Submerged arc welding method

p0001The invention relates to a submerged arc welding method having the features indicated in the preamble of claim 1, consisting of <patcit id="pcit0001" dnum="DE1918953"><text>DE 1918953</text></patcit> are known, and a welding apparatus for carrying out this method, the specified in the preamble of claim 6 features that also the <patcit id="pcit0002" dnum="DE1918953"><text>DE 1918953</text></patcit> will refer to.

p0002The submerged arc welding process is a self-assembly process, in which one or more wire electrodes are sealed under a layer of welding powder.

p0003In this process, a gap formed between the wire electrode and the workpiece, the arc melts a portion of the accumulated over the welding point welding powder, with some powder components evaporate. Together with the vapors of the molten metal form the vaporized powder constituents above the weld a gas-filled cavity. This is powder bounded by a layer of powder melt or slag and the overlying welding flux. The vaporized powder ingredients act in the cavity as a protective gas that protects the molten end of the electrode, the detached drop of the electrode material and the weld before the effects of air atmosphere.

p0004A disadvantage of the submerged arc welding is that the method has few powers in order to improve the welding results or adapt the method to specific welding tasks. Measures used in this context are usually a variation of the welding parameters such. As the welding current, the welding voltage and the welding speed. Further, the change of electrode polarity and the current type, and the welding powder composition of the wire type and the wire diameter.

p0005<patcit id="pcit0003" dnum="DD37867"><text>DD 37 867</text></patcit> describes a submerged arc welding process in which a gas or gas mixture is introduced directly into the Schweißkaveme. by a gas nozzle is immersed in the Schweißkaveme. The gas is fed in at an angle to the orientation of the arc and below the arc approach point of the welding electrode. Through the gas supply to the burning of alloying elements should be reduced.

p0006In one of <patcit id="pcit0004" dnum="US3752951A"><text>US 3,752,951</text></patcit> known method for welding aluminum bronze is supplied via an annular gap surrounding a welding electrode of the welding torch of the welding point, a welding powder. In order to reduce an evolution of toxic gases by chemical reactions during the melting of the welding powder and to prevent the weld through the annular gap is also fed to a gas.

p0007<patcit id="pcit0005" dnum="CH458887A"><text>CH 458 887 A</text></patcit> describes a submerged arc welding process, which is especially designed for horizontal submerged arc on a vertical wall. Since the protective gas produced during melting of the powder is not sufficient to protect the root layer due to the air gap between the sheets to be welded from the rear side from the atmosphere, an additional inert gas to the welding point is supplied which flows through the air gap and an adequate back shielding at the back the sheets to be welded gewährteistet.

p0008Further developments of the submerged arc welding process are essentially limited to the use of new welding flux and new solid and flux-cored wire.

p0009Against this background, the present invention has the object, a submerged arc welding process and to develop a device suitable therefor, in which the welding process is improved so that the energy input is improved in the workpiece and the weld geometry is changed positively.

p0010This object is achieved by a submerged arc welding method having the features specified in claim. 1 Advantageous developments of the invention result from the dependent claims, the following description and the drawings.

p0011In the submerged arc welding method of the invention a welding electrode is melted under a layer of powder in an arc. The welding electrode is performed in the welding direction behind a welding powder feed. An above the arc approach point of welding electrode supplied gas, the arc is thermally constricted. Here, a water cooling prevents preheating of the supplied gas.

p0012The constriction of the arc through the gas supply leads to a reduction of the arc diameter and thus to a reduction of the arc cross-section. This increases the power density of the arc increases the extent that forms a plasma arc. This results in several advantages, which include a lesser influence of welding parameters on the arc shape, a lesser influence of changes in distance between the torch and workpiece on the penetration shape, a deep penetration and high welding speed. Furthermore, a low heat transfer to the base material, the very smooth weld surface and a good Endgasung the highly heated molten bath prove advantageous.

p0013The Lichtbogeneinschnürung is introduced from the outside, in which an additional gas is introduced into the forming cavity beneath the welding powder. In contrast to the original, caused by vaporized constituent powders and metal vapors gas filling of the cavern, the externally added gas at a significantly lower temperature. This makes it cools the arc edge zone and there is a thermal contraction of the arc.

p0014Suitably, the additional gas is introduced above the arc approach point of the welding electrode into the cavern. In this way it is ensured that the entire arc edge zone is cooled by the additional gas.

p0015the gas volume flow is advantageously in a range of 10 to 45 l / min, wherein the outflow velocity of the gas 7 to 30 m / s. At these flow rates and / or the gas outlet velocities penetrates the Schweißpulveraufschüttung and then the liquid slag layer without welding powder to blow away entirely, and disturb the welding process. After flowing around the gas flow, the wire electrode and the arc, wherein the gas stream is sufficient to dissipate as much heat from the arc edge zone that the arc is thermally constricted. Another positive effect of a gas stream with the dimensions described above is reflected in its appearance to the melt of the base material. Due to its kinetic energy the flow of protective gas exerts a pressure to the molten bath, so that this mechanical influence the melt promotes the penetration addition.

p0016active gases are preferably used as additional gases provided. So showed welds with carbon dioxide very good results. This is due to the high thermal conductivity of the CO₂That the energy input into the workpiece additional improved. Finally, the gas choice will depend on the welding task, in particular on the type of materials to be welded, so that inert gases and gas mixtures can be composed of inert and active gases used.

p0017An apparatus for the submerged arc welding method according to the invention comprises a submerged arc welding torch, and a powder feed, the torch is arranged in the welding direction behind the welding powder feed. The combustion head of the welding torch has a water cooling. In addition, means are expediently provided with which additional gases can be introduced into the weld. The funds are intended for the targeted control of the arc and the workpiece melt.

p0018The torch has a concentric thereto for welding electrode gas nozzle. In contrast to the welding torches, which are used in the conventional submerged arc welding and essentially consist of an electrode holder with a current contact nozzle, is guided by a consumable electrode, is connected to the welding torch for the submerged arc welding method according to the invention an additional nozzle to the electrode and the electrode holder arranged enveloping. In this way, this welding torch is similar to the burners used in gas metal arc welding, wherein the gas supply is provided mainly for the focusing of the arc, while it serves from the atmosphere and for ionizing the arc gap in gas metal arc welding for the protection of the weld.

p0019The outlet opening of the gas nozzle is annular. Here, the opening of the nozzle ring is formed by the inner wall and the opening concentrically erupting welding electrode. This arrangement ensures that the electrode and thus the faceted this arc over the entire periphery are coated evenly from the gas stream. In a preferred embodiment of the welding torch, the lower edge of the gas nozzle at a distance of 8 to 12 mm for the lower edge of the current contact nozzle. The distance between the lower edge of the gas nozzle and the work-piece surface is preferably in a range of 15 to 25 mm. If using a submerged arc welding wire having a diameter of 4 mm, a gas nozzle inside diameter of 6 to 10 mm has proved particularly advantageous. This information is purely exemplary. Thus, the size and distance information in the application may be adapted to optimally.

p0020Preferably, an outer wall of the burner head forming cap on a water cooler. This is generally required because the head of the welding torch and thereby the cap are performed as close to the welding point, that they come with the warmed Schweißpulveraufschüttung in touch and dive into this. In addition to protection of the burner head, water cooling also prevents the supplied gas is preheated before the nozzle outlet and so loses some of its arc kontraktierenden effect.

p0021The invention is explained below with reference to a drawing exemplary embodiments illustrated. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic diagram of the submerged arc welding method and the welding apparatus provided therefor, in which an additional gas is supplied via a gas nozzle arranged on the welding torch in a section along the weld seam,</dd><dt>FIG. 2</dt><dd>a longitudinal section of the burner head with a gas nozzle, which is used in the welding method according to the invention and</dd></dl>

p0022<figref idrefs="f0001">Fig. 1</figref> shows a workpiece 2, on which a welding powder supply 4 has a layer welding powder piled up. 6 In the welding powder feed 4 is a powder feed, as is known in the submerged arc welding per se and is shown in the drawing only by the end portion of the feed tube.

p0023In welding direction A behind the welding powder supply 4 a submerged arc welding torch 8 is arranged. Between the consumable electrode 10 and the workpiece 2, an arc burns 12 and forms a layer formed from vaporized powder constituents and metal vapors of melt gas filled Schweißkaverne 14. Schweißkaverne 14 is powder-sided, limited by a layer of liquid slag 16, which was formed from molten powder constituents. This slag layer 16 is pierced with the above accumulated welding powder 6 of the electrode 10th

p0024In <figref idrefs="f0001">FIG. 2</figref> is shown in detail a torch head of the submerged arc welding torch. 8 This has an electrode holder 18 for guiding the electrode 10th The electrode holder 18 is formed heel-shaped and tapers welded side to a paragraph 20. In the longitudinal direction, the electrode holder 18 is pierced centrally by a passage 22nd

p0025At the paragraph 20 of the electrode holder 18 closes welded side to a current contact nozzle 24th This has welded side a shoulder 28, on which it tapers radially. This tapering is continued in the area of ​​the welding end of the current contact nozzle 24 by a conical tapering on. Also, the current contact nozzle 24 has an opening 26 in the longitudinal direction.

p0026Through the channel 22 of the electrode holder 18 and the perforation 26 of the current contact nozzle 24, the electrode 10 of the welding point is supplied. The dimensions of the opening 26 are designed so that the electrode 10 for applying the welding voltage at the conductive inner wall of the opening 26 is present.

p0027The electrode holder 18 is extended in the direction of the weld through a hollow, open on both sides rotating body 30th In this case, the contact area between the electrode holder 18 and the rotary body 30 is sealed by an axial sealing ring 32nd Welding side, the opening of the rotary body 30 is closed by a gas nozzle 34th The gas nozzle 34 has a central opening 36 through which the welding-side opening of the rotary body 30 is concentrated. The rotary body 30 and the gas nozzle 34 form the cap 38th

p0028In the cavity of the rotary body 30, a part of the paragraph 20 of the electrode holder 18 and the current contact nozzle 24 into it, wherein the inner wall of the rotary body 30 is profiled such that an opening is formed, whose shape is complementary to the outside shape of the shoulder 20 of the electrode holder 18 and the outer mold the current contact nozzle 24 is. This is broken by the shoulder 20 and the current contact nozzle 24 partly justified and partly with little play. In the region of the conical tip of the current contact nozzle 24 widens the opening and forms the weld side is closed off by the gas nozzle 34 space 40. The space 40 and the opening 36 of the gas nozzle 34, the consumable welding electrode 10 of the welding point is supplied.

p0029Inside its outer wall of the rotating body 30 has channels 42 for water cooling. This is in the<figref idrefs="f0001">FIG. 2</figref> represented by three cooling channels 42 which rotate the rotating body 30 circumferentially near its outer wall.

p0030Furthermore, are provided on the rotary body 30 feed channels 44 for introducing a gas stream b. These extend from the outer wall of the rotary body 30 near the sealing ring 32 initially radially inwardly and then obliquely inwards and to the welding point by the rotary body 30 in the space 40. The introduced through the supply channels 44 the gas leaves the chamber 40 through an annular gap, which by of the opening 36 of the gas nozzle 34 and the electrode 10 is formed along the electrode 10th

p0031Again <figref idrefs="f0001">Fig. 1</figref> It can be seen, the gas passes through the welding powder 6 and the subsequent slag layer 16 and enters the Schweißkaverne 14 where there is the arc 12 constricts and influences the material melt mechanically.

LIST OF REFERENCE NUMBERS

p0032<dl id="dl0002" compact="compact"><dt>2</dt><dd>workpiece</dd><dt>4</dt><dd>Welding powder feed</dd><dt>6</dt><dd>welding powder</dd><dt>8th</dt><dd>Submerged arc welding torch</dd><dt>10</dt><dd>electrode</dd><dt>12</dt><dd>arc</dd><dt>14</dt><dd>Schweißkaverne</dd><dt>16</dt><dd>slag layer</dd><dt>18</dt><dd>electrode holder</dd><dt>20</dt><dd>paragraph</dd><dt>22</dt><dd>channel</dd><dt>24</dt><dd>current contact nozzle</dd><dt>26</dt><dd>perforation</dd><dt>28</dt><dd>paragraph</dd><dt>30</dt><dd>rotating body</dd><dt>32</dt><dd>seal</dd><dt>34</dt><dd>gas nozzle</dd><dt>36</dt><dd>perforation</dd><dt>38</dt><dd>cap</dd><dt>40</dt><dd>room</dd><dt>42</dt><dd>Channels for water cooling</dd><dt>44</dt><dd>supply channels</dd></dl><dl id="dl0003" compact="compact"><dt>A</dt><dd>welding direction</dd><dt>B</dt><dd>gas flow</dd><dt>C</dt><dd>gas flow</dd></dl>