All practice items can be selected from seamless steel pipes with a wall thickness of 3-6mm and an outer diameter of 22-60mm, with a length of 100mm. The orifice plate is made of 12mm steel plate, and its size is 100mmx100mmx12mm.
Processing requirements are shown in Figure The structure of the tube-sheet joint and the grinding area before tig welding. It is recommended to use a seamless steel pipe with a diameter of 51 mm and a wall thickness of 3 mm as the test piece.
Choose H08Mn2Si or HO5MnSiAITiZr welding wire with a diameter of 2.5mm and a length of 800~1000mm each, and use emery cloth to polish the welding wire until it has a metallic luster.
The purity of argon gas is required to be not less than 99.5%.
Brand WTh- 15, specification φ2. 5mm x 175mm, the end is ground into a conical shape, as shown in Figure Tungsten ground shape.
The argon arc welding specimen must be carefully polished before welding to remove oil, rust and other dirt in the welding area.
There are 3 positioning welds, which are evenly distributed on the outer circumference of the pipe. The welding quality must be ensured. The positioning welds must be well fused, and the length of each position shall not exceed 10mm. No air holes, slag inclusions or other defects are allowed. If defects are found, all defective tack welds must be ground off and re-welded. Remelting is not allowed. The position of tack welds is shown in Figure Location of tack welds.
See Figure Stamp position and mark for requirements
The plug-in tube-sheet butt joint can be divided into impermeable plug-in tube-sheet welding and plug-in tube-sheet welding that requires penetration according to actual production needs.
Insertion tube-sheet welding without penetration is a relatively easy project to master, as long as the root penetration, symmetrical weld leg size, beautiful appearance, uniform size and no defects are sufficient during welding. The impermeable penetration tube-sheet welding mainly includes tube-sheet vertical fixed bottom welding, tube-sheet vertical fixed overhead welding and tube-sheet horizontal fixed all-position welding.
The TIG welding steps are as follows:
①Adjust the extension length of the tungsten electrode. The adjustment method of the protruding length of the tungsten electrode is shown in Figure- Adjust the extension length of tungsten electrode.
②The welding seam strikes the arc. Ignite the arc on the positioning weld on the right side of the test piece, do not add welding wire first, after igniting the arc, swing the welding torch slightly, wait until the positioning weld starts to melt and form a bright molten pool, start adding welding wire, and weld to the left .
③ weld seam welding. During the welding process, the arc should start to swing horizontally centered on the top angle of the pipe and the orifice plate, and the swing range should be appropriate to make the welding feet even. Pay attention to the two sides and the front of the molten pool. When the melting width of the pipe and the orifice plate is basically equal , The solder pin size is symmetrical. In order to prevent the undercut of the pipe, the arc can be slightly away from the pipe wall, and the welding wire is added from the front and upper part of the molten pool, so that the heat of the arc is biased towards the orifice plate.
④ welded joints. Strike the arc on the weld seam 15 ~ 20mm on the right side of the original arc extinguishing place. After the arc is ignited, quickly move the arc to the left to the original arc extinguishing place. First, do not add welding wire. After the required joint is melted to form a molten pool, start to add welding wire , weld at normal speed.
⑤ Weld arc closing. Stop wire feeding when a circle of weld is almost finished, and add welding wire after the original weld metal melts and integrates with the molten pool to fill up the arc crater and then break the arc. Usually, the final joint of the closed weld is easy to be incompletely penetrated. When welding, the root must be heated with an arc, and the welding wire should be added after the top corner is melted. If you are afraid that the weld will not penetrate, you can also grind the original weld head into a slope, which makes it easier to connect the head.
Overhead welding is a difficult welding position. The molten base metal and welding wire droplets are easy to fall, so the welding heat input and cooling speed must be strictly controlled. The welding current is slightly smaller, the welding speed is slightly faster, and the wire feeding frequency is accelerated, but the amount of wire feeding should be reduced, the flow rate of argon gas should be increased appropriately, and the arc should be kept as low as possible during welding. The welding seam adopts two layers and three passes, and the left welding method.
①bottom layer. When welding the bottom bead, the depth of penetration at the top corner should be ensured. The inclination angle of the welding torch and the centering position of the arc are shown in Figure-Tilt angle and arc centering position of bottom welding torch for overhead welding.
Ignite the arc on the tacking weld on the right, do not add welding wire first, after the tacking weld starts to melt and form a molten pool, start to add welding wire, and weld to the left.
During the welding process, the arc should be lowered as much as possible, and the arc should be aligned with the top corner to weld to the left to ensure that both sides of the molten pool are well fused, and the molten droplet of the welding wire should not be too large. Then withdraw the welding wire. When the surface of the molten pool is found to be concave, the welding speed should be increased, and the welding wire should be added after the molten pool is slightly cooled.
Cover layer. There are two weld passes in the cover layer weld, and the inclination angle of the welding torch and the centering position of the arc are shown in Figure-The inclination angle of welding torch and the centering position of arc in overhead welding. Weld the lower bead first, then the upper bead.
The welding procedure is the same as welding the bottom bead.