RU2797469C1 - Aluminothermic mixture for welding metal elements - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention can be used for joining steel elements, including rails, by aluminothermic welding. The aluminothermic mixture contains iron scale, previously crushed and calcined to transfer metal oxides to the highest oxidation states, aluminium powder and alloying additives selected from the group containing: ferromanganese, ferromolybdenum, ferronickel, ferrochromium, ferrovanadium, as well as ferroalloys of silicon, tungsten, selenium, titanium, niobium, cobalt, zirconium. The amount of alloying additives ensures their total content is not more than 10% by weight of the aluminothermic mixture. Iron scale with a particle size of not more than 0.50 mm is used, containing not more than 2.5% by weight of non-metallic impurities, and aluminium powder has a particle size of not more than 0.5 mm. The particle size of alloying additives is not more than 0.65 mm.

EFFECT: implementation of the aluminothermic mixture is to improve the quality of the weld while simplifying the method of producing the mixture.

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Description

The invention relates to the field of aluminothermic welding of steel elements, including rails, and can be used in various fields of technology for a rigid long-term connection of metal elements.

Known (RU, patent application 97121417, publ. 10.10.1999) the composition of the aluminothermic mixture containing aluminum, iron oxides and ferrochrome ligature, which includes iron, carbon, silicon and chromium, while iron oxides contain variables in qualitative and quantitative composition dopants.

The disadvantage of the known aluminothermic mixture should be recognized as a significant variation in the parameters of the weld obtained using the specified aluminothermic mixture due to qualitative and quantitative differences in its composition.

Known (SU, copyright certificate 475234, publ. 04/10/1972) composition of aluminum thermite containing aluminum 20-22%, iron oxide-oxide 60-63% and aluminum oxide 15-20%

The disadvantage of this composition is the poor phase separation of the metal from the slag.

Also known (RU, patent 2574144, publ. 10.02.2010) is the composition of the aluminothermic mixture, which contains iron-containing components and an aluminum-containing component, and powders of carbides, carbonitrides or nitrides of transition metals, as well as nanopowders of carbides, carbonitrides or nitrides transition metals.

The disadvantage of the known composition of the aluminothermic mixture should be recognized as the complexity of the composition itself, and the complexity of the application of the aluminothermic mixture of this composition.

Known (RU, patent 2578271, publ. 03/27/2016) aluminothermic mixture for welding steel elements, containing iron scale, pre-crushed and calcined to transfer metal oxides to higher oxidation states, aluminum powder and alloying additives, and alloying additives are selected from the group: ferromanganese, ferromolybdenum, ferronickel, ferrochrome and ferrovanadium, and introduced in an amount that ensures the content of each of them in the aluminothermic mixture from 0.1% to 10%, while using iron scale, divided into fractions mixed in the following ratio: from 0, 25 to 0.45 mm 20-35%), from 0.45 to 0.65 20-35%, over 0.65 mm 20-40% from the condition of obtaining the maximum thermal effect.

Preferably, the dopants are used in the form of a powder with a particle size of not more than 0.65 mm.

The disadvantage of the known aluminothermic mixture should be recognized as the complexity of the composition, low cold resistance of the weld.

The specified source of information is accepted as the closest analogue of the developed technical solution.

The technical problem solved by using the aluminothermic mixture of the developed composition is to improve the quality of the weld, as well as to expand the scope of the aluminothermic mixture.

The technical result achieved by the implementation of the aluminothermic mixture of the developed composition is to improve the quality of the weld while simplifying the method of producing the mixture.

To achieve this technical result, it is proposed to use an aluminothermic mixture of the developed composition. The aluminothermic mixture of the developed composition contains iron scale, previously crushed and calcined to transfer metal oxides to the highest oxidation states, aluminum powder and alloying additives, and alloying additives are selected from the group containing: ferromanganese, ferromolybdenum, ferronickel, ferrochromium and ferrovanadium, silicon compounds, tungsten , selenium, titanium, niobium, cobalt, zirconium, while alloying additives are introduced in amounts that ensure their total content is not more than 10% by weight of the aluminothermic mixture, while iron scale is used, containing not more than 2.5% of non-metallic impurities and with a particle size of not over 0.50 mm.

In some embodiments, the alloying additives are used in the form of a powder with a particle size of not more than 0.65 mm.

In other embodiments, compounds of silicon, tungsten, selenium, titanium, niobium, cobalt, zirconium are used (including in the form of ferroalloys)

Preferably, an aluminum powder with a size of not more than 0.5 mm is used.

The achievement of the specified technical result is due, in addition to the use of complex iron oxide (iron scale is FeO and Fe ₂ O ₃ ) of the indicated alloying additives in the form of particles of the specified size in the quantities used, the use of aluminum powder of an experimentally selected size

In the production process, iron scale is crushed, then it is further oxidized in a continuous furnace at a temperature not lower than 850°C. To create an aluminothermic mixture, aluminum powders of the following grades are usually used: PA-1, PA-2, PA-3, PA-4, (GOST 6058-73), APZH and AKP according to TU 1791-99-023-99, Tu-48- 5-38-78, choosing batches of powder of acceptable size. The use of alloying additives can occur either together or separately, or in any combination. The choice and quantity of alloying additives depends on the purpose of the welded joint, but without going beyond the limits indicated in the claims

The developed technical solution is implemented as follows.

From the iron scale collected in the metallurgical production by any known method (in particular, a magnetic separator), foreign impurities are separated as much as possible. Then the selected iron scale is crushed and passed through a continuous furnace, sometimes with forced air supply, to transfer all metal oxides present in the scale to higher forms of oxidation.

For each specific case of application of aluminothermic welding of steel elements (taking into account the mass of the elements to be welded, the gap between them, external conditions, etc.), the most preferred mixture is made to obtain the maximum thermal effect. A prescribed amount of aluminum powder and prescribed amounts of alloying additives are added to the resulting mixture and mixed thoroughly. Thermite mixture is ready to use.

The developed method of aluminothermic welding will be illustrated by the example of railroad rail welding. Two rails are placed in line with a gap relative to each other. A casting mold is placed on the welded ends of the steel rails, the ends of the welded rails are heated by an external heat source for a specified time interval until the rail ends are heated to a temperature of at least 900°C, a reaction crucible with the previously obtained aluminothermic mixture is placed on the casting mold, the ignition of the aluminothermic mixture is initiated with filling obtained in the crucible by aluminothermic reaction with a metal melt from the mold of the gap between the ends of the welded steel rails to obtain a weld.

To obtain an aluminothermic mixture, iron scale was used, calcined in a continuous furnace at 850 ° C for 25 min 8 kg, aluminum powder 2.3 kg, ferromanganese, crushed to particles 0.65 mm in size 0.3 kg, ferrochrome, crushed to particles 0.65 mm 0.1 kg, ferronickel, crushed to particles of 0.65 mm 0.1 kg, ferromolybdenum, crushed to particles 0.65 mm 0.1 kg, ferrosilicon 0.1 kg, ferrotungsten and ferrotitanium 0.15 each kg. The resulting mixture was thoroughly mixed. The rail ends to be welded were placed at a distance of 25 mm from each other, a mold was placed on them, and the rail ends to be welded were heated to a temperature of 900°C using a gas burner. A crucible with 13.0 kg of aluminothermic mixture was placed in a mold and combustion of the aluminothermic mixture was initiated. Molten metal filled the gap between the rails to form a weld.

The resulting welded joint does not contain cavities and cracks, the tensile strength is not less than (1400 kN).

Using an aluminothermic mixture of the developed composition, it is possible to connect metal parts with different chemical composition of the metal. Those. alloyed steels with unalloyed, parts made of various metals (copper and steel for example), including domestic rails with Japanese rails containing chromium.

When welding railway rails using an aluminothermic mixture of the developed composition, the following indicators of the quality of the welded joint are achieved:

1. Increased wear resistance of the welded joint by 20%.

2. Increasing the hardness of the welded joint by 20%

3. Increase in yield strength by 6%.

4. Increase in tensile strength by 5%

5. Increased cold resistance from 45 to 70 C.

6. Increased resistance to dynamic loads (including impact bending) by 5%.

7. Increasing the parameters of impact strength by 7%

8. Increase in tensile test parameters by 6%

9. Increase in the modulus of elasticity (Young's modulus) by 4%.

Claims (2)

1. An aluminothermic mixture for welding metal elements, containing iron scale, previously crushed and calcined to transfer metal oxides to the highest oxidation states, aluminum powder and alloying additives selected from the group containing: ferromanganese, ferromolybdenum, ferronickel, ferrochromium, ferrovanadium, characterized in that that it additionally contains alloying additives selected from the group containing ferroalloys of silicon, tungsten, selenium, titanium, niobium, cobalt, zirconium, while alloying additives are introduced in amounts that ensure their total content is not more than 10% by weight of the aluminothermic mixture, with In this case, iron scale was used, containing not more than 2.5% of non-metallic impurities and with a particle size of not more than 0.50 mm, and aluminum powder with a size of not more than 0.5 mm. 2. A mixture according to claim 1, characterized in that the alloying additives are used in the form of a powder with a particle size of not more than 0.65 mm.