Transcript JIGGING - Ranjit

JIGGING
Prepared By:Prabir Kumar
Roll No.254/08
Ravi Kumar
Roll No.497/08
INTRODUCTION
The jig, in one form or another, continues to hold
a leading place among the machines designed to
separate two or more minerals of different
specific gravities.
 It is simple in construction , easily operated,
capable of treating large quantities in a short
time, and highly efficient under various
conditions.
 It is macroscopic phenomena in which the
heavier and bigger particles concentrate at the
bed bottom while lighter and smaller particles
move to the upper part of the bed.

The basic construction of a jig is shown above.
Essentially it consists of an open tank, filled with a
fluid, with horizontal or slightly inclined jig
'screen' near the top upon which the particles are
supported, and through which the fluid flows in
alternating directions.
HISTORY OF JIGGING:The history of jigging likely goes back to antiquity, and the
phenomenon was undoubtedly known in Grecian times.
Very quickly humans learned that sizing and washing particles
of ores such as silver, lead, copper, and tin greatly facilitated
the sorting process. Soon thereafter it was likely learned that if
a wicker basket containing particles to be sized and washed
was jogged up and down in water, the heavy particles soon
congregated at the bottom and the light particles at the top.
This act of alternately fluidizing and collapsing a bed of
particles to concentrate the denser mineral on bottom is the
essence of jigging process.
PRINCIPLE OF OPERATION:Although jigging has been practiced for more over
1000 years, there is no one single theory that can
fully explain the process by which separation is
expected.
This is because it is very difficult to examine
exactly what take place in actual process of
practical jigging.
 The mechanism which have been postulated in
classical theories include :
(1)Differential acceleration
(2) Hindered Settling
(3) Interstitial trickling

DIFFERENTIAL ACCELERATION:
Differential acceleration of a particle is the initial
acceleration at the start of particle movement.
this acceleration is dependent only on the
relative density of the mineral and fluid. size of
the particle is not a factor.
HINDERED SETTLING:AFTER A SLIGHTLY LONGER TIME PARTICLES WILL
REACHED THEIR TERMINAL VELOCITY.
AS THE QUANTITY OF PARTICLES IN THE FLUID
INCREASES, THE EFFECT OF PARTICLES CROWDING
BECOMES APPARENT AND THE SETTLING RATE OF
THE PARTICLES DECREASE.
INTERSTITIAL TRICKLING:AT THE END OF A DOWNSTROKE,AS THE BED BEGINS
TO COMPACT, THE LARGER PARTICLES INTERLOCK,
WHILST THE SMALLER GRAINS MOVE DOWNWARDS
THROUGH THE INTERSTICES UNDER INFULENCE OF
GRAVITY.
SOME IMPORTANT POINTS ON JIGS: Very
fine material, less than (1/10) millimeter
in diameter, can be treated successfully on jigs.
For the treatment of fine stuff on jigs, close
sizing is a positive disadvantage.
 Bodies falling through water in a tube do not
attain as high a velocity as in falling through
the same medium in large vessels.
The falling velocity is the more retarded as the diameter
of the body approximates that of the tube.
 The size of the mesh of the jig-sieve has a very important
influence, and must be proportioned to the work to be
done.

 The
falling velocity is but little affected when the
diameter of the body is less than one-tenth that of
the tube.
PROCESS:The two chief reactions of jigging are pulsion and
suction. The reactions occurring during pulsion
and suction are the only reactions of jigging.
 Jigging cycles are said to consist of pulsion and
suction.
All jigs use pulsion , and most jigs
suction but the latter is avoided in some jigs.
Below some examples of jigging cycles shown:

JIGGING CYCLES:-
A
D
PULSION:-
The pulsion-reaction is by far
the most important one in the process of jigging.
In pulsion the fluid is moving upward with
respect to stationary reference point. During
this period, with sized grains of different
specific gravities, with proper pulsion-velocity,
the separation between them will be complete.
The size-limit is indicated by the hinderedsettling ratio
SUCTION:In suction, the fluid is moving downward with
respect to stationary reference point. Suction due
to the movement of water-columns supplements
gravity.
 Any advantage that the small heavy grain would
have over a large light one would, of course,
appear in the resultant tending to carry it to the
hutch.

TYPICAL HYDRAULIC JIGS
Hand jigs
 Hurz Jigs
 Fixed Pulsator Jigs
 Air Pulse Jigs
 Movable Sieve Jigs
 Pneumatic Jigs

HURZ JIG
The Hurz has a fixed sieve . Hurz jig are
usually built of wood, but construction
of concrete has been reported. They
are built of several compartment in a
series . The tailing from one
compartment passing as feed into next
compartment. The amplitude in the
jigging is greatest in the first cell and
least in last, so as to make concentrate
in the first compartment And middling
in the other compartment. Rising water
is added to compensate the excessive
suction either above or below the
plunger.
SCHEMATIC DIAGRAM FOR HARZ JIG
ADVANTAGES OF JIGS

For treatment of coal.
1) after the process of jigging they yield a dry
as well as wet finished products.
2) in treatment of course coal the moisture
drained readily, and dry product is used.
3) but in treatment of fine coal it needs wet
washed products.
4) its mixed treatment method, gives synthesis
a blend of suitable moisture content for best coke
making.
USES OF JIGS
Jigs are generally course mineral concentrating
devices.
In
coal washing ,pieces as course as 4 to 5 inches can
be washed in jigs.
In ore concentration pieces as course as 1 inch. Can be
treated.
Hydraulic jigs treat coal as fine as 1/8 inch and mineral
as fine as 20 mesh.
Pneumatics jigs can treat minerals as fine as 65 mesh,
as course as 1to 1.5 inches.
They retains a dominant position for the basification
of non magnetic iron ores, and for the many nonmettalics.
REFERENCES
 Investigation
on Jigging.
BY ROYAL PRESTON JARVIS
 Mineral
processing technology
By B.A. Wills
 Gravity
concentration technology
By Richard O. Burt
 Principles
of Mineral Dressing
By A.M. Gaudin
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