An extrusion die is a simple shaping device with a streamlined orifice that reduces the extruder's stream of melted plastic and creates a particular shape. Extrusion dies are machined from alloy tool steel and then hardened. The die opening controls the thickness and width of the extruded part. Rod dies are most often used in the compounding of plastic with additives prior to pelletizing.
Plate die are the easiest to construct.
They are steel plates that have the profile machined through the plate. However, a plate die creates turbulence and stagnated flow as shown in Figure 5-23. The degraded material will release into the extrudate melt stream and cause staining or rejected products. To overcome the stagnation and degradation of this material, a streamlined land transition is constructed. An profile extrusion line is illustrated in Figure 5-24.