With magnesium pressure pouring preheated ingot in the bloom and holding furnace are chargiert, which are equipped with steel crucibles with each pressure casting machine. Electrically or gas fired melting furnace is usually used. From security reasons the ingots before immersing in the melted metal must be preheated. Because of the strong oxidizing tendency of the melted magnesium to atmospheric oxygen it is precondition that a protecting gas atmosphere takes the melted metal off. For this purpose a mixture of 0,2% SF6 in dry air or a mixture of 0,5-2% SO2 in dry air is used. The inert gas must be supplied in such a way that when melting burning and the oxidation are prevented.
The metal surface must be smooth and clean.
SO2 is preferred opposite SF6 because of that ozone to damage effect. SO2 is a poisonous gas and with appropriate precautions is this inert gas easily recommended.
Because liquid magnesium alloys in heated nickel free steel tubes can be transported, variety of dosing equipment is in the use. In warm chamber pressure casting machines also clean magnesium parts can be melted. Liquid magnesium has a low solubility against iron, for this reason can different kinds by pumps across heated steel tubes melted magnesium to the dosage the firing cylinder be too led. The casting temperature varied from an alloy to others and has influence on the casting process. The casting temperature for AZ91 (MgAl9Z1) is typical within the range of 650 -680"°C for cold chamber pressure casting machines and 620-640"°C for warm chamber pressure casting machines. Alloys with lower contents of aluminum, are poured in such a way with somewhat higher temperatures around 660-690"°C.
Generally cold chamber pressure casting machines, which are used for aluminum, can be used also for magnesium. Important differences between aluminum and magnesium are the density, which amounts to about only 2/3 of aluminum. The lower density of magnesium opposite aluminum means that the inertia is smaller and for the same quantity metal a higher flow rate under pressure obtained.
With shorter time a form is thus filled with magnesium than with aluminum. Also for cast parts with thin wall thicknesses with large flow paths the filling time for magnesium will be shorter. For this reason work some magnesium pressure casters with firing piston speeds, which exceed 10 m/s. Spec. Casting pressures are generally within the range of 30-70 MPa. Cold chamber pressure casting machines with closing forces up to over 4000 tons are commercially available.
On warm chamber pressure casting machines mainly smaller parts with Schuss-Gewichten is produced by 2 bis3 kg. Spec. Casting pressure is smaller than typical with cold chamber machines, within the range of 20 to 30 MPa.
Cold chamber pressure pouring: Transmission case, clutch housing, engine housing, Zylinderkopfhauben, body of construction units, drill press housing, steering wheel warm chamber casting: PC housing, carrier, housing for mobile telephones.
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