Several commonly used welding methods for welding steel pipes

Welding means passingHigh temperature or other means to make two pieces of metalmelt, after the melt mixThe process of cooling the crystallization firmly connects the two pieces of metal together.

Since the welded workpiece is closely attached to each other, under the action of temperature field, gravity, etc.No need to apply pressure to two pieces of metalMelting meltAt onceMixed phenomenon occurs,After the temperature drops, the melted partsolidification, the two workpieces are firmly welded together.

Several commonly used fusion welding methods are: welding rod arc welding, submerged arc welding, carbon dioxide gas protective welding,MIG/MAG weld,TIG Welding, plasma arc welding, etc..

• Welding rod arc welding

1. Principle: The arc welding method of using manual welding rods to welding is the most basic welding method in fusion welding. The stable combustion arc established between the welding rod and the weldment is used to melt the welding rod and the weldment, thereby obtaining a solid welded joint, which is a joint gas-slag protection.
2. Advantages: Flexible process, strong adaptability, and easy operation; low assembly requirements for joints to be welded; a wide range of weldable metal materials.
3. Disadvantages: Low welding productivity; strong dependence on weld quality (relying on the welder's operating skills and on-site performance).
4. Application: Widely used in welding of various metal materials, thicknesses and structural shapes in shipbuilding, boilers and pressure vessels, mechanical manufacturing, building structures, chemical equipment and other manufacturing industries.

• Submerged arc welding

1. principle:Arc burns under the flux layer,Using the heat generated by the arc burning between the welding wire and the weld, melting the welding wire, flux and base material (welding) to form a weld, which is slag protection.
2. advantage:weldingefficiencyhigh,Good quality of weld,Low welding cost, high degree of automation,Good working conditions.
3. shortcoming:Difficult to weld in space,High requirements for weldment assembly quality,Not suitable for welding thin plates (welding current is less than100AWhen the arc stability is poor) and short welds.
4. application:It is widely used in shipbuilding, boilers, bridges, lifting machinery and metallurgical machinery manufacturing industries. All welded parts whose welds can be kept in a horizontal position or whose inclination angle can be submerged arc welding. The thickness of the board must be greater than5mm(Anti-burn through).Applicable toWelded carbon structural steel, low alloy structural steel, stainless steel, heat-resistant steel, composite steel, etc.

• Carbon dioxide gas protective welding

1. principle:The melting electrode arc welding method using carbon dioxide as a protective gas is gas protection.
2. advantage:High welding productivity,Low welding cost,Welding deformation is small (arc heating concentration),High welding quality,Easy to operate.
3. shortcoming:High splash rate,It's hard to solder with AC power supply,Poor wind resistance and strong arc light,Nonferrous metals that are prone to oxidation cannot be welded.
4. application:Mainly weld low carbon steel and low alloy steel, suitable for various thicknesses. It is widely used in automobile manufacturing, locomotive and vehicle manufacturing, chemical machinery, agricultural machinery, mining machinery and other departments.

• Melting extremely inert gas protective welding (MIG) and metal reactive gas protective welding (MAG)

1. principle:MIGweldyesAn arc welding method is used to use an inert gas as the protective gas and a welding wire as a melting electrode. The protective gas is usually argon or helium orArgon+Helium mixture;MAGAdd a small amount of active gases, such as oxygen, carbon dioxide, etc. to the inert gas.
2. advantage:Good welding quality,weldingefficiencyhigh.
3. shortcoming:No deoxygenation and dehydrogenation reaction (it is easy to form welding defects, and the surface cleaning requirements for welding materials are particularly strict),Poor wind resistance,Welding equipment is complex.
4. application:Almost all metal materials can be welded, mainly used in non-ferrous metals and their alloys.High priceWelding of stainless steel and certain alloy steels. The thinnest thickness is approximately1mm, the large thickness is basically unlimited.

• Tungsten gas protective welding (TIG)

1. principle:Under the protection of inert gas, the welding method of forming a weld is formed by using arc hot melting of the base material and filler wire (or without filler wire) generated between the tungsten electrode and the weld. The electrode does not melt during welding.
2. advantage:Strong adaptability (stable arc, no splash).
3. shortcoming:Low welding productivity (poor current carrying capacity of the tungsten electrode (anti-tungsten electrode melting and evaporation, and tungsten weld joint),High production costs.
4. application:Almost all metal materials can be welded, and are often used in the welding of stainless steel, high-temperature alloys, aluminum, magnesium, titanium and their alloys, refractory active metals (zirconium, tantalum, molybdenum, niobium, etc.) and heteroclock metals. The welding thickness is generally6mmThe following weldments, or base welding of thick parts. It can be achieved by using small angle bevel (narrow bevel technology)90mmNarrow gap of the above thicknessTIGAutomatic welding.

• Plasma arc welding (PAW)

1. principle:With the help of water-cooled nozzles to restrain the arc, high energy density can be obtainedMethod for welding plasma arc.
2. advantage:Compared with argon arc welding, energy concentration and temperature are high, and small hole effects can be obtained on most metals within a certain thickness range, which can obtain fully penetrated and evenly formed on the reverse side; the arc stiffness is good, and the plasma arc is basically cylindrical, and the change in arc length affects the heating area and current density on the weldment. Therefore, the change in arc length of plasma arc welding has no obvious impact on weld formation; the welding speed is faster than argon arc welding; it can be welded thinner and thinnerofProcessing parts.
3. shortcoming:Compared with argon arc welding, the equipment is complex and costly; it is difficult to operate and limited in use.
4. application:

①Penetration type (small hole type) plasma arc welding: Taking advantage of the characteristics of small plasma arc diameter, high temperature, large energy density and strong penetration, under appropriate process parameters (large welding current).100A~500A), completely penetrate the weldment and in plasma flowofUnder the action, a plasma arc welding method is formed to penetrate the weldment and partial plasma arc is sprayed from the back of the weldment. Can be welded on both sides, and is most suitable for welding 3~8mm Stainless steel,12mm The following titanium alloy,2~6mm Butt welding of low carbon steel or low alloy structural steel and copper, brass, nickel and nickel alloys. (The plate is too thick and is limited by the energy density of the plasma arc, making it difficult to form small holes; the plate is too thin and the small holes cannot be completely sealed by liquid metal.ThereforeSmall hole welding method cannot be realized. )

②Permeable (dissolved) plasma arc welding: use a smaller welding current (30A~100A) and lower plasma gas flow rate, the hybrid plasma arc welding method is adopted. No small pore effect is formed. Mainly used in thin plates (0.5~2.5mm The welding of each layer and the welding of fillet weld seams after the welding of multi-layer welding bottom beads.

③Microbeam plasma arc: welding current is 30A The following plasma arc welding. The nozzle diameter is very small (Φ0.5~Φ1.5mm), obtain a fine plasma arc of needle-shaped shape. Mainly used for welding1Ultra-thin, ultra-small, and precise weldments below millimeters.

In actual production and manufacturing, it is necessary to comprehensively consider the material, thickness and other factors of the welded material to be selected to choose a suitable welding method. A combination of two welding methods can also be used to improve production efficiency while ensuring the welding seam is qualified.