Practical 1 Ball Miling

10/29/2016

Pr acti cal 1 : Bal l Mi l li ng | TF Lab 1

 A fine presentation of lab work 

December 23, 2013

Experiment 1

Practical 1: Title: Ball Milling

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Practical 1 : Ball Milling | TF Lab 1

Sieve. The sieving process in this experiment uses a stack of sieves which have the smallest mesh above a collector tray followed by meshes which get progressively coarser  towards the top of the stack. Objective:

To grind the coarse salt to a smaller size by using a ball mill and to obtain the particle size distribution of the initial and the sieved final mixture. Introduction:

‘Ball milling is a method used to break down the solids to smaller sizes or into a powder. A ball mill is a type of grinder which consists of a cylinder. It is used in g rinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. The cylinder rotates around a horizontal axis. It is partially filled with the grinding medium and the material to be ground. Materials which can be used as media are ceramic balls, pebbles and stainless steel balls. Large to medium-sized ball mill is mechanically rotated on its axis, but small one (as in our laboratory) has its container sits on two drive shas (where pulleys and belts are utilised to transmit rotary motion). There are di埏erent types of milling equipment used in which they can be categorized according to the principal method applied. No matter what principal method is applied, the extent of size reduction is always associated to the milling time. We have cutting methods, impact method, compression method and attrition method. Ball mills uses combined impact and attrition methods. In this experiment, we are required to break the coarse salt down using a ball mill and then by using a sieve, the particle size distribution is known. Method: Materials:

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Practical 1 : Ball Milling | TF Lab 1

Coarse Salt  Apparatus:

Ball milling machine Steel balls (of two di埏erent sizes) Weighing boat Weighing balance Sieve Procedures:

1. 300-500g coarse salt was weighed. 2. Ball bearings of various sizes were inserted into the ‘mill’. 3. Coarse salt was added into the ‘mill’. 4. The process of milling was started for between 10 or 20 minutes with the appropriate speed. (refer Result) 5. The product obtained was weighed again. 6. The powder obtained was sied by using sieving method (sieve nest). 7. A graph (histogram) of particle size distribution was plotted. Result and Calculations:

Particle

5rpm10

5rpm20 min

3rpm 10 min

3rpm20 min

Before size (mm)

312.50 min

400.00

340.79

327.15

≥501

281.85

358.87

311.14

296.67

301-500

14.11

30.18

12.92

18.56

251-300

4.10

3.78

4.14

1.49

milling  Aer milling  Mass of  course salt collected/ g

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Practical 1 : Ball Milling | TF Lab 1

151-250

5.79

3.37

2.05

0.27

1-150

3.83

2.48

0.00

0.06

Total

309.68

398.68

330.25

317.05

Graph of Mass of Coarse Salt Collected(g) Against Particle Size (mm) – 3rpm, 10minutes

Graph of Mass of Coarse Salt Collected(g) Against Particle Size (mm) – 3rpm, 20minutes

Graph of Mass of Coarse Salt Collected(g) Against Particle Size (mm) – 5rpm, 10minutes

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Practical 1 : Ball Milling | TF Lab 1

Graph of Mass of Coarse Salt Collected(g) Against Particle Size (mm) – 5rpm, 20minutes

Questions: 1. What are the factors which influence the process of particle size reduction (milling)?

Particle size, number of balls, particle density, hardness, number of media used, time of grinding, and speed of the ball mill (rpm) are factors which will a埏ect the process of milling. Size: The smaller the media particles, the smaller the particle size of the final product. Meanwhile, the size of grinding media particles should be larger than the material to be ground. Density: The grinding media should be denser than the material being ground. It becomes a problem if the grinding media floats on top of the material to be ground.

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Practical 1 : Ball Milling | TF Lab 1

Hardness: The grinding media needs to be durable enough to grind the material, but not to be too hard that it could wear down the tumbler at a fast pace. Number of media used: The more the number of media, the faster the process of size reduction. But at the same time, there will be less capacity le the mill, less production. In fact, using a mixture of  two di埏erent sizes of media can produce much faster results, than milling with either size of media alone. Time of grinding: The longer the time of grinding, the faster the process of particle size reduction. Speed of the ball mill (rpm): The faster the speed of ball mill, the faster the process of size reduction. 2. What tools can be used to reduce the size of the particles?

A microfluidizer achieve uniform particle size reduction by bottom-up crystallization and e埏icient cell disruption. A homogenizer reduces particle sizes under very high pressures, sheer, turbulence, acceleration and impact. A mixer transports phases or ingredients into a main continuous phase (liquid), with which it would normally be immiscible. An array of rotors is used to create shear in a tank or pi pe through which the solution passes. Mills grind the particles using the mill or milling media and can quickly produce fine powders from coarse grains. Mills are commonly used in the mining industr y. In cutter mill, size reduction occurs by fracture of particles between the two sets of knives. In hammer mill, size reduction occurs by impact, by four hammers attaching on a central sha. In end-runner and edge-runner mills, compression is carried out on a small scale in a mortar-and-pestle form. In roller mills, the principle of attrition is used where material is sheared as it passes through a gap and is transferred from slower roll to a faster roll, and is removed by a scraper. In ball mill, size reduction is done by both impact and attrition of particles. Rod mill is similar to ball mills but it uses long rods for grinding media. Autogenous mill is a self-grinding mill which is used in breakage of larger rocks. SAG (Semi-Autogenous Grinding) mill is an autogenous mill which uses grinding balls, i t is similar to ball mill but has large diameter and short length. Vertical mill is used in grinding material at smaller particle sizes, which is used aer ball mill. Pebble mill is used when product contamination by iron from steel balls must be avoided. Fluid energy or jet mill consists of a hollow toroid. A fluid, usually air, is injected as a high-pressure jet through nozzles at the bottom of the loop. High velocity of air creates zones of turbulence into which solid particles are fed. The high kinetic energy causes particles to collide with momentum for fracture to occur. The turbulence produces the impact and attrition. Together with ball mill and jet mill, pin mill also acts by producing impact and attrition. Two discs with closely spaced pins rotate against one another at high speeds. Particles experience impaction with pins and attrition between pins when they travel outwards under influence of centrifugal force. 3. What are the factors which influence the selection of a device for particle size reduction?

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Practical 1 : Ball Milling | TF Lab 1

Particle shape desired: Particle shape may vary due to methods (e.g. impact or attrition). Fineness of particles desired: Some other properties of powder will be altered if the fineness is changed. The degree of size reduction depends on the use of a powder (where is it applied to) Particle size desired: When small particle size is desired, more time is needed in the size reduction process, thus cost of size reduction also increases. Hardness of the particle to be ground: The harder the particle, the tougher the device should be and more abrasion is needed in the process. Contamination of product: Pebble mill is used to prevent product contamination by iron from steel balls. Discussion:

From the result the size reduction increases as we increase the number of rotations of the ball milling. Meanwhile, increase in the time taken for ball milling will also increase the size reduction. From the graphs, we can see that as the size reduction increases, the particle sizes obtained will form a less steep curve in the graph. This can be correlated with the values in our table due to the following reason. As we can see in the table, more and more particles can go through to the smaller meshes and thus the weight of particles remained in the first mesh decreases. A less steep curve can then be obtained. Another thing to consider is that our curves had all been skewed to the le (negatively skewed). This indicated that majority of our particles size has been distributed to the le side. However, this may be due to the fact that we do not have sieves which have aperture of >500mm or else we might be able to have a plot of particle size distribution (histogram) showing normal distribution (no skew). Finally, less weight is obtained aer milling compared to before milling because some particles were le in the ball mill. Not all particles can be removed from ball mill as some particles which are small tend to stick to wall and some were ba埏led by the narrow opening of the ball mill. Conclusion:

Size reduction increases as the number of rotations and time taken for ball milling i ncreases. Meshes of larger aperture should be used in sieving to obtain a complete curve of particle size distribution. Some particles were lost when transferring them out of the ball milling, which results in lighter weight obtained aer ball milling. References:

1. M. E. Aulton. (1988) Pharmaceutics – The Science Of Dosage Form Design. 2nd Edition. Churchill Livingstone, UK. Pg. 166-172 2. Robert E. Schilling, Union Process Inc. (n.d.) Citing Websites. Choose The Right Grinding Mill. Retrieved date. 21st December 2013. From http://www.unionprocess.com/tech_papers/ChooseTheRightGrindingMill.pdf  https://beautifultf.wordpress.com/2013/12/23/practical-1-ball-milling/

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Practical 1 : Ball Milling | TF Lab 1

3. Citing Websites. Rod Mills, How Do They Work? (1994-2012) Retrieved date. 21st December 2013. From http://www.mine-engineer.com/mining/rodmill.htm 4. Citing Websites. Ball Mills. (2013) Retrieved date. 21st December 2013. From http://www.unitednuclear.com/index.php?main_page=index&cPath=25_35 5. A. Sahoo* and G. K. Roy. (2008) Citing Websites. Correlations for the Grindability of the Ball Mill As a Measure of Its Performance. From http://dspace.nitrkl.ac.in/dspace/bitstream/2080/879/1/correlations1.p

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