VIBRATING SCREENS

Vibrating screens are the most important screening machines primarily utilised in the mineral processing industry. They are used to separate feeds containing solid and crushed ores down to approximately 200 μm in size, and are applicable to both perfectly wetted and dried feed. The frequency of the screen is mainly controlled by an electromagnetic vibrator which is mounted above and directly connected to the screening surface. Its high-frequency characteristics differentiate it from a normal vibrating screen. High-frequency vibrating screens usually operate at an inclined angle, traditionally varying between 0° and 25° and can go up to a maximum of 45°. They should operate with a low stroke and have a frequency ranging from 1500 to 9000 RPM. Frequency in High frequency screen can be fixed or variable. Variable High Frequency screen is more versatile to tackle varied material condition like particle size distribution, moisture and have higher efficiency due to incremental increase in frequency. G force plays important role in determining specific screening capacity of screen in terms of TPH per sqm. G force increases exponentially with frequency.

Conventional and general design for a high frequency vibrating screen consists of mainframe, screen web, eccentric bock, electric motor, rub spring and coupler.The two most common types of vibrators which induce the high frequency vibrations are hydraulic or electric vibrators,these electric vibrators are either electric motors or solenoids.Common designs for screening decks are either single or double deck. In addition, another feature of high frequency vibrating screens are the static side plates which provide benefits such as smaller support structure, less noise, longer life, and hence less maintenance. In industry, the screens are operated at a tiled angle up till 40 º. The high frequency (1500 – 7200 rpm) and low amplitude (1.2 – 2.0 mm) characteristics leads to the vertical-elliptical movement that rapidly transports oversized particles down the screen.[9] Creating a thin bed of particles, this improves the efficiency and capacity of the screen.

Common industrial applications include dewatering of materials, processing of powder in coal, ores and minerals, wood pelleting, fractionated reclaimed asphalt pavement, od, pharmaceutical and chemical industry.