Techne IFB-131 Operator's Manual page 19

Special Operating Pprocedures for use when Removing Plastic Residue
The industrial fluidised bath detailed in this manual is suitable for "burning off" plastic
residue from plastic machine tools, and is effective on the full range of polymers. In addition, the
bath is also effective on rubber, epoxy resins and various paints. The bath provides a safe, dry,
and fast means of removing all plastic residue with the minimum effort.
The process is controlled at a uniform temperature so that distortion of tooling due
to uneven heating which occurs when using other heating methods is avoided. Furthermore, as
the fluidised bed is non-abrasive, physical damage to parts is minimal.
The cleaning process relies on heat being transferred from the fluidised bed to the
immersed tools, the heat degrading the plastic residue. Objects to be cleaned should be
supported in a basket or suitable holder for ease of handling and lowered into the fluidised bed.
To avoid physical damage and local overheating, it is important to ensure that any items placed
in the bed are supported and not allowed to rest either on the porous plate at the bottom of the
bed or against the wall of the inner container. The bath should be operated generally in the
temperature range of 450°C to 500°C, depending on the polymer to be removed. The process
time depends upon the thermal mass of the object, the amount and type of polymer to be
removed. During the first two thirds of the process time the polymer is reduced to a tar mix, in
this phase all the initially combustible products of the polymer are emitted from the fluidised bath
in the form of fumes that must be extracted and treated by suitable fume handling equipment.
During the last third of the process time the polymer is reduced to carbon which either burns
away or remains loosely bound to the object being cleaned.
Any carbon or incombustible filler that remains on the processed item can be
removed by a secondary cleaning operation, either by brushing or some form of water wash.
It is important to ensure that the items being processed do not exceed the maximum
loading capacity (see Technical Specification) and that they are loaded into the fluidised bath in
such a way that the fluidisation is not impended.
THE PROCESS RELIES UPON GOOD FLUIDISATION TO ENSURE GOOD HEAT
TRANSFER; OVERLOADING OR INCORRECT LOADING OF THE BATH WILL RESULT IN
EXTENDED CYCLE TIMES GIVING INFERIOR RESULTS. LOCAL OVERHEATING MAY ALSO
OCCUR, GIVING RISE TO PREMATURE HEATER FAILURE AND POSSIBLE DISTORTION
OF THE INNER CONTAINER.
The aluminium oxide fluidising medium does not degrade but will need to be
replenished due to loss from spillage or entrainment in the exhaust (from where it may be
recovered by a cyclone trap).
All articles should be completely cleaned and removed from the bed before shut
down. Corrosion of processed parts could be seriously increased if they are left immersed
overnight. Furthermore, residual polymer, instead of being burned off in a fluidised state, could
percolate down through a static bed and settle on the porous plate to cause a blockage and
result in poor fluidisation.
When parts are removed from the bed they should be allowed to cool in air and,
whilst still warm, treated to prevent rusting.
It should be noted that some plastics and, in particular, paints contain fillers. These
fillers are usually inorganic materials and will not therefore burn when put into a fluidised bath,
with the result that the material falls away from the article being cleaned and is retained in the
I F B - 1 3 1 O P E R A T O R ' S M A N U A L
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