Size Reduction - Mechanical Operations

Ways of size reduction

smashing

splitting

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breaking

cutting

attrition

crunching

Size Reduction Equipments Classified based on: • •

•

Mode of Operation Method by which a force is applied, and Size of feed and product

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Mode of Operation •

Batch

•

Continuous

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•

•

Method by which a force is applied Impact –

Impact at one surface

–

Impact between particles

Compression between two solid surfaces –

Crushing

–

Grinding

•

Rubbing the materials between two surfaces

•

Shear action of the surrounding medium

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Non-mechanical introduction of energy –

Thermal shock

–

Explosive shattering

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•

Size of feed and product

Coarse crushers (large feed size to 50-5mm product size –

Jaw crusher (Blake and Dodge)

–

Gyratory crusher

–

Cone crusher

–

–

Crushing rolls (smooth and toothed rolls) Bradford breaker

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•

Size of feed and product

Intermediate crushers (50-5mm to 5-0.1mm product size) –

Roller mill

–

Cage mill

–

Granulator

–

Hammer mill

–

Impactor

–

Vertical shaft impactor

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•

Size of feed and product

Fine crushers/grinders (5-2mm to ≅200-mesh) –

Ball mill

–

Pebble mill

–

Rod mill

–

Tube mill

–

Attrition mill / Pulveriser

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•

Size of feed and product

Ultrafine grinders (6mm to 150� m) –

Fluid energy or jet mill

–

Colloid mill

–

Classifying hammer mill

–

Fine impact mill

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•

Size of feed and product

Cutting machines (definite size between 2 to 10mm length) –

Knife

–

Cutter

–

Scissors

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Abrasio Moisture n limit content

Reductio Main use n ratio

Type

Hardness

Jaw crushers

Soft to very hard

No limit

Heavy mining, Quarried Dry to slightly 3/1 to 5/1 materials, sand & gravel, wet, not sticky recycling

Gyratory crushers

Soft to very hard

Abrasive

Dry to slightly Heavy mining, Quarried 4/1 to 7/1 wet, not sticky materials

Cone crushers

Medium hard Dry or wet, not Quarried materials, Sand Abrasive 3/1 to 5/1 to very hard sticky & gravel

Compound crusher

Medium hard Dry or wet, not Abrasive 3/1 to 5/1 Mine, Building Materials to very hard sticky

Horizontal shaft impactors Vertical shaft impactors (shoe and anvil)

Soft to Slightly Dry or wet, not 10/1 to medium hard abrasive sticky 25/1

Medium hard Slightly Dry or wet, not 6/1 to 8/1 Sand & gravel, recycling to very hard abrasive sticky

Vertical shaft Soft to very impactors hard (autogenous)

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Quarried materials, sand & gravel, recycling

No limit

Mineral sizers Hard to soft Abrasive

Dry or wet, not Quarried materials, sand 2/1 to 5/1 sticky & gravel Dry or wet and 2/1 to 5/1 Heavy mining sticky

Size-Reduction Equipment The principal types of size-reduction machines are as follows: A. Crushers (coarse and fine) 1. 2. 3.

Jaw crushers Gyratory crushers Crushing rolls

B. Grinders (intermediate and fine) 1. Hammer mills, Impactors 2. Attrition mills 3. Tumbling mills a. Rod mills b. Ball mills C. Ultrafine grinders 1. Fluid-energy mills D. Cutting machines 1. Knife cutters, slitters

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Coarse mine material into lumps of 250 to 150 mm. Again these lumps are broken into particlse of 6 mm in size. The product from an intermediate grinder might pass a 40-mesh screen and product from fine grinders pass a 200-mesh screen with a 74 � m opening. Feed < 6 mm Product: 1- 50 m 2 to 10 length

mm

in

Comminution equipment: crushers and mills

a

b

c

d

e

f

Rys. 3.15. Wybrane urządzenia do rozdrabniania: a – kruszarka walcowa, b – młyn kulowy, Selected devices size reduction.a) rolls, c – młyn wahadłowy, d for – kruszarka młotkowa, e – łamacz szczękowy,crushing f – kruszarka stożkowa b) tumbling mills, c) pendular mill, d) hammer mill, 4/14/12 e) jaw crusher, f) gyratory crusher

Jaw Crusher

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Jaw Crusher •

•

•

A Jaw Crusher reduces large size rocks or ore by placing the rock into compression. A fixed jaw, mounted in a "V" alignment is the stationary breaking surface, while the movable jaw exerts force on the rock by forcing it against the stationary plate. The space at the bottom of the "V" aligned jaw plates is the crusher product size gap, or the size of the 4/14/12 crushed product from the jaw crusher.

•

• •

•

Manganese Dies in the Jaw Crusher

The jaw crusher pitman is covered on the inward facing side with dies made of manganese, an extremely hard metal.  These dies often have scalloped faces.  The dies are usually symmetrical top to bottom and can be flipped over that way.  This is handy as most wear occurs at the bottom (closed side) of the jaw and flipping them over provides another 4/14/12

Crush ers Crusher are slow-speed machines for coarse reduction of large quantities of solids. The main types are jaw crushers, gyratory crushers, smooth-roll crushers and toothed-roll crushers.

The first three operate by compression and can break large lumps of very hard materials, as in the primary and secondary reduction of rocks and ores. Toothed-roll crushers tear the feed apart as well as crush it, they handle softer feeds like coal.

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Jaw jaw, one fixed plate, Crushers

Based on human one moving. One jaw, the fixed, is nearly vertical and does not move. Other jaw, the swinging jaw, reciprocates in a horizontal plane. It makes an angle of 20� to 30� with the fixed jaw. As the material moves down the crushing action increases.

Blake Jaw Product size is Crushers adjusted by adjusting the gap size. 4/14/12 The jaws open and close 250 – 400 times per

Gyratory Gyratory crushers are crusher

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characterized by a gyrating mantle mounted within a deep bowl.  Gyratory crushers provide continuous crushing action and are used for both primary and secondary crushing of hard, tough, abrasive rock. Gyratory Standard Cone crushers are used as secondary or tertiary crushers.  Cone crushers are capable of producing large quantities of uniformly fine crushed stone A cone crusher differs from a true gyratory crusher in the following respects: It has a shorter cone.

Gyratory Crusher

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Crushing Rolls

Two or more heavy steel cylinders revolve towards each other. An overload compression spring protects the roller surfaces from damage.

The distance between the surfaces of the rollers is termed as nip

Smooth roll crusher

Force applied to the product is mainly compressive •Size reduction ratios are normally below five •Capacity is affected by speed, nip, diameter and length of the rollers •Roll speeds range from 50 to 300 r/min 4/14/12

Crushing Rolls Toothed-roll crushers may contain two or one roll working against a stationary curved breaker plate. They are more versatile than smooth-roll crushers, within the limitation that they cannot handle very hard solids.

Single-roll toothed crusher

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They operate by compression, impact and shear, not by compression only as do smooth-roll, and therefore reduce much larger particles.

Grinders The term grinder describes a variety of size-reduction machines for intermediate and fine duties. The product from a crusher is often fed to a grinder, in which it is reduced to powder. The chief types of commercial grinders are hammer mill, attrition mills and tumbling 4/14/12 mills.

Grinders Hammer Mill A high speed motor carries a number of hammers around its periphery, inside a close fitting case containing a toughened breaker plate. The individual hammers could weight as much as 100-150 kg. Reduction is mainly by impacts as the hammer drives the material against the breaker plate (shear may also have role under “chock” feeding conditions) Regarded as general purpose mill, handling crystalline solids, fibrous materials, sticky materials etc. Due to excessive wear, hammer mills are not recommended for the fine grinding of very hard materials.

Grinders Attrition Mill Mainly utilize shear between a plate and a stationary surface, or between two plates for fine grinding.

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Tumbling Mills

Ball Mills and Rod Mills

A rotating (tumbling) or vibrating chamber is filled with steel balls or rods. Feed material is subjected to impact and shear due to the movement of the balls or rods. Shear predominates at low speed while impact becomes more important at higher speeds (if speed is too high, balls can be carried around the periphery and grinding ceases). Finer product is produced by smaller balls, higher ball density and longer residence time (ie lower feed rate). Rod mills 4/14/12

are useful for sticky materials which

Tumbling Mills Ball Mill

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Grinding media

Tumbling Mills

Standard Chrome Plated Steel Grinding Media

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Ultrafine commercial powders grinders

Many must contain particles averaging 1 to 20 � m in size with substantially all particles passing a standard 325-mesh screen that has opening 44 m wide. Mills that reduce solids to such fine particles are called ultrafine grinders. The fluid used is either superheated steam or compressed air. It produces essentially uncontaminated product, thus, these are used extensively in industries such as paints, cosmetics, drugs etc. It can handle safely heat sensitive and explosive materials. 4/14/12

Fluid-

Cutting Machines In some size reduction problems the feed stocks are too resilient to be broken by compression, impact or attrition. In other problems the feed must be reduced to particles of fixed dimensions. These requirements are met by devices that cut, chop or tear into a product with the desired characteristics.

Rotary knife cutters These devices are well adapted to size4/14/12 reduction problems in the manufacturing

Applications

Cutting Machines

The Cutter uniformly slices with precision at high capacities and is ideally suited for elongated products. Products effectively cut on the machine include potatoes, beans, peppers, bread sticks, carrots, and many other applications. 4/14/12