GB2102837A - Manufacture of spheroidal graphite iron - Google Patents

Abstract

A bed of a known nodularizing agent is formed within a ladle, and over it a protective crust or cover, at least one orifice being provided in said cover. Pretreated molten iron is introduced into said ladle to a level such as to allow the molten iron to flow into said bed whereby the nodularising agent is converted into a gaseous phase, the vapour being discharged through said orifice into the bath of molten iron. The bed may be inclined at an angle to the base of the ladle, and the cover may be formed of chemically bonded refractory.

Description

SPECIFICATION A process for the manufacture of spheroidal graphite iron This invention relates to a process for the manufacture of spheroidal graphite iron.

Processes are known in the art for the manufacture of spheroidal graphite iron which consists in an initial pretreatment step of the molten iron, and which is effected prior to the step of nodularization. Such a step of pretreatment consists in the desulphurization and deoxidation of molten iron by treatment with various compounds for removal of sulphur and oxygen therefrom. It is known that magnesium, and which is the nodularizing agent generally employed in the step of nodularization, also causes a desulphurization of molten iron. However, due to the costs associated with magnesium and the resultant high magnesium content, molten iron is first subjected to a pretreatment step for removal of sulphur.

This invention relates only to the step of nodularization and that any known pretreatment step may be employed for causing a deoxidization and/or desulphurization of the molten iron.

Various processes are also similarly known in the art which relate only to the step of nodularization, and for which magnesium or magnesium alloy is normally employed as the spheroidizing agent. Thus, it is known to introduce molten iron at a temperature of approximately 1450 to 1 4800C into a ladle having therein a nodularizing or spheroidizing agent to consist of magnesium or magnesium alloy. As the melting point of magnesium is 6300 C, and that the boiling temperature is 1 1050C, and as molten iron is introduced at a temperature of 14500 to 14800 C, it is immediately converted into a vapour phase.

Such an immediate conversion of magnesium from the solid to a vapour phase causes an undesirable spurting action. Yet another disadvantage is that the density of magnesium is substantially lower than that of iron. Thus, when the pretreated molten iron is introduced into the ladle, and as magnesium has a density lower than that of iron, the magnesium floats on the surface of the bath of the molten iron and without influencing a spheroidizing action on the graphite present in said molten iron on account of its burning out in the air.

In order to avoid such disadvantages, various methods are known in the art for the nodularization of molten iron. One such method consists in using a special construction of a ladle having a pocket at the base thereof for accommodating the nodularizing agent therein.

The nodularizing agent is then covered with steel chips. The purpose of providing such a layer or cover of steel chips is to avoid an immediation reaction of the nodularizing agent with the molten iron. However, it will be apparent that though the reaction is delayed, higher temperatures of the molten iron must be employed so as to cause a melting of the steel chips. Further such a method does result in a substantial loss of heat required for melting of the steel chips.

Besides the disadvantages described hereinabove, other disadvantages are also associated with such a known process. One such disadvantage is that of the ladle has a pocket at the base and, whereby, a particular and distinct construction of a ladle is required for carrying out such a process. Yet another disadvantage is that the steep chips constituting the the cover for the nodularizing agent are nct always of a uniform size and, whereby, the chips do not melt. In order to ensure that the steel chips may melt, the steel chips could be of a small size. However, a danger that can arise, in such an instance, is that the chips may melt faster than desired. It will be apparent that a required property is that the nodularizing agent should react with molten iron for a maximum possible time with least temperature loss.Such a desired feature cannot be achieved by reducing the chips to a substantial thinness. Simultaneously, the chips cannot be of a substantial thickness as, in such an instance, the reaction would be delayed and, further, the chips may not go into solution.

Yet another disadvantage is the manner of forming the covering of steel chips. Such a covering is formed when the ladle is in a red hot condition. A consequential disadvantage is that the steel chips may not completely cover the spheroidizing agent. In practice, it has been found that 5 to 6% heats are rejected.

Accordingly, a primary object of this invention is to propose a novel process for the manufacture of nodular or spheroidal graphite iron.

Another object of this invention is to propose a process for the manufacture of nodular or spheroidal graphite iron and which obviates the disadvantages associated with those of the prior art.

Yet another object of this invention is to propose a process for the manufacture of nodular or spheroidal graphite iron and which does not require a modification of the ordinary construction of a ladle.

Still another object of this invention for the manufacture of nodular or spheroidal graphite iron and, wherein, the rejection or heat losses are minimized.

According to this invention there is provided a process for the manufacture of nodular or spheroidal graphite iron which comprises in forming a bed of a known nodularizing agent within a ladle, forming a protective crust or cover on said bed, at least one orifice being provided in said cover introducing pretreated molten iron into said ladle, and to a level such as to allow the molten iron to flow into said bed so as to allow the nodularizing agent to be converted from a solid to a liquiduous phase and, thereafter into a gaseous phase, said vapours being discharged through said orifice into the bath of molten iron to cause a nodularization.

Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein: Fig. 1 shows the ladle in accordance with one embodiment of the present invention; and Fig. 2 shows a ladle in accordance with another embodiment.

Referring to the drawings, the ladle 1 of the present invention comprises sidewalls 2 and an ordinary flat base 3, said sidewalls and base being made of any known refractory material. Such a construction of a ladle is known in the art.

Accordingly, one of the aspects of the present invention resides in employing a ladle normally known in the art, but which simultaneously has distinct advantages over the known sandwich method described hereinabove and which requires a special construction of a ladle. Thus, the ladle 1 used for the process of the present invention does not require the incorporation of a pocket as required in the said sandwich method.

Accordingly, the disadvantages associated with the costs of a special construction of the ladle or the rapid wear and tear or blockage of the pocket are not associated with the process of the present invention.

In accordance with this invention a bed 4 is formed within ladle 1, said bed consisting of a known spheroidizing agent, such as magnesium, magnesium alloy or a substance capable of producing magnesium. In the embodiment of fig.

1, bed 4 is formed at an inclination with respect to base 3 of the ladle. Thus, and with reference to fig. 1, bed 4 extends upwardly from base 3 and at an inclination along a part of the sidewall 2.

Further, the spheroidizing agent extends only along a part 3a of the width of said base and such that the remainder 3b, of the base is occupied by the pretreated molten iron. In practice, the ladle is tilted and the spheroidizing agent is introduced therein such that the agent extends up to a part 2a of sidewall 2. Thereafter, a layer or crust 5 of a polymerized chemical bonded refractory is formed on said nodularizing or spheroidizing bed.

However, layer or crust 5 does not comprise a preformed crust. Such a crust is formed in a manner described subsequently herein. Layer 5 is formed such as to define an orifice 6 at the upper end thereof.

Upon introduction of molten metal into the ladle, it will be apparent that a reaction is not initiated immediately as layer or crust 5 prevents a contact of the nodularizing agent with the molten iron. Such a delay in the reaction is a desired feature. However, and upon further introduction of the molten metal, the molten metal reaches the level of orifice 6 and such as to allow the molten iron to enter therethrough. It would be apparent that as an initial flow takes place only through orifice 6, all of the nodularizing agent comprising bed 4 does not immediately react with the molten iron. Thus, a controlled vaporization takes place, and that as the heat is gradually transferred to the bed, more of the nodularizing agent is converted into a liquiduous and, thereafter, into a vapour phase.It will be apparent that the magnesium or nodularizing agent does not vapourize immediately, and that only as the heat is transferred gradually to the spheroidizing agent.

Thus, a maximum absorption of the nodularizing agent by the molten metal is achieved. Yet another advantage is that the molten metal can be tapped at a lower temperature, and which is a distinct advantage over the prior art. Yet another advantage is that the reaction pressure is lower and, whereby, magnesium recovery is greater and the loss on vapours is reduced.

Reference is made hereinabove to the reaction time of the nodularizing agent and that such a reaction does not initiate immediately upon introduction of the molten iron. Generally such a reaction is initiated when the ladle is almost full.

However, once again, it will be apparent that the initiation of the reaction would depend on the temperature of the molten iron. As one of the advantages of the present invention is to tap the molten iron at lower temperatures, and with such a tapping temperature the reaction would start when the ladle is full or substantially full.

Orifice 6 is located between the upper end of inclined crust 5 and sidewall 2. The size of the orifice would depend on the capacity of the ladle.

However, it will be apparent that the orifice cannot be too small, as it would then not allow the molten iron to enter into bed 4. Simultaneously, if orifice 6 is too big in size, the reaction would be faster and, whereby magnesium recovery would be less.

Thus, for a 500 kg capacity ladle, the diameter of the orifice could be 20 to 40 mm.

As described hereinabove, protective crust 5 disintegrates upon completion of the reaction and floats at the top of the surface of molten iron and is slagged off. The protective crust is formed by sprinkling a chemical bonded refractory material on inclined bed 4 and which is polymerized at the red hot temperature of the ladle to form said crust.

Any suitable chemical bonded refractory material may be employed and which is capable of being polymerized at the red hot temperature of the ladle, and which further does not contaminate the molten iron. The chemical bonded refractory material can consist of resin bonded silica, zirconium, chromite or any refractory sand.

It will be apparent that if the thickness of crust 5 is substantial, it may not disintegrate.

Simultaneously, if crust 5 is too thin, it may then disintegrate at a rapid rate and thereby present a controlled vaporization of magnesium or magnesium alloy. In accordance with this invention crust 5 has a thickness of about 10 to 40 mm.

As described hereinabove, the hydrostatic pressure of the molten iron is also a factor responsible for the controlled vaporization of the magnesium or magnesium alloy. Thus, the height and width of the inclined bed also controis the reaction. Inclined bed 4 should have a height of 1/8 to 1/2 of the height of the ladle. Preferably, the height of inclined bed 4 should be 1/5 to 1/8 of the height of sidewall 2.

The ladle of fig. 2 is similar in construction to that of fig. 1 and the process is carried out in a manner as described hereinabove. However, bed 4 is formed over base 3 to any convenient height depending upon the capacity of ladle 1. Further, bed 4 is a horizontal or substantially horizontal bed. Thus, reference to a horizontal bed made herein is meant and includes a bed which is substantially horizontal. In such an instance, the nodularizing agent is introduced from the top of the ladle and without the necessity of tilting the ladle, as with reference to fig. 1.

Fig. 2 illustrates only one such orifice as being provided in said crust or layer. However, a plurality of such orifices may be provided and disposed in a spaced relationship to each other. Further, a barrier means is provided at orifice 6 and which prevents an immediate entry of molten iron into bed 4 when the molten iron is introduced into ladle 1. Due to the pressure and temperature of the molten iron, the barrier means melt and allows a flow of the molten iron into bed 4. By way of example, the barrier means consist of steel chips 7.

The height of bed 4 of fig. 2 can be 1/10 to 1/8 of the height of ladle 1.

Claims (13)

1. A process for the manufacture of nodular or spheroidal graphite iron which comprises in forming a bed of a known nodularizing agent within a ladle, forming a protective crust or cover on said bed, at least one orifice being provided in said cover introducing pretreated molten iron into said ladle and to a level such as to allow the molten iron to flow into said bed so as to allow the nodularizing agent to be converted from a solid to a liquiduous phase and, thereafter into a gaseous phase, said vapours being discharged through said orifice into the bath of molten iron to cause a nodularization.

2. A process as claimed in claim 1 wherein said bed is an inclined bed.

3. A process as claimed in claim 2 wherein said bed is an inclined bed formed along a part of the base and a part of the sidewall of said ladle.

4. A process as claimed in claims 2 and 3 wherein said bed has a single orifice formed at the upper end of said inclined bed.

5. A process as claimed in claim 1 which comprises in forming a horizontal or substantially horizontal bed in the base of said ladle, forming said crust or cover with at least one orifice, providing a barrier means with said orifice.

6. A process as claimed in claim 5 wherein said barrier means consist of, for example, steel chips and which allows a flow of the molten iron into said bed only after a melting of said barrier means.

7. A process as claimed in claim 1 wherein said protective layer consists of a chemically bonded refractory material which polymerizes at the red hot temperature of the ladle.

8. A process as claimed in claim 7 wherein said refractory material comprises resin bonded silica, zirconium, chromite or any refractory sand.

9. A process as claimed in claim 1 wherein said cover has a thickness of 10 mm to 40 mm.

10. A process as claimed in claim 1 wherein said protective cover disintegrates upon completion of the reaction and floats to the surface of molten metal and which is slagged off.

11. A process as claimed in claims 2 and 3 wherein said inclined bed extends along 1/8 to 1/2 of the length of the sidewall.

12. A process as claimed in claims 5 and 6 wherein said bed extends along a height of 1/10 to 1/8 of the height of the ladle.

13. A process for the manufacture of nodular or spheroidal graphite iron substantially as herein described and illustrated.