Role of the electromagnetic stirrers (EMS)

Role of the electromagnetic stirrers (EMS)

Nowadays, with the development of science and technology, the electromagnetic stirring has been widely used. A large number of metallurgical practices and industrial operations have proved that the reasonable use of electromagnetic stirring on the continuous casting machine can effectively improve the internal structure of the strand, improve the surface quality, reduce center segregation and center porosity, eliminate center shrinkage and cracks, and greatly increase equiaxed grain rate. In addition, the requirements for continuous casting process can be lowered, and the casting speed can be increased. However, the continuous casting process conditions will significantly influence the metallurgical effect. Therefore, the control of metallurgical quality should be considered from the metallurgical process and metallurgical theory of the continuous caster itself. Electromagnetic stirrer can lower requirements for such process measures.

Let us introduce in detail the role of the electromagnetic stirrers (EMS).

Here is the content list:

• M-EMS Improvement Quality of the Strand

• S-EMS Improvement of Internal Quality of the Strand

• F-EMS Improvement of Internal Quality of the Strand

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M-EMS Improvement Quality of the Strand

The mold electromagnetic stirrer (M-EMS) is installed in the mold zone. The movement of unsolidified molten steel is accelerated through the electromagnetic force generated by the electromagnetic stirring, thereby changing the flow, heat transfer and migration process of the molten steel during the solidification process, so as to achieve the purpose of improving the quality of the strand.

It can control the surface quality and subsurface quality, which is reduce the inclusions, blowhole and airhole.

1） The scouring effect of the convective molten steel at the solidification front makes the solid-liquid interface smooth, and the inclusions larger than 5 microns are difficult to stick. That is, the subcutaneous inclusions of the casting section larger than tens of microns disappear; it is helpful to eliminate the bubbles formed in the molten steel and the gas formed by excessive lubrication oil;

2) The rotating force causes the molten steel to be subjected to centrifugal force, and the inclusions with lighter specific gravity are subjected to centripetal force. The centripetal movement of the inclusions causes them to accumulate. The size of the inclusions becomes larger, and the floating speed accelerates, leading to the disappearance of accumulation of inclusions at the 1/4 inner side of the strand for curved CCM.

3) Increase the ratio of equiaxed grain zone; it can reduce segregation and porosity to a certain extent. However, if the stirring speed in the mold is too high, the meniscus fluctuates severely and wash the nozzle, which will cause serious erosion to the nozzle. Therefore, the stirring intensity (speed) should be taken into consideration.

S-EMS Improvement of Internal Quality of the Strand

The secondary cooling zone electromagnetic stirrer(S-EMS) is an electromagnetic stirrer installed in the secondary cooling zone. The current passes through the electromagnetic stirrer to generate an alternating magnetic field. The alternating magnetic field cuts the conductor to generate electromagnetic force. The molten steel circulates in a certain direction under the action of electromagnetic force, so as to achieve the purpose of uniform temperature and molten steel, thereby increase the equiaxed grain rate of the strand.

Generally, the installation position of the secondary cooling zone electromagnetic stirrer is in the area where the unsolidified rate of the strand is about 50%-40%. This position is just at the end of the influence of the mold electromagnetic stirring flow field, the strand shell is thick, and there will be no bulging.

F-EMS Improvement of Internal Quality of the Strand

For special steels such as high-carbon steel and high-alloy steel, problems such as center segregation, center shrinkage, and center cracks still exist after using MEMS, and even a "V"-shaped groove, which is V-shape macro segregation, is formed at the end of the so-called mushy zone. To solve these problems, final electromagnetic stirrer (FEMS) is a very effective method.

Due to the FEMS needs to solve metallurgical problems, the installation position of the FEMS is very essential.Stirring too early will not get expected metallurgical effect; while stirring too late, the molten steel has solidified at this time, it’s pointless.

According to Zhongke Electric’s statistics on the effect of applying FEMS on different continuous casting machines in the past few years, it is preferably to install the FEMS for billet of high carbon steel in the area where the unsolidified rate is 25%-33% (section length ratio).

It is worth noting that the position of the final solidification is affected by the casting speed. Therefore, it is very important to maintain the stability of the casting speed.

After reading the above contents, have you know more about electromagnetic stirrer?

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