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Size Reduction
Saloni Ambasana
PhD Scholar
PGT-SFC
Gujarat Ayurved University
INDIA
1
• Definition
• Objectives
• Factor Affecting
• Energy requirement
• Mechanism
• Methods
2
Size Reduction
Physical
Dimension
of an object
Decrement
or Decrease
So, Size Reduction means decreasing size of an object...
• It is a unit operation in which materials are reduced
to smaller pieces/ to coarse particles, or to still finer
powder, ...
Why Size reduction ??????????
? ?
?
?
?
?
?
?
? ?
?
????
?
?
???
?5
• Materials are rarely found in the size range required.
• So, there is a need either to decrease or to increase
the parti...
1. Improve Appearance: -
o Smooth texture and elegant appearance (Ointments,
Pastes and Creams).
o Improve physical stabil...
4. Improve Stability: -
o Sp. for biphasic systems – Suspension, Emulsion etc.
o Emulsion –  Size of oil droplets  Rate ...
7. Aerosol and Inhalation preparations: -
o Size determines the position and retention of particles in
bronchioles & less ...
10. Ophthalmic suspension: -
o Very fine to avoid eye-irritation.
11. To Increase Viscosity: -
o Viscosity of Acacia incre...
ADVANTAGES & DISADVANTAGES
11
AFFECTING FACTORS
Size
Reduction Degree of Size
Reduction
12
FACTORS AFFECTING SIZE REDUCTION
1. Hardness: -
o Harder the material difficult is the size reduction.
2. Toughness: -
o E...
3. Stickiness: -
o Cause difficulty in size reduction.
o Material may stick to the surface or mesh may get
choked.
o Solut...
5. Moisture content: -
o Influences properties such as Hardness, Toughness &
Stickiness.
o Less than 5 % moisture – Dry gr...
7. Material Structure
8. Abrasiveness: -
o If material is abrasive the final powder may be
contaminated with the metal wor...
FACTORS AFFECTING DEGREE SIZE REDUCTION
1. Formulation: -
o Pills, Powders (in suspension & in mixtures) – Fine
powder.
o ...
b. Solvent/ Menstruum used: -
o Water (Causes more expansion of vegetable tissue and
penetrates easily) – Coarse powder.
o...
• Consists of two parts: -
1. First opening up of any small fissures (cracks)
which are already present.
2. Secondly forma...
• Fine grinding needs more energy to initiate cracks.
• So, from Energy utilization point of view – Size reduction is
an i...
• There are four main methods effecting size
reduction: -
1. Cutting (Slicing)
2. Compression (Bruising)
3. Impact
4. Attr...
1. Cutting (Slicing): -
• The material is cut into pieces.
• It may be effected by a sharp pen knife, a pair of
scissors, ...
3. Impact: -
• The material is stationary and is hit by an object moving at
high speed or Moving particles strikes a stati...
5. Impact and Attrition: -
• Here, both impact and attrition are combined.
• Equipment: - Ball mill and Fluid energy mill
...
Method Common example Approx. particle size
(m)
Approx.
increase in
fineness of
the product
Cutting • Scissors
• Shears
•...
ENERGY LAWS
Rittingers law
Kick’s law
Bond’s law
Used to predict the energy requirements for size
reduction 26
• Although it is impossible to estimate accurately the amount of
energy required for size reduction of a given material, s...
• Rittinger’s Law: -
• “Energy required (consumed) is proportional to the fresh
surface produced (sheared)”.
• More applic...
• Kick’s Law: -
• “Energy necessary for crushing material is proportional to
the logarithm of the ratio between initial an...
• Bond’s Law: - (Intermediate between Rittinger’s & Kick’s law)
• “The useful work is directly proportional to the new sur...
Methods
31
CUTTER MILL
• PRINCIPLE: - Cutting
32
• CONSTRUCTION: -
o Cutter mill has two type of knives
– Stationary & Rotatory.
o Stationary knives are mounted in
the cas...
• WORKING: -
o Rotor disc rotate at 200-900 revolution per minute.
o Feed material is loaded through hopper.
o Size reduct...
• ADVANTAGES: -
o Simple set-up.
o Easy to clean, operate and maintenance cost is less
due to less complicated machinery i...
• DISADVANTAGES: -
o Not suitable for fine grinding.
o Very hard material cannot be grinded.
o In case of fine particle si...
• APPLICATIONS: -
o For coarse degree (20 – 80 #) of size reduction.
o For tough, fibrous, soft, materials. Ex. Roots, Pee...
HAMMER MILL
• PRINCIPLE: - Impact
38
• CONSTRUCTION: -
o Stout metal (S.S.) casing.
o Metal casing enclosing central
shaft.
o Four or more hammers attached to
...
• CONSTRUCTION: -
o Upper part – Feed hopper.
o Lower part – Screen of desired
size.
o Screen is replaceable as per size
r...
• WORKING: -
o Material is fed in the grinding zone.
o In the grinding zone the hammers revolve at very
high speed (5000-1...
• ADVANTAGES: -
o Rapid size reduction.
o Different types of materials can be grinded – Dry,
Wet filter press cake, ointme...
• ADVANTAGES: -
o Operation is continuous.
o Simple to install and operate.
o Easy to clean.
43
• DISADVANTAGES: -
o Not suitable for thermolabile material as high speed
causes heat generation.
o Sticky material cannot...
• APPLICATIONS: -
o Used for producing intermediate grades of particle
size.
o Powdering of barks, roots, leaves (dry), cr...
• MODIFICATIONS: -
o Different types of hammers: -
Square-faced
Tappered to cutting edge – fibrous material
Stepped form
F...
ROLLER MILL
• Also known as Crushing rolls.
• PRINCIPLE: - Compression & Attrition
47
FEED
PRODUCT
• CONSTRUCTION: -
o Consists of two cylindrical rolls of stone or metal, mounted horizontally & rotate
along ...
• WORKING: -
o Material is fed into the hopper and then it is dropped
into the gap.
o The rolls rotate at different speeds...
• ADVANTAGES: -
o Simple construction.
o Easy to clean and operate.
o Gives uniform product.
o Suitable for abrasive mater...
• DISADVANTAGES: -
o Do not produce very fine powder.
o High Wear & Tear.
51
• APPLICATIONS: -
o For wet grinding – Pastes, Ointments etc.
o For cracking of the seeds before extraction of fixed
oils....
BALL MILL
• PRINCIPLE: - Impact & Attrition
53
• CONSTRUCTION: -
o Consists of a hollow,
cylindrical shape vessel-
jar or POT rotating
horizontally.
o Pot may be made up...
• CONSTRUCTION: -
o The mill is filled with “balls”
or “pebbles” of flint,
porcelain, steel or S.S. which
act as grinding ...
• WORKING: -
o The material to be reduced is fed into the cylindrical
vessel (pot).
o The vessel rotates horizontally on i...
• PRECAUTIONS: -
o The amount of material charged must be equal to
void-space in the ball charge. As too much feed
produce...
• ADVANTAGES: -
o Simple construction.
o Easy to clean and operate.
o Economical and Cheap.
o Afford large grinding surfac...
• DISADVANTAGES: -
o High Wear and Tear.
o Not suitable for soft & sticky materials.
o Very noisy.
o Slow process.
59
• APPLICATIONS: -
o For grinding of drugs & suspensions.
o For dry or wet grinding.
o For sterile grinding.
60
• MODIFICATIONS: -
o Rod Mill (Bar Mill) (Contains rods instead of balls)
Used for sticky material.
Rods are cheap.
Unifor...
o Hardinge mill (Colloidal mill)
Conical in shape & tapered at the discharge end.
Requires less time
No cushioning of the ...
FLUID ENERGY MILL
• PRINCIPLE: - Impact & interparticulate Attrition
63
• CONSTRUCTION: -
o Loop of pipe (20 to 200 mm in
diameter & upto 2 m in height)
form cylindrical grinding
chamber made up...
• CONSTRUCTION: -
o Premilled coarse is fed
near the bottom of the
mill through a venturi
injector.
o There is an internal...
• WORKING: -
o Material is fed near the bottom of the mill.
o Material is then exposed to high pressure stream of air or g...
• ADVANTAGES: -
o Simple construction and Easy to operate.
o Fine particle size can be obtained.
o There is no moving part...
• DISADVANTAGES: -
o High cost.
o If feed is not controlled the material may choke.
o If the air fluid is not clean it cau...
• APPLICATIONS: -
o Fine powdering
o Thermolabile materials
o Dehydration of wet materials
o Coating of fine particles
• I...
END RUNNER MILL & EDGE RUNNER MILL
• PRINCIPLE: - Impact & shearing
70
• CONSTRUCTION: -
End Runner Edge Runner
Mechanical Mortar & Pestle Mortar-Mixer
Mortar made up of Steel or granite Heavy ...
• WORKING: -
End Runner Edge Runner
Material is fed into the machine. Material is fed into the machine
Pestle is free to r...
• ADVANTAGES: -
End Runner Edge Runner
Suitable for coarse grinding & moderately
fine powder
Very fine powder
Require less...
• DISADVANTAGES: -
End Runner Edge Runner
Require more floor space than disintegrator
High wear & tear
Not a continuous pr...
• APPLICATIONS: -
End Runner Edge Runner
Fibrous material Very tough & fibrous roots & barks
Wet grinding Wet & Dry grindi...
COLLOIDAL MILL
• PRINCIPLE: - Shearing (Hydraulic shear)
76
• CONSTRUCTION: -
o Inlet Hopper – used to feed the
material into the mill.
o Consists of a high speed rotor
& stator (whi...
• CONSTRUCTION: -
o Between the rotor & stator
there is an adjustable clearance
ranging from 0.002 to 0.03
inches.
o Here,...
• WORKING: -
o Material is placed into the mill through the inlet hopper.
o It is then passed through the narrow gap betwe...
• ADVANTAGES: -
o High through-put with excellent grinding result.
o Infinitely adjustable gap settings between rotor/ sta...
• DISADVANTAGES: -
o High power required for running the mill.
o Consumes more energy.
o Wet materials needed for grinding...
• APPLICATIONS: -
o Dispersion of solid particles into the liquid.
o Reduce the particle size in suspension in a liquid or...
• MODIFICATIONS: -
o Water jacketed.
o Toothed colloid mill.
83
84
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Size reduction w.s.r. Pharmaceutical Industry

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Size reduction - its principle, affecting factors, mechanism and instruments employed in Pharmaceutical as well as food industry

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Size reduction w.s.r. Pharmaceutical Industry

  1. 1. Size Reduction Saloni Ambasana PhD Scholar PGT-SFC Gujarat Ayurved University INDIA 1
  2. 2. • Definition • Objectives • Factor Affecting • Energy requirement • Mechanism • Methods 2
  3. 3. Size Reduction Physical Dimension of an object Decrement or Decrease So, Size Reduction means decreasing size of an object 3
  4. 4. • It is a unit operation in which materials are reduced to smaller pieces/ to coarse particles, or to still finer powder, before they can be formulated into suitable dosage forms. • Other terms: - Comminution Grinding Milling Pulverizing Crushing DEFINITION 4
  5. 5. Why Size reduction ?????????? ? ? ? ? ? ? ? ? ? ? ? ???? ? ? ??? ?5
  6. 6. • Materials are rarely found in the size range required. • So, there is a need either to decrease or to increase the particle size. WHY ????? 6
  7. 7. 1. Improve Appearance: - o Smooth texture and elegant appearance (Ointments, Pastes and Creams). o Improve physical stability. 2. Increase Surface Area: - o Increase Dissolution rate  Increase therapeutic efficiency (Griseofulvin – frequency of administration decrease). 3. Facilitate Absorption & Bioavailability: - o Rate of absorption depends on particle size. o Finer the particles faster the rate of absorption (Nasya dravya) OBJECTIVES 7
  8. 8. 4. Improve Stability: - o Sp. for biphasic systems – Suspension, Emulsion etc. o Emulsion –  Size of oil droplets  Rate of creaming  o Suspension –  rate of sedimentation 5. Extraction: - o More surface expose to solvent hence more extraction of drug (Yavkuta in kwatha formation). 6. Mixing: - o Easy mixing o Assure uniform dosage 8
  9. 9. 7. Aerosol and Inhalation preparations: - o Size determines the position and retention of particles in bronchioles & less irritation. 8. Parenteral Suspension: - o Rheology o Product Syringeability 9. Facilitate drying: - o Drying of wet masses may be facilitated by milling. o Milling  surface area – Drying . 9
  10. 10. 10. Ophthalmic suspension: - o Very fine to avoid eye-irritation. 11. To Increase Viscosity: - o Viscosity of Acacia increases on fine sub-division. 12. To decrease bulkiness of crude drugs 13. Chemical reactivity 10
  11. 11. ADVANTAGES & DISADVANTAGES 11
  12. 12. AFFECTING FACTORS Size Reduction Degree of Size Reduction 12
  13. 13. FACTORS AFFECTING SIZE REDUCTION 1. Hardness: - o Harder the material difficult is the size reduction. 2. Toughness: - o Ex. Fibrous drugs, Green fresh leaves etc. are soft but tough. o Toughness can be reduced by lowering the temperature. The advantages of this method are: Less decomposition of thermolabile material No loss of volatile material No oxidation No explosion 13
  14. 14. 3. Stickiness: - o Cause difficulty in size reduction. o Material may stick to the surface or mesh may get choked. o Solution: Dryness Addition of inert materials such as Kaolin to sulphur o Ex. Gums & Resinous materials (Guggulu, Mochras etc.) 4. Slipperiness: - o As material acts as lubricant. 14
  15. 15. 5. Moisture content: - o Influences properties such as Hardness, Toughness & Stickiness. o Less than 5 % moisture – Dry grinding. o More than 50 % - Wet grinding. 6. Melting or Softening point: - o Heat generated during grinding creates problems with materials which tend to melt/ stick/ decompose due to heat. o Ex. Camphor, Thymol, Stearic acids, Waxes, Fats, Resins etc. 15
  16. 16. 7. Material Structure 8. Abrasiveness: - o If material is abrasive the final powder may be contaminated with the metal worn out from the machine. 9. Size of the starting material 10. Quantity of material to be reduced 11. Size, Shape, Flow & Bulk density of the product 12. Ratio of feed size to product size 16
  17. 17. FACTORS AFFECTING DEGREE SIZE REDUCTION 1. Formulation: - o Pills, Powders (in suspension & in mixtures) – Fine powder. o Suspension (to be injected) – Very fine powder. 2. Extraction: - a. Physical character of the drug: - o Soft drug (fresh) – Sliced/ Crushed. o Hard drug (yashti) – Coarse to Moderately Coarse. o Solubility – If constituents are less soluble fine powder. o Localization of drug constituents. 17
  18. 18. b. Solvent/ Menstruum used: - o Water (Causes more expansion of vegetable tissue and penetrates easily) – Coarse powder. o Alcohol (Hardens the vegetable drug tissues and so penetration is slow) – Fine powder. c. Drug/ Menstruum ratio: - o Menstruum large – Coarse powder (Weak preparation). o Small – Fine powder (Strong preparation). d. Process: - o Infusion & decoction – Drug/ Menstruum ratio is high & Menstruum is water – Coarse to Moderately coarse. o Maceration & percolation – Drug/ Menstruum ratio is small & Menstruum may or may not be water – Fine. 18
  19. 19. • Consists of two parts: - 1. First opening up of any small fissures (cracks) which are already present. 2. Secondly formation of new surfaces. • Large particles with several cracks – More rapid size reduction. • Small particles with less no. of cracks – Slow size reduction. • Ex. Coal contains no. of small cracks – Large particles are broken more rapidly than the small ones. MECHANISM OF SIZE REDUCTION 19
  20. 20. • Fine grinding needs more energy to initiate cracks. • So, from Energy utilization point of view – Size reduction is an inefficient process. • Efficiency of the process depends on: - a. Load applied b. Magnitude c. Nature of force exerted (Compressive/ Impact/ Shear) • If applied force must be more than the elastic limit. • If not on removing the load the expanded particle again returns to its original size. • The energy is stored in the particles in form of heat & no size reduction is done. 20
  21. 21. • There are four main methods effecting size reduction: - 1. Cutting (Slicing) 2. Compression (Bruising) 3. Impact 4. Attrition 5. Impact and Attrition METHODS OF SIZE REDUCTION 21
  22. 22. 1. Cutting (Slicing): - • The material is cut into pieces. • It may be effected by a sharp pen knife, a pair of scissors, or a root cutter. • Equipment: - Cutter mill 2. Compression (Bruising): - • Material is crushed by application of a pressure. • Particle disintegration by two rigid forces. • Equipment: - Mortar and Pestle (Laboratory) and Roller mill (Industry) 22
  23. 23. 3. Impact: - • The material is stationary and is hit by an object moving at high speed or Moving particles strikes a stationary surface. • Size reduction occurs by a single rigid force. • Equipment: - Mortar and Pestle (Laboratory) and Hammer mill & Disintegrator (Industry) 4. Attrition: - • Arising from particles scraping against one another or against a rigid surface. • Here, the material is subjected to pressure as in compression, but the surfaces are moving relative to each other. • Equipment: - Roller mill 23
  24. 24. 5. Impact and Attrition: - • Here, both impact and attrition are combined. • Equipment: - Ball mill and Fluid energy mill 24
  25. 25. Method Common example Approx. particle size (m) Approx. increase in fineness of the product Cutting • Scissors • Shears • Guillotine • Cutter mill 100 – 80,000 Compression • Pestle – Mortar • Nutcrackers • Roller mill 50 – 10,000 Impact • Hammer mill • Disintegrator 50 – 8,000 Attrition • Pestle – Mortar • File • Roller mill • Colloidal mill 1 – 50 Impact & attrition • Ball mill • Fluid-energy mill 1 – 2000 25
  26. 26. ENERGY LAWS Rittingers law Kick’s law Bond’s law Used to predict the energy requirements for size reduction 26
  27. 27. • Although it is impossible to estimate accurately the amount of energy required for size reduction of a given material, still a no. of empirical laws have been proposed. • These three laws can be derived form the basic differential equation: - • A common failure of these three laws is that they do not give any information on the relation of size put through a mill or on optimum operating conditions. 27
  28. 28. • Rittinger’s Law: - • “Energy required (consumed) is proportional to the fresh surface produced (sheared)”. • More applicable to fine powders. 28
  29. 29. • Kick’s Law: - • “Energy necessary for crushing material is proportional to the logarithm of the ratio between initial and final diameters”. • More closely relates to the energy required to effect elastic deformation before fracture occurs and more accurate than Rittinger’s law. 29
  30. 30. • Bond’s Law: - (Intermediate between Rittinger’s & Kick’s law) • “The useful work is directly proportional to the new surface area, & since the crack length is proportional to the square root of the new surface area produced, the useful energy or work in inversely proportional to the square root of the product diameter minus the feed diameter”. 30
  31. 31. Methods 31
  32. 32. CUTTER MILL • PRINCIPLE: - Cutting 32
  33. 33. • CONSTRUCTION: - o Cutter mill has two type of knives – Stationary & Rotatory. o Stationary knives are mounted in the casing of the machine. o Rotating knives are attached to a horizontal rotor which rotate at high speed. o Upper part has a hopper for the feed and lower part has a detachable screen. o Reduced material is collected beneath the screen. 33
  34. 34. • WORKING: - o Rotor disc rotate at 200-900 revolution per minute. o Feed material is loaded through hopper. o Size reduction occurs by fracture of particles between two knives (rotating and stationary) which have a clearance of few millimetres. o Particles pass through the screen product which is collected into receiver. 34
  35. 35. • ADVANTAGES: - o Simple set-up. o Easy to clean, operate and maintenance cost is less due to less complicated machinery involved. o Operation is continuous. o Less wear and tear. o Good for coarse grinding. o Wide range of materials (soft-hard-fibrous-tough). o Sieve being detachable – different sizes can be used as per need. 35
  36. 36. • DISADVANTAGES: - o Not suitable for fine grinding. o Very hard material cannot be grinded. o In case of fine particle size further processing needed thus increases the cost of production. o Sticky materials cannot be used. 36
  37. 37. • APPLICATIONS: - o For coarse degree (20 – 80 #) of size reduction. o For tough, fibrous, soft, materials. Ex. Roots, Peels, Woods, other plant parts, animal tissue etc. o Also useful in manufacture of rubber, plastics, recycling of paper waste and plastic material. o Reduction of dried granules prior to tableting. • MODIFICATIONS: - o No stationary knives. o Shape of knives. o Water jacketed – for thermolabile materials. 37
  38. 38. HAMMER MILL • PRINCIPLE: - Impact 38
  39. 39. • CONSTRUCTION: - o Stout metal (S.S.) casing. o Metal casing enclosing central shaft. o Four or more hammers attached to central shaft. o Hammers are mounted with swivel joints. Hammers swing out to a radial position when shaft is rotated. o Hammers may be either square, tapered or stepped form. 39
  40. 40. • CONSTRUCTION: - o Upper part – Feed hopper. o Lower part – Screen of desired size. o Screen is replaceable as per size required. o Mill is connected with fan and cyclone separator. 40
  41. 41. • WORKING: - o Material is fed in the grinding zone. o In the grinding zone the hammers revolve at very high speed (5000-10000 RPM). o Material is thrown out centrifugally and is grinded by impact of hammers or against the plates along the periphery of mill casing. o If the particle-size of the material (feed) is less than that of the mesh size it will pass. Oversize particles will retain which will be recycled. 41
  42. 42. • ADVANTAGES: - o Rapid size reduction. o Different types of materials can be grinded – Dry, Wet filter press cake, ointments & slurries. o Product size can be controlled by variation of Rotor speed Hammer type & no. Size of mesh Feed rate Clearance between hammer & casing 42
  43. 43. • ADVANTAGES: - o Operation is continuous. o Simple to install and operate. o Easy to clean. 43
  44. 44. • DISADVANTAGES: - o Not suitable for thermolabile material as high speed causes heat generation. o Sticky material cannot be grinded as it may choke the screen. o If rate of feed not controlled mill may choke. o Not useful for abrasive material. 44
  45. 45. • APPLICATIONS: - o Used for producing intermediate grades of particle size. o Powdering of barks, roots, leaves (dry), crystals and filter cakes. o For preparation of wet granules for tablets. • MODIFICATIONS: - o Different types of screen. o Water jacketed – for thermolabile material. 45
  46. 46. • MODIFICATIONS: - o Different types of hammers: - Square-faced Tappered to cutting edge – fibrous material Stepped form Flat (Blunt) – Brittle Knife edges – Wet granulation 46
  47. 47. ROLLER MILL • Also known as Crushing rolls. • PRINCIPLE: - Compression & Attrition 47
  48. 48. FEED PRODUCT • CONSTRUCTION: - o Consists of two cylindrical rolls of stone or metal, mounted horizontally & rotate along their axis. o The gap between the rolls is adjustable to control the size of product. o The rollers are from few centimetres to a meter or more in diameter. o The surface of the rollers may be smooth, furrowed or toothed. o Upper part – hopper and lower part – collector/screen. 48
  49. 49. • WORKING: - o Material is fed into the hopper and then it is dropped into the gap. o The rolls rotate at different speeds, so that the material is sheared as it passes through the gap and is transferred from the slower to the faster roll, from which it is removed by means of a scraper. o The speed of the rollers & the gap between the rollers determine the product size. 49
  50. 50. • ADVANTAGES: - o Simple construction. o Easy to clean and operate. o Gives uniform product. o Suitable for abrasive material. 50
  51. 51. • DISADVANTAGES: - o Do not produce very fine powder. o High Wear & Tear. 51
  52. 52. • APPLICATIONS: - o For wet grinding – Pastes, Ointments etc. o For cracking of the seeds before extraction of fixed oils. o Bruising the soft tissue to help the menstruum to penetrate easily. o Also useful in gun powder industry. • MODIFICATIONS: - o Triple roller mill 52
  53. 53. BALL MILL • PRINCIPLE: - Impact & Attrition 53
  54. 54. • CONSTRUCTION: - o Consists of a hollow, cylindrical shape vessel- jar or POT rotating horizontally. o Pot may be made up of metal (S.S.), porcelain, or rubber lined. o Length of cylinder is slightly greater than its diameter. 54
  55. 55. • CONSTRUCTION: - o The mill is filled with “balls” or “pebbles” of flint, porcelain, steel or S.S. which act as grinding medium. o For effective grinding 30 – 50 % volume of the mill should be filled with balls (Ball charge). o Ball size depends on the size of the feed & diameter of the mill. o Smaller balls give slower but fine grinding. o Varying sizes of balls gives a better product, since large balls crush the feed & smaller ones give fine product. 55
  56. 56. • WORKING: - o The material to be reduced is fed into the cylindrical vessel (pot). o The vessel rotates horizontally on its long axis. o Balls move causing combined Attrition & Impact thereby doing size reduction. (A)Low Speed with Sliding (B) High Speed with Centrifuging (C) Correct Speed with Cascading 56
  57. 57. • PRECAUTIONS: - o The amount of material charged must be equal to void-space in the ball charge. As too much feed produces cushioning effect while too little causes loss of efficiency & wear & tear of the mill parts. o Optimum speed of rotation should there. Low speed – Only Attrition – Negligible size reduction – As balls roll over each other High speed – No Impact + Attrition – No size reduction – As balls are held against the mill & revolve with mill 57
  58. 58. • ADVANTAGES: - o Simple construction. o Easy to clean and operate. o Economical and Cheap. o Afford large grinding surface within a limited space. o Useful for Batch or Continuous operation. o Being a closed system useful for toxic substances. o May be sterilized and sealed for sterile milling in the production of ophthalmic & parenteral products. o Wide degree of materials can be grinded with different degrees of hardness. o Very fine powder (100 #) can be produced. o Useful for grinding explosive due an inert atmosphere being created. o Used for both wet & dry grinding. 58
  59. 59. • DISADVANTAGES: - o High Wear and Tear. o Not suitable for soft & sticky materials. o Very noisy. o Slow process. 59
  60. 60. • APPLICATIONS: - o For grinding of drugs & suspensions. o For dry or wet grinding. o For sterile grinding. 60
  61. 61. • MODIFICATIONS: - o Rod Mill (Bar Mill) (Contains rods instead of balls) Used for sticky material. Rods are cheap. Uniform size obtained. Low power consumption. o Tube Mill Length is four times than the diameter & balls are smaller than in ball mill. Grinds more finely than in ball mill. 61
  62. 62. o Hardinge mill (Colloidal mill) Conical in shape & tapered at the discharge end. Requires less time No cushioning of the product. More uniform & fine product. More capacity Low power consumption o Vibration Mill Vibration instead of rotation. Very fine product & faster grinding. Low power consumption. Size distribution is narrow. o Compartment Ball Mill – Mill is partitioned by different sized mesh screen. Product is shifted from coarse to fine. 62
  63. 63. FLUID ENERGY MILL • PRINCIPLE: - Impact & interparticulate Attrition 63
  64. 64. • CONSTRUCTION: - o Loop of pipe (20 to 200 mm in diameter & upto 2 m in height) form cylindrical grinding chamber made up of S.S. or alloy steel. o Fluid (air/ steam/ inert gas) – introduced through nozzles at the bottom of the loop under pressure (25 to 300 PSI (pounds per square inch). 64
  65. 65. • CONSTRUCTION: - o Premilled coarse is fed near the bottom of the mill through a venturi injector. o There is an internal classifier too, by which finer & lighter particles are discharged and heavier particles are retained until reduction to small size. 65
  66. 66. • WORKING: - o Material is fed near the bottom of the mill. o Material is then exposed to high pressure stream of air or gas & is swept into violent turbulence by the sonic & supersonic velocity of the streams. o The particles are accelerated to high speed & they collide with each other, which causes fracture of the particles. o The high degree of turbulence causes impact & attritional forces between the particles, which reduce the material to finer state. o The finer particles are employed by the drag of gas leaving the mill, while larger, heavy particles are carried downward & back to the grinding chamber. 66
  67. 67. • ADVANTAGES: - o Simple construction and Easy to operate. o Fine particle size can be obtained. o There is no moving part in the mill, so no abrasion hence no contamination of the product. o The classifier, permits close control of the particle size thereby narrow size distribution. o Expansion of gases leads to cooling, so useful for thermolabile pharmaceuticals such as Vitamins, Antibiotics, Enzymes & Hormones. o For sensitive materials inert gas can also be used. o Product is smoother than by any other method. 67
  68. 68. • DISADVANTAGES: - o High cost. o If feed is not controlled the material may choke. o If the air fluid is not clean it causes contamination of the product. o Premilling is required. 68
  69. 69. • APPLICATIONS: - o Fine powdering o Thermolabile materials o Dehydration of wet materials o Coating of fine particles • INDUSTRIAL PRODUCTS: - o The Trost Pulverizer o The Jet – O – Mixer o Gem Jet Mill o Sturtevant micronizer 69
  70. 70. END RUNNER MILL & EDGE RUNNER MILL • PRINCIPLE: - Impact & shearing 70
  71. 71. • CONSTRUCTION: - End Runner Edge Runner Mechanical Mortar & Pestle Mortar-Mixer Mortar made up of Steel or granite Heavy cast iron or granite wheel weighing several tonnes A doumble shaped heavy pestle made of similar material is mounted eccentrically in the mortar. The diameter of the roller may vary from 0.5 to 2.5 meter. The rollers are mounted vertically in a horizontal shaft. Mortar is rotated by a motor. The pestle rotates by friction. Each roll revolves on its own axis, while both travel round a shallow steel or granite base. 71
  72. 72. • WORKING: - End Runner Edge Runner Material is fed into the machine. Material is fed into the machine Pestle is free to rise & fall in the mortar due to which both impact & shear is created. The outer part of the wheel has to travel a greater distance than the inner so that size reduction is achieved by shear & crushing. Material is continuously scraped from the sides of the mortar with a doctor knife. Material is continuously thrown in the path of the moving stones by an arrangement of scrapers. Pestle can be raised from the mortar which facilitates emptying & cleaning. Generally wheels rotate but sometimes the bed also rotates. Height between the rollers & base is adjustable, which governs the size of the product. In some the outer wall is perforated so the material can be removed as soon as the size is reduced. 72
  73. 73. • ADVANTAGES: - End Runner Edge Runner Suitable for coarse grinding & moderately fine powder Very fine powder Require less operation during operation. Easy to clean & operate Low Maintenance No question of chocking 73
  74. 74. • DISADVANTAGES: - End Runner Edge Runner Require more floor space than disintegrator High wear & tear Not a continuous process 74
  75. 75. • APPLICATIONS: - End Runner Edge Runner Fibrous material Very tough & fibrous roots & barks Wet grinding Wet & Dry grinding Viscous material such as ointment & paste Grinding paints, clays & sticky materials 75
  76. 76. COLLOIDAL MILL • PRINCIPLE: - Shearing (Hydraulic shear) 76
  77. 77. • CONSTRUCTION: - o Inlet Hopper – used to feed the material into the mill. o Consists of a high speed rotor & stator (which are used to reduce the particle size by shear force), with a conical milling surfaces. o The rotor speed is 3000 to 20000 rpm. o Rotors & the stator may be smooth or rough surfaced. 77
  78. 78. • CONSTRUCTION: - o Between the rotor & stator there is an adjustable clearance ranging from 0.002 to 0.03 inches. o Here, there is a thin uniform film material which is subjected to maximum amount of shear. o The Rough surfaced mill provide intense eddy current, turbulence & impact to the particles to shearing action. 78
  79. 79. • WORKING: - o Material is placed into the mill through the inlet hopper. o It is then passed through the narrow gap between the rotor & stator. o Then, heavier liquid is added into the chamber of the mill that produces the shearing process. o After addition of the heavier material, lighter material whether it is a solid mass or a liquid of different viscosity. o The materials are then both stirred together within the mill at a high rate of speed. o The suspended particles are thus size reduced. 79
  80. 80. • ADVANTAGES: - o High through-put with excellent grinding result. o Infinitely adjustable gap settings between rotor/ stator for control particle size reduction. o Suitable for products of high viscosity range. o Capable of operation under pressures upto 16 bar. o Easy to clean & operate. o Fine grinding obtained – Particle size as small as 3 microns can be obtained. o Good for fibrous materials also. o Low noise levels. 80
  81. 81. • DISADVANTAGES: - o High power required for running the mill. o Consumes more energy. o Wet materials needed for grinding. o Due to shear heat is generated, thus not suitable for thermolabile material. 81
  82. 82. • APPLICATIONS: - o Dispersion of solid particles into the liquid. o Reduce the particle size in suspension in a liquid or to reduce the droplet size of a liquid suspended in another liquid. o To increase the stability of suspensions & emulsions. o For emulsification, homogenization, dispersion & mixing. o Useful in the manufacture of food pastes, emulsions, coatings, ointments, creams, pulps, grease etc. o Useful for fibrous material. o Colloidal mill can be sterilized so mainly used in the production of sterile products. 82
  83. 83. • MODIFICATIONS: - o Water jacketed. o Toothed colloid mill. 83
  84. 84. 84

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