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This article describes screening of fine granular materials, including minerals. The first part of the study presents a description of screening and an analysis of resulting conclusions. The second part describes screens that have been developed in Lodz Technical University labs. From a number of screens only three have been chosen and described in this article. Additionally, results of some pilot-plant-scale tests involving these screens made at Lodz Technical University are discussed. Experimental tests covered first motion of the sieves, and then the process of screening on these sieves. Results are presented both in a graphic form as diagrams and in the analytical form as correlations.

This paper addresses the process of sieve holes blocking taking place while screening fine-particulate materials and provides an analytical description of the phenomenon. Empirical tests performed as part of this research provided dependences specifying the parameters of sieve holes blocking that could be applied in practice. The process of sieve holes blocking is unfavourable and inevitable. It is related with the screen clearance coefficient which is one of the fundamental characteristics of all screens. The grains whose dimensions are similar to the dimensions of the sieve holes block those holes, causing their exclusion from the active surface area of the screen. This phenomenon results in diminished performance and efficiency of the screening process. Screening is a very common industrial practice, and various designs of screens and types of sieves are available. That is why the subject of this paper is so important. The screen blocking coefficient is the measure of sieve holes blocking. In order to describe the process of screen blocking, a mathematical model is presented and a method for determining the screen blocking coefficient is proposed. Furthermore, the authors list the factors that have a significant influence on the degree of sieve holes blocking, i.e. the shape of the screened material, the toss indicator and the content of hard-to-screen grains in the feed. This paper is the first one to have thoroughly described the issue of screen blocking. B Lawinska Katarzyna

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