Group B5 : 1)NUR AQILAH BT NORDIN )RITCHIE LIM LI ZHI ) NUR IZZATY BT NOORAZIMI ) NURUL SAFIKA BT ABDUL FATAH ) MOHD. RIDZHUAN BIN JINAL ) NURFARAHIN BT MAHADI 10100

Definition of size reduction : particles in solid are cut into smaller pieces How ? 4 common ways : impact Attrition Rubbing Cutting Example of equipments : grinders, crushers, ultrafine grinders, cutting machines

When the mill rotated, the balls collide to the mill wall and each other and caused it to break particle. Centrifugal Force – keep the ball in contact during upward movement. Zone of impact – most grinding occur. - free falling ball strike bottom Faster the speed, higher collision, more power consumption Centrifuging – cause : speed too high - little/no grinding Critical speed – speed at which centrifuging occurs Hence, [operational speed < critical speed]

2 forces acting on the balls : gravitional force centrifugal force centipetal component Centripetal force (in gravity) <centrifugal force Particle not break contact to wall α decrease, centripetal force increase

Forces on ball in the mill :

At critical speed, (α=0, cos α=1, n= ) Ball mill ususally run at : 65-80% critical speed As product become finer capacity mill diminish energy requirement increase

To demonstrate a batch cylindrical ball mill operation. Students shall carry out simple analysis for each experiment at different speed. Procedures : The ball mill has been cleaned. The grinding balls then being added. 300g of coarse sample (16 mesh size or larger) was weighted and poured into the ball mill through the inlet. The inlet cap being secured tightly. The speed control knob was set to about 45% of the critical speed. Time was recorded. After that, the ball mill has been switched on and ran for 15minutes The ball mill was stopped. The balls and powder was collected into the tray and then being seperated for screen analysis later on. Steps 3 to 6 has been repeated at different percentage of critical speed : 70%, 100% and 130% Experiments was repeated using different grinding balls.

Grinding Material: Zirconia Mass of Zirconia = 635g Critical speed (RPM);

The graph of mass fraction vs. size of the sand :

Grinding Material: Stainless Steel Mass of stainless Steel = 635g Critical speed (RPM):

The graph of mass fraction vs. size of the sand

CALCULATION Formula for critical speed: Where,g = 9.81 m/s 2 R = radius of the ball mill r = radius of the particle (sand) Radius of sand, r : 1 mesh = 25.4mm 16 mesh = 1.18mm

For 45%, 70% and 100% of critical speed:

DISCUSSION Efficiency of ball mill at different rotational speed In respect of rotating speed control, the high-efficiency production is very limited. When the rotating speed is high,the height of the ball raised is high. The ball weight get away from the barrel when the ball rises to certain height,and falls along the parabolic path.

DISCUSSION When the rotating speed exceeds a certain speed, the mill ball will rotate with the barrel and won’t fall down, in a condition of centrifugal movement. There will be no impact force, so the grinding function is much less

DISCUSSION In the production of ball mill, controlling the rotating speed can effectively control the mill ball consumption thus decrease the production cost. It also will increase the ball mill production efficiency and decrease energy consumption.

ERRORS Human error starting and stopping the stopwatch starting and stopping the ball mill and shaker Parallax error reading the weight measurement of sands. Systematic Error The ball mill opener is hard to open it once it has been used due to the dust. The setup of ball mill is hard, needs to tighten the screw to prevent the leakage. Time allowed for the separation of sand to settle down may be not enough Random error mechanical noise upon conducting experiment.

RECOMMENDATION Make sure that the stopwatch working properly and the person in charge give the time precisely. Make sure we tighten the ball mill screw to prevent any leakage. After using the ball mill the opener of the ball mill need to clean to remove the dust for other experiment. The grinding balls need to be more to easily the sand break into tiny pieces. After enough time, need to stop the experiment precisely. The measurement of weight need to be more precise and accurate by avoid parallax error by making sure there has no other unwanted sand to be measured.

CONCLUSION Size reduction process (grinding) using ball mill with TWO(2) different grinding materials. i.zirconia ii.Standard steel ball Results show that standard steel ball preformed better grinding effect. Effect of rotational speed on size reduction As rotational speed, the better the grinding effect. (Suppose rotational speed ≤ critical speed, )

Factors Affecting Grinding I. Size of grinding media The smaller the particles, the smaller the final product in size. *Grinding material should be larger than samples. II. Density Denser the grinding media, higher impact on sample III. Hardness Grinding media should be durable enough to achieve better grinding effect

Q & A SESSION