Eliminate Degradation in PVC Flat Die
What was the problem?
Material degradation in a PVC sheet die!
The customer observed degradation and corrosion near the end of the manifold section of their PVC sheet die, requiring frequent cleaning and repair. Materials would collect in that region and degrade over time. When PVC degrades, it releases corrosive by-products, which break through the chrome layer and corrode the base metal. The following image shows a photo of a die that has experienced this problem and was sent back to the manufacturer for repair.
What was the root cause?
Low Shear Stress at the wall!
The following image is from a simulation using the VEL™ Flat Die module and shows the shear stress along the walls of the flow channels within the flat die
Adequate shear stress at the walls is required to keep the flow channels "self-cleaning". After the analyzing the simulation of the geometry, we found that shear stress at the walls, near the ends of the manifold, was too low and this led to build up of material which, eventually, degraded and corroded the base metal.
How it was solved?
Increase the shear stress near the walls!
Using the COMPUPLAST® VEL™ Flat Die module the geometry was modified/optimized until the simulation results showed that the shear stress at the walls was above the minimum required value. After the new die was built and installed, the customer found that they significantly increase the time before the line needed to be shut down for scheduled maintenance and, there was no longer any excessive degradation in the manifold region.
Bottom Line
Frequently stopping and starting the line to remove degraded material, and repair the die, results in wasted time and money. Furthermore, degradation of PVC releases corrosive and poisonous gases which can damage the equipment and be hazardous to the health of the employees in the plant.
With the help of simulation, we were able to find the root cause of the problem and determine the optimized geometry in less than 2 hours. The solution ultimately saved the customer many thousands of dollars every year.