Welding electrode

It describes about welding electrode flux coating, specification of welding rod and specification

1. WELDING ELECTRODE
P.GANESAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
KAMARAJ COLLEGE OF ENGINEERING AND TECHNOLOGY
VIRUDHUNAGAR

2. 1.Specifications of AC transformer / DC generator
2.AC Vs DC welding
3.MIG Vs TIG welding
4.Flux coatings
5.Coding of electrodes
6.Selection of electrodes

3. SPECIFICATIONS
•AC transformer
•Stepdowntransformer
•Oilcooled
•3Ø
•50Hz
•50to400A
•OCV:50to90V
•Energyconsumption:4
KWhperkgofmetal
deposit
•PowerFactor=0.4
•Ƞ=85%
•DC generator
•Motorgenerator
•3Ø
•50Hz
•125to600A
•OCV:30to80V
•Energyconsumption:6to
10KWhperkgofmetal
deposit
•PowerFactor=0.4
•Ƞ=60%

4. Comparison between AC & DC arc welding
Sl.
No.
Aspect AC welding DC welding
1 Power consumptionLow High
2 Arc stability Arc unstable Arc stable
3 Electrode Only coated electrodes Bare electrodes are also used
4 Polarity Work cathode, Electrode
anode.
Vice versa is also possible
Electrode is mostly negative,
Work is positive
5 Suitability Non-ferrous metals cannot
be joined
Suitable for both ferrous &
non-ferrous metals
6 Weldingof thin
sections
Not preferred Preferred
7 Operation Noiseless (transformer)Noisy (generator)
8 Efficiency High(85%) Low (60%)
9 Weight Light Heavy
10Cost Less More

5. Differences between MIG & TIG welding
Sl.
No.
Aspect MIG TIG
1Name Metal Inert Gas Welding Tungsten Inert Gas welding
2Electrode Consumable metallic Non-consumable Tungsten
3Electrode feedMotorfeeds the wire from the
reel
Notrequired
4Electrode holderWelding gun or Torch with facility
to continuously feed the wire
Welding torch, with a cap
fitted at the back to cover the
tungsten electrode
5WeldingcurrentDC, reverse polarity Both AC & DC can be used
6Feed metal Fine wire Filler metal may or may not be
used
7Base metal
thickness
Upto40 mm Upto5 mm
8Welding speedFast Slow

6. Flux coatings
➢Coating layer thickness: 1 to 3 mm
➢Weight of the coating: 15 to 30 % of the electrode
INGREDIENTS:
1.Slag forming ingredients
2.Arc stabilisingingredients
3.Deoxidizing ingredients
4.Alloying constituents (to improve strength & quality of weld)
5.Binding materials

7. 1. Slag forming ingredients
•Asbestos
•Mica
•Silica
•Fluorspar (CaF2)
•Titanium dioxide
•Iron oxide
•Magnesium carbonate
•Calcium carbonate
•Aluminium oxide

8. 2. Arc stabilisingingredients
(ionisingagents)
•Potassium silicate
•Ti O2 + ZrO2 (Rutile)
•Mica
•Calcium oxide
•Sodium oxide
•Magnesium oxide
•Feldspar (K Al Si3 O8)
Major types of feldspars:
i) Potash feldspar (K2 O. Al2O3. 6SiO2)
ii) Sodium feldspar (Na2O. Al2O3. 6SiO2)
iii) Lime feldspar (CaO. Al2O3. 6SiO2)

9. 3. Deoxidizing ingredients
•Cellulose
•Calcium carbonate
•Dolomite
•Starch
•Dextrin
•Wood flour
•Graphite
•Aluminium
•Ferro-manganese

10. 4. Alloying constituents
(to improve strength & quality of weld)
•TiO2 & Potassium compounds:
To increase the melting rate of the base metal
for better penetration
•Fe powder:
For higher deposition rate
•Va, Ca, Mb, Zr, Cr, Ni, Mn, W

11. 5. Binding materials
•Sodium silicate
•Potassium silicate
•Asbestos

12. TYPES OF ELECTRODE COATINGS
•Four main types:
i) Cellulosic coating
ii) Rutilecoating (TiO2)
iii) Iron Oxide coating
iv) Basic coating (Lime stone coating)

13. CODING OF ELECTRODES
➢IS:815-1974…Code designation for coated stick
electrodes for metal arc welding
……To select a correct electrode for a
specific application
➢The coding consists of
i) a prefix letter,
ii) a code number of 6 digits,
iii) one or more suffix letters.
e.g. E 426 513 H
MethodofManufacture
TypeofCovering
WeldingPosition
Current
Tensilestrength
Yieldstress
%elongation
Specialproperties

14. ➢Prefix letter indicates the method of manufacturing
of electrode
e.g. E…solid extrusion
R…extruded with reinforcement

15. ➢Thefirstdigitindicatesthetypeofcovering
e.g.
1…high cellulose content
2…high titaniacontent; fairly viscous slag
3…appreciable amount of titania; fluid slag
4…high content of oxides/silicates of Fe, Mn;
produces an inflated slag
5…high content of oxides/silicates of Fe;
heavy solid slag
6…high content of Ca Co3, Ca F2
9…a covering of any other type, not classified
above

16. ➢Theseconddigitindicatestheweldingposition
e.g.
0…F, H, V, D, O
1…F, H, V, O
2…F, H
3…F
4…F, Hf
9…any other welding position not classified
above
F=Flatwelding
H=Horizontal
V=Verticalup
D=Verticaldown
O=Overhead
Hf=Horizontalfillet

17. ➢Thethirddigitindicatestheweldingcurrent
conditionsrecommended bytheelectrode
manufacturer
e.g.
0…D +
1…D +, A 90
2…D -, A 70
3…D -, A 50
4…D +, A 70
5…D±, A 90
6…D±, A 70
7…D±, A 50
9…any other current conditions not classified above
D+meansDCwithelectrodepositive
D–meansDCwithelectrodenegative
D±meanselectrodepositiveornegative
A90meansAC,withanopencircuitvoltagenotlessthan90
V
A70meansAC,withanopencircuitvoltagenotlessthan70
V
A50meansAC,withanopencircuitvoltagenotlessthan50
V

18. ➢Fourth&fifthdigitsindicatemechanicalproperties
viz.tensilestrength&yieldstress
e.g.
Range of tensile
strength(N/mm2)
Minimum yield stress
(N/mm2)
41 410 to 510 330
51 510 to 610 360

19. ➢Sixthdigitindicatesthe%elongationincombination
withimpactvalueofdepositedmetal
e.g.
Strength codeMinimum elongation in %
0 41 0 %
1 41 20 %
2 41 22 %
3 41 24 %
4 41 24 %
5 41 24 %
0 51 0 %
1 51 18 %
2 51 18%
3 51 20 %
4 51 20 %
5 51 20 %

20. ➢Suffixlettersindicatethe special
properties/characteristics
e.g.
H…hydrogen controlled electrode
J…iron powder covering; metal recovery 110 to 130 %
K…iron powder covering; metal recovery 130 to 150 %
L…iron powder covering; metal recovery above 150 %
P…deep penetration
X…radiographic weld quality

21. SELECTION OF ELECTRODES
•Selectionofaproperelectrodeforelectricarcweldingisvery
importanttoobtainagoodweldedjointwithproperstrength.
•Selectiondependson:
1)Powersource(ACorDC)
2)Compositionofthebasemetal
3)Thicknessofbasemetal
4)Weldingposition
5)Weldingcurrent(asperelectrodemanufacturer’s
recommendation)
6)Mechanicalpropertiesdesiredinthejoint
7)Penetrationrequired
8)Costconsiderations
➢Thediameteroftheelectrode,current&voltagerequirements
arebasicallyrelatedtothethicknessofthemetaltobejoined.

22. SELECTION OF ELECTRODE