Method for preparing hard alloy waste for recycling

Abstract

The present invention relates to a method for preparing cemented carbide waste for recovery by removing any residue and / or coating from the cemented carbide waste. The method involves acid treatment of the cemented carbide waste followed by mechanical removal of any residue and / or coating. The removal of the residue and / or coating limits the amount of unwanted particles and elements that may affect the quality of the recovered powder and the quality of the cemented carbide produced thereby.

Description

[0001] The present invention relates to a method for preparing hard alloy waste for recycling. The method involves cleaning and / or removing any coatings before the recycling step of the waste without generating additional waste. Background Art

[0002] The recycling of hard alloys has been known for a long time, and several methods for recycling are used in the art, such as direct recycling methods or indirect recycling methods. Then, the recycled materials obtained by these methods at least partially replace the original materials when remanufacturing hard alloy products. Generally, in recent years, the proportion of recycled materials in hard alloy production has increased, and when recycling hard alloys repeatedly, certain elements may accumulate in the recycled materials over time.

[0003] Hard alloys can be used in many different applications, in mining tools, wear-resistant components, rolls, and cutting tools (such as inserts, drills, end mills, etc.). In the art, wear-resistant coatings are usually provided for cutting tools to extend the tool life. Typical coatings are CVD coatings (such as TiCN, Al2O3) and PVD coatings (such as nitrides of Si, Ti, Cr, Al, etc.).

[0004] If not removed during recycling, some elements from the coatings and / or residues (such as brazing residues) may cause defects in the microstructure of the hard alloy if the amount is too high. As the proportion of recycled hard alloys in hard alloy manufacturing increases, the elements and other residues from the coatings will accumulate over time, or the quality of the hard alloy will be reduced.

[0005] Several attempts have been made to remove coatings from cutting tools. Many of these methods are based on the idea of chemically dissolving the coatings. For drills, there are methods that can remove the coatings without damaging the underlying hard alloy. This is beneficial when the drill is to be repaired (i.e., reground and recoated). See, for example, US 20110056914. However, these methods generally involve expensive and difficult-to-handle chemicals.

[0006] Mechanical removal of residues and / or coatings can also be used, however, the removal rate is not sufficient to meet the growing demand for avoiding the accumulation of elements from the coatings and avoiding negative impacts on the product.

[0007] Hard alloy waste can also contain other unwanted elements or residues that are preferably removed before any recycling step, such as rock residues, solder, brazing residues, etc. in mining tools. These unwanted residues may reduce the quality of the powder and the final product.

[0008] An object of the present invention is to obtain a method for removing coatings from coated hard alloy waste with a high removal rate.

[0009] One object of the present invention is to obtain a method for removing residues and / or coatings from cemented carbide scrap, wherein the remaining cemented carbide scrap is recycled.

[0010] One object of the present invention is to obtain a method for removing residues and / or coatings from cemented carbide scrap, which method is time-efficient and wherein the chemicals are easy to handle.

[0011] One object of the present invention is to obtain a method for removing residues and / or coatings from cemented carbide scrap, wherein both the cemented carbide and the removed material can be recycled in a sustainable manner. Summary of the Invention

[0012] The present invention relates to a method for removing residues and / or coatings from cemented carbide scrap, the method comprising the steps of:

[0013] - acid-treating the cemented carbide scrap in an acid solution having a concentration between 0.2 and 10 N at a temperature between 15 and 99 °C for a period of time between 30 minutes and 72 hours;

[0014] - mechanically removing the residues and / or coatings.

[0015] The acid used in the acid solution can be any acid capable of dissolving the metal binder under the residues and / or coatings, 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).

[0016] When the cemented carbide scrap contains brazing residues such as solder, the solder can also be at least partially dissolved in the acid.

[0017] The concentration (normality) of the acid solution is between 0.2 and 10 N, preferably between 0.3 and 6 N, more preferably between 0.5 and 3 N.

[0018] The temperature of the acid solution can be between 15 and 99 °C, preferably between 50 and 90 °C.

[0019] The time for acid-treating the cemented carbide is between 30 minutes and 72 hours, preferably between 10 and 48 hours. This time depends on the concentration and temperature of the acid solution.

[0020] In one embodiment of the present invention, the acid treatment is carried out without any applied pressure or current.

[0021] After acid treatment, it is preferred to wash the cemented carbide workpiece to remove any residual acid. This is mainly done to avoid corrosion of the equipment.

[0022] After acid treatment, any residues and / or coatings will still be present, but with poor adhesion because the acid treatment has dissolved the metal binder in the outermost part of the cemented carbide, and thus the residues and / or coatings can be removed more easily. Therefore, the coating is not necessarily affected by the acid treatment itself. Instead, due to the dissolution of the metal binder, the adhesion to the underlying cemented carbide substrate will be impaired.

[0023] After acid treatment, the residues and / or coatings are removed from the cemented carbide scrap mechanically. By "mechanically" in this context is meant any type of mechanical treatment capable of removing the residues and / or coatings. Preferably, the residues and / or coatings are removed by sandblasting or tumbling. After the mechanical treatment, the removed residues and / or coating residues are separated from the cemented carbide scrap by any suitable means (such as sieving, magnetic means, etc.).

[0024] In one embodiment of the present invention, after acid treatment, the residues and / or coatings are removed from the cemented carbide scrap by sandblasting. Sandblasting can be used for all types of cemented carbide scrap, but is particularly suitable for drills and end mills provided with grooves. If there are coatings in the grooves, it may be difficult to achieve using other types of mechanical removal methods. The exact parameters of the sandblasting step, namely the type of sandblasting medium, sandblasting pressure, wet or dry sandblasting, nozzle size, etc. may depend on several factors, such as the type of sandblasting equipment used, and are adjusted by those skilled in the art so as to achieve the desired result.

[0025] In one embodiment of the present invention, after acid treatment, the residues and / or coatings are removed from the cemented carbide scrap by tumbling. The most common type of tumbling is to place the workpieces in a rotating drum, where the workpieces collide with each other and with the walls of the drum. Tumbling is particularly suitable when dealing with a large volume of cemented carbide scrap. The parameters of the tumbling process, such as the load of the drum, rotation speed, etc. are set by those skilled in the art according to the type and size of the drum, the size of the cemented carbide scrap, etc.

[0026] Herein, cemented carbide scrap refers to solid cemented carbide workpieces in the shape of cutting inserts, drills, end mills, mining button bits, rolls, etc.

[0027] Herein, cemented carbide refers to a sintered material containing hard phase grains embedded in a metal binder, where the hard phase contains at least 50 wt% of WC. Other hard phase components that may be present are one or more carbides, nitrides or carbonitrides of Nb, Ti, Ta, Cr, V, etc.

[0028] The metal binder can be any metal binder used in the field of cemented carbides, such as one or an alloy of Fe, Co, and Ni. The most commonly used binder is Co.

[0029] The most common type of coated cemented carbide scrap is cutting tools, such as inserts, drills, end mills, etc. The coating to be removed can be any coating used on the cemented carbide. Typical coatings are those deposited using conventional PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). More recently, more advanced deposition techniques have also become more common, such as HIPIMS (High Power Impulse Magnetron Sputtering), which is a PVD technique.

[0030] Cutting tools such as inserts are typically deposited using PVD or CVD techniques, while cutting tools such as drills or end mills are typically coated using PVD techniques.

[0031] In this article, residues refer to any unwanted particles or elements that are not part of the cemented carbide substrate or coating. It is beneficial to remove these residues from the cemented carbide scrap before recycling the cemented carbide. Examples of residues are brazing residues, rock residues, residues of workpiece materials welded to the cutting tool during mechanical operations, etc.

[0032] Mining tools and wear parts of cemented carbides are usually brazed to brackets, drills, etc. with solder. Before being recycled, the cemented carbide parts are separated from the brackets, and some solder can still remain on the cemented carbide parts as brazing residues. Mining tools can also contain parts of rocks wedged into the mining tools during operation. Cutting tools can also contain brazed parts, which may leave brazing residues.

[0033] In one embodiment of the present invention, the cemented carbide scrap is mechanically pretreated before acid treatment. The mechanical pretreatment can be any technique capable of causing defects (such as cracks in the coating) or even breaking the cemented carbide scrap into smaller pieces. Examples of such techniques are tumbling, sandblasting, and crushing. Causing defects or breaking the scrap can make the acid in the acid treatment more easily penetrate the coating, thereby dissolving the metal binder. This step can be beneficial if the coating thickness is too large and / or if the coating has a very dense type (such as HIPIMS coating, etc.).

[0034] Example 1 (Invention)

[0035] A batch of coated inserts was acid-treated in 12 wt% H2SO4 at 70 °C for 24 hours. After acid treatment, the inserts were washed with water and tumbled in a mill with a volume of 800 ml for 1500 g of inserts. The mill was filled with water up to 2 / 3. Then the mill was run for 36 hours.

[0036] After tumbling, the cemented carbide waste is separated from the fine coating residues by a sieve (1 mm).

[0037] When comparing the cemented carbide waste before and after the coating removal process, it can be determined by visual inspection that more than 70% of the coating has been removed.

[0038] Example 2 (Invention)

[0039] 13.75 tons of coated inserts are treated in 12 wt% H2SO4 at 80 °C for 24 hours. After the acid treatment, the inserts are washed and tumbled using a large mill (1 ton). Then the mill is run for 36 hours.

[0040] After tumbling, the cemented carbide waste is separated from the fine coating residues by a sieve (3 mm).

[0041] When comparing the cemented carbide waste before and after the coating removal process, it can be determined by visual inspection that more than 70% of the coating has been removed.

[0042] Example 3 (Comparison)

[0043] A batch of coated inserts is tumbled in water for 36 hours. The inserts are washed and more than 60% of the coating remains after visual inspection when studied.

[0044] Then the inserts are recycled (Zn treatment) to form recycled cemented carbide powder. When analyzing the recycled cemented carbide powder, coating fragments and coating residues can be detected when the powder is observed under a microscope.

[0045] Example 4

[0046] Drills and end mills coated with a PVD coating were prepared.

[0047] A batch is acid-treated in 12 wt% H2SO4 at 60 °C for 24 hours. This batch is hereinafter referred to as Invention 1.

[0048] For comparison, parts of coated cutting tools that were not acid-treated were divided into 3 batches, Comparisons 1 - 3.

[0049] The dry sandblasting treatment was carried out on Invention 1 and Comparisons 1-3 using an injection blasting system, where the spray gun was manually moved in a suction sandblasting box "Boy 100" equipped with a filtering device. The sandblasting medium was Al2O3 (120 mesh). The pressure was 5 bar, the nozzle diameter was 8 mm, and the nozzle distance was 70 mm. The sandblasting time varied, as can be seen in Table 1. The cutting tools were visually inspected, and the results are given in Table 1.

[0050]

[0051] As can be seen from the examples, only by sandblasting, even with a long sandblasting time, the removal rate of the coating is insufficient, while the method according to the present invention shows a high removal rate.

Claims

1. A method for removing residues and / or coatings from cemented carbide waste, the method comprising the following steps: - Acid treating the cemented carbide waste in an acid solution having a concentration between 0.2 N and 10 N at a temperature between 15 °C and 99 °C for a period between 30 minutes and 72 hours; - Removing the residues and / or coatings mechanically.

2. The method according to any one of the preceding claims, wherein the mechanical means is tumbling.

3. The method according to any one of the preceding claims, wherein the mechanical means is sandblasting.

4. The method according to any one of the preceding claims, wherein the concentration of the acid solution is between 0.3 N and 6 N.

5. The method according to any one of the preceding claims, wherein the acid is one or more of sulfuric acid (H2SO4), hydrochloric acid (HCl), acetic acid (CH3COOH), phosphoric acid (H3PO3).

6. The method according to any one of the preceding claims, wherein the acid is sulfuric acid (H2SO4).

7. The method according to any one of the preceding claims, wherein the cemented carbide waste has been mechanically pretreated before the acid treatment.

8. The method according to claim 7, wherein the mechanical pretreatment is selected from tumbling, sandblasting, and crushing.

9. The method according to any one of the preceding claims, wherein the cemented carbide waste consists of a cutting tool comprising a coating.

10. The method according to claim 9, wherein the coating has been deposited by any one of PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), or HIPIMS (High Power Pulsed Magnetron Sputtering), and HIPIMS is a PVD technology.

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