In principle, the size of a bin activator is dictated by the 'critical arch dimension' of the bulk material stored. The procedure for establishing this figure is by the classical Jenike shear test method as described in the I.Chem.E. manual of standard procedure for shear cell testing or ASTM D - 6128.

In practice, bin activators are usually empirically selected in relation to the diameter of the silo used. The reason, apart from the fact that not many manufacturers use Jenike testing, is that activators are normally much larger than strictly neccessary for flow, but used to save headroom rather than sized purely on flow criteria.

Whilst these devices are extremely widely used, they have drawbacks in connection with feed control and lack of flow regime control, being generally fitted to cones of 60 degrees wall inclination that is rarely adequate for mas flow. Anyone considering a modern hopper design would be well advised to examine all the options for hopper selection. A design chart for this is given on the Ajax web site www.ajax.co.uk, together with various useful calculation matrixes.

For a more detailed explanation of the behaviour of Bin Activators, apply to Ajax Equipment at ajax.co.uk for a thorough explantion of the mechanics and operating factors. Other publications are also available on the flow of solids, powder testing, segregation and a range of associated bulk behaviour topics.

Lyn Bates ■