Water-cooled induction or channel furnaces must be fitted with an emergency collection pit which drains off accumulating cooling and surface water and hydraulic oil (Animation 1) and, in the case of failure, collects the leaking molten metal safely. Information sheet S 80 from the VDG (Association of German Casting Professionals) describes the necessary minimum requirements for an emergency casting pit.
A physical explosion in the emergency collection pit at the moment when the metal and cooling agent meet must be prevented reliably through the use of a suitable drainage material (ceramic foam). The drainage material in the emergency collection pit must melt and sinter in the contact zone. A verification of suitability with regard to this must be obtained in accordance with the respective metal.
Furthermore, the ceramic foam must be permeable enough to water and steam, whereby, at the same time, the size of the pores must be kept as small as possible in order to prevent contaminating particles passing through.
The construction of the emergency collection pit and the construction materials used are chosen so that the steam which accumulates can escape quickly enough (Animation 2) and under no circumstances becomes trapped, in order to reliably prevent an explosion which would destroy the structure. Therefore, there must always be an open evaporation surface available which is defined by an equation.
The relationship between the heat input surface and required evaporation surface is calculated according to Eq. 1:
Av: open evaporation surface (if the steam must escape through the drainage material, the open porosity must be considered carefully in the calculation)
Aw: heat input surface (floor and/or wall surfaces which are in direct contact with metal drainage material)
Animation 1: Drainage of water in an emergency collection pit, left using ceramic foam as a drainage system from Silmeta Systems GmbH, right with standard floor drainage
Animation 2: Accumulation and drainage of steam, left construction from Silmeta Systems GmbH, right standard construction