Hot Manifold

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Hot Manifold

Postby not related to on Thu Jul 14, 2011 9:41 am

Does it make sense to do a Viscosity curve Graph (RVM) on a DME Hot Runner/Manifold tool. I would think that the hot runner would interfere with the actual outcome? Im running PP with moderate speed , 1.1 sec fill time.
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Re: Hot Manifold

Postby rickbatey on Thu Jul 14, 2011 7:41 pm

My first questions is 'Did you do a pressure loss' check of the manifold? For me, I do shear rate studies as well for every tool, with valve gates and not.....
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Re: Hot Manifold

Postby not related to on Mon Jul 18, 2011 9:44 am

Pressure Loss? Please Explain. i sure hope theres no pressure loss in the manifold?
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Re: Hot Manifold

Postby Louis on Mon Jul 18, 2011 10:57 am

Pressure drop, pressure variation, or pressure loss....?

Some manifolds have tortuous melt paths.
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Re: Hot Manifold

Postby rickbatey on Mon Jul 18, 2011 11:42 am

Any hot runner/manifold requies some melt pressure, to distribute the melt from the center of the mold out to the injection point(s). This is like an automotic transmission, it takes say 9 HP just to make the system run! I have seen times when the pressure loss was so great, a new manifold system had to be built because we knew we could never consistently fill the tool and achieve the quality/scrap rate required. Then I've seeen other molds that required replacement of drop(s), valve gate pins, and tip orifice and styles due to the same loss.
It sounds like you've never done this before, so here it is short and sweet. Inject through the nozzle and record the peak injection pressure. Now do the same thing but through the open mold, record the peak injection pressures. The differance is the 'pressure loss' of the hot runner. I expect you will be surprised to know how much pressure you are losing on good running molds!
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Re: Hot Manifold

Postby not related to on Thu Jul 21, 2011 9:34 am

I will do this. Now what would be a normal pressure loss? Obviousley you are going to get some pressure loss.
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Re: Hot Manifold

Postby rickbatey on Thu Jul 21, 2011 12:29 pm

For me, a hundred to maybe two hundred psi is normal. That loss, can be the difference between making full parts, or non-fills! Just knowing that number, and seeing your requirements on your tools, may shed some light on why some molds are so much trouble!
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Re: Hot Manifold

Postby dadayzook on Wed Apr 11, 2012 3:15 am

This is like an automotic transmission, it takes say 9 HP just to make the system run! I have seen times when the pressure loss was so great, a new manifold system had to be built because we knew we could never consistently fill the tool and achieve the quality/scrap rate required. Then I've seeen other molds that required replacement of drop(s), valve gate pins, and tip orifice and styles due to the same loss.
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Re: Hot Manifold

Postby M&M on Wed Apr 11, 2012 10:35 pm

Not related to don't look at a hot runner as anything other then a runner system. Don't read anything more into it, the melt has no idea it is going through a hot runner or a cold runner. The results of the study IS the shear the melt sees as it is flowed through the melt channel, which is exactly what you want :wink:

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Re: Hot Manifold

Postby Louis on Thu Apr 12, 2012 1:37 pm

Dumb question open for discussion,

Does the previous shear history have anything to do with the shear when filling the mold?
Can it be totally discounted?


I would think the viscosity curve would be strongly influenced by the runner system, be it hot or cold. Although cold runner systems generally have relatively large flow paths.

I'm and old extrusion guy at heart, but always willing to learn more about plastics
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Re: Hot Manifold

Postby M&M on Thu Apr 12, 2012 2:05 pm

I am doing a study on shear related hangover for another project, so far find that once the melt passes a "shear inducing event" minus the added heat, and provided the melt was not fractured, it can regroup for the next shear event if you will. I ask the question like this, is effect of shear cumulative during fill? Does not appear so but it needs more study.

You right about manifolds, they have a profound impact on shear studys but so does everything in the melt path and that is what is shown with a shear rate study, just what that impact is.

There are two topics here:

1. Should you consider or some how weigh / discount melt curve data because of a hot runner?
Answer is no.
2. Should you review a feed system the appears to have a huge dynamic pressure loss during fill?
Answer is yes.
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Re: Hot Manifold

Postby Homebrew II on Fri Apr 13, 2012 11:38 am

Hey M&m

This is a skern, good answer. Way back when you sent me your RV spreadsheet for review in comparison to you know who's, have you updated it for this type analysis? Man, that would be great! Even if not could you re_send it to me since my old computer crashed? [email protected]

I'd be forever grateful! Also would love to talk to you again 864.285.7839

Take care friend !

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