short shot study with valve gates

[back4more]

I am going to be running a short shot study on a 4 cavity valve gated mold. This is on a vertical machine with inserts loaded into each bottom every cycle. What is the easiest way to control the short shots. keep in mind that with sprue valve, I am controlling 5 gates each cycle. So unless really necessary, I don't want to change valve gate times after each cycle. Just moving x-fer position does not sufficiently short the part due to 9sec gate open timer.

[Suhas]

Unless you have a true zero pressure during pack and hold, you will not be able to successfully have short shots. If the mold is not full, then the system pressure will keep filling the part for (9 minus Inj time) seconds. I think your option is to use less time and add that time to your cooling time.
Regards,
Suhas

[ArikB]

I am going to be running a short shot study on a 4 cavity valve gated mold. This is on a vertical machine with inserts loaded into each bottom every cycle. What is the easiest way to control the short shots. keep in mind that with sprue valve, I am controlling 5 gates each cycle. So unless really necessary, I don't want to change valve gate times after each cycle. Just moving x-fer position does not sufficiently short the part due to 9sec gate open timer.

Is your fill time approaching 9 seconds? If not, why would you keep the gates open for that long?

I work with a lot of multi cavity sequential valve gates running D3 processes and they do present a challenge for finding the ideal fill only. Is there a reason you couldnt leave the gates open the whole cycle to find fill only, balance the cavities etc.? Keep i mind that the valve will actually for a minute amount more polymer into the cavity when it closes.