Welding Essentials - Questions and Answers

517 Pages·2006·18.09 MB·English

by  Galvery

Welding Essentials:
Questions & Answers
Second Edition
_______
William L. Galvery, Jr.
Professor of Welding Technology
American Welding Society QC-1, CWI, CWE
Orange Coast College
Costa Mesa, California
and
Frank M. Marlow, PE
_______
Illustrations by
Pamela Tallman
&
Lawrence Smith
Industrial Press Inc.
STATEMENTOFNON-LIABILITY
The process of welding is inherently hazardous. Welding is often used to assemble build-
ings, structures, vehicles, and devices whose failure can lead to embarrassment, property
damage, injury, or death. The authors have carefully checked the information in this book,
have had others with professional welding experience and credentials review it as well and
believe that it is correct and in agreement with welding industry practices and standards.
However, the authors cannot provide for every possibility, contingency, and the actions of
others. If you decide to apply the information, procedures, and advice in this book, the
authors refuse to be held responsible for your actions. If you decide to perform welding,
use common sense, have a competent person check your designs, the welding processes,
and the completed welds themselves. Seek the help of people with professional welding
inspection credentials to check critical welds until you gain experience. Do not attempt
life-critical welds without competent on-the-spot assistance.
Copyright © 2006
All rights reserved. With the exception of quoting brief passages, no part of this publica-
tion may be reproduced, or transmitted in any form without written permission from the
copyright owner.
ISBN 978-0-8311-3301-6
Manufactured in the U.S.A.
Visit us at our website:
www.industrialpress.com
10 9 8 7 6 5 4 3 2 1
Introduction
The authors had the following objectives in mind when writing this book:
•
Develop an easy-to-read, concise book with all the technical and safety infor-
mation a beginning welder needs.
•
Use a question-and-answer format to divide this information into small,
easily understandable blocks.
•
Provide illustrations to clarify and detail every explanation.
•
Eliminate non-essential items to prevent overloading the reader.
•
In a single chapter cover each major, commercially important process:
oxyacetylene welding, oxyfuel cutting, brazing & soldering, SMAW, GMAW/
FCAW, and GTAW/PAW.
•
Describe less important welding processes in a survey chapter.
•
Explain the effects of welding heat on metals.
•
Present welding power supply and electrical safety issues.
•
Introduce the beginning welder to weld inspection, welding symbols
and qualification and certification issues.
Because this book initially did not provide much practical how-to-do-it advice in this
expanded first edition we have added a chapter on fabrication and repair tips: assem-
bling angle iron frames, repairing cracked heavy truck C-channels, and soldering
copper tubing. These are relatively common tasks the welder will see and we want
him to know how to do them.
We have not included torch manipulation instructions. This is a hands-on skill that is
best learned from classroom demonstrations, personal instruction.
Although this book is primarily based on English measurement units, we have usual-
ly included metric units also.
WILLIAM L. GALVERY, JR. FRANK M. MARLOW
Costa Mesa, California Huntington Beach, California
ix
Contents
Introduction . . . . . . . . . . . . ix
CHAPTER 1 OXYACETYLENEWELDING . . . . . . . . . 1
CHAPTER 2 THERMALCUTTING . . . . . . . . . . 35
CHAPTER 3 BRAZING & SOLDERING . . . . . . . . . 77
CHAPTER 4 COMMONWELDING ELEMENTS . . . . . . . 103
CHAPTER 5 SHIELDED METALARCWELDING . . . . . . . 127
CHAPTER 6 WIRE FEEDWELDING PROCESSES —
GMAW& FCAW . . . . . . . . . . 151
CHAPTER 7 NON-CONSUMABLE ELECTRODEWELDING PROCESSES —
GTAW& PAW . . . . . . . . . . . 197
CHAPTER 8 SURVEYOF OTHERWELDING METHODS . . . . . 229
CHAPTER 9 CONTROLLING DISTORTION . . . . . . . . 245
CHAPTER 10 WELDING SYMBOLS . . . . . . . . . . 259
CHAPTER 11 INSPECTION & DISCONTINUITIES . . . . . . . 287
CHAPTER 12 WELDING METALLURGY . . . . . . . . . 317
CHAPTER 13 POWER SUPPLIES & ELECTRICALSAFETY . . . . . 361
CHAPTER 14 QUALIFICATION & CERTIFICATION . . . . . . . 413
CHAPTER 15 FABRICATION & REPAIRTIPS . . . . . . . . 429
Appendix
A: ENGLISH-METRIC CONVERSION FACTORS . . . . 457
B: PROPERTIES OF ELEMENTS & IMPORTANTCOMPOSITIONS . 458
C: AWS DESIGNATIONS FORWELDING &ALLIED PROCESSES . 461
Glossary . . . . . . . . . . . . 463
Index . . . . . . . . . . . . . 517
Picture Credits . . . . . . . . . . . 525
Chapter 1
Oxyacetylene Welding
The chapter of knowledge is a very short one, but the chapter of
accidents is a very long one.
Philip Dormer Stanhope
Introduction
Oxyacetylene welding was first used industrially in the early years of the twen-
tieth century. Although this process makes excellent welds in steel, it is little
used for welding today except for a few specialties (light aircraft, race car
frames and American Petroleum Institute natural gas distribution), since there
are other more efficient welding processes available. However, oxyacetylene
has many other important uses: cutting, hardening, tempering, bending, form-
ing, preheating, postheating, brazing, and braze welding. Because of the pre-
cise control the welder has over heat input and its high-temperature flame,
together with its low equipment cost, portability, and versatility, it remains an
essential tool. No industrial shop is complete without an oxyacetylene outfit.
As with all effective tools, using oxyacetylene carries risk. We will cover the
theory and use of oxyacetylene equipment so you can use them with confidence
and safety. It will also prepare you for the next chapter on oxyfuel cutting,
because many components and issues are common to both processes.
Process Name
What is the name covering all welding processes using oxygen and a fuel
gas?
Oxygen fuel (oxyfuel) welding.
What is the American Welding Society (AWS) abbreviation for oxyfuel
welding?
The abbreviation for all oxyfuel welding processes; those using oxygen and
any fuel gas is OFW.
2 CHAPTER 1
OXYACETYLENE WELDING
A particularly important member of the OFW process family is oxy-
acetylene welding. What is the AWS abbreviation for this process?
The abbreviation for oxyacetylene welding is OAW.Note that OAWis just one
member of the OFW family.
Equipment
Figure 1-1 shows and labels the components of the basic oxyacetylene
welding equipment (outfit) showing how they are connected.
Figure 1–1 Adrawing of oxygen acetylene welding equipment
Process
How does oxyacetylene equipment perform the welding process?
Oxygen and acetylene gases when combined, in the proper proportions, in the
torch handle’s mixing chamber, produce an approximately 5600°F (3100°C)
flame at the torch tip. This flame melts the edges of the base metals to be joined
into a common pool. Sometimes additional filler metal is added to the molten
CHAPTER 1 3
OXYACETYLENE WELDING
pool from a welding rod. When this common pool cools and the metal freezes
solid, the joined metals are fused together and the weld complete.
What are some advantages of the OAW process?
• Low cost
• Readily portable
• Excellent control of heat input and puddle viscosity
• No external power required
• Good control of bead size and shape
• Fuel mixture is hot enough to melt steel
Setup (and related safety)
List the steps for installation of oxygen and acetylene pressure regulators
on full cylinders. Be sure to include all safety precautions.
• Put on your welding safety equipment: tinted safety goggles (or tinted face
shield), cotton or wool shirt and pants, high-top shoes, and welding gloves
at a minimum.
• Make sure the valves on previously used or empty cylinders are fully closed
and their valve protection covers are securely screwed in place. Then
remove the empty cylinders from the work area and secure them against
tipping during the wait for a refill shipment. Secure the newly replaced or
full cylinders to a welding cart, building column, or other solid anchor to
prevent the cylinders from tipping over during storage or use.
• Momentarily open each cylinder valve to the atmosphere and reclose the
valve quickly purging the valve; this is known as cracking a valve.
Cracking serves to blow out dust and grit from the valve port and to pre-
vent debris from entering the regulators and torch.
• With a clean, oil-free cloth, wipe off the cylinder valve-to-regulator fittings
onboth cylinders to remove dirt and grit from the fittings’connection faces
and from the fittings’threads. Do the same to both regulators’threads and
faces. Remember, never use oil on high-pressure gas fittings. Oxygen at
high pressures can accelerate combustion of oil into an explosion.
• Make sure reverse-flow check valves are installed on the torch or the regu-
lators.
• Check to see that both the oxygen and acetylene regulator pressure adjust-
ment screws are unscrewed, followed by threading each regulator to its
respective cylinder. Snug up the connections with a wrench. Caution:
Oxygen cylinder-to-regulator threads are right-handed; so are oxygen hose-
4 CHAPTER 1
OXYACETYLENE WELDING
to-torch screw fittings. Acetylene cylinder-to-regulator fittings and acety-
lene hose-to-torch fittings threads are left-handed. This arrangement pre-
vents putting the wrong gas into a regulator or torch connection.
• Stand so the cylinders are between you and the regulators, S-L-O-W-L-Y
open the oxygen cylinder valves. Open the oxygen cylinder valve until it
hits the upper valve stop and will turn no further. Also standing so the cylin-
ders are between you and the regulator, open the acetylene cylinder valve
gradually and not more than 1 1⁄2 turns. If there is an old-style removable
wrench on the acetylene cylinder, keep it on the valve in case you must
close it in an emergency.
• Look at the high-pressure—cylinder side—pressure gauges to indicate
about 225 psi (15.5 bar) in the acetylene cylinder and 2250 psi (155 bar) in
the oxygen cylinder. Note: 1 bar = 1 atmosphere = 14.5 psi = 0.1 MPa.
Cylinder pressures vary with ambient temperature. The pressures given
above are for full cylinders at 70°F (21°C).
• Purge each torch hose of air separately: Open the oxygen valve on the torch
about three-quarters of a turn, then screw in the pressure control screw on
the oxygen regulator to your initial pressure setting—about 6 psi (0.4 bar).
After several seconds, close the torch valve. Do the same for the acetylene
hose. Comment: We do this for two reasons, (1) to make sure we are light-
ing the torch on just oxygen and acetylene, not air, and (2) to set the regu-
lators for the correct pressure while the gas is flowing through them.
• Caution: never adjust the acetylene regulator pressure above 15 psi (1 bar)
as an explosive disassociation of the acetylene could occur.
• Recheck the low-pressure gauge pressures to make sure the working pres-
sures are not rising. If the working pressure rises, it means the regulator is
leaking. Immediately shut down the cylinders at the cylinder valves as con-
tinued leaking could lead to a regulator diaphragm rupture and a serious
accident. Replace and repair the defective regulator.
• Test the system for leaks at the cylinder-to-regulator fittings and all hose
fittings with special leak detection solutions; bubbles indicate leaks.
If you are using a small to medium torch tip on a job for the first time,
what regulator pressures should be set as a starting point?
Set both the acetylene and the oxygen regulator pressures to 6psi (0.4 bar).
What are the steps for adjusting the torch to a neutral flame?
• Open the acetylene valve no more than 1⁄16 turn and use a spark lighter to
ignite the gas coming out of the tip. A smoky orange flame will be the
result, Figure 1–2 (A).
CHAPTER 1 5
OXYACETYLENE WELDING
• Continue to open the acetylene valve until the flame stops smoking (releas-
ing soot). Another way to judge the proper amount of acetylene is to open
the acetylene valve until the flame jumps away from the torch tip, leaving
about 1⁄16 inch gap (1.6 mm), Figure 1–2 (B). Then close the valve until
flame touches the torch tip.
• Open the oxygen valve slowly. As the oxygen is increased, the orange acety-
lene flame turns purple and a smaller, white inner cone will begin to form.
With the further addition of oxygen, the inner cone goes from having ragged
edges, Figure 1–2 (C), to sharp, clearly defined ones. The flame is now neu-
tral and adding oxygen will make an oxidizing flame, Figure 1–2 (D).
• If a larger flame is needed while keeping the same tip size, the acetylene
may be increased and the oxygen further increased to keep the inner cone’s
edges sharp. This process of increasing the acetylene, then the oxygen is
usually done in several cycles before the maximum flame available from a
given tip is achieved. Adjusting the flame below the minimum flow rate for
the tip orifice permits the flame to ignite insidethe nozzle. This is flashback
and makes a popping sound. If you need a smaller flame, use a smaller
torch tip. See the section on flashback.
Figure 1–2 Shows flame adjustments from carburizing to a neutral flame
6 CHAPTER 1
OXYACETYLENE WELDING
What it the hottest part of a neutral flame?
The tip of the inner cone is the hottest part of the flame. The inner cone is where
the optimum mixture of oxygen and acetylene burn. The outer envelope where
any unburned acetylene burns with oxygen from the atmosphere. A neutral
flame is when enough oxygen is present in the flame to be burning all of the
acetylene gas and is used for most welding processes. See Figure 1–3.
Figure 1–3 Graph of an oxyacetylene flame temperature profile
What effect do oxidizing and carburizing flames have on molten metal in
the weld pool?
An oxidizing flame contains more oxygen than the flame can burn and this
oxygen combines (or burns) with carbon in the steel to carbon dioxide gas. The
result is the weld metal has a change in carbon content and in its properties.
Strength is always degraded and brittleness increased.
A carburizing flame contains more acetylene than the flame can burn and the
carbon in the acetylene adds to the carbon in the weld pool causing gas bubbles
in the weld. When the weld freezes these gas bubbles create porosity holes.