Material mix: New furnace plant enables simultaneous melting of aluminium chips and ingots1 July 2019
Due to the different shapes of ingots, return material and aluminium chips, different furnace types were previously required for melting the respective material. However, separate plants for the different types of material do not pay off for die casting foundries with too low volumes of aluminium chips or return material, so that only ingots are molten down. ZPF GmbH have now developed a melting furnace which is qualified for melting down aluminium chips as well as recycling material and ingots - a sustainable utilisation of the system is thus always ensured. The plant is equipped with an automatic charging system and is able to melt up to 500 kg raw material per hour, for example 250 kg aluminium chips and 250 kg ingots. The new melting furnace technology will be presented for the very first time at this year's GIFA with an exhibit.
Production by-products such as scrap material and runner systems or even aluminium chips are usually collected and recycled externally in most foundries, as they cannot be returned directly to the melting process for economic reasons. This results in high costs for storage and transport, and the logistical effort should not be underestimated. "Until now, our aluminium melting furnaces were only designed for charging with unmixed material; a material mix of ingots and recirculation aluminium parts was previously only possible to a limited extent due to the desired boundary parameters such as melting loss and melting rate",reports Sven-Olaf Sauke, head of R & D at ZPF GmbH.
"For some foundries, a pure chip furnace is uneconomic, since the metal-cutting share in the cast product is often too low." ZPF has taken this market need as an opportunity to develop a new technology for melting furnaces enabling the simultaneous melting of chips, ingots or return material while still keeping the melting loss values at an extremely low level. This offers companies greater flexibility in the recycling process and new opportunities to optimize the melting process.
Sump melting furnace with chips as main material
For an optimal constructive design of the new furnace, simulations were used in the course of development to be able to assess the basic system behaviour. In addition, power and exhaust gas measurements were carried out under foundry conditions which were used to determine the functional parameters. "The decisive factor for us was the optimum melting of the metal and the required temperature control in the furnace," explains Sauke. "In addition to energy consumption, numerous other factors that strongly influence the melting result play a role here in a modern furnace system - for example the quality of the raw material and the melting loss. For practical implementation, ZPF analysed the data collected and determined the parameters required for simultaneous melting of chips and other aluminium materials. Based on these results, a prototype with the new technology was implemented.
The melting furnace has dimensions of 575 cm x 380 cm x 445 cm. (L x W x H) at an empty weight of approximately 28 tons. It is dimensioned for a maximum throughput of 500 kg/h in total. The furnace system is extended by an automatic charging unit. This modular unit is designed in such a way that different types of material can be loaded according to customer requirements. "For the simultaneous melting of different material forms in one furnace, the first step is to determine the leading material variant," Sauke says. "For our prototype, we opted for aluminium chips as the main material and therefore designed the furnace as a heel melter. As a result, the chips can be molten down in combination with return material, return wheels or ingots". Which variant is added to the chips can be selected by the operator. The only important thing is to pay attention to the optimum quantity ratio between chips and secondary material in order to achieve optimum melting performance.
In addition to R&D projects with universities and other research institutions, ZPF uses the direct dialogue with the foundry industry to continuously further develop its melting furnace technology in order to find out additional optimisation potential through feedback from practical experience. "This helps us to be prepared for future challenges in melting plants. For example, the modularity of the automatic charging unit makes it possible to introduce precisely metered quantities of aluminium scrap into the furnace," adds Sauke. "This has the special feature that, depending on the sprue system, it has a large or small weight-to-volume ratio and must be handled accordingly - mechanically but also in terms of melting technology."