Transfer Moulding From Bottom-Up

[ManeaInsulationFr]

Hi everybody,

I am not an expert in polymer processing and wanted to ask you guys for advice.
We are working on developping a transfer moulding process for a part and the idea has come up to mould from the bottom, I mean then injecting the material from the bottom.
I personnally not in favour of this option because I wonder how the flow of polymer would be affected, maybe introducing turbulent flow, air voids,...
I tried to find some evidences in books and in the net if this is feasible but I did not encounter any sign of it being impossible, neither did I find examples that support this option...
I really appreciate your help!
Thanks ik advance!

 

[btrueblood]

I don't see much difference in flow conditions for a downwards- or upwards-flowing viscous fluid like typical polymers. Probably slightly less air (bubble) entrainment for an upwards flowing liquid, but again, at the typical mold pressures used and the scale of typical molds, there will be little gravity contribution to pressure differentials during the injection process.

What might be of concern, for a typical press mold design, is that there might be a longer pot hold time (and risk of scorch) for the undershot mold, as the mold cavity must be aligned and stacked onto the transfer cavity before sliding into the press. Though, there is no reason the mold cavity could not be stacked and loaded on the top of the press, and mated to the pot only when it closed, which is how we run our transfer mold (except in the other direction). Comes down to design preference, I guess.

 

[ornerynorsk]

So with the pot on the bottom and one side of the mold mounted to the top platen, how would you propose to open and close your mold with minimal operator fatigue? Sounds like a very awkward arrangement. As btrueblood mentioned, you are not relying on gravity to assist in pushing air out of the cavity.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Compositepro]

The only reason to consider bottom-up flow is if gravitational forces are significant to the injection process. With very low viscosity fluids like water this could be important. However, in most cases gravity is an insignificant factor.

 

[ManeaInsulationFr]

Thank you all for your advices.
Our set-up might be a bit particular but in our case we would not have any additional pot hold time, so scorch should not be an issue.
However I agree with ornerynorsk, I am concerned with a working area of minimum 1,4m and heavy mould parts (being quite short myself it seems actually impossible).
I was just looking at other advantages/ disadvantages to support or not the process.
It seems that otherwise, it is pretty similar.
Thank you again.