Ball mill – Working and Its Advantages

April 17th, 2014 by Acmas No comments »

Ball mill works on impact principle that is size reduction is done by the impact. It contains a hollow cylinder shell that rotates around its axis and is partially filled with the balls. The ball mill may be operated in a batch or continuous fashion and wet or dry.

In case of continuously operated ball mill, the material to be ground is fed from the left through a 60 degree cone and the product is discharged through a 30 degree cone to the right. As the shell rotates, the balls are lifted up on the rising side of the shell and then they cascade down from near to the top of the shell. In doing so, the solid particles in between the balls are ground and reduced in size by impact.

The ball mill contains the balls of various sizes. As the shell rotates, the large balls segregate near the feed end and small balls segregate near the end product that is going to be discharge. The initial breaking of the feed particles, therefore, is done by the largest balls dropping the largest distance and the small particles are ground by small balls dropping from much smaller distances. If the rate of the feed is increased, coarser product will be obtain and if the speed of the rotation is increased (that should be less than critical speed), the fineness for a given capacity increases.

During grinding the balls themselves wear and are constantly replaced by new ones so that the ball mill contains balls of various ages and of various sizes. In case of batch operated ball mills, a measured quantity of solid to be ground is charged into the ball mill through the opening in the shell. The opening is then closed and the ball mill is rotated for several hours. It is then stopped and the product is discharged.

In case of wet grinding, there is low power consumption, increased capacity, reduction in the formation of fines, facilitates the removal of product and no dust formation.

Advantages of Ball Mill

The cost of installation is low.
The cost of power required is low.
It is suitable for materials of all degree of hardness.
It is suitable for batch as well as continues operations.
The grinding medium is cheap.

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Ball mill- factors influencing the size of product

April 17th, 2014 by Acmas No comments »

Ball mill that works on the principle of impact is an efficient technique of size reduction through grinding. The size reduction is an important factor for many industrial applications as this process is carried out to increase the surface area, to intimate mixing and to improve dissolution rate, solubility, binding strength and dispersion properties. Therefore it is important to maintain the size of products there are many factors that influence the size of product, some of these factors are;

Feed rate – With a high feed rate, less size reduction is effected since in this case the material is present in the mill for a shorter time.

Properties of the feed material – with a hard material, a smaller size reduction is achieved.

Weight of balls – With a heavy charge of balls, there is production of fine product. One can increase the weight of the charge by increasing the number of balls or by using a ball material of high density. Optimum grinding conditions are obtained when the volume of the balls is equal to 50 percent that of the ball mill. So the variation in the weight of balls is done by using materials of different densities.

Speed of rotation of mill – At low speeds, the balls simply roll over one another and little grinding is obtained while at very high speeds, the balls are simply carried along the walls of the shells and little or no grinding takes place, so for an effective grinding, the ball mill should be operated at a speed that is optimum speed equal to 50 to 75 percent of the critical speed (the minimum speed at which centrifuging occurs is called the critical speed of the ball mill, and under these conditions, centrifugal force will be exactly balanced by the weight of the ball, little or no grinding takes place when mill is centrifuging, therefore to operate practically the mill, the operating speed must be less than the critical speed).

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Ball mill-factors

April 16th, 2014 by Acmas No comments »

Influencing the size of product

Ball mill that works on the principle of impact is an efficient technique of size reduction through grinding. The size reduction is an important factor for many industrial applications as this process is carried out to increase the surface area, to intimate mixing and to improve dissolution rate, solubility, binding strength and dispersion properties.

Therefore it is important to maintain the size of products there are many factors that influence the size of product, some of these factors are;

Feed rate; with a high feed rate, less size reduction is effected since in this case the material is present in the mill for a shorter time.
Properties of the feed material; with a hard material, a smaller size reduction is achieved.

Weight of balls; with a heavy charge of balls, there is production of fine product. One can increase the weight of the charge by increasing the number of balls or by using a ball material of high density. Optimum grinding conditions are obtained when the volume of the balls is equal to 50 percent that of the ball mill. So the variation in the weight of balls is done by using materials of different densities.

Speed of rotation of mill; at low speeds, the balls simply roll over one another and little grinding is obtained while at very high speeds, the balls are simply carried along the walls of the shells and little or no grinding takes place, so for an effective grinding, the ball mill should be operated at a speed that is optimum speed equal to 50 to 75 percent of the critical speed (the minimum speed at which centrifuging occurs is called the critical speed of the ball mill, and under these conditions, centrifugal force will be exactly balanced by the weight of the ball, little or no grinding takes place when mill is centrifuging, therefore to operate practically the mill, the operating speed must be less than the critical speed).

Level of the material in the mill; a low level of material in the ball mill reduce the power consumption. If the level of material is raised, the cushioning action increases and power is wasted by the production of undersized material in an excessive quantity.