Lesson 1/Learning Event 2
Expedient Screen Manipulation. In certain aggregate producing operations gradation specifications are stringent
and equipment processing capability is limited. In these situations it is difficult to produce material size ranges
that will fall entirely within the limits of specifications. After every crusher adjustment and screen size selection
possibility has been exhausted, gradation of the product can be influenced to a certain extent by an expedient
means. Damming and splitting are the two expedient means available.
Damming: One or more lengths of chain may be secured to extend on top of the screen surface at 90
degrees to the flow of material (Figure 4). This will create a damming effect, retarding material flow, and keeping
the particles exposed to the screen openings longer. This ensures that the maximum of the upper sized particles is
obtained. The result is a greater proportion of larger sized particles to fines in the product.
FIGURE 4. DAMMING
Splitting: A screen section with somewhat smaller openings can be installed in the lower end of the
screen box (Figure 5). In this case, the smaller particle size will pass either section of the screen readily, while the
screen area that will pass the larger sized particles has been reduced by one-half. This will result in a greater
proportion of fine particles to coarse in the product.
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