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Aug 12, 2020
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Causes and control measures of four major surface defects of billet

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Successful thermal test of induction heating and refining system for tundish
  •  reconnect

Reasons:

a. Pouring is interrupted due to various operating failures, and reconnection defects are easily caused on the surface of the cast slab after re-pouring.

b. Slow drawing speed results in too deep vibration marks on the surface of the cast slab, forming a reconnection.

Control measures:

a. Fully do all the preparations for pouring steel to ensure the normal and stable pouring of steel and avoid stop-flow accidents.

b. Ensure that the speed is normal and reasonable.

  • Inclusions and scars

Reasons for formation

a. The liquid level of the mold fluctuates violently, so that the mold powder or other inclusions on the molten steel level are involved in the casting slab, forming inclusions on the surface of the casting slab.

b. The molten steel overflows at the drawing leak and is cooled by the mold, forming defects on the surface of the cast slab. The drawing speed fluctuates too much and frequently.

Control measures

a. Improve the technical quality and work responsibility of the operators to ensure the stability of the crystallizer liquid level.

b. Improve the performance of the mold flux, increase the thickness of the molten slag layer, and increase the absorption capacity of inclusions. Strict process operation procedures and stable pulling speed.

c. Improve the corrosion resistance of the tundish nozzle and plug.

  •  scratches

Reasons for formation

a. There is scrap steel on the foot roll of the second cold section frame, which causes scratches on the surface of the casting billet.

b. Uneven stretching and straightening rolls or uneven secondary cooling will cause the cast slab to deviate, and the cast slab will be in contact with the stretching and straightening frame and scratch the surface of the cast.

Control measures

a. Strengthen the maintenance of the second cold section, and find that the steel leakage should be cleaned in time.

b. Strengthen the maintenance of the tension-straightening system to ensure the levelness of the tension-straightening rollers, and install side guides to prevent deviation of the casting billet.

  • vibration marks

Reasons

a. Vibration marks are the inevitable result of mold vibration and are difficult to completely eliminate. The greater the fluctuation of the mold liquid level, the deeper the vibration marks.

b. The slower the pulling speed, the lower the vibration frequency and the deeper the vibration mark.

c. The solidification characteristics of steel grades have a great influence on vibration marks. Shrinkage-sensitive steel has deep vibration marks, and crack-sensitive steel has shallow vibration marks.

Control measures

a. Using low-amplitude, high-frequency sinusoidal vibration.

b. Take measures to ensure the stability of the crystallizer liquid level.

#mgo-c bricks#refractory material

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Continuous Casting Technology
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