10/16/2014

1

FLUXES FOR WELDING

BY

JABIN MATHEW BENJAMIN

13MY04

DEPT. OF METALLURGICAL ENGINEERING

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

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

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

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

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

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

Functions of flux components

10/16/2014

8

CaO

Strong desulfurizer

MnO

Increased penetration

SiO2

Lower content increases the width to depth ratio.

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.

Shielded Metal Arc Welding

10/16/2014

10

Electrode is covered with flux material which performs the functions.

10/16/2014

11

Flux-cored Arc Welding (FCAW)

Uses a hollow wire filled with flux reagents and ferro-additions.

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

Submerged Arc Welding

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.

FLUXES USED:•Manganese silicate•Aluminate basic•Alumina

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

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.

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

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.

THANKYOU

10/16/2014

18