The principle of Rotoform pastillation
The Rotoform pastillation system consists of a heated cylindrical stator which is supplied with molten product – pumped from a vessel, pit or supply pipe system – and a perforated rotating shell that turns concentrically around the stator, depositing drops of the product across the whole operating width of the steel belt.
A system of baffles and internal nozzles built into the cylindrical stator provides a uniform pressure across the whole width, providing an even flow through all holes of the perforated outer shell. This ensures that every pastille is of a uniform size, from one edge of the belt to the other.
The circumferential speed of the Rotoform pastillator is synchronised with the speed of the belt: drops are therefore deposited without deformation. Heat released during solidification and cooling is transferred by the stainless steel belt to the cooling water sprayed underneath. This water is collected in tanks and returned to the waterchilling system; at no stage does it come into contact with the product.
After the droplet has been deposited onto the steel belt, some product will remain around the holes of the outer shell. A special heated refeed bar forces this product into an internal gap in the Rotoform pastillator from where it is mixed with new product and re-fed onto the steel belt.
Designed for effective pastillation
The design of an effective Rotoform pastillation system takes into consideration a number of factors. For instance, the minimum diameter of a pastille depends on the diameter of the holes in the rotating shell, the density and viscosity of the product itself, the surface tension and the mechanical acceleration applied to the droplet.
Furthermore, the drops need to be of a certain weight and volume in order to be deposited onto the steel belt, and the distance between the outer shell of the Rotoformer and the steel belt will also need to be determined from case to case.
All these parameters have to be finalised before choosing the appropriate Rotoform oastillator component configurations. These will be defined by means of specially developed computer programs and/or test runs using the particular product to be processed.
Different types of Rotoform pastillators
There are now a number of different types of Rotoform pastillators available, each with its own specific benefits and applications. However, all are based on the same principle.