FOAM CANISTERFinal version: 18/11/2010 1. Background and purposeThe dimensional stability (DS) of PU foams is measured by looking at the dimensions of a joint filled with foam. After a specified period of fixation, during which the foam is expected to get cured and at certain intervals, the width of the joint is measured.2. Tools• Chipboard type V100, dimensions: 200 x 100 x 10 mm, stored for 1 week at norm climate conditions (23 °C/50 % RH)• Spacers made from PE, 20 mm • Slide rule with accuracy of 10 μm • Screw clamps • Water bath 3. MethodOne setup consists of 3 plates, giving data for 8 points in 2 joints. The chipboard pieces and spacers are put together as follows:
3.1. Pre-moisteningWhen pre-moistening is required, the chipboard plates are wetted abundantly.The plates are immersed in water for 20 sec, taken out and stored vertically for 2 minutes on a water sucking tissue, until excess water is dripped off (pic 2). 2 component foams usually don’t require moisturized substrates as well as tests of 1c foams in humid climates (e. g. 40° C/90 % rH). See P 4 “test climates”. 3.2. AssemblingWith the chipboard plates and spacers, joints or stacks of joints are made like above illustration (pic 3) (The inner plate of the specimen is turned up side down, opposite to the outer plates , in order to provide a homogenous humidity profile between the plates).The spacers are placed roughly 5 mm from the side of the plates to be able to put the slide rule between the plates. The clamps are used to fix the joints (positioned at each corner or in line of the spacers). Fasten the clamps with moderate force to avoid deformation of the panels. When building more than 2 joints in one stack, an extra plate is used after every 2nd joint to give it enough resistance against bending in the middle due to the expansion force of the foam. Marks are put on the front and back as shown above (pic 1). At these marks the width will be measured (4 reading points per joint). Important: Dry and pre-wetted joints are never put together in one and the same stack. 3.3. FoamingThe joints are filled without voids from both sides, in such a way that at least 1 cm, but no more than 3 cm of foam comes out of the joints during the curing phase. The stacks are kept upright (pic. 3) at norm condition (23 °C/50 % rH) during the curing period.3.4. MeasurementFixation period (time between foaming and removing clamps): the standard fixation period for 1-component foams is 24 h., for 2-component foams the Jig Dwell time as specified by the manufacturers, in case no fixation time is known, a standard period of 2 hours is used.After the fixation period the excess foam is cut away. Before the fixation is removed from the stack, the width of each joint is measured between the boards at the four corners, using the digital slide rule. Measurements are done between the boards (inside). The initial value serves as reference value A0 for the future measurements. The clamps and spacers are removed and the samples are put into the required climate for further storage (see P. 4.). Next measurements are done after 1 day, 2 days, 3 days, 7 days and 14 days. (If the values measured after 14 days still point significant changes in dimensions, further measurements after 3 weeks and/or 4 weeks may be necessary). Before the measurements are taken, the stacks are removed from the climate chamber and acclimatised for 2 h at norm climate (if stored at different conditions). The specimens are stored upright all the time. 4. Storage conditionsStorage conditions should reflect actual end use conditions. The conditions below are provided only as a guideline for extreme results (shrinkage / expansion) :1c foams:
2c foams:
5. EvaluationAfter each measurement at time n the average values are calculated (An) and the dimensional stability is determined in reference to A0 as follows:
A0 = initial value (with clamps still on the stack) An = value of the measurement at time n From all DS-values per joint, the average minimum and maximum value per condition is taken for reporting. Please note, that a statistical relevant number of measurements, at least of 3 joints, must be available to get informative results. 6. Example (1 joint, 1 condition)The reported figure was -8,6 % (extreme average after 2 days)
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