Sintering of powder metallurgy machine parts manufacturing

The sintering process in the production and processing of powder metallurgical machinery parts is one of the most basic processes of powder metallurgy, which plays a decisive role in the physical and mechanical properties of powder metallurgy parts.
Sintering is a kind of high temperature heat treatment, which involves the knowledge of sintering furnace, sintering atmosphere, selection and control of sintering conditions. Therefore, sintering is a very complicated process. At the same time, sintering is a special process of high energy consumption, high equipment investment, and the quality characteristics of the product can not be fully measured. So it is one of the most important links to influence the quality and cost of powder metallurgy parts. The sintering process is very critical and must be strictly controlled to ensure the quality of sintered parts. Therefore, the operators need special skills training to fully understand and master the basic principles of sintering, the process of sintering (such as materials, temperature and time, sintering atmosphere, environment, etc.), the effect of sintering atmosphere, and the factors affecting the quality of the sintered products, so as to master the sintering skills and the skills of sintering skillfully. Improve the ability to analyze problems.
How do the press billets of powder metallurgy be sintered? Sintering is heat treatment of powders or compacts at temperatures below the melting point of major components. The purpose is to make metallurgical bonding between powder particles, even though the powder particles are transformed from mechanical agglutination to grain boundary bonding between atoms.
The purpose of sintering of powder metallurgy parts is that the blank of pressing has the shape and size of the mechanical parts, but its strength is very low, so it can not meet the requirements of use. Before sintering, the blank is only a mixture of powder particle interface, rather than a true atomic binding material. Therefore, sintering must be made to make the billet become metallurgical material and endow the powder metallurgy parts with mechanical and physical properties. The strength and elongation of the iron powder press after sintering are greatly improved. For example, the tensile strength can be increased from zero to 200MPa, and the elongation increase from zero to 8%, if the temperature is 1200 C.
The requirements for pressing and sintering of powder metallurgy machinery parts.
1. precision requirements for size and shape. The size and shape accuracy of sintered parts, including surface roughness, should meet the design requirements. Sintering will cause the sinter to shrink or expand, and the sinter will be deformed because of the uneven distribution of the density of the press and the uneven temperature of the furnace, so the size and shape of the sintered product will change.  This requires strict control of sintering conditions to ensure the size and shape accuracy of sintered products.
2. density requirements. In sintering, the density, porosity, porosity and shape of the sintered products change with the sintering of powder particles and the shrinkage or expansion of the sintered products.  Relative density and porosity characterize the density of powder metallurgy parts. As a self-lubricating powder metallurgy oil bearing, there is also a requirement for connecting voids.
3. the requirements of the organization. Powder metallurgy parts, like other materials, depend on the structure of the structure, which represent the structure factors of the powder parts: grain size, phase structure, distribution of phase, distribution of alloy components, porosity, pore size and pore shape. The formation and change of the microstructure of powder metallurgy parts mainly occurs in the sintering process.
4. the requirements of mechanical and physical properties. The final sintered parts need to achieve the required mechanical and physical properties. Mechanical properties include strength, hardness, elongation and impact toughness. Physical properties include density, conductivity, thermal conductivity and magnetism.
Sintering of powder metallurgy parts is divided into solid phase sintering and liquid phase sintering. Solid phase sintering is simply a metallurgical bonding between powder metallurgy particles. Liquid phase sintering is the sintering of certain molecular particles in powder metallurgy which produces liquid at higher melting point temperatures. The sintering process of powder metallurgy parts can be divided into pre sintering, grease removal, high temperature sintering and cooling.