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Fluxes in welding

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

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Fluxes in welding

  1. 1. 10/16/2014 1 FLUXES FOR WELDING BY JABIN MATHEW BENJAMIN 13MY04 DEPT. OF METALLURGICAL ENGINEERING
  2. 2. NEED FOR FLUXES 10/16/2014 2  Oxide Formation  Sources of O2  Oxide fluxes  Atmosphere air  Slag-metal reactions  Effects  Reduces hardenability of weld  Promotes porosity  Produces inclusions
  3. 3. NEED FOR FLUXES 10/16/2014 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. 4. FLUXES 10/16/2014 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. 5. Types Of Fluxes 10/16/2014 5  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. 6. Basicity Index 10/16/2014 6  B.I = B.I < 1 : ACIDIC FLUX 1 < B.I < 1.2: NEUTRAL FLUX B.I > 1.2 : BASIC FLUX
  7. 7. Oxide Fluxes 10/16/2014 7 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. 8. Functions of flux components 10/16/2014 8  CaO  Strong desulfurizer  MnO  Increased penetration  SiO2  Lower content increases the width to depth ratio.
  9. 9. Slag Formation 10/16/2014 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. 10. Shielded Metal Arc Welding 10/16/2014 10 Electrode is covered with flux material which performs the functions.
  11. 11. 10/16/2014 Flux-cored Arc Welding (FCAW) 11  Uses a hollow wire filled with flux reagents and ferro-additions.
  12. 12. FCAW Fluxes 10/16/2014 12  Carbon-dioxide-shielded FCAW  Titania  Lime  High CO2 content as carbonates  Self-shielded FCAW  Fluorspar-aluminum  Fluorspar-titania  Low CO2 content
  13. 13. Submerged Arc Welding FLUXES USED: •Manganese silicate •Aluminate basic •Alumina 10/16/2014 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.
  14. 14. 10/16/2014 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. 15. Fluxes and Weld Penetration 10/16/2014 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. 16. Finally a welding flux must also.. 10/16/2014 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. 17. Reference 10/16/2014 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. 18. THANKYOU 10/16/2014 18

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