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CHAPTER 1

INTRODUCTION

1.1 About Crusher and its classification

Crusher is a machine which is used to reduce the size of a raw material to make it suitable

for the purpose of the specific uses. In a crusher force is generated through the principle of

mechanical advantage of machine and that amplified force is exerted on the object between

two parallel surfaces or two tangential surfaces. The object in between is crushed due to

huge compressive force which break the ionic bond of the materials. In the earlier days of

civilization materials used to be crushed with help of impact force generated through

muscle power. But the mechanized crusher do not exert impact force it actually holds the

object between two parallel or tangential surface and materials molecular lattice separate

from each other or distort the orientation which leads to crack and then breakage of the

object.

Many types of crushers are there. They are –

a) Jaw Crusher

b) Gyratory Crusher

c) Cone Crusher

d) Impact Crusher

Jaw crusher is a machine designed to reduce large solid particles of raw material into

smaller particles. Crushers are major size reduction equipment used in mechanical,

metallurgical and allied industries. They are available in various sizes and capacities

ranging from 0.2 ton/hr to 50 ton/hr. They are classified based on different factors like

product size and mechanism used. Based on the mechanism used crushers are of three types

namely Cone crusher, Jaw crusher and Impact crusher.

There are two types of Jaw crushers available in market.

a) Blake type Jaw Crusher

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b) Dodge type Jaw Crusher

Blake type Jaw crushers are again two types.

a) Single Toggle type

b) Double Toggle type

Fig1.1: Single-Toggle Jaw Crusher

Fig 1.2: Double-Toggle Jaw Crusher

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Fig1.3: Dodge Type Jaw Crusher

1.3 Major components of a Jaw Crusher

Major components of Jaw crushers have been shown below

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Fig1.4: Components of a Jaw Crusher.

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1.3.1 Crusher Frame or Main Frame

Crusher Frame is made of high welding. As a welding structure, it has been designed with

every care so as to ensure that it is capable of resistant to bending stress even when crushing

materials of extremely hard.

1.3.2 Jaw Stock:

Jaw Stock is also completely welded and has renewable bushes, Particular importance has

been given to jaw Stock of a design resistant to bending stresses. All jaw stocks are

provided with a renewable steel Alloy or manganese steel toggle grooves.

1.3.3 Jaw Crusher Pitman

The pitman is the main moving part in a jaw crusher. It forms the moving side of the jaw,

while the stationary or fixed jaw forms the other. It achieves its movement through the

eccentric machining of the flywheel shaft. This gives tremendous force to each stroke. As

an interesting aside the term "pitman" means "connecting rod", but in a jaw crusher it really

doesn't perform this function, which is it doesn't connect two things. Other mechanisms

called pitman such as linkages in car/truck steering systems actually do connect things.

Thus it appears this is just the name that was applied to this part. Pitman is made of high

quality steel plates and carefully stress relived after welding. The Pitman is fitted with two

renewable steel Alloy or manganese steel toggle grooves housings for the bearings are

accurately bored and faced to gauge.

1.3.4 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.

1.3.5 Jaw Crusher Fixed Jaw Face

The fixed jaw face is opposite the pitman face and is statically mounted. It is also covered

with a manganese jaw die. Manganese liners which protect the frame from wear; these

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include the main jaw plates covering the frame opposite the moving jaw, the moving jaw,

and the cheek plates which line the sides of the main frame within the crushing chamber.

1.3.6 Eccentric Jaw Crusher Input Shaft

The pitman is put in motion by the oscillation of an eccentric lobe on a shaft that goes

through the pitman's entire length. This movement might total only 1 1/2" but produces

substantial force to crush material. This force is also put on the shaft itself so they are

constructed with large dimensions and of hardened steel. The main shaft that rotates and

has a large flywheel mounted on each end. Its eccentric shape moves the moving jaw in

and out. Eccentric Shaft is machined out of Alloy Steel Fitted with anti-friction bearings

and is housed in pitman and dust proof housing.

1.3.7 Jaw Crusher Input Sheave/Flywheel

Rotational energy is fed into the jaw crusher eccentric shaft by means of a sheave pulley

which usually has multiple V-belt grooves. In addition to turning the pitman eccentric shaft

it usually has substantial mass to help maintain rotational inertia as the jaw crushes

material.

1.3.8 Toggle Plate Protecting the Jaw Crusher

The bottom of the pitman is supported by a reflex-curved piece of metal called the toggle

plate. It serves the purpose of allowing the bottom of the pitman to move up and down with

the motion of the eccentric shaft as well as serve as a safety mechanism for the entire jaw.

Should a piece of non-crushable material such as a steel loader tooth (sometimes called

"tramp iron") enter the jaw and be larger than the closed side setting it can't be crushed nor

pass through the jaw. In this case, the toggle plate will crush and prevent further damage.

1.3.9 Tension Rod Retaining Toggle Plate

Without the tension rod & spring the bottom of the pitman would just flop around as it isn't

connected to the toggle plate, rather just resting against it in the toggle seat. The tension

rod system tensions the pitman to the toggle plate. The toggle plate and seats. The toggle

plate provides a safety mechanism in case material goes into the crushing chamber that

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cannot be crusher. It is designed to fail before the jaw frame or shaft is damaged. The seats

are the fixed points where the toggle plate contacts the moving jaw and the main frame.

1.3.10 Jaw Crusher Sides Cheek Plates

The sides of the jaw crusher are logically called cheeks and they are also covered with

high-strength manganese steel plates for durability.

1.3.11 Jaw Crusher Eccentric Shaft Bearings

There are typically four bearings on the eccentric shaft: two on each side of the jaw frame

supporting the shaft and two at each end of the pitman. These bearings are typically roller

in style and usually have labyrinth seals and some are lubricated with an oil bath system.

Bearings that support the main shaft are normally spherical tapered roller bearings on an

overhead eccentric jaw crusher.

Anti-Friction Bearings are heavy duty double row self-aligned roller-bearings mounted in

the frame and pitmans are properly protected against the ingress of dust and any foreign

matter by carefully machined labyrinth seals. Crushing Jaws are castings of austenitic

manganese steel conforming to IS 276 grade I & II. The real faces of the crushing jaws are

levelled by surface grinding in order to ensure that they fit snugly on the crusher frame and

jaw stock. The crushing jaws are reversible to ensure uniform wear and tear of grooves.

1.3.12 Jaw Crusher Adjustment: Closed Side Opening Shims

Depending on the disposition of the material being crushed by the jaw different maximum

sized pieces of material may be required. This is achieved by adjusting the opening at the

bottom of the jaw, commonly referred to as the "closed side setting". Shims (sometimes

implemented and a more adjustable or hydraulic fashion) allow for this adjustment.

1.3 Working Principle of a Jaw Crusher

Jaw crushers are designed to impart an impact on a rock particle placed between an fixed

an moving plate (jaw). The faces of the plate are made of hardened steel .Both plates could

be flat or the fixed plate flat and the moving plate convex. The surfaces of both plates could

be plain or corrugated. The moving plate applies the force of impact on the particle held

against the stationary plate. Both plates are bolted on to a heavy block. The moving plate

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is pivoted at the top end (Blake Crusher) or at the bottom end (Dodge type crusher) and

connected to an eccentric shaft. In universal crushers the plates are pivoted in the middle

so that both the top and bottom ends can move.

The Blake crushers are single or double toggle drivers. The function of the toggle is to

move the pivoted jaw. The retrieving action of the jaw from its furthest end of travel is by

springs of small crushers or by a pitman for large crushers. As the reciprocating action

removes the moving jaw the broken rock particle slips down but are again caught by the

next movement of the swinging jaw and crushed. This process are repeated until the particle

size are smaller than the smallest opening between the crusher plate at the bottom of the

crushers(the closed set).For a smooth reciprocating action of the moving jaws, heavy fly

wheels are used in both type of crushers.

Fig1.5: Working of a Jaw Crusher.

Fig 1.5 shows a sketch of Blake crushers operated by double toggles and controlled by a

pitman. These are commonly used as primary crushers in the mineral industry. The size of

the feed opening is referred to as the gape. The opening at the discharged end of the jaws

is referred to as the set

The factors of importance in designing the size of primary crushers, like a jaw crushers are:

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Vertical height of crushers = 2 * Gape

Width of jaw > 1.3 * Gape (1.1)

< 3.0 * Gape (1.2)

Throw = 0.0502 (Gape)^0.85

where the crusher gape is in meters.

These dimensions vary as individual manufacturers have their own specification and their

catalogues are a good guide to the geometry and design of individual makers.

Crusher Size and Power Ratings

The size of jaw crushers is usually described by the gape and the width, expressed as gape

* width .The common crusher type, sixe and performance is summarized in Table 1.2.

Currently the dimension of the largest Blake type jaw crushers in use is 1600mm * 2514

mm with motor ratings of 250 – 300 kW. Crushers of this size are manufactured by

Locomo, Nordberg (Metso) and others. The Metso crushers are the C200 series having

dimensions 1600 * 2000 mm driven by a 400 kW motor.

Table1.1: Performance summarize of Jaw Crusher

For sizing a crushers and ancillaries for open circuit operations. Eqs (1.1) and (1.2) are

helpful as an approximation .From the equation it can be seen that once the gape has an

assigned value the rest of the dimension follows .To size the gape of the largest particle to

be charged is considered and the following relation applied :

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Largest particle size = 0.9 * Gape (1.3)

Jaw Crusher Operation

The ore or rock is feed to the crusher where the jaw are furthest apart i.e at the maximum

opening or gape. When the jaws come together the ore is ore is crushed into smaller size

and slip down the cavity. In the return stroke further eduction of size is experienced and

the ore moves down further. The process is repeated till particle have size less than the

bottom opening or set pass through a product.

The rule of thumb applicable for opening a jaw crusher with respect to it’s design

characteristics can be summerised as follows

Feed size = 0.8 - 0.9 * gape

Reduction ratio, R = 1:4 to 1:7

Throw Lt = 1 – 7 cm

Speed = 100 to 359 rpm

Freequency of stroke,v == 100 – 300 cycles per min

Length of stroke = 0.0502 * gape ^0.085

In practice the operator has to decide on the spacing of the set at the discharge end. This

setting has to include the maximum and minimum positions that the bottom has to open

during the oscillation of the bottom end of the jaw. The manufacturer of the jaw crusher

provides all the control to adjust the settings. The actual are best measured by taking a soft

metal, like lead or a ball of aluminum foil and squeezing it between the jaws at the desired

width forming a template. This piece of lead metal is used to check the change of setting

during operation.

During the operation of a crusher the bulk density of the material increases and the particle

size decreases. With time wear on the plate surfaces develop resulting in a change in the

crusher surface profile. This could alter the size and the throughput of the crusher product.

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The operation of the jaw crusher has been best described by Whiten. According to Whiten

if a certain particle size, d in the size distribution curve of a mineral (Fig 4.3) is less than

K1 then it would pass through uncrushed, Being smaller than the opening of the set. But

all particle size greater than K2 were smaller than the largest opening between the jaw of

the jaw crusher and therefore will always be crushed. The probability P of a particle being

crushed or not may be written as:

P(d) =0 for d< K1

P(d) = 1 for d> K2

P(d) = 1 – [K2−d

K2−K1]2 K1 < d <K2 (1.4)

The values of K1 and K2 are primarily function of the crushed set but also depend on the

throughput feed size and linear length and are determined statistically by regression

analysis of the operating data . Such relationships were initially determined by Lynch [12]

and later revised by Anderson [13] as :

K1 = a0 +a1 Lmin – a2Q + a3F80 + a4 Llinear

K2 = b0 ± b1 Lmin + b2Q + b3F80 – b4 tLinear + b5Lt

Where tLinear is the age of the linear in hours and Llinear is the liner length.

Or

K1 = 0.67 Lmin ± 1.956mm

K2 = 1.131 Lmin + 58.67 q + 25.4 T(t) ± 1.8 mm

Where q = the fraction > 25.4 mm in feed and

T(t) = an interpolating spline function of tonnage.

For a single feed , k1 and K2 can be obtained by size analysis. From a alarge number of

data the value of exponent of Eq (1.4) was found to closer to 2.3 [14]. This mathematical

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concept of jaw crusher operation has been developed for modeling and subsequent

throughput prediction from jaw crushers.

Fig 1.6 Particle size vs Probability of crushing particles in a Jaw Crusher (from Eq (1.4))

4.3. Jaw Crusher Capacity

Rhe capacity of jaw crushers is a measure of the mass and volume of crushed material

produced in unit time of operation . The capacity is primarily a function of :

Crusher design characteristics like width and depth of the crushing chamber.

Open and closed side settings

Options on feeding methods eg intermitted feeding,(manual or direct by haulage trucks)

and continuous by conveyor belt

Operating charecteristics like length of stroke , the number of strokes per minute, the nip

angle

Mathematically the capacity can be expressed by the general formulae:

Q = f ( w,L,Lmax,Lmin,Lt,n, θ,K)

Where Q = capacity

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w = width

L = height (or depth of jaws).

,Lmax = set maximum (Open Set)

Lmin = set minimum (Closed Set)

Lt = length of stroke or throw

n = frequency(Revolution rpm = cycles per unit time)

θ = jaw angle

K = constant related to machine characteristics.

The mechanism of movement of rocks down the crusher chamber determine the capacity

of jaw crushers. The movement can be visualized as a succession of wedges (jaw angles)

that reduce the size of particles progressively by compression until the the smaller particle

pass through the crushers in a continuous procession. The capacity of a jaw crusher per

unit time will therefore depend on the time taken for a particle to be crushed and dropped

through each successive wedge until they are discharged through the bottom. The

frequency of opening and closing of the jaws therefore exerts a significant action on

capacity.

Following the above concept several workers, like Herman [15], Gaudin[16], Taggart[17],

Rose and English[18] , Lynch[12], Broman[19] have attempted to establish mathematical

model determine the capacity.