Fluxes in welding- different types of fluxes, their constituents, basicity index, flux properties and function.

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FLUXES FOR WELDING
BY
JABIN MATHEW BENJAMIN
13MY04
DEPT. OF METALLURGICAL ENGINEERING

2. NEED FOR FLUXES
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 Oxide Formation
 Sources of O2
 Oxide fluxes
 Atmosphere air
 Slag-metal reactions
 Effects
 Reduces hardenability of weld
 Promotes porosity
 Produces inclusions

3. NEED FOR FLUXES
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 Inclusion Formation.
 Sources of inclusions
 Mechanical entrapment of nonmetallic slag
 Reactions between metallic alloy elements and nonmetallic
tramp elements
 Types
 Oxides
 Sulfides
 Nitrides
 Carbides

4. FLUXES
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 Added to the welding environment to improve arc stability
 The flux, by providing easily ionized atoms, plays an important
role in welding by improving arc stability.
 To provide a slag and with low density
 Covers the hot weld metal and protects it from the atmosphere.
 To add alloying elements
 To improve weld metal properties
 Refine the weld pool (deoxidation and desulfurization)
 To avoid formation to oxide and sulphide inclusions

5. Types Of Fluxes
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 Halide-type fluxes
 CaF2–NaF
 CaF2–BaCl2–NaF,
 KCl–NaCl–Na3AlF6
 Halide–oxide-type fluxes
 CaF2–CaO–Al2O3
 CaF2–CaO–SiO2
 CaF2–CaO–MgO–Al2O3.
 Oxide-type fluxes
 MnO–SiO2
 FeO–MnO–SiO2
 CaO–TiO2–SiO2.
•Oxygen free
•Used for Al and Ti
•Slightly oxidizing
•High-alloy steels
•Low-carbon or low alloy steels

6. Basicity Index
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 B.I =
B.I < 1 : ACIDIC FLUX
1 < B.I < 1.2: NEUTRAL FLUX
B.I > 1.2 : BASIC FLUX

7. Oxide Fluxes
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Basic Oxides
K2O, Na2O, CaO, MgO
Acidic Oxides
SiO2, TiO2, P2O5
Amphoteric Oxides
Al2O3, Fe2O3, Cr2O3
•Donors of free
oxide ions
•Cleaner weld
•Lower non metallic
inclusions
•High toughness of
weld
•Greater tendency
to absorb moisture
•Slag detachability
not be very good
•Acceptors of oxide
ions
•Excellent slag
behavior
•Improves weld bead
morphology
•High deposition rate
•Moderate strength
weld
•Rust proof
•High welding speed
•Neutral oxide

8. Functions of flux components
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 CaO
 Strong desulfurizer
 MnO
 Increased penetration
 SiO2
 Lower content increases the width to depth ratio.

9. Slag Formation
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 Slag  a mixture of glass and crystalline structure
 Properties required
 Melt below the melting temperature of base metal
 Density less than base metal to reduce slag entrapment
 Must possess proper viscosity in the temperature range of
1450 to 1550 °C
 Easily detach from the weld deposit
 Function
 Solidify on the weld deposit to protect the surface from
oxidation during cooling.

10. Shielded Metal Arc Welding
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Electrode is covered with flux material which performs the functions.

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Flux-cored Arc Welding (FCAW)
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 Uses a hollow wire filled with flux reagents and ferro-additions.

12. FCAW Fluxes
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 Carbon-dioxide-shielded FCAW
 Titania
 Lime
 High CO2 content as carbonates
 Self-shielded FCAW
 Fluorspar-aluminum
 Fluorspar-titania
 Low CO2 content

13. Submerged Arc Welding
FLUXES USED:
•Manganese silicate
•Aluminate basic
•Alumina
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The flux is supplied from a hopper, which travels with the torch. No
shielding gas is needed because the molten metal is separated
from the air by the molten slag and granular flux.

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 Bonded fluxes
 Non metallic and ferro additions with low temperature
binders
 Agglomerated fluxes
 Similar to bonded but used with ceramic glass binder
cured at high temperature
 Fused fluxes
 Homogeneous glass mixture of proper flux mixture into
water

15. Fluxes and Weld Penetration
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 High viscosity
 Confine the molten weld pool
 Increases the heat input for a given area
 Deeper penetration.
 Flux composition
 Affects arc stability
 More ionized particles more stable arc
 A more stable arc will produce deeper penetration
 Surface tension
 Increases weld penetration.

16. Finally a welding flux must also..
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 Stabilize arc and control arc resistivity
 Permit use of different types of current and polarity
 Promote slag detachability
 Produce smooth weld contour
 Reduce spatter and fume

17. Reference
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 Jackson, C. E., "Fluxes and Slags in Welding," W. R. C Bulletin, 190,
(1977).
 Janzen, H. E„ "An Investigation of the SiO-MnO-CaO/CaF2 Welding
Flux System, "Thesis, Colorado School of Mines,T-1970, (1977).
 ASM handbook, Vol. 6.

18. THANKYOU
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