Size reduction is a process in which the particle size of a solid is made smaller. The term size reduction is applied to ways in which particles of solids are cut or broken into smaller pieces. Size reduction is necessary if the starting material is too coarse, and the final product needs to be a fine powder.
2. SIZE REDUCTION
Definition
Size reduction or comminution is the process of
reducing drugs (vegetable and chemical
substances) into smaller pieces, coarse particles or
fine powder.
3.
4. PROCESS OF SIZE REDUCTION
1.Precipitation Method
2.Mechanical Process
9. PRINCIPLES OF SIZE
REDUCTION (MECHANISMS)
Mechanism Description Machine (Example)
Cutting Material is cut by sharp blade Cutter Mill
Compression Material is crushed between roller by pressure Roller Mill
Impact Material breaks by hammer or bars at high speed Hammer Mill
Ball Mill
Moving particle strikes against a stationary surface Fluid Energy Mill
Attrition Break down of material by rubbing action
between two surfaces
Ball Mill
Fluid Energy Mill
Impact & Attrition
Combined
Ball Mill
Fluid Energy Mill
26. THEORIES OF SIZE REDUCTION
A number of theories have been proposed to
establish a relationship between energy input and
the degree of size reduction produced.
1. Rittinger’s theory
2. Bond’s theory
3. Kick’s theory
27. RITTINGER’S THEORY
Rittinger’s theory suggests that energy required in a size
reduction process is proportional to the new surface area
produced.
where, E = energy required for size reduction
KR = Rittinger’s constant
Si = initial specific surface area
Sn = final specific surface area
Application: It is most applicable in size reducing brittle materials
undergoing fine milling.
28. BOND’STHEORY
Bond’s theory states that the energy used in crack propagation is
proportional to the new crack length produced.
where, E = energy required for size reduction
KB = Bond’s work index
di = initial diameter of particles
dn = final diameter of particles
Application: This law is useful in rough mill sizing. The work
index is useful in comparing the efficiency of milling operations.
29. KICK’STHEORY
Kick’s theory states that the energy used in deforming (or
fracturing) a set of particles of equivalent shape is proportional
to the ratio of change of size/diameter
where, E = energy required for size reduction
KK = Kick’s constant
di = initial diameter of particles
dn = final diameter of particles
Application: For crushing of large particles Kick’s theory most
useful.