ES2240728T3 - PROCEDURE FOR THE MANUFACTURE OF HIGH CONCENTRATION MANGANESE MINITABLETS FOR ALUMINUM BATH ALLOY AND EXECUTION DEVICE OF THE SAME. - Google Patents

Abstract

The purpose of the procedure is to produce Mn minitablets with a concentration of between 90 and 98% of this metal, the binding material being Al particles. The procedure is based on using electrolytic Mn ground from flakes of a chemical purity of 99.7% or more, while this product is screened by means of a sieve with a mesh of 450 microns or less, where the fine powder content must be below 15%. Similarly, atomised Al powder produced by mechanical means must be used, with a grain size of 100 to 800 microns and with over 80% of the powder between 350 and 720 microns. The procedure is executed in a device with a storage hopper (1), a product diffuser (4) in that hopper (1), a hopper for compacting (6) and forming the minitablets in dies (9), in combination with pressing punches (7) and (8) and with the assistance of a honeycomb dispensing valve (10) interposed between the feeder chamber (5) and the compacting chamber (6). <IMAGE>

Description

Procedure for the manufacture of minitabletas High concentration manganese for alloy baths aluminum and its execution device.

Object of the invention

The present invention relates to a procedure for the manufacture of manganese minitabletas (Mn) High concentration for aluminum bath alloy (Al), whose purpose is to obtain minitabletas of Mn with a concentration between 90 and 98% of said metal, to be added in the Al foundry.

It is the object of the invention to obtain a product in minitabletas, in which Mn and Al are involved in powder, whose first component is obtained by electrolysis and milling, while the second component is atomized powder achieved by processes mechanics, mixing and compacting both components to get the minitabletas with high concentration of Mn.

It is also the object of the invention, the device for execution of the referred procedure, device in which loading, dosing, compaction and shaping takes place definitive of the minitabletas.

Background of the invention

The aluminum bath manganese alloy has varied substantially in recent decades, from the primitive addition of metal billets, which resulted in serious problems of purity of dissolution rate, passed to two concepts Different from the alloy. On the one hand, the use of mother alloys, consisting of Al and Mn alloys with a content of Mn between 10 and 25%, and, on the other, the addition of Mn powder by powder injection into the oven. Although both techniques are have continued to use, their employment has been drastically reduced since that at the end of the seventies the first were introduced Mn compact pads. These pills, which were presented in their form of tablets, minitabletas or briquettes, combine concepts of the two previous techniques, take advantage of their advantages and decrease Your inconveniences The tablets consist of Mn powder in one concentration generally greater than 75% compacted using as Al binder powder, a flux, or a mixture of both, in a concentration less than or equal to 25%. These materials considerably reduced the amount of cold material that was Add to Al oven in alloy operation compared with the mother alloys. In addition, mother alloys usually contain from 75 to 90% of second fusion aluminum, which can give problems in the broth, in addition to assuming a stock 4 times superior to compacted powder alloys. On the other hand, They are easy to use materials and do not need investments in equipment and safety that requires the injection of dust.

The important economic step that occurred at change the mother alloys, which contain a maximum of 25% of Mn, to the compact alloys, whose content in Mn is equal to or exceeds 75%, has generated continued pressure on the manufacturers of compact alloys to get materials that are effective In the Al alloy bath process allow in turn to increase the concentration of Mn in the compact alloy. In this sense, no Materials containing a percentage above 85% of Mn, mainly due to the Mn compatibility problems, an abrasive material and little malleable. In addition, it is suspected that the material may not dissolve as quickly as smaller compact materials concentration in Mn, due to the decrease in the percentage of Al and / or flux, which also acts as disintegrating elements of the compact once it has been introduced into the oven, as collected by the scientific literature about it.

Since the active element aleante of the Compact is the Mn, the decrease in Al content means a series of advantages for the smelter. The amount of material to add in the oven is smaller, which means that less is added cold material to Al bath, and that stocks of materials are reduced cousins. Similarly, there is a decrease in the costs of material transport, which will be significantly lower than those of the compact 75% or 80%. In addition to this, the price of products depend less on the value of Al, subject to changes in its exchange price (London Metal Exchange), and being currently more expensive than Al than Mn, the cost of all Raw materials used in production would also be inferior. Finally, we must consider that the smelter / user is not interested in adding to his oven a material (Al powder) that he same can sell and that also has an added value for atomization that is lost when melted again.

Despite these economic advantages, it has not verified the existence in the market of compact materials of Mn with a concentration greater than or equal to 90%. The achievement of This objective poses a series of scientific challenges when it comes to get continuously produce these materials. On the one hand, the experience indicates that the pressing process must be improved to allow to reach these percentages of Mn. On the other, the subjects premiums have a number of factors that can be modified to the Time to get better benefits. In addition, it is necessary check if it is really necessary to have in the oven compact with Al dust concentrations greater than 10% or at 15% so that the dissolution rate of the Mn is acceptable, or if compact with less than 10% of Al dissolve in the oven with adequate speed

The present study focuses on production in continuous and behavior in the oven of Al of minitabletas alloys (cylindrical) that contain Mn in concentration greater than 90%, with Al remaining material. Although it would be desirable to have this concentration also in tablets of size standard, the need to apply high pressures to the material it makes the study complicated if the diameter size of the Compact is greater than 40 mm. On the other hand, the fluxes are initially rejected in this study when it comes to materials whose binding action is much lower than that of Al in powder.

Regarding the raw materials to be used, the Mn It is the first limitation of the study. The chemical requirements of Al baths involve the use of high purity Mn chemical, generally above 99.7% purity, which only It can be ensured if Mn is produced by electrolysis. Currently only electrolytic Mn is produced in the Republic South Africa and the People's Republic of China, which reduces possibilities of finding materials with different specifications. The Mn, which is usually in the form of scales, must be Powdered by grinding. The material usually used in the compaction of minitabletas of Mn presents a grain size less than 450 microns. Mn powder is highly abrasive, behavior that is favored if the amount of fines (powder below 100 micrometers) increases, and which directly affects the quality of the pressing and the half-life of the materials (punches and shirt) of the press in which Compact the material.

The situation is very different in regards to the dust of Al involved. There is a great variety of Al powders that can be used in industrial processes in continuous and with different applications. In the case of Mn semitableta compaction, it is usual to use fractions of Al found above 100 micrometers and by below 1000 micrometers as far as the grain size is refer. These fractions are what in general the producers of Al Powder understands as a byproduct in its processes of production, as long as they are the fine fractions of Al (by below 100 micrometers) which due to the explosive capacity del Al find applications of great interest in aeronautics or pyrotechnics This fact makes again the production of a material with specific characteristics for compaction of Mn tablets, be biased or subject to conditions production independent of the application you want to study in this work.

In general, the Al used in the production of Mn minitabletas is a gas atomized powder, but also materials obtained by methods of mechanized atomization, annealed materials, chips or micronized In general, atomized powders are the most adapted to the demands of the great functions of Al.

In the production of the minitabletas of Mn, the Al acts as a binder, while the electrolytic Mn, highly abrasive and not very malleable, it is a material that alone is not compact Process improvements seem to go through a application on the material of higher pressures that allow the compaction of these materials. Apart from the use of hydraulic groups of higher performance and the application of greater efforts in pressing punches. Other possibility it comes from the reduction of the diameter of the minitabletas, since in a smaller area of force application results in a increased effective pressure This is a problem at the industrial level, since minitables of a smaller diameter give rise to a lower productivity (minitabletas weigh less). To avoid this problem, it is necessary to work with several punches at once, and the pressing process must be effective for all minitabletas manufactured in a cycle. This implies that all Shirts must be properly filled with the material to be compacted, which it must be properly mixed and not be different in each one of the shirts in which they are received, and that the material must flow Well, even these shirts. In this regard, it is very important to avoid that the mixture of Mn and Al powders is not segregated in any time of the process (problem that can easily occur at be both materials of very different densities) and, on the other side, that the equipment is sized properly for apply the pressure necessary for compaction.

Description of the invention

The recommended procedure allows to overcome the problems and difficulties discussed in the section previous, for which it is expected that, from the two components used and to be mixed, which are Mn and Al, the compaction of minitableta of Mn of concentration higher than 90% will be made through the use of Mn obtained by electrolysis and milling from Mn scales of purity chemical equal to or greater than 99.7%, which is subjected to a process of mesh screening with a light less than 450 micrometers; with the particularity that the milling process of Mn is controlled so that the fine powder content of Mn, with a size less than 100 micrometers, do not exceed 15%, since above this percentage the compaction cannot be assured of minitabletas of Mn with more than 90% of Mn in its composition.

The procedure also includes the fact that the most appropriate Al to achieve compaction of minitabletas of Mn, be atomized powder that is obtained by mechanical processes, with a controlled granulogy, being their nominal grain size ranges between 100 micrometers and 800 micrometers, with more than 80% dust between 350 and 720 micrometers

This grain distribution results thick enough to allow compaction of the material, and fine enough not to delay the dissolution rate, having reduced the number of grains of Al with the increase in the concentration of Mn in the minitableta.

The invention also relates to the device for the execution of the referred procedure, constituted from of a hopper receiving the mixture of Mn and Al with the characteristics referred to above, existing in said hopper a central diffuser of the product that forces it to flow through the side of the hopper to prevent the mixture from reaching directly feeding a second hopper that discharges into the respective pressing or compaction chamber, in which Pressing punches will act.

The device has appropriate means that allow to maintain a controlled maximum, minimum and security, in the compaction chamber, so that it is permanently with a filling level such that none of the punches try to perform a vacuum compaction.

The device includes, as one of the fundamental characteristics of novelty, in addition to the aforementioned central diffuser, an alveolar dosing valve arranged between the feed hopper and the compaction chamber, existing in this one a series of matrices that are mounted in a supportive support of the feed hopper itself, so that the hopper support assembly is susceptible to run through some guides, one way or another, as a result of pneumatic device, on whose guides a turn is mounted mobile punch holder that is also operated by a pneumatic cylinder, so that the movement hopper support is independent of the movement of the mobile punches, although such movements must be synchronized to fill, press, compact and eject the minitableta shaped.

In addition to the central diffuser already referred to and the location and use of the alveolar metering valve, the device also includes as a novelty feature, three electrical control means, to control the maximum level, a minimum level and safety level, corresponding to filling of the compaction chamber.

Description of the drawings

To complement the description that is being performing and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical realization of it, is accompanied as an integral part of said description, a set of drawings where with character Illustrative and not limiting, the following has been represented:

Figure 1. - Shows the graph corresponding to the granulometry type of the Mn used in the process of the invention. The Y axis contains intervals of grain size in millimeters, and the X axis the volume percentage of each fraction. The granulometry was performed by laser diffraction and introduction of the sample via
dry

Figure 2. - Shows a representation corresponding to the micrograph of Al powder in granules used in the process of the invention.

Figure 3. - Shows the corresponding graph to the granulometry type of Al used in the procedure of the invention. The Y axis contains the grain size intervals in millimeters, and the X axis the percentage by weight of each fraction. The Granulometry was performed using a sieve tower.

Figure 4. - Shows an elevation view schematic side, with sectioned part, of the device for Execution of the process of the invention.

Figure 5. - Shows an elevation view, in this frontal and sectioned case, of the same device of the figure previous.

Preferred Embodiment of the Invention

The process of the invention, intended for obtain minitabletas of Mn by compaction, with a concentration greater than 90% of this metal, it is based on using electrolytic Mn milled from Mn flakes of equal chemical purity or greater than 99.7%, screening the product by light mesh less than 450 micrometers, since it has verified that materials containing important fractions of higher grain size result in very dissolution rates low in the aluminum oven. The grinding process is controlled so that the fine powder content of Mn (below of 100 micrometers) does not exceed 15%, since above This percentage has been proven that the compaction of minitabletas with more than 90% of Mn in its composition. Figure 1 shows the graph corresponding to the granulometry type of the Mn used.

Tests performed indicate that Al dust more appropriate for compacting Mn tablets with concentration greater than 90%, is the powder atomized by mechanical procedures, due to the special behavior of this powder Al to its structure, in the form of spongy granules that allow adequate fluidity on the metal surfaces of hoppers, but that keeps enough air holes inside of the grains that allow greater compressibility of the material. Figure 2 shows the micrograph of Al powder in grains, according to an extension to the microscope of this type of powder.

The aforementioned Al powder also has a controlled granulometry, being its nominal ranges of size of grain between 100 and 800 micrometers, with more than 80% dust between 350 and 720 micrometers. This grain distribution is what thick enough to allow compaction of the material, and fine enough not to delay the dissolution rate having reduced the number of grains of Al (which initiate the dissolution reaction of the Mn of the minitableta in the oven) with the increase in the concentration of Mn in the minitableta. Figure 3 shows the graph corresponding to the Al grain type granulometry used.

The device for the execution of the procedure, is represented in figures 4 and 5, comprising a hopper (1) for receiving and storing the mixture that is enter through the corresponding filling mouth (2), mix that as already said is from Mn and Al. The mixture has to be homogeneous and on reception on the hopper (1) affects a diffuser (3) centrally established, diffuser (3) that has a conical configuration and is supported by legs (4), of so that diffuser forces the product to flow along the sides of the hopper (1) and never directly on the feed hopper (5) provided at the exit of the hopper (1) and from whose hopper (5) the product accesses the compaction hopper (6). The diffuser (3) prevents the effects of product segregation and ensures a fluidity in continuous at the same product level inside the hopper (1). The compaction hopper (6) is a vertical continuation of the hopper power supply (5), so that it determines a camera that maintains a product level and at which the compaction is performed  by means of fixed punches (7) and mobile punches (8).

In the compaction hopper (6) a series of nuances (9) are established, in variable number and depending on the dimensions of the device, whose matrices (9) access the product or powder mixture of Mn and Al through an alveolar valve (10) intercalated between the outlet of the feed hopper (5) and the compaction hopper (6), so that through that valve the product is dosedly loaded onto each of the dies (9) , since the alveolar valve (10) constitutes a kind of drum-sectors that are loaded with a certain amount of product so that when said valve rotates an angle, the corresponding sector load discharges onto the compaction hopper (6) and the product reaches the corresponding matrix (9). The matrices are provided on a support (11) that is integral with the compaction hopper itself (6), and that support-hopper assembly is mounted on guides (12), along which it can move in one direction and another by the effect of a pneumatic device, and on whose guides (12) a support (13) of the corresponding mobile punches (8) is in turn mounted, said support (8) also being driven by a pneumatic cylinder or device. The support-hopper movement is independent of the movement of the mobile punches, although such movements must be synchronized to fill, press, compact and eject the minitableta
conformed

The fixed punches (7) are arranged facing coaxially to the mobile punches (8), being those mounted on a static support (14).

In this way, when the support (11) with the compaction hopper (6) advances, the matrix (9) is filled, to the mobile punch (8) then enters into operation Advance and compact the material between it and the fixed punch (7). Then move the moving punch (8) and the assembly hopper support advances slightly so that the punch fixed (7) eject the minitableta, then restarting the cycle.

It is essential in said device to maintain a minimum level of product column in the compaction chamber (6), so that none of the punches attempt to compact an empty matrix, which would mean the breaking of punches and column or chamber. This level is maintained through the use of three electrical controls and the already mentioned alveolar valve (10), controls that correspond to references A, B and S, and that indicate, the maximum level, the minimum level and the safety level of the product in the compaction chamber (6), all in such a way that the safety level S causes that if the product descends from said level the device stops, because there will be danger of emptying the chamber, while level B is the level of product that allows to maintain a reproducible column weight capable of ensuring adequate fluidity and a homogeneous and reproducible filling in all punches. When the product has reached that level, the alveolar valve (10) opens and more product from the hopper is dispensed, said alveolar valve (10) being closed when the product reaches the maximum level
TO.

To obtain adequate compaction of the Half concentration of Mn equal to or greater than 90% is it is necessary to work with punches capable of applying a pressure 7500 Kg / cm2 punch. In a practical example, the mechanical strength of the product obtained with 90% and 95% of Mn, under the conditions explained, resistance check mechanics that have been performed using a consistent drop test in dropping on a cement floor several minitabletas from 1 m height, recording the number of hits recorded for your breakage and for the loss of a 2% weight of the minitableta.

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Minis Mn 90% Minis Mn 95% Number of tests 5 5 Falls for 2% weight loss 3 \ pm one 1.3 ± 0.6 Falls for breaking off 3.7 ± 0.6 2.3 ± 0.3

Dissolution tests of these have been performed minitableta of Mn with concentrations equal to or greater than 90% in Al bathrooms, an oven having been used for this semi-industrial 400 kg Al capacity, of gas heating and rotary. Experiments has been performed following standard and usual processes for addition of minitabletas, the clipping of the bath, the agitation and the taking of sample. Samples were analyzed by expectrophotometry of spark.

Claims (5)

1. Procedure for the manufacture of high concentration manganese minitabletas for the alloy of aluminum baths, whose purpose is to obtain minitabletas or Mn tablets with a concentration between 90 and 98% of said metal, from a mixture Mn and Al powder, for the alloy of baths of aluminum and other metals, is characterized in that it consists of using milled electrolytic Mn, from scales of chemical purity equal to or greater than 99.7%, and Al in atomized powder by mechanical means, with a controlled granulometry between 100 and 800 micrometers, and with more than 80% of the powder between 350 and 720 micrometers, a control of the milling of Mn being carried out to prevent the content of fine powders of Mn, with a size less than 100 micrometers, be less than 15%. 2. Process for the manufacture of high concentration manganese minitablets for the alloy of aluminum baths, according to claim 1, characterized in that the milled electrolytic Mn is subjected to a sieving process by means of a light mesh of less than 450 microns. 3. Method for the manufacture of high concentration manganese minitableta for the alloy of aluminum baths, according to previous claims, characterized in that the level of the mixture of Mn and Al, inside the corresponding compaction medium, is controlled by respective sensors to maintain said level of mixing between limits that ensure the execution of the compaction itself. 4. Device for manufacturing high concentration Mn minitables for the alloy of aluminum baths, which is intended for the execution of the process of the preceding claims, starting from a mixture of molded electrolytic Mn powder and Al atomized powder, including the device a storage and reception hopper of the mixture, as well as compacting means in an appropriate compaction chamber with matrices in which the minitablets are formed, including also pressing and ejecting punches of the shaped tablets, is characterized in that in the storage hopper (1) is provided with a central diffuser (3) that deflects the product towards the sides of the hopper, preventing the direct passage of said product towards the corresponding feeding chamber (5) and compaction (6), including between the feed hopper (5) and the compaction hopper (6) an alveolar valve (10) for product dosing or towards the corresponding matrices (9) that are part of the compaction chamber (6) and in which the minitabletas are formed; it being provided that said alveolar valve (10) is divided by sector to supply unit dose to the compaction chamber (6), producing the filling of each of the matrices (9) for subsequent compaction, conformation of the minitablets and expulsion of these by means of the corresponding fixed punches (7), which in combination with other mobile punches (8) perform the compacting and pressing of the product in the matrices (9). 5. Device for manufacturing high concentration Mn minitables for the alloy of aluminum baths, according to claim 4, characterized in that it includes three electrical sensors of product level inside the compaction chamber (6), to control the level maximum A, the minimum level B and the safety level S, which determine a correct compaction of the product in the matrices (9).