MHD stirrers with plain linear inductors

Such MHD devices contribute to stirring of the melt bulk at charge melting with the aim to intensify the heat/mass transfer phenomena when prepare alloys, namely, high alloys, multi- component and high temperature alloys, to average the melt temperature throughout the melt volume.

MHD stirrers are produced with different dimensions for casting furnaces and mixers containing different volumes of the molten metal.
Volumes: 5-10 t, 15-25 t, 40-60 t, 70-95 t, 100-145t.
Voltage: 220-380 — 400-440 V; frequency — 50-60 Hz;
Productivity at stirring and pumping of the molten metal varies from 10-40 t/h to 600-900 t/h.

The length of the active zone of such MHD stirrer is 600 -1360 mm and determined by the type and size of the MHD stirrer.

  • Active power — Pact 35-130 kW
  • Reactive power — Preact 320 — 1100 kvar;
    • current 100 — 250 A;
    • the non-magnetic gap (between the molten metal and the inductor) is about 50 — 80 mm.
    • Water cooling of the inductors winding;
    • the water flowrate is (0.7-2.3)10 ³m/s;
    • water pressure is (2 5)10 ³Pa.

MHD stirrers with plain linear inductors are used mostly in single-section (a casting furnace or a mixer) or double-section (a charging chamber + a section for alloy preparation) furnaces. Such stirrers could be used in furnaces of different design.

Signle-chamber furnace

The application of the MHD stirrer with plain linear inductors allows:

  1. To enhance the productivity of the casting furnace by strengthening the processes of heat/mass transfer;
  2. To reduce the time of melt preparation (by 20-50 %)
  3. To reduce fuel consumption for melting and preparation of the alloy (by 20%);
  4. To provide high homogeneity of the chemical composition of the molten melt (5%) and equalizing of the meit temperature throughout the furnace volume (by 5-10 C);
  5. To decrease the number of alloy composition corrections during its preparation;
  6. To decrease the metal loss (by 15-25%).

The advantages of the MHD stirrers if compared to the known devices applied in industry are:

  1. a high reliability due to the absence of moving mechanical elements in the melt;
  2. convenience in assembling and disassembling of the equipment;
  3. simple control, a possibility to control the productivity and strength of stirring from 0 to 100%;
  4. a possibility to stir the aluminium melt without breaking the film on its surface;
  5. a possibility to intensify the processes of heat/mass transfer at all stages of the aluminium alloy preparation and refinement in furnaces;
  6. a possibility to strengthen additionally the melt stirring within the bath volume by changing the travelling magnetic field. direction that changes the metal flow direction to opposite (back and forth motion);
  7. a possibility to prepare alloys and alloying compositions at temperatures lower than usual 100-150 C;
  8. heating of the pumped melt by inductive currents at metal melting (within the MHD stirrer. channel) and at its circulation in the furnace bath; no additional heating sources of the flow path are needed;
  9. a high opportunity for unification of different design versions of the stirrer.

The MHD stirrers with plain linear inductors are widely used to intensify the melting of aluminium alloys on the base of primary | aluminium and their decontamination from sodium and oxide dopants, to produce alloys of Al-Si, Al- Mn-Mg, Al-Si-Mg, Al-Mn, Al-Cu.

The application of the MHD stirrers with plain linear inductors allows:

  1. to enhance the productivity of the 25-t- melting aggregate to 130 t/day;
  2. to decrease Si consumption needed to prepare Al-Si alloy by 1.5 kg per 1 t of the alloy;
  3. to reduce hydrogen content by 0.2 cm ³/100 g of the metal, aluminium oxide by 0.02%, sodium by 5,10 ⁴% (in mass);
  4. to reduce metal losses at its oxidation by 0.5%;
  5. to reduce the time of decontamination to 20 min, with: the energy consumption for decontamination being 2-3 kW/h per 1 t of the alloy;
  6. to considerably improve the structure of metal ingots;
  7. to enhance the rate of dissolution for Cu, Si, Mn in aluminium; to distribute them uniformly over the cross-section of ingots, to enhance the yield of systems Al-Cu, Al-Si, Al-Mn.

The MHD stirrer with plain linear inductors consists of:

  1. an inductor with a frame
  2. a flow path (channel)
  3. systems of electric power supply and controla condenser set.

The inductor is designed to induce a traveling magnetic field and consists of a magnetic circuit with slots, in which the coils of the winding made of copper pipes are placed, through which cooling water runs. In some cases, a high temperature winding wire could be used as a winding.

The TMF inductors with a magnetic circuit. where the slots are filled with three-phase coils, embracing the yoke of the magnetic circuit, can be used.

The inductors are arranged on the frame welded to the wall of the furnace body. The metal flow path (the channel) of special shape; made of a heat-resistant material (heat-resistant concrete, borosilicicated graphite, silicicated graphite, silicium carbide, etc.), is produced in the furnace wall: it is resistant against aluminium and its alloys.

Fig. 11 and Fig. 12 illustrate the MHD stirrer set with a frame, fastening elements and the colling system.

The MHD stirrer is operated by a system of electric power supply and control, consisting of

  • an electric board
  • acondenser set
  • acontrol panel
  • temperature probes installed in the inductor
  • a water pressure gauge
  • a metal leakage gauge.

The system of power supply and control allows to operate the MHD stirrer following the programs, providing different directions and duration of stirring cycles under hand-held and automated regimes as well as under computer control.

The MHD stirrer is AC power supplied (50 … 60 Hz), voltage 220/380 or 400/440 V. The MHD Stirrer has a multi-layer electric isolation.

To protect the personnel from shock by the electric current, to prevent the device from intrusions of extraneous bodies and water, the — inductor and the condenser set are JP 21 made, the control panel and electric board JP 54, meeting the requirements of ST SEV 778-77.

On demand of the customer, the electric equipment is supplied from the producers of the companies specified by the customer.

The MHD stirrer should be used (employed) in closed rooms in the zones with moderate climate. As to vibro-acoustic characteristics, it Is | classified (the noise level does not exceed 50 DB). The stirrer does not create radio noise.

The power to the inductor, condenser set, to the electric board and the control panel is supplied according to the attached scheme of the electric circuit.

MHD stirrer with sloped slots in the magnet of a plain linear inductor

Such design of the MHD stirrer allows to stir the molten metal in opposite directions, from the center of the inductor (Fig. 15)

MHD stirrer with reverse plain linear inductor

Fig. 16 shows a schematic of the MHD stirrer with reverse inductors and no-pressure metal flow path in the zone of action. The surface of the metal flow path has a triangle-shaped projection.

The stirring process is strengthened by driving opposite to each other, not coliding flows. The projection directs the molten metal flows.

  1. inductors;
  2. channel of the metal flow path;
  3. triangle-shaped projection.

Magnetohydrodynamic cylinder—shaped pumps

Magnetohydrodynamic cylinder-shaped pumps consist of an electromagnetic inductor produced as a Set of cylindrical coils, placed among teeth 4, 6 or 8 of magnetic circuits, arranged as a ceramic tube (pipe) made of a material resistant to molten aluminium, outside the coils and the metal flow path. In case of need, an inner core could be placed inside the metal flow path tube.

Technical charactertsics of the MHD cylinder—shaped pumps

  • Active power, Pact, kW 100 — 130
  • Reactive power, Preact, kvar 750 — 1100
  • Non-magnetic slot between the molten metal and the inductor, mm ~35 — 50
  • Current in the circuit, A 200 -250
  • Current in the inductor, A 1100 — 1200
  • Diameter of the inner tube of the channel, mm 100 — 130 — 140:
  • Length of the active zone of the pump, mm 750 - 10000
  • Number of magnetic circuits, piece 4, 6, 8
  • Level of the melt rise, mm 1000 — 1500
  • Water cooling: Water flowrate, m3/s (0.7-1.0)10 ⁻³; Water pressure, Pa (2.00.5)10 ⁵;

Magnetohydrodynamic cylinder-shaped pumps are used when the molten metal must be risen to a high enough level among the furnace sections or separate furnaces, for the molten metal pouring into the crystallizer UNR, in some technological processes when a high-pressure metal flow is to be driven in a semi-closed space, for instance, for quick melting of alloying compositions at the production of alloys and so on.

Fig. 17-20 show principal design schematics of the cylinder-shaped pumps; a single-chamber furnace with a MHD cylinder shaped pump and photos of the MHD cylinder-shaped pump for aluminium.

Magnetohydrodynamic plain linear pumps

Plain liner pumps with two inductors are used as MHD plain linear pumps for aluminium. Fig. 21 illustrates a principal schematic of such a pump. MHD plain linear pumps are arranged at the both sides of a rectangular-shaped metal flow path made of a material resistant against molten aluminium. The inductors could be arranged parallel to the bottom of the metal flow path, embrace the metal flow path from two sides or arranged at certain angles to the bottom or side wall of the metal flow path.

MHD chutes for aluminium output from the furnace

MHD chutes are used for pumping of the molten metal from the melting furnace into a ladle, into other furnace for alloy preparation, for the molten metal pouring into casting moulds, into the crystallizer UNR, etc. It could be also used for dosed pouring (output).

The MHD chute consists of a sloped metal flow path mounted in one of the furnace walls and an inductor. Single- double- or three-chamber one-side plain linear inductors are used in the MHD chute. The inductors could be mounted under the bottom of the metal flow path channel, embrace the metal flow path from two side walls _ or arranged at the top and at the bottom of the metal flow path. One of the inductors could be passive, made of a ferromagnetic material. The metal flow paths could be open or equipped with covers. The inductors and the magnetic circuits above the metal flow path have a possibility to vary the interval to the molten metal (to vary the non-magnetic gap) or to slope to the channel plane. This assures additional control of the flowrate and developed pressure.

The MHD chute pumps the molten metal from the furnace up to 1500 mm until the furnace is completely empty. The angle of MHD chute slope to the furnace bottom under certain conditions varies within 15 - 90.

The active length of the MHD chute inductor is about 300 — 1350 mm when one inductor Is used, and it could reach some meters when several inductors are used; the width of the active. part of the inductor is 100 — 400 mm; the non- magnetic gap is about 50 — 80 mm; the productivity of the MHD chute depends on the angle of chute sloping and the power of the inductor and varies from 5-10 t/h to 150/200 t/h; the active power of one inductor varies from 15 kW to 150 kW; the inductor coils are cooled either by water or air.

The application of the MHD chute allows to solve many practical problems of the molten metal transporting and dose pouring in different technological processes.

At KL ferromagnetic magnetic circuits or passive plates above the molten metal were used in the MHD chutes. The ferromagnetic inductors assured the increase of the magnetic field (in the zone of molten metal) by 30%, of electromagnetic pressure in 1.69 times, of productivity in 2.5 times (by increasing the electromagnetic field and damping the reverse flows in the channel of the MHD chute).

When a two-chamber MHD chute Is mounted, its upper chamber could be switched on separately, when the metal level in the furnace Is under its action. The lower chamber at that time could be switched off or switched on in opposite direction for metal stirring. Both chambers of the MHD chute are switched on for pouring when the level of the molten metal in the furnace is out of the zone of the top chamber action.

MHD equipment for zinc and its alloys, for magnesium, tin and other metals

The MHD equipment, which is used for aluminium and its alloys, could be used for the alloys based on magnesium, tin and other metals. We have enough experience of work with these metals for different technological processes. For example, the MHD pump for magnesium with the following characteristics: flowrate — 12 m3/h; pressure — 3.5 kg/cm2; T = 700 — 800° C; active power — 14.5 kW; voltage — 220/380 V — has been used for pumping (transporting) the molten magnesium.

The use of the MHD equipment is simpler when the metal flow path is made of non-magnetic steel and a wire with high-temperature-resistant isolation could be used for winding and no water cooling.