WO2022194413A1

WO2022194413A1 - Process for recycling metallic materials, for producing raw materials for additive manufacturing

Info

Publication number: WO2022194413A1
Application number: PCT/EP2021/085840
Authority: WO
Inventors: Matteo VANAZZI
Original assignee: F3Nice S.R.L.
Priority date: 2021-03-18
Filing date: 2021-12-15
Publication date: 2022-09-22
Also published as: IT202100006527A1; BR112023017536A2; EP4221981A1

Abstract

A process for recycling metallic materials, for providing raw materials for additive manufacturing, which includes the steps of: a) finding a plurality of materials to be recycled; b) identifying the chemical composition of the materials to be recycled; c) separating the materials to be recycled according to their chemical composition; d) selecting two or more materials to be recycled with different chemical compositions; e) introducing the selected materials to be recycled in a crucible; f) melting the selected materials to be recycled so as to form a mixture; g) checking whether the chemical composition of the mixture is substantially identical to that of a target material for additive manufacturing; h) extracting the mixture from the crucible if the outcome of the checking step g) is positive, or selecting and introducing additional materials to be recycled into the crucible if the outcome of the checking step g) is negative; i) producing the target material for additive manufacturing.

Description

PROCESS FOR RECYCLING METALLIC MATERIALS, FOR PRODUCING RAW MATERIALS FOR ADDITIVE MANUFACTURING

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

More precisely, the present invention relates to a process adapted to provide raw materials for additive manufacturing.

As is known, the recycling of exhausted material is currently an important driver in the global market, which is increasingly oriented toward green policies that are respectful of the environment.

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

The methods and percentages of reuse of metallic alloys vary considerably depending on the various alloys of interest. in fact, while for some of these alloys recycling is relatively simple, in view of the Sow percentage of alloying elements contained inside them, this is not equally true for other high-alloy alloys.

Considering for example the recycling of stainless steel, it is estimated that a significant fraction thereof, comprised 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 down to 40%.

The remaining fraction is recycled as low-value steel, often mixing it with carbon steel, producing a true waste in terms of resource reuse: the more the initial material is high-alloyed, the more its incorrect recycling will have a negative impact from this point of view.

At the same time, the heterogeneous nature of the production systems still causes a relatively low addition of exhausted material in new metal.

It should be considered that while in electric arc furnace systems the content of recycled material reaches even 80-90%, in basic oxygen furnace systems this value never exceeds 20-30%,

The situation does not change much considering the recycling of metal for the production of alloys for additive manufacturing (AM). Here, too, the percentages are highly variable and depend from one material to another.

As regards high-alloyed ferrous alloys, for example, this value shifts between 70% and 80% in the case of the most virtuous manufacturers.

The remaining volume is constituted by newly extracted metal, be it in the form of pure elements or as an alloy, which is added to the initial material.

This process is currently considered indispensable both to correct the chemical composition of the alloy towards a standard ASTM specification and to further enrich the material in its most valuable alloy elements, so as to obtain the desired characteristics in the finished product.

US2020/086390A1 discloses a process for manufacturing metal parts including deploying a manufacturing center to a desired location, forming an alloy powder from a raw material using a deployable foundry module, and then forming the metal parts from the alloy powder using an additive manufacturing module.

US2020/189000A1 discloses a method for manufacturing metal components using recycled feedstock and additive manufacturing. The method includes the steps of providing a waste feedstock having a selected chemical composition; producing an additive manufacturing grade alloy powder from the waste feedstock using a cold hearth mixing process; providing an additive manufacturing system; controlling the production of the alloy powder such that the properties of the alloy powder optimize building of the components using the additive manufacturing system; and building the components using the alloy powder and the additive manufacturing system.

US2018/297122A1 discloses a system for producing metal spheroidal powder products by utilizing a microwave plasma, control over spheroidization and resulting microstructure.

The aim of the present invention is to obviate the drawbacks of the cited prior art.

Within the scope of this aim, a particular object of the present invention is to provide a process for recycling metallic materials, for providing raw material for additive manufacturing, that allows to optimize the addition of exhausted material in materials for additive manufacturing. A further object of the present invention is to provide a process that is effective, easy to implement and has a limited number of operating steps.

A further object of the present invention is to provide a process that can be applied to various types of metallic alloys but also to pure metals.

A further object of the invention is to provide a process which, being based mainly on the use of exhausted material, is advantageous from the economic standpoint and from the ecological standpoint.

This aim and these objects, as well as others which will become better apparent hereinafter, are achieved by a process for recycling metallic materials, for providing raw materials for additive manufacturing, as claimed in the appended claims.

Further characteristics and advantages will become better apparent from the description of some preferred but not exclusive embodiments of a process according to the invention, illustrated by way of non-limiting example in the single accompanying figure, which is a schematic block diagram of the process according to the invention.

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

More precisely, the materials to be recycled are treated in such a manner as to allow to obtain raw materials for additive manufacturing or, in other words, feedstock for additive manufacturing (AM).

The expression "materials to be recycled" is intended to refer preferably to steel alloys, among which the most important are alloyed steels, which have a minimum content of alloying elements of 10-12%, high-alloy steels, which have a minimum alloying element content of 25-30%, nickel-based alloys, such as for example Inconel® and Hastelloy®, as well as other metallic alloys.

However, it is apparent to the person skilled in the art that, in alternative embodiments, the materials to be recycled might also include alloys other than those here indicated by way of example.

The process according to the present invention includes a step a) which includes finding a plurality of materials to be recycled, which are found on the market in the form of WO 2022/194413 -A- PCT/EP2021/085840 manufacturing byproducts, waste or exhausted components.

The finding step a) is followed by a step b) which includes identifying the chemical composition of the materials to be recycled, preferably in accordance with ASTM standards.

The identification of the chemical composition of the various materials to be recycled occurs essentially by using instruments such as certificates of origin and certificates of conformity of the materials, which attest their chemical composition and allow to take into account the origin of the individual batches.

The quality of the materials to be recycled is further verified by means of sample checks, performed preferably with instrumental PMI (Positive Material Identification) methods.

PMI is in fact a spectrometry method which allows to know the chemical composition of ferrous and nonferrous materials without compromising or damaging them.

The identification step b) is followed by a step c) which includes separating the materials to be recycled according to their chemical composition.

This operation allows to avoid any dispersion and/or contamination of the alloys having the highest added value in the subsequent steps of the process.

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

After the separation step c), the process according to the invention optionally also includes a step d) which comprises pretreating the materials to be recycled, which, if necessary, are subjected to cutting, crushing and/or chemical washing.

The separation step c) and the optional pretreatment step d) are followed by a step d) which includes selecting two or more materials to be recycled having different chemical compositions, according to criteria which will become better apparent in the continuation of the description.

Subsequently, a step e) includes introducing the materials to be recycled in a crucible, such material being selected in the preceding step d). A further step f) includes melting the materials to be recycled so as to form a mixture.

Advantageously, the introduction step e) can be performed in different manners according to the size of the apparatus and/or of the required specificities.

More 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 simultaneously into the crucible and the entire mixture is brought to the melting point. in an aiternative embodiment, the materials to be recycled are fed to the crucible already in the liquid phase. in this circumstance, multiple sub-crucibles are used in order to melt the individual batches of materials to be recycled.

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

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

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

The base material preferably has a chemical composition which is substantially equivalent to that of the target additive manufacturing material.

The expression "chemical composition which is substantially equivalent" is understood to mean that the two materials have the same alloy elements but with different concentrations by weight on the total weight of the alloy.

In the specific 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 with respect to that of the corresponding elements of the target additive manufacturing material.

The comparison is performed by taking into account the acceptability intervals provided for each element of the alloy by the ASTM standards or reference specifications.

In alternative embodiments, the base material may however have a chemical composition which is at least partially different from that of the target additive manufacturing material.

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

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

However, the enrichment materials must have a high concentration by weight, on the total weight of the alloy, of elements needed to obtain the correct chemical composition of the target additive manufacturing material.

In the selection step d), therefore, the enrichment materials are chosen from the materials to be recycled which are available according to their chemical composition and are dosed in the mixture so as to obtain, after mixing, the correct chemical composition of the target additive manufacturing material.

The addition process is performed so as to ensure that the alloy elements that characterize the mixture are in line with the requirements related to the target additive manufacturing material, which in the specific case is constituted by an alloy that is optimized for 3D printing.

The addition is performed so as to prevent unwanted and/or unnecessary elements added by the enrichment materials from interfering with the chemical composition and with the properties of the mixture.

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

The percentages by weight on the total weight of the mixture to be associated with each enrichment material are calculated so as to optimize the efficiency of the consumption of the initial quantity of the associated material to be recycled and at the same time meet all the requirements in terms of chemical composition of the target additive manufacturing material. if, at a given moment, a material to be recycled that is indispensable in order to obtain a particular product is not present in a sufficient quantity, materials to be recycled that originate from external sources are supplied.

In any case, this supply is performed by minimizing the associated economic expenditure.

The found material to be recycled therefore replenishes the reserves of metal available, allowing to provide the requested products.

After the melting step f), there is a step g) which includes checking whether the chemical composition of the mixture contained in the crucible is substantially equal to that of the target additive manufacturing material.

The expression "chemical composition which is substantially identical" is understood to indicate that the two materials have the same alloy elements with the same concentrations by weight on the total weight of the alloy.

If the checking step g) yields a negative result, or if the chemical composition of the mixture is not substantially equal to that of the target additive manufacturing material, the process resumes substantially from the previous selection step d).

In practice, additional enrichment materials are selected which are then introduced in the crucible so as to correct the chemical composition of the mixture.

The additional enrichment materials may have a chemical composition that is substantially equal to that of the enrichment materials previously introduced in the crucible or can have a chemical composition that is at least partially different from them.

If the checking step g) has a positive outcome, i.e., if the chemical composition of the mixture is substantially equal to that of the target additive manufacturing material, a subsequent step h) is provided which comprises extracting the mixture from the crucible to then, in a further step i), produce the target additive manufacturing material.

Advantageously, the production step i) can be performed in different manners depending on the type of additive manufacturing material that one wishes to obtain with the process according to the invention.

According to a first embodiment, the process is used to produce additive manufacturing material in powder form.

In this case, the production step i) provides for using one of the known gas atomization processes, such as for example Vacuum inert Gas Atomization (VIGA), Electrode Induction Melting Gas Atomization (EIGA), or Plasma-melting Induction-guiding Gas Atomization (PIGA).

According to an alternative embodiment of the invention, the process is used to produce additive manufacturing materia! in wire form. in this case, the production step i) provides for example the use of dies.

The process according to the present invention allows to ensure an effective recovery of waste materials, such as residues of manufacturing processes or exhausted components, bringing the quantity of recycled materia! in the final product substantially to 100%.

Differently from the processes known in the art, therefore, the process according to the present invention allows to obtain a considerable economic and ecological saving.

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

This is due to the higher content of alloy elements in the additive manufacturing material, which are required to ensure the correct properties in the printed part.

In the processes known in the art, correction of the lacking elements occurs by adding pure metal in appropriate quantities.

This process entails a significant cost for two main reasons.

From an economic standpoint, the added pure metal has a significantly higher market price than waste metal, even if it is a highly alloyed alloy based on Fe or Ni.

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

Further characteristics and advantages of the process according to the invention will become apparent from the examples that follow, given by way of non-limiting illustration.

The examples relate to so-called "dual systems", obtained by mixing a base material and an enrichment material; the examples also relate to so called "triple systems", obtained by mixing a base material and two enrichment materials.

Dual systems and triple systems have been used to produce materials for additive manufacturing materials, indicated in the tables by the expression "Target AM”.

AISI 316L (UNS S31603) austenitic steel was used as a base materia! in the experimental tests.

Various materials commonly used by the reference industries in the field, and in particular F44 super austenitic steel (UNSS31254), F51 duplex steel (UNS 31803) or F53/F55 super duplex steel (UNS S32750/S32760) and the alloys Inconel® 625 (UNS N06625) and Inconel® 718 (N07718), were instead considered as enrichment materials.

EXAMPLE 1

In order to produce a target additive manufacturing material, a dual system composed of AISI 316L austenitic steel as base materia! and Inconel® 625 alloy as enrichment material was used initially.

The Inconel® 625 alloy has a concentration by weight, on the total weight of the mixture, equal to approximately 7%.

Table 1 lists the sampled chemical compositions with respect to the materials of interest together with the final composition given by the weighted mix thereof.

The values given in the last column relate to the fraction by weight of the material that was added to the 316L.

TABLE 1

Analysis of the results shows that the addition of Inconel® 625 on the order of approximately 7% by weight is capable of bringing the mixture to acceptable values of Ni, Cr and Mo. On the other hand, the concentration of S remains higher than the maximum acceptable value indicated in the specifications of the target additive manufacturing material (Target AM).

However, this value is not a problem for the process according to the invention, since desulfuration of additive manufacturing materials is a practice that is already widely applied and commercially available.

As regards the content of Cr, it is noted that it remains relatively low, close to the upper limit set by the specification being considered.

A decision was therefore made to shift to a triple system, adding F51 duplex steel as a further enrichment material. F51 duplex steel was added with a concentration by weight, on the total weight of the mixture, equal to approximately 4%. Table 2 lists the sampled chemical compositions with respect to the materials of interest together with the final composition given by the weighted mix thereof.

The values listed in the last column relate to the fractions by weight of the materials that were added to the 316L. TABLE 2

Analysis of the results shows that the addition of F51 duplex steel on the order of approximately 4% by weight produces the desired effect of increasing the value of Cr in the mixture.

EXAMPLE 2 Starting from the dual system of Example 1, composed of A!SI 316L austenitic steel as base material and Inconel® 625 alloy as an enrichment material, a shift was made to a triple system by adding F55 super duplex steel as an additional enrichment material.

The F55 super duplex steel was added with a concentration by weight, on the total weight of the mixture, equal to approximately 3%. Table 3 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof.

The values listed in the last column relate to the fractions by weight of the materials that were added to the 316L. TABLE 3

Analysis of the results shows that the addition of F55 super duplex steel on the order of approximately 3% by weight also produces the desired effect of increasing the value of Cr in the mixture.

EXAMPLE 3 Starting from the dual system of Example 1 , composed of AISI 316L austenitic steel as base material and Inconel® 625 alloy as enrichment material, a shift was made to a triple system, adding the F44 super austenitic steel as an additional enrichment material.

The F44 super authentic steel was added with a concentration by weight, on the total weight of the mix, equal to approximately 5%. Table 4 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof.

The values listed in the last column relate to the fractions by weight of the materials that were added to the 316L. TABLE 4

Analysis of the results shows that the addition of F44 super austenitic steel on the order of approximately 5% by weight does not yield significant improvements with respect to the Inconel® 625 alloy alone.

EXAMPLE 4 In order to produce a target additive manufacturing material, a dual system composed of AISI 316L austenitic steel as base material and inconel® 718 alloy as enrichment material was used initially.

The inconel® 718 alloy has a concentration by weight, on the total weight of the mix, equal to approximately 11%. Table 5 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof.

The values listed in the last column relate to the fraction by weight of the material that was added to the 316L, TABLE 5

Analysis of the results shows that the addition of inconel® 718 alloy on the order of approximately 11% by weight produces good results although not completely in line with the target values.

The base material is in fact in any case enriched with Ni, Cr and Mo without however being able to bring these values to specification.

A decision was therefore made to shift to a triple system, adding F51 duplex steel as additional enrichment material.

F51 duplex steel was added with a concentration by weight, on the total weight of the mixture, equal to approximately 14%. Table 6 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof. The values listed in the last column relate to the fractions by weight of the materials that were added to the 316L.

TABLE 6

Analysis of the results shows that the addition of F51 duplex steel on the order of approximately 14% by weight produces good results, although the value of Mo remains relatively close to the lower acceptability limit.

EXAMPLE 5

Starting from the dual system of Example 4, composed of AISI 316L austenitic steel as base material and inconel® 718 alloy as enrichment material, a shift was made to a triple system, adding F55 super duplex steel as additional enrichment material.

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

Table 7 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof. The values provided in the East column relate to the fraction by weight of the material that was added to the 316L.

TABLE 7

Analysis of the results shows that the addition of F55 super duplex steel on the order of approximately 10% by weight produces good results, although the Mo value remains relatively close to the lower acceptability limit.

EXAMPLE 6

Starting from the dual system of Example 4, composed of AISI 316L austenitic steel as base material and Inconel® 718 alloy as enrichment material, a shift was made to a triple system, adding F44 super austenitic steel as additional enrichment material.

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

Table 8 lists the sampled chemical compositions with respect to the materials of interest, together with the final composition given by the weighted mix thereof. The values provided in the last column relate to the fractions by weight of the materials that were added to the 316L.

TABLE 8

Analysts of the results shows that the addition of F44 super austenitic steel on the order of approximately 15% by weight produces good results.

The advantages achieved by means of the process according to the present invention are evident from the detailed description and from the examples given above.

The process for recycling metallic materials, particularly for providing raw materials for additive manufacturing, according to the invention is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; ail the details may furthermore be replaced with technically equivalent elements.

This application claims the priority of Italian Patent Application No. 102021000006527 filed on March 18, 2021 , the subject matter of which is incorporated herein by reference.

Claims

1. A process for recycling metallic materials, for providing raw materials for additive manufacturing, characterized in that it comprises the steps of: a) finding a plurality of materials to be recycled; b) identifying the chemical composition of said materials to be recycled; c) separating said materials to be recycled according to their chemical composition; d) selecting two or more materials to be recycled with different chemical compositions; e) introducing the selected materials to be recycled in a crucible; f) melting said selected materials to be recycled so as to form a mixture; g) checking whether the chemical composition of said mixture is substantially identical to that of a target material for additive manufacturing; h) extracting said mixture from said crucible if the outcome of said checking step g) is positive, or selecting and introducing additional materials to be recycled into said crucible if the outcome of said checking step g) is negative; i) producing said target material for additive manufacturing.

2. The process according to claim 1, characterized in that said identification step b) is performed by using certificates of origin and/or certificates of conformity of said materials to be recycled and by means of sample checks performed with PMI techniques.

3. The process according to one or more of the preceding claims, characterized in that it comprises, after said separation step c) and before said selection step d), a step d) of pretreating said materials to be recycled by crushing and/or chemical washing.

4. The process according to one or more of the preceding claims, characterized in that said selection step d) comprises choosing said one or more enrichment materials and optimizing the consumption of said materials to be recycled found in said finding step a).

5. The process according to one or more of the preceding claims, characterized in that, in said introduction step e), said two or more materials to be recycled are fed to said crucible in the solid phase.

6. The process according to one or more of the preceding claims, characterized in that, in said introduction step e), said two or more materials to be recycled are fed to said crucible in the liquid phase.

7. The process according to one or more of the preceding claims, characterized in that said mixture comprises a base material and one or more enrichment materials chosen from said materials to be recycled; said base material having a concentration by weight, on the total weight of said mixture, that is higher than that of the other selected alloys.

8. The process according to one or more of the preceding claims, characterized in that said base material has a chemical composition equivalent to that of said target additive manufacturing material.

9. The process according to one or more of the preceding claims, characterized in that said base material has a chemical composition that is at least partially different from that of said target additive manufacturing material.

10. The process according to one or more of the preceding claims, characterized in that said one or more enrichment materials have a chemical composition that is at least partially different from that of said target additive manufacturing material.

11. The process according to one or more of the preceding claims, characterized in that, in said production step i), said target additive manufacturing material is produced in the form of powder and/or in the form of wire.

12. The process according to one or more of the preceding claims, characterized in that said materials to be recycled belong to the group composed of alloy steels, high alloy steels, nickel-based alloys, or other metallic alloys.