The Working Principle of Pharmaceutical Roller Compactor

Roller Compactor

What is Roller Compaction :

The Roll Compactor machine is used for increased bulk density, making granules, dust free processing and reducing particle size of pharmaceutical ingredients in pharmaceutical industry, in food as well as chemical industry for densification and granulation of powder.

Roller compaction is a method of powder compaction of dry powders into a solid mass known as the ribbon. This process is achieved by feeding powder through a set of directly opposed, counter-rotating rollers under very high pressure. The process avoids the use of liquids and high temperatures. As the volume decreases through the region of maximum pressure, the material is formed into a solid compact sheet or flakes of ingredients. These flakes or compact sheet of ingredients are reduced in size to obtain the desired grain size. Finally, using an oscillating granulator machine, a multimill machine, a continuous mill, or a sizing machine, these chips or flakes are reduced in size to the desired granules or grains. The sieve size should be selected very carefully in order to prevent the generation of fines. The selected sieve defines the final granules’ or grains’ size. The purpose of dry granulation is to increase the bulk density of powders and particle size to ensure a better flow of distributed material; an important factor in the manufacturing of tablets and capsules using production equipment.

The most important parameters in the dry granulation process are powder feeding, compaction pressure applied, and the gap diameters. The powder is fed into the rollers and – depending on the feed rate of powder, gap diameter and force – the powder will be ‘compacted’ into a pre-defined ribbon thickness. To ensure an end result of suitably uniform granule properties, a precise process control is critical. This is determined by the pressure at which the powder is forced through the rollers.

Benefits of roller compaction over wet granulation and other dry granulation techniques :

The benefits of roller compaction over wet granulation depend on the compound itself. In a moisture-sensitive compound, for example, wet granulation could prove unsuitable in terms of inducing potential impurities. In contrast, the roller compaction process does not require a liquid binder and could be a more suitable option. In addition, should a compound be heat-sensitive, wet granulation with a drying stage would not be appropriate and roller compaction would the suitable option.

Other forms of dry granulation exist such as slugging. Slugging is large compact produced on a tablet press prior to milling to granules. This method may cause some inherent challenges such as powder flow not being sufficient for compaction, leading to inconsistent compaction results. This method of dry granulation is being used less, particularly given that roller compaction is able to offer an effective alternative.

Another advantage of roller compaction is that pilot batches can occur on the same machine as commercial batches. This mitigates scale-up issues that can occur during GMP bulk production.

Different types of roller compaction and advantages:

The two main categories of roller compaction are essentially based on the gap between the rollers.  The first being fixed gap rollers and the second described as ‘floating’, meaning it is possible to change the distance between the rollers depending on the powder properties.

The generally accepted opinion is that a ‘floating’ option is more advantageous. A fixed gap can lead to production of inconsistent ribbon due to inconsistent powder flow. With a floating gap option, the distance between the rollers will alter depending on the amount of powder provided, the force applied then remains constant, ensuring that fluctuations in the granules are minimised, resulting in a more uniform or homogenous granulate.

Following compaction, the ribbons are milled with a sizing mesh which limits the upper particle size. Oscillating milling provides a gentle process to avoid creating fines. The granules can be further processed into either a tablet or capsule dosage form with increased confidence of dose uniformity.

Parts of a Pharmaceutical roller Compactor Machine :

Feeding system; it is an opening that conveys powder to the compaction chamber.

Compaction unit; in this section, the powder is compacted as two roller rotate. The magnitude of force is enough to produce a ribbon.

Size reduction unit; the compacted sizes are reduced to the desired unit.

How Pharmaceutical roller Compactor Machines Work :

The working principle of roller compactor machine is simple; it involves the following key processes:

Basically, the idea behind dry granulation is that a fine powder that is subjected to a predetermined amount of force that transforms it into a compact sheet or solid. The key factors that determine the efficiency of the compaction process include:

  • Roller surface
  • Diameter
  • Type of material being processed
  • Feed screw
  • Separating force
  • Peripheral speed
  • Pressure capabilities

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