Size Separation

Particle size is usually defined as the narrowest regular aperture through which mineral practice can pass through. By the help of this applicable to polyhedrons, it is not valid for the shape narrow particle. It determine by

1. Microscopic Measurements
2. Sieve Analysis.

Sieve Analysis 

This is the most important method of sizing the mineral particle. This is widely used to determine the crushing and grinding efficiencies and used as a yard stick for assessing the fineness of a ground product.

Laboratory sizing 

As the processes are diffusion control the particle size plays a very important role during different unit processes rapid and efficiently working of roaster, smelter, froth flotation and leaching tanks, largely depends on the size of the benification ore. These are several methods of the size analysis.

1. Sieve analysis
2. Classification
3. Microscopy

Sieve or Screen Analysis

Screen analysis is the method of the calculate out the avg. size of the crushed product. The product from jaw crusher or any other machine us hardly of uniform size. In fact the product consist of particles of different sizes which is difficult to known the each size. For this reason an average size of the product is found out by sieve analysis method.
Laboratory sizing analysis in size separation
Laboratory sizing analysis summery

Average size of the particle is calculated out basing on previous standard opening and the opening of the screen on which the weight is retained

The avg. Size =  (Previous aperture size + present aperture) / 2

Weight retained : This is the percentages of weight retained on a particular screen basing on the original weight of sample.

Cumulative weight percentage retained :
● It on a particular screen means what would the total weight that would be retained on the screen if there would have been no other screen above it during the screen analysis.
Laboratory screen opening
Screen opening

● As the screen arrange in descending order, the cumulative weight retaining on a particular screen would be the addition of all individual weight. This analysis carried out in a RO - tap sieves shaker.

Industrial Screening

The screening has been discussed only on a small or labrolabor scale but for the industrial need, this is done in a much large scale, thus that is called industrial screening. It affecting such processes.
Screening surface : parallel rods, punched plate and woven wire.

Parallel rods : These surface are usually of steel bars, steel rails, cast iron or wood.

Punched plats : These are steel sheets punched by dies in varrious pattern like circular, square or slots.

Woven wires : These are woven by gauged wires like steel, bronze, copper and Monel metals.

Mechanism of Screening :

1. The absolute size of the screen openings.
2. The relative size of the particle to that of opening through which it must pass.
3. The percentage of open area available on the screening surface.
4. The angle at which particle strick the screening surface.
5. The speed with which the particle strike the screening surface.
6. The moisture content of the material to be screened.
7. The opportunity offered to each particle to hit the screening surface.

Type of Screens :

 1. Stationary          2. Moving
Again moving screen are
Moving grizzlies ----- Trommels
Vibrating --------------- Shaking Screen.

Operating characteristics of screens

1. Capacity
2. Efficiency
3. Operating cost.

Capacity : 

1.The area of the screening surface
2. The size of the opening
3. Characteristic of the ore such as Specific gravity moisture contents, temperature, proportion of fines.
4. Type screening mechanism used.
Industrial screening
Industrial screening

Screening Efficiency : 

It is difficult to quantify the screen efficiency. According to mechanical engineering efficiency is defined as the ratio of energy output to the energy input perform a particular work.

● Screen efficiency defined here a mesurme of effectiveness of a screening operation as compared to a perfect screening operation.

              E = 10,000 u/vf.

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