Dry Granulators

Dry granulators are machines used for dry granulation. Dry granulation is a type of granulation process in which granules are formed without using liquid solution. Formation of dry granules requires dry powder densification and for agglomeration.

Factors that affect the rate and size of granules produced by a dry granulators

• Roller speed
• Feed rate
• Roll design
• Difference in shape and size of screws
• Powder cohesiveness, density and flow characteristics
• Particles size
• Machine type
• Die diameter
• Feed hopper and feed frame
• Tooling features
• Compression speed.
• Slugging pressure

Sub-classes of dry granulators

Dry granulator sub-classes are primarily distinguished by the densification force application mechanism and they include;

• Slugging
• Roller compaction

Slugging

In slugging, a large tablet (slug) is produced in a heavy-duty tabletting press. This mechanism of dry granulation leads to variation in the weight of one slug to another. This variation is as a result of the poor flow rate of powders with small particle size which in turn causes large fluctuation in the forces applied onto the individual slugs which bring about differences of the slug’s mechanical strength.  The mechanism of dry granulation is hardly used because the properties of the granules obtained by milling of the slugs cannot be controlled well either.

Other disadvantages of slugging include;

• Single batch processing
• Frequent maintenance change over
• Poor economic of scale
• Low manufacturing throughput per hour
• Excessive air and sound pollution
• Increased use of storage containers
• Increased need for manufacturing space.
• Increased logistics
• More energy and time is required to produce 1kg of slug than 1kg of roller compact.

Factors affecting slugging process 

• Powder cohesiveness, density and flow characteristics
• Powder particle size distribution
• Machine type
• Feed hopper and feed frame
• Die diameter
• Compression speed
• Slugging pressure

Roller Compaction

Roller compactors commonly referred to as chilsonator is a dry granulating equipment that produces a sheet of powder material by squeezing powder between two rollers. The roller compactor consists of two driver rollers running in opposite directions from the inside to the outside. The rollers are made of stainless steel and are equipped with teeth to produce a powerful grinding action by forcing the material against a series of breaking combs.

The roller compactor or chilsonator generally consists of three major units.

• Feeding system: This unit conveys the powder to the compaction area between the rolls.
• A compaction unit: This is where the powder is compacted between two counter-rotating rolls to a ribbon by applying a force.
• A size-reduction unit: This is for milling the ribbons to the desired particle size.

Fines produced during granulation are very low (max 25%) and can be reduced to 15% by careful adjustment of the process.

Roller compactors can be classified into;

• Fixed roller compactor: Roller compactor equipped with a fixed gap.
• Variable gap roller compactor: A roller compactor with a floating gap.

Classifications still possess the three major units of a roller compactor. But they differ in the way in which the gap between the rolls is realized.

Advantages of Roller Compactor

• Simplifies processing
• Facilitates powder flow
• Uses minimal energy to operate
• Improves drug dosage weight control.
• Requires less man-hours to operate
• Reproduces consistent particle density
• Produces good tablet and capsule disintegration
• Eliminates aqueous and solvent granulation
• Uses fewer raw materials
• Eliminates water-induced degradants
• Improves process circle time
• Prevents particle segregation
• Facilitates continuous manufacturing
• Improves content uniformity
• Does not require explosion-proof room or equipment
• Produces a dry product that is process scalable.

Pharmaceutical uses of Dry granulators

• Dry granulators are used when the drug do not compress well after wet granulation.
• Dry granulator is the best choice for moisture sensitive drugs like Aspirin, vitamins.
• It is used in granulating thermolabile drugs.

Advantages of Dry Granulators

• It requires minimal floor space
• The machine is easy to clean after use
• The roller compactor is suitable for hard continuous operation as well as batch production
• Dry granulators eliminate addition of moisture and heat
• Mechanical strength of the product is uniform
• Low running cost/low operating cost and highly efficient process
• It eliminates the need for binding solution

Disadvantages of Dry Granulators

• It does not permit uniform colour distribution
• Dry granulation process creates more dust
• There is increased potential for cross-contamination

 REFERENCES

• Dilip M. Parikh (2010). Handbook of Pharmaceutical Granulation Technology, Third Edition. CRC Press, Taylor and Francis Group, LLC.
• http://solidswiki.com/index.php?title=Dry_Granulators
• http://www.erweka.com/products/item/granulator/dry-granulator-tg-2000.html
• http://www.gerteis.com/en/applications/technology
• http://www.pharmaceuticalonline.com/doc/basic-principles-of-dry-granulation-and-0001
• Jim Litster, and Bryan Ennis (2004). The Science and Engineering of Granulation Processes. Kluwer Academic Publishers, Dordrecht, Netherland.
• Larry, L. A. and Stephen, W. H. (2008), Pharmaceutical Dosage Form: Tablet. Third edition. CRC Press, Taylor and Francis Group, LLC.
• Namdeo Shinde, Nagesh Aloorkar, Ajit Kulkarni, Bhaskar Bangar, Suyog Sulake, and Pratik Kumbhar (2014). Recent Advances in Granulation Techniques. Asian Journal of Pharmaceutical Sciences. 4(1): 38-47.