Vibrating Compaction Tables

Vibrating tables can be used for both the compaction and detachment of bulk materials. The vibrated load can be applied to the table loosely, or as a fixed load and it is important to distinguish between these two methods of vibration.

Loose mounting of the load is mainly suited to compaction of bulk materials and concrete mixture but can also be used for detachment of material, such as the shaking out of moulds. As the container impacts against the vibrated surface it receives an acceleration impetus that is random and can not be precisely determined.
The rebound impacts increase in acceleration with larger oscillation amplitudes however the number of impacts starts to decrease, therefore it is important to experiment with high frequency low amplitude and weaker impacts as well as the high amplitude low frequency stronger impacts to determine the most suitable for any given application.

The second method of vibration involves clamping vibrated load rigidly to the table surface. In this case the acceleration can be accurately determined before and during the compaction process.

Compaction of bulk materials in bags or containers

The following factors must be considered for the efficient filling of containers or bags.

Properties of the material such as
Bulk weight
Particle shape
Internal friction
Particle size

Properties of the container
Height
Rigidity
Side-wall friction
Dimensions

Mode of operation of the vibrating table.
Number of oscillations per minute
Acceleration
Vibration time.

In the process of compaction any internal cavities, or voids within the product are encouraged to collapse through vibration and thus the storage of bulk material is thus achieved in as compact a volume as possible. The walls of larger diameter containers contribute less in terms of internal friction than smaller diameter containers and, further more, materials with a low internal friction will require less vibration to compact that a material with high internal friction. Interestingly, in the case of flour, the air to be expelled has a greater resistance to overcome than would be experienced with many course grained materials. Compaction usually tends to occur with an exponential function for example powdered milk can be compacted by 36% in 15 seconds, a further 5 seconds resulting in only 1% further.
The vibration time plays a decisive part in the compaction of wet mixtures such as concrete. If the vibration lasts too long undesired segregation may occur. An oscillation frequency of 6000/min is suitable for small containers and 3000/min for large ones. The use of cover mats of rubber or flexible plastic to protect the container and diminish the noise entails higher oscillation amplitudes to obtain the same compacting results.

We hope this serves to show the great variety of influential factors that effect the compaction process. For this reason we strongly recommend that trials are conducted to determine the optimum settings for equipment and the degree to which the material can be compacted. We are able to conduct these trials on our range of test equipment and require only sample containers and materials.