Quality and efficiency in the dosing process: these are the aspects under which the StrikoWestofen Group (Gummersbach, Germany) is constantly optimizing its Westomat dosing furnaces. As a result of this development work, the well-known manufacturer of thermal process technology now offers a wide range of supplementary technologies which make the Westomat dosing furnaces even more efficient: an extended riser tube prevents the formation of oxid skins during the transfer of the melt from the dosing furnace to the die-casting machine. An additional riser tube edge cleaning system keeps the run-out edge of the riser tube free of deposits, thus effectively preventing fluctuations in the dosing quantity due to mechanical causes. This increases the dosing accuracy. Also, the biscuit correction improves the constancy of the dosing weight.
Structure castings usually have a supporting function, which makes them safety- or crash-relevant. The resulting demands made on strength and expansion of the castings are especially high. For this reason, it is important to have a high-quality melt with a low content of hydrogen or oxid contaminants. To accommodate these requirements, the StrikoWestofen Group has put a wide range of new technologies onto the market. These also permanently increase the process reliability and dosing accuracy of the systems.
Increased dosing accuracy
High-precision dosing of the metal quantity requires the dosing weight to be adjusted several times a day. The newly developed patent pending biscuit correction from StrikoWestofen turns this into an automatic process: it constantly and automatically adjusts the dosing weight to the casting process so that the biscuit remains within the individually defined range of tolerance. Our system achieves a permanent improvement of the process reliability and prevents the dosing weight from being set wrongly, explains Rudolf Riedel, manager of the StrikoWestofen Group. In addition, the biscuit correction automatically optimizes other empirical setting parameters of the dosing control. This includes the so-called furnace chamber correction, which compensates for the reduction in the dosing quantity as the furnace empties as well as the refill correction. The latter corrects the dosing quantity during the filling of the Westomat dosing furnace. Dosing precisions of plus/minus 0.8 percent have already been achieved in foundry practice.
Furthermore, depending on the alloy processed, adhesions of cooling melt can build up on the edge of the riser tube during foundry operation. These can be compensated for via the biscuit correction. Nevertheless, the deposits have to be removed now and then in order to guarantee precise dosing at all times. Up to now these were removed manually in an additional work step by an employee of the foundry company, Riedel explains, describing the usual procedure. In order to rationalize this work step and improve dosing accuracy; we now offer a new pneumatic riser tube edge cleaning system. It is especially useful where riser tubes are hard to access. The system, for which patents are pending, blows a short pulse of compressed air onto the edge of the riser tube and cuts off the aluminum thread. The integration of the control parameters into the ProDos control system guarantees the high-precision timing of the pulse. As the dosing tube is a wearing part of the furnace, the nozzles of the cleaning unit were designed for easy assembly and disassembly. The setting parameters of the compressed air pulse depend on the dosing quantity and pressure. The system is available as an optional add-on unit for all Westomat automatic dosing units and all existing systems can be retrofitted with it.
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