This presentation is about the force distribution in tablet compression, energy involved in compression,compression mechanism and evaluation of the tablet formulations.

1. Mr. Sagar N Firke
Dept of Pharmaceutics
Nanded Pharmacy College
Nanded

2.  Compression : Is a reduction in bulk volume as a
result of applied load.
 Consolidation: is a phenomenon of increase in
mechanical strength of the consolidated mass.
 Deformation: Change in a geometry due to applied
forces,
 Strain: The relative amount of deformation
produced by force called as strain.
 Stress: The ratio of force(F) to cause this strain at
area (A) called stress.

3.  When external forces are applied to a powder
mass, there is a reduction in its bulk volume
because of following reasons.
 Closure repacking of the particles &
 Particle deformation at there point of contact.
 Deformation may be plastic(irreversible) or elastic
(spontaneously reversible)

4. Fig: Particle Deformation

5. CONSOLIDATION
 It is defined as increase in mechanical strength
of the consolidated mass.
 When two particles approach each other closely
enough (e.g, at separation less than 50 nm) their
surface free energies result in strong attractive
force, a process known as Cold Welding.
CONSOLIDATION
COLD
WELDING
FUSSION
BONDING

6.  When applied load is transmitted through the
particle contacts; results in generation of
considerable frictional heat.
 If this heat is not dissipated, it causes local rise
in temperature which is sufficient to cause
melting of low melting point substances.

7.  Effects of friction
1. Interparticulate Friction
2. Die wall Friction
 Interparticulate Friction: This arises at the
particle/particle contacts & expressed as
coefficient of Interparticulate friction.
Expressed as µi.
 Die Wall Friction: This is due to material being
pressed against the die wall & moved down it.
Expressed as µw.

8. FA = FL + FD
Where,
FA = Is the force applied to the
upper punch.
FL = Proportion of applied force
transmitted to lower
punch.
FD = Is the reaction at the die
wall.
FR = Radial force.
FA + FL
FM = -----------
2
FM= Mean compaction force
Fig:02 Force distribution

9.  When the compressive stress is applied in one
direction results in a decrease (ΔH) in the height.
 In the case of unconfined solid body would be
accompanied by expansion in the horizontal
direction (ΔD)
 The ratio of two dimensional changes is known as
Poisson ratio λ
λ = ΔD/ΔH
 Consequently radial die wall force (FR)
perpendicular to the die wall surface.

10.  According to classic friction theory axial frictional
force FD is related to FR by the expression.
FD = µw x FR
Where, µw is coefficient of die wall friction
 Degree of lubrication can be compare by the ratio of
FL to FA i.e., Coefficient of lubricant efficiency.
Expressed as R value.
R = FL/ FA
 The ratio near to unity indicate perfect lubrication
(0.98) & value less than 0.8 indicate poorly
lubrication.

11.  Radial die wall forces & die-wall friction affects
the ease of tablet ejection from the die.
 Ejection forces follows three stages.
 Stage1- Peak force required to initiate ejection by
breaking tablet/die-wall adhesion.
 Stage-02- Smaller force is required to push the
tablet up the die.
 Stage03- Final stage is marked by declining force of
ejection as tablet emerges from the die.

12. Work is required,
 To overcome particulate friction.
 To Overcome friction between particle & machine .
 To induce elastic or plastic deformation.
 To operate various machine parts.
Compression Process Energy Expended (Joules)
Un-lubricated Lubricated
Compression 6.28 6.28
Overcome die wall
friction
3.35 Negligible
Upper Punch withdrawal 5.02 Negligible
Tablet Ejection 21.35 2.09
Total Energy 36.00 8.37

13.  Tablets are made by compressing a formulation
containing a drug with excipients on stamping
machine called as ‘presses’
 The components of tablet machine are:
Fig: Hopper Fig: Set of Die & Punch Fig: Feed Frame

14.  Hopper: For holding of the granules
 Dies: Define the size and shape of the tablet
 Punches: For the compressing the granules
within the dies
 Cam tracks for guiding the movement of the
punches.
 Feeding mechanism: distribution of granules
from the hopper into the dies.
Fig: Cam-Tracks

15.  Die Filling: Accomplished by
gravitational flow.
 Tablet Formation: Upper punch
enters the die & powder is
compressed.
 Tablet Ejection: Lower punch
rises until its tip reaches the
level of top of the die.
Fig: Sequence of tablet compression events

18.  Granules stored in hopper empties into feed frame (A).
 Pull down cam (C) guides the lower punch to the bottom &
dies are allowed to overfill.
 Punches then pass over the weight adjustment cam(E).
 Wipe-off blade (D) at the end of feed frame removes the
excess granules.
 Lower punch travel over the lower compression roll (F).
 Upper punch rides below the upper compression roll(G).
 During decompression upper punch follows raising cam(H).
 The lower punch ride up the cam (I).

19.  GENERAL APPEARANCE
Tablet Size: Can be determine by Calliper
Shape: Defined by the die shape
Color: Micro reflectance Photometer
Presence or absence of odour: Manual
Taste: Taste Panels

20. HARDNESS
“Hardness of tablet has been defined as the force
required to break a tablet in a diametric compression
test”
Monsanto Hardness Tester
1. It consist of barrel containing a compressible spring
held between two plungers.
2. The lower Plunger placed in a contact with tablet
and zero reading is taken.
3. The upper plunger is then forced against the spring
by turning threaded bolt until the tablet fractures.

21. PFIZERTESTER
1. It Consist of pairs of Pliers , as the pliers handles
are squeezed, the tablet is compressed between a
holding anvil and piston connected to pressure gauge.
2. The dial indicator remains at the at the reading
where the tablet breaks and it can be returned to zero
pressing reset button.
Fig:
Monsanto
Hardness
Tester
Fig: Pfizer Tester

22.  FRIABILITYTEST
1. Tablets are subjected to combined effect of
abrasion and shock
2. Apparatus consist of plastic chamber that revolves
at 25 RPM dropping the tablets from the distance
of 6 inches with each revolution.
3. Pre-weighed sample is placed in a friabilator
which is then operated for 100 revolutions.

23. 4. Tablets are then dusted and reweighed.
5. Material loss less than 0.5 to 1 % is
acceptable.
Fig: Roche Friabilator

24. WEIGHT VARIATION
1. USP tablet weight variation test is run by weighing 20
tablets individually
2. Calculate the average weight
3. Compare the individual weight with average weight.
4. The tablets meet the USP test if no more than two
tablets are outside the given % limit & no tablet differs
by more than two times the given % limit.
Average Weight (mg) Max % difference
allowed
130 mg or less 10
130-324 mg 7.5
More than324 mg 5
Table: Weight variation tolerance for uncoated tablets

25.  CONTENT UNIFORMITY
1. In this test 30 tablets are randomly selected.
2. At least 10 of them are individually assayed.
3. Nine of the 10 tablets must contain not less than
85 % or more than 115 % of the labled drug
content.
4. The 10th tablet may contain less than 75 % or more
than 125 % of the labeled content.
5. If these requirements are not met, the tablets
remaining from 30 must be assayed & none may
fall outside the given percentage limit.

26. DISINTEGRATION TEST:
Def: Disintegration It is a process in which tablet is
breakdown into smaller particles known as disintegration.
Instrument: The USP device consist of a basket having 6
glass tubes.
 Tubes are open at the top and held against 10 mesh screen
at bottom.
 Each tablet is placed in the tube and basket rack is
positioned in 1 L beaker of water, simulated gastric fluid at
37± 2O C.
 A basket assembly moves up and down 5 to 6 cm at a
frequency of 28 to 32 cycles/min.

27.  Perforated plastic discs may be placed on top of the
tablets, there are useful in low density tablets.
 To be compliance with the USP standards, the tablet
must pass through the 10 mesh screen in the
specified time.
Fig: USP Disintegration test apparatus

28.  DISSOLUTION STUDY
 Testing & interpretation can be continued through three
stages if necessary.
 Six tablets are tested & are acceptable if all of the
tablets are not less than the monograph tolerance
limit(Q) + 5%.
 If tablet fails S1, an additional six tablets are tested(S2).
 The tablets are acceptable if the average of 12 tablets
is greater than or equal to Q & no unit is less than Q-15%.
 If the tablet still fails , an additional 12 tablets are
tested. Tablets are acceptable if the average of all 24
tablets is greater than or equal to Q& if not more than 2
tablets are less than Q-15.