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Tech Tip September 1996

Mold Flow Impact on Part Quality:


The last tip went through mold flow and how to do it on the press by yourself to see what the various pressure loses were. We can, by analysis now determine what is going on in the tool and runner and must now evaluate the results. Where it becomes important is if you are using all the available pressure in the machine and still have shorts, and or non-packed parts. Further the gate is sealing in the proper amount of time. If it is a multicavity tool you may be able to block off a cavity or two and see if you now can pack out the parts. If so you know you don't have enough plastic pressure.

If going through the system on the pressure drop you can now determine where is the largest drop in the pressure in your tool. From that you have to make a determination to the fact of can you decrease the pressure drop by opening up the system. An example of this may be that you have 3,000 psi drop through the runner. Though this is not large it could be that in your case that you have a flat small diameter profile on the runner. By opening the depth of the runner to a nominal diameteer you might be able to pick up 1500 psi pressure. Further do the gates have large pressure drops. What is the land area of the gate. This would be the largest contributor to the pressure drop..( remember that if you open the gate you can change the gate seal time.) Shortening up the land may have an effect but the greatest effect is the pressure lost. If you are not at 0.040" but 0.250" on the land length that would be an area of concern.

What happens if there is nothing that sticks out. If by reducing the number of cavities that you fill provides the pack and quality you wish than you must find a press that has higher plastic pressure capabilities.



Thanks for the time.

Steven L Silvey
Sr. Technical Service
General Polymers