SIZE REDUCTION

Objectives, Advantages, Disadvantages, Mechanisms of size reduction, factors affecting size reduction, principles, construction, working, uses, merits and demerits of ball mill.

1. SIZE REDUCTION PROF. TAUFIK MULLA ASST. PROFESSOR DEPT. OF PHARMACEUTICS SPBC COLLEGE OF PHARMACY

2. SIZE REDUCTION Raw material are generally present in large size which can not be used by industry so it needed to be converted into small size particle or powder. Size reduction is the operation carried out for reducing the size of bigger particles into smaller one of desired size and shape with the help of external forces. Conversion of large size material into small size particle or powder called as size reduction. It increase surface area of material which increase dissoulution rate, drying rate.

3. OBJECTIVE Increase surface area. It increase chemical reaction, drying, dissolution rate, rate of absorption. It form narrow size particle which can easily get mixed. In suspension, it need fine particles to reduce rate of sedimentation. Capsule, paste, ointment require small particle size. Small particle size allow rapid penetration of solvent in crude drug. To dispose solid wastes easily

4. ADVANTAGES Content uniformity Uniform flow Effective drying Increases surface area or viscosity Uniform mixing and drying Improve rate of absorption . Smaller the particles greater is absorption. Improve dissolution rate.

5. DISADVANTAGE Drug degradation (It happen because of heat produce during milling. Thermo labile substance are most affected). Contamination (During milling and griding generally iron cast and ceramic equipment are used which may cause impure our product so avoid using this type of equipment).

6. MECHANISM It involve following mechanism : Cutting Compression Impact Attrition Combination of impact and attrition

7. CUTTING Material cut down in small pieces with sharp blade, knife. It involve application of force. In industry, cutter mill is used to cut larger material or reduce size of material.

8. COMPRESSION Size reduction done by crushing material by applying pressure. Roller mill used in industry to reduce size which involve compression mechanism

9. IMPACT It occur when the material stationary (not moving) and it hit by object moving at high speed. Hammer mill work on this principle.

10. ATTRITION It involve collision between two particle have high kinetic energy or high velocity particle. Roller mill work on this principle.

11. COMBINATION OF ATTRITION AND IMPACT In this both mechanism, impact and attrition involve. Ball mill work in this mechanism

12. FACTOR AFFECTING SIZE REDUCTION Hardness Toughness Stickiness Material structure Moisture content Softening temperature Purity Physiological effect Ratio of feed size to product size Bulk density

13. HARDNESS It is a surface property of the material. So its like a strength. it is possible for a material to be very hard, but if it is brittle also then size reduction may present no special problems. The harder the material the more difficult it is to reduce in size . Its easy to break soft particle as compared to hard material.

14. TOUGHNESS Generally crude drugs are fibrous in nature. Those compound have higher moisture content are tough in nature. Soft but Tough material cause problem during size reduction compared to hard but brittle substance (glass).

15. STICKINESS Because of sticky in nature, material adhere to the grinding surface or in sieve surface. Difficult process to make powder of a drug having property like gummy or sticky. To overcome this, need to dry whole material completely.

16. MATERIAL STRUCTURE Material having special structure cause difficulty in size reduction. Some substances are homogeneous in nature. Mineral substances may have lines of weakness which produce flakes like particle on size reduction. Vegetable drugs have a cellular structure which produce long fibrous particles.

17. MOISTURE CONTENT It is found that materials do not flow well if it contain moisture. Presence of moisture cause some changes in property of material like hardness, toughness or stickiness which affect size reduction. Material should be either dry or wet. Should not be damp. Material have 5% moisture in dry grinding and 50% moisture in wet grinding does not create any problem.

18. SOFTENING TEMPERATURE Waxy substance like stearic acid or some other drug contain oil or fat, become soft during size reduction if heat generated. This problem avoided by cooling the mill.

19. PURITY Mills or cutter we are using to done size reduction of specific material which is made up of iron / aluminum cast. During process, surface of mill get adhere with mill so chances of entering impurity in final product. If we require high purity material then need to avoid use of this type of mill. Mills need to clean in between every batches of different material to gain purity.

20. PHYSIOLOGICAL EFFECT Some drugs are potent (highly effective) During size reduction, mills are used, during this process dust are produced which get contaminated with product and cause effect on potency of drug. So to overcome this cause, enclosed mill are used to avoid dust.

21. EQUIPMENTS USED IN SIZE REDUCTION Equipment Mechanism Hammer mill Impact Ball mill Impact & Attrition Fluid energy mill Impact & Attrition Edge runner & End runner mill Compression

22. BALL MILL / PEBBLE MILL Principle : Ball mill work on principle of impact and attrition between rapidly moving ball and powder material both packed in cylinder.

23. Construction : Ball mill also called as pebble mill. It’s a milling machine contain hollow cylinder equip on metallic frame like it can be rotated on longitudinal axis. Length of cylinder should be higher than that of diameter. Cylinder made up of metal. Cylinder having balls which help in reducing size of material. Balls occupy 30 to 50% volume of cylinder. Ball size depend on size of material and diameter of mill. Large ball breakdown material into coarse material while small ball breakdown into fine particles. Balls are made up of steel or iron. Its like grinding machine.

24. Working : 60% cylinder filled with material. Remaining balls are introduced to cylinder. And closed it with lid. Mills are allowed to rotate on axis. Speed of rotation play important role. At low speed , balls roll over each other and size reduction not occur at optimum level. At high speed , ball will stick to the wall of cylinder and no size reduction occur. At correct speed (optimum speed), ball just taken up to top and fallen down.

25. Uses : Used to grind brittle drugs to fine powder. Fine grinding , particle size around 100 to 5 mm or less can be obtain with this mill. Stainless steel ball used for production of ophthalmic and parenteral product. At low speed it used for milling dyes, pigments and insecticides. Merit : Produce very fine powder Used for batch operation / continuous operation. Suitable for both wet and dry grinding. Toxic substance ground because of it’s a closed system. Cost effective

26. Demerit : Very noisy machine Difficult to clean after operation Time consuming as slow process Impurity may be entered in product because of its cylinder, ball made up of iron or aluminum cast. Soft, fibrous material can not be grinding by ball mill.