A method of welding scaffold tubes

Abstract

The application discloses a welding method of a scaffold steel pipe, which comprises the following steps: (1) steel pipe cutting; (2) port processing; (3) steel pipe welding; and (4) passivation treatment. By adopting non-melting electrode inert gas protection arc welding, controlling welding process and selecting suitable welding rods, the welding quality is good, the welding port surface is smooth, and the material requirement of the building scaffold is met.

Description

Technical Field

[0001] This invention relates to the field of B23K9 / 16, and more specifically to a welding method for scaffolding steel pipes. Background Technology

[0002] Scaffolding is a working platform erected to ensure the smooth progress of various construction processes. It is widely used in my country's construction industry. Steel pipes are used to erect external scaffolding and formwork support frames. In actual construction and use, shorter steel pipes need to be welded to obtain longer steel pipes that meet construction needs and can be adapted to various application scenarios.

[0003] CN104668908A discloses a processing technology for stainless steel welded pipes. After two rounds of surface rinsing, heat treatment, precision rolling, welding, and cleaning, the resulting finished stainless steel welded pipe forms a durable protective film on its surface, preventing the regeneration of oxide spots and rust, effectively improving corrosion resistance, and extending the service life of the stainless steel welded pipe. However, the use of argon arc welding, due to the large heat-affected zone, often causes deformation of the workpiece, requiring straightening of the steel pipe.

[0004] Based on the above situation and analysis, it is necessary to study a safe, efficient and low-cost welding technology for steel pipes. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a welding method for scaffolding steel pipes, comprising the following steps:

[0006] (1) Steel pipe cutting;

[0007] (2) Port processing;

[0008] (3) Steel pipe welding;

[0009] (4) Passivation treatment.

[0010] In one embodiment, step (1) specifically involves cutting the steel pipe with the cutting plane perpendicular to the centerline of the steel pipe to obtain a welding port.

[0011] Preferably, the steel pipe is a φ48.3×3.6 steel pipe.

[0012] In one embodiment, step (2) specifically involves using a chamfering machine to create a V-shaped bevel at the welding port of step (1).

[0013] Preferably, the angle of the bevel is 50-70°.

[0014] More preferably, the angle of the bevel is 55°.

[0015] In one embodiment, step (3) specifically involves fixing the steel pipe to be welded on a welding machine tool for welding.

[0016] In one implementation, the steel pipe needs to be pretreated before welding.

[0017] In one embodiment, the pretreatment process involves cleaning the steel pipe with a strong acid solution, a corrosion inhibitor, and a mist suppressant.

[0018] Preferably, the mass ratio of the strong acid solution, corrosion inhibitor, and mist suppressant is 100:(1-3):(5-10).

[0019] More preferably, the mass ratio of the strong acid solution, corrosion inhibitor, and mist suppressant is 100:2:7.

[0020] In one embodiment, the strong acid solution is one or more of sulfuric acid, hydrochloric acid, and nitric acid.

[0021] Preferably, the strong acid solution is hydrochloric acid.

[0022] More preferably, the concentration of the hydrochloric acid is 25wt-35wt%.

[0023] In one embodiment, the corrosion inhibitor is selected from one or more of sodium tripolyphosphate, ammonium polyphosphate, magnesium polyphosphate, potassium polyphosphate, potassium silicate, sodium silicate, magnesium silicate, sodium phosphate, and potassium phosphate.

[0024] Preferably, the corrosion inhibitor is sodium silicate.

[0025] In one embodiment, the anti-fogging agent is a hydrochloric acid anti-fogging agent.

[0026] In one embodiment, the welding process specifically involves using an automatic welding machine to assemble and position the steel pipes to be welded before welding, requiring that the assembled steel pipes have the same wall thickness, and fixing the two sections of steel pipes on the three-jaw chucks on both sides of the welding machine to ensure that the two butt-jointed steel pipes are on the same axis.

[0027] Preferably, the welding process employs non-consumable electrode inert gas shielded arc welding, with argon as the inert shielding gas, a tungsten electrode as the negative electrode, ER309 welding wire, a welding current of 140-150A, an arc voltage of 10-15V, a welding speed of 6-15cm / min, an argon flow rate of 5-10L / min, an advance gas supply time of 1-10s, and a delay gas stop time of 10-30s.

[0028] More preferably, the welding process employs non-consumable electrode inert gas shielded arc welding, with argon as the inert shielding gas, a tungsten electrode as the negative electrode, ER309 welding wire, a welding current of 140A, an arc voltage of 12V, a welding speed of 7cm / min, an argon flow rate of 5L / min, an advance gas supply time of 5s, and a lag gas stop time of 20s.

[0029] In one embodiment, step (4) specifically involves taking the steel pipe welded in step (3), using a fiber cloth soaked in sodium hydroxide, and using a high-pressure air gun with a pressure ≥2.5 MPa, pushing the fiber cloth through the inside of the steel pipe obtained in step 3 to wipe it multiple times for degreasing and cleaning. Then, immersing it in a passivation solution for 5-10 minutes, removing it, and washing it, thus obtaining the final product.

[0030] In one embodiment, the passivation solution comprises 2wt%-3wt% potassium permanganate, 0.5wt%-1wt% hydrogen fluoride, 20wt%-30wt% citric acid, and the balance being deionized water.

[0031] Preferably, the passivation solution comprises 2.5 wt% potassium permanganate, 1.2 wt% hydrogen fluoride, 23.8 wt% citric acid, and 72.5 wt% deionized water.

[0032] The classic chromate passivation method has been banned by the new EU standards due to the high toxicity and pollution of hexavalent chromium ions, which pose a great threat to environmental sustainability and human health. Therefore, it is necessary to develop chromium-free passivation solvents. Nitric acid and sulfuric acid pickling and passivation formulations are very difficult to passivate and have little effect due to sulfide inclusions. By optimizing the passivation solution formulation, the inventors discovered that the passivation solution comprises 2wt%-3wt% potassium permanganate, 0.5wt%-1wt% hydrogen fluoride, 20wt%-30wt% citric acid, and the balance deionized water. The inventors believe the likely reason is that the strong complexing ability of hydrofluoric acid can quickly achieve the passivation effect. In existing technologies, a strong acid system of more than 3wt% hydrofluoric acid combined with 10wt% nitric acid is commonly used for passivation treatment for more than 30 minutes. However, this is prone to over-corrosion, the time is not easy to control, and hydrofluoric acid is quite harmful to humans and the environment. The inventors used citric acid instead of nitric acid, which not only effectively removes free iron and oxides on the surface, further improving the corrosion resistance of steel pipes, but also reduces the amount of hydrofluoric acid used, and can quickly complete passivation in 5-10 minutes.

[0033] Beneficial effects

[0034] 1. By adopting non-consumable electrode inert gas shielded arc welding, controlling the welding process, and selecting appropriate welding rods, the welding quality is good, the weld surface is flat and smooth, and it meets the material requirements of building scaffolding.

[0035] 2. The passivation solution includes 2wt%-3wt% potassium permanganate, 0.5wt%-1wt% hydrogen fluoride, and 20wt%-30wt% citric acid, which can quickly achieve the passivation effect and improve the corrosion resistance of steel pipes. Passivation can be completed quickly in 5-10 minutes.

[0036] 3. The process is simple, safe and environmentally friendly. Detailed Implementation

[0037] Example 1

[0038] This embodiment 1 discloses a welding method for scaffolding steel pipes, the steps of which are as follows:

[0039] (1) Steel pipe cutting: Cut the steel pipe with the cutting plane perpendicular to the center line of the steel pipe to obtain the welding port.

[0040] (2) Port treatment: Use a chamfering machine to set a V-shaped bevel on the welding port of step (1), with the bevel angle being 55°.

[0041] (3) Steel pipe welding: The steel pipe is pretreated by cleaning it with a strong acid solution, corrosion inhibitor and mist suppressant. The mass ratio of the strong acid solution, corrosion inhibitor and mist suppressant is 100:2:7. The strong acid solution is hydrochloric acid with a concentration of 30wt%. The corrosion inhibitor is sodium silicate and the mist suppressant is hydrochloric acid mist suppressant. After cleaning, the steel pipes to be welded are assembled and positioned using an automatic welding machine tool. The assembled steel pipes are required to have the same wall thickness. The two sections of steel pipe are fixed on the three-jaw chucks on both sides of the welding machine tool to ensure that the two butt steel pipes are on the same axis.

[0042] The welding process employs non-consumable electrode inert gas shielded arc welding, with argon as the shielding gas, a tungsten electrode as the negative electrode, ER309 welding wire, a welding current of 140A, an arc voltage of 12V, a welding speed of 7cm / min, an argon flow rate of 5L / min, a pre-gas supply time of 5s, and a post-gas stop time of 20s.

[0043] (4) Passivation treatment: The steel pipe welded in step (3) is treated by wiping it repeatedly with a fiber cloth soaked in sodium hydroxide and a high-pressure air gun with a pressure of ≥2.5MPa. Then, it is soaked in a passivation solution for 8 minutes, and then taken out and cleaned.

[0044] The passivation solution consists of 2.5 wt% potassium permanganate, 0.8 wt% hydrogen fluoride, 23.8 wt% citric acid, and the remainder is deionized water.

[0045] Example 2

[0046] The difference between this embodiment and Embodiment 1 is that the passivation solution is 2.5 wt% potassium permanganate, 3 wt% hydrogen fluoride, 10 wt% nitric acid, and the remainder is deionized water.

[0047] Example 3

[0048] The difference between this embodiment and Embodiment 1 is that the passivation solution is 2.5 wt% potassium permanganate, 3 wt% hydrogen fluoride, 10 wt% citric acid, and the remainder is deionized water.

[0049] Example 4

[0050] The difference between this embodiment and Example 1 is that the passivation solution consists of 28wt% hydrochloric acid, 3.1wt% potassium permanganate, 10.4wt% potassium dichromate, 4wt% benzodiazole, and the remainder is deionized water, with a soaking time of 25 min.

[0051] Example 5

[0052] The difference between this embodiment and Embodiment 1 is that the welding process uses non-consumable electrode inert gas shielded arc welding, the inert shielding gas is argon, the tungsten electrode is used as the negative electrode, the welding wire is ER50-6, the welding current is 140A, the arc voltage is 12V, the welding speed is 7cm / min, the argon flow rate is 5L / min, the advance gas supply time is 5s, and the lag gas stop time is 20s.

[0053] Performance testing

[0054] 1. Blue spot detection: Dissolve 1g of potassium ferricyanide K3 [Fe(CN6)] and 3mL of 65%-85% nitric acid HNO3 in 100mL of deionized water to prepare a solution; attach filter paper moistened with the solution to the surface of the stainless steel pipeline, and observe whether a blue spot appears after 30s. Record it as A, otherwise record it as B.

[0055] 2. Corrosion resistance: Stainless steel tube samples were placed in Cl... - The sample was immersed in a 500 mg / L sodium chloride solution at 60°C for 2 hours. After immersion, the sample was removed, dried, and left at room temperature for 24 hours. The weight difference before and after immersion was then measured, and the corrosion rate was calculated. The lower the corrosion rate, the better the corrosion resistance.

[0056]

Claims

1. A method for welding scaffolding steel pipes, characterized in that, Includes the following steps: (1) Steel pipe cutting: Cut the steel pipe with the cutting plane perpendicular to the center line of the steel pipe to obtain the welding port; (2) Port treatment: Use a chamfering machine to set a V-shaped bevel on the welding port of step (1); (3) Steel pipe welding: Fix the steel pipe to be welded on the welding machine tool for welding; Before welding, use strong acid solution, corrosion inhibitor and fog suppressant in a mass ratio of 100:(1-3):(5-10) to clean the steel pipe; (4) Passivation treatment: The steel pipe welded in step (3) is used to wipe the inside of the steel pipe multiple times with a fiber cloth soaked in sodium hydroxide and with the help of a high-pressure air gun with a pressure of ≥2.5MPa. Then, it is soaked in a passivation solution for 20-40 minutes. After cleaning, it is obtained. The passivation solution comprises 2wt%-3wt% potassium permanganate, 0.5wt%-1wt% hydrogen fluoride, 20wt%-30wt% citric acid, and the balance being deionized water.

2. The welding method according to claim 1, characterized in that, The angle of the bevel is 50-70°.

3. The welding method according to claim 1, characterized in that, The strong acid solution is one or more of sulfuric acid, hydrochloric acid, and nitric acid.

4. The welding method according to claim 1, characterized in that, The corrosion inhibitor is selected from one or more of sodium tripolyphosphate, ammonium polyphosphate, magnesium polyphosphate, potassium polyphosphate, potassium silicate, sodium silicate, magnesium silicate, sodium phosphate, and potassium phosphate.

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