Experiment Part C: Powder Flow - Hopper

Title

Powder flow- hopper

Objective

To study the powder flow ability of various sand with different particle sizes by using hoppers with different dimensions and orifice size.

Date of Experiment

30th September 2014

Introduction

The largest pharmaceutical use of powders is to produce tablets and capsules. Powder flowability is the ability of the powder to flow in a desired manner in a specific piece of equipment. The flowability of a powder is of critical importance in the production of pharmaceutical dosage forms. 

Physical properties such as particle size, size distribution, shape, surface area, and density all play a role in how powder flow. Uniform flow of powder is important from bulk storage containers or hoppers into feed mechanism of the tableting or capsule-filling equipment. This is to ensure uniform particle packing and a constant volume-to-mass ratio in maintaining each tablet’s weight.

Material and Apparatus

5 hoppers (big 8mm, big 13mm, small 13mm, small 16mm), various size of sand( 150μm, 355μm, 500μm, 800μm), newspaper, electronic weighing balance, stopwatch

Procedure

1. 4 or 5 hoppers of different sizes were prepared.

2. Sand samples of varying particle sizes were prepared.

3. The hopper’s orifice was closed and 100g of sand was placed inside the hopper.

4. The orifice was opened and the sand was allowed to flow out.

5. The time required was measured for all the sand to flow completely out of the hopper.

6. The above steps were repeated with different sand and hopper sizes.

Results

Discussion

From the results obtained in this experiment, it is clearly showed that powder flow is influenced by sand particle size and the diameter and orifice size of hopper. The sand of various particle size have the best flow through the hopper which small in size and 16mm orifice diameter with n average of 2.25s. This flow rate is fast when compared to the other three hoppers which are 8mm/big(11.48s), 13mm/big(3.75s), 13mm/small(3.48s). The lowest flow rate is through the 8mm/big hopper. Therefore we can conclude that hopper with a smaller size and larger orifice diameter promotes better particle flow whereas the hopper with bigger size and smaller orifice diameter causes slower flow of sand. This is due to the larger the orifice diameter and also the smaller the hopper size, the less the contact surface of the particle with the wall of hopper. Thus this reduces the friction and gives better flow ability.

One more factor that affect powder flow is the particle size, in this case is the diameter of sand particle. Among the four types of sand sample, the 150μm sand has the longest flow rate with an average of 8.4s. This flow rate is long compared to 355μm(5.68s), 500μm(6.53s), 800μm(6.65s). This shows that the smaller the particle size, the slower the particle flow. This can be explained by the smaller particle are generally cohesive and more difficult to flow freely.

Questions

1. What are the factors that influence the flow of a powder?

The factors influencing powder flow are particle size, size distribution, shape, surface area and density of particle, size and diameter of orifice of instrument.

2. Based on the above experiment, which sand and hopper size resulted in the best powder

flow?

The sand that resulted in best powder flow is 150μm whereas the hopper size that give the best flowing reading is 16mm/small.

3. What other methods can you use to determine the flow of a powder?

The other methods used for testing powder flow are angle of repose, compressibility index or Hausner ratio, shear cell.

Conclusion

Powder flow depends on the particle size of powder and the dimensions and orifice diameter of hopper. Powder has better flow with larger orifice diameter and smaller size of hopper and also larger particle size. Powder has lower flow ability with smaller orifice diameter and larger size of hopper and also smaller particle size.

References

1. www.pharmacopeia.cn/v29240/usp29nf24s0_c1174.html

2. www.rxtimes.com/improving-powder-flow-during-pharmaceutical-operations/

3. Aulton, M.E.2013. Pharmaceutics: The Design And Manufacture Of Medicines. Edinburgh Churchill Livingstone.