Posted on June 07, 2000 at 10:54:36:

In Reply to: Blockages of Woodchip Conveyors & Bins posted by Randolph Wong on May 20, 2000 at 14:13:10:

Wood chips are notoriously difficult to flow in bulk form in a confined converging channel because they interlock under pressure due to the elastic and fibrous nature of the particles of composition. Problems of a different kind occur in screw conveyors and feeder with lamiated wedging and trapping of flakes in narrow clearances between screw flight tips and the casing. The solution to the latter is to employ large casing clearances and pregressively expanding pitch from a flood feed region to dilate the contents.

For storage it is necessary to substantially reduce overpressures on the approach to the bin outlet. This type of material can sustain substantial arch and rathole dimensions in a bulk condition but will defrom to an extent and can be made to flow through a system, provided that the material is not subjected to high pressure due to self weight. This requires that inserts are provided to relate the compacting stresses to the dimension of the flow opening. Much depends upon the scale of the installation as to what threshold pressures can be tolerated. Conventional shear testing techniques are not adequate to derive prctical bin designs and a very pragmatic approach in necessary. The use of multiple screws or hydraulic actuated blades requires an experienced approach to avoid high resisting forces. Brute force is an expensive option and not always sucessfull. Lifting agitators, such as inclined screws may be used to 'tease' out settled material. ■