The Role of Furnace Atmosphere in the Sintering Process

June 3, 2019

Above and around the powdered metal, the sintering atmosphere is also being regulated. Now, if someone were to ask, “What gas is used to control the different sintering vectors,” the answer wouldn’t be short. You see, the equipment used to sinter metals is composed of several discrete stages. So, for every equipment zone, there’s a range of possible atmospheric gases.

High Heat Zone De-Oxidization

High temperatures cause metals to oxidize. They rust, that’s what you’re hearing here. A compacted Green part moves into a sintering chamber, heat causes the discrete metal grains to neck and press together, and a very nearly solid metal workpiece is manufactured, although it contains a slightly porous structure. By introducing nitrogen and extracting oxygen, an inert atmosphere is created in this thermally active sintering zone. Without oxygen, the hot metals can’t oxidize. The nitrogen is injected through a series of angularly adjusted ports, straight into the furnace area. Alternatively, nitrogen “curtains,” which use gas injection technology, provide transverse laminar jet streams. In effect, the inert gas functions as an invisible deoxidizing zonal barrier.

Water as a Multipurpose Atmospheric Regulator

There’s more than one application area where water is found in sintering equipment. In its fluid state, the liquid cools the pressed and sintered workpiece after it has been treated. Sinter hardening stages also use water as a quenching medium. Used as a vapour, the steam combines with the evaporated pressing agents and oils to form harmless gaseous by-products. After all, many lubricants are hydrocarbon-based. If they’re heated and vaporised in a sintering chamber, hydrogen-rich compounds will take flight. Free-floating, rising in the steamy atmosphere, the hydrocarbons combine with the water. All that’s left now is harmless CO or CO2 (Carbon Monoxide or Carbon Dioxide). Those byproducts are quickly ejected from the sintering zone. Of significance here, released carbon could combine with carbon in an iron alloy. That undesirable consequence must be avoided.

There are other gases in the sintering atmosphere. For further decarburization, Methane (CH4) is added to the steamy atmosphere. A hydrogen and nitrogen mix could also be in use as a carbon restoration gas. Again, there’s no single solution. For every sintering zone, there’s a gaseous supplement that’ll refine certain process vectors. One option is to remove the atmosphere, at which point oxidation becomes impossible. That vacuum serves an important purpose, but it’s not exactly the most dynamic sintering aid. No, to regulate all process factors, including those that cause decarburization and deoxidization, active oxygenless atmospheres are applied. They’re the hydrogen and nitrogen mixes and Methane additives that keep powdered metals carbon-rich, free of pressing lubricants and entirely deoxidized.

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