Magnesium

In vertical continuous casting of Magnesium alloys, the melt is usually poured into a ring-shaped mold where a cast skin forms on the cooled wall. If the melt in the mold reaches a certain level, the hardened casting is continuously lowered steadily to the same extent that new liquid metal enters. The casting skin is cooled further by a secondary cooling system so the inside of the casting hardens. The speed of hardening is on average 10 times greater than with block casting in iron molds without water-cooling. This means segregation can be avoided and a more homogeneous structure is produced. The Mg parts producible by a subsequent extrusion press can be heat treated and achieve excellent mechanical characteristics.

Two important innovations compared to conventional procedures characterize the continuous casting system:

First innovation:

• Exact compliance with the level of melting in the tundish via rise pump.
• Formation of a protective layer on the surface of the molten material prevents any more oxide formation in the flow of melted material below the layer.
• Exactly preserved level of molten material in the tundish ensures a constant hydrostatic pressure and facilitates the control of the flow rate to the mold.

Second innovation:

• Pouring device from the tundish into the mold with stopper from below to avoid gas inclusions in the pipe; the melt distributor is integrated in the stopper.
• Tempered stopper and outflow pipe, so heat losses of the melt on the way between tundish and mold are manageable; this allows for a low melting temperature in the casting furnaces and in the tundish as well as flow of the melt into the mold with the lowest possible overheating, which results in a consistently fine structure of the casting .
• Customization of the requirements, such as lowering speed of the casting head, mold size, cooling capacity etc. of the melt stream into the mold, and interruption of the casting process without emptying of the tundish, e.g. for removal of the casting for maintenance purposes via the ventilation system.

Advantages of the RAUCH continuous casting system:

• Drastic reduction of oxides.
• Improvement of the structure.
• Reduction of flow-back of head and foot parts as well as the peeling off of the casting to a minimum; this results in a significant increase in output.
• Consistently high quality.

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With the RAUCH Magnesium sheet-metal casting system MBG, the customer is able to continually cast liquid Magnesium (e.g. AZ31HP) into sheets, which can then be coiled on a winder.

Construction of the RAUCH Magnesium sheet-metal casting system:

• The Magnesium ingot heating system, the Magnesium melting furnace and the casting furnace are placed in a depression in front of the twin roll caster.
• A pump system mounted in the furnace transports the liquid metal via a heated pipe system into the temperature-controlled head box, which is mounted at the entrance of the twin roll casters.
• The winder placed after the twin roll caster rolls the cast sheet-metal up.
• Determination of the sheet-metal to be cast via the width of the distributor.
• When a system failure happens, liquid Magnesium flows by gravity back into the furnace where it is held under control by continuous inert gas.

Advantages:

• Continuous feeding of the twin roll casters with liquid Magnesium.
• Modular expandable melting capacity with additional equipment.
• Designed for continuous operation (24 x 7).
• Ongoing cleaning possibilities during operation.
• Turbulent-free melting system to reduce the formation of oxide.

Due to confidentiality agreements, we cannot present photos of the existing systems or disclose the customer.

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The RAUCH continuous casting mold and lowering equipment are used for the production of Magnesium casts. In a water-cooled mold, the Magnesium is poured over a volume valve in the tundish. The cast is lowered in a water-filled container via a hydraulic cylinder. This means at the same time 2 casts with a diameter of 125 mm to 350 mm and a length of up to 6 m can be produced in batch mode.

Advantages:

• Modular expandable melting capacity with additional equipment.
• Ongoing cleaning possibilities during operation.
• Turbulent-free melting system to reduce the formation of oxide.
• Exact control of the volume valve casting speed.
• Short set-up times when changing the mold.
• Molds can be poured in rectangular or cylindrical form.
• High safety standard.

The RAUCH Siphon MSI transports the liquid Magnesium from the melting furnace into the moulds and thereby avoids additional oxide formation, which happens with conventional turbulent transport.

Functioning of the RAUCH siphon:

• Filing via a vacuum pump; this creates low pressure and the siphon is filled with liquid Magnesium.
• The Magnesium flow functions according to the principle of communicating vessels, from one furnace to another.

Advantages:

• Installation in the unfilled state as connection between two furnaces.
• Temperature control of electric heating.
• Simple heating change through improved design, i.e. no removal of the siphon tube required.
• High-quality materials for long life of the transport pipe.

RAUCH Magnesium casting furnaces MGO are used for keeping Magnesium warm and ready for the casting process as well as for the installations of the casting system.

RAUCH Magnesium casting furnace MGO enables:

• The provision of liquid Magnesium melt for processing in continuous casting and sheet-metal systems, for ingot casting etc.
• 2 separate heating zones by means of electrical heating.
• Safe handling of molten material by covering the surface with an inert gas.

Advantages:

• Precise temperature control of molten material by heating to compensate for short-term temperature fluctuations.
• Easy cleaning capability during operation.
• Calm zone for homogeneous melt.

The RAUCH Magnesium head box MHB is used for the supply of liquid Magnesium to tips on the twin roll caster or the continuous casting system.

Functioning of the RAUCH MHB:

• No-contact level detection system, which regulates the Magnesium pump through communication with the controller thereby keeping the level in the head box constant.
• The pneumatic valve opens automatically on reaching the optimum level of the head box and lets liquid Magnesium into the heated distributor between the two rolls of the twin roll caster via a heated pipe.
• The head box and the distributor system are pressurized with inert gas to prevent the oxidation of the molten material.
• Regulation of output pressure in the distribution system via the molten material level in the head box.
• When a system failure happens, liquid Magnesium flows by gravity back into the furnace where it is held under control by continuous inert gas.

Advantages:

• Independent level control in the head box compared to the molten material in the casting furnace.
• Constant temperature control of the molten material during the casting process.
• Easy cleaning capability during operation.
• Accurate alignment of the head box to the casting system (twin roll caster, lowerer).