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VIB

OSCILLATIONS LIBRES

SCREENS ACTUATED BY: VIBRATING MOTOR OR ECCENTRIC MASS

VIB technology can be applied to produce oscillating suspensions for vibrating screens actuated by “on board” eccentric rotating masses (example: vibrating motors). In order to produce a vibrating screen where vibrations move uniformly the material along the chute, the vibrating channel must be as rigid as possible and, if necessary, with reinforcing ribs into the direction where the force is applied. Excitation force applied is generally between 45° and 60° compared to the feed plane and is the result of two eccentric masses rotating synchronously. One vibrating motoris provides vibrating forces along all directions at 360° (fig.1) while two syncrophased vibrating motors with opposite rotation direction produce one harmonic vibration only, whose direction is perpendicular to the application plane of the two motors (fig. 2). The straight line of the excitation force must fall in the centre of gravity of the channel. The rotation velocities of the masses must range from 750 and 3000 rounds/min in order to avoid any excessive unbalances. Oscillating mountings made with VIB technology, thank to their natural rubber inserts, allow to generate harmonic vibrations all along the vibrating plane, avoiding their propagation to the fix structure of the plant. VIB oscillating elements have no metal parts in touch and this allow toinsulate from electrostatic charges, which may be induced by friction while the material is being conveyed.

System with one vibrating motor

These systems can be used for charghing and discharging chutes, hoppers and vibrating tables, to help the smooth movement of the material avoiding any accumulations during transportation. They are also ideal to realize inclined screens (fig.3)

Key:

1: Loading hopper

2: Oscillating feed plane

3: Oscillating mounting VIB type DE R

4: Vibrating motor

System with two vibrating motors

This system is used to produce conveyors, separators, screens, calibrators, feeders, etc. (fig. 4). The sense of rotation of vibrating motors must be opposite and their straight line must pass by the centre of gravity of the machine.

Key:

1: Loading hopper

2: Oscillating feed plane

3: Oscillating mounting VIB type DE R

4: Vibrating motors

CALCULATION SYSTEMS AND FORMULA

(with two on board vibrating motors)

It is essential to know the total weight of the oscillating mass in order to select the appropriate size of the VIB oscillating mount. The oscillating mass is the sum of the weight of the chute and the weight of the vibrating motor plus approximately 20% of the weight of the carried material. Once this value has been defined, divide it by the number of suspensions that you need to use. You should be well aware that VIB suspensions performance depends on the precise distribution of the load on each suspension. Generally, vibrating screens with “on board” vibrating motors, these are mounted over the channel on the unloading section (fig. 5) or under the channel on the loading section (fig. 6). This however causes a shift of the centre of gravity. As a consequence, you should use 6 supports (4 in the front and 2 in the rear for the configuration of figure 5, or 4 in the rear and 2 in the front for the configuration of figure 6) ensuring that they are equally charged with the same load.

Nomenclature

Main calculation formula

Theoretical velocity graph

This graph can be used to determine the theoretical feed velocity of the material in a conveyor with two on board vibrating motors which are positioned at 45° compared the sliding plane. The real feed speed Vr depends on the type of product being carried. Real velocity Vr is given by the relation: Vr = Va · λ Where λ is the coefficient of reduction generated by the cohesion which depends on the type of material to be carried.

Carried product type

λ

Carried product type

λ

Gravel

0,95

Wood chips

0,75

Sand

0,70

Leaf vegetable

0,70

Coal (small granulometry)

0,80

Sugar

0,85

Coal (coarse granulometry)

0,85

Salt

0,95

CALCULATION EXAMPLE

Calculation of the real feed velocity of the material on a leaf vegetable conveyor actuated by two on board vibrating motors and elastic suspension VIB DE R.

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