Mixer Selection – An alternative consideration!
Agitators, Blenders, High-Speed Dispersers and Rotor/Stator Mixers
On a regular basis, we speak with dozens of experienced manufacturers of coatings, cosmetics, foods, pharmaceuticals, plastics and adhesives – virtually every process industry alive and thriving at this day and age. They are experts in the chemistry of their product formulations and the dynamics of producing them. They understand every nuance of color development, particle size reduction, viscosity build-up, etc. They can predict the effect of a subtle change at any step in their process. Yet, when we speak of mixing equipment, we invariably go right back to basics.
1. "What equipment options are available now for low-shear let down?"
2. "What rotor size, tip speed, and horsepower are now considered reasonable for high-shear pre-mixing?"
3. "When do tank/batch size and viscosity require a switch from a single-shaft high-shear mixer to a multi-agitator mixer in order to prevent excessive heat build-up...?"
Most agree that a periodic review of the basics in mixer design is valuable,at least to make sure that their process lines are still competitive. Technology is evolving quickly in many categories of mixing equipment, and a quick review of the "new" fundamentals may reveal that last year's workhorse in your mixing operation is now obsolete.
A cookbook-style review can certainly be useful, but it can also be deceiving. It places equipment like high-speed dispersers and rotor/stator pre-mixers in neat categories, and that is not the way the real world works. Mixer selection is just not that simple. It's a balancing act. We balance the need for shear against the need for pumping action and sufficient flow to disperse the heat created by a high-shear device. We trade horsepower for greater agitator and tank diameters.