Ball Milling
Objectives:
Objectives:
1. To study the technique of using ball mill.
2. To determine the distribution of the particle sizes.
3. To study the factors affect the milling process.
Introduction:
2. To determine the distribution of the particle sizes.
3. To study the factors affect the milling process.
Introduction:
Grinding or milling is a process to break the solid material into smaller pieces or even into powder. It is widely used in industrial to obtain desired size of the product. The size of the product depends solely on the time of grinding and the speed of the grinder.
In our experiment, a device known as ball mill will be used. Ball mill is a type of the grinder which is cylindrical in shape and the cylinder is a hollow cylinder. It rotates around a horizontal axis and partially filled with the media and the material to be ground. The materials of the media are stainless steel balls. It follows the theory of combined impact and attrition methods.
During the rotation, the metal balls will be raised up and fall back to the base in the hollow cylinder. This will produce a cascading action to crunch the medium in the cylinder. Therefore, the desired sizes of the particles are produced.
Sieving is one of the methods to determine the particle sizes. The device used in sieving is sieve. Sieve contains known sieve diameter of small holes whereby it allows the particles to pass through the holes. By doing this, we are able to obtain the particles with known range of sizes.
In our experiment, a stack of sieves will be used. The ranges of the sieve that we used were 150µm, 250µm, 300µm and 500µm.
Chemicals and Apparatus:
During the rotation, the metal balls will be raised up and fall back to the base in the hollow cylinder. This will produce a cascading action to crunch the medium in the cylinder. Therefore, the desired sizes of the particles are produced.
Sieving is one of the methods to determine the particle sizes. The device used in sieving is sieve. Sieve contains known sieve diameter of small holes whereby it allows the particles to pass through the holes. By doing this, we are able to obtain the particles with known range of sizes.
In our experiment, a stack of sieves will be used. The ranges of the sieve that we used were 150µm, 250µm, 300µm and 500µm.
Chemicals and Apparatus:
Coarse salt
Ball mill
Sieve
Electronic balance
Sieve
Electronic balance
Methods:
1. 369.3g of coarse salts were weighted by using electronic balance.
2. Same number of same size metal balls was put into the hollow cylinder of the mill.
3. Then, the coarse salts were filled into the hollow cylinder of the mill.
4. The “milling” process is begun for 10 minutes with the speed of 5.
5. The product was obtained and weighted again to check the amount of the salts.
6. Next, the fine particles were put into the sieve for sieving.
7. After that, the fine particles from each sieve net were collected for weighing purpose.
8. Lastly, a graph (histogram) was plotted by using the weight of the obtained fine particles.
Results:
Weight of salt before milling = 369.3g
Weight of salt after milling = 358.5g
2. Same number of same size metal balls was put into the hollow cylinder of the mill.
3. Then, the coarse salts were filled into the hollow cylinder of the mill.
4. The “milling” process is begun for 10 minutes with the speed of 5.
5. The product was obtained and weighted again to check the amount of the salts.
6. Next, the fine particles were put into the sieve for sieving.
7. After that, the fine particles from each sieve net were collected for weighing purpose.
8. Lastly, a graph (histogram) was plotted by using the weight of the obtained fine particles.
Results:
Weight of salt before milling = 369.3g
Weight of salt after milling = 358.5g
Discussion:
In our experiments, we found out that there are 2 factors that influence the particles size during the milling process. First factor is the time of grinding. It is found out that the longer the time of grinding, the more the finest particles we can obtain. This is because longer time frame of grinding allows more collision of the particles with the metal balls. Therefore, higher time frame of rotation allows more finest particles to be obtained. This statement is shown in the data of group 5&6 and group 7&8 whereby group 7&8 contains more finest particles (0.4682g of particles in the range of 150µm < x ≤ 250µm) compare to group 5&6 (0.2967g). Both of these groups used the same rotating speed but different time frame of grinding. Group 5&6 carried out their experiment for 10 minutes but group 7&8 carried out their experiment for 20minutes. Therefore, group 7&8 obtained more finest particles.
When we compared the data from group 1&2 and group 3&4, we found out that group 1&2 has more finest particles (5.0079g) compare to group 3&4 (2.8825g). This is not following the correct manner because group 1&2 and group 3&4 carried out their experiment with the same speed but different time frame whereby group 1&2 carried out their experiment in a shorter time compare to group 3&4. The amount of finest particles collected by group 1&2 should be lesser than group 3&4. This usual of data may due to errors occurred throughout the experiment. One of the most common errors that might occur was the speed of agitation during sieving. Group 3&4 might not agitated the sieve properly and caused most of the finest particles stayed in the top sieve net. Besides, group 3&4 might not put in the same number of metal balls into the hollow cylinder as other groups. This caused the milling process did not reach the optimal level and leave out a lot of large particles.
The second factor that may influence the result of the data is the speed of the rotating cylinder. It is found out that higher speed of rotation will result in higher production of finest particles. At low angular velocities, the metal balls move with the drum until the force due to the gravity exceeds the frictional force of the bed on the drum, and the balls then slide back to the bed of the drum. Instead, at higher angular velocities, a motion known as cascade will be produce whereby the metal balls are lifted up until their dynamic angle of repose is exceeds, they will fall back to the bed of the drum in a cascade across the diameter of the cylinder. This allows the maximum size reduction. In the data that we had collected, we supported the theory. Group 1&2 and group 5&6 used the same time frame of rotation but different speed of rotation whereby group 1&2 used higher angular velocities to carry out the experiment. Therefore, group 1&2 able to collect more finest particles compared to group 5&6.
In our experiment, we found out that group 3&4 contained the most amount of large particles compared to the rest of the group. This unusual data may because the cylinder moved at high speed with less amounts of metal balls inside and the balls are thrown out of the mill (cylinder) wall by centrifugal force and caused less size reduction of the materials. Therefore, it was found out that group 3&4 had the highest amount of large particle due to incomplete milling process.
In our experiment, we used the ball mill as the grinder to reduce the particle size. Ball mill uses combined impact and attrition methods. Besides the ball mill that we used, there are several other devices can be used to reduce the size. There are cutter mill, hammer mill, vibration mill, roller mill and fluid energy mill.
Cutter mill is an equipment that used the principal of cutting method whereby it able to produce the particle size from the range of 100µm up to 100 000µm. Next, hammer mill is a device that uses the principal of impaction. Hammer mill able to produce the particle size from the range of less than 10µm up to nearly 100 00µm. Vibration mill also uses the principal of impaction but it is different from the regular hammer mill whereby it is filled with steel ball and vibration of whole mill will occur. During the vibration, impaction between the steel balls and the materials will reduce the materials into small particles.
There is a device known as roller mill where it uses the principal of attrition to produce size reduction of solids in suspensions, pastes or ointments. This roller mill can produce the particle as small as 20µm. Fluid energy mill is a device that had the same principal as the ball mill as mentioned above. The high kinetic energy of the air of the fluid energy mill causes the particle to impact with other particles and fracture occurs. These fractures break the particles into smaller size.
In our experiments, we found out that there are 2 factors that influence the particles size during the milling process. First factor is the time of grinding. It is found out that the longer the time of grinding, the more the finest particles we can obtain. This is because longer time frame of grinding allows more collision of the particles with the metal balls. Therefore, higher time frame of rotation allows more finest particles to be obtained. This statement is shown in the data of group 5&6 and group 7&8 whereby group 7&8 contains more finest particles (0.4682g of particles in the range of 150µm < x ≤ 250µm) compare to group 5&6 (0.2967g). Both of these groups used the same rotating speed but different time frame of grinding. Group 5&6 carried out their experiment for 10 minutes but group 7&8 carried out their experiment for 20minutes. Therefore, group 7&8 obtained more finest particles.
When we compared the data from group 1&2 and group 3&4, we found out that group 1&2 has more finest particles (5.0079g) compare to group 3&4 (2.8825g). This is not following the correct manner because group 1&2 and group 3&4 carried out their experiment with the same speed but different time frame whereby group 1&2 carried out their experiment in a shorter time compare to group 3&4. The amount of finest particles collected by group 1&2 should be lesser than group 3&4. This usual of data may due to errors occurred throughout the experiment. One of the most common errors that might occur was the speed of agitation during sieving. Group 3&4 might not agitated the sieve properly and caused most of the finest particles stayed in the top sieve net. Besides, group 3&4 might not put in the same number of metal balls into the hollow cylinder as other groups. This caused the milling process did not reach the optimal level and leave out a lot of large particles.
The second factor that may influence the result of the data is the speed of the rotating cylinder. It is found out that higher speed of rotation will result in higher production of finest particles. At low angular velocities, the metal balls move with the drum until the force due to the gravity exceeds the frictional force of the bed on the drum, and the balls then slide back to the bed of the drum. Instead, at higher angular velocities, a motion known as cascade will be produce whereby the metal balls are lifted up until their dynamic angle of repose is exceeds, they will fall back to the bed of the drum in a cascade across the diameter of the cylinder. This allows the maximum size reduction. In the data that we had collected, we supported the theory. Group 1&2 and group 5&6 used the same time frame of rotation but different speed of rotation whereby group 1&2 used higher angular velocities to carry out the experiment. Therefore, group 1&2 able to collect more finest particles compared to group 5&6.
In our experiment, we found out that group 3&4 contained the most amount of large particles compared to the rest of the group. This unusual data may because the cylinder moved at high speed with less amounts of metal balls inside and the balls are thrown out of the mill (cylinder) wall by centrifugal force and caused less size reduction of the materials. Therefore, it was found out that group 3&4 had the highest amount of large particle due to incomplete milling process.
In our experiment, we used the ball mill as the grinder to reduce the particle size. Ball mill uses combined impact and attrition methods. Besides the ball mill that we used, there are several other devices can be used to reduce the size. There are cutter mill, hammer mill, vibration mill, roller mill and fluid energy mill.
Cutter mill is an equipment that used the principal of cutting method whereby it able to produce the particle size from the range of 100µm up to 100 000µm. Next, hammer mill is a device that uses the principal of impaction. Hammer mill able to produce the particle size from the range of less than 10µm up to nearly 100 00µm. Vibration mill also uses the principal of impaction but it is different from the regular hammer mill whereby it is filled with steel ball and vibration of whole mill will occur. During the vibration, impaction between the steel balls and the materials will reduce the materials into small particles.
There is a device known as roller mill where it uses the principal of attrition to produce size reduction of solids in suspensions, pastes or ointments. This roller mill can produce the particle as small as 20µm. Fluid energy mill is a device that had the same principal as the ball mill as mentioned above. The high kinetic energy of the air of the fluid energy mill causes the particle to impact with other particles and fracture occurs. These fractures break the particles into smaller size.
There are few factors needed to be aware when we want to select the correct device for the reduction of particle size. One of the factors is the shape of the particles that we wanted to produce. Besides, we must know that each device will give different size of the final particles. Therefore, we must know the particle size that we are required before we select the correct device. Next, the surface hardness of the material should be considered before the selection of the equipment as the surface hardness may varies the particle size. The surface hardness can be determined by using the Mohs’ scale.
Conclusion:
From our experiment, we learnt how to setup the ball mill and we were able to use it correctly throughout the experiment. Besides, we found out that most of the fine particles were produced with higher speed or longer time frame of the grinding process. Therefore, we conclude that angular velocity of the ball mill and the time of grinding process affects directly to the particle size. Angular velocity of the ball mill inversely proportional to the particle size yet the particle size will remain unchanged if the angular velocity is too high. Instead, the time frame of grinding is inversely proportional to the particle size.
References:
1. M.E.Aulton. 2004. Pharmaceutics, The Science of Dosage Form Design 2nd Ed. Churchill livingstone. Pg 166 – 173
Conclusion:
From our experiment, we learnt how to setup the ball mill and we were able to use it correctly throughout the experiment. Besides, we found out that most of the fine particles were produced with higher speed or longer time frame of the grinding process. Therefore, we conclude that angular velocity of the ball mill and the time of grinding process affects directly to the particle size. Angular velocity of the ball mill inversely proportional to the particle size yet the particle size will remain unchanged if the angular velocity is too high. Instead, the time frame of grinding is inversely proportional to the particle size.
References:
1. M.E.Aulton. 2004. Pharmaceutics, The Science of Dosage Form Design 2nd Ed. Churchill livingstone. Pg 166 – 173
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