Current situation of recycling technology of the h

2022-08-09
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Current situation of cemented carbide recycling process (Part I)

since the advent of cemented carbide, The problem of recycling has always been "Our high gloss materials create an elegant appearance similar to glass, which is of great concern to people in the industry. Due to the high economic value and manufacturing cost of cemented carbide, which uses tungsten carbide and rare metal drills as the main raw materials, the recycling of tungsten drills is a very valuable recycling field. Since the 1950s, some recycling processes have been developed and applied to the actual production process. The earliest recycling processes consume energy High, complex equipment, and great impact on the environment. Cemented carbide has very large hardness and high density, which is difficult to be dissolved by some inorganic acids and bases at room temperature. Therefore, it takes a lot of trouble on how to recover cemented carbide. According to the information we have, the existing recycling processes mainly fall into several categories. First, the so-called high-temperature treatment methods, including: nitrate melting method, air oxidation sintering method, oxygen calcination method, etc; The second is mechanical crushing method, including cold crushing method, hot crushing method, zinc melting method, etc; The third is chemical treatment, including metal multivalent salt treatment, chlorination, phosphoric acid leaching, hydrochloric acid treatment, etc; The fourth is electrochemical method, which has different process routes with alkali as dielectric, hydrochloric acid or sulfuric acid, nitric acid as dielectric; There are also methods of high-pressure oxygen and ammonia or amine solution leaching; Light base compound method and decomposition method of tungsten trioxide by steam sublimation, etc

in recent years, patients are comfortable to wear; In the practice of recycling cemented carbide with soft texture, due to the increasingly strict requirements for environmental protection, some recycling processes will be discontinued due to pollution. At present, mechanical crushing method, zinc melting method and electrochemical selective electrodissolution method are widely used. The hard phase of cemented carbide - tungsten carbide and burgeoning phase - drilling is committed to sintering through innovation and multi-party cooperation, forming the microstructure of powder metallurgy. How to decompose the dense and hard alloy structure and re separate these hard phases from the nodular metals is the first and key step to be solved in the recycling process. For the disintegration of cemented carbide, many researchers have adopted different ideas, and the recycling process routes are also different. For the evaluation of these processes, it is difficult to choose a more reasonable, more economical and more worthy of promotion and application, because the first and basic principle of the selection of process route is that the quality of recycled products should be high, the process flow should be simple, there will be no secondary pollution to the environment, and the working conditions should be clean and safe. Now several commonly used recycling processes are briefly introduced

I. high temperature treatment method

cemented carbide is sintered by protective gas at a certain temperature. If the alloy is heated in a protective atmosphere above the sintering temperature, the volume of the cemented carbide will expand, and the drill, which is a burgeoning metal, will liquefy and boil. The volume of the alloy will become loose and porous, and the hard alloy will become very easy to be broken and processed. After crushing and grinding, the same mixture of tungsten carbide and bonding metal as the original cemented carbide can be obtained. The principle of high-temperature treatment method is to use a special high-temperature furnace to break down the hard bonded metal from the alloy structure at a sintering temperature much higher than that of cemented carbide by turning 00 ℃. Due to the high-temperature treatment, the recycled cemented carbide raw materials obtained by this process have been treated. The trace other metal and non-metallic impurities originally contained, as well as the beams, columns and lateral force resistant components of buildings, are all made of hot-rolled or welded I-beams and concrete filled steel tubes produced in the factory. The harmful gases are removed, the tungsten carbide grains are obviously long and thick, the intragranular defects are reduced, and the alloy structure and performance are also improved, Therefore, it has good mechanical properties and long service life. This kind of recycled mixture is suitable for reproducing cemented carbide with coarser grain and higher drilling content. For cemented carbide with fine grain and low drilling content, not only the temperature should be increased during high-temperature treatment, so as to make the cemented carbide waste have enough stress to produce expansion and porosity, but also the preparation and sintering process of mixture should be changed when making cemented carbide with medium and fine grain. The high-temperature treatment method has the characteristics of short process flow, simple equipment matching, relatively clean recycled cemented carbide mixture, low environmental pollution, and high recovery rate. However, this process consumes high energy, and some drilling will be lost in the high-temperature process. The biggest problem is that the recycled mixture is only suitable for making coarse-grained carbide alloy. At present, some manufacturers in some industrialized countries such as Japan and Sweden still use this method to treat waste cemented carbide

II. Crushing method

for some cemented carbides with low drilling content, due to their relatively low hardness, they can be crushed manually or mechanically to a certain fineness and then loaded into a wet mill for grinding for a period of time, reaching a certain particle size for remanufacturing cemented carbides. This force one method has the advantages of simple process, short process, low energy consumption and no pollution to the environment. However, when the cemented carbide is broken manually, the metal material debris of the tool will be brought into the broken material to cause pollution. In addition, because the cemented carbide with high drilling content is not easy to break, the mechanical crushing method is greatly limited; It is also difficult to ensure the quality of recycled products with this method for cemented carbide mixtures with complex components. The technological process of crushing method is: artificial crushing, crushing it into powder of about 200 mesh, or using a ball mill with large cemented carbide as the impact ball, then adding alcohol into the octagonal ball mill for wet grinding, and then entering the cemented carbide reproduction process. Some enterprises use the quenching method to crush: first heat the waste cemented carbide in the muffle furnace to more than 80 and immediately put it into water for quenching, causing the cemented carbide to crack, and then enter the mechanical crushing process. This method was popularized in Qinghe and other places in Hebei Province in the 1990s. There are dozens of recycling plants of different sizes in the county that use this method to recycle and remanufacture cemented carbide. The annual output of remanufactured cemented carbide is more than 1000 tons, with a total output value of more than 300 million yuan, making it one of the local pillar industries. At present, there is still a certain development space for the crushing method. The crushing method still needs to be improved by using relatively advanced and clean crushing equipment or by using the force one method which is efficient and does not damage the microstructure of cemented carbide

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