BS EN 3475-418:2019 pdf free.Aerospace series – Cables, electrical, aircraft use – Test methods.
4.1 General Various bi-metal conductors exist among which the most usual are tin-coated copper, copper clad steel and copper clad aluminium. Inter-metallic compounds may appear at the interface of the various layers of such conductors. As these compounds have generally an increasing growth rate when exposed to elevated temperature, the characteristics of the cables (mechanical and electrical) can be affected depending on the time and the temperature of exposure. A good example is tin-coated copper where the diffusion of tin into copper is a fast, well-known and important phenomenon between ambient temperature and 230 °C. 4.2 Theory The inter-metallic layer formation at the interface of the various layers in the wires is due to a diffusion mechanism in association with solubility phenomenon. The diffusion rate is characterized by a coefficient of diffusion of the two metals in contact at a given temperature. This coefficient of diffusion has generally the form of an Arrhenius law and is given by the formula.When appeared, such inter-metallic compounds will affect the mechanical and electrical behaviour of the conductor. Even if all these characteristics do not evolve proportionally in relation with its thickness, it has been shown that an easy way to survey the growth of the inter-metallic part is to measure the increase of the linear resistance.On this initial length take a minimum length of three meters to make three samples of at least one meter, make three measurements of the electrical resistance per unit length, according to EN 3475-301. Record the arithmetic mean value, of this sampling corrected to 20°C, as the initial measurement without thermal ageing. NOTE The temperature correction coefficient is generally given in the relevant conductor product standard.An air-circulating oven shall be required for this test. Its size must be sufficient to hold all necessary specimens during the complete duration of the test.BS EN 3475-418 pdf download.