KR880000911B1 - Filtration block for liquid & alloyo coith a mechanical & physical-chemical effect - Google Patents

Abstract

An appts is used for the physico-chemical purificn. of a molten stream of Al, Mg, Zn, Pb, Sn or alloys based on one of these metals. The appts. includes a removable filter catridge, which is at least partly filled with grains of solid flux(I) with a melting point above the temp. of the molten stream. At least the outer part of grains (I) consists of one or more simple or complex fluorides of Na, Li, K, Ca, Ba, Mg, Al or Mn. The filter outlet is closed by a porous plate made by sintering one or more cpds. with a melting point above the temp. of the molten metal stream. At least the outer portion of these cpds. consists of one or more of the fluorides listed above.

Description

Filter block for molten metal with mechanical and physico-chemical effects

The present invention relates to filtration blocks with mechanical and physico-chemical effects for molten metals, in particular aluminum, alloys based on aluminum, magnesium, alloys based on magnesium.

In casting and semi-continuous casting and continuous construction of plates, billets or ingots, it is necessary to treat metals to remove impurities and cast-invasive inclusions in order to produce flawless parts. These include simple mechanical treatments such as filtration or physico-chemical treatments such as contacting a metal with a solvent.

In fact, the treatment involves mechanical filtration and, in most cases, cleaning with solvents consisting of one or more molten alkali metals and alkaline earth metal halides, where the cleaning process is dross (wetting) the inclusions. It facilitates the combination in the form of).

Inclusions that are not wetted by the metal but wetted by the solvent reach the contact surface between the liquid metal and the liquid solvent and are incorporated into the liquid solvent at the contact surface, thereby being removed from the molten metal during the cleaning operation.

Many patents describe metallurgical cleaning with solvents and apparatus and methods for filtering molten metal through porous materials, for example US Pat. Nos. 2,863,558, 3,006,473, 3,010,712, 3,025,155, 3,039,864. , 3,821,238, 3,737,305, British Patent 1,266,500, French Patent 2,061,246, French Patents 1,254,899 and 1,258,674, British Patent 1,148,344, United States Patent 3,277,547, and recently liquid aluminum US Pat. Nos. 3,893,917, 3,962,081, 3,947,363, 4,075,303, and the like, which describe porous ceramic materials for filtration.

The devices and methods as described in the above patents have long been satisfactorily used, but today the aviation industry requires thin strips, thin sheets and thin wires for packaging, thus making light alloys and metal semifinished products. In the field of production of natural alloys, there is a constant effort to improve the quality of the alloys and metals, and the microscopic inclusions that have been neglected until now by analytical refining not only damage specific mechanical properties, but also eutectic It has also been found that the heat treatment near the melting point of the constiuents is also harmful.

Accordingly, the present invention is to provide a filtration block for molten metal that can make the cleanliness of the metal higher than before,

It is an object of the present invention to provide a filtration block having a mechanical and physico-chemical effect formed by forming a microporous structure by sintering a block forming component having at least an outer melting point formed of an active inorganic compound and having a higher melting point than the metal to be filtered. By doing so.

Among the terms described in the text,

"Metal to be filtered" means a metal or alloy to be filtered by the filtration block of the present invention,

"Active inorganic compound" means a mixture of metal salts that acts as a solvent that exerts a physico-chemical effect on the various impurities and inclusions present in the metal to be treated and means impurities and inclusions from the metal filtered by this active inorganic action. Will be removed,

"Agglomeration" means a method for forming the active inorganic compound in a microporous structure that maintains mechanical stability at the filtration temperature, in the embodiment of the present invention is used a sintering method, "block forming component "Refers to the formation of a filtration block by agglomeration, regardless of its shape, the shape of this component being regular geometric particles, crystals, unevenly ground particles, elongated particles and needle-like particles. , Small rods or rods, in the form of fibrous bodies of circular or other cross-section.

The present invention provides a simple mechanical filtration that enables to retain inclusions and other foreign components of a size that cannot pass through a filtration block in a single filtration block, and allows removal of the inclusions in contact with molten metal. At the same time, it has a physico-chemical clean action provided by an active inorganic compound that acts as a solvent.

The present applicant can obtain the physico-chemical cleaning effect by the action of the solvent under the predetermined conditions, at least as well as the solid solvent in the form of particles as well as the liquid solvent, and the conditions which can obtain such effects are to be treated with the solid solvent particles. It was found that the contact area between molten metals should be increased. In addition, the applicant can massify the solid solvent component by sintering or the like, thereby forming a microporous structure that forms a sinuous passage between the components, thereby not only mechanically filtering the inclusions. It has been found that the corridor of the passage increases the contact area with the liquid metal, thereby enabling the physical-chemical clean. Applicants have also found that inorganic fluorides, in particular alkali and alkaline metal fluorides, and fluorides of magnesium and aluminum are suitable for bulking and are suitable as solvents having a melting point higher than the melting temperature of the metals and alloys to be treated.

Theoretically, sodium salts can be used. However, when these salts are used to treat aluminum and most alloys, sodium may penetrate into the filtered metal. Should not. It is well known that sodium salts have a particularly bad effect on such alloys even when they are contained in very small concentrations in Al-Mg and Al-Si alloys containing large amounts of silicon.

Among the possible mixtures of the above fluorides, mixtures up to binary, tertiary or quaternary, preferably having a melting point of at least 800 ° C., may suitably be used.

As an example thereof, the following composition may be mentioned, but it is of course not limited to such a composition.

In addition, the nature and form of the components forming the filtration block according to the invention can also vary widely.

That is, such block forming components may be formed homogeneously by forming the whole with an active inorganic compound, or may be formed by coating sulfuric inorganic compounds on an inert substrate or inhomogeneous by infiltrating an active inorganic compound with a porous inert substrate. There will be. The filtration block formed in a single body is composed of a block forming component having homogeneity (homogeneity or heterogeneity) or a mixture of block forming components having different properties.

The above-mentioned incompatible substrate may be selected from inorganic compounds that do not react with the metal to be treated, for example, electromelted alumina coringdon, electromelted alumina-zirconia compound (corindon containing zirconia), and Other silico-aluminum products and silicon carbide.

Carbonaceous materials such as graphite or certain coke can also be used. In addition, other compounds such as nitrides or oxynitrides of boron or silicon may also be used but are not widely used because of their high cost.

The shape and size of the block forming component is also an important factor for achieving the effect of the present invention. The shape of the block forming component determines the filtration block active surface area and the shape of the passage, which is minimal when using spherical particles. The active surface area can be increased by using flat or needle-shaped particles formed by grinding balls or other simple geometrical shapes.

Small rods or rods, or those of elongated fibers in which the ratio between length and average diameter is in the range of about 5 to 200, can be used as a block-forming component to form a felt-type filter block. The structure of the mold provides a great effect in that the shape of the passage is serpentine, the density of the formed holes, that is, the porosity is very large, and the active surface area is very large.

The heterogeneous block forming component, for example, by agglomerating a stable compound such as alumina with a high temperature decomposition or sublimable compound to remove the sublimable compound during such high temperature agglomeration or sintering, It can be manufactured by making it invade.

As above, homogeneous block forming components can also be prepared by activating inorganic acid mixtures in a mixture that can be removed by heating, evaporation or pyrolysis upon agglomeration. The size of the block forming component and the particle distribution are one of the factors that determine the porosity and permeability of the filter block, that is, the filtration capacity per hour.

For example, in the filtration block of the present invention having a thickness of 40 mm and a particle size of 4-8 mm, it had the ability to filter liquid aluminum at about 750 ° C. at 12 kg / cm ₂ per hour. It was about 10-20 mm. The porosity of such filtration blocks is about 40%.

It is also possible to use very small block forming components, such as tens of micrometers, as long as they can provide sufficient permeability to achieve the high filtration rates industrially required by bulking.

When the block-forming component in the form of a small rod or rod having a diameter of 1 mm and a length of 15 mm is agglomerated, a felt-like structure having a porosity of 80-90% is formed, and the filtration capacity of the liquid aluminum at 750 ° C is thick. 50 mm is about 25 kg / cm ₂ for 1 hour.

The filtration block according to the present invention is formed by agglomerating block forming components into a suitable shape and size according to the purpose of use, so that a plate, a cylinder, a tub, a crucible, a plug, or a plug of a relatively complex form can be formed from a simple plate. It may have the form of a nozzle, and is installed on the ladle or at the inlet of the mold. When the filtration block is installed at the inlet of the mold, the final processing of the metal is performed immediately before the molding bar at the position where the possibility of contamination does not occur, thus obtaining a high quality cast product that could not be realized in the past.

The manufacturing process of the filter block may be performed in various ways depending on the nature of the particles constituting the block forming component.

As an example of such fixation, after the active inorganic compound is melted, the molten compound is cast into a thin plate of a few mm thickness, pulverized and sieved to a desired size to adjust the particle size of the block forming component, and then The block forming component is injected into the mold, heated in a dry atmosphere to a temperature slightly below the melting point of the activated inorganic acid mixture and then sintered.

At this time, the sintering process is performed without applying pressure. Of course, in order to reduce the temperature and processing time, an appropriate pressure may be applied during the sintering process. In general, the agglomeration by sintering can be carried out in a dry atmosphere for a period of 5 minutes to one to two hours while avoiding contact with the flame at a temperature of 5-150 ° C. lower than the melting point of the active inorganic compound.

As a result, the microporous structure formed is mechanically very stable and resistant.

As another example of the manufacturing process, the mixture of inorganic compounds may be compacted or pelletized, and the compacted product or pellets are pulverized, followed by sieving to form a block-forming component having an appropriate particle size, and then bulking the component. have.

Block-forming components in the form of small rods or elongated fibers may be prepared by other means, for example by gravity casting molten-active inorganic compounds through a graphite die having a plurality of orifices adjusted to the desired diameter. After that, a die is formed by means of a die which is formed by an active inorganic compound which is rapidly cooled or in the form of fine crystals or powder and a binder which can be removed by evaporation or pyrolysis under high temperature conditions such as when agglomerated. It can manufacture by drawing. In the latter case, the resulting product is made of fibers or rods with a microporous structure.

When a heterogeneous block forming component is used, various manufacturing methods can be used depending on whether the component is porous or not, and a general method is to form a block by immersing the block forming component in an active inorganic compound in a molten state, for example. After coating or penetrating the active inorganic compound into the components, it is cooled and pulverized, and then sintered after controlling the particle size by filtration.

If the first material is an active inorganic compound in the form of very small particles ranging from tens of micrometers to 1-2 mm in order to create a structure with sufficient porosity, for example, it can be removed under high temperature conditions such as when agglomerated. Manipulating in a known manner to produce preliminary mixtures with sublimable organic compounds such as camphor, naphthalene, hexachloroethane, or thermally degradable binders such as polyethylene or polyurethane It is possible.

As another production method, an inert material having a microporous structure is prepared by a known method first, and an active inorganic compound is infiltrated into the inert material structure. For example, the particles of alumina are agglomerated by sintering to form a microporous structure, and the microporous structure is immersed in a bath of molten active inorganic compound to infiltrate the active inorganic compound into the microporous structure, and The excess amount of active inorganic compound is then removed by vibration, absorption and centrifugation. In addition, a sponge-like block forming component in the form of an organic substance which can be removed or destroyed by heat such as, for example, expanded polyurethane foam by a known method is prepared, and the component is prepared by using an active inorganic compound and an aqueous or non- It can be made to penetrate by immersing in a slop composed of a water-soluble solvent or dispersant, and then heat-dried to form a bulk of the active inorganic compound at the same time as destroying the polyurethane foam.

This method used to form porous ceramic structures is described in detail in US Pat. Nos. 3,090,094 and 3,097,930, in particular.

The following examples relate to a method for producing a filter block according to the present invention, and the present invention is not limited to such examples.

Example 1

The _binary mixture consisting of 50% by weight of NaF _{2 and} 50% by weight of CaF ₂ is melted at a temperature of about 1000 ° C., the molten mixture is cast into a 5 mm thick plate and then cooled, followed by crushing the plate to pulverized particles. Was adjusted to a particle size of 4-8 mm by sieving. Then, 2% by weight of LiF was added to the adjusted particles and mixed well for a long time. The mixture was injected into a mold having a disc shape having a thickness of 40 mm and a diameter of 190 mm, pressed by vibration, and then sintered by holding at a temperature of 950 ° C. for 20 minutes.

After cooling, the product obtained was disc-shaped with a porosity of about 40%, and had the ability to filter 3.6 t of molten aluminum per hour at about 750 ° C., at which time the pressure strengthening of the liquid aluminum was about 15 mm.

Example 2

Ternary mixture consisting of 49% by weight of MgF _2, 49% by weight of CaF ₂ , and 2% by weight of LiF was melted at a temperature of about 1000 ° C. and treated in the same manner as in Example 1, so that the particles had a particle size of 5-8 mm. The mold was 200 × 200 × 40 mm in size, and the sintering was carried out by holding at 930 ° C. for 35 minutes.

The resulting filtration block had a porosity of 40% and the ability to filter 5t of molten aluminum per hour at about 750 ° C.

Example 3

So-called "tabular" alumina and 5-6 mm particle size alumina were immersed in a bath consisting of 49% by weight of CaF _2, 49% by weight of MgF ₂ , and 2% by weight of LiF at a temperature of about 1050 ° C. for 30 minutes. After that, the alumina was removed from the bath, dehydrated, cooled, and ground, and then the particle size was adjusted to 5-6 mm. The products were then sintered and molded under the same conditions as in Example 2.

The resulting product had a porosity of 40% and the ability to filter 4.6t of molten aluminum per hour at about 750 ° C.

Example 4

A small rod or rod with a cross section of 1 mm and a length of 8 to 20 mm is cast by casting a molten mixture composed of 49% by weight of MgF _2, 49% by weight of CaF ₂ , and 2% by weight of LiF through a graphite die having a plurality of holes having a diameter of 1 mm. Cooled rapidly.

Thereafter, a small rod was placed in a graphite mold in the form of a square plate of 200 × 200 × 40 mm, and the rods were alternately placed by vibration to sinter for 30 minutes at a temperature of 920 ° C. to agglomerate.

The resulting product had a porosity of 85% and the ability to filter molten aluminum by 10t per hour at about 750 ° C.

Example 5

A filtration block having a thickness of 60 mm and a diameter of 40 mm obtained by treating in the same manner as in the above embodiment was placed on top of the supply pipe of the low pressure casting machine. The active inorganic compound used in the filter block is a ternary mixture composed of 85 wt% B ₄ F ₂ , 13 wt% MgF ₂ , and ₂ wt% CaF ₂ , with an A-S7G alloy (7% silicon and 0.9% magnesium). When the alloy containing aluminum as a base material) was processed, very good filtration was achieved.

The filtration block according to the present invention makes it possible to produce a high purity aluminum, magnesium joints that can meet the needs of the user.

In addition, the filtration block according to the present invention enables the treatment of other metals or alloys whose melting points can match the melting points of active inorganic compounds such as lead, tin, zinc, copper or their alloys. If necessary, the composition of the active inorganic compound can be adjusted by adding other substances such as borate or carbonate.

In addition, the filtration block of the present invention has very high mechanical strength and cohesion, and as a result of continuous use, no rupture or loss or destruction was found in the aggregated particles or any part thereof.

Prior to use, the block must be preheated to a temperature comparable to that of the metal to be filtered without directly contacting the flame. If work is interrupted, work must be resumed by cooling and then reheating the block.

Claims (1)

A microporous structure is formed by sintering a block-forming component having at least the outer side formed of an active inorganic compound of at least one inorganic salt selected from alkali and alkaline earth metal fluorides, magnesium and aluminum fluoride, and having a higher melting point than the metal to be treated. Filter block for molten metal having a mechanical and physicochemical effect formed.