Lesson 1/Learning Event 2
FIGURE 3. MECHANICAL VIBRATING SCREEN BOX
Capacity. Capacity is the rate in tons per hour at which a screen produces (passes) the material
desired. The capacity of a screen is not the total amount of material that can be fed and passed over the surface,
but the rate at which it separates desired material from the feed.
Feeding Materials to Screens. Care must be taken to spread the flow of material evenly across the full
width of the screen. The thickness of the bed of feed material should be approximately four times the screen
opening size. If this is exceeded, the screen will be overloaded, the vibrations dampened, and the finer particles
will be unable to find their way to the screen wire openings. If, on the other hand, insufficient material is fed, the
total capacity of the screen is not being used.
Variable Factors. There are numerous factors that will affect the performance of screens. Some
examples of these are shape, weight, and gradation of particles, degree of inclination and vibration, type of wire
screen cloth, position of the screen within the deck, and wet screening (washing). Experience and testing have
proven that the effects of the most significant of these can be calculated, and an accurate estimate of actual screen
capacity can be made. Since these factors will differ, the capacity of each screen must be calculated separately.
These instructions will be given in Lesson 2.
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