screener

ORE SEPARATION BY SCREENING

Objectives:

One of the main reasons for the processing of minerals is to reach maximum value production of raw materials. There may be several goals in the processing of minerals, this may include a crushed product of a predetermined size and shape, or achieving the maximum recovery of metals from a very complex ore.

Originally, this mineral purity, whether metallic or industrial, indicates the value and price of minerals. All minerals are free to separate from each other, where at the first liberation by reducing size and size control has performed. Different methods can be used to separated minerals, most of which are selected according to the properties of the individual minerals.

1.0 Introduction:

Practice Using granular grinding ore material and separating it in specified and different sizes with specified particle size is called just screening and in a full name we call it mechanical screening. This process is called size control.

 In fact, this is a size control process that helps us to better understand the process of separating solids into two or more other products based on size. We can also use optimal measurement or size control methods to improve the results related to the capacity, size and shape of the particles.

 Therefore, it can easily be claimed that one of the very necessary step in the processing of minerals is Sizing or Ore Sorting. The sorting of minerals is that the separation method.

The process of separation is the same as separating the ore in its different constituent parts. Separation of ore today is used in many industries like industrial mineral mines, diamond mines, underground mines or precious metal mines and expensive mines.

For this purpose, the separation of ore in order to increase the efficiency of the purification or refining process is arranged by reducing the amount of material required for processing and increasing their purity significantly.

2.0 Size control:

To be able to get the right size for the final products, you cannot count on crusher or grinding mills because they are both not accurate enough.

The reason for this is the variety in mineral crystal compounds (hard-soft, abrasive – nonabrasive), in design and in the operation of the equipment. For this reason, the size control is used to improve size reduction in the process steps and in the final products.

3.0 Theory of Screening:

By screening, we can separated smaller particles from a granular substance particle when they are smaller than screen and separate small particle from larger particles. This is a complicated task, and it does not seem as simple as it sound and it is difficulties compound as the opening becomes smaller.

For example, if a sample of crushed ore contains 50% of the weight of particles smaller than 1.8 on a static test sieves, very small amounts of small pieces of small size remain on the screen and only trickle particles pass through it.

But when the minus 1/8 particles begin to pass through the screen, that the sieve subjected in some kind of reciprocating, motion or gyratory in the horizontally way or shake such a reciprocating motion, which includes vertical and horizontal movements. This will continue until it reaches a reduction rate, and until all particles are separated to a certain size

 The shaking duration time of the sieve in order to reach this stage must be roughly proportional to the size of sample placed on the test sieve1, which the depth of the static material bed have to determines before the performing the shake.

3.1 Controlling factors of Screening:

The graph below shows the controlling factors for screening operations in mineral processing.

3.2 Particle size distribution

For many reasons, it is necessary to control the particle size distribution in a mineral processing plant. These reasons can be for any of the following reasons:

• In order to enable standardized materials to bypass from grinding or crushing circuit, and subsequently returning larger particles to perform particle size reduction operations to reach standard size
• In order to provide optimum particle size materials to achieve efficient processing in downstream and separation systems
• In order to provide a product that is proportional to the size of the particle size needed base on market needs.

Generally, either by screening or by using the classification of particle separation work is done on a size basis.

3.4 Particle Sizes and the Mesh Numbers:

4.0 Mechanical screening method:

A mechanical screening, generally known only as a screening, is one of the methods for separating materials using granulated ore materials, which disassociate materials in different amounts and in different particle sizes. Mechanical screening is used in a variety of industries, the most important of which can be mining and mineral, agriculture, food, recycling, pharmaceuticals, plastics, etc.

4.1 Types of mechanical screening:

In general, different types of mechanical screening equipment are used in various industries to separate materials. Often the difference between this types of screening is due to the movement of the device through the motor drive.

• Circle-throw vibrating equipment: This kind of mechanical screening works with an eccentric shaft that makes the shaker frame lurch at a given angle.
• Circle-throw vibrating equipment: This kind of mechanical screening works by using vibrating gear and a shaker and set of shaker where the drive movement the whole structure. At first, the structure extends to the maximum throw or length, and then reaches a base state.

Under the structure, there is a pattern of springs, where shaking and shock absorption are high and as the structure reaches the base state. Typically, this kind of mechanical screening with this type of structure is used for materials or particles at a very large size, sizes that measure the size of the pebble size to the boulder material.

• Vibratory equipment with high friction: In this type of screening, the screen is applied only on the cloth. Unlike the screening methods described above, the frame of the equipment is quite stable and only vibration is generated on the screen.
  • Gyratory equipment: This type of mechanical screening is very different with the above methods. In fact, in this type of machine gyrates there is a circular motion at a level near the surface at a low angle.
• Trommel screens: This screening method does not require shaking and the materials are fed to a horizontal rotating drum with screening panels around the drum diameter.

5.0 Screening:

A screening in a simple configuration has a level of hard perforated with a matrix of fixed dimension apertures. Materials are sent to the screening surface in such a way that materials of appropriate size fall from the aperture to the screen and the larger particles move to the end of the screen to evacuate.

Screening is usually less than 0.5 mm. It uses two screening work processes: screening using free fall and screening by stratification.

1. a) Screening by stratification

In this way, a screen deck is created for materials bed, when the screening device starts to move, internal friction in materials is reduced and materials are stratified. This means that materials with finer particles or, with the right size, can pass through the particles of the larger ones and giving a sharp separation.

1. b) Screening by free fall

If our method is to classify the double inclination method (from 10-15 to 20-30 degrees), we use a free fall screening method. It means that no particle will be placed on the screen deck. In this method, the particles are measured directly through the screening media, which means they will have higher capacity (or a compact set), but the sharpness of separation will be less. This method is optimal when a large amount of fines is to be removed soon.

We said that screening is often done using a mechanical screening method. But there are several types of screening.

5.1 Types of Screen Media:

Care should be taken when selecting the screen for its correct size and the type of screen. In addition, screening media selection is also very important. Therefore, it is important to be careful when selecting two correct aperture factors related to the cut size and also the function of the screen wearer in selecting the correct screen.

 Generally today various types of screening media are produced and sent to the market that use different materials in their production. But the two most common types of screen media media available on the market are tensioned and modular.

1. a) Woven wire cloth :

Stainless steel is commonly used to produce Woven wire cloth. Woven wire cloth is used as a filtration medium for screening, and may vary depending on the industry, which has caused a wide range of Woven wire cloth in the industry.

1. b) Perforated & Punch Plate :

Perforated plates or punch plates are mainly used in crushing or screening plants on scalable vibration screens and after crude crops pass through grizzly bar. Punching plates are likely to be mounted on a tensioned deck, which results in very high wear and long life of the punch plates for high pressure applications and high flow of materials.

1. c) Artificial or Synthetic screening media (mainly rubber or polyurethane)

Artificial or rubber screening media are used in places where the subject of wear is of great importance. Typically, this type of screening media is used in large quarries and mines or any other large producers, which minimizes the repetition of the line of production to repair the screen deck.

 Whereas rubber is used as a high-impact screen media material for screening and is usually mounted on top deck of the screening scalper.

1. d) Self-Cleaning Screen Media :

The reason for the unveiling and engineering of the self-cleaning screen media was initially to clean up the screen cloth blinding and clogging and pegging problems. The idea was to put the crimped wires together, side by side on a flat surface, create openings and then somehow place them together on the support bars (crown bars or bucker bars). This could lead to the wires being loosened and free for vibration between the support bars, preventing blinding, clogging and pegging of the cloth

5.2 types of Screen

Although screening samples are numerous and varied, we can generally classify them into four types.

More than 80 percent of the screenings used worldwide are of type single inclination, stratification screens. Double, triple, or multiple inclination are other types of screening. However, in some specific applications screening may be considered a combination of stratification and free fall.