The millig experiment- LAW JIA JUIN

Aim

1.     To introduce the students to the practical aspects of milling

2.     To appreciate some of the processing variables that affect milling

3.     To introduce the students to analysis of comminuted material

Materials and Procedure

As referred to the relevant practical manual.

Results

Table 1 Weights and percentages of unmilled granules according to the sieve sizes

Sieve sizes / mm	Weight of the granules/g	Percentage of granules retained / %
2.00	58.28	57.40
1.70	39.70	39.10
1.40	3.35	3.30
1.18	0.03	0.03
1.00	0.02	0.02
0.71	0.02	0.02
0.50	0.01	0.01
< 0.50	0.13	0.13
	Total = 101.54	Total = 100.01

Table 2 Weights and percentages of milled granules at low speed (80rpm)

Sieve sizes/mm	Weight of granules / g	Percentage of granules retained / %
2.00	6.50	13.50
1.70	13.93	28.92
1.40	12.58	26.12
1.18	3.02	6.30
1.00	3.48	7.22
0.71	2.95	6.12
0.50	1.40	2.91
< 0.50	4.31	8.95
	Total = 48.17	Total = 100.04

Table 3 Weights and percentages of milled granules at high speed (100rpm)

Sieve sizes/mm	Weight of granules / g	Percentage of granules retained / %
2.00	8.33	17.00
1.70	17.54	35.80
1.40	11.67	23.81
1.18	2.44	7.92
1.00	2.79	4.98
0.71	2.33	4.75
0.50	1.05	2.14
< 0.50	2.87	5.85
	Total = 49.02	Total =  102.25

Observation and discussion.

            Milling is a vital process in drug manufacturing. During milling, larger granules are reduced to smaller granules this is done by breaking the larger granules into smaller ones. There are many way in which milling can be done example of them are through cutting ,compressing, impact, attrition or even combination. In this experiment we used cutting, and the milling machine used was a roller mill with blades. There are many factors affecting the effectiveness of granule size reduction of our milling machine, example of these are speed of the rotating blades and rate of granules addition. Our group had done the practical to study the effect of speed of the rotating blades on the granular size reduction.

From table 1, it is observed that more than half of the unmilled granules are having particles size bigger than 2.00 mm , this can be proved when majority of the unmilled granules are trapped above 1^st sieve. There are only 0.13% of unmilled granules passed through the 7^th filter sieve successfully .This tells us that the granule of particle size less than 0.5mm are very little in quantity. Most of the granules remain their large particle size. Majority of the granules are within the size of 1.40-more than 2.00mm

After the granules have been milled under high speed (120rpm) via the roller blades milling machine ,we can see that there are less granule trapped above the 1^st sieve layer now, the percentage of granules having particle size of more than 2.00mm decreased to 17.00%. There are also more particles passed through 7^th sieve layer, this shows that the particles with size less than 0.50mm increased after cutting by rotating blades under high speed, around 5.85% of them. But we had also found that if the granules are milled under slower speed (80rpm) there will be even more granules passed through the 7^th sieve ,around 8.95% . The granules are also distributed more evenly in different sizes after milling. Slow speed milling is more effective in size reduction than fast speed milling.

Under slow speed milling, the milling shafts of the milling machine turn at a slower rate. The granules added into the milling machine will have a longer contact time with the milling shafts or blades. This provides a more effective size reduction to our granules and so more small size granules are produced. On the other hand ,if the blades are rotating at very fast speed, there will be insufficient contact time for the blades to cut the granules. Some granules can just escaped through the gap of the blades without been cut or changed.

Conclusion

Slow speed rotating blades will give a more effective granules size reduction than fast rotating blades.

Reference

1.     http://elearning.imu.edu.my/file.php/4292/Gorajana/Particle%20size%20reduction%20and%20analyses.pdf