DE19648369C1 - Alumino:thermal mixture for welding rails - Google Patents

Abstract

An aluminothermal mixture for welding rails, comprises iron oxides and aluminium and also additives such as alloy formers and damping agents. The additives contain in weight % 0.1-16 silicon dioxide or 0.1-20 metallic silicate of formula: Me-Si-O or Me-Si-C-O in which Me is Fe, Mn, Cr, Al, Mg or Ca.

Description

The invention relates to an aluminothermic mixture from a finely divided mixture of iron oxides and aluminum and Zu substitutes such as alloying agents and damping agents.

The invention particularly relates to an aluminothermic Ge mix for the joint welding of rails.

In the known aluminothermic rail connection welding Solution, where the laid with a gap and with a pour form surrounding rail ends by aluminothermic The steel should be melted and connected to one another serving as weld metal aluminothermic steel in strength properties from the rail steel as far as possible speak.

The well-known - also weld portions - meet this requirement mentioned - aluminothermic mixtures in that the basic mixture Le consisting of aluminum and iron oxides Alloying elements, such as carbon, manganese, vana in particular dium and titanium. For damping and cooling are the aluminothermic mixture iron or steel scrap mixed in, thereby reducing the steel yield is increased.

The preferred rail steels with tensile strengths from 690 to 880 N / mm² have carbon contents from 0.4 to  0.82% and manganese levels from 0.8 to 1.7% and a corresponding predominantly pearlitic structure.

According to DE-PS 36 44 106 an aluminothermic mixture be Provides the creation of a weld metal with it Ensures higher reproducibility of the composition. This is intended in particular to ensure that the structure of the Weld metal corresponds to the structure of the rail material.

Additives are in shape in this aluminothermic mixture contain a homogeneous granulate, in particular alloy metals such as B. Mn, Cr, Ni, V, Ti, which in pure form or as alloys, e.g. B. with Fe, can be used, damper means such. B. Fe or Fe alloys, and carburizing solvents such as carbon or C-containing metals, alloy stakes or carbides.

To weld rails, the mixture is granulated, consisting of carbon, manganese and iron, in an amount too which is the formation of a pearlitic structure in guarantees the aluminothermic steel. Preferential the granules consist of 1.5 to 3% by weight of carbon, 8 up to 12% by weight of manganese and 85 to 90.5% by weight of iron. Partially Manganese contents of up to 80% are used.

In published Japanese patent application 7-299572 describes the addition of a master alloy, which is derived from the Ele elements carbon, silicon, manganese, molybdenum, vanadium, niobium, Copper, chrome and / or nickel, which is an aluminothermi mixture is added, which is used to weld two Rail pieces is used. By adding this Vorle It is possible to add the necessary carbon into the alloy Introduce weld metal in a simple and advantageous manner and optionally also other alloy elements, such as silicon, Manganese, molybdenum, vanadium, niobium, copper, chromium and / or  Nickel. These alloy additives are made exclusively in metal of the aluminothermic mixture.

The advantage of this master alloy method is said to be but more in particular the introduction of carbon other metallic alloy elements, such as silicon, than in the conventional master alloys.

The security requirements for a connection technology, its To find application especially in the field of passenger transport is, but also in freight transport, are constantly increasing. Take next to it in addition, the loads on the rails continuously increase what leads to increased wear and failure. Often be purely visual impressions increasingly impair this Many users of such a ver driving.

The quality of a weld is not only defined by fixed nated parameters, such as chemical composition or mechani described the properties of the thermite welded joint, but also through a visual assessment. Here wins ben the assessment of the flawlessness of the fracture surface according to ei After a violent breach, the surface of the weld increasingly interpretation and becomes more and more an important quality criterion rium. The type of surface defects - crack, pore, Inclusion of sand or slag - their size and general visual impression of the surface roughness recorded.

There is therefore a need for measures which, on the one hand, Occurrence of defects within the weld and the removal facilitate the molding sand and on the other hand the appearance Minimize surface defects. With one accordingly Improved weld connection will increase security claims and the economic constraints.  

One reason for the formation of surface defects is Interface between form and thermite steel.

The present invention is based on the object to provide an aluminothermic mixture which has a white improve the morphology of the joint weld possible. The invention has the object in particular reasons, the composition of the aluminothermic mixture so to change that an interface modification such he follows that on the one hand by influencing the interfacial chip tion and / or on the other hand by generating an additional Separating layer on the steel the surface quality of a Connection welding is improved.

It has now surprisingly been found that the addition of Silicon dioxide or metallic silicates of the formula Me-Si-O and / or Me-Si-C-O in the aluminothermic mixture for training a glass-like separating layer on the thermite steel and thus to improve the surface quality the connection welding.

The effect of the si Licensed connection are shown:

Fe₂O₃ + 2 Al → 2 Fe + Al₂O₃ (1)

3 SiO₂ + 4 Al → 3 Si + 2 Al₂O₃ (2)

2 Fe₂O₃ + 3 Si → 4 Fe + 3 SiO₂ (3)

The reaction (1) describes the known thermite reaction. This reaction essentially turns the thermite steel or generates the heat for the welding process.

Due to the higher thermodynamic stability of Al₂O₃ the SiO₂ added to the sweat portion is reduced by Al. The Si reacts with the Fe₂O₃ to form Fe and SiO₂,  which in turn reacts with the Al. This way, while the reaction a continuous, glass-like interface on the Thermit steel as a delimitation to form by reaction (3) det and maintain and also ver the mold filling behavior improves by influencing the viscosity of the Stahls reaction (2) -.

Further advantageous and expedient proportions by weight of the inventions Additives according to the invention result from the subclaims 2 to 7.

By using the aluminothermic Ge according to the invention can mix number and size of the surface defects and the Surface roughness can be significantly reduced. This is possible along with a much easier and almost complete Removability of the mold remnants after the welding process. The surface roughness was thereby metallographically true, surface defects by measuring and counting.

Only through the use of SiO₂ or other silicate Ver In particular, bonds in an aluminothermic mixture which significantly reduces the surface defects. A reduction tion of up to 40% is possible when using SiO₂.

For the exemplary production of a conventional 13 kg heavy 2500 g of aluminum, 7500 g of iron oxide are added to the sweat base and 300 g of metallic aggregates mixed. This mixture who the 650 g of silicon dioxide or 1050 g of metallic additives Formula Fe-Si-O or 1350 g metallic additions of the formula Fe-Si-C-O added.

The reduction of surface defects such as pores and sand conclusions, cracks, etc. is about 40%. The surfaces roughness could also be reduced by 40%.

Claims (7)

1. aluminothermic mixture of a finely divided mixture of iron oxides and aluminum and additives, such as alloying agents and damping agents, characterized in that it contains 0.1 to 16% by weight of silicon dioxide or 0.1 to 20% by weight of metallic silicates as additives of the formula Me-Si-O or Me-Si-CO, in which Me, Fe, Mn, Cr, Al, Mg, Ca can be based on the total weight. 2. aluminothermic mixture according to claim 1, characterized records that it contains 0.5 to 8 wt .-% silicon dioxide. 3. aluminothermic mixture according to claim 2, characterized records that it contains 1.5 to 5 wt .-% silicon dioxide. 4. aluminothermic mixture according to claim 1, characterized records that it contains 1 to 8 wt .-% metallic silicates Formula contains Me-Si-O. 5. aluminothermic mixture according to claim 4, characterized records that it is 2.5 to 4.5 wt .-% metallic silicates Formula contains Me-Si-O. 6. aluminothermic mixture according to claim 1, characterized records that it contains 2 to 10 wt .-% metallic silicates Formula contains Me-Si-C-O. 7. aluminothermic mixture according to claim 6, characterized records that it is 2.5 to 6 wt .-% metallic silicates Formula contains Me-Si-C-O.