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According to the statistics of the China Machine Tool Powder Metallurgy Branch, the shipment of powder metallurgy parts in 2016 was 480,000 tons, and the sales amounted to 6.4 billion yuan, of which the automobile industry had sales of 4 billion yuan, accounting for 62% of the total sales. In 2017, the powder metallurgy market is expected to reach 6.9 billion, achieving steady growth.
Automotive engines and gearboxes are the two most widely used and market segments for powder metallurgy components. The domestic automotive powder metallurgy market has a space of up to 20 billion yuan. In addition, in 2018, the metal powder market is expected to expand further in the first year of metal 3D printing powder explosion.
Preparation of metal powder
The huge potential of the market is also driving the advancement of technology. With the increasing application of powder metallurgy products, the size and shape requirements of metal powder particles are getting higher and higher, and the properties and size of metal powders depend to a large extent on the production method of the powder and its preparation. Process, so the powder preparation technology is constantly developing and innovating.
At present, many methods have been developed for the preparation of metal powders, which are mainly classified into physical chemical methods and mechanical methods according to the production principle. The most important in the mechanical method are the atomization method and the mechanical pulverization method. The most important physical and chemical methods are the reduction method, the electrolysis method and the hydroxyl method.
1 mechanical method
The mechanical method is a processing method for breaking a metal into a powder of a desired particle size by means of a mechanical external force, and the chemical composition of the material in the preparation process is substantially unchanged. The methods currently in common use are atomization and mechanical pulverization. The advantages are simple process, large output, and preparation of ultrafine powders of high melting point metals and alloys which are difficult to obtain by conventional methods.
Mechanical pulverization
The mechanical pulverization method is not only an independent milling method, but also often an indispensable supplementary process for other milling methods. Mainly by crushing, crushing and
The solid metal is broken into powder by cutting and the like. There are two types of crushing equipment:
Crushed equipment mainly used for crushing: coarse crushing equipment such as crusher, rolling mill, jaw crusher;
Fine crushing equipment mainly used for crushing and grinding: hammer mill, rod mill, ball mill, vibrating ball mill, agitating ball mill, etc.
Preparation of metal powder by high energy ball milling
The mechanical pulverization method is mainly suitable for pulverizing brittle and easy-work hardening metals and alloys such as tin, manganese, chromium, high carbon iron, iron alloys and the like. The method has low efficiency and high energy consumption, and is used as a supplement to other milling methods or for mixing powders of different properties.
Atomization method
The method of directly crushing a liquid metal or alloy to obtain a powder is called an atomization method, and is a widely used metal powder preparation method which is second only to the reduction method in production scale. The atomized powder has the advantages of high sphericity, controllable powder particle size, low oxygen content, low production cost and adaptability to the production of various metal powders. It has become the main development direction of high performance and special alloy powder preparation technology, but the production efficiency is low. The defect of ultra-fine powder is not high, and the energy consumption is relatively large, which limits the application of the atomization method.
Preparation of metal powder by atomization
2 physical chemistry
The physico-chemical method refers to a method for producing an ultrafine powder by changing the chemical composition or the state of aggregation of the raw material during the preparation of the powder. According to different chemical principles, it can be divided into reduction method, electrolysis method, carbonyl method and chemical replacement method.
Reduction method
Reduction of metal oxides and metal salts to produce metal powders is one of the most widely used milling methods. In particular, the reduction method is the most economical when directly using ore and metallurgical industrial waste such as rolled steel scales. The advantages of the reduction method are simple operation, easy control of process parameters, high production efficiency and low cost, and are suitable for industrial production. The disadvantage is that it is only suitable for metal materials which are easy to react with hydrogen and become brittle and easily broken after hydrogen absorption.
Electrolysis
The electrolysis method is a method in which a metal powder is deposited on a cathode by electrolytically melting an aqueous solution of a salt or a salt. It plays an important role in powder production. Its production scale is second only to the reduction method in physical and chemical methods, and it can control the milling particle size. The purity of the prepared powder is high, and the elemental powder can reach 99.7% or more. However, the electrolysis method consumes more electricity, and the cost is higher than that of the reduced powder and the atomized powder. Therefore, in the total powder output, the proportion of electrolytic powder is relatively small.
Carbonyl method
Since the metal carbonyl is easily decomposed into a metal and a CO gas at a low temperature, a metal carbonyl metal powder can be obtained by a reverse reaction of a synthetic carbonyl metal. The carbonyl method can be used not only to obtain micron-sized powders, but also to obtain nano-sized powders; not only can a single pure metal and alloy powder be prepared, but also a coated powder can be obtained. The highly developed surface of the carbonyl powder itself is incomparable to the powders produced by other methods and is the best material for chemical power plates and catalysts.
Chemical replacement
According to the activeness of the metal, the less active metal is displaced from the metal salt solution by a highly active metal, and the metal (metal powder) obtained by the replacement is further processed into a metal powder by other methods. The method is called chemical replacement. The method is mainly applied to the preparation of inactive metal powders such as Cu, Ag, and Au.
to sum up
With the advancement of technology, metal powder has shown good application prospects in metallurgy, chemical industry, electronics, magnetic materials, fine ceramics and sensors. However, due to the limitations of traditional preparation techniques, the application of metal powder is restricted. Although many new production processes and methods have been applied, the problems of smaller scale and higher cost are still not well solved. In order to promote the development of metal powder materials, it is necessary to intensify innovation, learn from each other's strengths, and develop production processes with higher output and lower costs.
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