Self-protection transverse position large-gap welding method for Q420-grade steel

Abstract

The invention discloses a Q420-grade steel self-protection transverse position large-gap welding method which comprises the steps that a welding groove is machined in an upper position plate before welding, then a to-be-welded joint is preheated, and if the thickness of the plate is smaller than or equal to 28 mm, preheating is not conducted; tapered iron with longitudinal grooves is plugged and connected between the welding horse plates and the panels which are arranged at intervals, and specially-made wide red copper gaskets are fixed to the back faces of the grooves in a penetrating mode; during welding, a self-protection flux-cored wire is adopted for carrying out transverse position large-gap multi-layer and multi-pass butt welding; and the welding horse plate and the inclined iron are removed after welding, and the wide red copper gasket, the welding horse plate and the inclined iron can be reused. In the welding process, the wind resistance is high, good back face forming after welding can be achieved through the wide red copper gasket, the problem of Q420-grade steel self-protection transverse position large-gap welding can be effectively solved, and the welding method is suitable for steel structure ring opening large-gap welding operation in bridge sites, mountainous areas and other field severe environments and high-altitude places where gas is inconvenient to use.

Description

Technical Field

[0001] The invention relates to a steel structure welding method, in particular to a Q420 grade steel self-protection horizontal position large gap welding method. Background Art

[0002] As bridges develop towards large spans, heavy loads, and multiple uses, the form of bridge towers has gradually changed from concrete towers to steel structure towers based on structural strength and force requirements. The height of a fully welded steel tower is generally around 100 meters. The bridge construction site is a special high-altitude operation with a harsh environment and great difficulty in welding, especially at high altitudes without shelter, where the wind speed is generally much higher than that of the bridge deck and the ground.

[0003] At present, most of the welding of steel bridges (including steel towers) is done by CO2 gas shielded welding. During the welding process, strong winds will weaken the CO2 gas protection effect, causing air to invade the molten pool, resulting in welding defects such as pores, affecting the internal quality of the weld. In addition, as the installation of steel tower segments gradually increases, the cost of lifting gas cylinders rises sharply, and the safety hazards of high-altitude storage of gas cylinders also increase. Similarly, the erection of bridges in mountainous areas inevitably involves the intrusion of strong winds in the valley, as well as a series of inconveniences in the transportation, lifting, and storage of gas cylinders. In the case of inconvenience in the use of gas, if the gas shielded welding method is abandoned, there are not many welding methods to choose from. If submerged arc welding is used, it can only be applied to horizontal and certain specific horizontal welding operations, and it is difficult to meet the full-position welding requirements of the bridge position; if arc welding is used, the welding efficiency is too low, and the bridge erection period cannot be guaranteed.

[0004] The self-shielded welding method does not require gas protection, but relies on the flux-cored wire's own coating to form "self-protection" by gasification and slag formation, and has excellent wind resistance (through tests, the quality of the weld welded by the self-shielded wire still meets the standard requirements under the wind speed of 17.2m / s at level 8 gale), and the appearance after welding is well formed. However, considering that the horizontal ring gap is difficult to control during the installation of the bridge steel tower, it is inevitable that there will be a large gap (generally referring to the gap exceeding 20mm). If the common wide ceramic liner is attached to the back of the groove for self-shielded welding, since the ceramic liner is generally weakly acidic, it will react chemically with the alkaline deoxidation and desulfurization alloy elements in the self-shielded flux-cored wire, resulting in a more serious sticky slag phenomenon on the back of the weld, and even pits in the local weld are lower than the parent material; and the ceramic liner has poor conductivity, and the arc is easily broken in the middle of the large gap, resulting in poor weld formation, time-consuming and labor-intensive processing, and seriously affecting the weld one-time inspection pass rate. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a Q420 grade steel self-protected horizontal large gap welding method to solve the welding operation of self-protected welds (especially the base layer) under the horizontal large gap of the ring mouth of the steel tower bridge, and to ensure the forming quality of the back of the weld.

[0006] Technical solution: A Q420 grade steel self-protection horizontal large gap welding method of the present invention comprises:

[0007] Process the upper plate welding groove, the maximum gap of the joint is 22~30mm;

[0008] Preheat the welding joint. If the plate thickness is ≤28mm, do not preheat.

[0009] A wide copper liner is fixed to the back of the groove, wherein the middle of the liner has an arc groove and the arc groove faces the back of the groove;

[0010] Self-shielded flux-cored wire is used for horizontal large-gap multi-layer and multi-pass butt welding.

[0011] In the present invention, a specially made wide copper liner is used on the back of the groove. The copper has good electrical conductivity and can prevent high-temperature scorching, oxidation and deformation during welding. At the same time, its good thermal conductivity and heat resistance can also ensure the stability of the welding process and beautiful appearance after welding. Since the melting point of copper is higher than that of steel, there will be no melting loss during the welding process, so the copper liner has a high reuse rate.

[0012] Furthermore, the upper plate is provided with a V-shaped groove, and the groove angle is 30° to 34°.

[0013] Furthermore, in order to prevent the molten iron from dripping, the lower plate is not grooved.

[0014] Furthermore, when the plate thickness is 28 mm < ≤ 50 mm, the preheating temperature is 60°C to 100°C; when the plate thickness is > 50 mm, the preheating temperature is 80°C to 120°C.

[0015] Furthermore, a welding plate is arranged on the back of the panel to be butt-welded, and an inclined iron is tightly plugged in the notch of the welding plate. A through groove for the wide copper liner to penetrate is opened on the flat bottom surface of the inclined iron.

[0016] Furthermore, there are multiple welding plates, which are spaced apart according to the requirements for welding deformation control, with a spacing of 400 to 600 mm.

[0017] Furthermore, the thickness of the welded plate is not less than 16 mm.

[0018] Furthermore, the welding plate and the face plate to be butt-welded are connected by intermittent single-sided fillet welds.

[0019] Furthermore, the self-shielded flux-cored welding wire model is T553T8-1NA-N3.

[0020] Furthermore, for self-protected horizontal large gap welding, the welding current of the base layer is 180-220A, the welding voltage is 17-19V, the welding speed is 220-260mm / min, and the heat input is 7.1-11.4KJ / cm; the welding current of the filling layer is 190-230A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, and the heat input is 7.3-11.5KJ / cm; the welding current of the cover layer is 200-240A, the welding voltage is 18-22V, the welding speed is 240-280mm / min, and the heat input is 7.7-13.2KJ / cm; the power polarity is DC positive connection, the wire feeding speed is 90-110in / min, the dry extension is 19-25mm, and there is no swing.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention adopts a wide copper liner with good conductivity, and fixes the wide copper liner on the back of the large gap groove, which can ensure that the back is well formed after the self-protection horizontal large gap welding, and effectively solves the problem of Q420 grade steel self-protection horizontal large gap welding. The wide copper liner can be removed after welding and reused. The present invention is suitable for large gap welding of steel structure rings in harsh outdoor environments such as bridges and mountainous areas and inconvenient places for high-altitude gas use. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of fixing a wide copper liner in an embodiment of the present invention;

[0023] Figure 2 yes Figure 1 Side view of

[0024] Figure 3 1 is a schematic diagram of the structure of a wide copper liner in an embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of the structure of the inclined iron in an embodiment of the present invention, wherein Figure 4 (a) Main view, Figure 4 (b) is a side view;

[0026] Figure 5 2 is a schematic diagram of the structure of a welded horse plate in an embodiment of the present invention;

[0027] Figure 6 yes Figure 1 Schematic diagram of the horizontal large gap joint groove at A in the middle;

[0028] Figure 7 1 is a schematic diagram of the welding bead deposition of the joint in the embodiment of the invention, wherein 1 to 33 are the order of the weld bead. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Attached Figures 1 to 7 The reference numerals in the figures are as follows:

[0031] 1, upper plate; 2, lower plate; 3, wide copper liner; 301, arc groove; 4, inclined iron; 401, through groove; 5, welding horse plate; 501, notch.

[0032] The embodiment of the present invention provides a Q420 grade steel self-protection horizontal position large gap welding method, comprising the following steps:

[0033] (1) The upper plate 1 is welded with a V-shaped groove with an angle of 30° to 34°. To prevent the molten iron from dripping, the lower plate 2 is not grooved. The maximum gap of the joint is 22 to 30 mm.

[0034] (2) Preheat the weld joint. When the plate thickness is 28 mm < ≤ 50 mm, the preheating temperature is 60°C ~ 100°C; when the plate thickness is > 50 mm, the preheating temperature is 80°C ~ 120°C; if the plate thickness is ≤ 28 mm, no preheating is required.

[0035] (3) A specially made wide copper liner 3 is fixed to the back of the groove by means of a designed tooling, wherein the middle of the liner has an arc-shaped groove 301 and the arc-shaped groove 301 faces the back of the groove.

[0036] like Figure 3 As shown, the wide copper liner 3 has a thickness of 8 mm and a width of 40 mm, and the arc groove 301 in the middle has a depth of 3 mm, which is conducive to the formation of the weld.

[0037] like Figure 4 and Figure 5 As shown, the tooling includes an inclined iron 4 and a welding horse plate 5, wherein the inclined iron 4 is 40 mm thick, 70 mm wide and 120 mm long, and a slope of 1:5 is set along the length direction, and a through slot 401 of 8.5 mm by 41 mm is opened in the middle of the flat bottom surface (considering the size of the wide copper liner 3, a 0.5 mm gap adjustment is reserved on the three sides in the width and thickness directions) to fit the wide copper liner 3. The wide copper liner 3 is placed on the inclined iron 4 through the slot.

[0038] The thickness of the welding plate 5 is not less than 16mm, and the width × length is 200 × 400mm. A 30 × 80mm notch 501 is opened in the middle of one long side to adapt the inclined iron 4 to be inserted and connected. There are multiple welding plates 5, which are set at intervals according to the requirements of welding deformation control, with a spacing of 400 to 600mm. The welding plate 5 is connected to the panel to be butt-welded by intermittent single-sided fillet welds. The inclined iron 4 is tightly inserted between the welding plate 5 and the panel to be butt-welded.

[0039] Figure 1 and Figure 2A schematic diagram of the structure of fixing the wide copper liner 3 to the back of the groove by using a tool is given.

[0040] (4) Use self-shielded flux-cored wire for horizontal large-gap multi-layer and multi-pass butt welding.

[0041] For Q420 grade steel, the self-shielded flux-cored welding wire uses the T553T8-1NA-N3 model, and the diameter can be Φ2.0mm.

[0042] For self-protected horizontal large gap welding, the welding current of the base layer is 180-220A, the welding voltage is 17-19V, the welding speed is 220-260mm / min, and the heat input is 7.1-11.4KJ / cm; the welding current of the filling layer is 190-230A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, and the heat input is 7.3-11.5KJ / cm; the welding current of the cover layer is 200-240A, the welding voltage is 18-22V, the welding speed is 240-280mm / min, and the heat input is 7.7-13.2KJ / cm; the power polarity is DC positive connection, the wire feeding speed is 90-110in / min, the dry extension is 19-25mm, and there is no swing.

[0043] A specific example is given below.

[0044] The material of the steel tower ring to be welded is Q420MD, the thickness is 20mm, and the joint groove form is shown in Figure 1 , which is a V-shaped groove. The welding material is T553T8-1NA-N3, and the diameter of the welding wire is Φ2.0mm. The welding equipment is Xionggu D7-500 (N) welding machine, and the power polarity is DC positive connection.

[0045] The chemical composition of the T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored welding wire core is shown in Table 1, and the mechanical properties of the welding wire cladding metal are shown in Table 2.

[0046] Table 1 Chemical composition of T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored welding wire core

[0047]

[0048] Table 2 Mechanical properties of T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored welding wire cladding metal

[0049]

[0050] Follow the steps below to perform welding:

[0051] (a) Welding groove and pre-welding cleaning

[0052] like Figure 1 As shown, the joint groove form is a single V-shaped groove, the groove angle of the upper plate 1 is 30°~34°, and the lower plate 2 is not grooved and has no blunt edge.

[0053] Grind away rust, oil stains and other impurities within 20mm on both sides of the groove of the upper plate 1 and the welding area of ​​the lower plate 2 to reveal the metallic luster of the groove area.

[0054] (b) The root of the groove is in a state of large gap of 22 to 30 mm, and is positioned by welding 5 welded horse plates at intervals of 400 to 600 mm.

[0055] (c) Insert a piece of inclined iron 4 into the notch 501 of the middle welding horse plate 5, and make the through slot 401 face the back of the groove to be welded. After adjusting the position of the inclined iron 4 up and down to the center, hammer it tightly to make it fit tightly with the upper plate 1 and the lower plate 2.

[0056] (d) Insert the wide copper liner 3 into the through groove 401 and place it on the inclined iron 4.

[0057] (e) According to the position of the wide copper liner 3, align with the through groove 401, install the inclined irons 4 at the remaining welding horse plates 5 in sequence, and apply close contact.

[0058] (f) Use self-shielded flux-cored welding wire without gas protection to carry out horizontal butt welding of base, filling and cover layers in sequence.

[0059] The molten droplet transition form during self-shielded flux-cored wire welding is mainly arc bridge coexistence surface tension transition and arc bridge coexistence explosion transition, especially the explosion transition makes part of the molten droplets transition into the molten pool while the other part of the molten droplets fly away from the arc as dispersed particles, thus generating large particle splashes in different directions up and down, front and back, and macroscopically causing the self-shielded welding interlayer slag removal to be weak and the splashes to be large. Therefore, during the welding process, special attention should be paid to the grinding and cleaning process between each weld (layer), and a small hammer + steel brush can be used to assist the grinder for slag removal to avoid slag inclusion defects as much as possible.

[0060] When performing self-protection horizontal large gap welding, the welding current of the base layer is 180-220A, the welding voltage is 17-19V, the welding speed is 220-260mm / min, and the heat input is 7.1-11.4KJ / cm; the welding current of the filling layer is 190-230A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, and the heat input is 7.3-11.5KJ / cm; the welding current of the cover layer is 200-240A, the welding voltage is 18-22V, the welding speed is 240-280mm / min, and the heat input is 7.7-13.2KJ / cm; the power polarity is DC positive connection, the wire feeding speed is 90-110in / min, the dry extension is 19-25mm, and there is no swing. See Table 3 for specific welding process parameters. In order to obtain excellent weld mechanical properties, a relatively dense multi-layer and multi-pass welding operation is adopted. See the schematic diagram of weld deposition. Figure 7 .

[0061] (g) After the welding of the cover weld is completed, remove the wide copper liner 3, the inclined iron 4 and the welding horse plate 5, and check the appearance of the back of the weld. The wide copper liner 3, the inclined iron 4 and the welding horse plate 5 can be retained for next recycling.

[0062] Table 3 Welding process parameters

[0063]

[0064] The present invention can be widely used in the construction of bridge rings of fully welded steel towers, and has important demonstration and reference significance for solving the welding operation difficulties of self-protection welds under large horizontal gaps and ensuring the quality of back weld formation.

Claims

1. A Q420 grade steel self-protection horizontal large gap welding method, characterized in that: include: Process the upper plate welding groove, the maximum gap of the joint is 22~30mm; Preheat the welding joint. If the plate thickness is ≤28mm, do not preheat. A wide copper liner is fixed to the back of the groove, wherein the middle of the liner has an arc groove and the arc groove faces the back of the groove; Self-shielded flux-cored wire is used for horizontal large-gap multi-layer and multi-pass butt welding.

2. The Q420 grade steel self-protected horizontal large gap welding method according to claim 1 is characterized in that: The upper plate has a V-shaped groove with a groove angle of 30° to 34°.

3. The Q420 grade steel self-protected horizontal large gap welding method according to claim 2 is characterized in that: The lower plate is not beveled.

4. The Q420 grade steel self-protected horizontal large gap welding method according to claim 1, characterized in that: When the plate thickness is 28mm<≤50mm, the preheating temperature is 60℃~100℃; when the plate thickness is>50mm, the preheating temperature is 80℃~120℃.

5. The Q420 grade steel self-protected horizontal large gap welding method according to claim 1, characterized in that: A welding plate is arranged on the back of the panel to be butt-welded, and an inclined iron is tightly plugged in the groove of the welding plate. A through groove for a wide copper liner to penetrate is opened on the flat bottom surface of the inclined iron.

6. The Q420 grade steel self-protected horizontal large gap welding method according to claim 5, characterized in that: There are multiple welding plates, which are set at intervals of 400 to 600 mm depending on the requirements for welding deformation control.

7. The Q420 grade steel self-protected horizontal large gap welding method according to claim 5, characterized in that: The thickness of welded plate shall not be less than 16mm.

8. The Q420 grade steel self-protected horizontal large gap welding method according to claim 5, characterized in that: The welding plate and the face plate to be butt-welded are connected by intermittent single-sided fillet welds.

9. The Q420 grade steel self-protected horizontal large gap welding method according to claim 1, characterized in that: The model of self-shielded flux-cored welding wire is T553T8-1NA-N3.

10. The Q420 grade steel self-protected horizontal large gap welding method according to claim 1, characterized in that: For self-protected horizontal large gap welding, the welding current of the base layer is 180-220A, the welding voltage is 17-19V, the welding speed is 220-260mm / min, and the heat input is 7.1-11.4KJ / cm; the welding current of the filling layer is 190-230A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, and the heat input is 7.3-11.5KJ / cm; the welding current of the cover layer is 200-240A, the welding voltage is 18-22V, the welding speed is 240-280mm / min, and the heat input is 7.7-13.2KJ / cm; the power polarity is DC positive connection, the wire feeding speed is 90-110in / min, the dry extension is 19-25mm, and there is no swing.

Images