Ball mill

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A section cut-through of ball mills Marcy Ball Mill - Shenandoah-Dives Mill, 135 County Road 2, Silverton, San Juan County, CO HAER CO-91 (sheet 21 of 27) (cropped).png
A section cut-through of ball mills

A ball mill is a type of grinder used to grind or blend materials for use in mineral dressing processes, paints, pyrotechnics, ceramics, and selective laser sintering. It works on the principle of impact and attrition: size reduction is done by impact as the balls drop from near the top of the shell.

Contents

A ball mill consists of a hollow cylindrical shell rotating about its axis. The axis of the shell may be either horizontal or at a small angle to the horizontal. It is partially filled with balls. The grinding media are the balls, which may be made of steel (chrome steel), stainless steel, ceramic, or rubber. The inner surface of the cylindrical shell is usually lined with an abrasion-resistant material such as manganese steel or rubber lining. Less wear takes place in rubber lined mills. The length of the mill is approximately equal to its diameter.

The general idea behind the ball mill is an ancient one, but it was not until the industrial revolution and the invention of steam power that an effective ball milling machine could be built. It is reported to have been used for grinding flint for pottery in 1870. [1]

Working

Operations of ball mill Ball mill.gif
Operations of ball mill

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 for grinding materials such as mining ores, coal, pigments, and feldspar for pottery. Grinding can be carried out wet or dry, but the former is performed at low speed. Ball mills are used often in scientific work to reduce the particle size, eliminate agglomeration, change the shape of particles, provide for mechanical alloying, mixing, producing powders and changing materials properties. [2] An open source ball mill has been designed that can be fabricated with a 3D printer for a few hundred dollars. [3] It is able to be operated both on grid for lab work and off grid with solar photovoltaics and a battery for field work. [3] Blending of explosives is an example of an application for rubber balls. [4] For systems with multiple components, ball milling has been shown to be effective in increasing solid-state chemical reactivity. [5] Additionally, ball milling has been shown effective for production of amorphous materials. [5] It may also be useful to separate gases such as hydrogen and store them in powder form. [6] [7]

Description

Benchtop ball mill Ballmill.jpg
Benchtop ball mill
Laboratory scale ball mill 8000M Mixer Mill (open) incl accessories.jpg
Laboratory scale ball mill
High-energy ball milling High-energy ball milling.gif
High-energy ball milling

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. 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 the principle of critical speed. Critical speed can be understood as that speed after which the steel balls that 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, [8] in which they are used for grinding and for cold welding, producing alloys from powders. [9]

The ball mill is a key piece of equipment for grinding crushed materials, and it is widely used in production lines for powders such as cement, silicates, refractory material, fertilizer, glass ceramics, etc., as well as for ore dressing of ferrous and non-ferrous metals. The ball mill can grind ores and other materials, wet or dry. There are two kinds of ball mills according to their ways of discharging material: grate type, and overfall type. Many types of grinding media are suitable for use in a ball mill, each material having its own specific properties and advantages. Key properties of grinding media are size, density, hardness, and composition.

The grinding chamber can also be filled with an inert shield gas that does not react with the material being ground, to prevent oxidation or explosive reactions that could occur with ambient air inside the mill.

Advantages of the ball mill

Ball milling boasts several advantages over other systems: the cost of installation and grinding medium is low; the capacity and fineness can be adjusted by adjusting the diameter of the ball; it is suitable for both batch and continuous operation; it is suitable for open and closed-circuit grinding; it is applicable for materials of all degrees of hardness.

Varieties

Aside from common ball mills, there is a second type of ball mill called a planetary ball mill. Planetary ball mills are smaller than common ball mills and mainly used in laboratories for grinding sample material down to very small sizes. A planetary ball mill consists of at least one grinding jar which is arranged eccentrically on a so-called sun wheel. The direction of movement of the sun wheel is opposite to that of the grinding jars (ratio: 1:−2 or 1:−1). The grinding balls in the grinding jars are subjected to superimposed rotational movements, the so-called Coriolis forces. The difference in speeds between the balls and grinding jars produces an interaction between frictional and impact forces, which releases high dynamic energies. The interplay between these forces produces the high and very effective degree of size reduction of the planetary ball mill.

See also

Related Research Articles

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Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the science and the technology of metals; that is, the way in which science is applied to the production of metals, and the engineering of metal components used in products for both consumers and manufacturers. Metallurgy is distinct from the craft of metalworking. Metalworking relies on metallurgy in a similar manner to how medicine relies on medical science for technical advancement. A specialist practitioner of metallurgy is known as a metallurgist.

<span class="mw-page-title-main">Heat treating</span> Process of heating something to alter it

Heat treating is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

<span class="mw-page-title-main">Metalworking</span> Process of making items from metal

Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges down to precise engine parts and delicate jewelry.

<span class="mw-page-title-main">Mill (grinding)</span> Device that breaks solid materials into smaller pieces by grinding, crushing, or cutting

A mill is a device, often a structure, machine or kitchen appliance, that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different types of mills and many types of materials processed in them. Historically mills were powered by hand or by animals, working animal, wind (windmill) or water (watermill). In modern era, they are usually powered by electricity.

<span class="mw-page-title-main">Grinding wheel</span> Abrasive cutting tool for grinders

Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines.

<span class="mw-page-title-main">Burr mill</span> Mill used to grind hard food products between two burrs

A burr mill, or burr grinder, is a mill used to grind hard, small food products between two revolving abrasive surfaces separated by a distance usually set by the user. When the two surfaces are set far apart, the resulting ground material is coarser, and when the two surfaces are set closer together, the resulting ground material is finer and smaller. Often, the device includes a revolving screw that pushes the food through. It may be powered electrically or manually.

<span class="mw-page-title-main">Foundry</span> Factory that produces metal castings

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

A pulverizer or grinder is a mechanical device for the grinding of many different types of materials. For example, a pulverizer mill is used to pulverize coal for combustion in the steam-generating furnaces of coal power plants.

<span class="mw-page-title-main">Cryogenic grinding</span>

Cryogenic grinding, also known as freezer milling, freezer grinding, and cryomilling, is the act of cooling or chilling a material and then reducing it into a small particle size. For example, thermoplastics are difficult to grind to small particle sizes at ambient temperatures because they soften, adhere in lumpy masses and clog screens. When chilled by dry ice, liquid carbon dioxide or liquid nitrogen, the thermoplastics can be finely ground to powders suitable for electrostatic spraying and other powder processes. Cryogenic grinding of plant and animal tissue is a technique used by microbiologists. Samples that require extraction of nucleic acids must be kept at −80 °C or lower during the entire extraction process. For samples that are soft or flexible at room temperature, cryogenic grinding may be the only viable technique for processing samples. A number of recent studies report on the processing and behavior of nanostructured materials via cryomilling.

<span class="mw-page-title-main">Cement mill</span>

A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Most cement is currently ground in ball mills and also vertical roller mills which are more effective than ball mills.

<span class="mw-page-title-main">Rawmill</span>

A raw mill is the equipment used to grind raw materials into "rawmix" during the manufacture of cement. Rawmix is then fed to a cement kiln, which transforms it into clinker, which is then ground to make cement in the cement mill. The raw milling stage of the process effectively defines the chemistry of the finished cement, and has a large effect upon the efficiency of the whole manufacturing process.

<span class="mw-page-title-main">Grinding (abrasive cutting)</span> Machining process using a grinding wheel

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<span class="mw-page-title-main">Impact mill</span> Class of milling devices

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Mass finishing is a group of manufacturing processes that allow large quantities of parts to be simultaneously finished. The goal of this type of finishing is to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, or break off die cast runners. The two main types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing. Both involve the use of a cyclical action to create grinding contact between surfaces. Sometimes the workpieces are finished against each other; however, usually a finishing medium is used. Mass finishing can be performed dry or wet; wet processes have liquid lubricants, cleaners, or abrasives, while dry processes do not. Cycle times can be as short as 10 minutes for nonferrous workpieces or as long as 2 hours for hardened steel.

<span class="mw-page-title-main">Mechanical alloying</span>

Mechanical alloying (MA) is a solid-state and powder processing technique involving repeated cold welding, fracturing, and re-welding of blended powder particles in a high-energy ball mill to produce a homogeneous material. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or pre-alloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys.

<span class="mw-page-title-main">Ball (bearing)</span> Machine component most commonly used as the rolling element in ball bearings

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<span class="mw-page-title-main">Centrifugal casting (industrial)</span> Casting technique that is typically used to cast thin-walled cylinders

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<span class="mw-page-title-main">Friction stir processing</span>

Friction stir processing (FSP) is a method of changing the properties of a metal through intense, localized plastic deformation. This deformation is produced by forcibly inserting a non-consumable tool into the workpiece, and revolving the tool in a stirring motion as it is pushed laterally through the workpiece. The precursor of this technique, friction stir welding, is used to join multiple pieces of metal without creating the heat affected zone typical of fusion welding.

The IsaMill is an energy-efficient mineral industry grinding mill that was jointly developed in the 1990s by Mount Isa Mines Limited and Netzsch Feinmahltechnik ("Netzsch"), a German manufacturer of bead mills. The IsaMill is primarily known for its ultrafine grinding applications in the mining industry, but is also being used as a more efficient means of coarse grinding. By the end of 2008, over 70% of the IsaMill’s installed capacity was for conventional regrinding or mainstream grinding applications, with target product sizes ranging from 25 to 60 µm.

References

  1. Lynch, A.; Rowland C (2005). The history of grinding. SME. ISBN   0-87335-238-6.
  2. Neikov, Oleg D. (2019), "Introduction", Handbook of Non-Ferrous Metal Powders, Elsevier, pp. xvii–xxi, doi:10.1016/b978-0-08-100543-9.09993-0, ISBN   978-0-08-100543-9 , retrieved 2023-07-30
  3. 1 2 Mottaghi, Maryam; Rahman, Motakabbir; Kulkarni, Apoorv; Pearce, Joshua M. (June 2023). "AC/off-grid photovoltaic powered open-source ball mill". HardwareX. 14: e00423. doi:10.1016/j.ohx.2023.e00423. ISSN   2468-0672. PMC   10176261 . PMID   37188059.
  4. US Army (1989), Department of the Army technical manual: military explosives (TM 9-1300-214), pp. 10–8.
  5. 1 2 Takacs, Laszlo (January 2002). "Self-sustaining reactions induced by ball milling". Progress in Materials Science. 47 (4): 355–414. doi:10.1016/S0079-6425(01)00002-0.
  6. "Mechanochemical breakthrough unlocks cheap, safe, powdered hydrogen". New Atlas. 2022-07-19. Retrieved 2022-07-28.
  7. Mateti, Srikanth; Zhang, Chunmei; Du, Aijun; Periasamy, Selvakannan; Chen, Ying Ian (2022-07-09). "Superb storage and energy saving separation of hydrocarbon gases in boron nitride nanosheets via a mechanochemical process" . Materials Today. 57: 26–34. doi:10.1016/j.mattod.2022.06.004. ISSN   1369-7021. S2CID   250413503.
  8. Florez-Zamora, M. I.; et al. (2008). "Comparative study of Al-Ni-Mo alloys obtained by mechanical alloying in different ball mills" (PDF). Rev. Adv. Mater. Sci. 18: 301.
  9. Mechanical Alloying Technology, Institute of Materials Processing