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SAW FUNDAMENTALS. Principles of operation Factors that determine whether to use SAW chemical composition and mechanical properties required for the.

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Presentation on theme: "SAW FUNDAMENTALS. Principles of operation Factors that determine whether to use SAW chemical composition and mechanical properties required for the."— Presentation transcript:

1 SAW FUNDAMENTALS

2 Principles of operation

3

4 Factors that determine whether to use SAW chemical composition and mechanical properties required for the weld depositchemical composition and mechanical properties required for the weld deposit thickness of base metal to be weldedthickness of base metal to be welded joint accessibilityjoint accessibility position in which the weld is to be madeposition in which the weld is to be made frequency or volume of welding to be performedfrequency or volume of welding to be performed

5 Principles of operation SAW methods semiautomatic - for relatively small diameter electrodes and moderate travel speedsemiautomatic - for relatively small diameter electrodes and moderate travel speed mechanised - the majority of applicationsmechanised - the majority of applications automatic - for mass production (e.g. pipes)automatic - for mass production (e.g. pipes)

6 Principles of operation SAW methods features Semiautomatic Mechanised Automatic Starts and maintains the arc Machine Machine Machine Feed the electrode Machine Machine Machine Control heat input Person Machine Machine Provide travel speed Person Machine Machine

7 Principles of operation SAW methods features Semiautomatic Mechanised Automatic Guides the arc along the joint Manipulates welding head to direct the arc Person Person Machine Corrects arc to overcome deviations Person Person Does not correct! Person Person Machine

8 Advantages/disadvantages Advantages of SAW high current density  high deposition rates (up to 10 times those for MMA)  high productivityhigh current density  high deposition rates (up to 10 times those for MMA)  high productivity deep penetration  small welding groovesdeep penetration  small welding grooves fast travel speed  less distortionsfast travel speed  less distortions deslagging is easydeslagging is easy uniform bead appearance with good surface finish  good fatigue propertiesuniform bead appearance with good surface finish  good fatigue properties can be easily performed mechanised  high duty cycle and low skill level requiredcan be easily performed mechanised  high duty cycle and low skill level required provide consistent quality when performed automatic/mechanised  assure radiographically sound weldsprovide consistent quality when performed automatic/mechanised  assure radiographically sound welds arc is not visiblearc is not visible little smoke/fumes are developedlittle smoke/fumes are developed

9 Advantages/disadvantages Disadvantages of SAW limited mainly to flat/horizontal positionlimited mainly to flat/horizontal position limited to carbon, low alloy, creep resisting and stainless steels; also nickel alloyslimited to carbon, low alloy, creep resisting and stainless steels; also nickel alloys due to the high heat input, impact strength of weld metal/HAZ may be low; also high dilutiondue to the high heat input, impact strength of weld metal/HAZ may be low; also high dilution slag must be cleared away after welding  danger of slag inclusionsslag must be cleared away after welding  danger of slag inclusions need flux storage, handling and recirculation controlneed flux storage, handling and recirculation control difficult to apply on-site due to complicated equipmentdifficult to apply on-site due to complicated equipment high capital costshigh capital costs weld line must be regular (straight or circumferential seams only) with accurate fit-upweld line must be regular (straight or circumferential seams only) with accurate fit-up

10 SAW equipment Power sources can be: transformers for ACtransformers for AC transformer-rectifiers for DCtransformer-rectifiers for DC Static characteristic can be: flat (CV) - most of the power sourcesflat (CV) - most of the power sources drooping (CC)drooping (CC)

11 SAW equipment Flat (CV) power sources: most commonly used supplies for SAWmost commonly used supplies for SAW can be used for both semiautomatic and automatic weldingcan be used for both semiautomatic and automatic welding self-regulating arc  simple wire feed speed controlself-regulating arc  simple wire feed speed control wire feed speed controls the current and power supply controls the voltagewire feed speed controls the current and power supply controls the voltage applications for DC are limited to 1000A due to severe arc blow (also thin wires!)applications for DC are limited to 1000A due to severe arc blow (also thin wires!)

12 SAW equipment Drooping (CC) power sources: can be used for both semiautomatic and automatic weldingcan be used for both semiautomatic and automatic welding not self-regulating arc  must be used with a voltage-sensing variable wire feed speed controlnot self-regulating arc  must be used with a voltage-sensing variable wire feed speed control more expensive due to more complex wire feed speed controlmore expensive due to more complex wire feed speed control arc voltage depends upon wire feed speed whilst the power source controls the currentarc voltage depends upon wire feed speed whilst the power source controls the current cannot be used for high-speed welding of thin steelcannot be used for high-speed welding of thin steel

13 Courtesy of ESAB AB SAW equipment Welding heads Wire feed motor Feed roll assembly Torch assembly Contact tip Tracking system Slides Wire reel Flux hopper Flux recovery system

14 SAW equipment Welding heads can be mounted on a: Tractor type carriage Column/beam carriage Courtesy of ESAB AB

15 SAW equipment Tractor type carriage provides travel along straight or gently curved jointsprovides travel along straight or gently curved joints can ride on tracks set up along the joint (with grooved wheels) or on the workpiece itselfcan ride on tracks set up along the joint (with grooved wheels) or on the workpiece itself can use guide wheels as tracking devicecan use guide wheels as tracking device due to their portability, are used in field welding or where the piece cannot be moveddue to their portability, are used in field welding or where the piece cannot be moved Courtesy of ESAB AB

16 Pilot lamp Guide wheel bogie Radius from 1500mm Inside welding from 1150 mm Simultaneous welding Guide rail with magnets Support-roller for fillet weld Idling-rollers SAW equipment

17 Column/beam carriage provides linear travel onlyprovides linear travel only are capable of linear motion in 3 axesare capable of linear motion in 3 axes because workpiece must be brought to the weld station, they are use mostly in the workshopbecause workpiece must be brought to the weld station, they are use mostly in the workshop Courtesy of ESAB AB

18 SAW equipment Ancillary equipment tilting-rotating positioners bring the area to be welded on irregular parts into flat positiontilting-rotating positioners bring the area to be welded on irregular parts into flat position Courtesy of ESAB AB

19 SAW equipment Ancillary equipment roller beads rotate cylindrical parts under the weld headroller beads rotate cylindrical parts under the weld head Courtesy of ESAB AB

20 SAW filler material Welding wires supplied on coils, reels or drumssupplied on coils, reels or drums coil (approx. 25 kg) random or line windingrandom or line winding reel (approx. 300 kg) drum (approx. 450 kg) Courtesy of ESAB AB Courtesy of Lincoln Electric

21 SAW filler material Welding wires can be used to weld: carbon steelscarbon steels low alloy steelslow alloy steels creep resisting steelscreep resisting steels stainless steelsstainless steels nickel-base alloysnickel-base alloys special alloys for surfacing applicationsspecial alloys for surfacing applications Welding wires can be: solid wiressolid wires metal-cored wiresmetal-cored wires

22 SAW filler material Welding wires: carbon and low alloy wires are copper coatedcarbon and low alloy wires are copper coated wires must be kept clean and free from oil and dustwires must be kept clean and free from oil and dust stainless steel wires are not coatedstainless steel wires are not coated Courtesy of Lincoln Electric

23 SAW filler material Copper coating functions: to assure a good electric contact between wire and contact tipto assure a good electric contact between wire and contact tip to assure a smooth feed of the wire through the guide tube, feed rolls and contact tip (decrease contact tube wear)to assure a smooth feed of the wire through the guide tube, feed rolls and contact tip (decrease contact tube wear) to provide protection against corrosionto provide protection against corrosion

24 SAW filler material Welding fluxes: are granular mineral compounds mixed according to various formulationsare granular mineral compounds mixed according to various formulations shield the molten weld pool from the atmosphereshield the molten weld pool from the atmosphere clean the molten weld poolclean the molten weld pool can modify the chemical composition of the weld metalcan modify the chemical composition of the weld metal prevents rapid escape of heat from welding zoneprevents rapid escape of heat from welding zone influence the shape of the weld bead (wetting action)influence the shape of the weld bead (wetting action) can be fused, agglomerated or mixedcan be fused, agglomerated or mixed must be kept warm and dry to avoid porositymust be kept warm and dry to avoid porosity

25 SAW filler material Fused welding fluxes Components are dry mixed Components are melted in an electric furnace Charge is cooled by: Shooting the melt through a stream of water Pouring melt onto large chill blocks Product is crushed and screened for size

26 SAW filler material Fused fluxes advantages: good chemical homogeneitygood chemical homogeneity easy removal of fines without affecting flux compositioneasy removal of fines without affecting flux composition normally not hygroscopic  easy storage and handlingnormally not hygroscopic  easy storage and handling readily recycled without significant change in particle size or compositionreadily recycled without significant change in particle size or composition Fused fluxes disadvantages: difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss)difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss) high temperatures needed to melt ingredients limit the range of flux compositionshigh temperatures needed to melt ingredients limit the range of flux compositions

27 SAW filler material Agglomerated welding fluxes Components are powdered and dry mixed Components are bonded The wet mix is pelletized Pellets are baked Pellets are broken up and screened for size

28 SAW filler material Agglomerated fluxes advantages: easy addition of deoxidizers and alloying elementseasy addition of deoxidizers and alloying elements usable with thicker layer of flux when weldingusable with thicker layer of flux when welding colour identificationcolour identification Agglomerated fluxes disadvantages: tendency to absorb moisturetendency to absorb moisture possible gas evolution from the molten slag leading to porositypossible gas evolution from the molten slag leading to porosity possible change in flux composition due to segregation or removal of fine mesh particlespossible change in flux composition due to segregation or removal of fine mesh particles

29 SAW filler material Mixed fluxes advantages: several commercial fluxes may be mixed for highly critical or proprietary welding operationsseveral commercial fluxes may be mixed for highly critical or proprietary welding operations Mixed fluxes disadvantages: segregation of the combined fluxes during shipment, storage and handlingsegregation of the combined fluxes during shipment, storage and handling segregation occurring in the feeding and recovery systems during weldingsegregation occurring in the feeding and recovery systems during welding inconsistency in the combined flux from mix to mixinconsistency in the combined flux from mix to mix Mixed fluxes - two or more fused or bonded fluxes are mixed in any ratio necessary to yield the desired results

30 SAW filler material From the chemical point of view, fluxes can be (see BS EN 760): Acid (contain acid oxides like SiO 2, Al 2 O 3, TiO 2, ZrO 2 ) NeutralBasic (contain basic oxides like FeO, MnO, NiO, CaO) High basic Welding characteristics (more stable arc, improved weld appearance, easier slag removal, higher welding speeds) Weld metal mechanical properties (YS, KV, UTS), amount in Mn and Si, melt temperature

31 SAW filler material Welding flux: can be supplied in bags/pails (approx. 25 kg) or bulk bags (approx. 1200 kg)can be supplied in bags/pails (approx. 25 kg) or bulk bags (approx. 1200 kg) handling and stacking requires carehandling and stacking requires care if flux is too fine it will pack and not feed properly  cannot be recycled indefinitelyif flux is too fine it will pack and not feed properly  cannot be recycled indefinitely Courtesy of Lincoln Electric

32 SAW filler material Wire/flux combination designation acc. BS EN 756: EN 756 - S 46 3 AB S2 Standard number Wire electrode and/or wire/flux combination Tensile properties Impact properties Type of welding flux Chemical composition of wire electrode EN 756 S 46 3 AB S2


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