JPS59110741A - Ignition method in plasma arc heating - Google Patents

Abstract

PURPOSE:To prevent the quality lowering of a molten metal and to prolong the life of a heating chamber, by a method wherein the lower end of the heating chamber equipped with a plasma torch is shallowly immersed in the molten metal and the level of the molten metal is raised by evacuating the heating chamber to perform ignition. CONSTITUTION:In a tundish 1 provided with a lid 2, a heating chamber having a front and a back walls 5, 6 and a top wall 7 of a plasma arc heating apparatus 3 is immersed in molten steel with a level 12 flowing to the direction shown by an arrow in a depth of about 600mm. and evacuated through a connection pipe 11 by a vacuum pump 10 to raise the molten steel level 12' in the heating chamber 8 to a level about 50mm. below a plasma torch 9. Subsequently, Ar is blown into the heating chamber 8 as plasma gas whlie a DC is supplied to between an anode 4 immersed in molten steel and the plasma torch 9 to easily ignite arc plasma. After ignition, the operation of the vacuum pump 10 is stopped to lower the molten steel level 12' which is then held at a position about 500mm. below the torch 9 and plasma gas is supplied to perform the heating of molten steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ignition method for plasma arc heating of molten metal.

It is already known to apply plasma arc heating to the heating of molten metals, for example molten steel. The main reasons why plasma arc is used for such heating are that there is little contamination of molten steel and that the heating effect is good. When performing plasma arc heating, it is first necessary to ignite (arc) between the plasma torch and the molten steel. During this ignition, the plasma torch and the molten steel surface are kept at about 50 degrees, and a voltage is applied to the plasma torch (cathode) and the anode connected to the molten steel to ignite.Then, the molten steel surface is lowered and the molten steel is turned into plasma. About 600 to 800
The molten steel is heated using a tin long frame.

As a conventional ignition method, for example, Japanese Patent Application Laid-Open No. 53-8
As shown in Publication No. 3932, by increasing the depth of immersion into the molten steel in the heating chamber, the distance between the torch and the molten steel surface is kept at the optimum value for ignition, and when the heating sheet hits, The method uses plasma gas supplied into the heating chamber to increase the pressure inside the chamber and lower the molten steel level.

However, the above method has the following problems. That is, for example, plasma arc heating +++
Cape, 1. −−＾−−−−− − unit
-%-L- Molten steel (If the depth of immersion into the molten steel in the tandy-to-sea heating chamber of continuous casting equipment is increased, the wall of the immersed heating chamber will be exposed to the flowing molten steel. Acting as a kind of weir, stirring and turbulence occur in the molten steel flow,
There was a risk that this would cause the entrainment of slag or difficulty in floating fine inclusions, resulting in serious defects in the quality of the obtained slab and, ultimately, the quality of the final product.

Further, in addition to the heat possessed by the molten steel, the flow of the molten steel acts on the refractory material in the heating chamber, resulting in a large area of erosion and damage to the refractory, resulting in a short lifespan of the heating chamber.

This invention was made to solve the above-mentioned drawbacks of the conventional method, and it reduces the depth of immersion of molten steel in the heating chamber, and operates a vacuum (depressurization) device connected to the heating chamber for ignition. This is a method of igniting the molten steel in the heating chamber by raising it to a level suitable for ignition (approximately 50 m).

According to this method, the depth of immersion in the molten steel in the heating chamber can be made shallow from beginning to end, so there is less turbulence in the molten steel, there is no entrainment of slag, etc., and high quality is obtained, and the melted surface of the heating chamber is reduced. This can significantly extend its lifespan.

Examples will be described below with reference to the drawings.

In FIGS. 1 and 2, 1 indicates a part of the container of the tundish, and 2 indicates a part of the lid of the tundish. 3 is a plasma arc heating device, and 4 is an anode. The plasma arc heating device 3 mainly consists of a heating chamber 8 having front and rear walls 5.6 and a top N7, and a plasma torch 9, into which plasma gas (Ar) can be blown and cooling can be performed by appropriate means. ing. 10 is a vacuum pump in the present invention, and this vacuum pump 10 and heating chamber 8 are:
They are connected through a connecting pipe 11 so as to be ventilable. Reference numeral 12 indicates a normal molten steel surface, and this molten steel is flowing in the direction of the arrow (or in the opposite direction).

In this invention, as shown in FIG. 1, for ignition, the vacuum pump 10 is operated to adjust the degree of decompression in the heating chamber 8, and the molten steel in the heating chamber 8 is ignited at 12'. Raise the temperature to a suitable level and ignite it. When this ignition is completed, the operation of the vacuum pump 10 is stopped, the molten steel level is lowered to 12 - 3- level as shown in Fig. 2, and plasma gas (Ar) is supplied to cause the molten steel in the heating chamber to rise by plasma arc. It performs heating.

Next, to describe an example of implementation, the immersion depth of the front and rear walls 5.6 of the heating chamber in the molten steel is set to 600 m, the vacuum pump 10 is operated, and the molten steel level 12' in the heating chamber is raised by the plasma torch 9.
When the temperature was raised to 50111II+ and ignition was performed using 1000KW DC arc plasma, ignition was achieved smoothly.

After ignition, the operation of the vacuum pump was stopped to lower the molten steel level, and plasma gas was supplied to maintain the molten steel level at about 500 tm below the plasma torch and heat the molten steel. Since the immersion depth of the front and rear walls 5.6 of the heating chamber was only 600 m, there was almost no stirring flow or turbulence of the molten steel on the exit side (left side) of the heating chamber 8, and the clean steel was gotten.

As described in detail above, the ignition method for plasma arc heating of the present invention is particularly effective in heating flowing molten metal, and greatly contributes to heating molten steel such as tundishes.

[Brief explanation of the drawing]

1 and 2 are cross-sectional explanatory views of an apparatus used to carry out the method of this invention. 3; Plasma arc heating device 8; Heating chamber 9; Plasma torch 10; Vacuum pump

Claims (1)

[Claims] The lower end of a heating chamber equipped with a plasma torch aimed at the molten metal to be heated is immersed into the molten metal, and a vacuum (depressurization) device connected to the heating chamber is activated to reduce the molten metal in the heating device. An ignition method using plasma arc heating, characterized in that the level of ignition is increased to an ignition level and ignition is performed afterward.