Full penetration joint composite material liner for closed small space and welding method of full penetration joint composite material liner

Abstract

The invention discloses a full penetration joint composite liner for a closed small space and a welding method thereof. The composite material liner comprises a structural stress steel layer A, a composite ceramic layer B and an adhesive layer C for compounding the structural stress steel layer A and the composite ceramic layer B; the composite ceramic layer B faces the joint groove and can be provided with a groove / groove for controlling the shape of a molten pool and an air hole for exhausting gas and preventing a root air hole, and the side, away from the steel layer, of the composite ceramic layer B is provided with an acidic or alkaline welding powder layer G. The problems that a traditional metal gasket is prone to beading and incomplete penetration and a traditional ceramic gasket is prone to downwarping and difficult to assemble are solved, the welding seam forming is excellent, the mechanical property is good, and full penetration welding of closed small spaces such as a bridge steel anchor beam and a steel box beam support area is adapted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel structure manufacturing and welding, in particular to a composite material gasket for a full penetration joint in a closed small space and a corresponding welding method. BACKGROUND

[0002] In large steel structure projects such as bridges, with the extension of design concepts to artistic and aesthetic, while taking into account the structural strength requirements, narrow and closed space structures such as steel anchor beams, steel box beam support areas, and steel truss joints often occur. The welds in such areas are often required to be fully penetrated, but due to the narrow space, dense steel plate arrangement, and blocked view, the welding operation is extremely difficult.

[0003] In the prior art, in order to achieve full penetration welding in a closed small space, a gasket is usually used to assist welding to avoid back carbon arc gouging and reduce overhead welding, which is difficult to ensure quality. However, the commonly used gaskets have obvious defects: Metal gasket defects: The metal gasket is rigid, and it is difficult to completely adhere to the welded steel plate during assembly, which is easy to form an assembly gap, and defects such as welding porosity, incomplete penetration, incomplete fusion, gas holes, slag inclusions, and root concave / undercut are easy to occur during welding, which cannot guarantee the welding quality of the joint, and may also cause local stress concentration and reduce the fatigue performance of the structure; Traditional ceramic gasket defects: The traditional ceramic gasket is too flexible, and is easy to locally sag under the action of the gravity of the molten pool, gas and arc impact force during welding, which leads to excessive height of the base layer weld and poor forming; and the traditional ceramic gasket needs to be pasted into the inside joint part of the structure, which cannot be pre-installed after the closed space is finally closed, and the assembly feasibility is low.

[0004] Therefore, there is an urgent need for a gasket and welding method that can adapt to a closed small space, balance stability and welding quality, to solve the problems of the prior art. SUMMARY

[0005] The purpose of the present application is to provide a composite material gasket for a full penetration joint in a closed small space and a welding method, which can reduce the welding defects of traditional metal gaskets, overcome the problems of poor stability and difficult assembly of traditional ceramic gaskets, and ultimately achieve excellent weld forming and excellent joint mechanical properties.

[0006] In order to achieve the above purpose, the present application provides a composite material gasket for a full penetration joint in a closed small space, comprising: a structure-stressed steel layer A; a composite ceramic layer B; and a glue layer C for composite connection of the structure-stressed steel layer A and the composite ceramic layer B; The composite ceramic layer B is configured to face the joint groove and be close to the base material during welding, and the structural stress steel layer A is configured to face the welding back and is fixed on the base material D by spot welding.

[0007] Further, the side of the composite ceramic layer B away from the structural stress steel layer A is further compounded with a welding powder layer G capable of melting and participating in metallurgical reaction; the composition of the welding powder layer is rutile type acid slag system or fluorine-alkali type basic slag system.

[0008] Further, the welding powder layer G is acid slag system or basic slag system; the acid slag system contains 35-55wt% TiO2, 15-30wt% iron powder, and is supplemented with SiO2, ZrO2, Al2O3 and MgO, and arc stabilizing agent containing K and Na elements, aluminum powder, aluminum-magnesium powder and a small amount of Si and Mn ferroalloy; the basic slag system has a filling coefficient of 24-28%, and contains CaF2 and CaCO3, supplemented with appropriate SiO2 or TiO2. The problems of unstable arc, large welding spatter, difficult slag removal, many impurities in the weld, poor mechanical property adaptability and the like that are prone to occur in traditional backing welding are solved through the slag system design of the welding powder layer G, from the three dimensions of welding process control, weld metallurgical purification and working condition adaptability, to improve the welding quality of full penetration joints in small closed spaces, and to match the performance requirements of different base materials. The arc stabilizing agent containing K and Na elements in the acid slag system welding powder layer can reduce the arc ignition voltage and reduce the arc fluctuation, to avoid the defects of "molten pool deviation and incomplete fusion" caused by unstable arc when the line of sight is blocked in the small closed space. The acid slag system has moderate flowability, can wrap the droplet and inhibit the generation of spatter, and can make the weld surface smooth, to solve the problems of "welding tumor and surface depression" in traditional metal backing welding, to reduce the difficulty of weld cleaning in the small closed space, and the rutile composition can reduce the adhesion between the slag and the weld metal, the slag is easy to peel off after welding, without the need for additional strong cleaning, to adapt to the scene of limited operation space in the small closed space. By adding Si and Mn ferroalloy, the chemical composition of the weld metal can be adjusted to ensure the mechanical property matching between the weld and the base material. The aluminum powder and aluminum-magnesium powder can absorb the gas in the welding process to reduce the root porosity defects and improve the weld density.

[0009] The high-alkalinity characteristic of the basic slag system welding powder layer can efficiently remove harmful impurities such as S and P (S and P are easy to cause weld hot cracking) in the weld, reduce the risk of cracks caused by impurities that cannot be cleaned in time in the small closed space, and improve the purity of the weld. At the same time, the low-oxidizing slag system can avoid the oxidation and embrittlement of the weld metal, and optimize the weld structure, so that the weld has excellent low-temperature impact toughness, and can adapt to the welding requirements of important steel structures such as bridge steel girder and steel box girder support area that need to bear dynamic load or low-temperature environment; the combination of S and P removal capability and low oxidation can reduce the content of harmful elements in the weld, and reduce the probability of cold and hot cracking.

[0010] Further, the surface of the composite ceramic layer B is provided with grooves or trenches for controlling the shape of the molten pool. The grooves / trenches on the surface of the composite ceramic layer B can constrain the molten pool by physical boundaries: on the one hand, limit the flow range of the deposited metal, prevent the molten pool from excessive diffusion or accumulation due to external force; on the other hand, guide the molten pool to fill uniformly, so that the thickness and reinforcement of the backing layer weld meet the design standards, and avoid the need for subsequent polishing due to excessive reinforcement. At the same time, the grooves / trenches can be designed with matching depth and width according to the joint groove form, such as V-shaped, U-shaped, J-shaped, on the one hand to ensure that the molten pool metal can fully fill the joint root to avoid un-melted areas in the root; on the other hand, through the guiding effect of the trench, the deposited metal and the groove edge of the base material D, E are fully melted to eliminate the defect of edge incomplete penetration, and meet the strength requirements of full penetration joint.

[0011] Further, the inside or surface of the composite ceramic layer B is provided with a gas hole for discharging gas during welding to prevent root porosity; the size of the gas hole is determined according to the welding heat input, the base material quality and the type of protective gas, wherein a gas hole with a diameter of 0.4-0.5mm is selected for welding of low carbon steel and low alloy steel, a gas hole with a diameter of 0.1-0.2mm is selected for welding of stainless steel, nickel-based alloy and high-temperature alloy, a gas hole with a diameter of 0.1-0.2mm is selected when the protective gas is pure argon or argon-rich mixed gas, and a gas hole with a diameter of 0.4-0.5mm is selected when the protective gas is CO2. Two types of gases need to be discharged during welding: one is the gas remaining after pretreatment of the base material / groove; the other is the gas generated during welding. In a closed small space, the gas diffusion space is limited and is easy to stay in the root of the molten pool; while the gas hole of the ceramic layer can be used as a directional exhaust channel to guide these gases to escape in time before the molten pool solidifies, avoiding the gas being wrapped in the root of the weld to form a gas hole. This is the key design to solve the traditional metal liner root porosity defect, which directly ensures the density of the weld.

[0012] Low carbon steel and low alloy steel are suitable for larger gas holes, because such base materials have relatively low purity requirements for the weld, and more gas is generated during welding due to rust and oil stains; a 0.4-0.5mm gas hole channel can quickly discharge a large amount of associated gas to avoid gas accumulation; at the same time, larger gas holes will not be blocked by deposited metal due to the welding heat input of the base material, ensuring the effectiveness of the exhaust channel throughout; stainless steel, nickel-based alloy and high-temperature alloy are suitable for smaller gas holes, because such base materials have high purity requirements, and the protective atmosphere needs to be strictly controlled during welding to prevent oxidation and brittleness. A small hole with a diameter of 0.1-0.2mm can balance the effective exhaust and the protection of the gas atmosphere, on the one hand, the small hole can discharge a small amount of metallurgical reaction gas to avoid root porosity; on the other hand, the small hole can reduce the excessive loss of protective gas, prevent the molten pool from being exposed to air during the exhaust process, and avoid the large hole diameter causing the deposited metal to penetrate into the gas hole to form slag, thereby ensuring the mechanical properties of the high-purity base material weld.

[0013] Pure argon / argon-rich mixed gas is suitable for small holes because argon has large density, the protection effect depends on stable gas layer coverage, and argon welding is accompanied by less gas. Small holes of 0.1-0.2 mm can minimize the loss of argon from the gas hole while discharging a small amount of gas, avoiding oxidation of the molten pool and slag inclusion in the weld due to insufficient protective gas, especially suitable for welding of stainless steel and nickel-based alloy.

[0014] CO2 protective gas is suitable for large holes because, during CO2 gas welding, on the one hand, the gas has strong fluidity and is easy to form vortex and stay; on the other hand, CO2 may react with the molten pool to generate a small amount of CO gas, which requires a more unobstructed exhaust passage. Large holes of 0.4-0.5 mm can quickly discharge excess gas generated during CO2 welding, avoiding gas retention and forming pores.

[0015] Further, the composite liner can be designed at different angles to adapt to the full penetration welding requirements of T-joints or angle joints.

[0016] Another aspect of the present application also provides a welding method using the above-mentioned composite liner, comprising the following steps: S1: positioning the liner, the composite liner is fixed on the base material (D) by spot welding the structural stress steel layer (A) thereof; S2: assembling the workpiece, assembling the base material (E) to be welded to the welding joint, pressing and ensuring that it is tightly attached to the composite ceramic layer (B), and adjusting the weld gap; S3: performing welding, selecting a welding material and welding parameters matched with the base material for backing welding, so that the molten pool (F) formed by the deposited metal is formed relying on the composite ceramic layer (B), thereby connecting the base material (D) and the base material (E).

[0017] Further, in step S3, the backing welding material is selected according to the welding position: solid wire is selected for horizontal and flat position welding, and flux-cored wire is selected for vertical and overhead position welding.

[0018] Further, after step S3, the method further comprises the following steps: S4: filling and surfacing, selecting a matched welding material for multi-layer and multi-pass welding filling and surfacing, and timely cleaning the weld and controlling the interlayer temperature; S5: post-welding inspection, performing appearance and non-destructive testing on the completed welding joint.

[0019] Further, after step S2 and before step S3, the method further comprises the step of preheating the welding joint and the liner.

[0020] The beneficial effects of the present application are: Excellent weld quality: composite ceramic layer B isolates molten pool from steel layer A, avoiding defects such as welding bumps and gaps; the air hole design of the ceramic layer can exhaust welding gas and reduce root porosity; the welding powder layer G can optimize the performance of the slag, reduce spatter, improve slag removal, and there is no metal pollution, which is suitable for stainless steel, high-strength steel and other base materials with high purity requirements, and can improve the purity of the weld; Strong joint mechanical properties: steel layer A provides rigid support to avoid poor weld formation caused by ceramic layer deflection, and the steel layer can also serve as a positioning point for assembly, improving welding accuracy; the thermal conductivity of the ceramic layer is lower than that of the metal liner, heat is concentrated, the heat-affected zone is reduced, deformation and residual stress are reduced, and the joint fatigue performance is improved; High operation feasibility: relying on the spot welding of the steel layer A, the liner can be pre-installed before the closed structure is closed, without the need to paste it from the inside of the structure, solving the assembly problem of traditional ceramic liners; and the ceramic liner is disposable, eliminating the need for preheating, cooling and anti-sticking treatment steps of the metal liner, improving welding efficiency; Wide adaptability: the liner can be designed in different angles and shapes to adapt to various joints such as T-type, corner joint, butt joint, and various grooves such as V-type and U-type, meeting the welding needs of different closed small spaces. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a cross-sectional view of the T-shaped joint penetrated by the present application; Figure 2 is a large sample drawing of the composite liner for the T-shaped joint penetrated by the present application; Figure 3 is a cross-sectional view of the butt joint; Figure 4 is a large sample drawing of the composite liner for the butt joint.

[0022] In the drawings, the components represented by each reference number are listed as follows: A - structural stress steel layer, B - composite ceramic layer, C - adhesive, D - welded joint base material, E - welded joint base material, F - weld pool, G - welding powder layer. DETAILED DESCRIPTION

[0023] The principles and characteristics of the present application are described below in conjunction with the drawings, and the examples are used only to explain the present application and not to limit the scope of the present application.

[0024] As shown in Figures 1-4 , the drawing is a composite material liner in the present embodiment, which includes a structural stress steel layer A, a composite ceramic layer B, and an adhesive C; the composite ceramic layer B is connected to the structural stress steel layer A through the adhesive C; during welding, the steel layer is spot-welded to the back of the welded joint, and the composite liner is fixed to the base material D.

[0025] The base material E is assembled close to the ceramic layer, the distance to the base material D is adjusted to control the appropriate welding gap, and the moisture is removed according to the actual welding conditions and the climate conditions. The welding joint and the gasket are preheated according to the plate thickness or the steel plate grade, and the preheating temperature is controlled within a reasonable range. The groove and the surrounding area are polished before welding to make the groove surface smooth, free of rust, free of spatter, free of carbon inclusion, and expose the metal nature, and remove rust, oil stains and other harmful impurities within 30mm range of the welding groove edge; According to the actual welding base material D and E, the steel plate grade is selected to match the welding wire, and the appropriate welding parameters are selected for backing welding. According to the welding process, different welding wires are selected. Solid welding wire can be used for backing in horizontal and flat positions, and flux-cored wire can be used for backing in vertical and overhead positions; The matching flux-cored wire and appropriate welding parameters are selected for filling and covering. For butt joints with wide groove space, matching submerged arc welding wire with flux can be used for filling and covering. The deposited metal relies on the ceramic layer to form a molten pool F in the assembly gap, and then D and E are welded together. During welding, the multi-layer and multi-pass welding is compacted, and the slag of each layer is cleaned in time. The cleaned weld should be free of spatter, carbon inclusion and inclusions. After polishing and removing impurities, the interpass temperature should be detected. If the interpass temperature is lower than the required interpass temperature, the weld should be reheated to the original interpass temperature; The appearance of the welded joint is detected, and the surface should not have cracks, incomplete fusion, slag inclusion, incomplete welding, and other defects. Non-destructive testing is carried out after 24h (for plates thicker than 30mm, after 48h). The inspection and evaluation are carried out in accordance with the relevant provisions of GB / T 11345; Mechanical property test is carried out on the welded joint, the test method is carried out in accordance with the current GB / T 2650-GB / T 2654, and macroscopic etching test is carried out. The test method should comply with the current provisions of GB / T 226. Macroscopic etching should not have cracks, incomplete fusion, porosity, slag inclusion and other excessive welding defects.

[0026] Example 1: 1. Gasket structure parameters The structural stress steel layer A is made of Q355 steel plate with a thickness of 5 mm and a width of 20 mm, which is mainly used to be fixed on the base material by spot welding and to support the composite ceramic layer to avoid the deflection of the ceramic layer during welding. The composite ceramic layer B is made of alumina-based ceramic with a thickness of 8 mm and a width of 18 mm, and a V-shaped groove with a depth of 3 mm is provided on the surface of the composite ceramic layer B for controlling the shape of the molten pool, and a gas hole with a diameter of 0.5 mm is provided inside the composite ceramic layer B for discharging welding gas. The adhesive layer C is made of epoxy modified high temperature adhesive with a thickness of 0.1 mm and a temperature resistance of ≥300℃, which is used to firmly combine the structural stress steel layer A and the composite ceramic layer B. The welding powder layer G is made of rutile type acid slag system with a thickness of 1 mm, and the composition includes 45wt% TiO2, 25wt% iron powder, 10wt% SiO2, 2wt% K2O and 3wt% aluminum powder, which can realize stable arc, reduce welding spatter and improve the slag removal effect. The gasket is designed as a 90° angle to adapt to the welding requirements of the T-shaped joint.

[0027] 2. Welding conditions and parameters The application scenario is the bridge steel box girder support area (closed small space, operation radius ≤300mm), and the base material is made of Q355 material, in which the base material D has a thickness of 20 mm and the base material E has a thickness of 20 mm. The welding process is as follows: the preheating temperature is controlled at 80℃ (the conventional preheating requirement for 20mm thick low carbon steel); the horizontal position welding method is used for the backing welding, and ER50-6 solid wire (diameter 1.2mm) is selected, the welding current is 180A, the welding voltage is 24V, and the welding speed is 150mm / min; E501T-1 flux cored wire (diameter 1.2mm) is selected for the filling and covering, the welding current is 200A, the welding voltage is 26V, and the multi-layer and multi-pass welding process is adopted (a total of 3 layers), and the interlayer temperature is maintained at ≥80℃; the protective gas is CO2, which is suitable for the 0.5mm diameter gas hole inside the composite ceramic layer B.

[0028] 3. Detection results The appearance detection shows that the weld has no welding tumor, depression and smooth surface, which is due to the V-shaped groove of the composite ceramic layer B for controlling the shape of the molten pool and the acid welding powder layer for reducing the welding spatter; the nondestructive testing is carried out according to GB / T 11345 for ultrasonic testing, and the result is grade I, there is no incomplete fusion and porosity defect, because the gas hole of the ceramic layer can effectively discharge gas, and the steel layer ensures that the gasket is closely attached to the base material; the tensile strength detection result is 510MPa (the standard value of Q355 base material is 490MPa, which meets the requirement of ≥90% of the standard value of the base material), because the weld has no impurity pollution and high density; the impact energy at-40℃ is 42J (the qualified standard is ≥34J), and the deoxidation effect of the acid welding powder layer reduces the weld embrittlement; the macro etching detection (GB / T 226) shows that there is no gas hole and slag inclusion at the root of the weld, and the fusion line is clear, which reflects the synergistic effect of the gas hole gas discharge and the groove guided fusion.

[0029] Example 2: 1. Gasket structure parameters The structure stress steel layer A is made of 304 stainless steel plate with a thickness of 6 mm and a width of 25 mm, which can avoid the pollution of carbon steel to the stainless steel weld during welding; the composite ceramic layer B is made of zirconia-based ceramic with a thickness of 10 mm and a width of 22 mm, and a U-shaped groove with a depth of 4 mm is provided on the surface for controlling the weld reinforcement, and a gas hole with a diameter of 0.2 mm is provided inside for reducing the loss of protective gas while ensuring exhaust; the adhesive layer C is a silicone modified high temperature adhesive with a temperature resistance of ≥400℃, a thickness of 0.1 mm, which can withstand the high temperature environment during stainless steel welding, and realize the stable composite of steel layer and ceramic layer; the welding powder layer G is a fluorine-alkali type alkaline slag system with a thickness of 1.2 mm and a powder filling coefficient of 26%, and the composition includes 30wt% CaF2, 25wt% CaCO3, 5wt% SiO2, and 3wt% TiO2, which can efficiently remove S and P impurities in the weld and improve the low temperature toughness of the weld; the gasket is designed as a flat plate to adapt to the V-shaped groove of the butt joint with an angle of 60°.

[0030] 2. Welding conditions and parameters The application scenario is a closed channel of a bridge steel anchor beam with a space height of ≤200 mm and obstructed view; the base metal is made of 304 stainless steel with a thickness of 25 mm; the welding process is as follows: the preheating temperature is controlled at 120℃ to prevent cold cracking during stainless steel welding; the backing welding adopts vertical welding method, ER308L flux cored wire with a diameter of 1.2 mm is selected, the welding current is 160 A, the welding voltage is 22 V, and the welding speed is 130 mm / min; the filler cap is also made of ER308L flux cored wire (diameter 1.2 mm), the welding current is 180 A, the welding voltage is 24 V, and the multi-layer multi-pass welding process (total 4 layers) is adopted, and the interlayer temperature is maintained at ≥120℃; the protective gas is rich argon mixed gas which is matched with the 0.2 mm diameter gas hole in the composite ceramic layer B to reduce the loss of protective gas.

[0031] 3. Detection results The appearance detection shows that the weld reinforcement is 2 mm (in line with the design standard), and there is no sagging phenomenon, because the structure stress steel layer provides rigid support, and the U-shaped groove of the ceramic layer controls the accumulation height of the molten pool; the nondestructive testing is carried out according to GB / T 11345, and the result is grade I, and there is no slag inclusion and crack defect, which benefits from the efficient removal of S and P impurities in the alkaline welding powder layer, reducing the generation of defects; the tensile strength detection result is 620 MPa (the standard value of 304 stainless steel base material is 515 MPa, meeting the requirements), because the gasket has no metal pollution, the purity of the weld is high; the impact energy at-40℃ is 58J (≥34J is the qualified standard), the alkaline slag system optimizes the weld structure and improves the low temperature toughness; the macro etching detection (GB / T 226) shows that the molten pool is filled and there is no oxide layer, because the small size pores reduce the loss of protective gas while exhausting, avoiding the molten pool from being exposed to air oxidation.

[0032] Example 3: 1. Gasket structure parameters The structure stress steel layer A is selected from Q460 steel plate, with a thickness of 6mm and a width of 22mm, which meets the strength requirement of high strength steel welding and ensures that the gasket does not deform during welding; the composite ceramic layer B is silicon carbide-based ceramic, with a thickness of 9mm and a width of 20mm, and a U-shaped groove with a depth of 3.5mm is provided on the surface, which is suitable for the shape of the fillet joint molten pool, and a gas hole with a diameter of 0.4mm is provided inside, which meets the exhaust requirement of CO2 protective gas; the adhesive layer C is phenolic modified high temperature glue, with a temperature resistance of ≥350℃, a thickness of 0.1mm, and high strength bonding performance, which can resist the stress action during high strength steel welding; the welding powder layer G is fluorine-alkali type alkaline slag system, with a thickness of 1.1mm and a powder filling coefficient of 25%, and the composition includes 28wt% CaF2, 26wt% CaCO3 and 6wt% SiO2, which can improve the crack resistance of the weld and meet the high reliability requirement of high strength steel welding joint; the overall design of the gasket is 60° angle to meet the welding requirement of 60° fillet joint.

[0033] 2. Welding conditions and parameters The application scenario is a steel truss beam joint sealed cavity (operation space ≤250mm); the base material is selected from Q460 high strength steel, and the thickness of the base material D and the base material E is 25mm; the welding process is as follows: the preheating temperature is controlled at 100℃ (to prevent cold cracking during high strength steel welding); the backing welding adopts flat position welding method, and ER55-G solid wire (diameter 1.2mm) is selected, with a welding current of 190A, a welding voltage of 25V and a welding speed of 140mm / min; the filling and covering uses E551T-1 flux-cored wire (diameter 1.2mm), with a welding current of 210A and a welding voltage of 27V, adopting multi-layer and multi-pass welding process (a total of 3 layers), and the interlayer temperature is kept ≥100℃; the protective gas is selected from CO2, which is matched with the 0.4mm diameter gas hole in the composite ceramic layer B, to ensure efficient exhaust.

[0034] 3. Test results The appearance test shows that there is no undercut at the corner joint, and the weld is uniformly shaped, because the custom angle of 60° of the gasket perfectly fits the corner joint, and the groove guides the molten pool to uniformly fill; the non-destructive test is carried out according to GB / T 11345 for ultrasonic testing, and the result is grade I, and there is no lack of penetration defect, which is due to the groove guiding the molten pool to fully fill the joint root; the tensile strength test result is 580 MPa (the standard value of Q460 base material is 550 MPa, which meets the requirements), and the purification effect of the alkaline welding powder layer improves the weld strength; the impact energy at -40℃ is 45J (≥34J is the qualified standard), and the low oxidizability of the alkaline slag system reduces the weld embrittlement; the macro etching test (GB / T 226) shows that there is no crack at the weld root, and the fusion is good, which reflects the crack resistance of the alkaline slag system and the exhaust effect of the gas hole.

[0035] Comparative Example 1 1. Gasket and process parameters The gasket only selects Q355 steel plate (thickness 5mm, width 20mm), without composite ceramic layer, adhesive layer and welding powder layer, and also without groove and gas hole design; the welding process is completely consistent with Example 1.

[0036] 2. Test results The appearance test shows that there is a welding bead with a height of ≥5mm at the weld root, and there is a local depression, because the metal gasket is rigid, and it is difficult to completely adhere to the base material during assembly, resulting in a gap that causes the molten pool to overflow; the non-destructive test is carried out according to GB / T 11345 for ultrasonic testing, and the result is grade III, with 2 un-fused defects, because the assembly gap causes the molten pool to be unable to fill the joint root; the tensile strength test result is 450MPa, which is only 92% of the standard value of Q355 base material, and the un-fused defect reduces the effective load bearing area of the weld; the macro etching test (GB / T 226) shows that there are 3 gas holes with a diameter of ≥1mm at the root, because the gasket has no exhaust passage, and the welding gas is retained at the root of the molten pool.

[0037] Comparative Example 2 1. Gasket and process parameters The gasket only selects pure alumina ceramic gasket (thickness 8mm, width 18mm), without structural steel layer, adhesive layer and welding powder layer, and also without gas hole design; the welding process is completely consistent with Example 2.

[0038] 2. Test results The appearance inspection shows that the underbead cracking is obvious, and the reinforcement is > 6 mm, because the traditional ceramic liner has large flexibility, and there is no steel layer to support, so the deformation occurs under the gravity of the molten pool during welding; the non-destructive testing is carried out according to GB / T 11345 for ultrasonic testing, and the result is level II, and there is one place of slag inclusion defect, because there is no welding powder layer to purify the weld, and the impurities remain in the molten pool; the tensile strength test result is 560 MPa, which reaches 109% of the standard value of 304 stainless steel base material, but the elongation is only 15%, which is lower than 20% of example 2, and the slag inclusion leads to stress concentration in the weld, and the plasticity decreases; the macro etching detection (GB / T 226) shows that there is an oxidation layer with a thickness of > 0.1 mm on the surface of the weld, because there is no pore control, the protective gas is lost, and part of the molten pool is exposed to air to be oxidized.

[0039] Comparative example 3: 1. Liner and process parameters The liner comprises a structural stress steel layer A (Q355, 5 mm thick), a composite ceramic layer B (alumina-based, 8 mm thick, with V-shaped grooves and φ0.5 mm pores), an adhesive layer C (epoxy modified high temperature adhesive), but lacks a welding powder layer G; the welding process is completely consistent with example 1.

[0040] 2. Test results The appearance inspection shows that the amount of welding spatter is more than 3 times of example 1, and the molten slag is difficult to peel off, because there is no acidic welding powder layer to stabilize the arc, no iron powder and TiO2 composition to reduce spatter and reduce the adhesion of molten slag; the non-destructive testing is carried out according to GB / T 11345 for ultrasonic testing, and the result is level II, and there is one place of pore, because there is no aluminum powder in the welding powder layer to absorb the welding gas, resulting in residual gas; the -40℃ impact energy test result is 28J (not reaching the qualified standard of > 34J), and the Si, Mn iron alloy in the welding powder layer is not enough to alloy the weld, and the weld toughness is insufficient.

[0041] Comparative example 4: 1. Liner and process parameters The liner comprises a structural stress steel layer A (304 stainless steel, 6 mm thick), a composite ceramic layer B (zirconia-based, 10 mm thick, with U-shaped grooves), an adhesive layer C (silicone modified high temperature adhesive), and a welding powder layer G (fluorine-alkali type alkaline slag system), but the composite ceramic layer B has no pore design; the welding process is completely consistent with example 2.

[0042] 2. Test results The non-destructive testing is carried out according to GB / T 11345 for ultrasonic testing, and the result is level III, and there are two places of root pores, because there is no exhaust passage, and the stagnant gas generated during the welding of the argon-rich mixed gas cannot escape; the macro etching detection (GB / T226) shows that the root porosity of the weld is > 5%, and the gas is wrapped during the solidification process of the molten pool, forming dense pores.

[0043] From the appearance defects, the welds of examples 1-3 have no welding bumps, under-arching, spatter problems, and uniform forming, which is achieved by the supporting effect of the structural stress steel layer, the arc stabilizing and spatter reducing effect of the welding powder layer, and the molten pool control function of the groove. However, the traditional gasket has the problems of welding bumps, under-arching, spatter, and slag, which highlights the structural defects and insufficient functions of the composite gasket.

[0044] From the non-destructive testing results, examples 1-3 all meet the I level standard, without defects such as incomplete fusion, porosity, and slag inclusion, which benefits from the exhaust function of the porosity, the purification effect of the welding powder layer, and the close assembly ensured by the steel layer. The traditional gasket of comparative example 1-4 can only reach the II-III level, and has incomplete fusion, porosity, and slag inclusion, which reflects the problems of no functional design of the traditional gasket and incomplete functions of the gasket lacking key features.

[0045] From the mechanical properties, the tensile strength and low temperature impact energy of examples 1-3 meet the standard requirements, and the plasticity is good, because the invention avoids metal pollution and realizes weld purification and microstructure optimization. The strength, toughness, or elongation of comparative example 1-4 is insufficient, which cannot fully meet the mechanical property requirements.

[0046] From the adaptability of the closed space, the gasket of examples 1-3 can be point-welded by the structural stress steel layer, without the need to operate inside the closed space, which solves the assembly problem of the traditional gasket. The traditional metal gasket of comparative example 1 needs to be repeatedly adjusted and assembled, and the traditional ceramic gasket of comparative example 2 needs to be pasted inside the closed space, which are not suitable for small closed space working conditions.

[0047] In summary, the examples fully verify the effectiveness of the invention composite structure combined with functional design, and the comparative examples further prove that the absence of any key feature, such as the steel layer, the welding powder layer, the porosity, and the groove, will lead to the degradation of the welding quality, highlighting the integrity and necessity of the invention concept.

[0048] Finally, the method of the present application is only a preferred embodiment, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite gasket for a hermetically sealed, full-penetration joint in a small space, characterized in that, Comprise: a structure stress steel layer (A); a composite ceramic layer (B); and an adhesive layer (C) for connecting the structure stress steel layer (A) and the composite ceramic layer (B); wherein the composite ceramic layer (B) is configured to face the joint groove and be close to the base material during welding, and the structure stress steel layer (A) is configured to face the welding back and be fixed on the base material (D) by spot welding.

2. The composite gasket of claim 1, wherein, The side of the composite ceramic layer (B) away from the structure stress steel layer (A) is provided with a welding powder layer (G); the composition of the welding powder layer (G) is rutile type acid slag system or fluorine-alkali type basic slag system.

3. The composite gasket of claim 2, wherein, The welding powder layer (G) is acid slag system or basic slag system; the acid slag system contains 35-55wt% TiO2, 15-30wt% iron powder, and is supplemented with SiO2, ZrO2, Al2O3 and MgO; and arc stabilizing agent containing K and Na elements, aluminum powder, aluminum-magnesium powder and a small amount of Si, Mn ferroalloy; the basic slag system has a filling coefficient of 24-28%, and contains CaF2, CaCO3, supplemented with appropriate SiO2 or TiO2.

4. The composite gasket of claim 1, wherein, The surface of the composite ceramic layer (B) is provided with grooves or trenches for controlling the shape of the molten pool.

5. The composite gasket of claim 1, wherein, The inside or surface of the composite ceramic layer (B) is provided with a gas hole for discharging gas and preventing root porosity during welding; the size of the gas hole is determined according to the welding heat input, the base material quality and the type of protective gas, wherein a gas hole with a diameter of 0.4-0.5mm is selected for low carbon steel and low alloy steel welding, a gas hole with a diameter of 0.1-0.2mm is selected for stainless steel, nickel-based alloy and high-temperature alloy welding, a gas hole with a diameter of 0.1-0.2mm is selected for pure argon or argon-rich mixed gas, and a gas hole with a diameter of 0.4-0.5mm is selected for CO2.

6. The composite gasket of claim 1, wherein, The composite material liner can be designed at different angles to adapt to the full penetration welding requirements of T-joints or angle joints.

7. A welding method using the composite gasket according to any one of claims 1 to 6, characterized by, Comprise the following steps: S1: positioning the liner, fixing the composite material liner on the base material (D) through the structure stress steel layer (A) by spot welding; S2: assembling the workpiece, assembling the base material (E) to be welded to the welding joint, pressing and ensuring that it is close to the composite ceramic layer (B), and adjusting the weld gap; S3: performing welding, selecting welding materials and welding parameters matched with the base material for backing welding, so that the molten pool (F) formed by the deposited metal is formed relying on the composite ceramic layer (B), thereby connecting the base material (D) and the base material (E).

8. The welding method of claim 7, wherein, In step S3, the backing welding material is selected according to the welding position: solid wire is selected for horizontal and flat position welding, and flux-cored wire is selected for vertical and overhead position welding.

9. The welding method of claim 7, wherein, After step S3, it further comprises the following steps: S4: filling and covering, selecting matched welding materials for multi-layer and multi-pass welding filling and covering, and cleaning the welds in time and controlling the interlayer temperature; S5: post-welding inspection, appearance and non-destructive testing of the completed welding joint.

10. The welding method of claim 7, wherein, After step S2 and before step S3, it further comprises the step of preheating the welding joint and the liner.

Images