INTRODUCTION:

A ball mill is a type of grinder used to grind, blend and sometimes for mixing of materials for use in mineral dressing processes, paints, pyrotechnics, ceramics, and selective laser sintering. Almost every year several billion tons of metallic ores, minerals, cement and various other solids used in the ceramic and chemical industries are subjected to size reduction in ball mills. It is important to establish the optimum values of various mill operating parameters, such as the mill speed, ball load, ball diameter and particle load, from the energy consumption point of view.^[1]

Ball mills are widely used in comminuting process in mineral industry. The comminuting in the ball mill takes place by impact, friction, and abrasion between rocks and balls inside the mill during rotation.

Steel balls are charged into a cylinder, along with the material to be ground, and rotated, allowing the balls to crush material which travels between them. Without the balls in the cylinder, or some other media to crush the material we wish to grind, little grinding will take place. To ensure the stability of the material in the ball mill, many parameters of the equipment should be adjusted of ten, such as, the speed of the scatter machine, the quantity of the feeding material, the speed of the dust collecting machine, the speed of the powder selecting machine, etc.^[2]

Fig. 1: Ball Mill

Principle:

It works on the principle of impact and attrition: size reduction is done by impact as the balls drop from near the top of the shell.^[3]

Construction:

The ball mill consists of hollow cylindrical rotating shell made of steel lined with porcelain or high carbon steel plate. Upto 50 % of its volume, the shell is filled with balls made of steel or pebbles. The balls are of constant weight and varying size which depend on the amount of feed. The size reduction happens due to the grinding of the balls against the material to be comminuted. The particle size and shape of the material to be comminuted depends on the size of the ball, speed of rotation of the shell and feed rate.^[4]

Cylindrical mills are classified according to the mode of product discharge taking place from the mill.

Different parts of ball mills are:

1. Cylindrical shell

2. Inner surface or liner

3. Grinding media

4. Drive

1. Cylindrical Shell:

It is the rotating hollow cylinder partially filled with the balls. The ore to be crushed is fed through the hollow trunnion at one end and the product is discharged through a similar trunnion at the other end. The material of construction for this hollow shell is usually high strength steel. The shell axis is either horizontal or at a small angle to the base. Large ball mills have a length of 4 - 4.25 mts, diameter of 3mts. They use hardened steel balls of size varying between 25-125 mm.

2. Inner Surface or Liners:

As the grinding process involves impact and attrition the interior of the ball mills is lined with replaceable wear resisting liners. The liners are usually high manganese alloy steels, stones or rubber. Least wear takes place on rubber lined interior. As the coefficient of friction between ballsand steel liner is specifically, large, the balls are carried up taken to a higher height along the inner wall of the shell and dropped down onto the ore with a larger impact force resulting in a better grinding.

3. Balls (Grinding Media):

The balls are usually cast steel unless otherwise stated. In some cases, flint balls may be Used. The diameter of the grinding media varies from 1-5inches. The optimum size of the ball is Proportional to the square root of the feed size. The ball and liner wear are usually in the range of 450 – 1250, and 0.50 – 250 grams per ton of ore ground.

4. Drive:

The mill is rotated by electric motors connected through reduction gear box – ring gear Arrangement.^[4]

Working:

In case of continuously operated ball mill, the material to be ground is fed from the left through a 60° cone and the product is discharged through a 30° cone to the right. As the shell rotates, the balls are lifted up on the rising side of the shell and then they cascade down (or drop down on to the feed), from near the top of the shell. In doing so, the solid particles in between the balls and ground are reduced in size by impact.^[6]

Fig. 2: Scheme of a ball motion pattern in a single pot of a planetary ball mill- (a) cascading, (b) cataracting, (c) rolling.

The grinding process is attributed to 3 different stages of ball mill working.

a. Cascading

b. Cataracting

c. Centrifuging

In the cascading regime (Fig. 2a) the milling balls are taken Along by the pot wall and unroll upon each other from the bulk Top to its base while in the cataracting regime (Fig. 2b) the balls Detach from the wall and impact with high intensity the bulk or the opposite wall. Rolling or centrifuging balls (Fig. 2c) align to the wall rotation with almost no relative velocity.20

If the speed of the ball mill is too low then only cascading occur, and particle lead to rolling Down of the ball and limiting grinding will occur. On the other hand, if the speed of the ball is very High (greater than critical speed) centrifuging occur leading to little or no grinding.^[5],[7]

Basic fragmentation mechanisms:

The main idea in modeling all comminution processes, including the grinding process, is to obtain mathematical relations between the size of the feed and the size of the product. Particles in the feed repetitively reduce their size due to the imparting energy of the grinding media which disrupts their binding forces. The size reduction is a result of the following three basic fragmentation mechanisms.

− Abrasion occurs when local low intensity stresses are applied and the result is fine particles taken from the surface of the mother particle and particles of size close to the size of the mother particle (Fig. 3a).

− Cleavage of particles occurs when slow and relatively intense stresses are applied (compression) which produce fragments of size 50-80 % of the size of the initial particle (Fig. 3b).

− Fracture is a result of rapid applications of intense stresses (impact) which produce fragments of relatively small sizes with a relatively wide particle size distribution (Fig. 3c).^[8]

Fig. 2:

Application of ball mill in Pharmacy:

1. The small and average capacity ball mills are used for the final grinding of drugs or for grinding suspensions.

2. The maximum capacity ball mills are used for milling ores prior to manufacture of pharmaceutical chemicals.^[⁹^]

3. To increase the therapeutic effectiveness of certain drugs by reducing the particle size.

4. Size reduction produces particles in narrow size range. Mixing of powders with narrow size range is easier.

5. The mixing of several solid ingredients is easier and more uniform if the ingredients are reduced to same particle size.

6. Pharmaceutical suspensions require finer particle size. It reduces rate of sedimentation.

7. The stability of emulsions is increased by decreasing the size of the oil globules.

8. All the ophthalmic preparations and preparations meant for external application to the skin must be free from gritty particles to avoid irritation of the area to which they are applied.

9. The rate of absorption of a drug depends on the dosage form, route of administration and particle size. The smaller the particle size, quicker and greater will be rate of absorption.

10. The physical appearance of ointments, pastes and creams can be improved by reducing its particle size

11. Pharmaceutical capsules, insufflations (i.e. powders inhaled directly into the lungs), suppositories and ointments require particles size to be below 60 mm size.^[¹⁰^]

Various types of ball mill:

1. Hardinge mill:

In this type of ball mill the cylinder has a conical end towards a discharge point. In this mill the larger balls remains inside the cylinder and the smaller ball are placed in the conical portion. As a result, coarser grinding occurs in the cylinder portion and a finer grinding takes place at the apex of the conical part. The product is finer and more uniform than the general cylinder ball mill.

2. Tube mill:

Tube mill are generally charged with Flint pebbles instead of metal ball. Tube mill can grind finer products than the conventional ball mill. Their construction is also simple and generally used for grinding hard material. Tube mill has higher length/diameter ratio as compared to ball mill.

3. Rod mill:

This is modifications of the tube mill. Instead of ball mill or pebble, rods are used as grinding material. This rods are useful with sticky material since rods do not form aggregates like balls.

4. Vibration mill:

In this type of Mill vibratory movement are given instead of rotation. The cylinder is mounted on spring which set up vibration by electromagnetic means. The cylinder moves through a circular parth with an amplitude of vibration up to about 20mm and a rotational frequency of 15 to 50 per second. Grinding efficiency is also better in this type of mill.

5. Continuous ball mill:

This equipment is placed on a small slope so that the powder can pass from one chamber to the next chamber through a screen attached to each chamber so that finally fine product can be obtained.^[1¹^]

CONCLUSION:

In this paper, it was attempted to Demonstration of ball mill and there applications in pharmacy. The ball mill should able to grind the material to nano-powder with the optimum speed and optimum amount of media ball. The rotation will be calculated to ensure a correct comminution occur. The grinded material is remove and measure in nano-powder form.

REFERENCE:

1. K. Vidyatharran “Design and Fabrication of Mini Ball Mill" 1Automotive Engineering Research Group (AERG), Faculty of Mechanical Engineering, Universiti Malaysia Pahang (UMP), 26600 Pekan, Pahang, Malaysia, Automotive Engineering Centre, Universiti Malaysia Pahang (UMP), 26600 Pekan, Pahang, Malaysia

2. Rutheravan Maria “Design and Fabrication of Mini Ball Mill." Automotive Engineering Research Group (AERG), Faculty of Mechanical Engineering, Universiti Malaysia Pahang (UMP), 26600 Pekan, Pahang, Malaysia, Automotive Engineering Centre, Universiti Malaysia Pahang (UMP), 26600 Pekan, Pahang, Malaysia

3. R S Fediuk “Mechanical Activation of Construction Binder Materials by Various Mills" Far Eastern Federal University, Vladivostok, Russia

4. Kumar, A, and Yedhu Krishnan. 2020. A Review On The Technology Of Size Reduction Equipment. International Journal of ChemTech Research, 2020,13(1): 48-54. DOI=http://dx.doi.org/ 10.20902/IJCTR.2019.130106

5. Dinesh Kumar Mishra, Asst. Professor, Dept. of MME. 2020. Mineral Processing Laboratory Manual. Department of Metallurgy and Materials Engineering.

6. “Ball Mill”. 2020. En.Wikipedia.Org.https://en.wikipedia.org/ wiki/Ball_mill#Working

7. Burmeister, Christine Friederike, and Arno Kwade. 2013. “Process Engineering With Planetary Ball Mills”. Chemical Society Reviews 42 (18): 7660. Doi:10.1039/c3cs35455e.

8. Monov, Vladimir, Blagoy Sokolov, and Stefan Stoenchev. 2012. “Grinding In Ball Mills: Modeling And Process Control”. Cybernetics And Information Technologies 12 (2). Doi:10.2478/cait-2012-0012.

9. "Ball Mill: Operating Principles, Components, Uses, Advantages And". 2020. Pharmapproach. Com. https:// www.pharmapproach.com/ball-mill/.

10. Sud, Sushant, and Archana Kamath. 2013. "Methods of size reduction and factors affecting size reduction in pharmaceutics". International Research Journal of Pharmacy 4 (8): 57-64. doi:10.7897/2230-8407.04810

11. Theory cum Practical Book of Pharmaceutical Engineering, Shalini Sharma Associate Professor Faculty of Pharmaceutical Science by PV Publication Page No:-33

Received on 07.09.2020 Revised on 25.09.2020

Asian J. Pharm. Tech. 2020; 10(4):285-288.

DOI: 10.5958/2231-5713.2020.00047.1