By analyzing
the typical characteristics of the rotary coater it is easy to
understand the high efficiency of the coating process. Basically it
is the same reason what makes this technology so effective for film coating.
While coating particles, the surface has to be covered with a uni-
or multi-layering of coating material from either a liquid
formulation or a combination of liquid and powder formulations. The
speed of covering and enlarging the particles is highly depending on
the surface area of the particles exposed in time and the
homogeneity in which the liquid and powder material is spread onto
the particle surface. These two elements are extremely effective in
the rotary coater.
The rotor rotating at 25-150 rpm creates a fast
horizontal circular movement of the particles which is combined with
a vertical circular movement when the particles hit the static wall.
The thus obtained intense spiral flow of particles creates a rapidly
changing mass and exposed surface which allows coating materials to
be taken up very fast while the agglomeration of particles is
prevented.
The
other essential element is the spinning disc which is as simple as
effective in applying the coating liquids. The centralized spinning
disc is rotating at high speeds varying from 1500-6000 rpm.
At these
speeds coating liquid will be broken down into a mist of droplets in
a large spraying zone which enables a fast and homogeneous wetting
of the individual particles in the rotating mass.
From here it is easy to perceive that with such a
fast and even wetting of the particle surface, the absorption of
powder material and subsequent building of a pellet progresses
equally effective.
While this may explain the potential success of
the rotary pelleting as such, there is a great deal of parameters
and variables involved which determine the overall effectiveness of
the process and the attractiveness for commercial application in
seed encrusting and pelleting.
