Pyrotek’s thermally formed (TF) combo bags deliver improved molten metal temperature distribution and optimal flow control for aluminium vertical direct chill (VDC) slab/rolling ingot casting.
Since Pyrotek introduced them in 2005, TF combo bags have outperformed standard sewn bags. Along with managing thermal gradients, TF combo bags reduce oxide generation, and collect oxide patches and small pieces of refractory in the metal. They can improve bottom block filling, and they can reduce butt curl and scalping compared with sewn bags.
TF combo bags improve working conditions, producing very little smoke, fumes, or flame when in contact with molten aluminium. For plant workers, they also easily slide into place onto existing mounting systems.
They are called “thermally formed” because they are permanently shaped by a hot die. This eliminates loose threads, which are common with sewn bags and can lead to inclusions. They maintain their rigidity at molten aluminium temperatures for up to 90 minutes, ensuring predictable and uniform molten metal flow and distribution in the mould.
They can be customized for specific applications in a variety of dimensions and fibreglass fabric styles and are treated with a Pyrotek coating.
Their design includes a bag, end patches, outer shell, and an optional spout sock or drain holes. Typically, open weave filter fabric is used to make the spout sock and bag, while a strong patch cloth is used to make the outer shell and end patches. But those component and fabric options can be modified as needed for different customer applications.
Water and computational analysis modeling by Pyrotek has demonstrated flow pattern differences that explain why TF combo bags outperform regular sewn combo bags. The modeling has shown TF combo bags produce a lateral flow under the metal surface, resulting in reductions in thermal gradient, turbulence, and oxide generation.
TF combo bags disperse molten aluminium outward and evenly toward the mould walls, delivering high temperature metal where it is needed in the mould to improve the microstructure of the casting.
Pyrotek TF combo bags are in use throughout the aluminium industry. Pyrotek supplies them as original equipment on leading casting technology.