What is Spheronization?

Spheronization is the process where extrudates (the output from an extruder) are shaped into small rounded or spherical granules.

In practice these usually vary in size from 0.4 to about 3.0 mm. The use of these spheroids can be relevant for a wide variety of industries.

The products produced from spheronization can be useful in several ways:

Product performance and functionality can be improved or changed to meet a wide range of requirements

Plant procedures can be simplified, to reduce costs or enhance security of operation

The process is well known and widely used in the pharmaceutical, nutraceutical, catalyst, petrochemical, materials science and other industries. Its use is becoming increasingly recognized in other areas of industrial material handling.

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Granulation

The influence of different mixing/granulating parameters should not be underestimated. It is true that in many cases mixing can have little or no effect on the process or final product performance but this should never be assumed. When doing development work, it is important to keep the mixing/granulation parameters constant (to remove a potential source of variation) or to make systematic trials and demonstrate the effect (or lack of effect) of changes in the mixing

Extrusion

The extrusion of the product is a required step prior to spheronization. The size of the spheres are determined by the diameter of the extrudate used for the spheronization process. For example, in order to obtain spheres with a diameter of 1 mm, a 1 mm screen is used on the extruder, although spheres with a slighter bigger diameter will sometimes be obtained. In a spheronizer, it is possible to obtain spheres with a diameter ranging from about 0.5 mm to about 10 m but in practical terms the range 0.7 to 3 mm is considered normal. Larger sizes would have a poor product appearance (not round) and a low yield of product and smaller sizes would be difficult to extrude.

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Spheronization

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Modern spheronizers have several additions and adaptations depending upon the needs of the particular product and process. The design principle of the spheronizer is relatively simple but the detailed development of auxiliary equipment and the specifics of the design have widened the range of applications and greatly improved the flexibility of the machines. In principle the basic machine consists of a round disc with a rotating drive shaft, spinning at high speeds at the bottom of a stationary cylindrical bowl. The spinning friction plate has a carefully designed groove pattern to the base. This is most often cross-hatched, but several sizes and other types are available. These discs are designed to increase the friction with the product. Extrudates are added to the spheronizer and they fall onto the spinning plate.

During the early contacts of the cylindrical granules with the friction plate, the extrudates are cut into segments with a length ranging from 1 to 1.2 times their diameter. These segments then collide with the bowl wall and they are thrown back to the inside of the friction plate. Centrifugal force sends the material to the outside of the disc. The action of the material being moved causes the extrudate to be broken down into pieces of approximately equal length relative to the diameter of the extrudate. These cylindrical segments are gradually rounded by the collisions with the bowl wall, the plate and each other. The ongoing action of particles colliding with the wall and being thrown back to the inside of the plate creates a “rope movement” of product along the bowl wall.

Spheronizer spheronization education process diagram

The continuous collision of the particles with the wall and with the friction plate will gradually turn the cylindrical segments into spheres, provided that the granules are pliable enough to allow the deformation without being destroyed. It is essential that this rope movement is present for an optimal spheronization. As processing continues, the shape of the pieces gradually changes as shown below. When the particles have reached the desired shape (usually in about 2 to 10 minutes) then the spheroids can be removed.