Web metallizing with dense, directional and energetic Al-vapour jets—a challenge to conventional evaporators

Abstract

A vapour source has been developed for evaporating aluminium in web coating plants. Instead of evaporating the liquid aluminium or other low melting reactive evaporant from open boats (slabs) or crucibles, the metal is evaporated from capillaries of a hollow body irradiated by photons and electrons. Dense, directional and energetic vapour jets are produced by providing the hollow body with beam shaping apertures. Directed to the web, the jets drastically reduce the extensive and expensive stray deposit of conventional evaporators, the source of airborne aluminium powder, the toxicity of which has only recently been discovered and is discussed in an appendix. To aid understanding of the problems arising in source design a short history of the emergence of web metallizing is also dealt with in an appendix together with an account of the materials currently used for Al-web/evaporators.