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Nitrogen and argon are protective atmosphere used in sintering of metal injection molding

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-05-24 08:30:00
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Metal injection molding technology is mainly divided into: injection, de-binding, sintering and post-processing or heat treatment process.

Sintering is the key process in metal injection molding. Sintering can eliminate pores between powder particles, so that MIM products can achieve full densification or nearly complete densification. Sintering atmosphere of metal powder metallurgy can be divided into three types: protective atmosphere, controllable atmosphere and air atmosphere. Protective atmosphere is divided into reductive atmosphere and neutral atmosphere, and reductive atmosphere is divided into hydrogen gas and dissociated ammonia.

In sintering process, main function of protective atmosphere is to protect sintered products from oxidation. Neutral atmosphere mainly includes nitrogen, argon and vacuum, which is widely used in high precision and complex parts. Vacuum sintering can avoid harmful factors in atmosphere causing pollution and other adverse effects on small complex metal parts.

Actual air composition by volume fraction is: nitrogen (N2) accounts for about 78%, oxygen (O2) accounts for about 21%, rare gas accounts for about 0.939%(helium He, neon Ne, argon Ar, krypton Kr, xenon Xe, radon Rn), carbon dioxide (CO2) accounts for about 0.031%, and other gases and impurities account for about 0.03%, such as ozone (O3), nitrogen oxide (NO), nitrogen dioxide (NO2), water vapor (H2O) and so on.

The air contains about 0.94% (by volume) of rare gases, most of which are argon.

In reality, nitrogen and argon are extracted and produced by separation method mainly using different boiling point of different gases. In this way, production cost of nitrogen is several times lower than that of argon. In addition, both nitrogen and argon are inert gases, but nitrogen is less inert than argon. These two kinds of gases are relatively easy to get as protective atmosphere gases, and price also has an advantage, MIM sintering is more general use these two kinds of gases as protective atmosphere of sintering.

Nitrogen is mainly used for negative pressure de-binding process in early stage of sintering and forced cooling in final stage. In this way, nitrogen plays a role in protecting atmosphere of sintering and relatively affordable. Argon is mainly used in medium-stage partial pressure sintering process after sintering in vacuum, so that product size is more stable when argon is used as protective atmosphere during high-temperature sintering. If nitrogen is used as a protective atmosphere throughout sintering process, hardness of product will be relatively high, because nitrogen will slowly infiltrate into product surface to improve hardness in partial pressure sintering process.

Keywords in the article: metal injection molding
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