Calumite Mill

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Quality Improvements

Reduced Seed Counts

Perhaps the most dramatic benefit from the use of Calumite Slag is the virtual elimination of seeds and blisters caused by excessive residual sulfate. Even at low levels of Calumite Slag , the reduction of seeds is dramatic and immediate. Not only is there a reduction in overall seed count but the variability is also reduced giving a more consistent product quality. Figure 4.1 shows the 66% reduction in seed count observed on addition of 13% Calumite Slag to a green container furnace. Figure 4.2 shows the 70% reduction in seeds observed when 6% Calumite Slag was added to a flint container furnace.

Effect of Calumite Slag implementation on the average seed count across 3 lines of a green container furnace Effect of Calumite Slag implementation on the total seed count in a flint container furnace Chart Key

Reduced Batch Stones

The combination of faster melting and lower temperature dissolution of silica grains when using Calumite Slag can result in a reduction in batch stones without the need to increase furnace temperature. Figure 4.3 shows how the implementation of Calumite Slag in a float furnace led to the virtual elimination of unmelted silica defects.

Effect of Calumite Slag  addition on unmelted silica defects in a clear float furnaceChart Key

Color Stabilization

Calumite Slag is particularly valuable in the production of amber glass, or glass with an amber component to their color, such as dead leaf green or UVA green. The amber chromophore that produces the color in these glasses consists of reduced sulfur in the form of sulfide, S2-, combined with the oxidized form of iron, Fe3+. Calumite Slag can be used to control redox such that the reduced sulfur and oxidized iron can co-exist.

Reduced Refractory Attack

The reduction in furnace temperature that can be achieved while using Calumite Slag will reduce the level of refractory attack, directly reducing the number of defects, e.g. due to refractory run off. This reduced refractory wear will also have significant additional benefits in terms of extending furnace campaign life.

Improved Redox Control

Calumite Slag is a weak reducing agent when compared to reducing agents such as carbon. As a result, comparatively large amounts of Calumite Slag are added to the recipe, resulting in more even distribution within the batch. In addition, the larger particle size of Calumite Slag compared to other reducing agents ensures the material is available to react over a longer period of time.

Reduction in seed count when Calumite Slag  replaced carbon as the reducing agent in a flint container furnaceChart Key

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