Applications of Sieving

A single sieve may provide a straightforward classification (or gradation) of particles where a clear threshold is desired. Crushing operations typically seek to ensure that all particles are below such a threshold and sieves provide a convenient means of doing so. However, in some operations it is equally important to remove particles less than a given size. The first case is referred to as scalping (removing oversize particles) while the second case is referred to as removal of fines. Sometimes it is desirable to do both. Thus, it can be useful to employ a set (or nest) of sieves varying in aperture size. Unsorted particles are applied to the topmost sieve and agitation begun. As the particles sort, smaller ones pass through from upper sieves to lower ones. This cascade of particle sorting continues as the smallest particles only gradually make their way past the smallest sieve.

A nest of sieves with a sufficient variation in aperture sizes may be used to construct a particle size distribution. Such distribution may in turn be used to describe the behaviour of the material under study. A particle size distribution obtained in this way should recognize that the errors associated with the top sieve (the coarsest fraction) may be different from the errors associated with the bottom sieve (the finest fraction). This occurs in part due to differing opportunity times for the particles to pass through the sieve that they are ultimately retained upon.

A third application of sieving is the use of sieving curves to develop a morphological characterization of the material being screened. Sieving curves represent the time dependence of the sieving process and are discussed in more detail in a later section. The goal is to infer particle shape or other morphological features (e.g. agglomeration) from the speed with which sieving proceeds. Unfortunately, these techniques are still in the developmental stages.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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