Physikalisch-Technische Bundesanstalt

Tasks

In the field of heavy-current engineering, electrical equipment which in normal operation contains ignition sources, e.g. switching sparks or hot surfaces, is installed in a housing - the flameproof enclosure - which will not be damaged in the case of an internal explosion, and which, in spite of unavoidable openings or gaps, will not allow flame propagation to the outer explosive atmosphere. In the course of type examination, extensive experiments must be carried out to check these properties. For smaller types, test vessels are available which also allow precompression of the test mixture and guarantee safe handling of the explosive gas/air mixture. The required basic investigations are first of all aimed at further developing the method of measurement for the internal explosion pressure. The dynamic load caused by the explosion represents a special stress for the housing. The mechanical load and a relation - adequate from the technical point of view - between dynamic type examination and static routine test were determined for metal housings and screwed joints. The specific problems encountered when plastics materials (in particular with fibre reinforcement) are used, were investigated and characteristic values for the reduction of strength due to ageing determined. A current project will contribute to a better understanding of flame propagation and possibly allow cheaper gap geometries of simpler technical design and to be developed.