size reduction pharmaceutics ball mill, hammer mill

Size reduction is a vital unit operation in pharmaceutical manufacturing that involves reducing the size of solid materials to enhance their dissolution properties, improve bioavailability, and facilitate further processing. It is a fundamental step in drug formulation and is employed in various dosage forms like tablets, capsules, and powders.

1. Pharmaceutics D-pharm 1 st Year Presented By Pragati K. Mahajan   Preparation date :May 2024 Aug -2023

2. Content Definition Importance of Particle Size Reduction Factors Affecting Size Reduction Methods of size reduction Hammer mill Ball mill Pragati K. Mahajan Size Reduction

3. Definition Size Reduction is the process of reducing large solid unit masses like vegetable and chemical substance into small unit masses, coarse particles or fine powder . Machines used for larger size particles are known as crusher while machines used foe smaller size particles are reduced by using mills. Size Reduction Pragati K. Mahajan

4. To increase the rate of absorption of a drug. The smaller the particle size, the greater is the rate of absorption. To allow the rapid penetration of the solvent in case of crude drugs for the extraction of active constituents from vegetable and animal drugs To get a uniform powder because particle size reduction helps in uniform mixing of drug To improve the stability of certain pharmaceutical dosage form such as suspensions. To help in the process of separation of solids from liquids by filtration or by sedimentation. Importance of Particle Size Reduction Pragati K. Mahajan

5. Hardness : It is easier to break soft material to a small size than hard material. Toughness : The crude drugs of fibrous nature or those having higher moisture content, are generally tough in nature. A soft but tough material may present more problem in size reduction, than a hard but brittle substance . Stickiness : Stickiness causes a lot of difficulty in size reduction. This is due to the fact that material adheres to the grinding surfaces or sieve surface of the mill. It is difficult to powder a drugs of having gummy or resinous nature, if the method used for size reduction generates heat. Complete dryness of material may help to overcome this difficulty Factors Affecting Size Reduction Pragati K. Mahajan

6. Material structure : Materials which show some special structure may cause problem during size reduction e.g. vegetable drugs which have cellular structure, generally produce long fibrous particles on its size reduction. Similarly a mineral substance having lines of weakness, produces flake like particles on its size reduction . Moisture content : The presence of moisture in the material influences a number of its properties such as hardness, toughness or stickiness which in its turn affects the particle size reduction. The material should be either dry or wet. It should not be damp. The material having 5% moisture in case of dry grinding and 50% moisture in wet grinding does not create any problem. Factors Affecting Size Reduction Pragati K. Mahajan

7. Softening temperature : Waxy substances such as stearic acid or drugs containing oils or fats, become softened during the size reduction processes, if heat is generated. This can be avoided by cooling the mill. Purity required : Various mills used for size reduction often cause the grinding surfaces to wear off and thus impurities come in the powder. The mills should be thoroughly cleansed between batches of different materials in order to maintain purity. Factors Affecting Size Reduction Pragati K. Mahajan

8. Physiological effect : Some drugs are very potent. During their particle size reduction in a mill, dust is produced which may have an effect on the operator. In such cases, the enclosed mills may be used to avoid dust . Ratio of feed size to product size : To get a fine powder in a mill, it is required that a fairly small feed size should be used. Hence it is necessary to carry out the series using different equipment e.g. preliminary crushing followed by coarse powder and then fine grinding Bulk density: The output of the size reduction of material in a machine, depends upon the bulk density of the substance Factors Affecting Size Reduction Pragati K. Mahajan

9. Methods of size reduction Pragati K. Mahajan

10. Principle :- It works on the principle of impact i.e. material is more or less stationary and is hit by an object moving at a high speed Construction :- It consists of a stout metal casing with central shaft Shaft is rotated it own axis Four or more hammers are attached with central shaft. Hammers are mounted with swivel joints. Hammers are also rotates. Hammers may be square faced, tapered or stepped form Lower part of casing consist screen or mesh. Screen help in size separation of materials Feed inlet placed side of casing. Hammer mill Pragati K. Mahajan

11. Hammer mill Pragati K. Mahajan

12. Working:- The material is put into the hopper which is connected with the drum. The material is powdered to the desired size, due to fast rotation of hammers and is collected under the screen. This mill has the advantage of continuous operation because the chance of jamming is less as the hammers are not fixed. The mill can produce coarse to moderately fine powder, Due to high speed of operation, heat is generated which may affect thermolabile drugs or materials. Moreover, high speed of operation also causes damage to the mill if foreign objects such as stone or metal is present in the feed . Hammer mill Pragati K. Mahajan

13. Uses Brittle material is best fractured by impact from blunt hammers. Fibrous material is best reduced by cutting edges. Advantages It is rapid in action, and is capable of grinding many different types of materials. They are easy to install and operate, the operation is continuous. There is little contamination of the product with metal abraded from the mill as surface move against each other. Disadvantages Heat build-up during milling is more; therefore, product degradation is possible. Hammer mills cannot be employed to mill sticky, fibrous and hard materials. The screens may get clogged. Hammer mill Pragati K. Mahajan

14. Principle :- It works on the principle of impact and attrition. Construction:- It consists of a hollow cylinder which is mounted on a metallic frame in such a way, that it can be rotated on its longitudinal axis. The cylinder contains balls that occupy 30-50% of the mill volume, The weight of the balls is kept constant. The ball size depends on the size of the feed and the diameter of the mill. The cylinder and balls are made of metal and are usually lined with chrome. In pharmaceutical industry, sometimes the cylinder of the ball mill is lined with rubber or porcelain. The balls used in these mills are also made of rubber or porcelain. Ball mill Pragati K. Mahajan

15. Pragati K. Mahajan Ball mill

16. Working:- The drug to be ground is put into the cylinder of the mill and is rotated. The speed of rotation is very important. At a low speed , the mass of balls will slide or roll over each other and only a negligible amount of size reduction will occur At a high speed , the balls will be thrown out to the walls by centrifugal force and no grinding will occur But at about 2/3rd of the speed , the centrifugal force just occurs with the result that the balls are carried almost to the top of the mill and then fall in. By this way the maximum size reduction is effected by the impact of particles between the balls and by attrition between the balls After a suitable time, the material is taken out and passed through a sieve to get powder of the required size. Ball mill Pragati K. Mahajan

17. Pragati K. Mahajan Ball mill

18. Uses The mill is used to grind brittle drugs to fine powder. Advantages . It can produce very fine powders. It can be used for continuous operation if sieve or classifier is attached to the mill. It is capable of grinding a large variety of materials of different character and of different degree of hardness It can be used to grind toxic materials as it can be used in completely enclosed form It is suitable for both wet or dry grinding processes. Disadvantages The ball mill is a very noisy machine. Wear occurs from the balls as well as from the casing, which may result in contamination of the product. Ball mill Pragati K. Mahajan