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Transcript of Submerged Arc Welding · PDF fileSubmerged Arc Welding (SAW) • Part 1 – The SAW...

Submerged Arc Welding:

A discussion of the welding process and

how welding parameters affect the

chemistry of Corrosion Resistant

Overlays (CRO)

1

Submerged Arc Welding (SAW)

Part 1

The SAW welding process

Part 2

Effects of welding parameters on weld metal

chemistry of corrosion resistant overlays (CRO)

2

Process Characteristics

High deposition rates compared to other welding processes

Faster travel speeds compared to other welding processes

Economical - High deposition rates and high travel speeds reduce overall costs

3

SAW Process Advantages

Simple - mechanized process, easy to train machine operators

Clean environment - minimal smoke or fumes

Operator friendly - no visible arc, no spatter

4

Process Limitations

Welding is done in the flat position

Can your part be positioned to weld in the flat

position?

Can circumferential welds be rotated?

5

SAW Process

Flux covers weld

zone in front of wire

Heat of the arc melts

the wire, flux and plate

Fused flux shapes and

protects weld metal

Weld metal

6

Welding Power Supply

Supplies electrical power to the electrode - The heat of the arc melts the electrode and base

plate to form the weld bead.

Electrical current can be:

AC or DC

CV (constant voltage) or CC (constant current)

7

Influence of Polarity

DCEP - Deep penetration

DCEN - Shallow penetration

AC - Penetration is in between DCEP and DCEN

DCEP AC DCEN

8

Function of the Wire

Carries the welding current for the welding arc

Weld filler metal

Weld metal chemistry

Weld metal mechanical properties

9

Function of the Flux

Molten flux shields the weld pool

Affects weld metal chemistry

Affects weld metal mechanical properties

Affects weld performance/characteristics

Fluxes have variable burn-off rates

10

Types of Fluxes

Neutral

Multi-pass, unlimited thickness, high toughness

Active

High in deoxidizers, high speed, weld over rust,

limited thickness

Alloyed

Addition of Cr, Ni , enhanced mechanical properties

11

Welding Variables

Welding current

Arc voltage

Travel speed

Wire size

Wire extension

12

Welding Current

Controls Penetration and deposition rate

current = penetration

current = burn-off rate

current = deposition rate

13

Welding Current

500 amps @ 35 V 600 amps @ 35 V

.256.336

20 ipm

0.651 0.780

14

Arc Voltage

Arc voltage is a measure of arc length

voltage = bead width

voltage = penetration

15

Welding Voltage

500 amps @ 35 V 500 amps @ 30 V

.256 .273

20 ipm

0.657 0.629

16

Welding Voltage

600 amps @ 35 V 600 amps @ 28 V

.336.427

20 ipm

0.7720.503

17

Travel Speed

Controls - penetration and volume of metal per unit length

speed = penetration

speed = weld size, width, reinforcement

18

Travel Speed

All welds made at 500 amps and 35 volts

20 ipm 25 ipm 30 ipm 35 ipm

0.669 0.635 0.547 0.490

0.277 0.236

19

Wire Size / Burn-off Rates

Wire Burn-off rates (ipm) vs. Amps

DCEP - 10-15% Less

DCEN - 10-15% More

Electrode Stick-out = 8X wire diameter

20

Wire Stick-out

Wire stick-out should be about 8 times the wire diameter - (1/8 wire = 1 )

Electrical Stick-Out (ESO) - Tip-to-work distance

Stick-out

Work

Tip

21

Effects of ESO

Longer stick-out At the same wire feed speed, decreases welding current and penetration

Longer stick-out At the same current, increases deposition due to the higher burn-off rate

As stick-out increases, the wire feed speed must be

increased to maintain the same welding current.

22

Effects of ESO on Deposition Rate

3/32 ERNiCrMo-3 wire at 250 amps

10.7

11.9

13

9

10

11

12

13

14

0.5 0.75 1 1.25 1.5 1.75 2

De

po

siti

on

ra

te,

lbs.

/hr.

ESO, in.

Effects of Electrode Stick-out (ESO) on

Deposition Rate, lbs./hr.

23

PART II

Effects of welding parameters on

weld metal chemistry of CRO

24

Everyone is looking for:

Increased production

Increased welding speeds

Increased deposition rates

Reduced base metal dilution

25

Deposition rates for CRO

0

10

20

30

40

50

60

GTAW-HW SAW Wire SAW 30 mm Strip ESW 60 mm Strip

De

po

siti

on

-lb

s./h

r.

PROCESS

26

Flux selection

Good slag peeling on SS and Ni alloy

Good edge wetting

Cr compensating (SS)

Cr or Ni additive (SS & Ni)

27

Flux selection

Slag sticking to weld

bead with flux - A

After slag removal some

small spots remain

Flux B was self-

peeling but still has tiger

stripes

28

Flux selection

Free peeling slag with flux - C

Smooth surface with

excellent wetting along

edges of weld bead

29

CRO requirements for ERNiCrMo-3

Two-layer deposit

Thickness 1/8per layer, 1/4 total

Chemistry Fe-5 or Fe-10 at 1/8 above original surface

30

Dilution

Dilution the percentage of base metal in the weld bead.

A

B

% Dilution = [B(A+B)] (100)

Weld BeadBase Metal

31

Objectives

Determine what welding parameters control weld metal chemistry.

Achieving Fe-10 or Fe-5 in two layers

32

Layer Thickness

First layer needs to be close to 0.125 thick so second layer fusion line is below 0.125.

The chemistry at 1/8 needs to come out of the second layer and not the first.

33

Weld cross sections

Second Layer fusion line needs to be

below the 1/8 above original surface.

Too much penetration will cause too

much dilution in the second layer

chemistry.

Second layer fusion line is below

the 1/8 above original surface.

There are thee small areas visible

from the second layer, but it wont

pass chemistry.

1/8

1/8

1/8

34

Factors Affecting Chemistry

Amperage

Voltage

Travel speed

Electrical stick-out (ESO), Tip-To-Work distance

Step-over distance

35

Amperage

Effects of Amperage on chemistry and

deposition rate.

3/32 wire, 1 ESO, 32 volts, 20 ipm

Amperage has little effect on chemistry

Amps / Sample 250 / A 300 / B 350 / C

Deposition, lbs./Hr. 10.7 13.0 15.5

Chemistry, % Fe 41.14 40.84 44.78

36

Amperage

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

200 220 240 260 280 300 320 340 360

We

ld D

ime

nsi

on

s, i

n

Amperage

Effect of Amperage on Weld Dimensions

Bead Height

Bead Width

Depth of Fusion

37

Voltage

Effects of Voltage on chemistry

3/32 wire, 1 ESO, 250 amps, 20 ipm

Voltage has no significant effect on

chemistry

Voltage / Sample 28 / D 30 / E 32 / F

Chemistry, % Fe 41.07 40.23 41.55

38

Voltage

0.000

0.100

0.200

0.300

0.400

0.500

0.600

27 28 29 30 31 32 33

We

ld D

ime

nsi

on

s, i

n

Voltage

Effect of Voltage on Weld Dimensions

Bead Height

Bead Width

Depth of Fusion

39

Travel Speed

Effects of travel speed on chemistry

3/32 wire, 1 ESO, 250 amps, 32 volts

Travel speed has little effect on chemistry

Travel Speed (ipm) 16 / G 20 / H 24 / I

Chemistry, % Fe 40.76 41.55 42.50

40

Travel Speed

0.000

0.100

0.200

0.300

0.400

0.500

0.600

15 17 19 21 23 25

We

ld D

ime

nsi

on

s, i

n

Travel Speed, in/min

Effect of Travel Speed on Weld Dimensions

Bead Height

Bead Width

Depth of Fusion

41

Weld Study Constants

All the welds for this study were made using 3/32 diameter ERNiCrMo-3 wire.

All the remaining welds were made at 32 volts.

All the remaining welds were made at 24 ipm travel speed.

42

Electrical stick-out (ESO)

If amperage is held constant:

Wire feed speed must increase as ESO increases

What happens to dilution?

% Dilution = [B(A+B)] (100) AB

43

Electrical Stick-out

Effe