IEC 60811-505 pdf download

IEC 60811-505 pdf download.Electric and optical fibre cables – Test methods for non-metallic materials
4 Test method
4.1 General This part of IEC 6081 1 shall be used in conjunction with IEC 6081 1 -1 00. All the tests shall be carried out not less than 1 6 h after the extrusion of the insulating or sheathing compounds. Tests shall be carried out at the temperature specified in the relevant cable standard. For tests on insulation, the test is intended for insulated conductors of circular cross-section having an external diameter greater than 1 2,5 mm and for sector-shaped cores large enough to prepare dumb-bells. Where it is not possible to prepare dumb-bells, a bending test suitable for testing the performance of cores of smaller diameter is described in IEC 6081 1 -504. This test is intended for the sheaths of cables not subjected to the bend test as specified in IEC 6081 1 -504. It is intended for cables with an overall diameter over 1 2,5 mm, or for flat cables having, a major axis dimension over 1 2,5 mm. Cables with an overall diameter up to and including 1 2,5 mm shall be subjected to the low temperature bending test detailed in IEC 6081 1 -504. 4.2 Elongation test at low temperature for insulation 4.2.1 Sampling Each core to be tested shall be represented by two samples of suitable length. 4.2.2 Preparation of test pieces After all covering (including outer semi-conducting layer, if any) has been removed, the insulation shall be cut open in the direction of the axis, after which the conductor and the internal semi-conducting layer, if any, shall be removed. The insulation need not be ground or cut if the inner and outer surfaces are smooth, and its mean specified thickness does not exceed 2,0 mm. Samples having a thickness exceeding this limit, or samples having imprints or ridges on the inner side, shall be ground or cut to obtain two parallel and smooth surfaces, and a thickness which does not exceed 2,0 mm. The minimum thickness after grinding or cutting shall be 0,8 mm but if the original thickness of the insulation does not allow it, then 0,6 mm shall be permitted as the minimum thickness. Grinding and cutting shall be carefully carried out to avoid undue heating and mechanical stresses in the insulation. All strips shall be conditioned at ambient temperature for at least 3 h. After this preparation, two dumb-bells from each sample in accordance with Figure 1 , or if necessary Figure 2, shall be punched in the direction of the axis of each sample; if possible, two dumb-bells shall be punched side by side. For sector-shaped cores, the dumb-bells shall be punched out of the rounded “back” of the core. If an apparatus is used which allows the direct measurement of the distance between the marker lines during the test, the dumb-bells shall be marked in accordance with IEC 6081 1 -501 .4.2.3 Apparatus The test may be carried out on a machine provided with a cooling device or on a machine installed in a cooling chamber. Using a liquid as the refrigerant, the conditioning time shall be not less than 1 0 min at the specified test temperature. When cooling in air, the conditioning time for cooling the apparatus and test piece together shall be at least 4 h. If the apparatus has been pre-cooled, this period may be reduced to 2 h, and if the apparatus and test piece have been pre-cooled, the conditioning time after the test piece has been fixed in the apparatus shall be not less than 1 h. If a liquid mixture is used for cooling, it shall not impair the insulating or sheathing material. An apparatus which allows direct measurement of the distance between the marker lines during the elongation test is preferred, but it is also permissible to use an apparatus with which the displacement between the grips can be measured.