Banbury Fill Factors 1

[polym3]

I would appreciate some info concerning the effects of usng too high of a fill-factor in mixing and dispersion.

The literature suggests average fill-factors (by volume) at about 0.75 - we seem to be running a lot higher than that; up to 0.9

How does this affect dispersion of blacks, heat, mixing efficiency etc.

Thanks

 

[tom1953]

Generally, too high a loading/fill factor in the mixer will result in poor dispersion (as can too low a loading, BTS). 75% loading is a good average number, but specific compounds can have lower or higher optimum loadings. If a compound is high viscosity and "nervy", it might be best mixed at a lower loading, while a soft, low viscosity compound, that has lots of liquid in the formula, might be better mixed at a high loading. A mentor used to tell me that, with soft compounds, figure the batch size with 1/2 the oil included, the other 1/2 of the oil being "free".
Another factor is the type of throat the mixer has. If there's a deep throat, a larger batch loading can probably be used.
If you have the luxury to do so, you could run several batches with different loading factors and see where the optimum is. It may be different for different compounds, especially if there's a big difference in filler and plasticizer levels.
tom

 

[GrahamBennett]

I agree with Tom to a certain extent. However, fill factors also depend on the wear of the chamber and rotors. The older these are, the higher the ff to maintain good mixing. Also, 4-wing tangential rotors, running at even speed, can allow you to use a ff of about 0.80 for high viscosity compounds and about 0.90 for low viscosity ones. The depth of throat is unimportant IMO - any overfill goes above the ram in any case and that will not enter the chamber leaving you with poor disersion and a load of trouble on dump under the mixer.