Calculate Uniformity Index for given sample using double cone blender, Pharmaceutical Engineering Practical

How to calculate uniformity index for given sample using double cone blender

Image result for double cone blender
Working Principle of Double Cone Blender: Double Cone Blenders are most often used for dry blending of free flowing solids. The solids being blended in these units can vary in bulk density and in percentage of the total mixture. Materials being blended are constantly being intermixed as the Double Cone rotates. Normal cycle times are typically in the range of 10 minutes, however they can be less depending on the difficulty of blending.

Material Required: Two different or distinguishable substances(As yellow and brown mustard seed with same size).

Instrument: Double cone blender


   Mixing of solids: The mixing of solids, whether free-flowing or cohesive, resembles to same extent the mixing of low- viscosity liquid. both processes intermingle two or more separate components to form a more or less uniform product. Some of the equipment normally used for blending liquids may, on occasion, be used of mix solids.
   Measure of mixer performance: Quantitative measures of mixing, based on statistical procedures, are sometimes used to evaluate mixer performance. their procedure are based on the analyses of spot samples taken from the mix at various times. A mixture in which one component is randomly distributed through another is said to be completely mixed.
   Consider a mixture of components A and B from which N spot samples, each containing n particles, are taken and analysed. The standard. The standard deviation,S is estimated from the analytical results by the equation:
s={sqrt {frac {sum _{i=1}^{N}(x_{i}-{overline {x}})^{2}}{N-1}}}
where, xi = Number of fraction of A in each sample
             = average value of measured number fractions.
            N = number of spot sample taken.
   Even if the mixture is completely mixed, the value of xi in the various spot samples will not be the same; there is always same chance that a sample drawn from a random mixture will contain a larger (or smaller) proportion of one kind of particles than the population from which it was taken.
  Mixing Index is calculated by the formula:
 = Minimum deviated Standard deviation value of mixer / Standard Deviation of mix of mixer
Note: Minimum deviated Standard deviation value of mixer is the nearest value to zero.


  • Clean the container of Double cone blender.
  • Pour Component A  and Component B uniformly making layer one over another in the container of Double cone blender from the feeding port. Use chemical admixtures such as air entraining agent in the mix to avoid segregation, if necessary.
  • Fix the RPM of the Double cone blender. 
  • Start the mixer and take spot samples at fix interval of time.

  • Standard Deviation Calculator is given below.
  • Use Standard Deviation Calculator to Calculate the Standard Deviation Calculator
  • Black Stands for Component A and Yellow Stands for Component B.
  • Calculate Standard Deviation for reading taken at each time interval.
  • Find out the Mixing Index after calculating standard deviation for all reading at different time intervals.
Graphical Representation:
  • Plot graph Standard Deviation vs Time.
  • Plot graph Mixing Index vs Time.

Related posts