Agitated mixer

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Agitated mixer is a mechanical device which is used to mix the powder and produces free flowing powder materials having uniform particle size and density.

HISTORY

Agitated mixers are introduced by paul in 1986, steiss in 1998, kent in 2002 and ramponi in 2002. 1

It mainly consists of an stationary shell which is used to mix the powder.

DESCRIPITION

Mixing of the powder is difficult is due to variation in there particle size, densities, pysical form and the bulk used. This problem is more serious when the liquid materails is added to the more potent medications (low bulk). In mixing process the particles should move relative to one another to ensure homogenous mixer. Hence localized shearing is necessary to move the particles, bulk of the materials also should come in the region of the shear. During the mixing proces no presssure is exert on the powder. Pressure results in cake formation and effects the diificulty in the homogenous mixing. The powder mixing is a neutral process and when the process is stoped the the mixture remins in steady state unless furthur agitation. 2

CONSTRUCTION

It consist of a stationary shell/ vessel or a trough in which an arm rotates and transmits shearing action of the particles.

The end to end movement is required for the general mixing which can be achieved by fitting helical blades to the agitator.

The mixer is commonly used for mixing of free flowing powdres. 3

PRINCIPLE

  • The priciple involved in agitated mixer is of both shearing and convection occuring within the mixer.
  • The mechanism of the powder mixing is either convective or diffusive.
  • Convective movement results in movement of bulk of powders or particles while the diffusive results in movement of the indiviual particles.
  • However both of them gives the homogenous mixer.
  • The efficiency of the mixing of the material can be done by introducing the baffles into the stationary shell.
  • Baffles acts as agitators resulting in the homogenous of the mixer.
  • The helical agitated mixer do not exerts pressure on the powder but exerts shifting bulk of the powders or particles into the drun to cause proper mixing. 2

WORKING

  • The mixing of the powder in agitated mixer is done in the stationary shell.
  • A typical agitated mixer consist of stationary shell with a single or stationary shafts on which the agitated devices are mounted.
  • During mixing the particles are thrown randomly and the produced is sheared or fluidized mechanically depending upon the tip speed of the paddles or plows.
  • These mixer can handle wide range of powders or bulk solids from free flowing to chosieve to pastes.
  • While mixeing takes place one can incorporate a liquid injection for furthur agglomerisations, chopping and delumpers for breaking upon the agglomersations depending on the requriment.
  • In agitating mixers the mixing is done predominatley due to partciles moving randomly from one point to another along with the bulk mass.
  • So there a principle of both shearing and convection occuring within the mixer.
  • Depending upon the handling characteristic of powders certain degree of aeration takes place and at higher tip speed the mass is capable of fluidized.
  • Once the material is aerated the frictional effects including the interparticule forces are reduced and sometimes eliminated.
  • So that the particles moves freely and randomly. 1

PHARMACEUTICAL APPLICATIONS

  • Agitated mixers are used to mix free flowing materials hving uniform particle size and density.
  • This are the mixers uses wetting materials during the mixing process to avoid agglomeration and forms homogenize mixing.
  • This are the mixers which are widely used in pharmaceutical industries, chemical industries, medicinal industries etc

ADVANTAGES

  • It is a continuous process.
  • Low cost
  • Low operating cost
  • Easy to clean
  • More versatile
  • Minimal space requirment
  • Easy of maintence
  • Rapid mixing time
  • Homogenous output

DISADVANTAGES

  • Slow rotation
  • Usage of power

REFERENCES

  1. Edward L. Paul, Victor Atiemo-Obeng, Suzanne M. Kresta, Handbook of Industrial Mixing: Science and Practice 2004
  2. Dr. P. V. Kasture, Pharmaceutics - I, 2008, page.no- 971.
  3. Mehta RM, Pharmaceutics-I: Mixing and Homogenisation (1996), Page no: 112-113.

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

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