AU723975B2

AU723975B2 - Aluminothermic mixture

Info

Publication number: AU723975B2
Application number: AU45330/97A
Authority: AU
Inventors: Robert H. Kachik; Michael Steinhorst
Original assignee: Elektro Thermit GmbH
Current assignee: Goldschmidt ETB GmbH
Priority date: 1996-11-22
Filing date: 1997-11-21
Publication date: 2000-09-07
Anticipated expiration: 2017-11-21
Also published as: DE19648369C1; AU4533097A

Description

S F Ref: 398642

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Elektro-Thermit GmbH Gerlingstrasse D-45139 Essen

GERMANY

Robert H Kachik, Michael Steinhorst Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Aluminothermic Mixture Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us:a.

5845 Aluminothermic Mixture The invention relates to an aluminothermic mixture comprising a finely divided mix of iron oxides and aluminium, as well as additions, such as alloy-forming ingredients and damping agents.

The invention relates in particular to an aluminothermic mixture for the weld joining of rails.

In the known aluminothermic rail-joining welding, in which the rail ends, which are installed with gaps between them and are surrounded by a mould, are fused and joined together by aluminothermically generated steel, it is intended for the strength properties of the aluminothermically generated steel, which serves as the welding material, to correspond as far as possible to the steel of the rails.

This requirement is catered for by the known aluminothermic mixtures which are also known as welding portions by admixing alloying elements, such as in particular carbon, manganese, vanadium and titanium, to the basic mixture consisting of aluminium and iron oxides. Furthermore, iron and/or steel scrap are mixed with the aluminothermic mixture for the purpose of damping and cooling, with the result that the yield of steel is increased at the same time.

The rail steels with tensile strengths of from 690 to 880N/mm 2 which are preferably used have carbon contents of from 0.4 to 0.82% and manganese 20 contents of from 0.8 to and correspondingly have a predominantly perlitic S: microstructure.

According to DE-C-36 44 106, an aluminothermic mixture is produced which ensures the production of a welding material with a high reproducibility of the composition. The effect which is intended to be achieved here is that the i" 25 microstructure of the welding material corresponds to the microstructure of the rail material.

This aluminothermic mixture contains the additions in the form of homogenous granules, in particular of alloying metals, such as for example Mn, Cr, Ni, V, Ti, which can be used pure or as alloys, eg. with Fe, damping agents, such for example Fe or Fe alloys, and also carburising agents, such as carbon or carboncontaining metals, alloys or carbides.

In order to weld rails, granules consisting of carbon, manganese and iron are added to the mixture in an amount which ensures that a perlitic microstructure is formed in the aluminothermically generated steel. Preferably, the granules consist of 1.5 to 3% by weight of carbon, 8 to 12% by weight of manganese and 85 to 90.5% by weight of iron. Sometimes manganese contents of up to 80% are employed.

The published Japanese patent application 7-299572 describes the addition of a master alloy, which consists of the elements carbon, silicon, manganese, molybdenum, vanadium, niobium, copper, chromium and/or nickel which is added Libc/02728 to an aluminothermic mixture which is used for welding together two pieces of rail.

Adding this master alloy makes it possible in a simple and advantageous manner to include the necessary carbon and, if appropriate, other alloying elements as well, such as silicon, manganese, molybdenum, vanadium, niobium, copper, chromium and/or nickel in the welding material. These alloying additions are admixed to the aluminothermic mixture solely in the metal form.

The advantage of this master-alloy method is said to lie in a more uniform introduction of, in particular, the carbon, but also of other metallic alloying elements, such as silicon, than with conventional master alloys.

There has been a continual rise in the requirements placed on the safety of a joining technique which is used in particular in the field of passenger transport, but also in the conveyance of goods. In addition, loads on the rails are increasing continuously, leading to increased wear and failure. In this connection, purely visual impressions frequently detract from the increasing feeling of safety of many users of such a process.

The quality of a weld is described not only in terms of rigidly defined parameters, such as the chemical composition or mechanical properties of the Thermit welding compound, but also by a visual assessment. In this connection, in addition to the assessment of the freedom of the fracture face from flaws following a forced fracture, the surface of the weld is becoming increasingly important and is more and more becoming an important quality criterion. Factors which are noted here are the nature of the surface defects cracks, pores, sand inclusions or slag inclusions the extent of these defects and the general visual impression of the surface roughness.

25 There is thus a need for measures which, on the one hand, reduce the occurrence of defects inside the weld and facilitate the removal of the moulding sand, and, on the other hand, minimise the occurrence of surface defects. A correspondingly improved welding join takes into account the increasing safety demands and also the economic constraints. A cause of the formation of surface flaws is the interface between the mould and the Thermit steel.

The object on which the present invention is based is to provide an aluminothermic mixture which enables the morphology of the joining weld to be improved further. In particular, the object on which the invention is based is to change the composition of the aluminothermic mixture in such a manner that the interface is modified such that the surface qualities of a joining weld are improved, on the one hand, by influencing the interface tension and/or, on the other hand, by producing an additional parting layer on the steel.

It has now been found, surprisingly, that the addition of silicon dioxide or metal silicates of the formula Me-Si-O and/or Me-Si-C-O to the aluminothermic mixture Libc/02728 3 leads to the formation of a vitreous parting layer on the Thermit steel and thus to an improvement in the surface qualities of the joining weld.

The action of the silicate compound is to be demonstrated on the basis of the following reaction sequence: Fe203 2 Al 2 Fe+ Al20 3 (1) 3 SiO 2 4 Al 3 Si 2 A1 2 0 3 (2) 2 Fe 2 03 3 Si- 4 Fe 3 SiO 2 (3) The reaction describes the known Thermit reaction. This reaction essentially generates the Thermit steel and the heat for the welding process.

Owing to the higher thermodynamic stability of the A1 2 03, the SiO2 added to the welding portion is reduced by Al. The Si reacts with the Fe 2 0 3 to form Fe and SiO 2 which in turn reacts with the Al. In this way, reaction forms and maintains a continuous In vitreous parting layer on the Thermit steel, as a separating partition from the mould, and, in addition, the mould filling characteristics are improved by influencing the viscosity of the steel (reaction The invention therefore provides an aluminothermic welding portion suitable for providing an aluminothermic weld between rail ends, said welding portion including an i5 aluminothermic mixture comprising a finely divided mix of iron oxides and aluminium, as well as additions, such as alloy-forming ingredients and damping agents, which contains, as additions, 0.1 to 16% by weight of silicon dioxide or 0.1 to 20% by weight of metal silicates of the formula Me-Si-O or Me-Si-C-O, in which Me may be Fe, Mn, Cr, Al, Mg, Ca, based on the total weight.

The aluminothermic mixture preferably contains from 0.5 to more preferably to 5% by weight of silicon dioxide. The preferred aluminothermic mixture contains from 1 to especially 2.5 to 4.5% by weight of metal silicates of the formula Me-Si-O. The aluminothermic mixture of the invention preferably contains from 2 to 10%, especially to 6% by weight of metal silicates of the formula Me-Si-C-O.

Using the aluminothermic mixture according to the invention allows the number and size of the surface defects and the surface roughness to be reduced considerably. This is accompanied by a significantly facilitated, and virtually complete removability of the mould remainders following the welding process. The surface roughness was determined here metallographically, and the surface defects by measurement and counting out.

[R.\LIBA103142.doctlt 3a In particular the surface defects are reduced considerably only by employing SiO 2 or other silicate compounds in an aluminothermic mixture. A reduction of up to 40% is possible when using SiO2.

Example By way of example, 2500g of aluminium, 7500g of iron oxide and 3 0 0 0 g of metallic additions are mixed to produce a conventional basic welding portion.

*t e RA.\LIBA]03142.doc.tlt weighing 13kg. 650g of silicon dioxide or 1050g of metallic additions of the formula Fe-Si-- or 1350g of metallic additions of the formula Fe-Si-C-O are added to this mixture.

The reduction in surface defects, such as pores, sand inclusions, cracks, etc., about 40 %It was likewise possible to reduce the surface roughness by 40 o.

:too.

.ov •Ott Libc/02728

Claims

2. The aluminothermic welding portion as claimed in claim 1, wherein said mixture contains from 0.5 to 8% by weight of silicon dioxide. ii 3. T'he aluminothermic welding portion as claimed in claim 2, wherein said mixture contains from 1.5 to 5% by weight of silicon dioxide.
4. The aluminothermic welding portion as claimed in claim 1, wherein said mixture contains from 1 to 8% by weight of metal silicates of the formula Me-Si-O.
5. The aluminothermic welding portion as claimed in claim 4, wherein said mixture contains from 2.5 to 4.5% by weight of metal silicates of the formula Me-Si-O. S6. The aluminothermic welding portion as claimed in claim 1, wherein said mixture contains from 2 to 10% by weight of metal silicates of the formula Me-Si-C-O.
7. The aluminothermic welding portion as claimed in claim 6, wherein said mixture contains from 2.5 to 6% by weight of metal silicates of the formula Me-Si-C-O.
8. The aluminothermic welding portion including an aluminothermic mixture comprising a finely divided mix or iron oxides and aluminium, as well as additions, such as alloy-forming ingredients and damping agents, substantially as hereinbefore described with reference to the example. Dated 29 June, 2000 Elektro-Thermit GmbH Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBA)03142.doc:tlt