DRYIT Semi-Continuous Tray Drier
Practical Action
Trays
The parts list for a tray is given on the engineering drawing TD 015.
The basic requirement of each tray is that it holds the material to be dried without damaging
it whilst allowing maximum airflow through it. Also the tray should be, durable, cheap, easy
to make, using locally available materials.
The trays are constructed of wood and each one has six sections: four with a mesh base and
two open at one end. By positioning the open ends alternately in the stack of trays, the air is
able to flow in a zigzag manner up through the stack.
To allow horizontal airflow in the tray stack (see figure 28) the internal partitions (dividers)
must be approximately 20 mm lower than the outside walls of a tray.
For correct operation the overall width (to outside of corner reinforcers) of the trays must be
1 -2 mm less than the distance between the tips of the lifting fingers when they are at their
lowest point.
Corner reinforcements at the lifting points protect the tray from being damaged by the lifting
fingers. In the standard design these reinforcements protrude from the tray side, and tend to
catch on the tray guides during batch unloading and loading. The design of the tray guides
means that this is not a problem during normal operation.
To overcome this, the angle can be recessed, or fillets can be put in to 'ramp' the protrusions
as shown in figure 16.
Recessed
Ramped
Figure 16: recessed and ramped
If the reinforcers are recessed care must be taken to increase the timber frame width and
alter the cutaways.
If ramps are used they must be well fastened to the tray, e.g. pinned and glued, using
waterproof glue.
The ends of the trays, which have the small, open compartments, should be clearly marked
to avoid confusion. When operating the drier ensure that the trays are alternately positioned
in the cabinet. This is best done by painting all these ends in colour so that when fully loaded
the stack of trays will alternate -painted, unpainted, painted, unpainted. This will then
facilitate zigzag airflow.
Bottom Tray Removal
This is a potentially dangerous operation. Never remove the bottom tray by hand. Always
use some device. The most common one in use is a metal crook {see operation and
maintenance).
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