Technology of vacuumization of steel in an intermediate ladle with the use of the vacuumator of circulation type “RH-IS”

During the last decades, the stable tendency for using so-called “dry” gas exhaust systems began to show, most of all for VD aggregates, which work as a part of the technological chain «ДСП-VD-АКП-МНЛЗ». Given scheme of cast billet production took hold because of rapid construction of mini-plants and reconstruction of electric steel-smelting and open-hearth workshops being part of metallurgical plants of full cycle.

Thus, the main methods of vacuumization of steel during mass production are VD, RH- and DH-processes and their versions developed for vacuum decarburization and desulphuration of steel. At the same time, despite the semicentennial history of industrial vacuumization of steel and constant improvements in construction and technology, existing technologies have a number of disadvantages which resist fundamental correction in the framework of classic constructions and technological schemes. In order to solve the problem the process of vacuum treatment in an intermediate ladle was designed. The process allows to obtain considerable improvement of quality of finished goods while investments and costs are relatively small. The offered concept of vacuumization of metal in a ladle using the circulation method “RH-IS” has a number of advantages over traditional methods of vacuumization.

Advantages of the vacuumator “RH-IS”:

  • small dimensions and possibility to be installed in any workshop where it is impossible to install a stationary vacuumator RH;
  • minimal capital investments and exploitation costs (costs are approximately 5 times smaller comparing to the costs of stationary vacuumators);
  • multiple vacuumization of steel during the process of casting with the control of multiplicity regulation;
  • treatment of steel under deep vacuum ≤ 100 Pa;
  • nitrogen removal 20-30% directly before steel crystallization;
  • guaranteed obtaining of hydrogen ≤ 2 ppm;
  • decrease in formation of nonmetal inclusions: secondary to 70% and tertiary to 50%;
  • removal and destruction of up to 50% of primary and secondary nonmetal inclusions;
  • removal of nonmetal inclusions of exogenous nature up to 30%;
  • improvement of steel casting characteristics. 

Table 1 - Technical and economic parameters of work of vacuumization systems

Name of parameter

Unit

Ejector system, vacuumator VD

Ejector system, vacuumator RH

Dry system, vacuumator VD

Dry system, vacuumator (RH-IS)

Parameters of pump installation

Air productivity

kg/hr

260

300

156

50

Exhaust velocity

m3/hr

200

230

120

39

Residual pressure (minimum)

mbar

<1,5

<1,5

0,5

0,5

Duration of vacuum intake

min

6-8

3-5

8-10

1-2

Parameters of vacuumization

Full duration of vacuumization cycle

min

40-60

20-40

50-70

continuously

Recirculation coefficient

 

-

1-8

-

1-4 (3,5)

Metal temperature decrease

°С

50-60

40-50

60-80

10-20

 

Table 2 - Comparative results of vacuumization systems work

Name of parameter

Unit

Ejector system, vacuumator VD

Ejector system, vacuumator RH

Dry system, vacuumator VD

Dry system, vacuumator (RH-IS)

Removal of harmful impurities

Hydrogen

%

70-80

80-90

70-80

80-90

Nitrogen

%

10-30

10-20

10-30

10-20

Combined oxygen

%

60-70

60-70

60-70

60-70

Nonmetal inclusions

%

80-90

80-95

80-90

80-95

Secondary pollution of metal after vacuumization

Hydrogen

ppm

0,5-2

0,5-2

0,5-2

-

Nitrogen

ppm

10-30

10-30

10-30

-

Combined oxygen

ppm

5-10

5-10

5-10

-

Nonmetal inclusions

% volume

0,010-0,020

0,010-0,020

0,010-0,020

-

Residual content (ladle trial)

Hydrogen

ppm

2-4

2-4

2-4

< 2

Nitrogen

ppm

70-90

70-90

70-90

<70

Combined oxygen

ppm

20-30

20-30

20-30

<15

Nonmetal inclusions

% volume

0,020-0,040

0,020-0,040

0,020-0,040

<0,015

 

Steelmaking

 
English (United Kingdom)Русский (Russian Federation)