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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.

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Factors that affect the rate and size of granules produced by a dry granulators
1. Roller speed

2. Feed rate

3. Roll design

4. Difference in shape and size of screws

5. Powder cohesiveness, density and flow characteristics

6. Particles size

7. Machine type

8. Die diameter

9. Feed hopper and feed frame

10. Tooling features

11. Compression speed.

12. Slugging pressure

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

1. Slugging

2. Roller compaction

1. Slugging
In slugging, a large tablet (slug) is produced in a heavy-duty tableting 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
2. 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.

picture of the parts of a dry granulator

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
1. Dry granulators are used when the drug does not compress well after wet granulation.

2. Dry granulator is the best choice for moisture sensitive drugs like Aspirin, vitamins.

3. It is used in granulating thermolabile drugs.

Advantages of Dry Granulators
1. It requires minimal floor space

2. The machine is easy to clean after use

3. The roller compactor is suitable for hard continuous operation as well as batch production

4. Dry granulators eliminate the addition of moisture and heat

5. Mechanical strength of the product is uniform

6. Low running cost/low operating cost and highly efficient process

7. It eliminates the need for binding solution

Disadvantages of Dry Granulators
1. It does not permit uniform color distribution

2. Dry granulation process creates more dust

3. There is increased potential for cross-contamination

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