PRACTICAL 1 : (A) BALL MILLING

Title : Ball Milling

Objectives :

To reduce the size of coarse salt imto smaller partickes and obtain the even even distribution size after sieving.

Introduction :

            Ball mill is an efficient tool for grinding many materials into fine powders.A ball mill is like a grinder which is used in grinding materials.Examples are ores, chemicals, ceramic raw materials and paints.It will rotate around horizontal axis.Ceramic balls,flint pebble and stainless steel balls can be used as the media.The ball mill used in our laboratory consist of a cylindrical capped container that sits on two drive shafts (pulleys and belts are used to transmit rotary motion).There are two ways of grinding are the dry process and the wet process.It can be divided into tubular type and flowing type according to different form of discharging material.To achieve a reasonable efficiency with ball mills,they must be operateed in a closed system.

Materials :

-Coarse salt

Apparatus :

-Steel balls

-weighing boat

-Weighing balance

-Ball mill

-Sieve

Procedures :

1. 300-500g of coarse salt was weighed.
2. Steel balls of varying sizes were inserted into the mills.
3. The weighed saltwwas placed inside the mill.
4. The milling proces was started using a suitable speed setting.
5. Upon completion, the crushed salt was reweighed.
6. The crushed was sieved using a sieve nest.
7. A histogram(graph) of particle size distribution obtained after sieving was plotted.

Result :

Duration (min)	Speed(m/s)	Weight (g)  after sieving
		500 um (layer 1)		300um (layer 2)	200um (layer 3)
20	3	312.7	17.6		0.5

Discussion :

Ball mill is an efficient tool for grinding many materials into a fine powder. The best overall choice for grinding media is Chrome Steel.Due to its fairly high mass and hardness, it grinds chemicals & powders quickly and efficiently with minimal contamination. longer to produce desired results.The longer a ball mill operates, the smaller the particles will become. They will even reach the sub-micron level if the mill is allowed to run long enough. Always use as little material in the barrel as possible for maximum grinding efficiency. The more material we place in the barrel, the more it will cushion the impact of the media, reducing the grinding action. The more media we use, the faster the material will be powdered. However, using more media will reduce the capacity of your mill.

For the experiment above,the result obtained should have the first stage largest scale and the amount of salt crushed decreases gradually to the second layer until the fourth layer.This shows that the ball milling has even distribution of the amount of salt.But the result show that it was deviated from the expected result because there were large difference between first ayer and the second layer.This is why there is no amount of salt being crushed because the third layer,amount of the salt crushed almost near to zero.So when there was quite large difference,it shows that the ball milling process was carried out wrongly.The graph also shows that the declining phase until zero from the first layer 

to the fourth layer.

Questions:

1. What are the factors that can influence the size reduction process of a ball mill?

The factors that can influence the size reduction process are size of particle, density,hardness ,speed of ball mill (rpm),

Particle size : the smaller the media particles, the smaller the particle size of the final product.Meanwhile, the grinding media particles should be larger than the largest pieces of material to be ground.

Density : The media should be denser than the material being ground.It will be aproblem if the grinding media floats on top of the material to e ground.

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 fast pace.

Speed of ball mill (rpm) : the faster the speed of the ball mill, the faster the rection process will occur.

 2. What other equipment can be used in size reduction of solid materials?

Specialized mill, a unit which is designed specifically for fine grinding of calcium carbonate.Cryogenic grinding which is the mill can run with liquid nitrogen to facilitate the nonfriable material such as plastics.

 3.  What are the factors that need to be considered in choosing the the suitable size reducing equipment?

Hardness:The harder the media the better the grinding efficiency and longer the life.

Final particle size:Smaller media are more efficient when ultrafine particles are desired.

pH:Some strongly acidic or basic material can react with certain metallite media.

Milling time :The longer a ball mill operates, the smaller the particles will become.

Conclusion :

The result of the ball milling obtained is not good as the practical theory.This is because there was large difference between the first layer which is 312.7 g and the second layer and third layer which are 17.6 g and 0.5 g.There is no data obtained  for fourth layer as the third layer near to zero.This shows that the ball milling result deviated from as usual.

References :

http://www.unionprocess.com/tech_papers/ChooseTheRightGrindingMill.pdf

http://dspace.nitrkl.ac.in/dspace/bitstream/2080/879/1/correlations1.p

http://www.unitednuclear.com/index.php?main_page=index&cPath=25_35