Title: ball milling
Objectives: to find size distribution of particles using sieving method
Apparatus: various sizes of ball milling, ball miller machine, sieve
Materials: coarse salt
A ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. Ball mills rotate around a horizontal axis, partially filled with the material to be ground plus the grinding medium. Different materials are used as media, including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. Industrial ball mills can operate continuously fed at one end and discharged at the other end. Large to medium-sized ball mills are mechanically rotated on their axis, but small ones normally consist of a cylindrical capped container that sits on two drive shafts (pulleys and belts are used to transmit rotary motion).
1. 300g-500g of coarse salt was weighed.
2. Ball milling with different sizes were put in the mill.
3. The weighed coarse salt was then put in the mill too.
4. The milling process was started with 5rpm for 10 minutes.
5. Then, the powder was sieved and weighed for each sieving stage.
6. Steps 1 to 5 were repeated with different speed and duration.
7. Histogram graph of particle size distribution was plotted.
1. What are the factors that influence the milling process?
Key properties of grinding media are size, density, hardness, and composition.
Size: The smaller the media particles, the smaller the particle size of the final product. At the same time, the grinding media particles should be substantially larger than the largest pieces of material to be ground. Density: The 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. Hardness: The grinding media needs to be durable enough to grind the material, but where possible should not be so tough that it also wears down the tumbler at a fast pace. Composition: Various grinding applications have special requirements. Some of these requirements are based on the fact that some of the grinding media will be in the finished product. Others are based in how the media will react with the material being ground.
2. What are the equipments that can be used to reduce particles size?
Cutter mill, end-runner mill, roller mill, mortar and pestle, vibration mill, hammer mill, pin mill and fluid energy mill
3. What are the factors that influence the choice of the equipments?
Particles properties and particles shape’s end product such as tough, sticky, abrasive and friable. Product size required such as degree of size reduction and economical.
Theoretically when a substance undergoes grinding process, particle size and mass of the substance will reduce. From large particles become small particles until some of them become dust. This dust then easily gone into the air causes lost of substance and reduction in mass.
From the experiment, the initial mass of coarse salt are more than the final mass, however for third trial, which is using speed of 3rpm for 10minutes, the result is contradict. The initial mass is 318.79g and the final mass is 330.25g. This is might be because of mistake using the experiment. For example, either the initial reading or the final reading is read or write mistakenly. Besides that, it is possible because of the residue of the previous sieving process was not clean wholly, then the residue was mixed with the current salt.
The second theory is the reduction of particles size is not distribute evenly and the distribution is depends on the speed and duration of the rotation. The size of the particles can be measured by using sieving. If the speed is slow and the duration is short, then the particles size is not reduce greatly. Thus, the size of the particles will accumulate at large size compare to small size.
From the experiment, the particles size reduction follows the theory where the particles sizes are accumulate at large size. It is proven when the mass of particles at sieves with the biggest diameters have the most masses for all trials while the smallest diameters have the least amount of salt or no salt at all. From the data, comparing between trials no 2 and no 3, trial no 3 has higher percentage of particles at 500mm sieve compared to trial no 2. The percentage of trial no 3 is 97.6% while trial no 2 is 89.7%. Besides that, trial no 3 has lowers percentage of particles at 0mm which is 0% compared to trial no2 which is 0.62%. Therefore, we can conclude that the slower the speed and the shorter the duration of the rotation, the particles distribution will be more at large size and will be less at small size.
Aulton's Pharmaceutics The Design And Manufacture Of Medicines, Third Edition, 2007, Churchill Livingstone Elsevier, M. E. Aulton