The paper is oriented to the field of engineering production. Specifically, it focuses on the field of surface finishing on parts made of different grades of steel. These are surface treatments, using thermo-chemical reactions. In particular, alkaline blackening, or else burning and phosphating of zinc, also called bonderization. The paper deals with increasing efficiency and production possibilities on the line, which provides just these two metal surface treatments. With the help of simulation, a digital model of this line was created, where possible improvements of its production possibilities were tested. The task was to increase the flexibility and elasticity of production and ensure the fulfilment of orders in the greatest possible satisfaction of customers and in the shortest possible time.