Metal weight loss during melting (see weight loss) represents an immediate financial loss for the foundry. An increased metal yield of the melting furnace, on the contrary, means shorter periods for return on investment (ROI) and therefore represents an important investment criterion.
Shaft melting furnacemetal yield
For being able to deliver documented data material on the metal yield of a shaft melting furnace and to give substantiated advices, StrikoWestofen performed a metal balancing on a StrikoMelter® where all incoming and outgoing melt flows at the furnace were weighed. This was aimed at obtaining reproducible results on the metal yield, performing a comprehensive metal balancing and thus creating the basis for investment calculations.
The financial equivalent of a 1 percent melting loss with a melting performance of 1 t/h in three-shift operations amounts to approx. 100,000 euros/year. The calculation is based on the price of 2,000 euros/ton for aluminum block material (1st Quarter 2010) and a yearly melting time of 5,000h.
The examination results of a customer foundry revealed the results listed in Table 1. These values confirm the efficiency of this furnace type. It has to be noted that the metal yield was not determined on the basis of weighing scum taken out of the furnace, but on the basis of the difference between metal initial and output weight. By comparing the scum quantity a low amount of pickup was balanced which results from metal oxidation during the melting process. Altogether, a closed and complete metal balancing was achieved during the examination.
The examination result represent a reference value for standard alloys (note: Aluminum die casting alloys). In reality, the melting process often has to be interrupted. Under certain circumstances a lower return scrap quality has to be expected. The material is either impure or contains high amounts of flash. It is also important not to underestimate the effect on the metal yield of extracting metal on the fuse link by stirring. The evaluation of shift protocols revealed a metal yield which was 0.5 percent lower than the reference measurement. In case of pure block material the difference tends to be a bit smaller, in case of return scrap material a bit larger.