milling final

MILLING

Dr.Ibtihal O. Alkarim

headlinesUnder this topic we’ll discuss:

1. What is milling?2. Pharmaceutical application3. Size distribution and

measurement4. Types of mills5. Selection of mills

What is milling?Milling is mechanical process of reducing the

particle size of solids.Various terms has been used cursing,

disintegration, dispersion, grinding, and pulverization.

why milling?

Increase specific surface of the substance. Increase the free surface energy of milled

substance. significantly increase the speed of

substance and diffusion processes. strengthen the pharmacological activity of

substances

Millingadvantages Mixing is more uniform if

ingredients are roughly the same size

Milling of wet granules can promote uniform and efficient drying

Increased surface area can improve dissolution rate and bioavailability

Improved content uniformity of dosage units

disadvantages:

Excessive heat generation can lead to degradation, change in polymorphic form

Increase in surface energy can lead to agglomeration

May result in excessive production of fines or overly broad particle size distribution

Pharmaceutical application Specific surface

( surface area per unit weight) increase by size reduction which affect the therapeutic efficiency of medical substance.

specially if the material have low solubility.

Examples: Griseofulvin Penicillin G procaine Aspirin suppository Calomel ointment Areosol suspension

GriseofulvinControl of fineness half of the oral regimentWhy?Control particle size and Specific surface influences the duration of adequate serum concentration

Penicillin GPenicillin G can be administered IMWhy?Product syringe-ability

Aspirin suppository Increase rectal absorption

Calomel ointment Increase of antiseptic action by reducing

the particle size

Aerosols and Suspension Particle size affect the position and

retentionOf the particle on broncho-pulmonary system. Size affect texture, taste, and rheology of oral suspension in addition of adsorption.

Potential Impact Processing Behavior

Product Quality Factors

Property Flow Blending Wetting Drying Mechanical Dissolution Stability

Particle Size X X X X X X XSurface Area X X X X X X X

Particle Shape X

Surface Energy X X X

Bulk Density X X X

Pore Size X X X

Internal Friction X X

Wall Friction X X

Hygroscopicity X X X

Introduction Representation of data Measurement methods

Size distribution

Measurement methodsThere are three method involved in size distribution measurement:a. Microscopyb. Sievingc. Sedimentation

Microscopy An ordinary direct method. Depend of resolving power of the lens. If size close to the wavelength of light

can't resolve. Ordinary microscope lower limit is 0.4

micron Ultraviolet lower limit is 0.1 micron Ultra microscope lower limit is

0.01micron

Sieving

Most widely used Inexpensive Rapid Little variation Lower limit is 50 micron (micromesh 10

micron)

What is sieve? A pan with a bottom of wired cloth with

square openings In U.S, two standard of sieves are used. The procedure involve shaking, weighing

of portion retained, and taping

sedimentation Used over size range from 1 to 200

microns. Based on the dependence of the rate of

sedimentation of the particle on their size expressed by stoke equation.

Pipet method is the simplest means of incremental particle size analysis.

Types of mills

A mill consist of three part:1. Feed chute2. Grinding mechanism3. Discharge chute

Milling forces The principle of

operation depends on:

1. Cutting2. Attrition3. Compression4. Impact

Continuing… Open-circuit and closed-circuit mills Rate of discharge equal rate of feed. Discharge chute designed at the bottom

of mills so that the force of gravity is sufficient to give free discharge.

Continuing Comminution is characterized by the

symbol index –”i” - the degree of comminution of substances. “I” equal ratio of the diameter of pieces of material to the milling (D) to particles diameter after ones (d). i = D / d

Types of milling in depend on degree of comminution in haw much times the particles size was reduced: 1. Great (large) – in 2-6 times; 2. Medium - up 6-10 times; 3. Fine - at 10-50 times; 4. Micro fine - in 50-100 times; 5. Super fine - thin (colloidal) – in 100-10000

times.

Classification equipment for milling: By the way of milling: 1. Cutting machine 2. Attrition machine 3. Compression machine 4. Impact machine 5. Impact - Centrifugal machine

Classification equipment for milling: By the degree of comminution:1. crushers:

for great, medium, fine milling.

2. mills:for micro fine, superfine (colloid) milling.

Classification equipment for milling:By the mechanism used to break the particles:

1. Disc 2. Boll 3. Rotor 4. Hammer 5. Rollers and others

Requirements for the milling process: 1. Substances must has initial its composition and

pharmacological properties during the milling process;

2. Periodically to remove enough milled particles from the sphere of comminution;

3. Prevent formation of dust (sealed enclosures); 4. Appropriate moisture of material5. The use of sequence connected crushing-milling

machines.

Mills selection: 1. Initial size of the material and

desirable size of final product 2. The total amount of material for

milling3. Physical and chemical properties of

material for milling

Mills selection

Cutting machine.are used to comminution herbal drug that has a fibers structure Grass cutting and straw cutting (grass, stalks). Root cutting with the guillotine knife - for grinding roots,

bark. Drum straw cutting - for grinding dry medicines. Knife mill - for milling volume materials, containing cellulose Motorized soft meat grinder - for fresh herbal drugs, animal

raw materials

Crushes machineswhich are used for milling solid materials: Cheek and jaw mill

Rollers mill

Cone mill

Hammer mill

Disk mill (Excelsior)

Hammer mills It’s an impact-centrifuge mill. Using high-speed rotor to which number of swining

hammers are fixed. The material is fed at the top or center Thrown out centrifugally Ground by impact of the hammers or against the plates

around the periphery of the casing. The material is retained inside the casing until it is small

enough to fall the the screen at lower portion of casing.

Hammer mill1. rotor2. hamm

er3. Corps4. plates.

Most popular Used almost at any type of size reduction Can be used for dry, wet, cakes, ointment,

slurries. Comminution is affected by impact of peripheral

hammer speed ( up to 7600m/minute). The size of product is controlled by speed of

hammers and type and size of the screen

advantages Narrow size distribution Simple to install and operate Speed and screen can be rapidly

changed Easy to clean May be operate as closed system.

Hammer mill

Ball mills It’s combined of attrition and impact mills. Consist of horizontally rotating hollow

vessel of cylindric shape. The mills filled with balls of steel or

pebbles ( grinding medium). Pebbles, rods, and tube mills

Work of Ball mill At low speed

attrition force At higher speed

impact force At sufficient

speed centrifug force

Factor affecting milling process1. size of ball 2. Charge of balls in mills3. Amount of material to be

mille4. Weight of balls5. Wet an dry milling6. Viscosity7. Wetting agent

Ball mill

Advantages of ball mill Used either for dry or wet Batch or continuous operations Sterile grounding possible Installation, operation, and labor costs

are low Unsurpassed for fine grinding of abrasive

and hard material

Fluid energy mill (Micronizer) At which material are

suspended and conveyed at high velocity by air or steam. Which pass through nozzle.

The violent turbulence of air or steam reduce the particle size by interparticular attrition

Internal classification Pre-milling (20-

100mesh) is required. Reduction of particle

size to 1-20 microns Fluid energy source

and dust collector required.

Cutting mills Used for tough

and fibrous material

Cutting and shearing

Horizontal rotor with rotary knife cutter 2-12 knives, with cylindrical casing with stationary knives.

With a screen at the bottom

The feed should not exceed the length of knife

Not more that 1 inch thick

Roller mill Consist of two-five

smooth roller. Operating at

different speed Reduction power is

combination of compression and shearing forces

Rollers mill

Colloid mill Consist of high speed

rotor and stator with adjustable clearance range.

Rotor speed up to 20.000 rpm

Premilling is required

Colloid mill Used to process suspension and

emulsion Not for dry material Pre mixing with liquid May be smooth or rough surface

regarding rotor and stator

Colloid millUsed for suspension and emulsion

Factor influence milling1. Properties of a solid (Hard (iodine), soft and

intermediate solid).2. Specification of the product.3. Physical nature of material (fibrous, friable)4. Water content5. Heat during milling (low melting point, heat

sensitive drug, pigment, unstable compound)

1. Shape of milled particle (flow specifications)

2. Milling may alter Crystalline structure and causes chemical change in some material

Selection of a mill The choose of the mill depend on:1. Product specification (size range, particle size

distribution, shape, moisture content, physical and chemical properties of material)

2. Capacity of the mill and product rate requirement3. Versatility of operation ( wet and dry milling,

rapid change of speed and screen, and safety requirement)

1. Dust control (loss of costly drug, health hazard, contamination)

2. Sanitation (ease of cleaning, sterilization)

3. Auxiliary equipment4. Batch or continuous operation5. Economical factor

Thanks….

milling final

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