JPH0373387B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a rail welding method.

[Conventional technology]

Generally, gas-shielded arc welding of rails involves creating a gap of 12 to 17 mm on the end surface of the rail.
The welding area is covered with a chamber filled with shielding gas, a small-diameter welding nozzle is inserted into the chamber, and an arc is generated between the welding wire passing through the nozzle and the base metal. At this time, the bottom of the rail is made of normal multilayer welding, but the rail abdomen and head are surrounded by a pair of water-cooled copper plates installed in the chamber to prevent leakage of weld metal, and holes are made in the water-cooled copper plates. Electrogas arc welding is performed while blowing out shielding gas from the shielding gas outlet.

Figure 3 is a perspective view of the rail gas shield welding device, Figure 4 is a sectional view of the rail bottom during welding, and Figure 5 is a perspective view of the rail gas shield welding device.
The figure is a sectional view of the rail abdomen and head when welded. In the figure, 1 is the rail, 1a is the bottom, 1b is the abdomen, 1c is the head, 1d is the top, 2 is the welding machine, 3 is the welding wire, 4 is the gas shield chamber, 5 is the welding nozzle, 6 is a water-cooled copper plate, and 6a is a shielding gas outlet. The series of welding is performed under full automatic control by a microcomputer that stores the rail shape and welding conditions at each position on the rail.

[Problem that the invention seeks to solve]

By the way, in order to improve welding efficiency in this gas-shielded arc welding, the simplest method is to increase the welding heat input, that is, increase the welding current, but in the case of rail welding, the following methods are used to increase the heat input: There are problems like this.

High-carbon steels such as rails are subject to high temperature cracks due to increased heat input, so the upper limit of heat input is limited.

When continuous welding is performed from the bottom to the top of the rail, the way heat accumulates differs depending on the position. In other words, heat is more easily trapped in the rail abdomen and head than in the bottom, and even less heat is dissipated near the top of the rail, so even with the same heat input, the amount of metal in the molten pool increases significantly, causing turbulence in the molten pool. It becomes easier.
This adversely affects the stability of the welding arc and causes spatter and welding defects.

Taking the above into account, it is thought that the following two methods should be used to increase the amount of weld metal while keeping the welding heat input constant.

Increase the protrusion length of the Γ welding wire.

The polarity of Γ welding is positive (the welding wire is the negative electrode, the base metal is the positive electrode).

FIG. 6 is a diagram showing the relationship between the protruding length of the welding wire and the amount of deposited metal. Increasing the protrusion length of the welding wire is an excellent method for increasing the amount of deposited metal with constant heat input, but if the protrusion length becomes long, the welding wire will bend due to arc force and other forces. The stability of the welding arc is disturbed. Figure 7 is a diagram showing the difference in the amount of deposited metal depending on the polarity during welding. In the case of the same current (same heat input), the positive polarity is the opposite polarity (the welding wire is the positive electrode and the base metal is the negative electrode). It can be seen that the amount of welded metal is larger. However, in gas-shielded arc welding using a consumable electrode, positive polarity has problems with arc stability, and furthermore, with positive polarity, the amount of penetration into the base metal is small, so in multilayer welding, weld bead The problem is that welding defects such as insufficient penetration and poor fusion can easily occur at the bottom.

Another problem is that at the boundary between the bottom of the rail and the abdomen, an overlap 7 as shown in FIG. 8 tends to occur on the ground terminal side P due to the influence of magnetic blowing.

The present invention aims to provide a welding method that eliminates the above-mentioned problems in gas-shielded arc welding of rails and that provides highly efficient welding and a high-quality welded part.

[Means for solving problems]

In order to solve the above-mentioned problems in gas-shielded arc welding of rails, the present invention has the following means.

A welding method (hereinafter referred to as a rotating arc welding method) is used in which a welding nozzle with a welding wire passing hole provided at the tip thereof is eccentrically rotated around the nozzle axis.

As shown in FIG. 9, positive polarity welding is used only for the first layer uranami welding part 13 at the bottom of the rail and the electrogas welding part 14 at the rail abdomen, and reverse polarity welding is used for the other parts.

Near the top of the rail head, a welding method was used in which the arc was cut for each weld layer and then re-ignited after the temperature of the molten pool had decreased.

Place the ground terminals on both sides of the rail, and cut either one of the ground terminals depending on the welding direction.

[Effect]

Adopting a rotating arc welding method increases the stability of the arc, making positive polarity welding possible. Generally, in positive polarity gas shielded arc welding, the first
As shown in FIG. 0, the cathode spots 11 of the welding arc 9 are distributed far above the wire surface, while other cathode spots are generated on the lower end surface of the molten metal at the end of the wire at the shortest distance, and the arc 10 is generated. In the case of positive polarity, compared to reverse polarity, the upward force of the arc 10 generated on the molten metal 12 at the wire end is stronger, and the molten metal falls due to the smaller current passing through the molten metal 12 at the wire end. Due to the small electromagnetic pinch force, the molten metal 12 at the end of the wire does not drip continuously, but forms a lump and adheres to the tip of the wire, and eventually becomes a large lump and falls discontinuously. Therefore, in conventional positive polarity welding, the droplets do not flow smoothly, and when the lumpy droplets fall from the tip of the wire 3, the arc length changes greatly. Furthermore, when a large lump of molten metal falls from the tip of the wire, the arc 10 emitted from the tip of the molten metal momentarily loses its cathode point. This will significantly impair the stability of the arc. Conventional positive polarity welding lacks arc stability due to the mechanism described above, but by adopting the rotating arc welding method, the centrifugal force caused by rotation allows the weld metal at the lower end of the wire to fall before it becomes a large lump. This increased arc stability and made positive polarity welding possible.

Next, we used the first layer uranami welding at the bottom of the rail and the positive polarity welding at the rail belly, but for the former, the
solid flux 15 as shown in figure a, or b
Since the backing material 16 made of refractory brick or copper plate and formed into the uranami bead shape shown in the figure is used, a relatively good uranami bead can be obtained even if the arc force exerted on the base material is weak. Regarding the latter, as shown in FIG. 12, the entire horizontal section of the weld becomes a molten pool 17, which only rises as welding progresses, so problems such as poor fusion do not occur even in positive polarity welding. In general, in positive polarity welding, there is little penetration into the base metal.Even in the case of high carbon steel like rails, there is little penetration of carbon from the base metal into the bead, which reduces hot cracking caused by carbon and reduces the weld metal. The quality of the products will improve.

Near the top of the rail head, the arc is cut for each weld layer and re-ignited after waiting for the temperature of the molten pool to drop. This reduces the amount of molten metal in the molten pool, and as a result, the amount of molten metal in the molten pool decreases. Arc instability caused by turbulence has been prevented, and welding defects that tend to occur at this location have been significantly reduced.

Furthermore, by switching the ground terminals on both sides of the rail according to the welding direction, the starting end ground is always set, so the arc is blown forward in the direction of travel, increasing the amount of penetration, and suppressing the phenomenon of overlapping. was completed.

[Embodiments of the invention]

FIG. 1 is an explanatory view showing a welding method in gas-shielded arc welding of rails according to an embodiment of the present invention, and FIG. 2 is a perspective view of a welding nozzle for rotary arc welding.

In FIG. 1, gas-shielded arc welding of the rail starts from point A. Arrow 23 indicates the direction of welding progress. First, an arc is generated at point A, and the first layer welding is performed from point A to point B using positive polarity welding, and at point B, the polarity is switched to reverse polarity.
Continue welding with reverse polarity up to point c. Next, at point C, the welding is again switched to positive polarity, and positive electrogas arc welding is performed, and at point D, the polarity is switched again, and continuous welding is performed up to point E, which is in the middle of the rail head. Near the top of the rail head after point E, heat is most likely to accumulate, the molten pool becomes large and the arc becomes unstable, so cut the arc after each weld layer and wait until the molten pool becomes smaller. It was configured to re-ignite. Point F indicates the restriking point. When re-igniting, if the molten pool is completely cooled and solidified, it will not only be difficult to re-ignite;
Since defects such as poor fusion are likely to occur, it is necessary to re-ignite the molten pool before it completely solidifies.

The above welding is performed by a rotating arc welding method, and FIG. 2 shows a welding nozzle for this welding method. A wire passing hole 5a at the tip of the welding nozzle 5 is bored eccentrically with respect to the nozzle rotation axis, and the nozzle 5 is connected to the motor 18 via a gear train 19.
When rotated, the arc forms a bead 20 while rotating. 21 is a feed roll for feeding the wire.

Also, as shown in Figure 4, ground terminals 22 for welding are provided on both sides of the rail, and when welding the boundary between the rail bottom and the abdomen, one of the ground terminals 22 is connected each time the welding direction changes. Since welding was carried out so that the starting end was always grounded, overlapping was prevented and a smooth bead appearance was obtained.

〔Effect of the invention〕

The present invention utilizes a rotating arc welding method in gas-shielded arc welding of rails, switches the welding polarity according to the position of the rail weld, and cuts and repoints the arc for each weld layer near the top of the rail head. We welded in an arc, provided ground terminals on both sides of the rail, and switched the ground terminals depending on the welding direction when welding the interface between the bottom and abdomen of the rails, resulting in the advantages described below. I was able to improve the effect.

By using positive polarity welding, the arc time was reduced by approximately 10%.

Hot cracking in the rail abdomen was reduced.

The stability of the arc near the top of the rail head has increased, and hot cracking due to increased heat input has been reduced.

Overlapping at the interface between the rail bottom and the abdomen was prevented.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of multilayer welding showing an embodiment of the present invention, Fig. 2 is a perspective view of a welding nozzle for rotating arc welding, Fig. 3 is a perspective view of a gas shield welding device, and Fig. 4 is a perspective view of a welding nozzle for rotating arc welding. The figure is a sectional view of the rail bottom when welded, Figure 5 is a sectional view of the rail abdomen and head when welded, Figure 6 is a diagram showing the relationship between wire protrusion length and amount of welded metal, and Figure 7 is A diagram showing the relationship between the welding current and the amount of deposited metal, Fig. 8 is an explanatory diagram of overlap, Fig. 9 is an explanatory diagram showing welding polarity in rail welding, Fig. 10 is an explanatory diagram of the welded part, and Fig. 11 is an explanatory diagram showing the welding polarity in rail welding.
The figure is an explanatory diagram of the backing material used for the welded part, and FIG. 12 is a cross-sectional view of the rail abdomen when welding. In the figure, 1 is a rail, 1a is its bottom, 1b is its abdomen, 1c is its head, 1d is its top, 3 is a welding wire, 5 is a welding nozzle, 5a is a wire passage hole, 8 is a molten pool, 9 , 10 is the arc, 22 is the ground terminal, A is the welding start point, B is the switching point from positive polarity to reverse polarity, C is the switching point from reverse polarity to positive polarity, D
is the switching point from positive polarity to reverse polarity, E is the end point of continuous welding, and F is the restriking point.

Claims (1)

[Claims] 1. A wire passage hole at the tip of a welding nozzle is bored eccentrically with respect to the central axis of the welding nozzle, and a rotating arc obtained by rotating the welding nozzle about the central axis is utilized. In gas-shielded arc welding of rails to be welded, positive polarity welding is performed on the first layer at the bottom of the rail and the rail belly, reverse polarity welding is performed on the bottom of the rail, excluding the first layer, and the rail head, and at the same time, welding is performed on the top of the rail head. Nearby, a rail welding method characterized by cutting the arc for each weld layer and re-igniting the weld pool before it completely solidifies.