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Multifunctional Systems of Sliding Gates

Conception of Application in Steelmaking

Creation and application of multifunctional systems of sliding ladle gates requires the use of slide-type teeming devices which allow, along with the main manufacturing operation - dosed steel tapping from the steel-teeming ladle, - to carry out a number of supplementary ones: to inject gas powder mixtures into the molten metal during its flowing out of the steel-making unit into the steel-teeming ladle; to inject crushed alloying additions under the steel stream; to provide gas-dynamic protection of the molten metal stream against the negative influence of the atmospheric oxygen, to vacuum in the space around the stream (if submerged nozzles are used for continuous casting).

The developed multifunctional system of sliding gates includes the basic unit - a two-plate balancer-type sliding gate. Several auxiliary units can be mounted on the basic one according to the structure chart (see below), to carry out the above-mentioned manufacturing operations.

 

 

Structure chart of the multifunctional sliding gate system

The blowing unit of the gate is equipped with a slot metal nozzle which provides gas injection into the melt in cavitation-stream mode. This mode allows to obtain the required metal stirring effect with minimal time, material and power consumption in comparison with other blowing modes (see the table).

Comparative efficiency values of the existent blowing devices:

60 ФЩС 90 3 0,075 8 1 0,125
ПФ 60 7 0,116 390 2 3,250
ПП 40 10 0,111 250 8 0,520
250 ФЩС 120 4 0,032 10 1 0,040
ПФ 100 10 0,066 600 2 1,208
ПП 60 15 0,060 300 7 0,171
300 ФЩС 150 6 0,050 12 1 0,042
ПФ 120 12 0,080 670 2 1,125
ПП 70 18 0,070 350 6 0,194
 

Note: SNG - slot nozzle of the gate; ST - submerged nozzle; PC - porous cork.

Steel blowing through the ladle gate port using the slot nozzle allows to reduce the temperature and chemistry inhomogeneity of the metal in the ladle by 3 - 5 times. Consequently steel teeming is improved and as a result surface defects of the ingots on the first process stage are reduced by 1,5 - 2,5 times.

The unit of crushed materials implementation under the steel stream allows to apply the "late steel modification" technology.

In the process of the device's operation, ferroalloy particles arrive from the loading hopper into the chamber of the distribution unit through the flexible conduit and get equally scattered over the surface of the central hopper. After that the particles are entrained by the steel stream and are carried into the moulds cavities, they melt and uniformly dissolve in the crystallizing metal. Introducing the alloys in such a way makes it possible to avoid negative consequences of the ladle outlet port clogging, which often happens during the dosed tapping of aluminium or titanium grain-refined steel.

In comparison with the methods of steel microalloying in the steel-teeming ladle, this steel treatment technology has a number of advantages due to zero contact of the introduced active components with the oxidizing furnace slag and acid lining, and also due to reduction of the total time of atmospheric oxygen influence on the microalloyed metal.

Implementation of the technology of 65Г steel refining with titanium and boron, thanks to the said advantages of the ladle gate equipped with a distribution unit, allowed to increase the assimilation degree of these elements up to 94.1 and 92.9%, respectively. In case of steel microalloying with the implementation of the reagents into the ladle, the degree of their assimilation didn't exceed 18 and 42% because of the increased waste.

Using the sliding gate equipped with the unit of gas-dynamic protection of the steel stream against the negative influence of the atmospheric oxygen, the attendants don't get distracted from the fulfillment of their direct duties, as the optimal rates of the shielding gas flow are automatically kept within the fixed limits. At the same time the acceptable level of the oxygen impoverishment (down to 5%) in the space around the steel stream, is achieved in case of the shielding gas supply (N2, Ar, CO2) at a rate within 40-50 m3/h.

Application of steel protection against secondary oxidation allows to reduce the oxygen concentration in the finished metal on average by 30-50%.

The sliding gate operating conditions can be improved by means of eliminating the overheating of its single components during the sequence casting process. For this purpose it is suggested to equip the ladle gate with an ejector which creates rarefaction to promote air exhaust from the cavity of the submerged nozzle, attached to it.

Compressed air from the shop main is used as the working gas which ensures the ejector's operation. If injected under overpressure through the nozzle into the ejector's mixing chamber, connected with the nozzle cavity by the pipeline, compressed air creates rarefaction in the nozzle cavity, which causes oxygen impoverishment. That allows to reduce the rate of secondary oxidation of continuously cast steel.

The described systems and equipment can be efficiently used at steel-making plants of metallurgical and machine building works.


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