RU2777495C1 - Method for contact welding of rails - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention relates to contact welding of rails of carbon and doped steels; it can be used in the connection of railway, tram and other rails. Welded ends of rails are preliminary mechanically processed with the provision of their perpendicularity to axes of rails. An insert in the form of metal mesh is placed in a gap between ends, and welding is performed with heating and melting of the insert and the surface of rails, and removal of the melt from a contact zone at a settlement stage. Mesh cells can have a geometrical shape in the form of a rectangle, or a square, or a rhomb. Mesh spacing Δ is selected from a condition of provision of a number of contact nodes, equal to at least three, in the minimal section of a rail neck. Overall dimensions of mesh should exceed maximal dimensions of the section of the rail for at least 2Δ, and dimensions of a mesh holder should be additionally taken into account by height.

EFFECT: invention provides for an increase in the stability of a process at a heating stage and quality of a welded joint due to the provision of controlled arrangement of primary contact spots and uniform heating of contact surfaces at the first heating stage, as well as reduction in size of a heat-affected zone (HAZ), increase in heat dissipation power, and reduction in time of heating surfaces due to an increase in current density on local contact sections.

3 cl, 2 dwg

Description

Technical field

The invention relates to the field of welding, in particular to methods of resistance welding of carbon and alloy steels and can be used when joining railway, tram and other rails.

Prior Art

There is a known method of flash butt welding by flashing, when in the first stage of the process, solid surfaces of parts come into contact, while the most heated volumes of metal are in the middle part of the contact (Paton B.E., Lebedev V.K. Electrical equipment for resistance welding. - M : Mashinostroenie, 1969. - 440 p. 24.)

The disadvantage of this method is that in the first stage of heating, the initial contact of the surfaces is carried out at the micro level at points associated with roughness, which are randomly located along the contact surfaces, while the number and size of simultaneously existing contacts can vary during the reflow process within very wide limits. This leads to uneven surface heating and process instability due to the fact that the volume and shape of the bridge do not remain constant.

A known method of resistance welding of rails (patent RU 2308362), including mechanical processing of their ends, heating and pressure welding, while machining is carried out to ensure that the ends are perpendicular to the axes of the rails, and then an antioxidant and anti-decarburizing film is applied with a thickness of 0.1 to 0.5 mm, which is an additional body in contact between the rails. The disadvantage of this method is that on the contact surface there are 100% non-metallic inclusions, which lead to a decrease in the quality of the welded joint.

A known method (I.Z. Genkin. Welded rails and turnouts. - Path. - 2000. - N 12. - S. 14-20) welding crosses made of high manganese steel 110G13L with rails made of carbon steel rail M76, according to which the connection of these elements of the turnout is carried out by contact welding by the method of pulsating flashing. In order to avoid the formation of hardening structures and cracks between the turnout cross and the rail, an intermediate insert made of austenitic chromium-nickel steel is welded. This method is adopted as a prototype of the claimed invention.

The disadvantage of this method is:

- chaotic arrangement of spots on the contact surfaces in the first stage of heating, associated with the roughness of the surfaces;

- the insert material does not completely melt and remains between the parts to be welded, which has a significant effect on the mechanical properties of the welded joint;

- the requirements and costs for the technological preparation of joints before welding increase sharply, since when using an insert, two welding operations are performed instead of one.

Disclosure of invention

The technical result is as follows:

1. Increasing the stability of the process at the stage of heating and the quality of the welded joint by providing a controlled, rather than chaotic arrangement of the primary contact spots and uniform heating of the contact surfaces in the first stage of heating.

2. Reducing the size of the HAZ, increasing the power of heat release and reducing the heating time of the surfaces due to an increase in the current density in the local contact areas.

The technical result is achieved by the fact that in the method of resistance welding of rails by flashing from carbon and alloy steels, including mechanical processing of the welded ends of the rails to ensure their perpendicularity to the axes of the rails, heating and flash welding, after mechanical processing of the ends of the rails, an additional body is placed in the gap between them. an insert in the form of a metal mesh, welding is performed, with heating and subsequent melting of the mesh and the surface of the rails and removal of the melt from the contact zone at the upsetting stage (Fig. 1).

In a particular case, the grid cells can have a different geometric shape in the form of a rectangle, square or rhombus, while the insertion step Δ is selected from the condition of ensuring the number of contact nodes equal to at least three in the minimum section of the rail neck b, from the following ratio Δ<b/3, the geometry of the insert must exceed the maximum dimensions of the rail section by at least 2Δ, and the dimensions of the holder are additionally taken into account in height (Fig. 1).

(Вид - I на фиг. 1). Ячейки сетки могут быть в виде прямоугольника

квадрата (A_x=A_y) или ромба (равностороннего A_x=A_y или неравностороннего

Grid spacing

(View - I in Fig. 1). Grid cells can be in the form of a rectangle

square (A _x \u003d A _y ) or rhombus (equilateral A _x \u003d A _y or unequal

Brief description of the drawings

In FIG. 1 shows the layout of the insert in the form of a metal mesh before flash welding.

In FIG. 2 shows a view of the R65 rail according to GOST 51685 with the layout of the perforation pitch Δ (View - II).

Implementation of the invention

Before welding the rails, the ends to be joined are mechanically processed, for example, they are ground, ensuring their perpendicularity to the axes of the rails. Then, an insert in the form of a metal mesh is inserted into the gap between the ends (Fig. 1). Distinctive features of the use of a metal mesh are:

1) transition from the chaotic arrangement of spots along the contact surfaces in the first stage of heating to controlled - uniform and stable heating of the welding zone due to the uniform arrangement of primary contact spots along the complex contour of the rails at the local level.

2) at the stage of melting, the grid and the surfaces of the ends of the rails are melted, after which the liquid phase is removed at the stage of upsetting with a burr from the contact zone, so the grid cells can have a simple shape (for example, square).

3) a decrease in the contact area and an increase in the current density leads to an increase in the heat release power and a decrease in the heating time of the welded ends of the rails.

The possibility of using the proposed technical solution was tested using a K1100 rail welding machine that implements flash welding. Rails of the R65 type were welded from E76HF steel, having a complex geometry (Fig. 2) in accordance with GOST R 51685 “Railway rails. General technical conditions".

For rail type P65, the minimum section of the rail neck is b=18 mm, the width of the base is L=150, the height of the rail is 180 mm. As an insert, a metal mesh with a square cell was chosen, the pitch of which is Δ=5 mm (Δ=5<18/3=6 mm) and the wire diameter is ∅=1.2 mm. Regardless of the location of the grid relative to the axis of the rail contour, the pitch Δ=5 mm is guaranteed to ensure that 3 grid nodes hit the thickness of the neck. Overall mesh size (Fig. 1):

- width - S=170>(L+2⋅А)=150+2*5=160 mm;

- mesh height -h=240 mm (selected based on the height of the rail - 180 mm, the gap between the mesh fasteners and the height of this fastening).

An additional operation consists of placing the mesh in the middle of the gap and fixing it in the holder to ensure reliable contact.

After that, the process of resistance flash welding was carried out at the established modes in two versions without a grid and with a grid installed.

Hardness measurements were carried out along the rail head and three-point bending tests were carried out on specimens of welded joints 1200 mm long. As a result, it was established: 1) at the stage of heating samples with a grid, the stability of the process increased (i.e., the current oscillation decreased); 2) reduction of the heat-affected zone according to hardness measurements by 20-30% and an increase in mechanical properties (breaking load increased by 5-10%, deflection - by 3-8%).

Claims (3)

1. A method for butt flash welding of rails made of carbon and alloy steels, including machining of the welded ends of the rails to ensure their perpendicularity to the axes of the rails, heating and flash welding with pressure, characterized in that after machining the ends of the rails in the gap between them, an insert is placed in the form metal mesh, welding is performed with heating and subsequent melting of the insert and the surface of the rails and removal of the melt from the contact zone at the upsetting stage. 2. The method according to p. 1, characterized in that the cells in the grid are made in the form of a rectangle, or a square, or a rhombus. 3. The method according to claim 1, characterized in that the grid pitch is selected from the condition of ensuring the number of contact nodes equal to at least three in the minimum section of the rail neck, and the overall dimensions of the grid exceed the maximum dimensions of the rail section.

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