General Information to the Performance of External Vibrators

Since compacting is one of the main areas of application of the external vibrator, the following general information primarily focuses this area. Special details for other areas of application are found at their particular chapters.


Vibration equipments are constructed right when the maximum degree of rigidity is reached at a low weight. Low weight and high rigidity are not contradictory requirements when the reinforcement is built with appropriate ribbings. The table construction in figure 15 has a high ribbing (trapezoidal) to the middle. The outcome of this type of reinforcement is high rigidity and even distribution of the vibration to the whole surface. The construction is vibration rigid when the height h averages 1/4 – 1/5 of the length l.

External vibrator - right constrution of a vibration table
Fig.15: Right construction of a vibration table
External vibrator - wrong construction of a vibration table
Fig.16: Wrong construction of a vibration table

The greater the centrifugal force the higher the ribbing has to be. The size of a vibrating table is 1x1m; the ribbing is 8mm thick. The weight of such a model is approx. 90 kg. The table construction of figure 16 in contrast throughout the table has a too thin ribbing at a ribbing thickness of 14-16mm.The table at the same size of 1x1m has a weight of 130kg. The result is uneven distribution of the vibration to the table surface. At soft-mounting, because of lack of rigidity, a ››flattering‹‹ appears at the outer area or at hard-mounting more deflection appears at the mid area. Vibration differences of up to 200% appear (amplitude blow-up).

The general requirements to a vibrator equipment are:

  • high rigidity to obtain vibration stiffness
  • even distribution of vibration and avoidance of amplitude blow-ups.
  • Low weight to save vibration energy (Fc = m ⋅ a)

Vibration-isolated Mounting of the Vibration Equipment

Vibration equipments have to be mounted in such a way, that they can vibrate freely and no vibration is transmitted to the fundament and to the building.

For elastic-mounting rubber-metal-elements or in conveyor technique coil springs are used, too. The static load of the rubber-metal-elements should average 5-6kg/cm2 rubber surface. The dynamic load at short vibration periods e.g. at a shutterings of precast concrete parts can be disregarded. In practice rubber-metal-elements with a Shore-hardness of 55 Shore A have proved themselves for mounting of vibration equipment. It is crucial – especially for small vibration equipment – that rubbers with equal Shore hardness are used. 2 Gummifläche betragen. Die dynamische Belastung kann bei kurzen Rüttelzeiten, wie sie z.B. bei Schalungen von Betonfertigteilen üblich sind vernachlässigt werden. In der Praxis haben sich Gummi-Metall-Elemente mit einer Shore-Härte von 55 Shore A zur Lagerung von Rütteleinrichtungen bewährt. Wichtig ist, vor allem bei kleinen Rütteleinrichtungen, dass gleiche Shore-Härten verwendet werden.

In conveyor technique rubbers with Shore hardness of 40-45 Shore A are used.

40 Shore A e.g. means ››soft‹‹, and 75 Shore A means ››hard‹‹. The meaning of elastic mounting in no means should be underestimated since all the previous considerations apply only at a functioning vibration-isolation.

The elastic mounting is a basic requirement for the function of a vibration equipment.

Since at laying out of vibration equipments above all there is operated with approximate formulas and values, based on experience, the adjustment prior to commissioning is particularly important.

  • current consumption
  • vibration amplitud
  • temperature

From the current consumption can be concluded the efficacy of the vibrator, type, and condition of the shuttering, it’s reinforcement, and as well as bolted and welded connections. By the vibration amplitude it is possible to find out, where reinforcers are necessary. The temperature (measured at the intermediate bearing) is an indicator of performance of the motor. A certain operating temperature (instruction manual) has not to be passed over.

Measurement of Current Consumption

At right construction of the vibration equipment and right dimensioned external vibrators, the current consumption of the external vibrator lies about at the same height as its nominal current. If the power consumption is way below the associated nominal current, the vibration equipment is too heavy. In this case the centrifugal force can be increased.Is the power consumption on the other hand greater than the nominal current, two factors could be the reason: The chosen centrifugal force is either too high. At this case either it has to be decreased or a smaller vibrator with smaller centrifugal force has to be mounted. Or the reason is lack of rigidity. At this case additional reinforcers have to be added.

Measurement of the Vibration Amplitude

For measurement of the vibration amplitude oscillographs qualify best. The vibration amplitude at all places of the equipment should be about the same. Table 3 lets detect if the intended vibration amplitude is reached.

Synch-ronous speed 1/min Vibration amplitude s in mms=
(at values within parentheses there is a risk of form breakage and cracks)
750 6,5 9,7 12,9 16,2 19,5 (25,9)
1000 3,6 5,5 7,3 9,1 10,9 (14,6) (18,2)
1500 1,6 2,4 3,2 4,0 4,9 (6,5) (8,1) (12,2) (4,1)
3000 0,41 0,61 0,81 1,0 1,2 1,6 2,0 (3,0) (2,81)
3600 0,28 0,42 0,56 0,70 0,84 1,1 1,4 (2,1) 1,25
5400 0,13 0,19 0,25 0,31 0,38 0,5 0,63 0,94 1,0 1,1
6000 0,1 0,15 0,2 0,25 0,3 0,4 0,5 0,76 0,45 0,78
9000 0,045 0,068 0,09 0,11 0,13 0,18 0,22 0,34 0,31 0,63
10800 0,03 0,047 0,06 0,078 0,094 0,125 0,156 0,234 0,253
12000 0,038 0,05 0,063 0,076 0,1 0,127 0,19
a* 20 30 40 50 60 80 100 150 200 500
*a: acceleration in m/s2
Table 3: Detection of a and/or s at familiar synchronous speed

Further Measures

Further measures, which in practice can bring vibration outcome improvement:

  • change of the direction of rotation
  • change of location of installation (turning, moving)
  • stiffening of the vibration equipment with additional reinforcement profiles
  • the use of softer rubber-metal-elements (mounting)