GB1592163A - Repair of ferrous metal bodies by filling surface depressions therein - Google Patents

Description

(54) REPAIR OF FERROUS METAL BODIES BY FILLING SURFACE DEPRESSIONS THEREIN (71) We, GORICON METALLURGICAL SERVICES LIMITED, a British Company, of Goricon Buildings, Picton Street, Kenfig Hill, Bridgend, Glamorganshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the repair of ferrous metal bodies by filling surface depressions therein.

In accordance with the present invention, there is provided a method of repairing a ferrous metal body by filling a depression in a surface thereof which comprises reacting in the depression a mixture of the kind which reacts exothermically on ignition to yield a molten metallic iron phase and a molten slag phase over the iron phase and, whilst at least the top of the slag phase remains molten, introducing further of such a mixture into the depression for ignition therein and continuing the introduction until the requisite amount of iron phase has been produced. A metallic flux may be employed to promote adhesion of the metal phase.

Mixtures of the kind aforesaid are widely used for repairing ferrous metal bodies. Best known, are pulverulent mixtures of the thermite type which consist of one or more oxides or iron and particulate aluminium which acts as a reducing agent and is converted in the exothermic reaction to an aluminous slag. The total volume of metallic iron and slag obtained by the reaction is substantially less than the volume of the original pulverulent mixture. Reaction of the mixture in a depression does not, in most practical cases, give complete filling of a surface depression with the metallic and slag phases together even when the mixture is piled as high as possible before ignition. The complete filling to the level of the surface with metallic and slag phases has been accomplished by a multi-stage operation. Complete filling with the metallic phase has been accomplished by reacting the mixture in a crucible of sufficient size and pouring the metal phase, whilst still molten, into the depression.

By the present method, complete filling is achieved by simple in situ reaction without such major interruptions as would be involved in removing solidified slag between the introduction of reactant mixtures.

An important application of the present method is to the repair of the ingot moulds used in the steel industry and bottom plates therefor. The bottom plates become eroded by the impact of molten metal in ingot castings and the seats at the lower end of the moulds themselves become damaged in use. Prolonging the use of the moulds and the bottom plates by repair is important for economic reasons.

In its application to the filling of erosion holes in bottom plates, and in other applications where the slag provides an acceptable surface for the fill, the introduction of the mixture may be terminated when the top of the slag phase has reached the level of the surface or when slag has overflowed but the top of the metal phase is still below the level of the surface. Where the fill is required to have a metal surface, the introduction is continued until the metal phase reaches the level of the surface, the whole of the slag (and perhaps some metal) being allowed to overflow.

The method may be applied where the depression is located at the edge of the body where the said surface meets a second surface (which is a common situation with ingot moulds) by applying to the second surface a dam member to enclose the cavily laterally.

Such a dam member is best formed of a slab of refractory material, but a metal plate of adequate melting point may be used in some cases. The dam member may be secured, for example by cartridge nails or magnetic clamps.

Especially simple control of the filling operation is obtained if the dam member is formed with a tapping notch.

In a modification of the method, the top of the cavity is fitted with a pre-formed ferrous metal plate. Since it is normally difficult to fit such a plate accurately within the periphery of the recess, filling to the level of the surface of the body is required, in most cases, even if the top of the plate is arranged flush with the surface of the body. By the use of a preformed plate of similar micro-structure and physical properties to the body, a repair may be achieved which provides substantial continuity.

To improve security of the fill, the shape of the cavity may be modified in a preparatory operation to provide one or more re-entrant formations, eg., by burning out one or more holes with a torch. Desirably, holes and other re-entrant formations of restricted ingress are pre-treated to prevent entry by un-reacted exothermic mixture. They may, for example, be plugged or packed with a material permeable or destructable by the molten metal phase, or provided with fusible covers e.g., of thin gauge aluminium.

In some cases, a discernible crack may remain at the boundary of the fill. Such a crack can be filled with a refractory filler or with metal in any desired manner such as by a conventional welding operation (which would be inordinately expensive if applied to filling the whole cavity.) It is possible to carry out the filling operation using a conventional Thermit mixture, but considerable care is necessary because the very high reaction temperature gives an extremely violent reaction. It is advantageous to use conventional thermite mixture for the first portion of the fill as the high temperature improves welding of the fill to the metal of the body. However, it is desirable to reduce the reaction temperature of the remainder of the addition by suitable formulation of the mixture. It is also desirable to minimise the ratio of slag to metal produced. The incorporation of non-reactive metal, preferably iron or steel is advantageous. This metal may be included in the mix or added during application, or both.

Pre-heating of the wall of the cavity is desirable in some cases and may be achieved by the ignition therein of a conventional Thermit mixture as a preliminary step.

The following description in which reference is made to the accompanying drawing is given in order to illustrate the invention. In the drawing.

Figure I shows an ingot mould with a bottom seating, Figure 2 is a partial cross-section taken at plane II--II of Figure 1, Figure 3 shows the mould in end elevation with a dam secured thereto, Figure 4 illustrates an early stage of the filling operation, and Figures 5 A, B & C are sections, taken at V---V of Figure 4 showing the continuation and completion of the filling operation.

Ingot mould 1 is a large hollow tapered cast iron structure open at both ends. It has lifting lugs one of which is shown at 2. End face 3, which is the seat rests in use upon a conventional bottom plate the walls of the mould then being vertical.

The mould as shown in Figure 1 has a recess 4 torn out of the seat during use. This recess may be regarded as being in inner surface 5 of the mould and communicating with end face 3.

To repair the mould a dam 6 of refractory material is positioned in contact with face 3.

Tapping notch 7 in dam 6 has its lower edge at the level of the inner surface 5. Dam 6 is secured in position by cartridge nails 8.

A small supply of exothermic mixture is introduced into recess 4 and ignited. Further mixture 9 is then poured in continuously or intermittently. Reaction of the mixture produces a lower molten metal phase 10 and an upper molten slag phase 11.

Eventually, as reaction mixture is supplied, the top of the slag phase reaches the level of surface 5 as shown in Figure 5A. The supply of mixture is continued to produce more metal 10 and more slag, the excess of which runs out of notch 7. Figure SB shows the resulting lower ratio of slag to metal. Eventually the metal 10 reaches the level of the surface 5 as shown in Figure SC and any further addition of mixture produces a flow of metal, as well as slag, through notch 7.

Addition of the mixture may be terminated at any desired slag layer thickness. After the metal in the recess 5 has set, dam 6 is removed leaving the recess filled with metal and the surfaces 3 and 5 substantially uninterrupted.

The reaction mixtures used in the present method preferably contain from 14 to 25% of aluminium, from 41 to 80% of iron oxide and the content of any added iron or steel is preferably from 5 to 35%. All of these percentages, like the other percentages mentioned hereinafter, are by weight and based upon the total weight of the composition.

Specific examples A to H of reaction mixtures which may usefully be employed are as follows: A B C D E F G H I Aluminium powder % 25 20 18 20 18 18 18 18 14 Ferrous oxide % 75 60 54 70 63 67 54 54 60 Refractory % - - - - - - - 10 Steel % - 20 28 10 19 15 20 10 20 Catalyst % - - - - - - 5 5 3 Potassium nitrate % - - - - - - 3 3 3 Mixture A is a plain thermite composition commonly used for welding and other applications. It is costly because of its high content of aluminium and gives a violent reaction with considerable evolution of fumes. Its use is preferably confined to the first portion of the fill to give a good initial heating effect.

Mixture B, like mixture A has the aluminium powder and ferrous oxide in stoichiometric proportions but the inclusion of the 20% of steel, in the form of a powder or granules, increases the yield of metal and gives a slower, safer reaction with significantly reduced fuming.

Mixture C has the aluminium powder and ferrous oxide in the same relative proportions as mixtures A & B but contains more steel than mixture B. It is useful where a large amount of metal product is required. Because of its slow reaction and low reaction temperature its main value is in completing the fill after the filling operation has been started using a hotter-reacting mixture, especially Mixture A.

Mixture C contains excess ferrous oxide and gives increased slag fluidity. Even higher slag fluidity is given by Mixture D.

Mixtures E & F because of their reduced amount of aluminium and the inclusion of steel combine reduced costs with a high yield of metal.

Mixture G has the aluminium and oxide in stoichiometric proportions and contains steel plus a catalyst for the reaction and potassium nitrate as an additional oxidising agent. This mixture is useful in completing the fill, with an improved chance of welding the metal product to the body being repaired, when the prior step or steps of the flling have not produced a very effective working temperature.

Mixture H contains a non-metallic refractory material, eg. crushed firebrick. It is useful where it is desired to give the repair a finishing layer of the refractory material, eg. to improve resistance to erosion.

Mixture I is shown as an example of a mixture which is not favoured because of its poor ignition properties, its slow reaction, and poor flowing and welding properties.

It is believed that with the foregoing examples of mixtures and comments thereon in mind, those skilled in the art will be able to formulate mixtures suitable for use in a particular application, if necessary after simple routine experiment.

Attention is directed to our Application No. 39230/76 (Serial No 1592164) which claims the adaptation of the body for re-entrant keying.

WHAT WE CLAIM IS: 1. A method of repairing a ferrous metal body by filling a depression in a surface thereof which comprises reacting in the depression a mixture of the kind which reacts exothermically on ignition to yield a molten metallic iron phase and a molten slag phase over the iron phase and, whilst at least the top of the slag phase remains molten, introducing further of such a mixture into the depression for ignition therein and continuing the introduction until the requisite amount of iron phase has been produced.

2. A method according to Claim 1 in which the introduction is continued at least until the top of the slag phase reaches the level of said surface.

3. A method according to either of Claims 1 or 2 in which the mixture is a pulverulent mixture which contains one or more oxides of iron and particulate aluminium which acts as a reducing agent and is converted in the exothermic reaction to an aluminium slag.

4. A method according to any one of Claims 1 to 3 in which the introduction is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. Specific examples A to H of reaction mixtures which may usefully be employed are as follows: A B C D E F G H I Aluminium powder % 25 20 18 20 18 18 18 18 14 Ferrous oxide % 75 60 54 70 63 67 54 54 60 Refractory % - - - - - - - 10 Steel % - 20 28 10 19 15 20 10 20 Catalyst % - - - - - - 5 5 3 Potassium nitrate % - - - - - - 3 3 3 Mixture A is a plain thermite composition commonly used for welding and other applications. It is costly because of its high content of aluminium and gives a violent reaction with considerable evolution of fumes. Its use is preferably confined to the first portion of the fill to give a good initial heating effect. Mixture B, like mixture A has the aluminium powder and ferrous oxide in stoichiometric proportions but the inclusion of the 20% of steel, in the form of a powder or granules, increases the yield of metal and gives a slower, safer reaction with significantly reduced fuming. Mixture C has the aluminium powder and ferrous oxide in the same relative proportions as mixtures A & B but contains more steel than mixture B. It is useful where a large amount of metal product is required. Because of its slow reaction and low reaction temperature its main value is in completing the fill after the filling operation has been started using a hotter-reacting mixture, especially Mixture A. Mixture C contains excess ferrous oxide and gives increased slag fluidity. Even higher slag fluidity is given by Mixture D. Mixtures E & F because of their reduced amount of aluminium and the inclusion of steel combine reduced costs with a high yield of metal. Mixture G has the aluminium and oxide in stoichiometric proportions and contains steel plus a catalyst for the reaction and potassium nitrate as an additional oxidising agent. This mixture is useful in completing the fill, with an improved chance of welding the metal product to the body being repaired, when the prior step or steps of the flling have not produced a very effective working temperature. Mixture H contains a non-metallic refractory material, eg. crushed firebrick. It is useful where it is desired to give the repair a finishing layer of the refractory material, eg. to improve resistance to erosion. Mixture I is shown as an example of a mixture which is not favoured because of its poor ignition properties, its slow reaction, and poor flowing and welding properties. It is believed that with the foregoing examples of mixtures and comments thereon in mind, those skilled in the art will be able to formulate mixtures suitable for use in a particular application, if necessary after simple routine experiment. Attention is directed to our Application No. 39230/76 (Serial No 1592164) which claims the adaptation of the body for re-entrant keying. WHAT WE CLAIM IS:

1. A method of repairing a ferrous metal body by filling a depression in a surface thereof which comprises reacting in the depression a mixture of the kind which reacts exothermically on ignition to yield a molten metallic iron phase and a molten slag phase over the iron phase and, whilst at least the top of the slag phase remains molten, introducing further of such a mixture into the depression for ignition therein and continuing the introduction until the requisite amount of iron phase has been produced.

2. A method according to Claim 1 in which the introduction is continued at least until the top of the slag phase reaches the level of said surface.

3. A method according to either of Claims 1 or 2 in which the mixture is a pulverulent mixture which contains one or more oxides of iron and particulate aluminium which acts as a reducing agent and is converted in the exothermic reaction to an aluminium slag.

4. A method according to any one of Claims 1 to 3 in which the introduction is

continued until the metal phase reaches the level of the surface.

5. A method according to any one of Claims 1 to 4 in which the ferrous metal body is an ingot mould or a bottom plate therefor.

6. A method according to any one of Claims 1 to 5 in which the depression is located at an edge of the body where the surface meets a second surface, and a dam member is applied to enclose the cavity laterally.

7. A method according to Claim 6 in which the body is an ingot mould.

8. A method according to either of Claims 6 or 7 in which the dam member is formed of a slab of refractory material.

9. A method according to Claim 8 in which the dam member is formed with a tapping notch.

10. A method according to any one of Claims 1 to 9 in which the top of the cavity is fitted with a pre-formed ferrous metal plate.

11. A method according to any one of Claims 1 to 10 in which the cavity is modified in a preparatory operation to provide one or more re-entrant formations and the re-entrant formation or formations is/are plugged or packed with a material permeable to or destructable by the molten metal phase, or provided with fusible covers, to prevent entry by un-reacted exothermic mixture.

12. A method according to Claim 11 in which the fusible covers are formed of aluminium.

13. A method according to any one of Claims 1 to 12 in which a first mixture is used for the first portion of the fill and a second mixture, giving a lower reaction temperature is used for the remainder of the fill.

14. A method according to any one of Claims 1 to 13 in which the reaction mixture used, at least for the further introduction is formulated to minimise the ratio of slag to metal produced.

15. A method according to Claim 14 in which said reaction mixture contains iron, steel or other non-reactive metal.

16. A metal according to Claim 15 in which the metal is added to the mix during the introduction thereof.

17. A method of repairing a ferrous metal body, substantially as hereinbefore described and illustrated by reference to the accompanying drawings.

18. A ferrous metal body when repaired by a method in accordance with any one of Claims 1 to 17.