Techne IFB-51 Bedienungsanleitung Seite 32

Consequently, fluidised beds used for burning off PVC require strict supervision to minimise
corrosion of the bed its self and of the parts cleaned in it, especially if these are of uncoated steel.
The purpose of most of the recommended maintenance procedure is aimed at keeping the bed
medium clean and free flowing, and free of gums, acids, agglomerates, partly decomposed plastic,
char and larger particles. These cleaning processes have the additional benefit of ensuring good
fluidisation and this, in turn reduces burn off time, reduces uneven heating of parts and thus
distortion, increases heater life by eliminating localised hot-spots, and makes cleaning easier on a
regular basis.
The following instructions apply generally to halogenated polymers and specifically to PVC. They are
aimed at minimising corrosion of the bath and of immersed metals.
a) DaIly IntervalS - at the end of each working day
1) Maintain the working temperature (about 400°C) for half an hour after the last processed
batch, to assist removal of corrosive acids from the bath.
2) If possible, maintain the temperature of the bath at about 100°C overnight and over
weekends and holidays to reduce absorption of water vapour into the batch. Overnight, the
residual heat in the bath will usually ensure this.
3) Scoop charred plastic residues, clods of media and articles being processed.
B) WeeKly IntervalS - at the end of each working week and before prolonged shut-downs
1) Ensure compliance with instruction A, above.
2) Add about 50g (2oz) of powdered mild alkali to the bath and mix in well by maintaining
fluidisation for 5 minutes. Suitable alkalis are limestone, dolomite, hydrated or slaked lime,
sodium bicarbonate, sodium carbonate, magnesia. The addition of corrosive alkalis such as
caustic soda (sodium hydroxide) and quick lime (calcium oxide) should be avoided.
C) MOnthly IntervalS
1) Empty the bath and inspect it for signs of corrosion, especially pitted surfaces and flaking
scale. The inside should be wiped out with a rag wetted with 5% washing soda (sodium
carbonate) solution.
2) Screen the medium through a 50 to 70 mesh sieve before returning it to the cleaned bath.
This removes scale, agglomerated medium, char, undegraded polymer and lost parts and helps
maintain a good quality of fluidisation.
D) halF-yearly IntervalS
1) The bath should be emptied, cleaned, inspected and the medium replaced by a fresh charge.
2) Alternatively, if the facilities are available, the medium may be thoroughly washed in several
changes of clean water, washed through a 70 mesh sieve, drained, dried and
returned to the bath where drying is completed by fluidisation and heating at 150°C, until the
medium fluidises in the normal manner. The washing procedure removes acidic residues and
accumulated soluble salts and residues.
Symptoms of neglect should be dealt with immediately. These include: pitting of metallic surfaces,
formation of lumps of agglomerated medium, accumulation of polymer or polymer filler material,
indications of bad or uneven fluidisation, blockage of the fluidising plate and wetness or stickiness
of the medium.
nOte A non-standard version of this industrial fluidised bath is available which is manufactured
from materials that resist the effects of corrosion experienced when processing items contaminated
with PVC and other halogenated polymers. We recommend that this version is utilised in applications
where continued use of PVC is envisaged.
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