HSIT – Horizontal Stirring Induction Technology is equipment for molten bath stirring in reverberatory furnaces. The electromagnetic inductor is installed on a furnace side wall moves molten metal in a horizontal way either in a single furnace chamber or between two separate wells.
Apart from melting furnaces, this technology is suitable for use in holding furnaces where steady bath surface is required. All the bath movement takes place below the molten bath surface, which does not create any turbulences and consequently dross generation.
Advantages of the HSIT:
What the inductor is and what it is good for
Electromagnetic induction stirrer operation is based on a travelling magnetic field (basically a linear motor) and continuous electromagnetic media interaction. The resulting electromagnetic forces cause movement of molten metal in front of the inductor. The stream of metal moves down the active face of the inductor and leaves it as a submersed jet along the base of the hearth.
Generally the inductor is intended for melting process intensification and shortening of alloying times in reverberatory furnaces. Most often the working media is molten aluminium and it’s alloys, zinc and other non ferrous metals.
When the induction stirring of molten metal is installed on reverberatory furnaces for melting of aluminium ingots or aluminium scrap and returns, the electromagnetic stirring will substantially increase furnace productivity, reduce melting cycle, reduce fuel consumption and dross generation during melting process.
Uniform composition of the melt
Induction stirring of molten metal in the Stinchcombe furnaces is a sign of chemical uniformity in the entire volume of the bat. It significantly helps to dissolve alloying components, reduces the need for door opening for mechanical stirring, reduces heat losses and shortens the time needed for the alloying process. This is of special importance for high alloy melts containing elements like magnesium, titanium and silicon. The homogeneity of the bath in combination with the uniform temperature obtained by stirring, increases the overall aluminium yield in the Stinchcombe furnaces with induction stirring of molten metal.
Uniform temperature distribution
The Graph No. 1 shows conditions in a 40 t reverberatory furnace, when operating without stirring, with a bath depth of 900 mm, the maximal bath surface temperature reached 900 °C, with a corresponding bottom temperature of 660°C. Using the electromagnetic induction stirring, this temperature difference was decreased to less than 12 °C within 15 to 20 minutes giving the bath an average temperature of 730 °C.
The Graph No. 2 shows conditions in the same furnace when the induction stirring of the molten metal was started during the melting process. The result is uniform temperature of the bath in its entire volume. It means it is not necessary to overheat the upper layers of the bath to reach the requested casting temperature at the bottom of the bath. This fact enables to operate the furnaces on lower temperatures that means less gas consumption of the burner system.
One big advantage of this system over many other electromagnetic stirrers is the ability to begin stirring before all the solid metal is molten.
The induction stirring of molten metal and the resulting temperature and chemical homogeneity of the bath enable increasing of furnace capacities by increasing of maximal height of the molten metal level.
Accurate temperature control
The uniform temperature distribution in the melt makes it possible to obtain accurate temperature control with a minimum of temperature samples without the need to put the bath thermocouple very deep into the melt.
Increased thermal efficiency and melting rate
The result of the induction stirring of molten metal is the lower surface temperature of the bath that increases the heat transfer to the melt. The heat transfer is also increased, by means of convection, between the submerged scrap and the melt. These two effects, due to the stirring, increase the melting rate and the thermal efficiency of the furnace. A typical reduction of the melting time is 5 to 15 %. The example of that is the guarantee test in Al Invest Bridlicna a.s., where after the installation of the inductor the melting time was shortened by 11 % comparing to the melting time without use of the inductor.
The overall energy consumption is decreased in proportion.
Alloying Time saving
The stirring action speeds up the melting process or dissolution of alloying components into the melt. Charging of silicon and other type of alloying components into the high stream of molten metal, the electromagnetic forces and the high aluminium flow rates stir the charge, which leads in rapid mixing into the entire melt.
The alloying time can be decreased up to 40 % of the original time and also together with that there is no need to open the furnace door and manually mix the bath.
Generation of dross
Rising of the molten metal temperature increases the dross formation drastically at bath surface temperatures above 770 °C. Using the induction stirring of molten metal, low metal surface temperature reduces the formation of dross, which in turn is advantageous for the heat transfer to the melt and the overall aluminium yield.
The use of induction stirring reduces the generation of dross by 15 to 40 % when melting charges with a solid content of 80 - 100%.