Case Histories

Proper Die Design

Our customer processing rigid PVC polymer complained of burning and degradation of material.

Proper Die Design Details

Our customer processing rigid PVC polymer complained of burning and degradation of material. Akron Tool & Die worked with the customer to eliminate as many variables as possible, including poor screw design and inadequate or non-uniformed heating. An evaluation of the transition adapter leading from the extruder to the sheet die was suspected to be the culprit.

ATD made calculations to determine the total pressure drop, shear rate, shear stress, and flow velocities through the adapter. A more streamlined design was proposed by ATD and then placed into service by the customer. The issue of burning and degraded material was eliminated, and, in addition, the design allowed for less pressure drop, shear and shear stress, allowing the customer to improve its output rate. In addition, the adapter clean time was vastly reduced as the streamlined features eliminated "slow" or "dead" velocity spots in the die and as mentioned eliminated material degradation and burning.

Better Productivity

Akron Tool's customer submitted a strand plate drawing for manufacture. After reviewing the provided engineering, Akron Tool and Die recognized a potential problem with the die's flow symmetry and design.

Better Productivity Details

Akron Tool's customer submitted a strand plate drawing for manufacture. After reviewing the provided engineering, Akron Tool and Die recognized a potential problem with the die's flow symmetry and design. This customer had frequently complained of excess system pressures and difficulty cleaning die plates between resin changes. A review of the die's flow path revealed a serious design flaw that would contribute to both of these customer issues. Our engineers made a simple suggestion to modify the channel geometry, which was ultimately accepted by the customer.

The die was put into service and system pressures and cleaning difficulties were reduced. In addition, subsequent evaluation of the production costs for the die plate revealed lower process time, meaning that in the end Akron Tool and Die was able to offer a lower cost on future die plate orders. It was a powerful example of the total solution we provide to our customers—value added engineering, improved pricing, and improved customer output.

Cascade Die Design

The "cascade" die was primarily developed for pelletizing and strand applications.

Cascade Die Design Details

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.

Efficient Flow

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.

Multiple Applications

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.