Rotary Furnace
In contrast to the pusher furnace, where a static powder layer passes the furnace, a dynamic powder flow exists in the rotary kiln. Furnace rotation and the incline continuously move the powder through the hot zone. Feed rate, rotational speed, incline, and lifters inside the tube determine the depths of the dynamic powder layer. High oxide feed, longer retention time (low rotation rate and low inclination), and higher temperature result in coarser tungsten grains.
The powder layer is constantly disturbed by the rotating motion and powder from inside moves to the surface, and vice versa. Therefore, the water-vapor retaining capability of the layer is less compared to a static layer, and the material exchange rate H2O→H2 is of the layer is enhanced. The humidity in a rotary furnace powder layer is thus lower and reduction proceeds under drier conditions as compared to the pusher. Lifters inside the tube combined with stepwise turning motion make sure that a powder bed is maintained for a certain time giving the chance to build up higher humidity both temporarily and locally.
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