Ways of size reduction

breaking attrition smashing

splitting cutting crunching

Size Reduction Equipments

Classified based on:• Mode of Operation• Method by which a force is applied, and• Size of feed and product

Mode of Operation

• Batch

• Continuous

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• Non-mechanical introduction of energy– Thermal shock– Explosive shattering– Electrohydraulic crushing– Cryogenic crushing– Ultrasonic grinding

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

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

Size of feed and product• Fine crushers/grinders (5-2mm to ≅200-mesh)–Ball mill–Pebble mill–Rod mill–Tube mill–Attrition mill / Pulveriser

Size of feed and product• Ultrafine grinders (6mm to 1-50𝜇m)–Fluid energy or jet mill–Colloid mill–Classifying hammer mill–Fine impact mill

Size of feed and product• Cutting machines (definite size

between 2 to 10mm length)–Knife–Cutter–Scissors

Type Hardness Abrasion limit Moisture content Reduction

ratio Main use

Jaw crushers Soft to very hard No limit Dry to slightly

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

Gyratory crushers Soft to very hard Abrasive Dry to slightly

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

Cone crushers Medium hard to very hard Abrasive Dry or wet, not

sticky 3/1 to 5/1 Quarried materials, Sand & gravel

Compound crusher

Medium hard to very hard Abrasive Dry or wet, not

sticky 3/1 to 5/1 Mine, Building Materials

Horizontal shaft impactors

Soft to medium hard

Slightly abrasive

Dry or wet, not sticky

10/1 to 25/1

Quarried materials, sand & gravel, recycling

Vertical shaft impactors (shoe and anvil)

Medium hard to very hard

Slightly abrasive

Dry or wet, not sticky 6/1 to 8/1 Sand & gravel, recycling

Vertical shaft impactors (autogenous)

Soft to very hard No limit Dry or wet, not

sticky 2/1 to 5/1 Quarried materials, sand & gravel

Mineral sizers Hard to soft Abrasive Dry or wet and sticky 2/1 to 5/1 Heavy mining

Size-Reduction Equipment

A. Crushers (coarse and fine)1. Jaw crushers2. Gyratory crushers3. Crushing rolls

B. Grinders (intermediate and fine)1. Hammer mills, Impactors2. Attrition mills3. Tumbling mills

a. Rod millsb. Ball mills

C. Ultrafine grinders1. Fluid-energy mills

D. Cutting machines1. Knife cutters, slitters

The principal types of size-reduction machines are as follows:

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 mmProduct: 1- 50 m

2 to 10 mm in length

Comminution equipment: crushers and mills

a b c

d e f

Rys. 3.15. Wybrane urządzenia do rozdrabniania: a – kruszarka walcowa, b – młyn kulowy,c – młyn wah adłowy, d – kruszarka młotkowa, e – łamacz szczękowy, f – kruszarka stożkowaSelected devices for size reduction.a) crushing rolls, b) tumbling

mills, c) pendular mill, d) hammer mill, e) jaw crusher, f) gyratory crusher

Jaw Crusher

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 crushed product from the jaw crusher.

• The rock remains in the jaws until it is small enough to pass through the gap at the bottom of the jaws.

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 equal period of use before they must be replaced.

CrushersCrusher 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.

Jaw CrushersBased on human jaw, one fixed plate, 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.

Product size is adjusted by adjusting the gap size. The jaws open and close 250 – 400 times per minute. Uncrushed rock can be passed through.

Blake Jaw Crushers

Gyratory crusherGyratory crushers are 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 stoneA cone crusher differs from a true gyratory crusher in the following respects:

It has a shorter cone. It has a smaller receiving opening.It rotates at a higher speed, about twice that of a true gyratory It produces a more uniformly sized stone.

Gyratory Crusher

Crushing RollsTwo 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

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

Smooth roll crusher

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.

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

Crushing Rolls

Single-roll toothed crusher

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 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.

Grinders

Ball Mills and Rod Mills

Tumbling 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 are useful for sticky materials which would glue balls together.

Ball Mill

Tumbling Mills

Standard Chrome Plated Steel Grinding Media

Tumbling MillsGrinding media

Ultrafine grinders

Fluid-energy mill

Many commercial powders 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.

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 size-reduction problems in the manufacturing of rubber and plastics.

Cutting Machines

Applications 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.

Cutting Machines