Process and waste gases

• Pages: 124-126

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8. Process and waste gases

Process and waste gases

8.1. Gases are added during specific processes and are

generated as waste by the action of heat on chemicals used

in various non-ferrous metals production processes. Be-

sides metal fume, which is described in section 6.1, gases are

associated with a variety of processes, including:

(i) Moulding. Resin-bonded sand is coated with phenol- or

urea-formaldehyde resin and heated until the mould has

set. In hot-box moulding, the resin-sand mix is forced

over a heated pattern to produce the mould. In cold-box

moulding (“no-bake” moulding), curing takes place at

room temperature. Gas catalysts (e.g. carbon dioxide,

sulphur dioxide) are sometimes used to facilitate curing.

Carbon dioxide causes hyperpnoea at concentrations of

3 per cent and above. At a concentration exceeding

10 per cent, rapid loss of consciousness occurs which can

be reversed if the worker is quickly removed from the

source and allowed to breathe oxygen. When sulphur

dioxide is dissolved in water, it produces sulphuric acid

which, if inhaled, causes acute irritation of the mucous

membranes. In extreme cases this leads to severe pul-

monary oedema and death. Exposure to sulphur di-

oxide can induce asthma in susceptible individuals.

(ii) Pattern making. Mould patterns are produced using

wood, reinforced polyester, plastics, foam or wax. The

wax material often contains colophony, a respiratory

sensitizer, that is given off during the heated aspects of

pattern making.

(iii) Core making. Where a central design or opening is re-

quired in the moulded item, cores made of refractory