Enarco VET Manuel D'instructions page 32

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Formula for calculating the necessary centrifugal force:
A: Weight of mould / form (kg)
B: Weight of concrete (kg)
en
C: Constant dependent on the consistency of the concrete
C = 0.5 for walls, beams,
2. Vibrating Tables
Vibrating tables are used for prefabricating various concrete parts, such as beams, piles, slabs, etc.
Vibrating tables can also be used like casting moulds for compacting granular materials or other powdery
materials. In this way it is possible to expel the air trapped inside.
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Formula for calculating the necessary centrifugal force:
Centrifugal force:
MONO-PHASE AND THREE-PHASE EXTERNAL VIBRATORS
VET VEM
14
As a general principle this means choosing vibrators whose centrifugal force (in Kg) is 1.5 times
the weight of the mould.
It is recommended to use a greater number of vibrators distributed over the mould even though
the centrifugal force could be achieved with a lower number.
The distance between vibrators should be between 1.5 and 2.5m.
The effect of the vibrator reaches a maximum depth of 30cm, so vibrators should be positioned
on both sides of the mould where the thickness makes this necessary.
The vibrators can be regulated, and it is advisable to regulate the force until the optimal
vibration is attained.
The vibrator should always be chosen so as not to have to work at a maximum level.
In certain types of structure it is recommended to combine external with internal vibration.
External vibrators should be positioned on the ribs of the mould used for the prefabrication. The
centrifugal force required depends on the size and shape of the prefabricated unit and on the
mass of the concrete.
Centrifugal force F = C(A+0.2B)
C = 0.5 – 1 for horizontal prefabrications,
Vibrating tables consist of a rigid base that rests on an elastic element (springs or absorbers).
The vibrators are rigidly attached to the base.
Accelerations of between 2 and 4g should be applied to the table depending upon the type of
vibration taking place.
A further application of vibrating tables is for fatigue-testing machinery.
1. If just one vibrator is placed at the vibrating table's centre of gravity, a circular vibration will be
produced.
2. If two identical vibrators are placed equidistant from the centre of gravity and rotating in
different directions, they will produce a linear vibratory movement.
Unattached mould:
C = 1.5 for vertical piping
F = C(D+0.2B+0.2A)