banbury mixing

[tmoon42]

Looking at mixing graphs, the banbury ram goes up during a batch. What is the purpose of raising the ram instead of just continuing the mix with the ram down? Will this allow volatiles or moisture to escape?

 

[GrahamBennett]

You've more or less answered your own question tmoon42. Raising the ram allows you to add other ingredients at different times during the mix cycle as well as allowing volatiles and moisture to escape. Additionally, raising (or floating) the ram reduces the pressure on the mix and, thus, allows the batch temperature to remain fairly constant, which will improve the dispersion of the ingredients within the polymer matrix.

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[tmoon42]

Ah, thank you Graham. I have a couple more questions I'd like to ask.

What is the typical duration for a ram raise to vent? (if the purpose was to vent moisture)

For epdm, how many ram raises would one typically see for upsidedown mixing in a Banbury of
Master
Final
Single pass?

 

[GrahamBennett]

Ram raise just to vent? 5 seconds or so.

Upside down mixing: Master - no ram raises for venting until about 3 mins into mix. Then just 1 or 2 max.
Final: I wouldn't vent during a final mix.
Single pass: Same as master batch mix.

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[tmoon42]

Hello Graham, I was wondering if you could explain some causes of variation in the s' curve.
Basically the initial dip has a longer sustained plateau before s' starts increasing. There is no correlation in shift/batch times/weightment deviations/drop temps. Though batch time varies up to +/- 25 seconds, there is no correlation to the shifts in the s prime curve.

 

[GrahamBennett]

1. Are you talking about the indicated drop temperature or actual bulk material temperature when you mention drop temps?
2. What equipment do you use below the mixer for cooling/sheeting off?
3. I should have asked this before - what make and model is your mixer and what fill factor do you use for this compound?

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[tmoon42]

1. Actual rubber temp measured at drop door
2. Sample taken between mixer and before extruder. No mill
2. 320liter banbury style by HF , roughly 66%

 

[GrahamBennett]

Thanks Tmoon.

Fill factors in the range of 65% or so are normally used for intermeshing rotor machines. If you have the true Banbury style rotors then you should be operating with a fill factor of about 75 - 80% for 2-wing rotors and 80 - 85% for 4-wing rotors.

From my experience, your s' variations are probably due to the samples' rate of cooling. You should try to establish a simple protocol for the sampling procedure so that each sample is allowed the same time and cooling procedure between sampling from the batch to testing on the rheometer.

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