Negative Flow Rate after transfer point (V to P)

By: Mac [IP: 1.47.237.xxx]
Posted on: 2018-01-23 17:45:17
Today wanna share the discussion from Moldflow Community.

Why not post in Moldflow webboard ? I think Molding is important concern on this because Molders cannot see " BACKFLOW" in the cavity. But it can happen, Molders can investigate from Peak of Pack presure (Pack is not Holding pressure).

The picture from this below link

https://www.dropbox.com/s/i8ps9erc2jm1ybw/Backflow.jpg?dl=0



The flow rate was (-) negative value mean inside cavity pressure is too high, it can cause of stress , flash , warpage , easy broken. .etc.
#1 By: Sachin [IP: 1.47.237.xxx]
Hello All,
Good morning. I have a small query in flow rate in Analysis Log. The flow rate shows negative value after V/P switchover. (See attachment for details). Firstly I thought it might be an error in the log. But in the same analysis it is showing the negative value for each iteration. Can anyone help me out with this?
but is it really practically possible to have backflow. How does it works in actual practice? Thanks in advance,
Sachin
#2 By: Olaf [IP: 1.47.237.xxx]
Hi sachin_bhosale, this might happen due to the pressure release down to 27MPa, in reality this might happen as well when switching over to packing. This is then called kickback and causes backflow which is indicated with negative values in the flow rate.
it is really possible in practice and you even might see it on the injection molding machine when switching from injection to packing. In that moment the screw of the injection molding machine might kick back. This is due to the fact, that the melt is crompressible. So if you release pressure (in your case from 38MPa down to 27MPa), the melt will try to expand. This behaviour is also linked to the melt volume that tries to expand, e.g if you have a high volume hot runner system, it might result in a higher backflow.
Cheers Olaf

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