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What determines the dew point reading actually measured in the hot zone of a sintering furnace?

Tom Philips
Sr. Principal Applications Engineer

The actual dew point in the hot zone of the sintering furnace is a net result of several factors or sources of O2 reacting with the available hydrogen, creating moisture, which then modifies the dew point of the input gases.

Assuming there is no cracked muffle, a water leak in the cooling sections or contaminated supply gases, the following are some known and unavoidable sources of O2.

  1. Diffusion and entrainment of outside air through the front and exit ends of the furnace. This is a function of the atmosphere flows rate, door height, exhaust hood designs, flame curtains and plant pressure conditions.
  2. Air entrapped in the part, function of part geometry.
  3. O2 content of the powder used. Usually a known quantity as measured by the H2 loss number provided by the powder manufacturer.
  4. Reduction of the belt oxides.
  5. Reduction of metallic oxides present in brick lined furnaces.

Once the actual dew point (H2O%) is measured, we can then and generally do, control the oxidation/reduction potential, by controlling the amount of H2 in the H2/H2O ratio as per the requirements of the material that is being sintered.

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