RU28535U1 - Induction melting crucible furnace for the manufacture of ingots and castings of magnesium alloys - Google Patents

Description

  5 3 5 8 - -

- ° MPK7R27V14 / 06

Induction melting crucible crucible for manufacturing ingots and castings from magnesium alloys

The utility model relates to the metallurgy of light alloys and can be used in the production of slabs and round ingots from magnesium and magnesium-lithium alloys, namely for melting, preparation of refining and modification of magnesium alloys.

The closest to the claimed utility model design of an induction melting furnace for magnesium alloys is disclosed in the reference book “Magnesium alloys, M., 1978, p.65. This furnace consists of a frame, an inductor with insulated turns, a steel crucible, its thermal insulation, consisting of a bed of ground diatomaceous brick, located between the crucible and the inductor. The backfill is separated from the inductor by a stainless steel protective cylinder coated with asbestos sheets on the outside.

The disadvantages of the known furnace include the following.

The high fluidity of the molten magnesium alloys at melting temperatures allows the liquid metal to pass through the defects of the welds and pores of the crucible metal and the lining to a sufficiently large depth and actively interact with the insulating material. In this interaction, silicon (Si) and aluminum (A1) in the diatonite lining pollute the melt, which leads to a complete rejection of the melted alloy, since the content of silicon in magnesium and its alloys is severely limited.

The objective of the utility model is to improve the quality of alloys.

The technical result of the utility model is the elimination of fouling of the melt by elements of a heat insulating material.

The technical result is achieved in that in an induction melting crucible furnace for the manufacture of ingots and castings of magnesium alloys containing an inductor and a crucible placed inside the inductor and surrounded by thermal insulation, enclosed in a steel frame, the thermal insulation is made in the form of a multilayer refractory packing material containing a mixture of magnesite particles and / or periclase with increasing particle size from layer to layer in the direction from the crucible, a glass of liquid sodium and sodium fluorosilicate or potassium, the first layer contains an hour no more than 0.8 mm in size, a second layer from 0.8 to 1.5 mm and a third layer at least 1.5 mm, the first and second layers being located between the crucible and

inductor in the zone of the lower part of the crucible, and the third layer in the zone of the lower part of the crucible, with the following content of fractions and components in the specified packing mass, wt.%:

magnesite or periclase:

fraction particles no more than 0.8 mm25-35

fraction particles from 0.8 mm to 1.5 mm

particles of a fraction of not less than 1.5 mm

sodium silicofluoride or potassium silicofluoride1 -3

the rest is liquid sodium glass.

In addition, the packing mass may contain powder as particles with a size of not more than 0.8 mm, sand as particles of a size of 0.8 to 1.5 mm, and crushed stone as particles with a size of not less than 1.5 mm .

The crucible is preferably further insulated in the upper part with magnesite brick.

The furnace crucible can be made of steel with a carbon content of not more than 0.02 wt.%, Including with a crucible wall thickness of 35-40 mm.

The furnace crucible can also be made of a refractory mass based on magnesite and / or periclase powder.

A cylindrical thin-walled screen with a cut along the axis of the crucible can be placed between the crucible and the inductor in the packing mass.

The inductor can be made of a copper tube of square cross section with the possibility of water cooling with coils insulated with micanite tape and rigidly fastened to prevent vibration and shape change.

The inductor can also have up to 10 branches, providing a change in the power supplied to the crucible and molten metal.

The drawing shows the design of an induction melting crucible furnace for the manufacture of ingots and castings of magnesium alloys.

The crucible 1, made of mild steel or of a refractory mass based on magnesite and / or periclase powder, includes the upper part (collar) 2 and the main part 3. The upper part 2 of the crucible is made of lining of magnesite brick 4, and is located around the main part 3 a multilayer refractory packing material 5 containing a mixture of particles of magnesite and / or periclase of various fractions with liquid sodium glass as a binder and sodium silicofluoride or potassium. Crucible 1 thermally insulated placed in

inductor 6. The packing mass 5 consists of a first layer 9 containing magnesite and / or periclase particles of a size not exceeding 0.8 mm, a second layer 10 containing these particles with a size of 0.8-1.5 mm, and a third layer And containing these particles are not less than 1.5 mm in size. The first and second layers 9 and 10 cover the surface of the crucible 1, surrounded by an inductor 6, and its lower surface. The third layer 11 is located in the bottom of the crucible 1 with a small upward step in the lower part of the inductor 6. The crucible 1, inductor 6 and thermal insulation 4, 5 are enclosed in a steel frame 7. In some cases, it is advisable to use a cylindrical screen 8 with a cut.

Experiments have shown that the most suitable heat-insulating material in furnaces for smelting magnesium alloys is magnesite or periclase, or a mixture thereof, since they have excellent heat-insulating properties and are also neutral with respect to molten magnesium.

To isolate the upper part of the crucible (collar), it is sufficient to use magnesite brick, for example, grade MO-91 GOST 4689-74.

The use of different fractions for packing periclase (magnesite) particles allows to achieve the best insulating and technological properties, in addition, this mixture is not explosive. Fine grinding particles (not more than 0.8 mm) ensure a tight fit of the crucible without play, and particles of medium (0.8-1.5 mm) and coarse grinding (more than 1.5 mm) increase the heat-insulating properties of the packing and make it possible for prolonged operation to compensate for the deformation of the bottom of the crucible.

For induction furnaces with capacities from 100 kg to 4000 kg, the most rational is the use of a steel crucible, mainly from low-alloy steel with a carbon content of less than 0.02 wt.%. The less alloying elements in steel, incl. and carbon, the less interaction of molten magnesium with iron. The most rational would be the use of pure iron, the so-called “Armco, but its low strength, especially at magnesium melting temperatures of 650-850 ° C, makes it necessary to use steel of the steel of grade 20.

It should also be noted that magnesium alloys are melted using flux, which includes chloride and fluoride salts of halide metals, moreover, this mixture of salts has a eutectic composition and, as a result, a low melting point of about 440 ° С. In addition, the molten flux has a fluidity equal to water, and therefore can penetrate into all cracks. This is another factor forcing the use of a steel crucible with wall thickness in induction furnaces.

35-40 mm. This wall thickness provides the ability of the crucible to absorb the transmitted power from the inductor and serve as an inertial heater. This prevents the movement of the melt during aging and precipitation of harmful impurities in the form of primary iron-based intermetallic compounds.

Steel crucible furnaces primarily use an industrial current frequency of 50 Hz. This naturally reduces the volume and price of equipment. However, it is possible to use the proposed utility model in high-frequency furnaces.

In some cases, it is possible to make the crucible from a refractory mass based on magnesite and / or periclase powder.

The utility model can be illustrated by the following examples. Refractory thermal insulation of crucibles was carried out as follows. In a mixer, such as a concrete mixer, three heat-insulating masses of the following total composition were prepared for induction furnaces of all types, wt.%: Magnesite powder (periclase) fine-ground, 0.08 mm fractions (for the mixture of the first layer 9) - 30%

magnesite sand (periclase) fraction 1 mm (for a mixture of the second layer 10) - 30%

crushed stone magnesite (periclase) fraction 3-5 mm (for a mixture of the third layer 11) - 25%

sodium-silicofluoride (potassium) - 1%

- liquid sodium glass - 14% For lining of low-frequency furnaces with a steel crucible it is required:

- with a capacity of 500 kg - 200 kg of mass

- capacity 1.6 t - 1200 kg

- with a capacity of 3 tons - 3000 kg of mass.

Loaded dry ingredients are mixed for 5 minutes. Refractory packing of each layer is carried out sequentially. First, the mass of the third layer 11 is laid on the bottom. Then, the first and second layers 9, 10 are filled using a separation template. The upper part of the crucible (collar) is lined with radial magnesite bricks of the grade MO-91-15 on a solution of aluminosilicate mortar of the grade MSh-42 or MSh-39.

Refractory insulation of the inductor.

A thin layer of refractory paint of the following composition is applied to the inner surface of the inductor:

Sodium silicofluoride -1%;

- liquid sodium glass with a density of 1.37 - 1.90 g / cm - 10%;

The rest is water. The consistency of the paint is semi-liquid.

The colored inductor is dried for 2 hours. Then a coating is applied followed by drying. Then follows gluing with asbestos cardboard or volostanit. Another roll or sheet type heat insulator is also possible. On top of this layer impose melevant brand LFK-TT with a thickness of 1.5-2 mm and a width of 500-700 mm. The following is a sticker of graphite fabric on the base of the inductor, lined with magnesite brick MO-91-1 and MO-91-15.

A collapsible template is installed and centered with respect to the inductor. Refractory mass is poured. The ramming of the refractory mass is carried out by pneumatic ramming under the pressure of compressed air 6.0-6.5 kgf / cm. During tampering, the alignment of the template should be ensured so that it does not mix. After tamping, drying is carried out at a temperature of 180 ° C.

The inductor is a rectangular conduit assembled in coils. The inductor is water-cooled. It has several switchable current leads. The turns are insulated with micanite tape and rigidly fastened into a stable cylinder with the specified parameters in height and diameter.

Example 1. Induction furnace industrial frequency (50 Hz) with a capacity of 500 kg In this case, the wall thickness of the crucible is 10-12 mm The crucible is placed in a diamite or periclase shell, prepared in accordance with the foregoing, separating the inductor from the crucible. The upper part of the crucible is lined with magnesite brick. The height of the inductor is equal to the cylindrical part of the crucible. The structure, consisting of a crucible, heat-insulating refractory packing and inductor, is placed in a frame made of steel structures, providing structural rigidity and the possibility of its rotation around an axis located at the level of the drain toe.

Example 2. Induction furnace industrial frequency (50 Hz) with a capacity of 1.6-2.0 tons. In this case, a crucible thickness of 20 mm is selected. Welded crucible. It has a joint seam connecting the bottom of the crucible with a cylindrical part. The crucible is separated from the inductor by refractory masonry (printed), in which a stainless steel cylindrical screen cut in height is installed. This is necessary to fix the possible penetration of the crucible and the ingress of liquid metal on the inductor, and a cut is required so that there is no closed cylinder. Cylinder open not

allows you to shield electromagnetic waves that must be completely absorbed by the crucible and melt. The inductor has from 1 to 9 taps, allowing it to be turned on at full power or only one tenth of the total power, which allows you to adjust the intensity of melt mixing in the furnace and to regulate the temperature regime. This whole structure is enclosed in metal structures for rigidity and the ability to rotate the furnace.

Example 3. An induction furnace of industrial frequency (50 Hz) with a capacity of 2.5 to 4 tons. It is considered as an example of a furnace with a capacity of 3 tons. In this case, a crucible with a wall thickness of 40 mm is selected. The crucible is welded with two seams, straight along the cylinder and circular, connecting the bottom to the cylindrical part. The bottom part on the outside has a welded pin for centering the crucible in a refractory, heat insulating packing located between the crucible and the inductor. A crucible having a thickness of 40 mm allows the process to be built in such a way that in this case it is possible to efficiently use this furnace, including as a mixer. After the metal is completely melted and refined, the power supplied to the inductor, which has 10 switching stages, is removed in such a way that all the energy is concentrated in the crucible. In this case, the crucible becomes a heating element, maintains the temperature of the melt, without mixing it, which ensures sufficiently rapid deposition of oxides and fluxes on the bottom of the crucible in an unalloyed residue that is removed from the furnace after casting is completed.

Example 4. A high-frequency induction furnace (2000-3000 Hz), Figure 16. The furnace consists of a crucible inductor with a packing of periclase, a frame. Inductor 3 has 3 stages of inclusion in power. The capacity of such furnaces does not exceed 1 t. This is due to the fact that an increase in capacity creates dangerous hydrostatic pressure on the walls and bottom of the crucible, and an increase in wall thickness leads to a significant loss of power. Furnaces of this type are most often used for shaped casting of pure magnesium ingots, since the absence of melt mixing due to the “pinch effect of electromagnetic mixing creates difficulties with alloy preparation and segregation of alloying elements, especially manganese, zirconium and others.

Claims (10)

1. Induction melting crucible furnace for the manufacture of ingots and castings of magnesium alloys, containing an inductor and a crucible placed inside the inductor and surrounded by thermal insulation, enclosed in a steel frame, characterized in that the thermal insulation is made in the form of a multilayer refractory packing material, consisting of a mixture of magnesite particles and / or periclase with increasing particle size from layer to layer in the direction from the crucible, a glass of liquid sodium and silicofluoride sodium or potassium. 2. The furnace according to claim 1, characterized in that the first layer contains particles no larger than 0.8 mm, the second layer 0.8 - 1.5 mm and the third layer at least 1.5 mm, the first and second the layers are located between the crucible and the inductor and in the zone of the lower part of the crucible, and the third layer is in the zone of the lower part of the crucible, with the following fractions and components in the packing mass, wt.%: Magnesite or periclase: fraction particles not more than 0.8 mm 25-35 fraction particles from 0.8 to 1.5 mm 25-35 particles of a fraction of not less than 1.5 mm 20-30 Sodium silicofluoride or potassium silicofluoride 1-3 Sodium Liquid Glass 3. The furnace according to claim 1 or 2, characterized in that the packing mass contains powder as particles with a size of not more than 0.8 mm, sand as particles of 0.8 - 1.5 mm, and sand as particles at least 1.5 mm in size - crushed stone. 4. The furnace according to any one of claims 1 to 3, characterized in that the crucible is additionally insulated in the upper part with magnesite brick. 5. The furnace according to any one of claims 1 to 4, characterized in that the crucible of the furnace is made of steel with a carbon content of not more than 0.02 wt.%. 6. The furnace according to claim 5, characterized in that the wall thickness of the crucible is 35-40 mm 7. The furnace according to any one of claims 1 to 4, characterized in that the crucible of the furnace is made of a refractory mass based on magnesite and / or periclase powder. 8. The furnace according to any one of claims 1 to 7, characterized in that a cylindrical thin-walled screen with a cut along the axis of the crucible is placed between the crucible and the inductor in the packing mass. 9. A furnace according to any one of claims 1 to 8, characterized in that the inductor is made of a square copper tube with the possibility of water cooling with turns insulated with a micanite tape and rigidly fastened to prevent vibration and shape change. 10. The furnace according to any one of claims 1 to 9, characterized in that the inductor has up to 10 branches, providing a change in the power supplied to the crucible and molten metal.