Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1995-02-10
1996-11-05
Kastler, Scott
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75511, 266225, C21C 546
Patent
active
055713076
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
In the production of steel, it is known to expose the metal melt contained in ladles, electric arc furnaces or converters to a vacuum and to use a lance to blow oxygen over the metal surface. The CO partial pressure reduction under vacuum allows decarbonization of high-alloy melts down to the lowest carbon content with simultaneous high chrome yield and without over-oxidations. Maximization of the bath surface along with obtaining the largest possible reaction space in a container are primary objects to achieve a high rate of carbon drop when oxygen is blown, even at high initial carbon contents.
2. Description of the Related Art
Typically the use of a lance to blow oxygen on to a metal melt results in an oxygen jet impinging relatively hard upon a bath surface. Influencing the blown steel may be accomplished by altering the number of blowing nozzles; altering the flow direction of the blowing nozzles; or having the oxygen jet emerge in pulses.
For example, DE-AS 27 09 234 discloses a device for blowing crude iron to steel in an oxygen blowing converter. Control valves within the device can be alternately activated by devices that provide for pulsation of the oxygen jet. However, this reference does not disclose a method of blowing-in oxygen under a vacuum. The primary disadvantage associated with the disclosed blowing arrangement is the use of a separately controlled fluidics control system.
EP 0 081 448 B1 discloses a process and a device for oxidizing a steel bath with an oxygen blowing lance. Use of the lance results in an oxygen jet impinging upon the bath surface at a speed within ultrasonic range. Overall oxygen flow is thereby divided into a hard and a soft jet. Furthermore, the disclosed metal bath operates in an environment with atmospheric pressure.
The disclosed blowing device creates an oxygen jet that impinges upon the surface of the steel bath in a relatively limited area, forming a deep erosion in the bath, and dispersing metal droplets into the gas space above the melt. Further, the oxygen jet cannot be adequately stabilized, thus causing the hard jet to drift within the overall flow.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process and an apparatus for blowing oxygen through a lance over a metal melt under vacuum using simple and easily-maintained structural means to bring the oxygen into the metal bath over a large surface with a large intermediate phase area while avoiding over-oxidations.
The oxygen flow within the lance is accelerated and compressed and is pulsed. The oxygen emerges from the lance in plug shaped successions at ultrasonic speed. Each plug comprises an oxygen core and an oxygen casing surrounding the core. The oxygen casing spreads out into the vacuum essentially parallel to the axis of the lance and laterally above the melt in a bell-shaped form. Before impinging upon the melt, the oxygen core and the oxygen casing move at a speed relative to one another in the following relationship: ##EQU1## wherein .rho..sub.z is the density of the oxygen core; .rho..sub.p is the density of the oxygen casing; v.sub.z is the speed of the oxygen core; v.sub.p is the speed of the oxygen casing. The relationship between the pressure of the oxygen in the lance (p.sub.O) and the pressure in the chamber (p.sub.K) is in the ranges of the pressure of the oxygen in the lance (p.sub.O) is in the range of ##EQU2##
The lance includes a wall which defines an interior opening. An abrasion-free annular nozzle is disposed in the opening interior in the base region of the lance. Further, an abrasion-free blind pipe, having an open top and a closed bottom, is disposed within the interior opening. The space between the annular nozzle and the top of the blind pipe defines an oxygen fan-forming compartment. The space between the bottom of the blind pipe and the head of the lance defines a pre-nozzle chamber. The wall at the head of the lance includes a head nozzle which defines a controllable opening. This hea
REFERENCES:
patent: 4057421 (1977-11-01), Fukui et al.
patent: 4746103 (1988-05-01), Takashiba et al.
patent: 4979983 (1990-12-01), Nishikawa et al.
Meyer Ulrich
Scholer Horst-Dieter
Sizov Anatoly
Kastler Scott
Mannesmann Aktiengesellschaft
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