Invar, also known as Invar, Invar, Invar, invariable steel, non-expanded steel, etc.; it is nickel-iron alloy, namely: Ni36%, Fe3.8%, C0.2%; The main characteristics are: the coefficient of expansion is extremely small; the strength and hardness are not high; the thermal conductivity is low; the plastic toughness is high; the ultra-low temperature resistant material is excellent; the applicable temperature is generally -250 ° C ~ +200 ° C; the material is extremely rusty. Mainly used for: display shadow mask; hot bimetal low expansion layer; electronic component sealing material; precision instruments, instrument parts; special transmission cable ; improve ion laser stability. At present, the main welding method is tungsten inert gas shielded welding, which has manual welding and automatic welding (TIG/MIG).
Second, pre-weld preparation
1, weldments, welding consumables mostly have protective film or sealed packaging, the material is annealed before welding, clean, no oil, scratches, marking paint.
2, the welding workload is large, the weld bead has rules mostly using automatic welding machine; otherwise, manual welding is used. Make necessary inspections on the TIG welder: 1 Whether the electric shock protection device is working normally; 2 Is the welding machine indicator light normal, the grounding is good, the cooling water pipe is leaking; 3 The welding torch and the cable protection air pipe are damaged; 4 Is the tungsten needle grinding? Meet the requirements and so on.
3, the guiding idea of ​​the welding process plan is: low heat input, small specification; the interlayer temperature should be lower than 120 °C.
4, no pre-heating before welding, post-weld heat treatment.
5, the welding consumables usually use M93; if the weld bead performance is designed to be the same as the base metal, it is necessary to use the same material as the base material or cut the base material into thin strips for use as the welding wire. Other alternative welding consumables: Nicrofer S 7020 W.-Nr. 2.4806 SG-NiCr20Nb AWs A 5.14 ERNiCr-3; W. -Nr. 2.4648 EL-NiCr19Nb AWS A 5.14 ERNiFe-3.
6, welding environment requirements must be equipped with dehumidification air conditioning, to ensure that the dryness of the welding station is maintained at more than 60%, in order to prevent Yinwa steel rust
Third, the welding operation
1. In the welding operation, it is necessary to absorb the sheepskin gloves, the combination of the dimming mask, the dust mask, the leather hammer, the soft brush, the welding wire bag and other necessary protective tools and necessary tools.
2, in the welding process, clean is the key, there can not be a drop of sweat or a handprint on the weldment, which requires the welder not only to be accurate on the hand, but also to be stable, any mood fluctuations of the welder, all affect the welding quality. The tungsten needle should be stored in a special box to avoid direct contact with the skin of the mountain.
3, according to the thickness of the section of the steel to select the appropriate wire diameter, the corresponding selection of welding current and other process parameters. M93 welding wire? 2.4~? 3.2mm TIG welding standard parameters are current 70~80A, voltage 15~20V. For different plate thickness (mm) welding parameters (current A) are as follows: 1.0 and 0.7 spot welding 50 welding 24; 1.0 and 1.5 spot welding 50 welding 28; 1.5 and 1.0 welding 70 welding 38; 1.5 and 1.5 points Welding 70 welding 48; 1.5 and 3.0 spot welding 100 welding 65; 3.0 and 3.0 welding 110 welding 95.
4, the operation method essentials: 1 tungsten needle to expose the end of the torch about 5mm, the tungsten needle and the base metal or welding direction is 75 °, the horizontal direction is maintained at 90 °. 2 When welding, the wire feeding speed and the welding speed should be consistent. The tip of the tungsten needle is kept at a distance of 0.5~1mm under the action of the inert gas, and the swinging amplitude is about 3 times the diameter of the wire. , requires a uniform rhythm. 3 Always clean the spear attachments and replace the spare tungsten needles, nozzles or guards. 4 When welding, the welding wire and the welding advance direction are 45°, 90° in the vertical direction of the base metal, and the tungsten needle is 90° in the welding direction and in the vertical direction to the base material; In case the droplets are dropped, burns. 5 Closing and relaying, when a weld is to be finished, fill the molten pool, the arc is lifted up, and the torch switch is released; when welding along the front weld, the arc should be at the end of the weld A molten pool is slightly left for 1~3s to reach the same size scale in the molten pool, and then continuous welding is carried out.
5, generally less than 1mm Yinwa steel board is widely used in LNG carrier (use temperature -163 °C) and other construction fields, welding generally uses tungsten inert gas shielded welding; due to thin sheet, base metal and welding consumables Particularly strict. Welding is very difficult. Once a quality problem occurs at one point, it will lead to the replacement and re-welding of a large segment of the adjacent steel tile; the repair time of a leaking point in one place exceeds 1000h; if there is a pinhole defect, it may cause an explosion. The whole ship is scrapped! In order to improve the quality, the base metal welding consumables are imported. Welding LNG vessels must be trained by GTT and obtain a joint certificate before they can be employed, and they must be reviewed monthly.
6. For the thicker Invar steel, Shanghai Baosteel has begun to produce Yinwa steel, which will be used in many fields. It can be welded by gas metal arc welding. The current should not be too large, small swing welding, and crescent-shaped weld bead.
Fourth, post-weld inspection
1, usually first visual inspection, timely detection of more obvious defects in a timely manner.
2, generally need 100% for coloring test.
3. Carry out its inspection if necessary.
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