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Control of carbon in de-bind of metal injection molding

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-05-07 08:25:00
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The removal of binder is most critical and important process in metal powder injection molding technology. If binder is left in green part, organic polymer will thermally decompose and volatilize during sintering, generating a large amount of gas, resulting in a large internal pressure, causing cracking or into pore. Meanwhile, pyrolysis process also easily generated carbonization or carbon contamination, which adversely affects on product performance.To reduce carbon content in thermal de-binding process, it is mainly considered from three aspects:

1. Reduce amount of binder to be removed during thermal de-binding. Less binder that is removed the less organic matter is involved in thermal decomposition, and less likely it is to produce residual carbon, making it easier to control carbon.

2. Adjust thermal de-binding process and atmosphere. By adding low temperature section and prolonging low temperature holding time, binder organic component is removed as much as possible by evaporation and slow decomposition, to reduce the amount of binder participating in rapid pyrolysis in high temperature, thereby lowering carbon content. However, the thermal debinding process is complicated and the production cycle is very long due to adding low temperature section and prolonging low temperature holding time. Atmosphere generally has a certain effect on residual carbon and thermal de-binding rate.  The carbon content of  green part can be fine-adjusted by changing the thermal debinding atmosphere.

3. Modified the binder, using relatively small amount of organic carbon residue as binder component.

The above three methods can reduce carbon content of thermal debinding parts, but each method has defects. Therefore, people tend to combine them organically to control carbon content of green part. Firstly, modify the binder by using organics with less carbon residue. Secondly, try to reduce the amount of binders removed during thermal debinding process. Finally, adjust thermal debinding atmosphere or its process. Since the composition of binder once determined, generally do not change. So in actual carbon control, people study the most to reduce the amount of binder removed during thermal debinding or adjust process and the atmosphere. In thermal debinding process, the atmosphere has great influence on carbon content. In order to prevent oxidation, debinding is generally carried out in reducing atmosphere, inert atmosphere or vacuum. Some studies have confirmed that N2 thermal debinding is easy to remain binder in form of carbon black in green part, resulting in alloy carburization. H2 thermal debinding can easily lead to the decarbonization. 75%N2+25%H2 mixture atomphere for thermal debinding can better control carbon content. Although it is easy to make decarbonisation by H2 atmosphere, the carbon content of green part can be kept withine normal range by adjusting process. To reduce the number of binders being removed in thermal debinding process, common methods are: solvent debinding + hot debinding, catalytic debinding + hot debinding or siphon debinding + hot debinding.

Keywords in the article: metal injection molding
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