Angle of repose
Aim :
To evaluate angle of repose and factors that influence angle of repose in certain material.
Introduction :
The angle of repose is the angle (relative to the horizontal base) of the conical pile produced when a granular material is poured onto a horizontal surface. It is related to the density, surface area and coefficient of friction of the material concerned.
Angles of repose have been used as indirect methods of quantifying powder flow-ability, because of their relationship with inter particulate cohesion. In general powders with angles of repose greater than 50 degree have unsatisfactory flow properties, whereas minimum angles close to 25 degree correspond to very good flow properties.
Apparatus and material :
Sand (size=150 mm, 355 mm,500 mm, 850 mm and mixed), Magnesium stearate,electronic beam balance,
hopper
Procedure :
1. 100 g 150 mm sand is weighted by using electronic beam balance.
weighting all the materials with care *,*
3. The hopper was pulled above and let sand flowed and heap or peak was forming.
See !! let the sand flowed and heap is forming ~~
4. Height, slope and peak diameter are measured.
5. The angle of repose is calculated.
6. Step 1 until step 5 are repeated by using 355 mm,500 mm,850 mm, mixed sand.
7. Step 1 until 5 are repeated with all the different size of sand by adding 1 % of magnesium stearate.
Result :
Diameter =48 cm
Table 4.1 : The height of different size sand
Table 4.2 : Angle of repose with or without magnesium stearate
Calculation :
Percentage difference :
Question :
1. What are the angle of repose of sand?
2. What are the factor affecting angle of repose?
Factors that affecting angle of repose are :
a.Coefficients
of friction between particles
b. Size of
the particles
c.Moisture
affects the angle of repose
3. What are the other methods that can be used to evaluate the angle of repose in certain materials?
The other method are :a.Tilting box method
b.Fixed funnel method
c.Revolving cylinder method
Discussion :
Based on table 4.2, the lowest angle of repose are 500 mm
and 850 mm sand which is 8.29° meanwhile the highest angle of repose are
150 mm (16.92°).As Particle size increases the angle of repose is decreases.
This is because, the smaller particles have dominant cohesive and adhesive
forces as compared to particle weight whereas in bigger particles gravity plays
a dominant role so less repose angle.
The glidant are often used to
decrease the frictional force and hence to increase the flowability. The angle
of repose in general goes on decreasing with increasing concentration of the
glidant. However, after a certain per cent, the change in the angle of repose
may not be appreciable. The glidant increase the flow of material by reducing
the friction between the particles.
The
angle of repose after adding glidant increase 1.5%. This is show that unsatisfactory
flow properties. There are certain error maybe occur during weighting the sand
and the glidant. The concentration of the glidant play important role. Beside
that the efficiency of magnesium stearate decreases
as the orifice size increases. The optimum glidant concentration is also
dependent upon orifice size.Thus effecting our result.
Conclusion :
As a conclusion, the angle of repose
depends on the coefficients of friction between particles,size of the
particles and moisture affects the angle of repose.The smaller the particle
size, the smaller the angle of repose. The addition of glidant will affect the
angle of repose.
References :
1. Aulton's Pharmaceutics, The Design and Manufacture of Medicine, Third edition,Michael E.Aulton,Churchchill Livingstone Elsevier:175-175
