Mechanical properties of insulating and sheathing compounds IEC 60811-501 UNE-EN 60811-501
Thermal ageing methods - Ageing in an air oven IEC 60811-401 UNE-EN 60811-401
Mechanical properties requirements
ensure quality, resistance, and
flexibility in plastic materials
Cables are designed to last. Some of them will remain in a fixed position once installed and others will be subjected to movements during their whole life, but all of them have to adapt their shape to the drums where they are stored and the installations they will be part of, and withstand the mechanical stress they might be subjected to.
All cable elements, including insulation and other plastic compounds used in cable coatings, must be ready to resist such deformations without damage, in the moment of their installation as well as along their product life.
Tensile strength and elongation at break:
key to a durable cable.
Samples for these tests consist of the plastic materials to be checked. Two sets of samples are prepared in one of the formats described in the test standards, as the cable size makes it possible: flat test pieces (a small plastic strip) or tubular test pieces (tube result of removing the conductor from inside the cable/wire).
Samples from the first set are then attached to the clamping jaws of the measuring equipment. While they separate from each other, the necessary force and the elongation reached is measured until the sample breaks.
Median of the series is considered as the test result to minimize the influence of possible irregular results.
Measuring units are, for the case of maximum tensile strength, N/mm2 (force is referenced to the cross-sectional area of the sample), and for the elongation, the percentage of elongation reached over the original length.
The second set of samples is subjected to high temperature ageing. After this process and depending on the cable type, the requirements for these values and their variation comparing to the initial ones before ageing must be met.
During the test, ambient conditions, separation speed of the clamping jaws, or the shape of the test samples have great influence and therefore test standards fix these conditions to obtain comparable results.
The purpose of this test is to guarantee
cables against these mechanical
efforts in normal handling in the
foreseen use conditions.
While pulling from a cable during its handling we are applying an amount of force that it must withstand without damage, and when bending the cables, the outer side of the curvature is put through some elongation. The purpose of this test is to guarantee cables against these mechanical efforts in normal handling in the foreseen use conditions.
Ageing processes aim to guarantee these properties will be within adequate values in the future.
In basic models of this test equipment the force is applied manually, this makes it difficult to have a uniform elongation speed and a homogeneous test method. Current models, in addition to automated control for these parameters, store the data obtained from the load cell.
Currently there are several technologies to measure sample elongation: the most common ones are contact extensometers and optical extensometers.
Based on the same principle, there are large-scale devices to measure the same parameters in other industries on big size samples made of hard materials.
The force/deformation curve result of matching the tensile strength and elongation data through time can be used to characterize materials or analyze the homogeneity of these properties along different samples.