Cooking method of Powder manufacturing
(1) Powder manufacturingThe powder manufacturing process includes steps such as powder preparation and powder mixing. To improve the moldability and plasticity of the powder, plasticizers such as engine oil, rubber, and paraffin are usually added.
(2) PressingMoldingThe powder is pressed into the desired shape at a pressure of 15 to 600 MPa.
(3) SinteringIt is carried out in a high-temperature furnace or vacuum furnace under a protective atmosphere. Sintering differs from melting of metals in that at least one element remains solid. In the sintering process, powder particles undergo a series of physical and chemical processes such as diffusion, recrystallization, welding, bonding, and melting to become a metallurgical product with a certain porosity.
(4) Post-treatmentGenerally speaking, sintered parts can be used as they are. However, parts that require high dimensional accuracy or high hardness and wear resistance require post-sintering processing. Post-treatment includes precision pressing, rolling, extrusion, quenching, surface hardening, oil immersion, and melt infiltration.
Powder preparation methodPreparing the powder is the first step in powder metallurgy. Powder metallurgy materials and products are increasing and their quality is improving, and the types of powders required are increasing more and more. For example, from the perspective of the material range, not only metal powders but also alloy powders, metal compound powders, etc. are used, and from the perspective of powder appearance, powders of various shapes are required. For example, when producing filters, powders need to be molded, but from the perspective of powder particle size, powders of various particle sizes are required, such as coarse powders of 500 to 1000 microns and ultrafine powders of less than 0.5 microns.
In order to meet various requirements for powder, there are also various methods for producing powder. These methods are nothing more than converting metals, alloys, or metal compounds in a solid, liquid, or gas state into a powder state. Various methods for preparing powder and powders prepared by various methods.
The methods for converting metals, alloys, or metal compounds into solid powder include the following.
(1) There are two methods for producing metal and alloy powders from solid metals and alloys: mechanical grinding and electrochemical corrosion.
(2) Reduction methods for producing metal and alloy powders from solid metal oxides and salts Reduction chemical methods for producing metal and alloy powders, metal oxides and nonmetallic powders
Methods for converting metals, alloys or metal compounds into liquid powders include the following:
(1) Atomization method for producing alloy powders from liquid metals and alloys
(2) Methods for producing metal alloys and coated powders by substitution reduction from metal salt solutions include the substitution method and solution hydrogen reduction method, methods for producing metal powders by precipitation from molten metal salts include the molten salt aging method, and methods for producing metal compound powders by precipitation from an auxiliary metal bath include the metal bath method.
(3) Aqueous solution electrolysis is used to produce metal powders and alloy powders from metal salt solutions, and molten salt electrolysis is used to produce metal powders and metal compound powders from metal molten salts.
Methods for converting metals or metal compounds into gaseous powders:
(1) Vapor condensation method is used to produce metal powders from metal vapor.
(2) Production of metal, alloy and coating powders from gaseous metal-carbon-based materials by pyrolysis of carbon-based materials
(3) Gas-phase hydrogen reduction method is used to produce metal, alloy powders and metal and alloy coatings from the gas-phase reduction of gaseous metal halides, and chemical vapor deposition method is used to produce metal compound powders and coatings from the deposition of gaseous metal halides.
However, from the perspective of the essence of the process, the existing milling methods can be roughly divided into two categories: mechanical methods and physical and chemical methods. Mechanical methods are methods that mechanically grind the raw material and do not basically change the chemical composition. Physicochemical methods are methods that change the chemical composition or agglomeration state of the raw material by chemical or physical effects to obtain powder. There are many methods for producing powder. The most widely used methods on an industrial scale are Hans reduction, spraying and electrolysis. Some methods such as vapor deposition and liquid deposition are also very important for special applications. [1]
