PRACTICAL 1: BALL MILLING

Introduction:

Ball milling is a method that is used to break the solid particles to the smaller sizes or to make it into powder. In this practical, the students were given two materials which are rock sugar and coarse salt. The students should break the materials by using ball mill and then used the sieve to determine the particle size distribution of both materials.

Apparatus and materials:

Metal balls with different sizes, ball milling machines, rock sugar, coarse salt, weighing boat, sieve and weighing

Methods

1.      300-500g of rock sugar and coarse salt was weighed

2.      Metal balls with different sizes were places in the mill

3.      Then, the weighed rock sugar and coarse salt were places together in the mill

4.      The milling process was between 15-20 minutes with the scheduled speed.

5.      After the process, the powder was weighed again.

6.      The powder was sieved by using the sieve nest

7.      A histogram about particle size distribution was plotted.

8.      The process was repeated with other substances.

Results:

Mass of course salt collected / g		Rotator speed: 5rpm	Rotator speed: 5rpm	Rotator speed: 3rpm	Rotator speed: 3rpm
		Duration: 10 min	Duration: 20 min	Duration: 10 min	Duration: 20 min
	Before milling	312.50	400.00	318.79	300.00
	500 mm Sieve	281.85	358.87	311.14	296.67
	300 mm Sieve	14.11	30.18	12.92	18.56
	250 mm Sieve	4.10	3.78	4.14	1.49
	150 mm Sieve	5.79	3.37	2.05	0.27
	0 mm Sieve	3.83	2.48	0.00	0.06
	Total after milling	309.68	398.68	330.25	317.05

 

 

 

 

 

 

 

 

Discussions:

            Based on the experiment, we had use different speed of ball miller machine and different duration of milling process. There were 5rpm and 3rpm for speed. The duration were 10 minutes and 20 minutes. For speed 5rpm, the final product that can pass through the sieve is higher than the amount final product for 3rpm. This is because the greater the speed causing to salt that be milled to the smaller size. Then, smaller size can pass through the sieve easier.

            The higher the duration, the greater the amount of finest particle can be obtained. For 20 minutes duration, the amount of finest particle was higher compared to 10 minutes duration.

            For overall, the total weight of salt after milling was reduced from initial reading. But for 3rpm, the total weight of salt increased due to some error which is caused by presence of salt residues from previous experiment.

Conclusions:

The higher the duration, the greater the amount of finest particle can be obtained. For 20 minutes duration, the amount of finest particle was higher compared to 10 minutes duration. The greater the speed, the greater the amount of finest particle can be obtained.

Questions:

1. What are the factors that affect ball milling process?

Speed of rotation of ball milling machine can give a direct impact to the process of ball milling. With the speed of mill rapidly increasing, the processing capacity of the mill will be improved and the average particle size will rapidly decrease. Furthermore, the duration of ball milling also one of a factor the process. The longer the duration for ball milling, smaller the final particle size. Grinding concentration also affect the process of ball milling. When the grinding concentration is 55%, the negative cumulative yield rate of a one-level in product is the smallest, when the mill mineral concentration of 70%, the viscosity of the slurry is density and will make the discharge not smooth. Therefore, making the grinding concentration selected for 60% -65% is more appropriate.

2. What is the equipment can be used in ball milling process?

Firstly, we need ball milling machine in the process of particle size reduction. There are many type of machine depend on the requirement of final product and type of material used. There are rotor mills, planetary mills, knife mills, and other type of milling machine. Porcelain jar also can be used if the media used is porcelain. Media also can be obtained from different type of matter such as iron, ceramic, stainless steel and others. Then, we need siever to analyse the particle size. Sieve shakers, test sieves and evaluation software provide the key to easy, rapid, reproducible and, above all, accurate analyses.

3. What are the factors that can influence in choosing equipment in ball milling?

One of the factors that play an important role is size of media (ball mill). The smaller the media particles, the smaller the particle size of the final product. Besides, media should be denser than the material that will be grounded. It is because, when grinding media floats on top of the material to be ground, it will become a problem and affect the grinding product. Another factor is type of media which are they could be from iron, stainless steel, ceramic, flint, or other that can be chosen based on suitability of material that be grounded. Each type media has interaction with certain substance. For example, iron may react with corrosive materials. For this reason, stainless steel, ceramic, and flint grinding media may each be used when corrosive substances are present during grinding. Moreover, the composition of machine also must be considered. 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.