Hot set test for cross-linked materials

Hot set test for cross-linked materials IEC 60811-507 / UNE-EN 60811-507

For thermoplastics, rising the temperature makes them softer and easy to deform, while thermoset resist better deformation. This temperature related behavior makes each type appropriate for certain uses.

The electricity Flow through conductors causes a temperature rise depending on resistance and amperage. That’s why, when compared to thermoplastic materials, thermoset made insulations allow higher current capacities or installations in higher temperature environments without compromising the cable features, because their integrity is better preserved.

When manufacturing cables with thermoset insulation it is critical to guarantee that the cross-linking process has been completed and the desired features have been achieved. By performing this test we check if the cable insulation has the desirable characteristics.

Before proceeding with the test the plastic is separated from the metal conductor and, depending on the conductor size, a tube sample or, when possible, a dumbbell sample is prepared.

The test consists of exposing the samples to a high temperature in an oven (conditions are usually set by the cable standard), hanging from a holder with a weigh attached to their low end. The weigh is determined according to the test standard and depends on the sample cross section.

When the specified time has past the cable elongation is measured and compared to its initial size (hot elongation). After that the weight is removed and the sample is left to cool to room temperature to obtain the permanent elongation value.

If the values obtained are within the limits required for the hot elongation and the permanent elongation the cross-linking grade is appropriate.