ball milling

8/2/2019 Ball Milling

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A ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing)

materials like ores, chemicals, ceramic raw materials and paints[1]

. Ball mills rotate

around a horizontal axis, partially filled with the material to be ground plus the grinding

medium. Different materials are used as media, including ceramic balls, flint pebbles and

stainless steel balls. An internal cascading effect reduces the material to a fine powder.

Industrial ball mills can operate continuously, fed at one end and discharged at the other

end. Large to medium-sized ball mills are mechanically rotated on their axis, but small

ones normally consist of a cylindrical capped container that sits on two drive shafts

(pulleys and belts are used to transmit rotary motion). A rock tumbler functions on the

same principle. Ball mills are also used in pyrotechnics and the manufacture of black

powder, but cannot be used in the preparation of some pyrotechnic mixtures such as flash

powder because of their sensitivity to impact. High-quality ball mills are potentially

expensive and can grind mixture particles to as small as 5 nm, enormously increasing

surface area and reaction rates. The grinding works on principle of critical speed. The

critical speed can be understood as that speed after which the steel balls (which are

responsible for the grinding of particles) start rotating along the direction of the

cylindrical device; thus causing no further grinding.

Ball mills are used extensively in the Mechanical alloying process[2]in which they are not

only used for grinding but for cold welding as well, with the purpose of producing alloys

from powders. One of most commonly used mills is the SPEX Mill

High energy ball milling for nanoparticle synthesis

High energy ball milling of powder particles as a method for materials synthesis has been

developed as an industrial process to successfully produce new alloys and phase mixtures

in 1970s. This powder metallurgical process allows the preparation of alloys and

composites, which cannot be synthesized via conventional routes. In nanomaterials

research, this top down technique is well used to fine-tune the grain sizes of the materials

Instructor - Dr Partha Sharathi Mallick,ProfessorSubject EEE204
http://en.wikipedia.org/wiki/Grinder_(milling)http://en.wikipedia.org/wiki/Oreshttp://en.wikipedia.org/wiki/Ball_mill#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Ball_mill#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Ball_mill#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Flinthttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Pulleyshttp://en.wikipedia.org/wiki/Rock_tumblerhttp://en.wikipedia.org/wiki/Pyrotechnicshttp://en.wikipedia.org/wiki/Black_powderhttp://en.wikipedia.org/wiki/Black_powderhttp://en.wikipedia.org/wiki/Flash_powderhttp://en.wikipedia.org/wiki/Flash_powderhttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Mechanical_alloyinghttp://en.wikipedia.org/wiki/Ball_mill#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/Ball_mill#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/Ball_mill#cite_note-1#cite_note-1http://nanospinel.blogspot.com/2007/09/high-energy-ball-milling-for.htmlhttp://nanospinel.blogspot.com/2007/09/high-energy-ball-milling-for.htmlhttp://en.wikipedia.org/wiki/Ball_mill#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/Mechanical_alloyinghttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Flash_powderhttp://en.wikipedia.org/wiki/Flash_powderhttp://en.wikipedia.org/wiki/Black_powderhttp://en.wikipedia.org/wiki/Black_powderhttp://en.wikipedia.org/wiki/Pyrotechnicshttp://en.wikipedia.org/wiki/Rock_tumblerhttp://en.wikipedia.org/wiki/Pulleyshttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Flinthttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ball_mill#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Oreshttp://en.wikipedia.org/wiki/Grinder_(milling)


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refinement ceases. Initially the kinetic energy transfer leads to the production of an array

of dislocations. This is accompanied by atomic level strains. At a certain strain level,

these dislocations annihilate and recombine to form small angle grain boundaries

separating the individual grains. Thus sub grains are formed with reduced grain size.

During further milling, this process extends throughout the entire sample. To maintain

this reduction in size, the material must experience very high stresses. But extended

milling could not able to maintain the high stresses and hence reduction of grain size is

limited in extended milling. The two other parameters which also causes this limit to

grain size reduction are the local temperature developed due to ball collisions and the

overall temperature in the vial. Temperature rise arises from balls to balls, balls to

powder and balls to wall collisions.

The impact speed and the impulsive load of the grinding balls are the two key parameters,

which determine the kinetic energy transfer. The impulsive load of grinding balls is given

by,

F = mv/t ---------- (1)

Where m is the ball mass, vthe ball velocity andt the ball-vial contact time.

ball milling

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