Powder preparation
Mechanical method:
Solid curshing is to crush the material by rolling or vibrating steel balls in the cylinder .It is suitable for brittle metals and alloys;liquid crushing ,namely atomization method ,uses high pressure gas ,liquid or high -speed rotaing blades to disperse the molten metal into mist droplets ,which become powder after cooling .It is suitable for metals with low melting point.
Physical and chemical methods:
Reduction method is to reduce metal oxides or salts with reducing agent to get metal powder ;electrolysis method is to pass direct current in molten salt ,so that the metal ions extracted by electricity become metal powder ;there are also thermal dissonciation method and chemical displacement method.
Mixing
Dry mixing :
Suitable for components with close density and low requirements for powder uniformity .
Wet mixing :
Adding volatile liquids such as gasoline and alcohol to the powder for ball milling can increase the uniformity of mixing and impove sintering performance.
Semi-dry mixing:
About 0.1% lubricating oil is added to the powder to reduce the density segregation of the powder.
Shaping
Pressing method :
Including room temperture pressing and heating pressing,through which the pressure increases the contact surface of powder particles,which are embedded with each other ,so that the pressed billet has a certain shape size ,density and strength.
Other forming methods:
Such as powder pouring ,freezing pouring and pressure-free impregnation and other pressure-free forming methods ,as well as injection molding ,isostatic pressing ,3D printing and so on.
Firing
Firing:
This is a critical process that can be classified according to different criteria .It can be divided into liquid phase sintering and solid phase sintering based on the presence or absence of a liquid phase;and into filler-protected sintering,gas -protected sintering ,and vacuum sintering based on oxidation protection conditions .Sintering facilitates physical and chemical reaction such as diffusion and fusion between particles,enhancing the strength of the product and ensuring it meets the required performance.
Post -sintering treatment:
According to the needs of sintered products ,such as pressure processing ,infiltration ,heat treatment ,surface treament and mechanical processing,in oder to improve the performance ,precision and surface quality of products.
