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Basics

Selecting a Vibrator

The acceleration available for moving the respective bulk material or component is determined by the centrifigual force of the vibrator. The frequency and amplitude of vibration are also essential to success of the vibrator application. The general rule is: the aceleration ,and hence the centrifugal force, must be high enough to produce the required movement. For chutes, slides, vibrating plates, sieves and filters, approx. 3-5 times greater centrifugal forces are required, since the combined mass must be moved. Adequate vibration amplitude must also be ensured. In such cases, only 20% of the mass of the bulk material being carried goes into the calculation.

For silos and hoppers, approx. 20% (a ratio of 1:5) of the weight in the conical section is sufficient (ie. for 100 kg bulk material in the conical section, a centrifugal force of 200 N). The hopper is not moved as a whole, but  the metal panels are subjected to an undulating vibration via the reinforcements.

Further criteria for the centrifugal force are angle of inclination and wall thickness. In difficult cases it is possible to go up to ratios of 1:1 using high frequency vibrators. These produce very short waves with a low vibration amplitude, which gives rise to elastic and not plastic deformation. The danger of fatigue fractures occurring can thereby be drastically reduced or eliminated.

It follows that low frequency vibrators, eg. electric vibrators (up to 1500 min-1) and knockers (type NTK) are preferable for conveying and shaking applications. Higher frequency vibrators, eg. electric vibrators (up to 3000 min-1 or more) and linear vibrators (types NTS and NTP) are better suited for compacting and emptying hoppers.

The exception proves the rule:

When emptying lumpy or sticky bulk materials, low frequency vibrators with high amplitudes are most effective. For strongly adhesive products, which stick to sheet metal in thin layers, it is possible to use either high frequency vibrators (type NCT) or knockers (types NTP and PKL). Knockers create the highest wall acceleration. For rigid or bulky components, high frequency devices, such as turbine or turbo vibrators (types NCT and NVT) should be used. In this case, only the highest frequency together with a low amplitude is effective. We will be pleased to advise you on your specific case_study problems.