In foundries with automatic moulding plants a complex system of different kinds of material flow exists. The multitude of technological constraints results in a dynamic and unstable production process. Therefore, small variances in process parameters may entail interruptions of a material flow and consequently cause downtime. Automatic moulding plants consist of rigidly chained units, so that to secure a high reliability corresponding expenditure is required. We present the results of an investigation of 21 automatic moulding plants in 15 German foundries. The analysis of the structure of downtime shows that the low efficiencies result not only from technical reasons, but also from missing materials and personnel, and technological disturbances due to planning and scheduling.