SU1500447A1 - Method of flash-butt resistance welding - Google Patents

Abstract

The invention relates to flash butt welding and can be used for welding parts with a developed cross section. The purpose of the invention is to improve the quality of welded joints by increasing the rate of plastic deformation of the welded parts in the process of settlement. The precipitation is carried out in stages. In the first stage, the precipitation amount is 20-30% of the total allowance. The precipitation at the first stage is carried out with the maximum rate of deformation. In the second stage, the deformation is carried out at a reduced speed. At the second stage, the precipitation welding current is turned off. By switching off the current, the upsetting speed is set to the corresponding upsetting speed in the first stage. Increasing the sedimentation rate at the second stage by cutting off the current makes it possible to increase the plastic properties of the metal in the welding zone due to compression and displacement of the liquid and solid metal oxides from the deepest craters. An increase in the deformation rate at the second stage of the precipitation upon cutting off the current reduces the time of plastic deformation, which makes it possible to increase the thermal activation of the joining surfaces and thereby increase the quality of the welded joint. 1 silt, 1 tab.

Description

The invention relates to flash butt welding, and can be used for welding parts mainly with a developed cross section about

The aim of the invention is to improve the quality of welded joints by increasing the rate of plastic deformation of the welded parts during the settlement process.

The drawing shows diagrams of changes in the movement speed and welding current at various stages of the precipitation process „

The drawing denotes: I - chart of the change in the rate of draft; 2 - diagram of the current measurement; Vj, sediment rate in the first stage; sedimentation rate at the allure stage; Vjjj - sedimentation rate at the second stage after the current is turned off; 1c - current In the process of forming1: the api of the welded joint at the stage (h:; the bridges usually distinguish 1 main gapa;

--four

3150

I - the formation of physical contact;

II — formation of metallic bonds; ,

III-crystallization and cooling In order to obtain a metallic compound, it is necessary to overcome the energy barrier of the setting, i.e., to expend additional energy, called the activation energy, which is divided into mechanical and thermal. Moreover, the mechanical activation is determined by the magnitude of the upsetting force, and thermally by the fact that part of the upsetting is carried out under current.

The separation of the precipitation process into two stages with different rates at the second stage in the described method is due to the following factors

At the first stage, the spark gap closes, Toe. the formation of physical contact between the parts to be welded. At the same time, atoms come closer together, irregularities and surface films of the oxidized metal are eliminated. Here, a high convergence rate is required to prevent the oxidation of the welded surfaces from spreading. The amount of precipitation 20-30% of the total allowance at the first stage is determined by the fact that the size of the gap between the melted ends and the thickness of the liquid metal layer do not exceed 1.5 mm,

At the second stage, the energy barrier of the setting is overcome, the electron shells are combined, and metallic bonds arise.

nation of atoms at this stage can

carry out in two ways, First — due to the large compressive force (mechanical activation) 5 of the second — by means of thermal activation. The second way is preferable by the following considerations: during thermal activation, the potential energy and kinetic increase, resulting in a decrease in the stability of the electronic configurations and an increase in the probability of the combination of the electron shells at increased distances. Consequently, when plastic deformation is carried out, the upsetting force required to overcome the repulsive forces that arise during electrostatic interaction of electrons requires MeH) iiiee than during mechanical activation.

A reduction in the sediment velocity of the a stage of the second stage is necessary so that during the precipitation process, under a thermal activation current, a larger amount of heated metal is subjected to i than at a constant high precipitation rate when the heated metal is squeezed out of the junction and thermal activation is ineffective. The decrease in velocity is also accompanied by a decrease in pressure, and as is known, a decrease in pressure facilitates the heating of the metal. The optimum value of the allowance for the draft under the current for parts with a developed cross section is 0.5-0.6 of the total allowance for the draft. A further increase in the duration of precipitation under current at a lower speed is impractical, since a splash of molten metal or its draining from the ends of the parts may occur. This is also explained. the magnitude of the decrease in speed in the second precipitation stage. It should not be lower than the final reflow rate (Vjj lsO-2, OVi reflow).

After the current is turned off, the final formation of the welded joint occurs. In this case, the deepest craters are leveled and liquid and solid metal oxides are expelled from them, as well as the metal is compressed in the joint zone in order to compact the metal and increase its plastic properties.

As you know, the craters depth. -. increases with increasing cross section of welded parts. After the current is turned off, the metal cooling () occurs very intensively and by the end of the precipitation in the deepest craters there may remain a frozen, usually oxidized metal, which causes connection defects and a decrease in its plastic properties due to intense recrystallization due to the slow deformation of the heated metal. Therefore, after the current is turned off, the speed is again increased to the maximum value and thereby shortens the plastic deformation time. A certain decrease in speed after the current is turned off at this stage is due to plastic deformation metal resistance, because by this precipitate the compression of the solid-liquid metal phase and the magnitude specified-, 15

increase in speed after switching off at this stage, as already noted, reduces the plastic deformation time and allows, without sacrificing quality, to carry out thermal activation at a reduced speed, which significantly reduces the deformation resistance, since its value depends on temperature. and the type of metal. Accordingly, the required upsetting force is reduced. In this connection, slipping of parts in the clamps is prevented and the quality of welded joints is ensured.

In pilot welding of a lot of rails using this method, high-quality welded joints are obtained by reducing the upsetting force up to 30% of that required in the traditional method. It is possible to reduce the machine hydraulic system and, in some cases, to refuse an additional energy source (pump accumulator) and accordingly reduce the size and weight of the design of welding machines. For mobile machines of type K-355, K-584j K-700-1 operating in field conditions, this is a significant indicator.

An example, the practical implementation of the invention was carried out on a K-355A rail welding machine equipped with an UEG electrohydraulic amplifier. The speed reduction at the second stage was programmed using UEGaS, changing pressure in control cylinders

The following parameters of the sludge process were set up during the welding of rs.cats: the total allowance for the draft was 12 mm (while the allowance at the third stage of the sludge was 0.6 of the total allowance - 7 mm) J speed of slump (specified) I stage 25 mm / s; slump speed (given) at stage II 2.5 mm / slump speed (given) at stage III 25 mm / s

The results of mechanical tests of rails, welded by traditional technology and the described method are shown in the table.

The analysis shows5 that the deflection arrow increased on average by 37%, and the breaking load by 13%.

Increasing the deformation rate in the second stage after turning off the current makes it possible to increase the thermal activation of the surfaces to be connected and, thus, the quality of the connection.

Claims (1)

The invention of bni is a flash flash butt welding method, in which the precipitation process is carried out in stages, in the first stage, by 20-30% of the maximum allowance at maximum speed, and in the second stage, before switching off the current at a reduced speed, characterized in that in order to improve the quality of the welded joint, after the current is switched off, the upsetting speed is set to the corresponding upsetting speed in the first stage. 230 235 235 240 235 55 59 59 62 60 Not Not No no Not  ioc, u t / ugls  YU