Wet Granulation

Granules are formed by the addition of a granulation liquid onto a bed of powder under the influence of an impeller.

This is typically carried out using a high-shear granulator or a simpler planetary mixer.


The wet granulation is extruded to form cylindrical extrudate (noodles or spaghetti) of a constant diameter (normally 0.5 – 3 mm).

The wet mass is passed through a screen or die forming a soft, pliable extrudate which breaks by its own weight into shorter units.

The size of the final pellets (spheres) is principally determined by the hole diameter of the screen (or die) used in the extrusion step.

For example, in order to obtain spheres with a diameter of 1 mm, then a 1 mm screen is used on the extruder, although spheres with a distribution of 0.8-1.2 mm may often be obtained.



Caleva, a UK based company, designs and manufactures extruders to work in concert with Caleva spheronizers. The Caleva extruders that are available for use in the laboratory include the Caleva Multi-Lab, Model 20 Extruder and Variable Density Extruder.

The Caleva Multi-Lab employs a low pressure, single, horizontal, helical screw in combination with a vertically oriented die, and was developed by Caleva to allow the Formulation Scientist to produce single or multiple extrudate for further processing or testing, even when there are only a few grams of granulate with which to work. The Caleva Multi-Lab extruder is generally used with the Multi-Bowl Spheronizer (MBS) configured with 60mm diameter disc and bowl.

The Caleva Model 20 extruder is a bench top, laboratory scale, low pressure, vertically oriented radial screen type extruder that is generally used in combination with the Multi-Bowl Spheronizer (MBS) configured with either the 60 – 85 mm diameter disc and bowl.

One of Caleva’s production extruders, the floor standing Model 25 extruder is like the bench top Model 20 extruder, being that they are both radial screen-type extruders. All results acquired using the Caleva Model 20 extruder are scalable to the Model 35 extruder.

For those products that require or can benefit from a higher density extrudate than that which can be attained through the use of the Model 20 or Model 35 screen-type extruders, consider a Caleva gear-type extruder. Laboratory through pilot plant production rates can be satisfied by the Model 40 gear-type extruder. The Caleva Model 100 gear-type extruder will satisfy higher production demand.

Access more detailed information call us at 732-249-6900.


Caleva, a UK based company, offers a very complete size range of Single Drum Spheronizers; starting with the Model MBS and ranging on up to the Model 700 Twin spheronizers.

The Model MBS is a multiple bowl spheronizer that is suitable for bench top / counter top use in a formulation laboratory environment. The following single drum and single disc configurations are available for use with Model MBS in four (4) sizes: 60 mm, 85 mm, 120 mm, and 250 mm diameters; all for use and interchangeable on a single base platform. Extrudate loadings, ranging from 10 grams on up to 1 kilogram, can be processed with the Caleva Model MBS spheronizer, depending of course on which bowl and disc size is in use.

Caleva’s mid-range spheronizers include the Model 380 spheronizer and the Model 500 spheronizer. These floor standing, portable spheronizers satisfy the need to process extrudate loadings ranging from 1 – 4 kilogram and 4 – 10 kilograms respectively per batch. The Model 380 spheronizer and the Model 500 spheronizer are suitable for use in clinical trial, pilot plant, and small to medium production environments.

The demand to spheronize extrudate batches at a production rate above the capacities of Model 380 spheronizer and Model 500 spheronizer, are satisfied by the Caleva Model 700 single floor standing spheronizer (5-20 kilogram per batch, depending on product).

Higher production demands, in excess of 5-20 kilograms per batch, can be accomodated by the Caleva Model 700 Twin floor standing spheronizers. For this arrangement, two (2) single Caleva Model spheronizers are combined into a dual (twin) configuration, such that 10 – 40 kilograms per batch (i.e 5-20 kilograms per batch per spheronizer x 2 spheronizers) can be spheronized.

In addition to satifying higher production demands above and beyond the capability of a single Caleva Model 700 spheronizer, the twin spheronizer configuration upgrades the normal batch spheronization unit operation to a continuous unit operation. The addition of automated feeding of the twin spheronizers saves labor and provides more consistentcy from load to load.

For more detailed information about Caleva spheronizers, call us at 732-249-6900.


Using interchangeable attachments, the Caleva Multi-Lab combines Mixing, Extrusion and Spheronization functions into one small bench top unit. The Caleva Multi-Lab is a new R&D tool for laboratories that have to Mix, Extrude and Spheronize (pelletize) very small quantities of material. The instrument is capable of producing batches ranging from 15 to 50 grams, with an effective yield of approximately 90%.

A typical mixing-extrusion-spheronization run is as follows:

1. The mixing bowl, which is basically a very small high shear mixer-granulator, is attached to the base unit containing the drive, controls and safety interlocks. The dry powder is than weighed and added to the mixing bowl and the safety cover put in place. The mixer is started and liquid binder is added during mixing until the resulting wet mass of the desired consistency is produced.

2. The mixing bowl is removed and the screw extruder and safety cover is attached to the base unit. The wet mass produced during the mixing step is fed into the extruder until the batch is completely extruded.

3. The Extruder is removed and the Spheronizer bowl is attached to the base unit. After the extrudate is added to Spheronizer bowl and the safety cover is attached, the unit is run (typically about 1-2 minutes) until all of the extrudate is converted into pellets approximately the same diameter as the extrudate.

The Caleva Multi Lab is very simple to operate and all of the attachments are added and removed without needing any tools. Using the Caleva Multi-Lab, it typically, it takes about 30 minutes to convert powder into high quality spheroids.

The Caleva Multi-Lab is ideal for:

– Basic research
– Commercial formulation development
– University teaching

For more detailed information about Caleva products, call us at 732-249-6900.



Tablet Coating


Wet Massing

Bench-top Screen


Extrusion Research Papers
Learn More


Spheronization Research Papers
Learn More

Tablet Coating

Tablet Coating Research Papers
Learn More

Wet Massing

All Caleva Research Papers
Learn More