The "cascade" die was primarily developed for pelletizing and strand applications. Its unique design provides for better distribution of material along the face of the die, delivering a more consistent flow of material than typical "coathanger" dies. "Coathanger" dies often struggle to get material to the ends of strand or pellet plates, resulting in little or no flow to outer holes. Often the problem becomes so pronounced that processors end up plugging non- performing outer holes in an attempt to establish better flow to existing inner strand holes.
The cascade die overcomes this problem with its unique design and "delivery" system. The flow stream is constantly split and branches out transversely to direct the flow to all areas of the die, not restricting flow as is the case with "coathanger" dies. Since distribution is made by directing the flow, not restricting it, the shear history of the material moving through the die is virtually identical. This uniform shear history results in uniform die swell upon exit from the die, allowing for more consistent mechanical properties and equal pellet size. The design is of particular benefit for shear sensitive or low viscosity materials but has been used successfully in other applications as well.
Another advantage of the cascade design is that residence time (amount of time it takes material to move through the die) is identical. With "coathanger" dies, material on the ends has a much longer flow path than material processed through the center of the die, so residence time is vastly different. Equal residence time not only promotes more uniform mechanical properties of material during resin processing but also is important in food applications where customers require equal "cook time" inside the die.
Actual field service revealed several other advantages of the cascade die. In particular, customers who process different color resins found that the die is virtually self purging and does not require expensive disassembly and cleaning after each color change. "Coathanger" dies suffer by comparison, as they always have areas of low velocity resulting in material hang up/degradation that can only be removed by disassembly and hand cleaning. In addition, "coathanger" dies are primarily designed around a certain output range and as a result have a limited "turn down" ratio (the amount of deviation from a specified output rate). Field use of the cascade die revealed a much better "turn down" ratio, allowing the customer flexibility to operate the die at full capacity or vastly reduced output rates without compromising flow integrity.
Finally, since the die accomplishes distribution by redirecting flow, not restricting and shearing to change flow viscosities as seen with "coathanger" designs, the cascade design successfully processes a wider range of materials. Akron Tool & Die’s cascade design has been utilized in both flat film and sheet applications and also can be utilized in round dies such as blown film and pipe. The die also lends itself to co-extrusion and color striping applications.