Monday, April 10, 2017

Jaw Crusher

Aim of the experiment: Crushing of ore using Jaw crusher.
Apparatus Required: Laboratory model Jaw Crusher, materials (for crushing), Vernier calipers.
Objective: To study the jaw crusher and measure the reduction ratio and capacity of the crusher.
Theory :“Crushing Process” is defined as the group of operation in a mineral dressing process whose object is to reduce large lumps to fragment.
“Crusher” is slow speed machines for coarse size reduction of large quantities of solids by using compressive force. The main significance of an ideal or grinder should: -
i.                     Have a large capacity.
ii.                   Require a small input per unit wet of production.
iii.                 Yield a product of single size or required size distribution.
Constructional Features of Jaw
 Crusher: The crusher mainly consists of:
1)      Frame 2) Fixed jaw plate 3) Left and right protecting boards 4) Movable jaw plate 5) Movable jaw 6) Eccentric shaft 7) Toggle plate 8) Toggle seat 9) Components and parts such as oil pressure lifter

The motor drives eccentric shaft via a belt fixed in a grooved pulley, which can make movable jaw move repeatedly so it can crush more material. Fixed jaw plate of frame front wall is fastened depending on left and right protecting boards and holding down bolts, while movable jaw plate is pressed tightly on movable jaw depending on battens. When the jaw plates are abraded (usually under side of the jaw Toggle plate) can not only bear the weight of movable jaw, but also protect other parts of the machine from hurting. When un-broken foreign materials come into crushing cavity which results in heavy load increase of toggle plate, the toggle plate breaks down itself to cut off the heavy load so as to protect other parts of the jaw crushers. Toggle seat is fastened on ear seat of the jaw crusher’s two sides by draw bolts; depend on hydraulic pressure lifter (lifting bolts) to lift out toggle seat, change pad thickness, and i.e. be able to adjust the width of discharge outlet. As the name suggest a jaw crusher has two jaws set to from a V shape at the top through which feed is admitted in to the jaws. One of the jaw is fixed to the main frame of the crusher almost vertically while the outer than the movable. The swinging jaw reciprocate in a horizontal plane and make an angle an 20-30 degree with the stationary jaw and is driven by an eccentric so as to that it applying a great compressive force on the ore lumps caught between the jaws. On the jaws, replaceable crushing faces are fixed by nut & bolt arrangement. The crushing faces are made from “Hardfiled Manganese” steels. When extensive wear is observed on any of the faces it is replaced by new one. The crushing jaw faces are flat. Initially the large lump is caught at the top and is broken materials drop to the bottom space (set). The jaw running speed vary from 100-400 rpm (100-400 times).
Jaw Crushers are basically in two types
(1) Blake jaw Crusher, (2) Dodge jaw Crusher

Blake jaw Crusher
The movable jaw is hinged at the top so that greatest amplitude of motion is at bottom of the crushing face.
Dodge jaw Crusher
The movable jaw is hinged at the bottom so that greatest amplitude of motion is at top of the crushing face.
Working Principle:
i.                    Before starting the experiment inspect the machine. Check the motor and gear drives.
ii.                  Set the jaw plate distance through using jaw plate moving handles. After setting of the jaw plates close the handles carefully.
iii.                Fill the raw material hopper before starting of crushing.
iv.                 After completion of primary preparation the start the motor.
v.                   Collect crushed material for the observation.

Observation Table:
Sample
weight
Max size of feed (mm)
Max size of product (mm)
Length of gap(mm)
Length of set(mm)
Time taken to crush (sec)
Weight of feed after crushing








Calculation
1.      Reduction Ratio: The reduction ratio of average feed size to the average product size is known as reduction ratio.

2.      Capacity: The capacity of the jaw crusher mainly depends on the length and width and width of receiving operation and the width of the discharge. As per target, the empirical formula for capacity of jaw crusher is,
T=0.6LS
Where T=T is the capacity tons per hour
 L= Length of receiving opening in inches.

S= Set or Width of discharge opening in inches

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