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| flame-free high temperature zone under protective gas |
Extremely light metal powder parts with a wall thickness of only some particle diameters needed to be sintered under reducing atmopshere.
Typically hydrogen and carbon monoxide are the reducing components of this so called protective furnace atmosphere. Both will burn in the presence of oxygen at the furnace entry foming the usual inlet flame.
At this position, PM parts passing the entry flame are heated up very fast but still under oxidizing condition. A loss of carbon and preoxidation is the result. Specially for small PM parts the danger of preoxidation is very much alike.
We changed the muffle entry completely, adding "cold" exothermic gas to the first furnace zone, which by the way improves delubing conditions and then soaking out the atmosphere gases towards the muffle top. Here outside the reaction area and above the muffle the gas burns and is then led to the chimney.
The result was surprising: the flame at the entry completely vanished. No more uncontrolled heating under oxidizing atmosphere, no preoxidation and a stable C- content of metal parts with carbon addition.
Today the flame-free furnace entry is one of many new features of all SARNES sintering furnaces and has improved PM part quality without additional costs for extra protective gas.
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