Other arc welding techniques. CTU in Prague Faculty of Mechanical Engineering

Transkript

1 1st semester 2015/2016 Other arc welding techniques CTU in Prague Faculty of Mechanical Engineering Ing. Petr Vondrouš, PhD., IWE

2 Arc welding processes Welding processes that employ an electric arc are the most prevalent in industry Already covered Shielded Metal Arc Welding Gas Metal Arc Welding Gas Tungsten Arc Welding For today Submerged Arc Welding Flux Cored Arc Welding

3 Arc welding processes comparison of effectivity Selection of welding processes is done on base of technological capability, quality and costs Deposition rates for various welding processes (Uhrig, 1983) Deposition rate comparison for consumable used in welding duplex stainless steels

4 SAW submerged arc welding - use of granular flux which is fed into the joint from a flux hopper - arc is struck between the wire and the workpiece beneath the flux - arc and weld pool are shielded by the resulting envelope of molten flux

5 SAW welding SAW is defined as arc welding beneath a bed of granulated flux. Method no. acc. ČSN EN ISO Submerged arc welding 121 with solid wire 122 with strip electrode 124 with metallic particle 125 with tubular electrode 126 with cored strip electrode

6 Basic parameters Positions Base material Welded thickness Current, voltage Diameter Welding source : all : MAG structural steels MIG- alloyed steels, Al, Cu, Ni alloys : mm short circuit : I = A U = V Spray : I = A U = V : 0,8 1,6 mm : flat, solid wire mostly DCEP, DC+

7 Welding source High power needed A -Transformers AC current -Rectifiers DC current ESAB LAF 631 -Invertors most modern, AC, DC, Pulse

8 Polarity - AC, DC +, DC- DC(+ ) very stable arc for lower currents Lower productivity For low thickness sheet DC(-) higher productivity DC For higher currents arc blow Magnetic influence AC no arc blow - stability SAW Welding polarity and productivity

9 Automation SAW is automated welding technique 1. Wire feed system 2. Movement system Rotational welds - Often the movement of the welded structure, weld in position PA Longitudinal welds often movement of welding head

10 Consumables Filler wire solid wire, flux cored, metal cored wire, stripe Flux-

11 Flux Granulated flux that is in solid state non conductive, while in molten state conductive. Functions: Protection from gases Metallurgy desoxydation, purification of WM, alloying Technology slag forms weld, insulates arc and weld, no spatter Electric arc stability, ionization Differently from SMAW gas production should be low

12 Types of flux Terminology :flux is the powdered material used before a welding. Its product after the welding is called slag. Chemical composition ČSN EN ISO Fluxes for submerged arc welding and electroslag welding Classification Symbol Chem. Comp. MS MnO + SiO 2 CS CaO + MgO + SiO 2 ZS ZrO 2 + SiO 2 Metallurgy effect described by Bazicity index =reducing/oxidizing oxides acidic oxidation occures Mn, Si neutral basic reduction of oxides to metals, little inclusions (500 ppm) oxidic The higher the B.I. of a flux mix, the less the residual oxygen is in a weld, and the better the mechanical properties are; the welding performance, will be worse. Production method molten and ground ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování AR Al 2 O 3 + TiO 2 AB Al 2 O 3 + CaO + MgO FB CaO + MgO + MnO + CaF 2 ST Metal containing network builder SiO 2 viscosity controller CaF 2 -liquid slag flow -inclusions -weld shape, surface tension -de-oxidation, de-nitridization -hydrogen removal -alloying

13 SAW Thermal bilance: High heat input 40 % WM melting 25 % heat flow into the WM 22 % flux melting 13 % wire melting

14 Use SAW

15 Use SAW

16 Use SAW

17 Use SAW

18 Use SAW

19 Twin, TANDEM, Multiwire

20 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

21 Narrow gap welding

22 Material consumption

23 SAW submerged arc welding Advantages high current (1000 A), high deposition rates for thick materials Smooth, high quality weld Minimal smoke and fumes continuous wire electrode high diameter (max 5-6 mm) no arc flash or glare flux and wire added separately - extra dimension of control easily automated joints can be prepared with narrow grooves twin wire, multiple torch Drawbacks - slag creation, much heat input, welding process not visible

24 FCAW Flux cored arc welding Uses tubular wire with flux, metal powder inside. Advantages High deposition rates (higher than SMAW, GMAW) Continuous electrode No creation Easily automated Drawbacks Gun size Many process variables

25 Filler materials solid and cored wires

26 FCAW Method no. acc. ČSN EN ISO not only 1 method 114 self shielded tubular cored arc welding no need for shielding gas Part of GMAW 132 MIG with flux cored electrode 133 MIG with metal cored electrode 136 MAG with flux cored electrode 138 MAG with metal cored electrode Part of SAW 124, 125, 126 tubular electrode

27 Basic parameters Positions : all positions Base material : structural steels, alloyed steels, Weld length : Welded thickness : 2-20 mm Current, voltage : I = A U = V Diameter Welding source : wires 0,8 1,6 mm : flat, AC, DC Filling: rutile, bazic, metal

28 Core filling Rutile the best outlook, easy removal, good operational properties All positions, shipyards CO 2 Bazic pure metal, good ductility and CTOD upto -60 C, need ceramic backing, all positions, yet welding is substantially different from solid wire, bridges, seashore platforms, Metal metal powder inside, no slag multilayer welds, thin and thick plates welding suitable Self shielding no need for shielding gas, mainly only structural steels

29 Ceramic backing for full penetration welding

30 Arc welding processes comparison of effectivity Selection of welding processes is done on base of technological capability, quality and costs Deposition rates for various welding processes (Uhrig, 1983) www.

31 FCAW characteristics Advantages Less cleaning, good self shielding protection High deposition rates (higher than SMAW) Continuous electrode Easily automated Deeper penetration Drawbacks Slag creation Fumes Price spatter