Presentation on theme: "JIGGING Prepared By:- Prabir Kumar Roll No.254/08 Ravi Kumar Roll No.497/08."— Presentation transcript:
JIGGING Prepared By:- Prabir Kumar Roll No.254/08 Ravi Kumar Roll No.497/08
I NTRODUCTION 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.
H ISTORY OF J IGGING :- 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.
P RINCIPLE OF O PERATION :- 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
D IFFERENTIAL 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.
H INDERED S ETTLING :- A FTER A SLIGHTLY LONGER TIME PARTICLES WILL REACHED THEIR TERMINAL VELOCITY. A S THE QUANTITY OF PARTICLES IN THE FLUID INCREASES, THE EFFECT OF PARTICLES CROWDING BECOMES APPARENT AND THE SETTLING RATE OF THE PARTICLES DECREASE.
I NTERSTITIAL T RICKLING :- A T 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.
S OME IMPORTANT POINTS ON J IGS :- 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.
P ROCESS :- 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:
P ULSION :- 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 hindered- settling ratio
S UCTION :- 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.
T YPICAL H YDRAULIC J IGS Hand jigs Hurz Jigs Fixed Pulsator Jigs Air Pulse Jigs Movable Sieve Jigs Pneumatic Jigs
H URZ 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.
A DVANTAGES 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 non- mettalics.
R EFERENCES 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