Process for preparing cemented carbide scrap for recycling

Abstract

The present invention relates to a method for preparing cemented carbide scrap for recycling by removing residues and / or coatings from the cemented carbide scrap. The process involves subjecting the cemented carbide scrap to an acid treatment followed by removing the residues and / or coatings by mechanical means. Removing the residues and / or coatings limits the amount of undesirable particles and elements that can affect the quality of the recycled powder and of the cemented carbide made from said powder.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing cemented carbide scrap for recycling (reclaiming), which process involves cleaning and / or removing coatings before subjecting the scrap to a recycling process without generating additional waste. [Background technology]

[0002] Recycling of cemented carbide has been known for a long time, and several processes for recycling, such as direct and indirect recycling methods, are used in the art. The recycled material obtained from such processes is then at least partially replaced by virgin material in the re-creation of cemented carbide products. The proportion of recycled material in the production of cemented carbide has typically increased in recent years, and repeated recycling of cemented carbide can cause certain elements to accumulate in the recycled material over time.

[0003] Cemented carbides can be used in a variety of applications in mining tools, as wear parts, rolls, and cutting tools (e.g., inserts, drills, end mills, etc.). To extend tool life, it is common in the art to apply wear-resistant coatings to cutting tools. Typical coatings are CVD coatings (e.g., TiCN, Al2O3) and PVD coatings (e.g., nitrides of Si, Ti, Cr, Al, etc.).

[0004] If not removed during recycling, some elements from the coating and / or residues (e.g. brazing residues) can cause defects in the microstructure of the cemented carbide if present in excessive amounts. Increasing the proportion of recycled carbides in cemented carbide production can cause elements from the coating and other residues to accumulate over time or degrade the quality of the cemented carbide.

[0005] There have been many attempts to remove coatings from cutting tools. Many of these methods are based on the idea of ​​chemically dissolving the coating. In the case of drills, the coating can be removed without damaging the underlying cemented carbide. This is beneficial if the drill needs to be reconditioned, i.e., re-ground and coated. See, for example, U.S. Patent Application Publication No. 2011 0056914 (US20110056914). However, these methods typically involve chemicals that are expensive and difficult to handle.

[0006] Mechanical removal of residues and / or coatings can also be used, however the removal rate is not sufficient to meet the increasing demand to avoid the build-up of elements from the coating and their adverse effects on the product.

[0007] Cemented carbide scrap may also contain other undesirable elements or residues that are preferably removed prior to the recycling process, such as rock residues from mining tools, solder, brazing residues, etc. Such undesirable residues may reduce the quality of the powder and thus the quality of the final product.

[0008] An object of the present invention is to provide a method for removing coating from coated cemented carbide scrap with a high removal rate.

[0009] The object of the present invention is to provide a method for removing residues and / or coatings from hardmetal scrap, whereby the remaining hardmetal scrap can be recycled.

[0010] The object of the present invention is to provide a method for removing residues and / or coatings from hardmetal scrap in a time-efficient manner, which is chemically friendly.

[0011] The object of the present invention is to obtain a method for removing residues and / or coatings from hardmetal scrap, which allows for the sustainable recycling of both the hardmetal and the removed material. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to a method for removing residues and / or coatings from cemented carbide scrap, comprising the following steps: subjecting the cemented carbide scrap to an acid treatment in an acid solution having a concentration between 0.2 and 10N at a temperature between 15 and 99°C for a time between 30 minutes and 72 hours; Removing residues and / or coatings by mechanical means, The present invention relates to a method comprising:

[0013] The acid used in the acid solution may be any acid capable of dissolving the metal binder under residue and / or coating, preferably the acid is one or more of sulfuric acid (H2SO4), hydrochloric acid (HCl), acetic acid (CH3COOH), or phosphoric acid (H3PO3), more preferably one or more of sulfuric acid (H2SO4) and hydrochloric acid (HCl), and most preferably sulfuric acid (H2SO4).

[0014] If the cemented carbide scrap contains brazing residues (eg, solder), the solder may also be at least partially dissolved in the acid.

[0015] The concentration (normality) of the acid solution is 0.2 to 10N, preferably 0.3 to 6N, and more preferably 0.5 to 3N.

[0016] The temperature of the acid solution can be between 15 and 99°C, preferably between 50 and 90°C.

[0017] The time for which the cemented carbide is subjected to the acid treatment is between 30 minutes and 72 hours, preferably between 10 and 48 hours, depending on the concentration and temperature of the acid solution.

[0018] In one embodiment of the present invention, the acid treatment is carried out without the application of pressure or electrical current.

[0019] The cemented carbide pieces are preferably washed after the acid treatment to remove any residual acid, primarily to avoid corrosion of the equipment.

[0020] Although residues and / or coatings may still be present after the acid treatment, they will be less adherent because the acid treatment has dissolved the metal binder in the outermost portion of the cemented carbide, making them easier to remove. Thus, the coating is not necessarily affected by the acid treatment itself, but rather loses adhesion to the underlying cemented carbide substrate due to the dissolution of the metal binder.

[0021] After the acid treatment, the residue and / or coating is removed from the cemented carbide scrap by mechanical means. By mechanical means herein is meant any type of mechanical treatment capable of removing the residue and / or coating. The residue and / or coating is preferably removed by blasting or tumbling. Following the mechanical treatment, the removed residue and / or coating residue is separated from the cemented carbide scrap by suitable means such as sieving, magnetic means, etc.

[0022] In one embodiment of the present invention, after acid treatment, residues and / or coatings are removed from the cemented carbide scrap by blasting. Blasting can be used with all types of cemented carbide scrap, but is particularly useful for drills and end mills with flutes. If coatings are present within the flutes, they may be difficult to reach with other types of mechanical removal methods. The exact parameters of the blasting process, i.e., type of blasting media, blasting pressure, wet or dry blasting, nozzle size, etc., may depend on several things (e.g., the type of blasting equipment used), and it is up to those skilled in the art to adjust the parameters to achieve the desired results.

[0023] In one embodiment of the present invention, after acid treatment, residues and / or coatings are removed from the hardmetal scrap by tumbling. The most common type of tumbling involves placing pieces in a rotating drum, where the pieces collide with each other and with the drum walls. Tumbling is particularly suitable when processing large amounts of hardmetal scrap. The parameters of the tumbling process (e.g., drum load, rotation speed, etc.) are set by those skilled in the art depending on the type and size of the drum, the size of the hardmetal scrap, etc.

[0024] As used herein, cemented carbide scrap refers to solid pieces of cemented carbide in the form of cutting inserts, drills, end mills, mining buttons, rolls, and the like.

[0025] By hardmetal herein is meant a sintered material comprising grains of a hard phase embedded in a metallic binder, wherein the hard phase contains at least 50 wt% WC. Other hard phase constituents that may be present are carbides, nitrides or carbonitrides of one or more of Nb, Ti, Ta, Cr, V, etc.

[0026] The metal binder may be any metal binder used in the field of cemented carbides, such as any one of Fe, Co and Ni, or alloys thereof. The most commonly used binder is Co.

[0027] The most common type of coated cemented carbide scrap is cutting tools (e.g., inserts, drills, end mills, etc.). The coating to be removed can be any coating used on cemented carbide. Typical coatings are deposited using traditional PVD (physical vapor deposition) and CVD (chemical vapor deposition) techniques. Recently, more advanced deposition techniques, such as HIPIMS (high power impulse magnetron sputtering), which is a PVD technique, have also become more common.

[0028] Cutting tools such as inserts are typically deposited with either PVD or CVD techniques, whereas cutting tools such as drills or end mills are usually coated using PVD techniques.

[0029] Residue, as used herein, refers to any unwanted particles or elements that are not part of the cemented carbide substrate or coating. These residues are useful to remove from cemented carbide scrap before recycling the cemented carbide. Examples of residues include brazing residues, rock residues, and residues of workpiece material welded to the cutting tool during machining operations.

[0030] Cemented carbide mining tools and wear parts are typically brazed to holders, drill heads, etc. with solder. Before being recycled, the cemented carbide parts are separated from the holders and some of the solder may still remain on the cemented carbide parts as brazing residues. Mining tools may also contain pieces of rock that have been wedged into the mining tool during operation. Cutting tools may also contain brazed parts, which may leave behind brazing residues.

[0031] In one embodiment of the present invention, before the acid treatment, the cemented carbide scrap is subjected to a mechanical pretreatment. The mechanical pretreatment can be any technique that can cause defects (e.g., cracks) in the coating or even break the cemented carbide scrap into smaller pieces. Examples of such techniques include tumbling, blasting, and crushing. Creating defects or breaking up the scrap can make it easier for the acid in the acid treatment to penetrate the coating to dissolve the metal binder. This process can be useful when the coating thickness is too thick and / or when the coating is a very dense type, such as a HIPIMS coating. [Example]

[0032] Example 1 (invention) The coated batch of inserts was subjected to an acid treatment in 12 wt% H2SO4 at 70°C for 24 hours. After the acid treatment, the inserts were washed with water and subjected to a tumbling process in which 1500 g of inserts were placed in an 800 ml mill and the mill was filled two-thirds full with water. The mill was then run for 36 hours.

[0033] After tumbling, the cemented carbide scrap and fine coating residue were separated by a sieve (1 mm).

[0034] Comparing the cemented carbide scrap before and after the decoating process, it was concluded by visual inspection that more than 70% of the coating was removed.

[0035] Example 2 (invention) 13.75 tons of coated inserts were treated in 12 wt% H2SO4 at 80°C for 24 hours. After acid treatment, the inserts were washed and subjected to a tumbling process using a large mill (1 ton). The mill was then operated for 36 hours.

[0036] After tumbling, the cemented carbide scrap and fine coating residue were separated by a sieve (3 mm).

[0037] Comparing the cemented carbide scrap before and after the decoating process, it was concluded by visual inspection that more than 70% of the coating was removed.

[0038] Example 3 (comparison) A batch of coated inserts was subjected to a tumbling process in water for 36 hours. The inserts were washed and examined, and after visual inspection, more than 60% of the coating was still remaining.

[0039] The inserts were then subjected to a recycling process (Zn process) to form recycled cemented carbide powder. When analyzing the recycled cemented carbide powder, coating flakes and coating residues were detectable when viewing the powder under a microscope.

[0040] Example 4 Drills and end mills with PVD coatings were prepared.

[0041] One batch was subjected to acid treatment in 12 wt% H2SO4 for 24 hours at 60° C. This batch is hereafter referred to as Invention 1.

[0042] For comparison, the coated cutting tool portions that were not subjected to acid treatment were divided into three batches (Comparative 1-3).

[0043] Invention 1 and Comparative Examples 1-3 were subjected to dry blasting in a suction blast cabinet "Boy 100" equipped with a filtration unit using an injection blasting system with manual movement of the blast gun. The blasting media was Al2O3 (mesh 120). The pressure was 5 bar, the nozzle diameter was 8 mm, and the nozzle distance was 70 mm. The blasting times were varied and are shown in Table 1. The cutting tools were visually inspected and the results are shown in Table 1.

[0044] TIFF2026500649000001.tif96170

[0045] As can be seen from these examples, blasting alone does not provide sufficient coating removal, even with long blasting times, whereas the process according to the present invention shows a high removal rate.

Claims

1. 1. A method for removing residues and / or coatings from cemented carbide scrap, comprising the steps of: subjecting the cemented carbide scrap to an acid treatment in an acid solution having a concentration between 0.2 and 10 N at a temperature between 15 and 99°C for a time between 30 minutes and 72 hours; Removing residues and / or coatings by mechanical means; A method comprising:

2. 10. The method of claim 1, wherein the mechanical means is tumbling.

3. 3. The method according to claim 1 or 2, wherein the mechanical means is blasting.

4. 4. The method according to any one of claims 1 to 3, wherein the acid solution has a concentration between 0.3 and 6N.

5. The acid is sulfuric acid (H ２ SO ４ ), hydrochloric acid (HCl), acetic acid (CH ３ COOH), phosphoric acid (H ３ P.O. ３ 5. The method of claim 1 , wherein the first and second nucleotides are one or more of the following:

6. The acid is sulfuric acid (H ２ SO ４ 6. The method according to claim 1, wherein

7. 7. The method according to any one of claims 1 to 6, wherein the cemented carbide scrap has been subjected to a mechanical pretreatment before the acid treatment.

8. 8. The method of claim 7, wherein the mechanical pretreatment is selected from tumbling, blasting, and crushing.

9. 9. The method of any one of claims 1 to 8, wherein the cemented carbide scrap consists of cutting tools comprising a coating.

10. 10. The method of claim 9, wherein the coating is deposited by either PVD (physical vapor deposition), CVD (chemical vapor deposition), or the PVD technique HIPIMS (high power impulse magnetron sputtering).

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