Thirteen-Tube Reduction Furnace

The hydrogen reduction process of tungsten oxide generally undergoes in a multi-tube furnace, of which the most widely used equipment are thirteen-tube reduction furnace and four-tube reduction furnace.

Modern multi-tube furnace is basically automatic operation, pushing a metal boat equipped with oxide into a tubular reducing furnace in a certain time interval.

Pushing into a boat, the furnace burden go ahead a charge length. The furnace tube is divided into two layers, and there are 6 in the upper stratum and 7 in the lower stratum, respectively supporting on the supporting seat. Spiral electric wire tube adopts Ni Cr alloy material. Heat insulating layer is made of super light refractory brick, asbestos cement board and asbestos board. Furnace shell needs cooling water(40-45℃) to lower the environment temperature. There are irregular refractory bricks and grooves in the furnace cavity, which are used for placing spiral heating pipes.

Loading boat is usually made of nickel molybdenum (72%Ni, 28%Mo) alloy, a few also use more expensive TZM alloy. It is reported that foreign countries mainly use a kind of nickel chromium iron alloy - Inconel alloy - to make loading boat, which is abandoned in China as the iron in reduction process is easily diffused to tungsten powder and polluted it.

Thirteen-tube reduction furnace has 3 to 5 loading containers, which loading and unloading materials according to the order in the production process. Along or against the direction of movement of tungsten material, excessive hydrogen is fed into the tubular furnace and react with the material. Corresponding control system is provided to record heating temperature and adjust the heating current of each belt.

Temperature in thirteen-tube reduction furnace is between 600℃—1100℃. Natural gas is generally used for heating in the place where the supply of natural gas is sufficient. Usually the process of producing ultrafine tungsten powder is presetting temperature and then heating in stages. As for tungsten powder of ordinary particle, the isothermal reduction method is used.

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