weld 1100 - shielded metal arc welding - College of Eastern Utah

WELD 1100 -
SHIELDED METAL ARC WELDING
Lon Youngberg
College of Eastern Utah
2006 Revision

Main Areas of Study
Welding Safety
Intro to Welding Power
Shielded Metal Arc Welding - Chapter 2
Electrode Classification and Selection
Common Terminology
Oxy-Fuel Cutting - Chapter 14

Input Power
Common household power is single phase 120 volts,
alternating current (120VAC) at 60 hertz frequency. Most
households also contain single phase 220 VAC for heavy duty
appliances (clothes dryers and furnaces).
Heavy industry also has single phase 120 and 220 VAC for
running lights and low-power appliances. However, most
heavy industrial equipment operates from 3-phase power at
voltages ranging from 220 to 480 VAC.
A welding power source must convert high voltage/low current
input power to low voltage/high amperage welding current.

Output Power
The electricity coming out of welding power
sources can be either Alternating Current
(AC), Direct Current Electrode Positive
(DCEP also called Reverse Polarity), or
Direct Current Electrode Negative (DCEN
also called Straight Polarity).
– REPublican SENator
(handout or demo for switching polarity.)

Output Power (cont.)
Typical open circuit voltage for the SMAW process is 60 to
80 Volts.
Typical arc voltage (while welding) is 23 to 27 volts. A
short arc gap will cause the number to be lower and a long
arc gap will cause it to be higher.
The amperage is set by the knob on the SMAW machine
and typically ranges from about 60 amps to 200 amps.
A recommended amperage range is available for every
type and size of rod. Then you adjust up or down from the
middle of the range depending on welding position,
desired depth of penetration, joint type, etc..

Output Power (cont.)
Welding machines are designed to deliver
constant current output, constant voltage
output, or some can provide both at the turn
of a switch/knob.
– Constant Current (CC) - Is used for SMAW
and GTAW processes.
– Constant Voltage (CV) – Is used for GMAW
and FCAW processes.

Welding Machine Types
1. AC Transformer
2. Transformer / Rectifier
3. Motor Generator (obsolete)
4. Inverter
5. Engine Generator
– Notice that machines are not classified by welding process
because most will do more than one process. The
advanced SMAW class will discuss welding power in
greater depth.

Shielded Metal Arc Welding
“Shielded Metal Arc Welding (SMAW) is an arc
welding process in which coalescence of metals
is produced between the tip of a covered
electrode and the surface of the base metal in the
joint being welded.” (AWS Handbook, vol. 2)
SMAW is the most widely used of all the arc
welding processes.
Temperatures above 9,000F are produced at the
arc center.

SMAW

Functions of the Electrode
Covering (flux):
Decomposition of the electrode cover (during welding)
provides a shielding gas (generally CO, CO 2, H 2 or even H 2O)
to prevent air from contaminating the weld pool.
Provides scavenging, deoxidizing and fluxing agents to
cleanse weld, prevent excessive grain growth and improve
wetting action. (See next slide)
Determines the electrical characteristics of the electrode
(ionization potential of the shielding gas determines AC/DC).
Produces a slag blanket to protect the solidified weld.
Influences the mechanical properties and bead shape.
Provides a method for introducing alloying elements and
thereby effect the mechanical and/or corrosion properties.

Example of Composition and Function of
Electrode Covering:

The Primary Effects of Common Alloying Elements
in Carbon Steel:
Carbon (C)- Increases strength, hardness and cracking tendency.
Chromium (Cr)- Increases corrosion resistance and hardenability.
Manganese (Mn)- Improves strength and hardenability, deoxidizes.
Aluminum (Al), Silicon (Si) & Titanium (Ti)- Serve as a deoxidizers.
Nickel (Ni)- Improves toughness while mildly increasing strength!
Molybdenum (Mo)- Improves stength at elevated temperatures,
increases hardenability.
Sulfur (S), Selenium (Se), Lead (Pb) and Phosphorus (P) - Are not
intentionally added to weld metal or steel intended for welding. The
elements may be present as impurities and should not be present in
weldments at levels above about 0.04%. These elements are often
intentionally added to improve machinabilty in “free machining steels”.

Covered Electrode Quick Facts:
Iron Powder is often included in the electrode covering to
increase deposition. Electrodes with heavy iron powder
coatings (E7024) require less skill because the welder can
simply “drag” the rod along the joint.
Electrode coverings are applied to the core-rod by extrusion or
dipping. Extrusion is most common.
Some rods convert their covering into mostly gas (E6010) and
produce a light slag. Other rods produce less gas and a heavy
slag (E6013). Thus a spectrum exists from primarily gas to
primarily slag shielding.
Electrode Lengths of 9 to 18 inches are available.

SMAW Capabilities and
Limitations:
Simple, inexpensive and portable equipment.
Covered electrode provides both filler metal and shielding
method.
Less sensitive to drafts/wind than gas-shielded processes.
Can be used in areas with limited access.
Suitable for most common alloys.
Suitable for sheet metal (1/16” min.) or thick sections.
Operator duty cycle and deposition rates are lower than with wire
feed processes.
Slag must be removed, (unlike GMAW or GTAW).

SMAW Equipment
Review the CC volt-ampere curve (see next slide), Open circuit
voltage, and power source selection from chapter 2 and the prior
power source notes.
Welding Cables- The size (diameter) is determined by the cable
length and maximum amperage to be used. Table 2.1 provides
recommended sizes.
Electrode Holder- Select the smallest, most comfortable holder
that is rated for required amperage.
Ground Clamp- Spring or screw mechanism?
Personal Equipment- Helment, dark lenses, safety glasses,
gloves, chipping hammer, wire brush and protective clothing.

Constant Current
Volt-Ampere Curve:

Base Metals and Electrodes:
Base Metal Example
Base Metal
Carbon Steel AISI 1018,
ASTM A36, A516
Low-Alloy Steel AISI 4140, 8620
ASTM A514, A519
Stainless Steel AISI 304, 316,
410, ASTM A240
Cast Iron Ductile Iron
Grey Iron
Aluminum A356, 5052,
3003, 6061-T6
Copper Alloys B505 UNS C95400
Brass, Bronze,
Nickel Alloys Inconel 625,
Hastelloy C22
AWS Electrode Example
Specification Electrodes
A5.1 E6010, E6013,
E7018, E7024
A5.5 E8018-C1
E9018-B2
A5.4 E308L, E316L,
E410NiMo
A5.15 ENi-CI
EniCu-A
A5.3 E1100
E4043
A5.6 ECuAl-A2
ECuMnNiAl
A5.11 ERNiCrMo-3
ERNiFe-1

Base Metals and Electrodes
Continued:
Surfacing Electrodes (per AWS A5.13) are commonly used for special
applications such as Corrosion, Wear or Impact resistant deposits.
Special metallurgical or dimensional properties can also be achieved by
strategically selecting your electrode.
Electrode Coverings are “Hygroscopic” --- They will absorb moisture
from the atmosphere. Some electrodes are intended to be “lowhydrogen”
and must be properly packaged and stored to prevent
moisture absorption. As the humidity level and base metal/electrode
strength increase, the likelihood of hydrogen cracking (due to damp
electrodes) also increase. Low-alloy electrodes ending with 15, 16 or
18 (E7018) are low-hydrogen types. Rod ovens are typically
maintained at 250F.
Most SMAW is performed on metal between 1/8” and 1.5” thick. Thicker
materials are more economically welded with FCAW or SAW

Welding Positions:
- Fillet Welds on Plate

Welding Positions:
- Fillet Welds on Pipe

Welding Positions:
- Butt Welds on Plate

Welding
Positions:

Basic Weld Joints

Weld Backing - Supports Weld Pool and
Provides Root Contour.
4 Types of Backing:
– Backing Strip - Usually made from the same material as the
weld joint. The root pass welds the backing strip to the back of
the joint. Can be left in place or removed later.
– Copper Backing Bar - Does not fuse (weld) to the joint.
Supports the molten weld puddle. Used for its high thermal
conductivity. (Aluminum is also sometimes used.)
– Nonmetallic Backing - Usually consists of ceramic segments
or a granular flux.
– Backing Weld - A weld made from the back-side of the joint
before the groove is filled from the face side.

Joint Geometry and Fit-Up
Fit-Up - Refers to the quality of joint dimensions and alignment.
You cannot make a high quality weld with poor quality fit-up.
Joint Geometry - Refers to the shape and dimensions of a joint
prior to welding.
– The book provides numerous examples of common joint
geometry (dimensions/angles).
– See Joint Geometry and terminology handout.
Runoff Tabs - See figure 2.9
Preheat - Heating the joint area prior/during welding.

Electrode Factors
Electrode Diameter Depends on:
– Base Metal Thickness >Welding Position
– Type of Weld Joint >Power Source Rating
The proper electrode diameter will produce a weld
of the required size and quality in the minimum
amount of time.
Deposition rate (lbs/hr) increases as the electrode
diameter increases.
Electrode Orientation - Study Table 2.3

Welding Technique
Striking the Arc: >Tap or Scratch technique
Strike E7018 ahead of the intended start location then quickly
move to the start position and weld over where the arc was
struck.
Breaking the Arc: When you run out of rod, push the stub down
tight on the puddle, then quickly pull it aside. This leaves a
clean crater to start the next rod.
When starting from a crater, strike the arc at the front end of the
crater, then quickly move to the back and proceed forward to
continue the weld.

Slag Removal
Slag inclusions are often caused by inadequate slag removal.
Each bead must be thoroughly cleaned prior to welding over it.
Slag removal is easier when there is a smooth transition from
bead to bead or the base material to the bead(s).
Slag entrapment often occurs where sharp notches are formed.
Undercutting, overlapping and excessive bead convexity promote
slag entrapment and inclusions.
Complete removal of slag is required to achieve high quality
welds.

Weld Quality
Arc Blow – Colliding magnetic fields.
– A magnetic field in the base metal, table or fixture interacts
with the magnetic field surrounding the weld rod. Can cause
porosity, slag inclusions, lack of fusion and other flaws.
– Corrective Actions: 1. Short arc gap, 2. Change rod angle to
counteract, 3. move work clamp, 4. Change welding
direction, 5. Use back-step technique, 6. Change from DC to
AC, 7. Add runoff plates & Tabs, 8. Last Resort: Wrap work
cable around work piece a few times.
Porosity – Gas bubbles
– Usually caused by contaminated rod or base metal.
Slag Inclusions – Non-metallic inclusions
– Causes: poor cleaning, rod angle (drag), amperage (too low),
and bead placement.

Weld Quality (cont.)
Incomplete Fusion – Failure to join/fuse
– Causes: poor bead placement, convex beads,
large “rolling” puddle, wrong amperage
Undercut – “Ditched” at toes
– Causes: excessive current, poor rod angle.
Cracks –Numerous types.
– As a welder, you need to take care of crater
cracks by filling your crater at weld completion.