Method for removing brass from a reinforcing element for a polymerised article
Patent Information
- Application Number
- EP2024711838
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-23
- Filing Date
- 2024-03-12
- Publication Date
- 2026-01-28
AI Technical Summary
The recycling of steel fibers used in polymerized articles, such as tires, is hindered by the difficulty in removing brass coatings, which contain copper and zinc, as conventional methods either fail to effectively strip the coating or pose environmental and safety concerns due to the use of ammonia.
An electrochemical treatment process using a sodium hydroxide solution with specific current intensity and residence time effectively removes the brass coating from steel fibers, reducing copper and zinc content to levels suitable for recycling, while minimizing iron extraction and maintaining mechanical strength.
This process allows for the efficient removal of brass coatings from steel fibers, enabling their recycling and reuse in producing high-quality reinforcing wires for polymerized articles, with reduced environmental impact and improved safety compared to traditional methods.
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Abstract
Description
[0001] METHOD FOR REMOVAL OF BRASS FROM A REINFORCING ELEMENT FOR A POLYMERIZED ARTICLE
[0002] Technical field of the invention
[0003] The present invention relates to the field of methods for treating metallic elements, in particular coated steel fibers intended for the reinforcement of polymerized articles, in particular rubber articles, and in particular to methods aimed at removing the brass coating present on these steel fibers in order to improve their recycling.
[0004] Prior art
[0005] Increasing pressure on natural resources and the desire to reduce the quantity of waste generated as much as possible are leading manufacturers to develop an increasing number of recycling solutions.
[0006] Steel recycling has been around for a long time. However, the proportion of recycled steel in a casting faces the problem of managing residuals, i.e., all elements other than iron. While some residuals such as carbon, silicon, or manganese can be adjusted or eliminated during steel production, other impurities, such as copper or tin, are more difficult to extract and can pose problems, particularly if the aim is to establish a so-called "circular" system in which used steel is recycled with a view to being used again for the same purpose. Indeed, any closed-loop process results in an accumulation of species that cannot be extracted, which can ultimately limit the quantity of recycled steel, particularly in the case of copper (Environ. Sci.Technol. 2017, 51, 6599-6606).
[0007] The steels used to manufacture metal wires for reinforcing polymerized articles, in particular rubber articles such as pneumatic or non-pneumatic tires, tracks and conveyor belts, have very low tolerances in terms of chemical composition, on the one hand to allow severe shaping by wire drawing, and on the other hand to have sufficient mechanical strength to ensure their reinforcing function. Thus, the residual contents present in the steel composition must be as low as possible.
[0008] Implementing a circular system for these metal wires therefore requires very careful management of the residual content. However, these metal wires are traditionally coated with brass, a copper and zinc alloy, to improve the adhesion of the rubber to their surface. Their recycling for reuse in the manufacture of tire-grade steels therefore requires the development of solutions to effectively manage residual content.
[0009] To do this, different solutions have been developed to de-plate steel, that is to say to remove the brass coating present on the surface of steel elements.
[0010] The document "Treatment of Coated Materials", M1458, Engineering Techniques, describes numerous demetallization solutions, by chemical or electrolytic means, notably based on alkaline solutions containing sodium cyanide.
[0011] Document DE2233157 describes the stripping of copper from copper-coated steel sheets by electrolytic treatment using an ammonia bath of ammonium phosphate or ammonium borate. However, copper alone does not behave like brass, which is an alloy. In addition, this method requires special management of the treatment products, particularly ammonia, which requires the implementation of special protective measures.
[0012] CN 103436899 describes the cleaning of the coating of steel cords for tires. To this end, the cords are treated in a strongly alkaline bath of ammonia and sodium nitrate. The volatility of ammonia requires frequent topping up and special protective measures.
[0013] Continuing its research, the applicant discovered that a detonning process implemented under specific conditions made it possible to effectively remove the brass coating from steel fibres intended for the reinforcement of polymerised articles, in particular rubber articles, whether these fibres were partially coated with rubber or not, thus opening the way for the recycling of these fibres into steelmaking processes with a view to their reuse for the manufacture of tyre-grade steel.
[0014] Detailed description of the invention
[0015] The invention relates to a method for detunning brass-coated steel fibers intended for reinforcing polymerized articles comprising at least one electrochemical treatment step in which the steel fibers are immersed in a treatment bath comprising a sodium hydroxide solution at a concentration of between 10 and 1000 g / l while being subjected to an anodic current, the mass current intensity ranging from 1 to 2500 A / kg of steel fibers, the residence time of the steel fibers in the bath being at least 7 min, preferably at least 10 min, and the temperature of the treatment bath being at least 30°C.
[0016] Definitions
[0017] In the present invention, unless expressly indicated otherwise, all percentages (%) indicated are percentages (%) by mass.
[0018] On the other hand, any interval of values designated by the expression "between a and b" represents the domain of values going from more than a to less than b (i.e., excluding the limits a and b) while any interval of values designated by the expression "from a to b" means the domain of values going from a to b (i.e., including the strict limits a and b).
[0019] By delamination, as known to those skilled in the art, is meant the removal of the brass layer covering a steel fiber.
[0020] The method according to the invention is a method for spooling steel fibers intended for reinforcing polymerized articles. By polymerized article is meant an article comprising a metal reinforcing element and a polymer matrix, such as a resin or a rubber composition. By rubber article is meant any rubber article reinforced with steel fibers. These articles are in particular chosen from vehicle tires, whether these tires are pneumatic or non-pneumatic (i.e. supporting the weight of the vehicle by a means other than a pressurized gas, for example by means of stays), conveyor belts, belts, tracks, the term rubber being understood here as any polymer compound exhibiting elastic behavior.
[0021] Steel fibers for reinforcing polymerized articles are understood to mean new steel fibers intended to be incorporated into polymerized articles, or steel fibers extracted from polymerized articles, whether these are in the so-called "raw" or uncrosslinked state, or in the "cooked" state, i.e. crosslinked or vulcanized. The steel fibers are reinforcing elements made of coated steel and cut so as to be treated in the process according to the invention.
[0022] Preferably, the rubber articles are chosen from vehicle tires, tracks, conveyor belts, and very preferably chosen from vehicle tires. Generally, a vehicle tire comprises a crown having two axial ends each extended, radially inwards, by a sidewall then by a bead intended to come into contact with a rim, the assembly delimiting an internal toric cavity. More precisely, the crown comprises, radially from the outside inwards, a tread, intended to come into contact with the ground via a rolling surface, a crown reinforcement and a portion of carcass reinforcement intended to ensure the reinforcement of the tire.The carcass reinforcement connects the two sides together by extending in a radially inner portion of the crown and is anchored, in each bead, to a circumferential reinforcing element, most often of the bead type.
[0023] The polymerized articles, in particular rubber articles, are treated, in a manner known to those skilled in the art, by cutting, sorting and grinding. The ground materials containing the metal reinforcing elements are then granulated in granulators and cleaned so as to reduce their rubber content. At the end of this treatment, the steel fibers obtained preferably have an individual length of at most 10 cm. Preferably, the steel fibers have a diameter ranging from 0.1 mm to 2 mm, preferably from 0.1 mm to 0.8 mm and very preferably from 0.1 mm to 0.5 mm.
[0024] The steel fibers treated in the process according to the invention preferably have a gum content ranging from 0 to 15% by weight of steel fibers, preferably ranging from 0 to 10% by weight of steel fibers and preferably ranging from 0 to 4% by weight of steel fibers.
[0025] The steel fibers treated in the process according to the invention are steel fibers coated with a brass metal coating, the brass content preferably ranging from 0.01 to 0.50% by weight relative to the mass of metal in the steel fibers. These fibers are preferably obtained from the crown reinforcement or the carcass reinforcement of vehicle tires when these elements are reinforced with metal wires.
[0026] Preferably, the copper content in the steel fibers ranges from 0.1 to 0.3% by weight and the zinc content in the steel fibers ranges from 0.05 to 0.20% by weight relative to the mass of metal in the steel fibers.
[0027] According to the invention, the steel fibers are immersed in a treatment bath comprising a sodium hydroxide solution at a concentration ranging from 10 to 1000 g / l, preferably from 50 to 500 g / l and very preferably from 75 to 300 g / l, while being subjected to an anodic current. Above 1000 g / l, the sodium hydroxide risks precipitating, while below 10 g / l the concentration is too low to allow efficient conduction of the electric current.
[0028] The residence time of the steel fibers in the bath is at least 7 min, preferably at least 10 min. Preferably, the residence time is adjusted so as to reduce the metal coating content relative to the mass of metal of the steel fibers by at least 90%. Preferably, at the end of the detonning process, the overall mass content of copper and zinc in the steel fibers is less than 0.005% for copper and 0.005% for zinc relative to the mass of metal in the steel fibers.
[0029] Electrochemical treatment of steel fibers using a soda solution makes it possible to detangle steel fibers even in the presence of a quantity of residual gum, with a reduced treatment time compared to a chemical treatment and excellent detangle selectivity. Indeed, the chemical treatments known from the prior art make it possible to remove part of the metallic coating, but also extract part of the iron from the steel.
[0030] The process according to the invention is operated at a temperature at least equal to 30°C, preferably at least equal to 40°C and preferably less than or equal to 80°C. These temperatures make it possible, in association with the other operating parameters, to operate with low risks of emissions due to evaporation, while maintaining excellent detonation performance.
[0031] The mass current intensity ranges from 1 to 2500 A / kg of steel fibers. Preferably, the mass current intensity ranges from 1 to 500 A / kg of steel fibers, preferably from 1 to 300 A / kg of steel fibers, preferably from 2 to 300 A / kg of steel fibers, very preferably from 5 to 20 A / kg of steel fibers. These intensities, in relation to the other operating parameters, make it possible to obtain a good compromise between the detongling of the steel fibers and the duration of the detongling treatment.
[0032] The invention also relates to the use of steel fibers resulting from the spooling process according to the invention for the manufacture of reinforcing wires for reinforced polymeric articles.
[0033] The steel fibres treated using the process according to the invention have a considerably reduced copper and zinc content, thus making it possible to push back the recycling limits linked to the presence of copper in recycled steel, the management of which is delicate, which opens up the possibility of their recycling at much higher contents in order to produce new steels for the reinforcement of reinforced polymeric articles, in particular for the reinforcement of vehicle tires.
[0034] Examples
[0035] In the following examples, different types of steel fibers are processed. A first batch, hereinafter referred to as "bare fibers," consists of scraps of brass-coated metal wires from the manufacture of reinforcing wires for tires. These fibers therefore do not contain any rubber, as they have not been incorporated into a polymeric article such as a rubber article.
[0036] A second batch, hereinafter referred to as "gummed fiber," comes from the processing of end-of-life tires. These tires are processed, in a manner known to those skilled in the art, by cutting, sorting, and grinding. The shredded material, which includes brass-plated cables, is then granulated in granulators and cleaned to obtain aggregates containing approximately 4% by weight of rubber (category E51 scrap metal according to AFNOR AF 08-821).
[0037] For each batch, the steel fibers individually have a length of no more than 10 cm.
[0038] The "bare fibers" comprise 160 mg of brass per 100 g of metal, or 0.16% by weight relative to the mass of metal in the steel fibers. An elemental analysis shows that brass is composed, by weight, of 64.4% copper and 35.6% zinc and that steel is composed, by weight, of 0.7% carbon, 0.5% manganese, 0.2% silicon and 98.6% iron, with other elements such as chromium, molybdenum, etc. being present in negligible quantities.
[0039] The "Gummed Fibers" contain 0.15% brass coating by weight relative to the mass of metal in the steel fibers. An elemental analysis shows that the brass is composed, by weight, of 63.6% copper and 36.4% zinc. The composition of the steel is identical to that of the "bare fibers".
[0040] Percentage of delinquency
[0041] To determine the percentage of detonation, the procedure is as follows. The content of brass coating Tl on the steel fibers is determined, expressed in mg / 100g of metal, before treatment. A sample of fibers is treated, then the content of coating T2 on the steel fibers is determined again. The percentage of extraction is then calculated according to ■ %extraction = (TLT2) / Tlxl00.
[0042] To determine the coating content on the fibres, the procedure is known to those skilled in the art, by chemical attack on the steel fibres and then by measuring the copper and zinc elements in the solution used for the chemical attack.
[0043] Attack of Steel
[0044] To assess the attack on the steel by the treatment carried out, the iron present in the chemical bath is measured at the end of the treatment. The more iron there is in the chemical bath, the more the steel in the steel fibers has been attacked by the treatment, which is detrimental. The amount of iron present in the treatment bath is reduced to the amount of iron present in the steel fibers before treatment.
[0045] The analyses show that the non-electrochemical treatments evaluated, with the exception of the treatment with soda and ammonia, lead to the presence of a significant quantity of iron in the treatment baths, with dissolved iron representing more than 20% by weight of the iron present in the steel fibers before treatment. Chemical treatment with ammonia diluted in a 30% by weight solution of hydrogen peroxide provides good performance, but this solution is not deployable due to the high constraints linked to ammonia.
[0046] The evaluated electrochemical treatments and the non-electrochemical treatment with soda lead to the extraction of very little iron from the steel fibers, with a quantity of dissolved iron less than 0.05% by weight of the iron present in the steel fibers before treatment.
[0047] Results
[0048] The conditions and results of the different treatments are presented in Table 1. It is observed that the process operated under the conditions of the invention makes it possible to obtain excellent detunning of the steel fibers while limiting the extraction of iron from the steel, in particular compared to known chemical treatments.
[0049] [Table 1]
[0050]
Claims
CLAIMS
1. A method of detunning brass-coated steel fibers intended for reinforcing polymerized articles comprising at least one electrochemical treatment step in which the steel fibers are immersed in a treatment bath comprising a sodium hydroxide solution at a concentration of between 10 and 1000 g / l while being subjected to an anodic current, the mass current intensity ranging from 1 to 2500 A / kg of steel fibers, the residence time of the steel fibers in the bath being at least 7 min and the temperature of the treatment bath being at least 30°C.
2. A method of detonating according to the preceding claim in which the temperature of the treatment bath is at least equal to 40°C.
3. A method of delamination according to any one of the preceding claims wherein the mass current intensity ranges from 1 to 500 A / kg of steel fibers, preferably from 1 to 300 A / kg of steel fibers, preferably from 2 to 300 A / kg of steel fibers, very preferably from 5 to 20 A / kg of steel fibers.
4. A method of detonating according to any one of the preceding claims in which the temperature of the treatment bath is less than or equal to 80°C.
5. A detonation process according to any one of the preceding claims in which the sodium hydroxide concentration in the treatment bath ranges from 50 to 500 g / l and very preferably from 75 to 300 g / l.
6. A method of delamination according to any one of the preceding claims wherein the steel fibers have a gum content ranging from 0 to 15% by weight of steel fibers, preferably ranging from 0 to 10% by weight of steel fibers and most preferably ranging from 0 to 4% by weight of steel fibers.
7. A method of delamination according to any preceding claim wherein the brass metal coating content of the steel fibers is from 0.01 to 0.50% by weight relative to the mass of metal of the steel fibers.
8. A method of detonating according to the preceding claim wherein the copper content in the steel fibers ranges from 0.1 to 0.3% by weight and the zinc content in steel fibers ranging from 0.05 to 0.20% by weight relative to the mass of metal in the steel fibers.
9. A method of spooling according to any one of the preceding claims wherein the steel fibers have a diameter ranging from 0.1 mm to 2 mm.
10. A method of spooling according to any preceding claim wherein the steel fibers individually have a length of at most 10 cm.
11. A de-silting method according to any preceding claim wherein the residence time is adjusted so as to reduce the metal coating content relative to the mass of metal in the steel fibers by at least 90%.
12. A method of rolling according to any one of the preceding claims in which the polymerized articles are rubber articles chosen from vehicle tires, tracks, conveyor belts, and very preferably consist of vehicle tires.
13. A method of rolling according to any one of the preceding claims in which the steel fibres come from the crown reinforcement or the carcass reinforcement of vehicle tyres when these elements are reinforced with metal wires.
14. Use of steel fibers from the spooling process according to any one of the preceding claims for the manufacture of reinforcing wires for reinforced polymeric articles.