Abschnitt 2.4 - 2.4 Sand casting
The casting of magnesium in sand (sand casting process) is a rare process in the prototype and small batch production. Hazards arise from the liquid molten metal (approx. 700° C). In addition, hazards to the skin and the respiratory tract exist due to contact with the molding material (e. g. phenol formaldehyde resins) and with the quartz sand used during molding, unpacking and cleaning. In addition, pyrolysis products from the molding material used are produced by the casting process.
In the special method of magnesium sand casting, the suppression of an advanced fire with sand can lead to a hazardous thermite reaction (silicothermal reaction). The magnesium extracts the oxygen from the sand (SiO2) which results in a violent fire ignition.
Special protective measures
Only completely water-free systems are suitable as molding auxiliaries and binders (dried core sand and phenolic resin, cold box cores); bentonite or furan resin bonded sand is unsuitable. It is recommended to add an inerting agent, for example potassium tetrafluoroborate (KBF4). A reprocessing of the molding sand is usually not possible.
Store sand and pour-off molds in a dry place.
Flood the mold with protective gas (argon), remove the protective gas supply shortly before pouring.
Observe the arrangement and keep clear of air pipes.
Only use preheated casting tools (150°C, stainless and dry)
For melting with approx. 400 °C or more, flood the crucible with protective gas, and constantly monitor the metal.
When transferring the liquid magnesium, ensure flooding with protective gas, if possible.
Excess of protective gas leads to deposits in the crucible and on the bath surface, which can burn in contact with ambient air.
Do not slosh when moving the cast metal.
Pour quickly; the metal quickly loses temperature.
In case of incipient burning, powder the feeder and the sprue with sulfur or add molten salt.
Keep extinguishing agent (fire class D) ready.