Fluxes in welding

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

1. 29-Jan-14 1 FLUXES FOR WELDING BY JABIN MATHEW BENJAMIN 13MY04 DEPT. OF METALLURGICAL ENGINEERING

2. NEED FOR FLUXES 29-Jan-14 2 Oxide Formation Sources of O 2 Oxide fluxes Atmosphere air Slag-metal reactions Effects Reduces hardenability of weld Promotes porosity Produces inclusions

3. NEED FOR FLUXES 29-Jan-14 3 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 29-Jan-14 4 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 29-Jan-14 5 Halide-type fluxes CaF 2 –NaF CaF 2 –BaCl 2 –NaF, KCl–NaCl–Na 3 AlF 6 Halide–oxide-type fluxes CaF 2 –CaO–Al 2 O 3 CaF 2 –CaO–SiO 2 CaF 2 –CaO–MgO–Al2O 3 . Oxide-type fluxes MnO–SiO 2 FeO–MnO–SiO 2 CaO–TiO 2 –SiO 2 . Oxygen free Used for Al and Ti Slightly oxidizing High-alloy steels Low-carbon or low alloy steels

6. Basicity Index 29-Jan-14 6 B.I = B.I < 1 : ACIDIC FLUX 1 < B.I < 1.2 : NEUTRAL FLUX B.I > 1.2 : BASIC FLUX

7. Oxide Fluxes 29-Jan-14 7 Basic Oxides K 2 O, Na 2 O, CaO , MgO Acidic Oxides SiO 2 , TiO 2 , P 2 O 5 Amphoteric Oxides Al 2 O 3 , Fe 2 O 3 , Cr 2 O 3 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 29-Jan-14 8 CaO Strong desulfurizer MnO Increased penetration SiO 2 Lower content increases the width to depth ratio.

9. Slag Formation 29-Jan-14 9 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 29-Jan-14 10 Electrode is covered with flux material which performs the functions.

11. 29-Jan-14 11 Flux-cored Arc Welding ( FCAW ) Uses a hollow wire filled with flux reagents and ferro -additions.

12. FCAW Fluxes 29-Jan-14 12 Carbon-dioxide-shielded FCAW Titania Lime High CO 2 content as carbonates Self-shielded FCAW Fluorspar-aluminum Fluorspar- titania Low CO 2 content

13. Submerged Arc Welding 29-Jan-14 13 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. FLUXES USED: Manganese silicate Aluminate basic Alumina

14. 29-Jan-14 14 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 29-Jan-14 15 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.. 29-Jan-14 16 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 29-Jan-14 17 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 29-Jan-14 18