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How To Minimize Zinc Ash And Zinc Slag In The Zinc Kettle Area?

Dec. 09, 2021

 Zinc Kettle


The formation of zinc ash and dross is unavoidable in the current production line format, so the direction of research in the hot-dip galvanizing industry is to minimize its generation and avoid adsorption to the strip surface through systems, equipment and technology.

 

Composition and causes of zinc ash and zinc slag

Zinc ash

The main component of zinc ash is zinc oxide, which is produced in the closed, high-temperature, slightly positive pressure space of the furnace nose through a redox reaction with water vapor in both gaseous and liquid forms of zinc: Zn+H20=Zn0+H2.

Zinc slag

The main components of zinc slag include Fe-Zn system, Fe-Al system and Fe-Zn-Al system intermetallic compounds. The formation process is the dissolution of iron elements in the zinc kettle, diffusion, and the formation of intermetallic compounds with aluminum and zinc. Because the elements involved in both of these substances are necessary for production, it is particularly difficult to carry out effective control.

 

Process system control

In the nose of the furnace, above the zinc surface, the gaseous zinc rises and reacts with the water vapor in the atmosphere to produce zinc ash. The important factor in this process is the temperature difference between the zinc liquid and the atmosphere, and the greater the temperature difference, the more zinc ash is generated.

The production line's practice is to control the temperature of the strip steel entering the pot, which is within the range of +5°C to +10°C of the pot temperature. This is slightly higher than the temperature of the zinc solution, so as to reduce the temperature fluctuation in the area between the nose partition and the zinc surface.

It is not enough to control the temperature of the strip steel into the zinc kettle, it is necessary to control the temperature of the zinc kettle, which is reflected in the standardized operation of adding zinc ingots. For production lines without automatic zinc addition devices, it is necessary to develop an effective system and to ensure that the time, timing and amount of addition specified in the system are actually implemented.

In terms of production scheduling, a strict thickness and temperature transition system should be implemented to give the process section sufficient conditions to adjust the dew point of the furnace nose, zinc liquid temperature, strip temperature, zinc pump power, as well as to vibrate the furnace nose to shake off the zinc ashes, to remove the slag and pull out the slag, to polish the surface in advance, etc. The timing of the manual knocking and vibrating of the furnace nose should be done during the transition phase.

 

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