It is obvious that the furnace capacity for smaller grain sizes, especially for submicron tungsten powder, is low. Only very thin powder layers can be applied to retain the grains from growing. In order to improve the capacity, a double or triple boat technique was invented. The reduction boat is topped with one or two upper boats in a way permitting hydrogen flow between the boats, so that the capacity also for smaller grain sizes could be increasing considerably.
Modern furnaces are fully automated, which means that all variables can be set and controlled. Loading, pushing, and discharge of the boats is done by machine.
The advantage of the push-type furnace in comparison to rotary kilns is its flexibility in switching from one condition (grain size) to the next and in its high capacity, especially for finer powder qualities. Disadvantages are higher energy consumption, broader grain size distribution, more contamination by the scale from the boats, and higher maintenance costs.
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