DE2405184A1 - METHOD AND SYSTEM FOR PURIFYING METALLIC MELT THROUGH FILTER CENTRIFUGING AND COLLECTION OF FILTRATE - Google Patents

Description

This invention deals with a new method and system for cleaning metals and / or alloys. The invention is particularly suitable for aluminum, its alloys and scrap alloys, but can also be used for other metals. The word 'TTetall ^11' is used in the following to denote pure metals as well as alloys.

Previously known methods remove hydrogen and suspended oxygen particles from liquid aluminum The help of chlorine, nitrogen or other gases or grass mixtures, which through graphite tubes through the melt be blown. Hydrogen escapes with the chlorine, the orid membranes swim to the surface of the enamel and become with it appropriate tools. The interaction between gas and melt is limited due to the limited surface contact between cleaning gas and melt. A significant amount of aluminum gets stuck in the scrape and cannot be easily recovered. Renewed contamination of the melt occurs before casting often on. Other methods use filter boxes, but they have metal flow problems and only certain ones Remove quantities of solid contaminants from the melt before the filter needs to be replaced. Especially for that No effective methods are known to process scrap alloys for reuse. Segregation of iron or manganese-rich crystals with subsequent decanting was attempted, but never used on a larger scale, because it is time consuming, expensive and not very effective.

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All such disadvantages are avoided by the invention. It was specially developed for use in the rapidly expanding field of cleaning and reuse of used and waste bottles and for cleaning of primary melts. The cleaning of the metal will be on best done shortly before pouring, which avoids renewed contamination. The aluminum losses are minimal.

The invention is a novel method and apparatus for cleaning metals using a filter centrifuge. Coarse solids, unwanted components in solution, and the finest solids become successful pus of the melt removed, all in one and the same apparatus under essentially constant pressure and pressure Temperature conditions. The invention specifically takes advantage of the centrifugal force around the area of contact between cleaning gas and metal, which in turn increases the effectiveness of the gas treatment. Each of the three cleaning processes has unique features. In connection they eliminate the difficulties of the previously existing systems and have many advantages. The three types of Cleaning operations performed with this invention are, in general terms:

1. The removal of suspended, non-metallic particles such as oxides and carbides from liquid Metal.

2. The removal of suspended, solid metallic Particles of liquid metal.

3 · The removal of gases and other elements in solution from liquid metal.

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Briefly, the metal cleaning npch of this invention is carried out in a novel metal centrifuge, in which a continuous flow of metal with suspended solid contaminant particles is introduced. The rotor holds most of the solid contaminant particles back while spraying the desired aluminum-rich melt into a metal-treating gas which either a cleaning device, a noble gas, or a reaction gas that adding one or more desired components to the filtrate, may be. The piltrate becomes, for example, nitrogen, chlorine or other gases or gas mixtures in order to prevent oxidation and / or to simultaneously hydrogen and others remove elements in solution. The solid contaminant particles left in the rotor only contain a minimal amount of metallic aluminum, as centrifugal force passes through practically all of the melt Filter is thrown into the collecting vessel, where it hits one impacts a fixed wall and sprayed it into small drops. Remaining, tiny, solid contaminant particles become removed from the metal while the drops run through a fluid salt bath that has a density lower than d ^ s metal to be cleaned.

The novelty of the method of the invention includes this Filter centrifugation of the metal to remove coarse contaminants and to take advantage of centrifugal force to enlarge the surface of the filtrate as it emerges from the rotor by spraying it into small drops or other fine configurations. This enables the

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optimal interaction between impurities dissolved in the metal and a cleaning atmosphere in the metal second cleaning operation and, if desired, further cleaning within the same apparatus by use a cleansing salt bath. The method enables the metal to be cleaned in a compact system in which dps metal filtrate is constantly protected from new contamination.

The apparatus of this invention consists of a centrifugal filter surrounded by a vessel that holds the The filtrate is collected in a semi-closed, protective Atmosphere and at a suitable temperature. The device is cheaper and easier to use than others so far known plants. The method and apparatus briefly described above are detailed below. Possible applications and advantages will be apparent to those skilled in the art from the following detailed description of the Best method of carrying out the invention in conjunction with the accompanying drawing, Figure 1 being a schematic Represents a side view, with a section mostly through the middle, which illustrates the best embodiment of the invention.

Figure 1 shows the centrifuge apparatus of this invention. A drive shaft (10) is connected to a motor with variable Speed connected (motor not in the picture). A cylindrical rotor (15), preferably made of cast iron, Steel, graphite, marinite, etc., is attached to a horizontal base plate (12) so that it can be lifted off. The bottom plate (12) in turn is attached to the upper end of the drive shaft (10).

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The rotor sidewall (20) is a rigid, liquid-permeable support which is easily removably attached to the bottom plate and which is designed so that filter material (22) can be attached to the inside thereof. The rotor sidewall (20) acts primarily as a support for the various types of filter materials (22) during centrifugation, but allows easy passage for the filtrate. It is preferably made of cast iron, but it can be made of other suitable materials. It can be constructed in the form of, for example, bars, girders, ribbons, grids or even grid wire. The removable cover plate (25), the pn the rotor side wall (20) is attached, has an opening in the center, suitable for the introduction of the contaminated melt, which is purified, while the rotor is driven by the drive shaft (10).

The rotor unit, consisting of the drive shaft, the The base plate, attached side wall and cover plate are surrounded by a S ^ -i ^ elgefass. The latter consists of one Outer wall (32) and an inner wall (35) with a heating system for heating the inner wall attached near the inner wall, preferably between the inner and outer walls. The heating elements (40), which are shown schematically in Figure 1, are radiators that are able to maintain the temperature in the The collecting vessel closes at the level of the temperature of the metal hold during this from the filter (22) and the rotor side wall (20) is ejected. As heating elements (40) are preferred electrical resistance heating elements with a external power source are connected. The inner and outer walls are connected to one another in order to be essentially gas-tight Chamber (42) to form including the heating elements.

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The chamber (42) has one or more inlets (4-5) provided and with one or more tangential gas vents (48). Cleaning gas is introduced through inlet (45), circulates around the heating elements and finally exits Chamber (A2) through outlet (48) and then circulates in the collecting vessel and finally escapes through outlet (50) and (52). While a construction with inner and outer wall is preferred, a single wall can also be used, with or without heating elements, since the temperature after start-up of the filtrate is high enough to cause the metal to solidify to prevent on the inner wall. For the same reason, the cleaning gas does not necessarily have to be heated. Before the When starting up, the system can be heated with various suitable heating devices, for example with one Heating flame.

The materials for the construction and the filter materials (22) are chosen so that no part with the liquid metal reacts at the working temperature. For aluminum, materials such as refractory can be used Stones, graphite, cast iron, glass cloth, clay, marinite, etc. The cleaning gas is preferably introduced tangentially into the chamber (42) and, after heating to the working temperature released into the collecting vessel (49), pus from which it can escape as previously described, or it can be sent to a desired one The body can be suctioned off by means of a corresponding conventional Suction device.

The apparatus is prepared for use by attaching a layer of filter material (22) to the inner rotor sidewall (20) is laid or fastened (e.g. one or more layers of glass fabric of the desired pore size) before the rotor side wall (20) is attached to the base plate (12),

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or by using loose filter material with one particle dimension redder than the perforations on the red or side wall (20) (e.g. alumina globules) is heaped on the base plate, after the side wall (20) has been attached to the base plate (12). Cover plate (25) is then attached to side wall (20) and the rotor cylinder is heated for a short time with the aid a heating flame which is introduced through the central opening in the cover plate (25). At the same time, the Sanmel jar (30) heated with the aid of heating elements (40). After sufficient heating, preferably a temperature slightly above that The temperature of the metal intended for cleaning is the Heating flame removed and protective or cleaning gas begins to circulate through the system (from inlet (45), port (48) to outlet (50) and (52)). Openings (50) and (52) can can also be closed and sealed and the gas escapes only at one point through a conventional gas collection system (Not shown). The motor is switched on and accelerated slow the rotor. Palis heaped on the base plate (12), If loose filter material is used, it is pressed by centrifugal force against the inside of the side wall (20), where it tends to spread out into an evenly thick layer, an even distribution can be facilitated by inserting a tool through the central opening of the cover plate (25) while the rotor is rotating.

In addition, if desired, the drain opening (55) can be closed and liquid cleaning salt of less Density than the metal to be cast can be added to the system through the central opening in the cover plate (25). The liquid one Salt collects in sump (60), which is preferably

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in Richtimg on the metal labIpuföffnung (55) is inclined to to facilitate the drainage of metal and salt. Additional drainage openings for dps draining the salt bath can be added in Collecting basin (60) or wall (35) are attached. The apparatus is now ready for commissioning,

The Metρ11 to be cleaned is through the central opening the cover plate (25) poured in, with the help of centrifugal force through filter (22) and the openings in the rotor side wall (20) pressed. It is sprayed into the collecting vessel (49) in the form of many small drops and jets (some of which are in the drawing indicated by dotted lines), whereby a large Mpss θπ metal surface the cleaning influence of the gas in the collecting vessel (49) is exposed. The inner wall (35) is partially suspended in steps (opposite the rotor wall (20)). The heated, vertical parts of the stepped distributor (75) redirect the direction of flow of the filtrate down to the collecting basin (60). The fine metal rays or Drops (70) collide with the heated, vertical surfaces of the distributor (75), and they spray up in the form of many small ones Droplets that drip downwards according to the force of gravity and are still exposed to the cleaning and / or protective gas. The purpose of such manifolds is the metal surface to enlarge even more and the metal droplets in almost the entire space between the collecting vessel wall (35) and to let rain down the rotor outer wall (20) instead of running down along a heated collection vessel wall. In this way, the metal jets and droplets maximally exposed to the action of the cleaning gas. if Collecting basin (60) contains a liquid salt (80) liquid an additional cleaning effect achieved during the

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Metal drops and rays through the liquid salt layer to the Drain the bottom of the sink before the metal drains (55) is tapped.

The mass of metallic and non-metallic solid contaminant particles of the metal to be cleaned is im Rotor retained by dps filter material. In the melt trapped gas is removed by the cleaning gas in Karmer (49) removed. Dps cleaning gas also prevents the oxidation of the metal thrown out of the rotor and removes some elements, which are in solution in the metal. The liquid salt layer in the collecting basin (6o) completes the cleaning process, so that the metal, which from the tap hole (55) is tapped, has a quality that could previously only be achieved through time-consuming and costly efforts, not about in such a simple and continuous way Process as npch of this invention.

As soon as the metal penetration is reduced because of the solid contaminant particles trapped in the filter material (22), which impede the normal flow of metal too much no further metal is added and the rotor is brought to a standstill as soon as the metal still in it is ejected has been. Cover plate (23), rotor side wall (20), Filter material (22) and the solid contaminant particles that have accumulated on it are removed and replaced with a new one Rotor of the same type, but of course free of contaminant particles, replaced. Usually the new rotor is heated up not necessary before metal cleaning is continued. Replacing the rotor only takes a minute if carried out by trained operators. The removed rotor assembly is cleaned, provided with new or cleaned filter material and is "ready for use again".

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The dimensions and the shape of each part of the apparatus can be changed and adapted to a specific cleaning process. For example, the rotor side wall (20) can be modified to a conical "truncated cone shape. The inner wall (35) of the chamber (30) can also be completely modified In addition, partitions or distributors in different sizes and shapes than the stepped shape can be placed on the inner wall (35) in order to split the filtrate into smaller droplets s slowing down of the metal droplets trickling down into collecting basin (60) are also within the scope of this invention Metal does not let through. Outlet (48) is closed and the GrPiS is under pressure through inlet (45) led. The G-PS then bubbles through the metal and the liquid salt (80) in the collecting basin (60) into the chamber (4-9) for maximum cleaning effect.

The following examples describe the preferred method of the invention:

Example I.

Aluminum alloy 3004, in a standard remelting furnace Melted from used aluminum cans, without any further Treatment passed through the filter centrifuge (Fig. 1) and shed into bars. Enamel samples taken before cleaning

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contained numerous suspended in the liquid metal Oxide flakes and become saturated with during melting hydrogen absorbed by humidity. In one There were numerous Straube-Pfeiffer vacuum testers Vesicles during the solidification of the sample. The metallographic examination also showed a high gas content and many oxide inclusions.

The filter centrifuge is placed between the smelting furnace and the casting unit and is equipped with a filter material consisting of an approx. 8 cm thick layer of alumina bowls with a diameter of approx. 1.3 cm and which is layered on the side wall of the rotor . The cylindrical side wall of the rotor should have perforations with cp. 2 to 3 mm (1/16 to 1/8 inch) diameter. Cleaning gas such as nitrogen, chlorine, COp, chloride gases, etc. is blown through the tank. The SsTpel vessel has a salt bath layer in the collecting base. The composition of the salt bath is $ NaCl ("He percentages are percentages by weight), A-5 ^ KCl and #>AlF.," 3NaF. Nachden the centrifugal filter has been heated to approximately 690 ⁰ C, the rotor is slowly accelerated to about 350 rpm, and the metal to be cleaned is continually added at a temperature of 680 ° C ± 5 ° C with the same casting speed as used for the continuous casting is needed. The drain of the filter centrifuge is opened as soon as a 13 cm (5 inch) high metal layer has collected in the collecting basin and the metal drain is then regulated at this opening according to the desired pouring speed. To improve the quality of the pieces cast from the metal, boron and / or titanium can be added to the Fitrat

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can be added by using boron chlorides and / or titanium chlorides as components of the cleaning gas.

Example II

Silicon was dissolved at high temperature in an aluminum scrap alloy with a high iron content. The melt was dpnn cooled so that silicon-containing crystalline particles consisting of approximately 14.8 ^ Si, 2.7 $ Fe and 82.5 $ Al and trace elements precipitate. The melt is cooled on 5QO ⁰ £ G in a manner DPSS separate Alpesi crystals are suspended from verhältnismäesig gross Grosse in the melt.

While the contaminant-rich particles are kept suspended by gentle agitation, the melt is poured into the Filter centrifuge introduced. The filter centrifuge is equipped with a filter material made of porous knot cloth that is attached to the Inside of the perforated cylindrical rotor side wall is attached. Nitrogen is admitted and, after heating to approx. 600 ° C, the rotor is brought to approx. 300 RPM.

The rotor, or at least the filter material, has to be replaced from time to time because of the accumulation of the Iron-rich crystals retained by the filter.

Example III

A high ferrous scrap aluminum alloy that too Contains silicon and has a composition of 14.8 $ Si, 2.7 $ Fe, 0.05 $ approx. And 82.5 $ Al and trace elements is used. The castability of cast alloys is seriously affected by calcium levels above $ 0.005. If undesirable Calcium should also be removed from the melt

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Claims (14)

apply the same method as in example II, however, chlorine is introduced instead of nitrogen. Dps Chlorine reacts with the calcium, and the cleaned alloy has less »Is ^ There are many other fields in which apparatus can be found this invention can be beneficially applied. Silicon kpnn dpmit can be cleaned by going more than 12 $ silicon alloyed with aluminum. The resulting aluminum-silicon alloy absorbs most of the trace elements, such as iron and calcium, that were originally contained in silicon, while clean, hypereutectic silicon crystals in the rotor lag behind. Any melt that contains solid, suspended particles or elements in solution or undissolved, which can be filtered out or cleaned with GPS npch of this invention can be treated successfully. This invention can also be implemented in another form without deviating from the concept or the essential characteristics thereof. The current "design must therefore In all respects, it should be considered a general description and not a specific limitation. The extent of the Invention is defined by the following claims, rather than the description above, and any amendments that may be made correspond to the spirit and scope of the claims, are therefore considered part of the invention. The claims are as follows: fl) / A filter centrifuge for metal and metal alloys consisting of a power-driven rotor with a side wall can leak through the liquid; a filling opening for the metal to be filtered and replaceable filter media, which are located on the inner side wall surface of the rotor; 409832/0393 a filtrate storage vessel that surrounds the rotor, which vessel has an outer and an inner wall, with free space between the two walls, both walls connected to one another to form an im essential closed double-walled sa ^ melkpmmer for The liquid filtrate was collected from the strung rotor kick; Device around the liquid filtrate near the lower To accumulate part of said inner wall and associated Outflow openings around the piltrat from the stringed app ^ ratiir to remove. An apparatus as described 2) in claim 1 wherein said Sa ^ melg-efäss is provided with gas intake and outlet, and may circulate elgefass ¹ wherein one or more gases through the S ^"17 * F for Kontaktnabme with the Piltrat when it ans exits the centrifuge rotor. 3) An apparatus as in claim 2, which also Contains devices around the inner wall of the collecting barrel a temperature equal to the temperature of the filtrate corresponds to that a \ is exiting the said rotor. 4) An apparatus as in claim 3, wherein said Heating means are installed in the space between the inner and outer outer walls and thus every Gbs that is in this Space circulates, can be heated. 5) An apparatus as described in claim 2, wherein said collecting vessel is additionally equipped with devices to distribute and disperse the Filtrpt over the whole Collection vessel. 6) An apparatus as described in claim 5, wherein the Device for distributing and scattering the piltrate from one or more, essentially vertical wall partitions 403832/0393 - 14 - "exists directly opposite the rotor side wall. 7) A filter centrifuge apparatus for metal melts consisting of a power-driven rotor, the top, bottom and side wall, an inlet in the top of said rotor to introduce the melt to be filtered, said side wall with openings to allow the "liquid to pass through, a ¹ ?!" Filter material, which is located in the inner side wall of the rotor, and a spinning vessel for dps of molten MetPllfiltrpt, which vessel surrounds the said rotor, the Sporne lire barrel consisting of a wall opposite the rotor side wall and a collecting basin with a drain for metal, connect with the vessel for the accumulation of the molten metal and for the controlled removal of it from the stringed apparatus. 8) A filter centrifuge as described in claim 7, wherein dps said collecting vessel additionally with devices is provided to distribute and spray the filtrate through the collecting basin, Q) A filter centrifuge as in claim 7, wherein the stringed devices for distribution and atomization consist of one or consist of several substantially vertical wall parts opposite the rotorwpnd. 10) A method of purifying molten metal, which consists of the steps of centrifugally pushing impurity particles, and utilizing the speed of the Filtrate, which is centrifuged out of said filter centrifuge, the ratio between surface and volume to enlarge the filtrate while the said filtrate is subjected to a selected gas treatment. 409832/0393 - 15 - 11) A method of purifying Mete IlsehmeIzen such as described in claim 10, wherein d ^ s said ratio of Surface area is increased to volume by adding the filtrate centrifugally, an essentially motionless one Blockage is centrifuged to df = s filtrate into smaller ones Splitting droplets. 1?) A method of cleaning molten metal like described in claim 11, wherein said droplets are formed in a cleaning gas atmosphere. 13) A method of cleaning molten metal such as described in claim 11 in which additionally said droplets pass through a metal cleaning salt bath and then the filtrate treated in this way is accumulated for the use. 14) A method as described in claim 13, wherein the said small droplets are evenly distributed over the salt bath. The patent attorney 409832/0393 Blank page