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XMOHAMEDX
23rd September 2013, 10:20 PM
HI ALL
I WANT TO ASK ABOUT THE INJECTION PRESSURE PROFILE , IN THE PAST I USUALLY USED TO make the pressure profile increasing with the flow advance
lately i began to make the pressure constant at a high value (95%) and make the velocity increase till the holding
is that ok or i should to return to the old method
any one can help me

rickbatey
24th September 2013, 01:19 AM
The most repeatable method is to perform the shear rate study, then set the max pressure with enough room at the top to compensate for changes in melt index. I try to never change injection speeds unless forced to by mold or part. I want to shoot every mold as fast as possible to reduce cycle time and drive melt viscosity variations out of my process. BUT the overriding factor would be a part that sticks, excessive flash causes a trip to the shop or damage, or several hours of work to remove the part and ribs.
Rick.

XMOHAMEDX
24th September 2013, 06:19 AM
Thanks for help Rick
but i don't know what you mean by shear rate study how can i record that,
in the heavy products i try to perform increasing speed profile for example :
65% 75% 85% then 50 % the prevent burning and reduce air trap
all that with injection pressure almost 90%
my question is : can i call that process as a speed control ?
i read that the speed control is to let the pressure at a maximum value the vary with speed
thanks again for your interest

Suhas
24th September 2013, 11:30 PM
Well Said Rick, very well said about stuck plastic and digging it out.
Mohamed, I think with the loop machine, to maintain the speed you had to do that. With a close loop machine you need not do that and the machine will adjust the pressure to maintain the speed. You are OK depending on the machine. Send me an email from 'request free resources' from my website fimmtech.com and I will send you some docs that will send you some info about viscosity etc.
Serious question: Why do you start off writing in CAPS and then switch to all lower case in your question above??? - Just kidding :)
Suhas

XMOHAMEDX
25th September 2013, 07:55 PM
Well Said Rick, very well said about stuck plastic and digging it out.
Mohamed, I think with the loop machine, to maintain the speed you had to do that. With a close loop machine you need not do that and the machine will adjust the pressure to maintain the speed. You are OK depending on the machine. Send me an email from 'request free resources' from my website fimmtech.com and I will send you some docs that will send you some info about viscosity etc.
Serious question: Why do you start off writing in CAPS and then switch to all lower case in your question above??? - Just kidding :)
Suhas
Thanks for your interest dear Suhast, it's honor for me to have a reply from you,
as for caps and lower case issue , i don't know exactly why that happened , but if you insist to know the actual cause, i promise you to ask my old keyboard
now my question is:
are all the modern injection machine (closed loop system) designed to maintain the speed programmed in the fill stage as a default , or that may be an optionally function in the machine software

thanks again Rick and Suhas
M.Hassan

Suhas
26th September 2013, 04:29 AM
Hi Mohamed,
We are all friends and brothers in molding here. It is always good to know people who are in molding, so the honor and pleasure is mine also. We all like to have fun also here.
In regards to your question, yes - all close loop machines are supposed to maintain the speeds you set and take the pressure required. That is why the pressure keeps increasing as the injection advances. Not sure if there is an option to turn off and turn on the closed loop (?)
Regards,
Suhas

rickbatey
27th September 2013, 11:50 AM
I agree with Suhas that it is our honor as well. When you get your info from Suhas it will have a much more detailed explanation of a shear rate study, so I'll give you the shorter one. A shear rate study is a study to see when the shear or injection speed to fill a mold results in reduced fill pressure due to the polymer being heated and filling faster when forced through the press and mold. The reason for finding this fill speed is so that changes in melt flow don't impact your process as severe causing you to work on the press every time it runs or you change lots of resin.
Suhas-on some old machines you could turn off closed or open loop. Most all now are velocity controlled.
Rick.

XMOHAMEDX
28th September 2013, 03:04 PM
I agree with Suhas that it is our honor as well. When you get your info from Suhas it will have a much more detailed explanation of a shear rate study, so I'll give you the shorter one. A shear rate study is a study to see when the shear or injection speed to fill a mold results in reduced fill pressure due to the polymer being heated and filling faster when forced through the press and mold. The reason for finding this fill speed is so that changes in melt flow don't impact your process as severe causing you to work on the press every time it runs or you change lots of resin.
Suhas-on some old machines you could turn off closed or open loop. Most all now are velocity controlled.
Rick.

thanks a lot Rick
i will stat a hard study for that subject based on your explanation here,
Suhas:
yesterday i tested the speed control on a stable process running machine, the filling stage was consist of one stage with pressure 45 bar and 45% speed,when i checked the spreed graph i noted that the speed line not reach the setting value (40%)
when i increase the injection pressure to 55 bar the speed line conform the setting value as in the image that i have drawn
thanks again Suhas