Vibratory screen also commonly referred to as
For many years, the majority of vibratory separators had a rectangular or square design and employed a simple reciprocating movement to classify the powder.
During the early 1930's, machines that used gyratory motion, i.e. small circular orbital movements, were introduced. This then led to the use of circular screens, which offered a much better usage of screen area, and therefore an increased capacity per unit mesh area. Since then, in addition to the outward appearance of sieves evolving, there have been major advances in their component parts and in developing machines for specific applications and/or industries.
Most machines vibrate at 1400 rpm, but by separating the motor from the rubber suspension in this type of design, it became possible to increase the operating speed of the machines up to 2800 rpm with high out-of-balance forces.
This development led to increased efficiency of sieves, enabling smaller diameter machines to be used without adversely affecting performance. For example, a 22' diameter machine operating at 2800 rpm can significantly out-perform a 48' diameter machine operating at 1400 rpm on materials which are traditionally difficult to screen.
These smaller sized sieves are now one of the most widely used screening solutions across numerous industries. Companies appreciate having units with a small footprint as space requirements are often limited, but capacity levels must remain high to ensure there are not bottlenecks in the process which would compromise profitability. For example, many food manufacturers experience difficulty safely sieving bagged ingredients. Operators face significant strain when lifting sacks of ingredients to the sieves. Added to this is the fact that many ingredients, flour being the most common, create a lot of dust during the screening process. This not only causes discomfort for operators inhaling the dust, but it poses a safety risk as charged flour particles are volatile by nature and can cause explosions if not safely handled.
The sieving industry responded by offering vibratory sieves with low-level bag-tip stations, incorporated into the design of the machine, as well as dust hoods to contain airborne particles.
In recent years, a new development has been the launch of the Spiroscreen TM, a mesh frame designed with a spiral shaped ultrasonic element. For companies using screens 900mm in diameter and above, it can sometimes be difficult for the ultrasonic frequency to be evenly distributed across the entire mesh frame. The Spiroscreen effectively eliminates this problem by allowing the frequency to be dispersed across the whole surface, allowing for maximum sieving efficiency across the whole mesh area. This technology allows the use of one single resonator, transducer and Vibrasonic generator system to drive mesh frames up to 2m in diameter while maintaining even ultrasonic activity across the whole mesh frame.
Additionally, sizing of equipment is not done based on any simple mathematical formula. Many variables, including particle size, density, moisture content, temperature and space available, must be considered. Most suppliers will use product testing and/or past experience to specify the right size of machine for the application.
In conclusion, though vibratory sieves and separators might on the surface appear to be quite simple machines, they represent years of development, testing and research to ensure they meet the needs of dry bulk powder manufacturers. Any company concerned with the quality of their products should place vibratory sieves or separators high on their list of priorities.
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