The possibility to join metal parts by fusion welding depends first of all on their metallurgical properties. This problematic is extremely wide, therefore, in this paper, we shall restrict our interest to only some specific questions, more important for our needs. Apart from those classical, commonly used materials, also some exotic ones, applied mainly in new branches of research and industry are also needed. This needs accelerated in the second half of 20. century the development of new methods of welding, applying laser or electron beam. The welding by electron beam in vacuum proved to be the most suitable, if not the only one applicable method for welding some materials.

In the past, as well as today, people looked for ways how to make use of that what the nature offered. The knowledge how to gain, process and use metals, up today belongs to the most important skills. Names of the first known metals, bronze and iron, had given names to the two important historic epochs. The processing of metals can not be done without heating. To the classical methods, fire, gas flame, electric current and electric arc, the new science added two other methods, the laser and electron beams. The technological applications of the latest we shall pursued in the following paper.

Modernized vacuum furnace PZ 810 produced by former company Tesla. The furnace has vertical cylindrical chamber.