gate seal study.

What is the best way to determine gate seal a hot runner mold? I'm just starting out and need all the assistance i can get.

Thanks in advance.

Hi Sublime,
I am writing a paper on this to be published at a conference and so can't give out the results yet. It is a little complicated but the procedure I have come up with works GREAT !! Quick answer - there is no easy way. For now simply 'play' with the time and pressure and you will get your answer. I will put up my paper and let you all know.
Suhas

after setting up speed ,pressure ,maje the hold pressure 80% of inj.pressure and make the hold.time 0, and 2nd stage h.pressure lesser than 1st stage to avoid banging,now set h.time 0 take two shots note the weight,now set h.time 1 note the weight,continue this steps till,the weight will become unchangable in particular time ,that is gate seal time.now this is your hold time

Thank for the help, guys.

With a direct hot tip gate, you never really freeze or seal the gate do you? I mean, wouldn't something very bad happen, on the subsequent shot, if the drops were frozen? I think you do your study to the "plateau", of weight gain.
This inability to truly seal a gate, may be a reason for hot runner molds, especially multi-cavity, not running truly tight tolerance parts.
Now if the HR is feeding cold mini sub runners, that may be a different proposition.

Suhas, you are late, the definitive paper on this subject has already been written. It is short though, as the guy writing it had a terrible accident while testing his hypothesis!

Keep on Molding ( but watch the freeze)!

brent

Now let's do it with a valve gate. Valve gate shuts at end of hold time. If the pin shuts on a slug...

I also need help in gate freeze study. I'm confuse with hot tip with valve pin gate (shut off automatically). Does it really need gate freeze? I will start to get gate vestige at around 4 or 5 sec hold time. Is there a valid statement that I can use to skip this study? Sorry for reviving this thread. I can't post a new thread.

You should perform the gate freeze, but you will see more of a plateau effect. The good thing about valve gates is once you have finished your DOE's and know the part weight, you can raise the psi and drop the time to get faster cycles.
Rick.

Thank you Rick.

I have another question, how should I enlighten our tooling guys that gate freezing is really necessary even for valve pin gate? What should I tell them?

The best method is data. The data should come from finished parts; you can't argue with success. Collect consequentive shots from both methods. Have them all weighed and measured on gauge or fixture. Collect the info, put it into Minitab or even a spread sheet. Then run numbers on ranges, averages, and Std Dev for each field. Even graph them for a huge impact!
Also a good idea is to include scrap rates and yields, before and after.
There will be folks that even then, refuse to change. Run over them or step over their corpse and keep making good parts!
Rick.

Thank you so much Rick. I'll try that.