Ball mill and applications

A ball mill is a grinding machine used to grind or mix materials for use in mineral beneficiation processes, paints, pyrotechnics, ceramics and selective laser sintering.It works on the principle of impact and friction: when the ball falls from near the top of the shell, it reduces in size through impact.A ball mill consists of a hollow cylindrical housing that rotates around its axis.The axis of the housing can be horizontal or at a slight angle to the horizontal.It is partially filled with balls.Grinding media are steel balls (chrome steel), stainless steel, ceramics or rubber.The inner surface of the cylindrical shell is usually lined with wear-resistant materials such as manganese steel or rubber lining.Rubber-lined mills wear less.The length of the mill is approximately equal to its diameter.The general idea behind a ball mill is an old idea, but it wasn't until the Industrial Revolution and the invention of steam power that an effective ball mill could be built.Flint reportedly used to polish pottery in 1870.

Working 

In case of continuously operated ball mill, the material to be ground is fed from the left through a 60° cone and the product is discharged through a 30° 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 (or drop down on to the feed), from near the top of the shell. In doing so, the solid particles in between the balls and ground are reduced in size by impact.

Applications

Ball mills are used to grind materials such as ore, coal, pigments, and feldspar for pottery.Grinding can be done wet or dry, but the former is done at low speeds.The mixing of explosives is an example of a rubber ball application.For systems with multiple components, ball milling has been shown to be effective in enhancing solid-state chemical reactivity.Furthermore, ball milling has been shown to be effective in producing amorphous materials.It may also be useful to separate gases such as hydrogen and store them in powder form.

Description

A ball mill is a grinding machine, a cylindrical piece of equipment used to grind (or mix) materials such as ores, chemicals, ceramic raw materials, and paints.The ball mill rotates around a horizontal axis and is partially filled with the material to be ground and grinding media.Different materials are used as media including ceramic balls, flint and stainless steel balls.An internal cascade effect reduces the material to a fine powder.The industrial ball mill can run continuously, feeding at one end and discharging at the other. Medium and large ball mills rotate mechanically on their shafts but small ball mills usually consist of a cylindrical, covered vessel on two drive shafts (pulleys and belts to transmit the rotational motion).Rock and roll works the same way.Ball mills are also used in the manufacture of pyrotechnics and black powder, but cannot be used to prepare certain pyrotechnic mixtures,such as flash powder, due to their sensitivity to shock.High quality ball mills can be expensive, mix particles as small as 5 nm, greatly increasing surface area and reaction rates.

Grinding works on the principle of critical speed.The critical speed can be understood as the speed at which the steel ball responsible for grinding the particles starts to rotate in the direction of the cylindrical device, so that no further grinding is possible.Ball mills are widely used in mechanical alloying processes  where ball mills are used for grinding and cold welding to produce alloys from powders.

Ball mill is the key equipment for grinding and crushing materials, widely used in cement, silicate, refractory materials, chemical fertilizers, glass ceramics and other powder production lines, as well as beneficiation of ferrous metals and iron ores. Non-ferrous metals.Ball mills can grind ores and other materials wet or dry. According to the discharge method, the ball mill is divided into two types: grate type and overflow type.Many types of grinding media are suitable for use in ball mills, and each material has specific characteristics and benefits.Key properties of grinding media are size, density, hardness and composition.Size:The smaller the media particles, the smaller the particle size of the final product.The grinding media particles should be substantially larger than the largest pieces of material to be ground.

Density: The media should be denser than the material being ground.It becomes a problem if the grinding media floats on top of the material to be ground.

Hardness: The grinding media needs to be durable enough to grind the material, but, where possible, not so tough that it also wears down the tumbler.

Composition: Various grinding applications have special requirements.Some of these requirements are based on some of the grinding media being in the finished product,while others are based on how the media will react with the material being ground.Where the color of the finished product is important, the color and material of the grinding media must be considered.Where low contamination is important, the grinding media may be selected for ease of separation from the finished product (e.g., steel dust produced from stainless steel media can be magnetically separated from non-ferrous products).An alternative to separation is to use media of the same material as the product being ground.Flammable products have a tendency to become explosive in powder form.Steel media may generate sparks and be a source of ignition for these products.Wet grinding or non-sparking media such as ceramic or lead must be selected.Certain media (eg iron) may react with corrosive materials.Therefore, when corrosive substances are present in the grinding process, stainless steel, ceramic and flint grinding media can be used respectively.The grinding chamber can also be filled with an inert shielding gas that does not react with the material being ground to prevent oxidation or explosive reactions with the ambient air inside the grinder.