It is always to avoid running a pressure-limited process. Any process which is pressure limited will have and inconsistent 1st stage injection weights and 1st stage injection times.
When to Optimize the Rear Zone
The optimal rear zone temperature is specific to each machine and material combination. For this reason, a rear zone temperature study should be performed each time a new material is molded on a particular machine.
- Set the molding machine to manufacture stable product
- Set the rear zone temperature to the manufacturers recommended minimum
- Allow the rear temperature to stabilize
- Record the ‘Rear Zone Temperature’ and the ‘Recovery Time’
- Increase the rear zone temperature incrementally
- Repeat steps 3-5, but do not exceed the manufacturer’s recommended maximum
- Graph the data: Time (Y axis) vs. Temperature (X axis)
- Evaluate the graph and select a temperature with a low recovery time
-Andy
Always Look for Correlation…
When one process output is inconsistent, check the process data in case there is not correlating data which can help pinpoint the actual cause of the problem.
Checking Your Check Ring Performance
All check rings leak, but over time the check ring will wear and leak more. The most important issue is how consistently it leaks during the velocity-controlled injection phase of the process.
Silverstreaking in PVC
PVC polymer chains break easily when they encounter shear. Any processing or equipment changes you can make to reduce the shear on the material will significantly improve your process.