Fluidized bed coating process

[offonoff]

I am researching methods for coating oddly shaped agricultural seeds with a hard spherical coating. A simple building up of layers of films will not make a long thin seed round, except perhaps with an excessively thick shell. Other methods involve isolating individual seeds and delivering them into the center of a drop, which falls into a curing vessel.

One of several possibilities is a fluidized bed method where the seeds are suspended in a jet of air and atomized coating material. I believe if the viscosity of the material before curing is low enough, the surface tension high enough and the collisions between particles kept minimum, that the suspended seeds would develop spherical drop like coatings.

I have found example of this making small spheres (microns to millimeters), but nothing up to several centimeters as large seeds would require.

If anyone has any experience or knows of references relating to this process, especially with water permeable, near ambient temperature setting coatings, please share.

thanks.

 

[witchdoc]

Much depends upon the thickness of the coatings and the type of coating operation that is used. We have used rotating drums or inclined disk type devices to do similar work. However, the amount of coating required is substantial. The action of the rolling bed action tends to "round" the ends. The viscosity and sharpness of the melting point of the coating agent also has a major impact.

Phillip
pforsythe@forsytheandlong.com

 

[UmeshMathur]

For large diameter particles (such as your seeds) where fluidization is not stable, I would look into spouted beds, which have been field-proven in such applications for over 3 decades. There is a description of this technique in Perry. For design details, such as maximum spoutable bed depth, go to Mathur & Gishler's original papers and the numerous more recent papers.