Since cast parts are used by the mankind -and the casting method should be one of the oldest metal forming technologies- the foundrymen struggle with various kind of difficulties. The most elementary ones are thermal problems during pouring. The basic condition, filling the mould before the metal solidifies to get the whole required shape, underlies primarily the thinnest wall within the casting and the thermal conditions. The empiric, experience-based knowledge was for a long time the single clue at the practical work with castings. Chvorinov, in German-speaking publications also written as Chworinoff, summarized and through his theoretical as well as experimental work complemented the knowledge of his time concerning the estimation of solidification development in sand-casted steel parts. His theory –expressed with the certainly best known formula in this speciality- was later expanded, modified and adapted to new scientific informations, although in a different way regarding the German-speaking respectively Anglo-Saxon technical literature. Nowadays, in time of more correct predictions supported through modern tools, estimation formulas are still very useful, acting as a preliminary stage of the design and development. Numerical simulation, in effect the efficient instrument for the subsequent steps of the processing, can also help to make the basic approximations more accurate, but it has his own possible traps as well.