WO1995027801A1

WO1995027801A1 - Vaporisation bell for metallurgical treatment in molten baths

Info

Publication number: WO1995027801A1
Application number: PCT/IT1995/000045
Authority: WO
Inventors: Ettore Bennati
Original assignee: Ettore Bennati
Priority date: 1994-04-07
Filing date: 1995-03-29
Publication date: 1995-10-19
Also published as: ITBS940032A0; ITBS940032A1; AU2113595A

Abstract

The invention covers the method and equipment for the addition and distribution of reaction material in vapour form (e.g. magnesium vapour) in cast iron baths in order to reduce the content of sulphur and/or modify the form of the graphite from lamellar to compact or nodular. Continuous variable-capacity vaporization is obtained by exploiting the heat of the bath but without direct contact between the reaction material -whether it be in a solid or in a liquid state- and the bath. The aim is attained by means of a high thermal conductivity and gas-tight bell which is plunged in the bath.

Description

vapori sati on bel l for metal l urgi cal treatment i n mol ten baths

DESCRIPTION

The aim of this invention is to improve the overall efficiency of metallurgical treatments such as that of cast iron which use pure magnesium and/or its alloys vaporized directly in the molten bath 5 for obtaining spheroidal graphite and modifications thereof or for desulphurization, deoxidation and similar treatments . Using known techniques,vaporization is obtained means of direct contact between the molten metal and magnesium; due to the high temperature, enormous volumes of Mg vapour ar generated instantly and cyclically which pass through the bath and generate the required reaction. It should be pointed out, however, that the majority of the Mg oxidizes outside the bath with typical glare and/or the generation of hot fumes, involving serious environmental damage and also high costs. The causes of the loss of Mg are attributed to the formation of large vapour bubbles and also the limited area of distribution of the same inside the bath. In effect, the molecular Mg of the bubbles does not dissolve completely in the bath due to local Mg oversatu ration which slows down or inhibits reactions with sulphur, oxygen and so on, and also 0 to the short contact time available.

The aim of this invention is to allow continuous formation and distribution in a set time of Mg vapour bubbles with reduced volume and in the entire mass of the bath in order to facilitate the complete development of the reactions and thus reduce loss. 5 The aim is attained by means of an air-tight vaporization bell which allows the Mg to melt and vaporize, exploiting the heat of the bath which is transmitted by conduction and radiation from the walls of the bell and also from the bath excluding, however, all direct contact between the same and the reaction material Mg, 0 whether it be in a liquid or solid state.

A further aim of the invention is to melt and superheat the reaction material directly in the reaction chamber/cavity of the bell and outside the bath, providing the necessary heat with subsidiary means of electric heating or combustion, thus reducing the bath's temperature loss and allowing the treatment to take place at lower temperatures.

The preheating / temperature maintenance outside the bath also reduces sudden changes in temperature affecting the life of the bell, which is made of refractory material with high heat conductivity.

The aims are attained by means of a vaporization bell as shown in Fig.1 , being treated and plunged in a bath 1. Such bell has a body 2 with a coupling for a plunging bar 3 and a chamber or gas-tight cavity 4 incorporating the tank 5 containing the reaction material in a solid 13a or liquid state 13b.

If plunged in a bath, the bell, which is completely enclosed at the top and air-tight, allows the formation and maintenance inside the inner chamber 4 of a gas or vapour pressure corresponding to the metallostatic pressure of the bath and which prevents the entry and contact of the same with the reaction material present in the tank. Melting and vaporisation are determined by the heat transmitted by conduction from the inner/outer walls 2ab of the tank and by radiation from the inner walls of the chamber and also the free surface of the bath circumscribed by the lower opening 6 of the bell.

Even uninterrupted distribution of the reaction vapour in the tank is ensured by means of a series of ducts 7 which connect the internal chamber with the external bath, thus ensuring an even pressure balance for the entire vaoprization time, the duration of which depends on the dimensions and physical properties of the bell materials, with particular reference to heat conductivity. Fig.2 shows the main equipment for treatment with the vaporization bell in accordance with this invention. The following should be noted in particular: the treatment ladle 8 containing the bath 1 in which is plunged the bell 2 connected by means of a plunging bar 9 to a bell swivelling mechanism 10 allowing even distribution of the vapour, and the system for plunging the bell 11 in and raising it from the bath.

Fig.3 shows a device 12 for introducing the reaction material 13a in the tank 5, an electric device 14 for melting and superheating the reaction material contained in the bell prior to the plunging of the same in the treatment bath and which reduces temperature loss and the risk of bell breakage due to sudden changes in temperatur. Figs. 4 and 5 show two variants in the assembly of the various components such as: the dome 2c with the coupling for the plunging bar, the external wall with the incorporated tank 2a, the internal wall 2b of the tank 5 with the locking segments 2d with the vapour distribution ducts 7, which may be made of materials that are not homogeneous.

Claims

C L A I M S

1). Vaporization chamber for treatment in molten baths, for example cast iron or steei, with the use of reaction materials with a high generation of vapour such as magnesium and its alloys, characterized in that vaporization of the reaction material occurs inside a chamber (4) in a continuous manner and only after plunging in the bath and with the appreciable heat given off by the same, but without any direct contact with the reaction material in a solid or liquid state contained in a tank (5) incorporated in the bell and indirectly connected to the chamber (4) by means of an upper tank charging and cleaning opening (2e), in that the pressure of the gas/vapour present in the chamber equalizes the metallostatic pressure maintaining the level of metal inside the bell and in all conditions below the opening (2e), melting and vaporization heat transmission occurring by conduction through the walls of the bell and by radiation transmitted from the same from the surface of the bath incorporated into the bottom of the bell, the vaporization time being determined by the formation and distribution of bubbles of vapour completely soluble in the bath through distribution ducts (7). 2). Vaporization bell as per claim 1 , characterized in that melting and superheating at temperatures approaching the reaction material vaporization temperature are obtained outside the bath and with the supply of heat provided by an independent source of electric heating or combustion (14). 3). Vaporization bell as per claims 1 and 2, comprising a swivel device (10) for the even distribution of reaction vapour in the bath and a bell plunging and raising device (11). 4) .Vaporization bell as per claims 1 and 2, comprising a monolithic structure or various assembled elements made of the same or different materials.

5). Bell for treatment by plunging in molten baths by means of the vaporization of reaction materials with high vapour generation properties, as substantially described above, illustrated and claimed for the aims specified above.