Submerged Arc Welding (SAW) Agenda. Functions, basic rules to choose consumables. Storage and treatments before application

Transcription

1 Submerged Arc Welding (SAW) Professor Pedro Vilaça * * Contacts Address: P.O. Box 14200, FI Aalto, Finland Visiting address: Puumiehenkuja 3, Espoo pedro.vilaca@aalto.fi ; Skype: fsweldone January 2015 Agenda Process fundaments Equipment and accessories Welding parameters Types of consumables Functions, basic rules to choose consumables Storage and treatments before application Variants from original SAW Advantages and limitations Typical applications and imperfections 2 1

2 Fundaments Contact Nozzle Electrode Molten Slag Slag Torch Flux Feeding Hose Bulk Flux Solidified Weld Metal Weld Pool Electric Arc Welding direction Base Material 3 Fundaments SAW is a fusion process where the electric arc is the source of the heat for fusion of: filler metal + flux + base material (with some dilution rate, DR) The electric arc (submerged by a granulated flux) is established between a consumable filler metal and the base materials in a plasmogenic environment mostly resulting from the evaporation of the flux 4 2

3 Fundaments Filler Metal Manual Torch Flux Hopper Bobbin of Filler Metal Control System Power Source Base Material Automatic Flux Feeder 5 Fundaments The flux protects the weld fusion zone and molten drops transferred from the filler metal The flux constituents enable: Creation of an appropriate easy to ionize gas environment to form the plasma for the electric arc Generation of a slag to cover molten metal during solidification and cooling Improve chemical composition of weld metal Promoting a stable transference of the filler metal into the weld bead 6 3

4 Fundaments Transformer Transformer/Rectifier: Conventional or Inverter Power Source: AC/DCEN/DCEP Static Characteristic: V=f(I)? Generator/Alternator (rotative equipment) 7 Deposit Rates 8 4

5 Arc-Start Technics Short circuit: Shape of tip of the solid filler metal wire: i) bezel; ii) conical Start in run-on tabs (eventually with steel wool ) There are power sources with special arc start unit enabling slower start of the wire feed speed WFS 9 Main Equipament Power source System for control of parameters Wire feeder Weld head Feeding and recovering of flux Power and ground cables Ground clamp 10 5

6 Welding Head Components Unbending wire system Wire feeder system Power cable connection Contact nozzle Flux hopper Flux feeder Joint sensoring system DC Power sources Influence in weld bead morphology: DCEP (+): Higher penetration Higher Dilution Rate, DR Less susceptibility of internal porosity DCEN (-): Lower Dilution Rate, DR (good for coating) Higher deposition rates 30% + versus DCEP (+) DCEN (-) or DCEP (+) multiwire, then only 1 wire with electric arc 12 6

7 AC Power sources Sinusoidal near Square Intermediate deposition and/or penetration efficiency Less sensitive to arc blow effects In multiwire the leading wire is DCEP for higher penetration and the remaining wire in AC 13 Flux Feeder System Gravity (concentric or preceding) Venturi effect with compressed air 14 7

8 Welding Parameters Current (AC / DCEP / DCEN) / WFS Voltage / length of EA Welding travel speed Binary: Filler wire + Flux (composition) Diameter of the filler metal /granulometry of flux Stick-out ( 8 x ) 15 Typical Control Unit Current / WFS Voltage Welding travel speed 16 8

9 Control of the Stability of the EA Horizontal static characteristic (enables Self-regulation effect ) Constant WFS system Joule effect is important (control of stick-out!) WFS=a. I + b. l. I 2 Vertical static characteristic: Electronic monitoring of EA voltage Variable WFS system 17 Influence of Current Weld Bead Morphology Square Groove V Groove

10 Influence of Voltage Weld Bead Morphology Square Groove V Groove Influence of Welding Speed Weld Bead Morphology Cracking (big width) + Inclusions (due to amount of slag) Square Groove Undercut + Porosity Less alloying effect V Groove

11 Influence of Wire Diameter Weld Bead Morphology Diameter Diameter Diameter 21 Influence of Thickness of Layer of Flux Weld Bead Morphology Lack of protection Layer of flux Weld bead Slag Layer of flux Weld bead Inclusions and porosity Weld bead Layer of flux Slag Slag 22 11

12 Influence of Stick-Out Deposition Rate Stick-Out Stick-Out WFS Current Deposition Rate 23 Data about Consumables Wire diameter 2.3; 2.4; 3.2; 4.0; 4.8; 5.6 and 6.4 mm Width of Strip 60; 80; 100; 120 and 180 mm Thickness of Strip 0.6; 0.8 and 1.0 mm Binary Wire/Flux depends: Material composition of BM Thickness to weld 24 12

13 Data about Consumables Diameter Current range 25 Consumables Solid or Fluxed Wire Strip 26 13

14 Strips: Solid and Fluxed Coatings (hardfacing) Difficult to achieve stable EA width > 120 mm 27 Type of Fluxes Classification in according to manufacturing: Fused Bonded (Agglomerated) Mixed 28 14

15 Type of Fluxes 29 Type of Fluxes 30 15

16 Type of Fluxes Types (level of PH): Neutral 1 IB 1,5 Acid IB < 1 Basic IB > 1,5 Do not insert alloy elements and deoxidants Insert alloy elements e.g. Mn ; Si Basic Index (BI): CaO + CaF MgO + K2O + Na2 + Li2O + BI = 2 SiO ( Al ) 2 2O3 + TiO2 + ZrO2 MnO + Fe 31 Type of Fluxes 32 16

17 Flux Granulometry Size Symbol Better for gases evacuation Better for conducting current 33 Storage Armazém Geral: About 25-30ºC Relative humidity 40 a 60% 34 17

18 Consumables- Basic fluxes Typically: 250ºC 50ºC, about 2h Manufacturer specifications 35 Consumables Recovering and dry of fluxes 36 18

19 Variants: SAW Strip Predeposit of Iron powder 37 Variants: SAW Multi-wire Parallel 38 19

20 Variants: SAW Multi-wire Tandem 39 Variants: SAW Multi-wire with rotation Parallel to Tandem 40 20

21 Conventional SAW One-wire 41 Variants: SAW Multi-wire 2 wires 2 power sources 42 21

22 Variants: SAW Multi-wire 2 wires 1 power source 43 Variants: SAW Multi-wire 2 wires 1 power source 44 22

23 Variants: SAW Multi-wire 2 wires 1 power source 45 Variants: SAW Multi-wire 3 wires 3 power sources 46 23

24 Variants: SAW Multi-wire 3 wires 3 power sources 47 Variants: SAW Multi-wire ESAB has developed Integrated Cold Electrode (ICE ) 48 24

25 Variants: SAW Multi-wire Integrated Cold Electrode (ICE ) 49 Variants: SAW Multi-wire Integrated Cold Electrode (ICE ) 50 25

26 Variants: SAW Multi-wire Integrated Cold Electrode (ICE ) 51 Variants: SAW Multi-wire 52 26

27 Variants: SAW Narrow Gap 53 Variants: SAW Narrow Gap 54 27

28 Variants: SAW with positional sensors 55 Variants: SAW with positional sensors 56 28

29 Variants: SAW with special positioners 57 Variants: SAW with special positioners 58 29

30 Variants: SAW with special positioners 59 Variants: SAW with special positioners 60 30

31 Variants: SAW with special positioners 61 Variants: SAW with special positioners 62 31

32 Butt Joint Design in SAW Chanfros / Juntas Square Groove t 12 mm V Groove 12 mm t 25 mm Weld root 63 Butt Joint Design in SAW X Groove 25 mm t 40 mm Weld root 64 32

33 Butt Joint Design in SAW Type of Grooves 65 Joint Preparation in SAW To avoid defects (e.g. lack of fusion, porosity, inclusions, cracking): Mechanical cleaning (joint line in BM) E.g: Oxides, galvanized (zinc), paint Chemical cleaning (joint line in BM and FM) E.g.: Oil, other lubricants Moisture (induce cracking and porosity) 66 33

34 Defects in SAW Lack of Fusion / lack of penetration (kissing-bonds) Joint preparation, Parameters Porosity Oil, Shielding effect, Voltage control Slag Inclusions Cleaning, Parameters Undercut Parameters, Operative Technic Hot/Cold Cracking Metallurgical Problems 67 Defects in SAW Alignment of FM with weld joint line: 68 34

35 Advantages Uses current DCEP/DCEN/AC Duty-cycle = 100% Deposition rates superior to 2.5 kg/h ( filling passes and coating) Automatize process that may use more than one electrode High penetration capacity Highly resistance to contamination 69 Disadvantages Limited weld positioning: accessibility and mobility Feasible for rectilinear joints Susceptibility of slag inclusions Not good for root pass Manual welding very difficult Non visible electric arc and metal transference Demand position sensors High set-up time 70 35

36 Typical Applications 71 Typical Applications 72 36