RU2076027C1 - Method of pig-iron electric arc welding - Google Patents

Abstract

FIELD: method of pig-iron pieces welding used in different branches of national economy. SUBSTANCE: in process of pig-iron welding operation heating, edges treatment, flash and welding are exercised in medium of carbon dioxide using steel wire with wire feeding speed by 10 % lower, than speed usually set for the modes. Heated edges before welding are cooled in the air and during welding - after each pas of arc from top downward along bead. After edges are filled seam is heated by arcing between electrode and plate adjacent to seam zone. EFFECT: improved process of pig-iron pieces welding.

Description

 The invention relates to welding production and can be used for welding parts and cast iron in various sectors of the economy.

 Known arc welding process of cast iron. Ulyanovsk UETS (magazine "Welding Production" N 3 1981, p. 33) where the cutting of the edges of non-through defects is performed by air-arc cutting, cutting with a pneumatic tool and milling. Mandatory shaping of the welding site with a special refractory composition. Fireclay bricks and graphite plates are also used. When preparing cracks for welding, they must be drilled at the ends and cut to a total angle of opening of the edges of 60–90. For cracks longer than 200 mm, inserts of type eight locks are used. Welding is carried out with special electrodes on a copper-nickel basis.

 The process is complex and not reliable. A known method of arc welding and surfacing of cast iron (ed. St. N 297443, class B 23 K 9/16 1971), mainly multi-pass in a mixture of oxygen and carbon dioxide, the first passes are carried out in a mixture with 95% oxygen content, and the subsequent ones with a gradual reducing its content to 5%. When welding according to this method, the weld is unstable and leaky due to a distorted thermal process, which is accompanied by popping and an abundance of splashes.

 Selected for the prototype (Method of electric arc welding of cast iron according to patent N 1811458A3, class B 23 K 9/14, 9/173 1993).

The method includes preheating, as well as cutting and welding. Preheating is carried out by an arc of a melting electrode, while heating and cutting of edges is performed with periodic arc burning, at a speed of at least 15 mm / s and pause duration twice as long as the duration of arc burning, after cutting the edges, the edges are melted to remove molten metal, and heating, cutting and flashing of edges is carried out at a current exceeding the welding current by a value of 30 to 50%
The method has several disadvantages:
1. The welded joint is subject to shrinkage and deformation, as the base metal at the edges during fusion changes from a looser to a denser state, contracting in volume, as a result of which the internal stress can outgrow the strength of the base metal, which leads to lobar rupture of the base metal adjacent to the fusion zone.

 2. The method does not incorporate techniques for relieving stress (annealing) from welds, which also leads to the accumulation of internal stresses in the weld.

 3. In the method for heating, cutting and flashing the edges, the welding current exceeds 30 to 50%, which makes it difficult to perform the operation, burn through thin-walled parts due to the large dispersion of the arc space.

 4. The method has not taken additional measures that contribute to the slow cooling of the thermal zone after welding, and well-known recommendations, such as coating the hot zone of parts with dry sawdust, can cause a fire. It is laborious and not always possible to fill up with hot sand.

 The aim of the invention is to improve the quality of the welded joint of various thicknesses and configurations of the seam.

 This goal is achieved in that, in contrast to the prototype (patent N 1811458A3), the heating, cutting and melting of the edges provide an arc of a melting electrode wire in a shielding gas medium, metal shrinkage in detachable (not connected), heated and melted edges is carried out until complete free crystallization during cooling stress relief from the rollers (annealing) of the seam is ensured by the passage of the arc of the melting electrode while maintaining the geometry of the roller, the cooling of the welded joint is slow by maintaining heating by the arc melting extinction electrode on a metal plate adjacent to the weld zone.

 An essential feature of this invention is that the heating, cutting, edge fusion and welding provide an arc of a consumable electrode wire in a shielding gas medium or in combination with coated piece electrodes. This essential feature acquires new properties consisting in the fact that it allows you to selectively influence the arc process by changing the ionization process, as well as the diameter and feed rate of the filler material.

 The second distinguishing feature is that in order to prevent cracks along the seam, the pre-heated, fused, not connected edges provide shrinkage of the heated metal, and then proceed to join them together.

 The third significant feature is that in order to increase the strength of the welded joint, stress is removed from the rollers (annealing) of the seam by passing the arc of the consumable electrode along the roller without changing its geometry.

 And the fourth significant feature is that in order to increase the ductility of the welded joint and its zone, they provide slow cooling by maintaining the arc of the melting electrode on a metal plate adjacent to the weld zone.

 The process begins with pre-heating the parts, which is carried out by semi-automatic welding in a shielding gas medium, the wire feed speed from traditional welding is reduced by about 10% for stable arc burning, and initially the arc passes for heat input pass quickly (filler material forms dust on the parts). The following arc passes are slower (filler material remains on the parts in the form of frozen drops and adhering weld sections). Further passages are even slower. After heating the edges to the desired temperature and parts to a temperature that excludes the possibility of formation of cracks and zones in the weld zone, conduct electric arc cutting of the edges by smelting the base metal to the desired configuration and size. To ensure unimpeded removal of molten metal, the parts are mounted in such a way that the welded edges are vertically or obliquely, allowing the molten metal to flow out through penetration or melt removal by a bar. Edge cutting in the proposed solution is a continuation of the heating of parts in the weld zone for the successful conduct of subsequent operations.

 The preparation of cut and heated edges for welding is carried out by several passes of a burning arc with a melting electrode wire along the edges from top to bottom, while ensuring the free flow of molten metal outside the edges, each time updating the metal in the edge matrix to form a transition layer that provides good weldability and consists of practically from filler metal. In this case, the size and configuration of the edges does not change significantly, i.e. at least nothing is being done to change them. The behavior of the metal in the molten bath is controlled visually and they achieve the cessation of the boiling of the metal, which is observed in the presence of harmful impurities that interfere with good welding. Harmful impurities are removed from the transition layer together with the melted (replaced) metal. The process of preparing the edges can be called washing, since in each new pass at the time of fusion, there is a strong dilution of the content of impurities and the flow of metal without impurities ensuring the purity of the edges. The thickness of the transition layer is usually 2 to 4 mm and is determined by the penetration depth of the metal in the moving bath in the arc burning zone.

 In the transition layer, when cooling, the base metal passes from a loose state to a more dense one, and tends to contract in volume (the so-called shrinkage), the shrinkage is carried out before the beginning of the connecting process of the edges, by providing free cooling in air until the metal crystallizes completely in the transition layer. When welding critical parts, the edges are filled in several passes with a roller and, after each passage, the roller is relieved of stress (annealing) by passing the arc of the melting electrode from top to bottom along the length of the roller. To preserve the shape of the seam, the filler metal melt is smelted outside the seam by tilting the arc downward; operations are carried out in conventional welding modes by semi-automatic or manual welding with a piece electrode.

 To increase the ductility of the welded joint and its zone, after the edges are filled with filler metal in the weld zone, the deposited metal is cooled for a long time by maintaining the arc of the consumable electrode on the metal plate adjacent to the weld zone, or by moving the heated plate to the required areas, it is possible to maintain heating carry out semi-automatic or manual welding with piece electrodes.

 The main factor determining the obtaining of positive results (improving the quality of welded joints of various thicknesses and configurations) when heated by an arc is the participation of a small amount of arc space obtained by semi-automatic welding using thin wires in a protective gas medium, ensuring preliminary shrinkage of the metal in the fused edges before joining seam them, relieving stress (annealing) from the seam rollers by the arc of the consumable electrode while maintaining the geometry of the rollers and providing slow cooling weld zone heated arc melting electrode while maintaining the shape of the seam.

 Example 1. In the process, a Romanian-made diesel engine block was welded, it was thawed and had cracks in the valves with a leak from the cooling jacket. The block was installed so that the welded edges were vertically. To perform the welding process, a welding power source BC 300 was used, equipped with a semi-automatic machine A 547U and filler wire CB 08G2S with a diameter of 1.2 mm. The welding mode was selected from the calculation: current strength 160 180 A, voltage 21 V, electrode overhang 9 15 mm. The welding mode was preliminarily adjusted on the plate (sample) and after obtaining the normal welding process, the wire feed speed was reduced to the formation of a vague seam and reliable arc excitation. The operation was started by heating the part with fast (at a speed of 75 150 mm / s) arc passes from top to bottom along future edges, then the operation was repeated, but the passage time was doubled (speed 40 50 mm / s) and again the passes were carried out at a speed of 30 40 mm / s In the following passes, the arc displacement speed was set at 15 mm / s, while the arc smelting of edges was ensured, and in 2 3 arc passes, the configuration and dimensions of the edges were set. After that, the wire feed speed was increased until an elevated bead was obtained in the weld while maintaining stable arc excitation and began to flush the edges, which was carried out at a speed of 30–40 mm / s, allowing the metal to drain from the edges to be melted, and then weld with filler metal. At the same time, the behavior of the bath was observed as it boils and fuses with the base metal. The washing was carried out until a dense structure was reached at the edges, good wettability of the metal bath in it, i.e. until a metal composition close to well-welded low-carbon steel is created within the edges of the metal.

 Then they made a stop for 1–2 min so that the shrinkage of the melted seams freely passed, it looked grayish in appearance; therefore, this roller was removed by arc smelting and a new one, which had a light color, was applied, annealing was conducted along the roller with the arc of the melting electrode from top to bottom, preserving the geometry of the seam.

 After the welding process was over, another metal plate was heated and placed on the sections of the seams and its zone, in which the arc of the melting electrode was periodically maintained for 20 minutes. After cooling, the parts produced a bore of the seams on the coordinate machine with a conventional cutter and the block took on a working state.

 Example 2. Welded together vertically detachable two planes of a cone of gray cast iron SCh-28, the diameter of the base and height were 600 mm The part was mounted with a base on a metal sheet, and metal washers were placed between the welding table and the metal plate to isolate heat loss. We used a source of constant welding current VDU - 504 1 and welding materials were UONI electrodes with a diameter of 4 m. Welding modes were selected at the rate of 250 A and began by heating the part with arc passages of the melting electrode along the future edges from top to bottom alternately from both sides, the top to bottom pass in time 4 6 s (speed 10 15 mm / s). These cycles were repeated four more times, then the metal was heated at the edges to such an extent that the heating operation turned into arc smelting of the molten metal and started cutting edges with alternating sides to a depth of 100 mm. After that, the welding current was reduced to 180 A and began welding and at the same time washing the edges from bottom to top with a vertical seam. First, the lower section 10 20 mm long was washed from poor weldability and a protrusion was formed on it in the form of the beginning of the seam, then the molten metal was washed in the molten bath by moving the melt with impurities of poor weldability to the creep edge of the weld ledge and it was removed beyond the seam by an arc electrode, then the weld ledge roller was supplemented with electrode metal without impurities, ensuring good wettability in the connecting layer of the bath. Such actions formed welds with alternation of both sides. After each complete passage of the weld bead, the edges of the weld were cleaned by the passage of the arc of the consumable electrode from top to bottom, while stress was removed from the weld bead (annealing). The edges were filled until the possible participation of a gas-electric torch, these were about 40 mm of unfilled edges, then they switched to semi-automatic welding in a carbon dioxide protective atmosphere with filler wire Sv 08G2S with a diameter of 2 mm, at current modes 280 300 A, voltage 28 30 V, electrode outreach 20 25 mm, the source of welding current remained the same, welding was performed with a vertical seam with alternation of both sides until the edges were filled.

 The welded part (thus) had good machinability with a conventional cutter on a lathe and was subsequently used as a mounting frame with loads of hammer blows.

Claims (1)

 A method of electric arc welding of cast iron, including heating, cutting edges and semi-automatic welding in a carbon dioxide environment, characterized in that, in order to reduce the cost of welding technology while improving welding quality, heating, cutting edges, melting and welding are carried out in a carbon dioxide steel wire with a wire feed rate of 10% less than that set for these modes, before welding, the heated edges are cooled in air until the metal crystallizes completely in the transition layer, the arch is led in several passes and, after each pass, annealing is carried out by passing from top to bottom along the roller, and after filling the edges, the weld is heated by an arc burning between the electrode and the plate adjacent to the weld zone.