IT202100006527A1 - PROCESS FOR THE RECYCLING OF METALLIC MATERIALS, IN PARTICULAR FOR THE CREATION OF RAW MATERIALS FOR ADDITIVE MANUFACTURING - Google Patents

Description

DESCRIPTION of the industrial invention entitled:

"PROCESS FOR THE RECYCLING OF METALLIC MATERIALS, IN PARTICULAR FOR THE CREATION OF RAW MATERIALS FOR ADDITIVE MANUFACTURING"

DESCRIPTION TEXT

The present invention refers to a process for recycling metallic materials.

Pi? precisely, the present invention relates to a process suitable for making raw material for additive manufacturing.

As known, the recycling of exhausted material is today an important driver in the global market, increasingly? aimed at environmentally friendly green policies.

In this context, the recycling of metals is certainly a profitable practice, as well as desirable from a sustainability point of view. public and environmental.

The modalities? and the percentages of reuse of metal alloys vary greatly according to the different alloys of interest.

Indeed, if for some of these recycling? relatively simple given the low percentage of alloying elements contained within them, for other highly alloyed alloys this is not? equally true.

Considering for example the recycling of stainless steel, it is estimated that a significant fraction of it, between 80% and 90%, is currently recycled.

However, of this material, the part that is "preserved" as stainless steel assumes highly variable values, with lower limits up to 40%.

The remaining fraction is recycled as low value steel - often mixing it with carbon steel - producing a real waste in terms of resource reuse: all the more? the starting material? high-tied, how much more? its incorrect recycling will produce? a negative impact from this point of view.

At the same time, the heterogeneity of production systems still causes a relatively low input of spent material into the new metal.

Suffice it to say that if in the Electric Arc Furnace systems the content of recycled material even reaches 80-90%, in the Basic Oxygen Furnace systems this value never exceeds 20-30%.

The situation does not change much if we think of the recycling of metal for the creation of alloys for additive manufacturing (AM - Additive Manufacturing).

Here too, the percentages are highly variable and depend from material to material.

For what? which concerns the high-alloy ferrous alloys, for example, this value moves between 70% and 80%, in the case of the producers pi? virtuous.

The remaining volume? made of newly extracted metal, both in the form of pure elements or in alloy, which is added to the starting material.

This process ? considered to be indispensable today, both to correct the chemical composition of the alloy towards specific ASTM standards, and to further enrich the material in its more alloying elements. valuable, in order to obtain the desired characteristics in the finished product.

Task of the present invention ? that of obviating the drawbacks of the cited prior art.

Within the scope of the aim set out above, a particular object of the present invention is that of providing a process for the recycling of metallic materials, in particular for the creation of raw material for additive manufacturing, which allows to optimize the input of spent material in the materials for additive manufacturing.

Another object of the present invention ? that of providing a method which is effective, easy to carry out and envisages a limited number of operating steps.

Another purpose of the present invention? that of providing a process applicable to different types of metal alloys, but also to pure metals.

Not the last purpose of the invention ? that of providing a process which, based mainly on the use of exhausted material, is advantageous from both an economic and an ecological point of view.

The task and the aforementioned purposes, as well as others that will appear better later, are achieved by a process for the recycling of metallic materials, in particular for the creation of raw material for additive production, characterized by the fact that it includes the phases of:

a) find a plurality? of materials to be recycled;

b) identify the chemical composition of said materials to be recycled;

c) separating said materials to be recycled according to their chemical composition;

d) select two or more? materials to be recycled with different chemical compositions;

e) introducing the selected materials to be recycled into a crucible;

f) melting said selected materials to be recycled so as to form a mixture;

g) verify if the chemical composition of said mixture ? substantially the same as that of a researched additive manufacturing material;

h) extracting said mixture from said crucible, if the outcome of said verification phase g) ? positive, or select and introduce further materials to be recycled in said crucible, if the outcome of said verification phase g) ? negative;

i) produce said researched additive manufacturing material.

Further characteristics and advantages will become clearer from the description of some preferred, but not exclusive, embodiments of a process according to the invention, illustrated by way of example and not as a limitation in the single attached figure, which shows a block schematic representation of the process according to the found.

The process according to the present invention ? suitable for the recycling of metallic materials with high added value and/or having a high internal alloying value.

Pi? precisely, the materials to be recycled are treated in such a way as to be able to obtain raw material for additive manufacturing, or feedstock for Additive Manufacturing (AM), if you prefer.

The expression "materials to be recycled" is intended to indicate, preferably, steel alloys, among which the most? important are alloy steels, with a minimum alloying content of 10-12%, highly alloyed steels, with a minimum alloying content of 25-30%, nickel-based alloys, such as Inconel<? >and Hastelloy<?>, as well as other metal alloys.

will result? however it is evident to the expert in the sector that, in alternative embodiments, the materials to be recycled could also include alloys other than those indicated purely by way of example.

The process according to the present invention comprises a phase a) which consists in finding a plurality of of materials to be recycled, which are found on the market in the form of processing by-products, waste or exhausted components.

Phase a) of finding ? followed by a phase b} which consists in identifying the chemical composition of the materials to be recycled, preferably in conformity? with ASTM standards.

The identification of the chemical composition of the various materials to be recycled takes place essentially using tools such as certificates of origin and certificates of conformity? of the materials themselves, which certify their chemical composition and allow the origin of the individual lots to be taken into account.

The goodness? of the materials to be recycled is further verified through spot checks, preferably performed with PMI (Positive Material Identification) instrumental techniques.

The SME ? in fact a spectrometry technique that allows you to know the chemical composition of ferrous and non-ferrous materials, without compromising them nor? damage them.

Phase b) of identification is followed by phase c) which consists in separating the materials to be recycled according to their chemical composition.

This operation allows to avoid any dispersion and/or contamination of the alloys at pi? high added value in the subsequent stages of the process.

Advantageously, the identification step b) and the separation step c) can be automated, for example through the use of conveyor belts and automatic checks performed preferably through magnetic probes and/or further spectrometry techniques.

After step c) of separation, the process according to the invention possibly also includes a step c) which consists in pre-treating the materials to be recycled, which, if necessary, are subjected to cutting, shredding and/or chemical washing.

Phase c) of separation and the possible phase c1) of pre-treatment is followed by phase d) which consists in selecting two or more? materials to be recycled with different chemical compositions, according to criteria which will be clarified further on in the description .

Subsequently, a phase e) is provided which consists in introducing the materials to be recycled selected in the previous phase d) into a crucible, and a phase f) which consists in melting these materials to be recycled, so as to form a mixture.

Advantageously, the phase e) of introduction pu? be implemented in different ways depending on the size of the plant and/or the specificities? requests.

Pi? precisely, according to a first embodiment, the materials to be recycled are fed to the crucible in the solid phase.

In this case, the different types of materials to be recycled are loaded into the crucible at the same time and the entire mixture is melted.

In an alternative embodiment, on the other hand, the materials to be recycled are fed to the crucible already in the liquid phase.

In this circumstance, multiple sub-crucibles are used to melt individual batches of materials to be recycled.

The molten metal is then taken from the individual sub-crucibles and mixed in the previously named crucible.

The mixture formed in phase f) ? essentially composed of a so-called "base material" and one or more? so-called "enrichment materials", chosen from the available materials to be recycled, during the selection phase d).

Preferably, the base material has a concentration by weight, on the total weight of the mixture, higher than that of the other selected alloys.

Furthermore, the base material preferably has a chemical composition substantially equivalent to that of the researched additive manufacturing material.

The expression "substantially equivalent chemical composition" is intended to indicate that the two materials have the same alloying elements, but with different concentrations by weight, on the total weight of the alloy.

In this case, at least part of the elements of the base material generally have a low concentration by weight, on the total weight of the alloy, compared to that of the corresponding elements of the desired additive manufacturing material.

Is the comparison carried out taking into account the ranges of acceptability? required for each alloy element by ASTM standards or reference specifications.

In alternative embodiments, the base material could for? have a chemical composition that is at least partially different from that of the researched additive manufacturing material.

The expression "at least partially different chemical composition" is intended to indicate that the two materials do not necessarily all have the same alloying elements.

The enrichment materials also generally have a chemical composition that is at least partially different from that of the additive manufacturing material sought.

The enrichment materials must for? possess a high concentration by weight, on the total weight of the alloy, of elements necessary to obtain the correct chemical composition of the material for additive manufacturing sought.

In phase d) of selection, therefore, the enrichment materials are chosen from the available materials to be recycled on the basis of their chemical composition, and are dosed into the mixture in order to obtain, after mixing, the correct chemical composition of the material for additive manufacturing wanted.

The addition process is carried out in such a way as to ensure that the alloying elements that characterize the mixture are in line with the requests relating to the material for additive manufacturing sought, which in this case is ? made of an alloy optimized for 3D printing.

Furthermore, the addition is carried out in such a way as to avoid unwanted and/or unnecessary elements brought about by the enrichment materials from interfering with the chemical composition and with the properties? of the mix.

The choice of enrichment materials to be used is essentially made on the basis of the availability? of the various materials to be recycled and the chemical characteristics of the additive manufacturing material sought.

Pi? precisely, the percentages by weight, on the total weight of the mixture, to be associated with each enrichment material are calculated in such a way as to optimize the consumption efficiency of the quantity? starting point of the relevant material to be recycled, and at the same time comply with all the requirements in terms of the chemical composition of the material for additive manufacturing sought.

If at a given moment a material to be recycled which is indispensable for obtaining a particular product is not? present in quantity? sufficient, will it be used? the procurement of material to be recycled from external sources.

In any case, this supply will come? carried out by minimizing the associated economic outlay.

The material to be recycled found will go? therefore to replenish the metal reserves available, allowing the production of the required products.

After phase f) of fusion ? foreseen a phase g> which consists in verifying whether the chemical composition of the mixture contained in the crucible ? substantially the same as that of the additive manufacturing material sought.

The expression "substantially equal chemical composition" is intended to indicate that the two materials have the same alloying elements with the same concentrations by weight, on the total weight of the alloy.

In the event that the verification phase g) gives a negative result, or in the event that the chemical composition of the mixture is not substantially the same as that of the material for additive manufacturing sought, the process substantially resumes from the previous selection phase d) .

In practice, further enrichment materials are selected and then introduced into the crucible, in order to correct the chemical composition of the mixture.

The further enrichment materials can have a chemical composition substantially the same as that of the enrichment materials previously introduced into the crucible, or they can have a chemical composition that is at least partially different from them.

In the event that the verification phase g) gives a positive result, or in the event that the chemical composition of the mixture is substantially the same as that of the material for additive manufacturing sought,? on the other hand, a subsequent phase h) is envisaged which consists in extracting the mixture from the crucible to then go, in a further phase i), to produce the material for the desired additive production.

Advantageously, phase i) of production can? be implemented in different ways according to the type of material for the additive production to be obtained with the process object of the invention .

Pi? precisely, according to a first embodiment, the method ? used to produce material for additive manufacturing in the form of a powder.

In this case, phase i) of production envisages using one of the known gas atomization processes, among which for example atomization with vacuum inert gas (VIGA Vacuum Inert Gas Atomization), induction atomization by electrode ( EIGA - Electrode Induction Melting Gas Atomization), or plasma induction atomization (PIGA - Plasma-melting Induction-guiding Gas Atomization).

In an alternative embodiment, however, the method ? used to produce additive manufacturing material in the form of wire.

In this case, phase i) of production envisages, for example, the use of dies.

The process object of the present invention allows to guarantee an effective recovery of waste materials, such as residues of manufacturing processes or exhausted components, bringing the quantity of recycled material in the final product almost at 100%.

Therefore, unlike the processes known in the art, the process object of the present invention allows to obtain a considerable economic and ecological saving.

As anticipated, the creation of alloys for 3D printing often requires an enrichment with respect to the base material used.

This ? due to the higher content of alloying elements in the material for additive manufacturing, necessary to guarantee the correct properties? in the printed piece.

In the processes known in the art, the correction of the defective elements takes place through the addition of pure metal, in suitable quantities.

This process involves a significant cost for two main reasons.

From an economic point of view, the pure metal added has a significantly higher market price. of the scrap metal, even if it is a high-alloy Fe- or Ni-based alloy.

At the same time, however, it also has environmental repercussions, given the need to to extract and process new material from nature reserves.

Other characteristics and advantages of the process according to the invention will become apparent from the following examples given for illustrative and non-limiting purposes.

The examples concern so-called "dual systems", obtained by mixing a base material and an enrichment material, and so-called "trial systems", obtained by mixing a base material and two enrichment materials.

The dual and trial systems have been used to produce the desired materials for additive manufacturing, indicated in the tables with the wording "Target AM".

As a basic material, in the experimental tests ? AISI 316L (UNS S31603) austenitic steel was used.

As enrichment materials, however, various materials commonly used by the reference industries in the sector were considered and, in particular, super austenitic steel F44 (UNS S31254), duplex steel F51 (UNS 31803) or super duplex F53/ F55 (UNS S32750/S32760) and Inconel<? >625 (UNS N06625) and Inconel<? >718 (N07718).

EXAMPLE 1

To produce a desired material for additive manufacturing, yes ? initially used a dual system composed of austenitic steel AISI 316L as base material and Inconel<? >625 as enrichment material.

the Inconel alloy<? >625 shows a concentration by weight, on the total weight of the mixture, equal to about 7%.

Table 1 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values shown in the last column concern the weight fraction of the material that been added to 316L.

TABLE 1

From the analysis of the results it can be seen that the addition of Inconel<? >625 in the order of about 7% by weight ? able to bring the mixture to acceptable values of Ni, Cr and Mo.

The concentration of S remains however higher than the maximum acceptable value that ? indicated in the specification of the desired material for additive manufacturing (Target AM).

However, this value does not represent a problem for the process according to the invention given that the desulphurisation of materials for additive manufacturing is a practice already? widely applied and available on the market.

As regards the Cr content, it is observed that it remains relatively low, close to the lower limit imposed by the specification considered.

Yes ? therefore decided to switch to a trial system, adding F51 duplex steel as an additional enrichment material.

F51 duplex steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 4%.

Table 2 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values reported in the last column refer to the weight fractions of the materials that have been added to the 316L.

TABLE 2

From the analysis of the results it can be seen that the addition of F51 duplex steel in the order of about 4% by weight produces the desired effect of increasing the Cr value in the mixture.

EXAMPLE 2

Starting from the dual system of example 1, composed of austenitic steel AISI 316L as base material and Inconel alloy? 625 as enrichment material, yes ? switched to a trial system by adding F55 super duplex steel as an additional enrichment material.

F55 super duplex steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 3%.

Table 3 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values reported in the last column refer to the weight fractions of the materials that have been added to the 316L.

TABLE 3

From the analysis of the results it can be seen that also the addition of F55 super duplex steel in the order of about 3% by weight produces the desired effect of increasing the Cr value in the mixture.

EXAMPLE 3

Starting from the dual system of example 1, composed of austenitic steel AISI 316L as base material and Inconel alloy? 625 as enrichment material, yes ? switched to a trial system by adding super austenitic steel F44 as an additional enrichment material.

F44 super austenitic steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 5%.

Table 4 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values reported in the last column refer to the weight fractions of the materials that have been added to the 316L.

TABLE 4

From the analysis of the results it can be seen that the addition of super austenitic steel F44 in the order of about 5% by weight does not give result in significant improvements over Inconel alloy alone? 625.

EXAMPLE 4

To produce a desired material for additive manufacturing, yes ? initially used a dual system composed of austenitic steel AISI 316L as base material and Inconel alloy? 718 as enrichment material.

The Inconel alloy? 718 has a concentration by weight, on the total weight of the mixture, equal to about 11%.

Table 5 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values shown in the last column concern the weight fraction of the material that been added to 316L.

TABLE 5

From the analysis of the results it can be seen that the addition of Inconel alloy? 718 in the order of about 11% by weight produces good results, even if not completely in line with the sought values.

In fact, the basic material is still enriched both in Ni, in Cr, and in Mo, failing for? to bring these values into specification.

Yes ? therefore decided to switch to a trial system, adding F51 duplex steel as an additional enrichment material.

F51 duplex steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 14%.

Table 6 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values reported in the last column refer to the weight fractions of the materials that have been added to the 316L.

TABLE 6

From the analysis of the results s? shows that the addition of duplex steel F51 in the order of about 14% by weight produces good results, even if the Mo value remains relatively close to the acceptability limit. inferior.

EXAMPLE 5

Starting from the dual system of example 4, composed of AISI 316L austenitic steel as base material and Inconel alloy? 718 as enrichment material, yes ? switched to a trial system, adding F55 super duplex steel as an additional enrichment material.

F55 super duplex steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 10%.

Table 7 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values shown in the last column concern the weight fraction of the material that been added to 316L.

TABLE 7

From the analysis of the results it can be seen that the addition of F55 super duplex steel in the order of about 10% by weight produces good results, even if the Mo value remains relatively close to the d? acceptability inferior.

EXAMPLE 6

Starting from the dual system of example 4, composed of AISI 316L austenitic steel as base material and Inconel alloy? 718 as enrichment material, yes ? switched to a trial system, adding super austenitic steel F44 as a further enrichment material.

F44 super austenitic steel? was added with a concentration by weight, on the total weight of the mixture, equal to about 15%.

Table 8 shows the chemical compositions sampled with respect to the materials of interest, together with the final composition given by the weighed mix of the same.

The values reported in the last column refer to the weight fractions of the materials that have been added to the 316L.

TABLE 8

From the analysis of the results it can be seen that the addition of super austenitic steel F44 in the order of about 15% by weight produces good results.

From the detailed description and the examples given above, the advantages achieved by the process according to the present invention are evident.

The process for the recycling of metallic materials, in particular for the production of raw material for additive manufacturing, according to the invention ? susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept; furthermore, all the details may be replaced by technically equivalent elements.

Of course, the materials used, as well as? the dimensions and shapes may be any according to the requirements and the state of the art.

Claims (12)

1. Process for the recycling of metallic materials, in particular for the production of raw material for additive manufacturing, characterized by the fact that it includes the phases of: a) find a plurality? of materials to be recycled; b) identify the chemical composition of said materials to be recycled; c) separating said materials to be recycled according to their chemical composition; d) select two or more? materials to be recycled with different chemical compositions; e) introducing the selected materials to be recycled into a crucible; f) melting said selected materials to be recycled so as to form a mixture; g) verify if the chemical composition of said mixture ? substantially the same as that of a researched additive manufacturing material; h) extracting said mixture from said crucible, if the outcome of said verification phase g) ? positive, or select and introduce further materials to be recycled in said crucible, if the outcome of said verification phase g) ? negative; i) produce said researched additive manufacturing material. 2. Process according to the preceding claim, characterized in that said identification phase b) takes place using certificates of origin and/or certificates of conformity? of said materials to be recycled and through spot checks carried out with PMI techniques. 3. Procedure, according to one or more? of the preceding claims, characterized in that it comprises, after said phase c) of separation and before said phase d) of selection, a phase c1) of pre-treating said materials to be recycled by shredding and/or chemical washing. 4. Procedure, according to one or more? of the preceding claims, characterized by the fact that said selection step d) takes place by choosing said one or more? enrichment materials in such a way as to optimize the consumption of said materials to be recycled found in said step a) of finding. 5. Procedure, according to one or more of the preceding claims, characterized by the fact that in said phase e) of introduction, said two or more? materials to be recycled are fed to said crucible in solid phase. 6. Procedure, according to one or more of the preceding claims, characterized by the fact that in said phase e) of introduction, said two or more? materials to be recycled are fed to said crucible in the liquid phase. 7. Procedure, according to one or more of the preceding claims, characterized in that said mixture comprises a base material and one or more? enrichment materials selected from said materials to be recycled, said base material has a concentration by weight, on the total weight of said mixture, higher than that of the other selected alloys. 8. Procedure, according to one or more of the preceding claims, characterized in that said base material has a chemical composition substantially equivalent to that of said researched additive manufacturing material. 9. Procedure, according to one or more of the preceding claims, characterized in that said base material has a chemical composition at least partially different from that of said researched additive manufacturing material. 10. Procedure, according to one or more? of the preceding claims, characterized by the fact that said one or more? enrichment materials have a chemical composition at least partially different from that of said researched additive manufacturing material. 11. Procedure, according to one or more? of the preceding claims, characterized in that in said production step i), said sought-after additive manufacturing material is produced in the form of a powder and/or in the form of a thread. 12. Procedure, according to one or more of the preceding claims, characterized in that said materials to be recycled belong to the group consisting of alloy steels, highly alloyed steels, nickel-based alloys or other metal alloys.