WO2012175770A2

WO2012175770A2 - Composition and method for producing mn tablets

Info

Publication number: WO2012175770A2
Application number: PCT/ES2012/070433
Authority: WO
Inventors: Ricardo FERNÁNDEZ SERRANO; Gaspar GONZÁLEZ DONCEL
Original assignee: Consejo Superior De Investigaciones Científicas (Csic)
Priority date: 2011-06-20
Filing date: 2012-06-08
Publication date: 2012-12-27
Also published as: ES2395550B1; WO2012175770A3; ES2395550A1

Abstract

The invention relates to a composition for manufacturing Mn tablets, characterized in that it includes: (a) between 70% and 99.5% by weight of Mn powder; (b) a first powder binder chosen from at least one organic polymer that is insoluble in water and at least one organic polymer that is soluble in water, or a mixture of the two, wherein said first binder is not a wax. The invention likewise relates to a method for producing said composition and to the use thereof as Mn tablets in the casting of metals.

Description

Composition and procedure for obtaining tablets from Mn Technical Sector

The present invention relates to a mixture of additives in the preparation of compacted tablets of metals to add as alloys to a casting of another metal, mainly aluminum. More specifically, it refers to the use of a mixture of organic polymers that, mixed in the appropriate proportions, allows to obtain Mn powder tablets with good consistency, in terms of mechanical strength, and of easy dissolution in metal casting.

State of the Art

In the metal alloy alloy industry, there have traditionally been two strategies to carry out the alloy process. On the one hand, mother alloys with low alloying element contents, typically less than 60%, have been used. Among the main disadvantages of the use of this type of mother alloy are: that they add a large amount of cold material to the laundry, that the stock and transport of this product entails significant costs for the foundry and that the aluminum used in These alloys commonly come from previous smelters, adding difficulty in controlling their composition. This type of mother alloy has raised interest very recently (US2010313712) while alloys (in the form of splashes) with up to 93% Mn content, up to 5% in total Si and Fe, have been obtained, and The rest aluminum. Its high alloy content minimizes the melting furnace temperature drop and alloy recovery rates close to 100% are announced in periods of approximately 15 minutes. However, the main disadvantage of these mother alloys remains their high cost.

On the other hand, in the seventies of the twentieth century, compact alloys of metal powder began to appear on the market in typical concentrations of around 70%. This strategy greatly reduces the problems derived from the use of traditional mother alloys.

Since the worldwide implementation of the powder compact method as the main method of alloying aluminum alloys, the market has put pressure on manufacturers to increase the content of Mn in their products. This increase also means reducing dependence on aluminum, which is an expensive material and subject to changes in its price.

Obtaining tablets with high or very high Mn content, however, involves a series of technological challenges such as:

a) Obtain homogeneous mixtures of the alloying metal (Mn) with aluminum or with other types of binders that have different densities and particle sizes. It is well known that the difference in densities and / or granulometries of two types of powders hinders their homogeneous mixing since the lighter ones and the smaller particles tend to go to the bottom of the mixing vessel, dehomogenizing it. This problem is critical when working with high concentrations of one of the mixing elements (> 80%); b) Ensure the fluidity of the powder mixture from the tanks to the presses where the compacts are made. Specifically, the handling of powders and their mixtures efficiently on an industrial scale requires their good flow through the different devices, hoppers, ducts etc. of the production plants. It is known that the presence of very fine powders (<100 microns in diameter) substantially increases the contact surface between particles, which greatly hinders the flow of the powder towards the compaction presses;

c) Minimize the compaction time of the powder mixture to increase productivity. The largest investment of powder compact manufacturing companies is focused on the press system. For this reason, it seeks to minimize its number. For the productivity levels of the factories to be competitive, the compaction times of the powder mixture tend to be reduced to a few seconds. This factor determines the consistency of the compacts obtained when working with low concentrations of binder element;

d) Minimize the degradation of presses and punches due to the abrasive effect of Mn and other similar metals; e) Obtain tablets with sufficient consistency, in terms of mechanical strength, to facilitate handling and transport. The mechanical consistency of the powder tablets decreases with the content of the binder element, a fact that presents two drawbacks. The first is that the fragility of the tablets increases. Therefore they break easily, which, in addition to complicating its handling, makes it difficult to control the amount of alloying material that is added to the laundry. The second is the significant risk of flammability as a result of the fine powders that are released from this type of tablets in a high temperature environment such as that of a foundry; f) Obtain dissolution rates fast enough to minimize casting times while achieving good homogeneity of the alloy in the casting. The dissolution rates of conventional tablets (up to 85% Mn) are industrially acceptable. In addition, the presence of small amounts of organic waxes used as lubricants accelerates the dissolution process of the tablets when aluminum is used as a binder (US6149710). However, these waxes do not have the same binding power as aluminum and, in addition, should not be added in percentages greater than 5% since they increase the slag of the laundry, cause excess fumes, and introduce hydrogen and carbon into the alloy resulting;

g) Reduce pollution. For this, the use of binder materials that are harmful to both human and environmental levels or that deteriorate the properties of the final resulting alloy must be avoided. At present, the use of aluminum as a binder material and materials such as fluorides, chlorides and carbonates, which favor the dissolution of tablets, is widespread. These components, in addition to being harmful to the environment At the same time, they have also proven to be so because of the inclusions they generate in the alloys obtained.

Brief Description of the Invention

In order to manufacture powder compacts, the Mn being the main element, in a concentration typically> 70%, the use of a mixture of organic polymers with double function, binder and lubricant, for its manufacture is presented. This mixture of polymers allows to obtain compact with a good mechanical resistance while reducing the loss of fine powders during handling. In addition, the dissolution of manganese during casting is favored compared to compacts that use aluminum as a binder element and the cost is reduced, since the use of this element is minimized, even being avoided.

Thus, it is a first object of this invention a composition for the manufacture of Mn tablets characterized in that it comprises: (a) Mn powder in a percentage between 70% and 99.5% by weight, and more preferably between 70% and 97% of the composition; (b) a first powder binder selected from at least one water insoluble organic polymer or at least one water soluble organic polymer, or a mixture of both, wherein said organic polymer is not a wax; and (c) a possible second powder binder preferably selected from aluminum, iron, or their respective alloys.

For the purposes of this patent, powder is understood as the product that remains of a solid after being reduced to very small parts, generally with a particle size between 1 and 1000 um. A typical range of sizes is that indicated in Tables II and III of the detailed description of the invention.

Likewise, the method of obtaining Mn tablets from the composition described above is object of the invention. Said procedure is characterized in that it comprises compacting the different elements that they form the composition at room temperature (10 ° C-45 ° C).

In addition, if a heat treatment, after compaction, is applied to the tablet formed by the mixture (or not) of polymers and Mn powder, at a temperature above the melting temperature of the polymers, it is achieved a great union between the components of the tablet, significantly improving its mechanical strength and to a lesser extent its dissolution in the broth. Therefore, in a preferred embodiment of the invention, the process may comprise a stage after compacting the heat treatment of the composition.

Finally, the object of the invention is the Mn tablets obtained from said process and their use in metal casting, preferably, in aluminum, iron, or their respective alloys.

Brief description of the figures

Figure 1 shows an Mn tablet obtained from 146 g of Mn and 3.75 g of PEG 5000;

Figure 2 shows the evolution in time of the Mn content of the experimental casting broth according to Mn tablets with different composition, compacting the powders of the mixture at different loading levels and with subsequent heat treatment;

Figure 3 shows the mechanical resistance normalized by the height (mm) of the tested Mn tablets and in which the load axis was applied in the transverse direction. The commercial tablet, represented by squares, contains 80% Mn and 20% Al, and is 200 grams in weight. The rest of the tablets have been manufactured according to the present invention and contain 95% Mn. The data represented by rhombuses correspond to a tablet with 5% PEG, weighing 80 grams, compacted at low load (25Tn) and without subsequent heat treatment. The data represented by circles correspond to a tablet with 2.5% PEG and 2.5% PVA, 150 grams in weight and with a subsequent heat treatment of 100 ° C for 20 min. The data represented by triangles correspond to a 5% PEG tablet, 80 grams of compacted weight at 45 tons and with a subsequent heat treatment of 65 ° C and 20 min. As seen in the figure, the results obtained from the tablets of the present invention are superior to those obtained from the commercial tablet. This improvement is very significant, taking into account the percentage of Mn of the tablets (95%), higher than 80% of Mn of the commercial tablets.

Detailed description of the invention

The invention relates to the use of a mixture of organic polymers for the manufacture of tablets with a high manganese content (> 70%) by compaction at a temperature close to the environment (between 10 ° C and 45 ° C) of the mixture of organic polymers with manganese and optionally, with a metal selected from aluminum, iron, or its alloys. It is ruled out to replace one of the two polymers of the invention with a wax among which are: paraffin, microcrystalline wax, polyethylene or polypropylene waxes (which are similar to paraffin but with greater strength and flexibility), oxidized polyethylene waxes or carnauba This is because they give rise to softer tablets compared to polymer / polymer blends. In addition, waxes containing phenolic or aromatic components are graphitized when the temperature is raised in a vacuum or in an inert gas atmosphere, contributing carbon to the laundry.

The organic polymer blend consists of a water insoluble polymer (Type A) and a water soluble polymer (Type B).

The Type A polymer may preferably consist of a polymer selected from a group consisting of polymers of vinyl alcohols, polyurethanes, polyamides, polyacrylates and polymethacrylates, as well as any combination thereof. More preferably, said polymer may consist of polyvinyl acetate (PVA), which has a good combination of properties and a low price compared to aluminum; polyvinylbutyral, for its clean combustion that minimizes carbon residues; or poly (oxymethylene).

In a preferred embodiment of the invention, the Type A polymer may consist of Kollidon®, which comprises 8 parts (w / w) of PVA and 2 parts (w / w) of polyvinylpyrrolidone.

Preferably, the weight percentage of said Type A polymer in the composition is between 0.05% and 5.0%.

The Type B polymer may preferably consist of a polymer selected from a group consisting of polyethylene glycol (PEG), polyethylene oxide, polyethylene, celluloses, copolymers of ethylene, polypropylene and propylene oxide, as well as any combination thereof.

Preferably, the use of polyethylene glycol is proposed for its good combination of properties and its low price compared to aluminum, as well as polyethylene for its low price. Polyethylene oxide, although it has good compatibility with Type A and Type B polymers and has good thermal decomposition properties, is much more expensive than polyethylene glycol.

In the same way as Type A polymer, the weight percentage of Type B polymer in the composition is preferably between 0.05% and 5.0%.

An additional feature, of great importance for the invention, is that the molecular weight of the constituent polymers of the mixture is high. Thus, preferably, the molecular weight of the polymers used in the composition is preferably greater than 1000 g / mol, and more preferably, greater than 3000 g / mol. In a preferred embodiment of the invention in which the Type B polymer is PEG, when selecting the molar weight of the PEG used in the composition, it will be necessary to take into account that the hydroxyl value decreases inversely proportional to the molecular weight . In addition, the price of polyethylene glycol depends on the molecular weight.

PEG 5000-7000 has the best combination of hydroxyl value and price, so it is especially preferred in the present invention. In addition, polyethylene glycol has a high oxidation index, so it decomposes into components of lower molecular weight without leaving residues around 200 ° C. Thus, among the polymers of Type B, polyethylene glycol (PEG) of molecular weight greater than 4000 g / mol is especially preferred.

In a preferred embodiment of the invention, the described composition is constituted by the elements shown in Table I, where the preferred percentage by weight of each of said elements is also collected, so that the total sum of all of them in The composition is 100%. In relation to the Type A polymer and the Type B polymer, said polymers may be present independently or in combination:

Table I. Intervals in percentage by weight of the elements comprising the composition

One aspect of vital importance to achieve a good binding agglomerant-Mn is that its granulometries are complementary. This requires that the particles of the polymer mixture efficiently fill the gaps between the Mn particles. In this way, the presence of weak tablet joints will be reduced [R. Fernández, G. González-Doncel, R. Antolín, T. Posada and G. Borge, Alton T. Tabereaux TMS (The Minerals, Metals & Materials Society), 2004, pp. 769-773]. In the case of Mn, which traditionally comes from grinding larger pieces obtained by electrolysis, granulometries are typically available as described in Table 11 (a):

Table II (a). Typical granulometry of Mn powders

Particle size (m) Percentage (%)

<50 0 - 20 50 - 150 5 - 25

150 - 350 30 - 60

> 350 15 - 35

In particular, an example of the granulometry of Mn powders may be that shown in the following table II (b):

Table II (b). Typical granulometry of Mn powders

That is, qualitatively, after the grinding process, particles of Mn of less than 1 mm are obtained, and the fraction of fines (particles whose size is <100μπι) is minimized to favor the flow of dust through the different Industrial manufacturing process devices. Once these data are known, it is possible to calculate the ideal particle size of the polymer mixture with binder purpose. For this, it must be taken into account that the gaps that remain between the spherical particles of the metal are of the order of the average diameter of the particles divided by three. Therefore, it is known that the distribution of starting sizes of Mn is necessary to have a mixture of polymers that has a size distribution similar to that of Mn, in percentage of appearance, but dividing each size by three. The granulometry of the powders of the polymer mixture used according to said criteria for the present invention is described in Table III (a):

Table III (a). General granulometry of PEG powders

In particular, said granulometry can same as shown in table III (b):

Table III (b). Particular particle size of PEG powders

In the powder mixing process there is a high probability of segregation due to the difference in densities between the constituents of the mixture, since the density of the polymers is approximately 1 g / cm ³ , while that of Mn is 7.5 g / cm ³ . However, this effect is significantly reduced because the polymers described are extremely ductile above 25 ° C. In this way, segregation is reduced when the mixing process is carried out on an industrial scale, with a mass of powder in the mixers typically exceeding 100 kg. In these cases, the Mn is impregnated by the polymers due to the friction between particles during mixing. Despite this fact, it is desirable to work with fine binder granulometries that allow a homogeneous distribution of the binder in the powder mixture as described in Table II. Additionally, the fluidity of the mixture is improved by using polymers for their lubricating characteristics, especially that of polyethylene glycol, with a molecular weight greater than 6000 g / mol.

One aspect to consider in parallel is that this fraction of fine dust usually oxidizes easily in contact with the atmosphere. For this reason it is desirable to use polymers that have polar groups (soluble in water) that have a strong interaction with ceramic materials or oxides. Typically, the bond between the polymer and the metal (or the metal oxide) increases with the molecular weight of the polymer used.

After consolidation of the tablet components (manganese, water insoluble polymer and / or water soluble polymer, and optionally aluminum), by compaction in A press at room temperature (between 10 ° C and 45 ° C), is beneficial to improve the mechanical consistency and dissolution of the tablets in the broth of the laundry, carry out a heat treatment of the consolidated tablet. This treatment consists in keeping the tablet at a temperature above the melting point of the polymer with the lowest melting point for a specific time, for example 20 minutes. It is also beneficial for the mechanical consistency and dissolution of the tablets in the broth of the laundry to perform said heat treatment, for a similar time, at a temperature above the melting point of the polymer with the highest melting point.

The main advantage of the invention is that the use of aluminum (or iron) as a binder can be completely eliminated and that the total amount of binders added to obtain the tablets can be reduced. For both reasons the cost of manufacturing tablets is reduced. In addition, the mechanical strength of the tablets improves several orders of magnitude and in parallel the dissolution times of the tablets in the broth are improved.

Next, a series of examples of particular and non-limiting embodiments of the invention are presented, which allow demonstrating the advantages indicated. Examples of embodiment of the invention

Example 1. Mix of 5% by weight of PEG in powder form, 10% by weight of aluminum in powder form and 85% by weight of electrolytic Mn from milling;

· Example 2. Mix of 5% by weight of PEG with 95% of electrolytic Mn from milling;

• Example 3. Mixture of 2.5% by weight of PVA + PEG with 97.5% by weight of electrolytic Mn from milling; Example 4. Measurement of the mechanical strength of the tablets obtained in examples 1 to 3. Example 1. Mix of 5% by weight of PEG in powder form and 10% by weight of aluminum in powder form and 85% by weight of electrolytic Mn from milling. The powders described in Table IV were mixed in a turbot for 15 minutes at a rate of approximately 1 revolution per second to optimize the powder mixing process.

In this example, the preparation of Mn tablets from a particular composition according to the object of the present invention was carried out. Table IV shows the intervals by weight of the different elements present in the composition:

Table IV Intervals in percentage by weight of the elements that comprise the composition

The granulometry of the Mn used in the procedure was that corresponding to Table II (b). On the other hand, the granulometry of PEG powders was the one shown in Table III (b).

On the other hand, the aluminum used in the mixture was atomized aluminum powder with particle size between 100 μπι and 800 μπι. The resulting mixture is poured minimizing the segregation of both components in the compaction tooling, with its inner surface lubricated with zinc stearate.

The powder mixture according to Tables II and III was compacted in a cold press at a temperature between 10 ° C and 45 ° C.

Subsequently, the tablet obtained was extracted by applying about 700 kg of pressure.

The resulting tablet had a diameter of 40 mm and a height of approximately 22 mm with a final weight of 75 grams. The apparent density resulting from the process of Compaction was 2.7g / cm ³ .

The mechanical strength of the obtained tablets was studied by a free fall test from approximately 1 meter in height. The results of this test are shown in Table VII.

In order to study the dissolution rate of the resulting tablets, a wash with 5kg of 99.99% pure aluminum at a temperature of 740 ° C was carried out using a resistance furnace and a sand and graphite crucible.

Figure 2 shows the concentration of Mn measured by optical emission spectroscopy by spark, at different sample extraction times. The recovery rate of Mn is 98%, obtaining this value in a time 2.4 times less than using only Al as the binding element.

Example 2. Mix of 5% by weight of PEG with 95% of electrolytic Mn from milling.

The powders described in Table V were mixed in a turbot for 15 minutes at a rate of approximately 1 revolution per second to optimize the powder mixing process.

In this example, the preparation of Mn tablets from a particular composition according to the object of the present invention was carried out. Table V shows the intervals by weight of the different elements present in the composition: Table V. Intervals in percentage by weight of the elements comprising the composition

The granulometry of the Mn used in the procedure was the one corresponding to table II (b). On the other hand, the granulometry of PEG powders was that shown in Table III (b):

The mechanical strength of the obtained tablets was studied by a free fall test from approximately 740 millimeters in height. The results of this test are shown in Table VII.

To study the dissolution rate of the resulting tablets, a wash with 5kg of 99.99% pure aluminum at a temperature of 740 ° C was carried out using a resistance furnace and a sand and graphite crucible.

Figure 2 shows the concentration of Mn measured by optical emission spectroscopy by spark at different sample extraction times. The recovery rate of Mn is 98%, obtaining this value in a time 2.4 times less than using only Al as the binding element. Example 3. Mix of 2.5% by weight of PVA and PEG with 97.5% by weight of electrolytic Mn from milling.

In this example, the preparation of Mn tablets from a particular composition according to the object of the present invention was carried out. Table VI shows the intervals by weight of the different elements present in the composition:

Table VI Intervals in percentage by weight of the elements that comprise the composition

Element Composition interval (%)

Manganese 97.5

Polyethylene glycol powders

(PEG) of molecular weight 1.25

greater than 5000 g / mol Acetate Powders

polyvinyl (PVA) weight

1.25

molecular greater than 5000

g / mol

The granulometry of the Mn used in the procedure was that corresponding to Table II (b). Finally, the PVA was ground to obtain PVA powders with a particle size between ΙΟΟμπι and 800μπι. On the other hand, the granulometry of PEG powders was that shown in Table III (b).

To study the dissolution rate of the resulting tablets, a wash with 5kg of 99.9% pure aluminum at a temperature of 740 ° C was carried out using a resistance furnace and a sand and graphite crucible.

Figure 2 shows the concentration of Mn measured by optical emission spectroscopy by spark at different sample extraction times. The recovery rate of Mn is 98%, obtaining this value in a time 2.4 times less than using only Al as the binding element. Example 4. Measurement of the mechanical strength of the tablets obtained in examples 1 to 3.

The mechanical strength of the obtained tablets was studied by means of the so-called drop test in which the tablets were dropped in free fall from 740 mm high against a hard and rigid ground and the amount of throws needed is quantified so that the tablet loses a certain amount of material and breaks in an obvious way. The results of this test are shown in Table VII. Table VII shows the number of falls that each tablet has withstood in the drop test from 740 mm, together with the compaction conditions and subsequent heat treatment performed on each tablet. All tablets were compacted at 25 ° C and approximately 94 Tn. The result of number of falls in If it is less than 2, it is the average of performing the test on at least three tablets.

Table VII Fall test results

* These tablets did not break even after repeated attempts at free fall from a height of about two meters

Claims

1. Composition for the manufacture of Mn tablets characterized by comprising:

(a) Mn powder in a percentage comprised between 70% and 99.5% by weight of the composition;

(b) a first powder binder selected from at least one water insoluble organic polymer or at least one water soluble organic polymer, or a mixture of both, wherein said first binder is not a wax.

2. Composition according to claim 1, wherein the first binder is between 0.05% and 5% by weight of the composition.

3. Composition according to claim 1 or 2, characterized in that it comprises a second powder binder selected from aluminum, iron, or any of its alloys.

4. Composition according to claim 3, wherein the second binder is in a percentage less than 30% by weight of the composition.

5. Composition according to any one of claims 1 to 4, wherein the water-insoluble organic polymer is selected from a group consisting of polymers of vinyl alcohols, polyurethanes, polyamides, polyacrylates and polymethacrylates, as well as any combination thereof .

6. Composition according to claim 5, wherein the water-insoluble organic polymer is selected from a group consisting of polyvinyl acetate or PVA, polyvinyl butyral and polyoxymethylene, as well as any combination thereof.

7. Composition according to claim 6, wherein the water-insoluble organic polymer comprises 8 parts (w / w) of PVA and 2 parts (w / w) of polyvinylpyrrolidone.

8. Composition according to any one of claims 1 to 7, wherein the water insoluble organic polymer is a polymer with a molecular weight above 1000 g / mol.

9. Composition according to any one of claims 1 to 8, wherein the water soluble organic polymer is selected from a group consisting of polyethylene glycol, polyethylene oxide, polyethylene, copolymers of ethylene, polypropylene and propylene oxide, as well Like any of your combinations.

10. Composition according to claim 9, wherein the water-soluble organic polymer is a polymer with a molecular weight above 1000 g / mol.

11. Method of obtaining Mn tablets from a composition according to any one of claims 1 to 10, characterized in that it comprises compacting the elements that comprise said composition at room temperature.

12. A method according to claim 11, characterized in that it comprises a stage, after compaction, of heat treatment at a temperature above the melting temperature of at least one water-insoluble organic polymer or at least one water soluble organic polymer.

13. Mn tablet obtained from a method according to claim 11 or 12.

14. Use of a tablet according to claim 13 as an alloying element in metal casting.