Industry Reports

What is slag spitting? What is the reason of causes the slag spitting for vertical roller mill?

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  • Feb 14, 2020  UTC+8
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  • Tags: Vertical mill slag mill
Vertical mill slag spitting means that under the standard wind that can blow the material, the metal and high-density debris contained in the material fall from the nozzle ring and are removed by the scraper to clear the mill, so a small amount of debris is discharged the process of. We can ignore the small amount of slag, but if the amount of slag is significantly increased, it needs to be adjusted in time to stabilize the working conditions. The reasons for the slag spitting of the vertical mill are introduced below.
(1) Segregation of materials in the vertical silo mixing bin is serious.
When the silo level is low, large pieces of material fall down, the grinding time of the material is not enough, and the coarse powder overflows from the slag outlet.
(2) Ventilation of vertical mill system is out of adjustment.
Ventilation of the system is greatly reduced due to misalignment of the gas flow meter or other reasons. The reduced wind speed at the nozzle ring caused a large amount of slag.
(3) The air leakage of the vertical mill system is serious.
Although the air volume at the fan and the gas flow meter has not decreased, due to a large amount of air leakage from the mill and the mill outlet pipe, cyclone, dust collector, etc., the wind speed at the nozzle ring is reduced, which causes serious slag discharge.
(4) The ventilation area of ​​the nozzle ring of the vertical mill is too large. This phenomenon usually occurs on the mill with poor abrasiveness of the material. Due to the poor abrasiveness, the vertical mill size selected for maintaining the same table capacity is large, and the output has not increased. The ventilation volume does not need to be increased in accordance with the specifications and is increased simultaneously, but the area of ​​the nozzle ring is increased. If the ventilation area is not reduced in time, the wind speed of the nozzle ring will be lower and the spit will be more.
(5) The seal inside the vertical mill is damaged.
Between the grinding disc base and the lower frame of the vertical mill, the three drawbar rods also have upper and lower sealing devices. If the seal is damaged in these places, the air leakage will be serious, which will affect the wind speed of the nozzle ring and cause increased slag spitting.
(6) The gap between the grinding disc of the vertical mill and the nozzle ring increases.
The gap is generally 5-8mm. If the iron parts used to adjust the gap wear or fall off, the gap will increase, and hot air will pass through this gap, which will reduce the wind speed at the nozzle ring and increase the amount of slag.
(7) The grinding pressure of the vertical mill is too low.
When the vertical mill is running, the normal grinding pressure is 9-12 MPa. When the grinding pressure is lower than 9 MPa, the thickness of the material layer in the mill is higher than the retaining ring, and the material is scattered to the surrounding area under the centrifugal force of the grinding disc, and the large slag is spit out.
(8) The nozzle ring of the vertical mill is severely worn.
Due to the severe wear of the nozzle ring, a good swirling wind cannot be formed in the grinding chamber, which causes unbalanced wind pressure or insufficient wind speed of the nozzle ring to cause slag spitting.