Alloy, Materials of construction

The shell of a rotary dryer is usually constructed by welding rolled plate, thick enough for the transmission of the torque required to cause rotation, and to support its own weight and the weight of material in the dryer. The shell is usually supported on large tyres which run on wide rollers, as shown in Figure 16.10, and although mild steel is the usual material of construction, alloy steels are used, and if necessary the shell may be coated with a plastics material to avoid contamination of the product. 

Figure 3.6o shows that there is an optimum reflux ratio. Using expensive materials of construction (ALLOY curves in Fig. 3.66) shifts the optimum to the right, and favors high-reflux designs. Hi eneigy cost (HEC curves in Fig. 3.6c) shifts the optimum to the left, favoring operation closer to minimum reflux. 

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