You want long life out of your screens, but what factors can affect their longevity? One of the most important things to check on a periodic basis is the shape of the screen’s vibratory motion.

In Figure 1, one can see and verify the shape of the vibratory motion: circular (A), elliptical (B) or even linear (C).

It is also possible to assess the amplitude of motion, as provided in Figure 2.

Let’s examine a few concepts related to amplitude:

The amplitude of vibration does not depend on the rotation of the vibrating mechanisms.

Amplitude combined with rotation imparts a certain amount of acceleration to the equipment, and that acceleration is responsible for the conveyance of the material.

The larger the material to be conveyed, the greater the vibration amplitude of the equipment should be.

{{image2-a:r-w:300}}There is an ideal relation between operating rotation, amplitude and the degree of inclination of the equipment, depending on the aperture of the mesh installed on the screens.

The nominal rotation is established observing the ideal operating conditions and, further, to ensure the equipment is operated safely below the vibrating structure’s critical frequency.

Operators are advised to never alter the rotation of vibrating equipment before checking with the relevant supplier’s equipment application area.

{{image3-a:r-w:300}}Changing the position of the moveable counterweight can alter the amplitude of vibration. Such adjustment is performed based on the application. The screening of coarse material demands higher amplitude than that required for the classification of fines.

Table 1 provides the recommended values for total displacement (twice the amplitude).

Figure 3 illustrates the adjustment levels of the vibratory mechanism of the V-100 series.

For other models of vibrating equipment (feeders, chutes, etc), operators should consult their manuals.

The higher the operating amplitude of vibrating equipment, the shorter the service life of the equipment’s bearings. Bearing service life will be satisfactory even if all available eccentric mass that was originally provided with the equipment is used.

{{image4-a:r-w:300}}Operators are advised to never utilise eccentric masses that are greater than those provided with the original equipment. This will lead to a considerable drop in the service life of the bearings, and a possible unbalancing of the vibrating equipment.

To precisely measure and analyse the dynamic performance of vibratory screens, Metso has developed the ScreenCheck kit, which includes numerous hand-held electronic testing devices featuring wireless electronic sensors and automated software.

The ScreenCheck devices can be fixed to the side of a screen and a number of tests performed, including orbit measurements, side displacement, structural movement and bump checks (the last with a mallet). These tests measure stroke, angle and peak Gs on the left and right corners of the screen (orbit measurement), the feed, mid and discharge data for the three screen shafts (side displacement), and the frequency spectrum for the spring mounts (structural movement and the mallet).

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