High-frequency vibrating screens
High frequency 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 200μm 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 differentiates it from a normal vibrating screen. The high frequency vibrating screens usually operates at an inclined angle, traditionally varying between 0 and 25 degrees and can go up to a maximum of 45 degrees. Besides, it should operate at a low stroke and has a frequency ranging from 1500 - 7200 RPM.
Pre-treatment of the feed is often required before the use of the high frequency screen as the apertures in the screen may become blocked easily.
High frequency screens have become more standardized and widely adopted in materials classification processes. It allows efficient cuts and fine separations, which can provide high purity and precise sizing control of the product (for sizes of fine particles up to 0.074-1.5mm). Common industrial applications include dewatering of materials, processing of powder in coal, ores and minerals, wood pelleting, fractionated reclaimed asphalt pavement, food, pharmaceutical and chemical industry. Fineness of the products and system capacities varies over a huge range between different models, to satisfy individual application requirements.
Most commonly, high frequency screens are used to separate "reclaimed" asphalt pavement (RAP) into multiple sizes and fractions, which allow producers to take full advantage of the recycled materials. RAP is a recycle material that is reused in new pavement construction; any recycled products are worth as much as what they replace. As compared to conventional screening methods which are limited to producing unacceptable sizes in the products, high frequency screens can produce more efficient sizing to obtain a finer product. Another advantage of using high frequency screens to recycle the reclaimed materials is the available aggregate and oil that can be reused, and reducing the amount of new material required. Therefore, the capital cost for the process is lowered while maintaining a high quality of the asphalt mixture. Moreover, high frequency screen applies intensive vibration directly onto the screen media, such high RPM allows asphalt pavement material to achieve a higher and separate at a faster rate.
In mineral processing such as ferrous metals ore (e.g. iron, tin, tungsten, tantalum etc.) and nonferrous metals ores (e.g. lead, zinc, gold, silver and industrial sand etc.), high frequency screens have a crucial role. After the ores get comminuted, high frequency screens such as Sepro-Sizetec Screens are used as a classifier which selects materials size that is small enough to enter the next stage for recovery. For example, the closed grinding circuit (e.g. recirculating network with ball mill). Firstly, it screens out the coarse particles and recirculates them back to the grinding mill machine. Then, the fine grain material will be unloaded timely, avoiding over crushing caused by re-grinding. The benefits of using high frequency screens in mineral processing can meet the requirement of fineness easily for recovery and is able to achieve a smaller size separation, reducing capacity needed for comminution stage and overall energy consumption. Hence, improving the grade of the final product and providing a better recovery and screening efficiency.
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