Unit operation
- 2. Topic BALL MILL Presented by:- Ali Haider 13-NTU-1005 Adil Naeem 13-NTU-1002 Hameed Ullah Bhatti 13-NTU-1022 Teacher:- Sir Muzammil Mehmood SB. Department of Polymer Engineering.
- 3. A ball mill is a type of grinder used to grind and blend materials for use in mineral dressing processes, paints, pyrotechnics, ceramics and selective laser sintering etc. Introduction to Ball Mill
- 4. Ball mill consist of a hollow cylindrical shell rotating about its axis. It is partially filled with balls made up of Steel, Stainless steel or rubber. Inner surface of the shell is lined with abrasion resistant materials such as Manganese, Steel or rubber. Length of the mill is approximately equal to its diameter Balls occupy about 30-50% of the volume. Dia of the ball 12 mm-125 mm. Shell is rotated through a drive gear (60-100 rpm) and large mills, shell might be in 3m in dia and 4.25 m in length. Operation may be batch or continuous, wet or dry…in a continuosly operated ball mill outlet is normally covered with coarse screen to prevent the escape of the balls.. Construction
- 5. Wet or Dry ball mill consist of:- 1. Feeding part 2. Discharging part 3. Turning and driving part ( gear, motor etc.) 4. Rotating balls Ball Mill
- 6. Working Principle Ball mill works on the principle of impact. Size reduction is done by impact as the balls drop from near the top of the cylinder..
- 8. Factors influencing the size of the product Feed rate:-With a high feed rate, less size reduction is effected since in this case the material is in the mill for a shorter time. Properties of the feed material:- With a hard material, a smaller size reduction is achieved. Level of the material in the mill:- A low level of material in the mill results into a reduction in the power consumption. If the level of material is raised power is wasted by the production of under size material. Weight of the balls:- With a heavy discharge of balls, we get a fine product. We can increase the weight of the charge by increasing the number of balls or by using a ball material of high density Speed & rotation of Ball mill:- low speeds, the balls simply roll over one another and little grinding is obtained while at very high speeds the balls are carried along the walls of the shell and the mill is said to be centrifuging.
- 9. Critical Speed of a Ball Mill The point where the mill becomes a centrifuge is called the "Critical Speed“. Ball mills usually operate at 65% to 75% of the critical speed. Nc = Critical Speed R = Radii of mill r = Radii of ball g = Acceleration due to gravity
- 11. Problam # 02
- 12. Advantages of Ball Mill The cost of installation is low. The cost of production is low. It is suitable for materials of all degree of hardness. The grinding medium is cheap. Suitable for both batch and continuous operations. Used for the grinding of explosive materials.
- 13. Disadvantages of Ball Mill Rotational ball loading difficulty Mill efficiency is low The mill feed size range is wide Not easy to get thinner end product
- 14. Applications Metallic powders Carbon and coal Phosphate rock Gypsum grinding Limestone milling Cement processing Fertilizers Silicate products Dressing production Granite
- 15. Video