:: Literature ::

Rotor/Stator In The Coatings And Ink Industry

By JEROME P. TIPPETT, Schold Machine Co., St. Petersburg, FL

The rotor/stator disperser is becoming more popular in the general dispersion field than ever, as a result of our recent developments and a better understanding of its function. It was primarily used in the cosmetic and adhesive industry for decades.

Through research and development, the uniqueness and high energy capabilities was realized. The rotor/stator however needed modification to make it perform to pre-determined coatings and ink demands. The demands, if not met, would surely inhibit its acceptance.

As in high speed applications, the rotor/stator had to have a top entering vortex, thorough turn-over of solids, similar flow patterns, horsepower demands of 7-10 HP Per 100 gallons of mill base, hydraulic clean operation and low/easy maintenance.

Judging from the existing design and copies already on the market, there needed to be a departure in design to suit all of these industries time-tested thumb rules.

Trough careful full-scale in-house and field-testing, these goals were achieved for all of the general dispersion formulas based on static and dynamic rheology at ambient and elevated temperature.

Old Design

The basic old designs were inefficient and generally overpowered to compensate for:

1. A wide nip annulus (the gap between the rotor & stator).

2. Bottom entering vortex (solids had to fall to the bottom of the vessel and be drawn up into the
dispersion head).

3. Anti-cavitation baffle plates that collected debris and inhibited a conventional turnover. The baffle plate also housed the lower shaft bearing. As the plate was moved up axially, it was drawn further away from the work area of the dispersion head and over a rough and dirty shaft OD Thus, a larger nip annulus was necessary due to the instability of the shaft as the bearing moved away from the stator.

4. Poor flow pattern due to large straight-cut stator slots, moveable baffle plate, smaller diameter dispersion head and a lower work related flow ratio (more turbulence than laminar flow).

New design

The new design provides an easy to maintain and replace fluid cushioned, lower bearing under, not on top of the dispersion head. By accomplishing this it would enable the vortex to be top entering and provide for a tighter nip annulus .010"-.032" per side. The bearing be checked or replaced in no time utilizing individual retainer without removing the dispersion head assembly.

The dispersion head required a closer look. To keep the HP demands acceptable industry -wide, the rotor vane profile, area and count were and are stipulated by the factory for a range of viscosities and rheologies. Angled stator vents and variable vent options are considerations also discussed for specific processes.

Once accomplishing these tasks, the rewards were immediate. Not only does Schold turbo rotor/stator provide the best pre-mix upstream the media mills, in some cases it eliminated milling entirely.

In cooperation with the processors in house chemists and the support the raw material vendors, outstanding quality and decreased dispersion time was surprising. However, virtually all applications to utilizing existing formulas and techniques showed immediately dispersion, higher gloss and reduced production time.

Turbo rotor/stator may look to be a great departure from the high disperser, but the performance is more basic than one would think it merely converts turbulent flow to laminar flow and back to turbulent at and after the nip annulus.

Full-size units are available at our two manufacturing facilities along with our laboratories for tests at now charge. Also available are full-size units for in-house evaluations.