Screening is the process by which granulated ore material gets separated into different grades of particle size. In other words, it’s a mechanical process that stratifies (divides) particles according to required size. Once particles have been divided, the surface opening then accepts or rejects the particles.
A “Screen Plant” can be simply defined as a machine with surfaces that are used to classify materials by size. For example – In a mining process, it is a type of machine used to extract ores from the ground using water and sedimentation processing.
They are designed to provide high-capacities, in various industries ensuring optimum productivity of your production process at a low maintenance cost.
The following are the key factors you must consider for your plant:
- Size and type of material
- Application and use of the crushed material
As explained above, the most common application is to separate a conglomerate of materials into different size fractions. Other popular uses are dewatering, scalping, dedusting, and washing.
They form an essential stage of any mechanical process and are used in a range of industries including mining and mineral processing, agriculture, pharmaceutical, food, plastics, and recycling.
Let us now understand how this machine works. It has an inbuilt drive that induces vibration and a media that helps in particle separation. There is a deck which holds the media and the drive and is basically the mode of transport for the vibration.
A simple example is of a single deck with an inclined frame. This inclined frame is mounted on springs. When the vibration is generated from an unbalanced flywheel it results in a very erratic motion which is developed due to the rotation of the wheel. This type of will typically be used in smaller operations and rock quarries where sizing is not the key consideration. Free fall is based on the theory of free fall of the material through and over the Deck i.e. in this way no particle layer will build up on its deck.
There are various physical factors that affect the process. For example, vibration, g force, bed density, and material shape. Sticking and Plugging can be caused due to water attraction. Further, Electrostatic forces can also affect efficiency. Very dry material can also generate a charge that causes it to attract to the screen itself.
Common Vibrating Applications
Various kinds and their applications are mentioned below:
Scalping: When a feed is mostly finer, this type is used to remove a small amount of oversize without taking into account crushed product sizes.
Sizing (Dry and wet): When there is a need to produce material sizes that meet requirements in particular range of sizes, they are used. They mostly operate at high and constant rate of efficiency.
Washing: These are built to facilitate water usage wherein water can be sprayed on the material. Usually water is used to clean material and /or assist in the sizing as well.
Dewatering: These are simply used to remove liquid from material Rescreen (Dry and wet): Often, material still have contaminants. They are used to remove contaminants from already screened material.
Screens are classified on the basis on pattern into Horizontal, Circular, Inclined and Rotary. They are further explained as below:
Horizontal: These vibrate back and forth facilitating removal of larger ores by this vibratory movement. Thesey have a huck bolted construction and power is generated through timed shafts with eccentric counterweights. Ideal for wet washing or low head operations.
Circular: These types are also called circular-motion vibrating screens. They are commonly used to classify medium to coarse-grained bulk materials (5.0 mm to 100 mm). They operate using indirect excitation of the mesh. Because of unbalanced massed, there is a circular vibrating motion. For a specific transport speed, the circular vibrating system may be tilted at different angles. However, the optimum angle has been 15° to 30° usually used in practice.
Inclined: It’s a single deck which is put on an inclined frame and uses gravity to help move material downwards and a circular stroke helps to classify the material for further sizing. The frame is mounted on springs. The vibrations is generated from an unbalanced flywheel. They are commonly used for crushing rocks, sand and gravel; recycling; ore processing; wet screening and for the chemical industry.
Rotary: A common usage is the separation of solid pollution in wastewater. They are equipped with a slot tube, which are rods in axial direction of the tube. Owing to the gravitational force, water falls on the slot tube and passes through slots. The solid material that does not fit the slot is a residual which is on the exterior of the rotating slot tube and it is scrapped and falls down in a container. Finally, treated water, flows out from the lower part of the rotary screen. It is commonly used in food-processing industry such as meat-processing factories, slaughterhouses, dairy works, canning factories etc.
In simple words, a Wash plant is defined as a plant where slimes are removed from relatively coarse ore by washing, tumbling, or scrubbing.
Nowadays, Portable crushing & screening plants are commonly used for rock crushing in quarries and mines. They are more efficient in terms of time and resources, since they can quickly move with ease around the jobsite by remote control features and can be moved from one location to another as well.
With screeners, there are several other terms which are frequently used such as blinding, contamination, frequency, amplitude, and others which describe the basic characteristics. They feature further define the overall process of dry or wet screening.
As also mentioned earlier, the way a deck is vibrated differentiates screens. Different types of motion have their advantages and disadvantages. In addition, media types also have their different properties that lead to advantages and disadvantages.
Finally, there are problems and challenges associated. Efficiency is often affected by tearing, contamination, blinding, and dampening.
Leading manufacturers of screeners include MCcloskey, Masaba, Kleemann, Nordberg, Sweco, Terex, Metso (Allis Chalmers), Sandvik, Telsmith, Deister, JOST and Derrick. However, a thorough research of the plant which suits your process is essential before buying one.
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- Rotary Screen: Savona Equipment