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what is the hot set test ?

Many important properties of polyethylene insulation of cables depend on the degree to which the material is cross-linked. Determination of whether or not the dependent properties are fully realized after cross-linking can be carried out with the help of a hot set test.

In this test the elongation of the insulating material at an elevated temperature under the action of a specified tensile load and its recovery after removal of the load are determined to evaluate the efficiency of the cross-linking. A dumbbell of specified shape and size is suspended from a vertical frame inside a hot air oven with a specified load suspended from its lower end. The elongation of the test specimen after fifteen minutes under the above conditions and its subsequent recovery after removal of the load are then evaluated.

Related standards

IS 7098 (Part 2) - 1985 : Specification for Cross Linked Polyethylene Insulated PVC Sheathed Cables

IS 10810 (Part 30) - 1984 : Methods of Test for Cables

Part 30 : Hot Set Test

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Conditioning - All the test specimens shall be kept at a temperature of 27 f 2°C for a period
of not less than 16 h Immediately before test.

Procedure

8.1 The distance between marker lines shall be measured.

8.2 The test pieces shall be suspended in the oven and weights attached to the bottom grips to
exert a force of the value specified for the material in the relevant cable standard.

8.3 After 15 min in the oven at 'the temperature specified for the material in the relevant cable
standard, the distance between the marker lines shall be measured. If the oven does not have a
window and the oven door needs to be opened to make the measurement, the measurement shall
be made not more than 30 s after opening the door.
fin the case of dispute the test shall be carried out in an oven with a window and the measure-
ment made without opening the door.

8.4 The tensile force shall then be removed from the test piece (by cutting the test piece at the
lower grip), and the test piece left to recover for 5 min at the specified temperature.

3.5 The test pieces shall then be removed from the oven and allowed to cool slowly to ambient
temperature, after which the distance between the marker lines shall be measured again.


Calculation
The percentage hot set elongation = (B-A)/A x 100
Permanent set percent = (C -A)/A x 100

initial Length Length of the Gauge mark A, mm
Between the Mark after 15 Min with load Gauge Mark B, mm
Length of the Gauge Mark at Room Temperature after Test, C mm