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C H A P T E R 7

SHIELDED METAL-ARC WELDING

AND W E ARF ACI NG

The shielded metal-arc welding process, referred to

as metallic-arc welding, arc welding, or stick welding,

is extensively used in welding ferrous and nonferrous

metals. It has many applications for producing a vast

assortment of metal products. Shielded metal-arc weld-

ing is found in th e ship building industry an d in th econstr uction in dustr y for fabricating girders, beams, a nd

columns. Because it is easy to use and portable, shielded

metal-arc welding is universally used in the repair and

servicing of equipment , machiner y, and a host of oth er

items.

MANUAL SHIELDED METAL-ARC

WELDING

Arc welding provides you the ability to join two

metals by melting them with a n a rc generated between

a coated-metal electrode and the base metal. The tem-

perat ures developed by the ar c can reach as h igh as

10000°F. The arc energy is provided by a power source

that generates either direct or alterna ting current . The

electrodes that carry the current produce a gas thatshields the arc from the atmosphere and supplies filler

metal to develop the weld shape.

ARC-WELDING EQUIPMENT

A wide variety of welding equipment is available,

and there are many differences between the makes and

models of the equipment produced by the manufactur-ers. However, all types of arc-welding equipment ar e

similar in their basic function of producing the high-am-

perage, low-voltage electric power required for the

welding a rc. In th is discussion, we are pr imar ily con-

cerned with the typical items of arc-welding equipment,

rather than the specific types For specific information

requires a number of accessories tha

nat ion chipping ha mmer and wire br

(for shopwork), C-clamps, and prote

Before we discuss t he differen

ma chines, you m ust first ha ve a basi

electrical terms used with welding.

E le c t r i c a l Te r m s

Many terms are associated with

following basic term s a re esp ecially

A L T E R N A T I N G C U R R E N T . —

rent is an electrical current that has a

and positive values. In the first half

flows in one direction an d th en r ev

next half-cycle. In one complete

spends 50 percent of the time flowin

other 50 percent flowing the other

change in direction is called frequen

cated by cycles per second. In the

alternating current is set at 60 cycles

A M P E R E . — Amperes, sometim

refers t o the amount of current tha

circuit. It is measu red by an “am p” m

C O N D U C T O R . — Conductor m

that allows the passage of an electric

C U R R E N T . — Current is the m

an electrical charge through a condu

D I R E C T C U R R E N T .— Direct

trical current that flows in one direct

E L E C T R I C A L C I R C U I T . — E

the path taken by an electrical curre

a conductor from one ter mina l of th e

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127.517

Figu re 7-1 .—A 300 am p a c /dc p o r t a b l e we l d i ng

m a c h i n e .

VOLT.— A volt is t he force required to ma ke th e

current flow in an electrical circuit. It can be

compar ed to pressure in a hydra ulic system. Volts ar e

measured with a volt m eter.

P o w e r S o u r c e

The power source used in arc welding is called a

welding machine or a welder. Three basic types of

welding machines are presently in use: motor-

generat ors, tran sformers, and rectifiers.

MOTOR-GENERATOR WELDING MA-

CHINES.— These types of welding machines are

powered by electrical, gasoline, or diesel motors. The

diesel and gasoline motors are ideal for use in areas

where electricity is not available. Portable gas/diesel

welding machines are part of the equipment

allowance for Naval Mobile Construction Battalions.

These machines usually have the capability of

generating alternating or direct current. On the

newer machines, when you are welding in the direct-

current mode, the polarity can be changed by turning

a switch. Some of the older machines require

reversing the cable connections. One of the

Figu re 7-2 .—An ac a r c -w

1. Machines ra ted 150 an d 2

ar e for light-shielded met al-arc

gas arc welding. They are also jobs or sh opwork.

2. Machines ra ted 200,300,

volts are for general welding pu

manual application.

3. Machines rated 600 amp

submer ged-arc welding or carbon

ALTER NATING-CURR EN

WELDING MACHINES.—

alternating current (at) arc-wel

are the static-transformer type,

2. These types of machines ar

expensive, and the lightest ty

Industrial applications for m

machines having 200, 300, and

Machines with a 150-ampere ra

indust rial, gara ge, and job/shop

The transformers are usual

stabilizing capacitors. Current c

several ways by the w

manufacturers. One such meth

t th t i t b t i

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Table 7-1.—Cable Size Select ion Guide

polar ity curren t. By flicking a switch

select the current that best suits the job

an example of a combination ac/dc re

Ca ble s

Welding cables car ry th e cur ren

workpiece. One of the cables run s f

machine to the electrode holder andconn ects th e workpiece to th e weldi

cable that connects the workpiece to

chine is called the ground. When the

on and the operator touches the elect

piece, the circuit is completed, curren

and the welding process commences.

The welding cables must be flexi

insulated, and large enough to carry thOnly cable that is specifically desig

should be used. A highly flexible cable

the electrode holder connection. This i

operator can easily maneuver the elec

ing the welding process. The ground

Figure 7-3 —Combina t ion ac dc t rans fo rmer - rec t i f i e r a rc we lde r so flexible because once it is conne

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difficult to handle, especially if you are working on a

structure that requires a lot of moving around. The best

size cable is one that meets the amperage demand but is

small enough to manipulate with ease.

As a rule, the cable between the machine and the

work should be as short as possible. Use one continuouslength of cable if the distance is less than 35 feet. If you

must use more than one length of cable, join the sections

with insulated lock-type cable connectors. Joints in the

cable should be at least 10 feet away from th e operator.

E le c t r ode H olde r

An electrode holder, commonly called a stinger, is

a clamping device for holding the electrode securely in

any position. The welding cable attaches to the holder

thr ough t he h ollow insulat ed ha ndle. The design of the

electrode holder permits quick and easy electrode ex-

change. Two general types of electrode holders are in

use: insulated and noninsulated. The noninsulated hold-

ers ar e not recommen ded becau se they ar e subject to

accidental short circuiting if bumped a gainst t he work-

piece during welding. For safety reasons, try to ensurethe use of only insulated s tingers on t he jobsite.

Electrode holders are made in different sizes, and

manufacturers have their own system of designation.

Each holder is designed for use within a specified range

of electrode diameters and welding current. You require

a larger holder when welding with a machine having a

300-ampere rat ing than when welding with a 100-am-

pere machine. If the holder is too small, it will overheat.

G r o u n d C la m p s

The use of a good ground clamp is essential to

producing quality welds. Without proper grounding, the

circuit voltage fails to produce enough heat for proper

welding, and there is the possibility of damage to the

welding machine and cables. Three basic methods areused to ground a welding machine. You can fasten the

ground cable to the workbench with a C-clamp (fig. 7-

4), attach a spring-loaded clamp (fig. 7-5) directly onto

the workpiece, or bolt or tack-weld the end of the ground

cable to the welding bench (fig. 7-6). The third way

t t d

Figu re 7 -4 .—C -c l a m p e d g r o u

Figur e 7-5.—A s p r i ng -l oaded g r oun d c l am

Figure 7-6.—B ol t ed and t ack - w e l ded

par t of th e welder’s equipmen t. After

a weld bead ha s been deposited, the

removed before additional beads ar

ping ha mmer was specifically desi

The chipping operation is then follow

ing, and this cycle is repeated until

removed. When th e slag is not rem

porosity in the weld that weakens th

Cleaning can also be accompli

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dangerous to your eyes and skin. In chapter 3, personal

safety items, such as helmets, lenses, and gloves, were

covered. An important item that needs to be covered

here is welding screens. The welder not only has to

protect h imself but he also must t ake pr ecaut ions t o

protect other people who may be working close by.

When you ar e welding in th e field, you m ust insta ll a

welding screen a round your work area. It can be an

elaborate factory-manufactured screen or as simple as

one constr ucted on site from heavy fire-resistan t can vas.

Never

proper eye

WARNI NG

look at thes welding arc without

protection. Looking at the arc with

the n aked eye could result in perm anen t eye

damage. If you receive flash burns, they should

be treated by medical personnel.

Another area often overlooked is ventilation. Weld-

ing produces a lot of smoke and fumes that can be

injurious to the welder if they a re a llowed to accumu late.This is especially true if you a re welding in a ta nk or

other inclosed area. Permanent welding booths should

be equipped with a exhaust hood an d fan system for

removal of smoke and fumes.

E Q U I P M E N T O P E R A T IO N A ND

MAINTENANCE

Learning to arc weld requires you to possess many

skills. Among these skills are the abilities to set up,

operate, and maintain your welding equipment.

W E L D I N G A R E A R E Q U I R E M E N T S

In most factory environments, the work is brought

to the welder. In the Seabees, the majority of the time

th e opposite is tr ue. You will be called to th e field for

welding on buildings, earthmoving equipment, well

drilling pipe, ship to sh ore fuel lines, pont oon cau se-

ways, and the list goes on. To accomplish these tasks,

you have to become familiar with your equipment and

be able to ma inta in it in the field. It would be impossible

literat ur e an d check with your sen

chief on the items that you do not u

setup involves selecting current type

rent settings. The current selection d

and type of electrode used, position o

properties of the base metal.

Cable size and connections are

distance required to reach the wo

machine, and the amperage needed f

Operator maintenance depends o

ing machine used. Transformers an

little maintenance compared to eng

machines. Transformer welders requ

dry and a minimal amount of cleanin

na nce should only be done by elec

possibilities of electrical shock E

chines require daily maintenance of

places you will be required to fill out

inspection form called a “ha rd card”

engine. This form is a list of items

water level, visible leaks, and other

the operation of the machine. Tran

ments are the ones who usually han

After all of the above items have

are now ready to start welding.

S H I E L D E D - M E T A L A R C Before you start to weld, ensur

the required equipment and accesso

are some additional welding rules

lowed.

Clear the welding area of all

Do not use gloves or clothing

grease.

Check t hat all wiring an d c

properly.

Ensure t hat the ma chine is gr

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Figure 7-7.—Elec t rode cove r ing and gaseous sh ie ld tha t p ro tec t sw e l d m e t a l f r o m t h e a t m o s p h e r e .

E L E C T R O D E S

In general, all electrodes are classified into five

main groups:

1. Mild steel

2. High-carbon steel

3. Special alloy steel

4. Cast iron

5. Nonferrous

The widest range of arc welding is done with electrodes

in the mild steel group.

Electrodes are manufactured for use in specific

positions and for many different types of metal. They

also are specially designed to use with ac or dc welding

ma chines. Some ma nufacturer ’s electrodes work iden-

tically on either ac or dc, while others are best suited for

flat-position welding. Another type is made primarily

for vertical and overhead welding, and some can be used

in any position. As you can see, electrode selection

depends on many variables.

T y p es o f E l ect ro d es

Electrodes are classified as either bare or shielded.

The original bare electrodes were exactly as their name

implied—bare. Today, they have a light covering, but

even with t his improvement t hey are ra rely used because

of their limitations. They are difficult to weld with,

produce brittle welds, and ha ve low str ength. J ust about

Figure 7 -8 .—Explana t ion o f AWS c la

the molten metal from oxidation or c

surrounding atmosphere.

As molten metal is deposited in

it attracts oxygen and nitrogen. S

takes place in the atmosphere, oxi

the m etal passes from the electrode

this happens, the strength and duct

reduced as well as the resistance

coating on the electrode prevents o

place. As the electrode melts, the hean inert gas around the molten met

atmosphere from the weld (fig. 7-7

The burning residue of the coati

the deposited metal th at slows down

produces a more ductile weld. Som

powdered iron th at is converted t o

heat of the arc as it flows into the w

E l e c t r o d e I d e n t i f i c a t i o n

Electrodes are often referred to

tra de na me. The American Welding

the American Society foresting and

have set u p certa in requirement s for

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Table 7-2.—E l e c t r o d e S e l e c t i o n G u i d e

electric-arc welding. The first two digits in the symbol The four th digit of the symbol r

designate the minimum al lowable tensile s t rength in character is t ics of the e lectrode, such

thousands of pounds per square inch of the deposited type of curr ent, an d amount of penetra

weld metal. For example, the 60-series electrodes have range from 0 through 8. Since the w

a m inimum t ensile strength of 60,000 pounds per squar e dependent on the manufacturer’s cha

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current types and welding positions for the most com-

mon electrodes.

As a rule of thumb, you should never use an elec-

trode that has a diameter larger than the thickness of the

metal t hat you a re welding. Some operators prefer larger

electr odes becau se they perm it faster tr avel, but t his

takes a lot of expedience to produce certified welds.

Position and the type of joint are also factors in

determining the size of the electrode. For example, in a

thick-metal section with a narrow vee, a small-diameter

electrode is always used to run the frost weld or root pass.

This is done to ensure full penetration at the root of the

weld. Successive passes are then made with larger elec-

trodes.For vertical and overhead welding, 3/16 inch is the

largest diameter electrode tha t you should use regardless

of plate thickness. Larger electrodes make it too difficult

to control the deposited metal. For economy, you should

always use the largest electrode that is practical for the

work It takes about one half of the time to deposit an

equal quantity of weld metal from 1/4-inch electrodes

as it d oes from 3/16-inch electrodes of th e sam e type.

The larger sizes not only allow the use of higher currents

but also require fewer stops to change electrodes.

Deposit rat e and joint pr eparat ion ar e also important

in the selection of an electrode. Electrodes for welding

mild steel can be classified as fast freeze, fill freeze, and

fast fill. FAST-FREEZE electrodes produce a snappy,

deep penetrating arc and fast-freezing deposits. They are

commonly called reverse-polarity electrodes, even

though some can be used on ac. These electrodes havelittle slag and produce flat beads. They are widely used

for all-position welding for both fabrication and repair

work

FILL-FREEZE electrodes have a moderately force-

ful arc and a deposit rate between those of the fast-freeze

and fast-fill electrodes. They are commonly called the

straight-polarity electrodes, even though they may be

used on ac. These electrodes have complete slag cover-age and weld deposits with distinct, even ripples. They

are the general-purpose electrode for a production shop

an d ar e also widely used for r epair work They can be

used in all positions, but fast-freeze electrodes are still

preferred for vertical and overhead welding.

Among th e FAST-FILL electr odes are t he h eavy-

quality deposits by reducing the abs

that causes porosity and cracks und

Welding stainless steel require

taining chromium and nickel. All s

low-th erma l condu ctivity th at cau

heating and improper arc action wh

used. In the base meta l, it causes

differentials between the weld and

which wa rps t he plate. A basic rule

steel is to avoid high currents and

reason for keeping the weld cool

corrosion.

There are also many special-pu

sur facing an d welding copper an dminum, cast iron, manganese, nicke

manganese steels. The composition

is designed to match the base meta

selecting electrodes is to pick on

composition to the base metal.

E l e ct r o d e S t o r a g e

Electrodes are expensive; thereterioration through improper hand

become very costly. Always store th

room temperature with 50-percent

humidity. Moisture causes the coat

disintegrate and fall off. Low-hydr

cially sensitive to moisture. After r

from their original packaging, you

a storage space maintained at a te

250°F to 400°F. Portable or stationa

used to store and preserve electrod

peratures. Care should be taken w

trodes because bumping or dropping

coatings to fall off, rendering the ro

P o l a r i t y

Ear lier in this chapter, ac an d d

covered. With ac welding machin

problem. When using dc welding

weld with either st raight polarity or

Polarity is the direction of th

circuit, as shown in figur e 7-9. In s

electr ode is negative an d t he wor

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Figure 7-9 .—S t r a i gh t a nd r eve r s e po l a r i t y i n e l ec t r i c w e l d i ng .

On s ome of the older m achines, polarity is changedby switching cables. On many of the newer machines,

the polarity can be changed by turning a switch on the

machine.

Polarity affects the amount of heat going into the

base met al. By cha nging polar ity, you can direct th e

amount of heat to where it is n eeded. When you u se

straight polarity, the majority of the heat is directed

toward the workpiece. When you use reverse polarity,the heat is concentrated on the electrode. In some weld-

ing situations, it is desirable to have more heat on the

workpiece because of its size and the need for more heat

to melt th e base meta l tha n t he electrode; ther efore,

when making large heavy deposits, you should use

STRAIGHT P OLARITY.

On the other hand, in overhead welding it is neces-

sary to rapidly freeze the filler metal so the force of

gravity will not cause it to fall. When you use REVERSE

POLARITY, less heat is concentrated at the workpiece.

This allows the filler metal to cool faster, giving it

greater holding power. Cast-iron arc welding is another

good example of th e need to keep th e workpiece cool;

reverse polarity permits the deposits from the electrode

Figur e 7-10.— S t r i k i ng o r b r u s h i ng m e t hod

opposite is true and the greatest heat i

negative side. Electrode coatings affe

tions differently. One type of heavy co

the most desirable heat balance with

while another type of coat ing on t he sa

provide a m ore desirable heat balapolarity.

Reverse polarity is used in the w

rous metals, such as aluminum, bro

nickel. Reverse polarity is also used w

electrodes for m aking vert ical a nd ov

You can r ecognize th e proper po

electrode by the sharp, crackling soun

wrong polarity causes the arc to emi

and the welding bead is difficult to co

One disa dvant age of direct-curren

blow.” As stated earlier, arc blow

wander while you a re welding in corne

or when using large-coated electrode

flowing through the electrode, workp

clamp generates a magnetic field aro

units. This field can cause the arc to

intended path. The arc is usually def

backward a long th e line of travel and

sive spatter and incomplete fusion. I

dency to pull atmospheric gases into

in porosity.

Arc blow can often be correcte

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Figure 7-11.— T app i ng m e t hod o f s t a r t i ng t he a r c .

TAPPIN G method (fig. 7-11). In ei ther m ethod, the a rc

is star ted by short circuiting th e welding curr ent bet ween

the electrode and the work surface. The surge of high

current causes the end of the electrode and a small spoton the base metal beneat h th e electrode to melt instant ly.

In the STRIKING or BRUSHING method, the electrode

is brought down t o the work with a lat eral m otion similar

to striking a mat ch. As soon a s th e electrode touches the

work surface, it must be raised to establish the a rc

(fig. 7-10). The arc length or gap between the end of the

electrode and the work should be equal to the diameter

of the electr ode. When th e proper ar c length is obtained,it produces a sha rp, crackling sound.

In the TAPPING method, you hold the electrode in

a vert ical position t o the su rface of the work. The ar c is

started by tapping or bouncing it on the work surface

and then raising it to a distance equal to the diameter of

the electrode (fig. 7-11). When the proper length of arc

is established, a sharp, crackling sound is heard.

When t he electrode is withdr awn too slowly with

either of the starting methods described above, it will

stick or freeze to the plat e or base m etal. If this occurs,

you can usually free the electrode by a quick sideways

wrist motion to snap the end of the electrode from the

plate. If this method fails, immediately release the elec-

trode from the holder or shutoff the welding machine.

After you strike t he a rc, the

melts an d flows into the m olten cra

To compensate for this loss of me

the length of the arc. Unless yo

electr ode closer t o the base m etal,

will increase. An arc that is too lo

ming type of sound. One that is

popping noise. When t he electrod

plate and along the surface at a co

metal is deposited or welded onto th

metal. After striking the arc, hold

the st art ing point t o ensure good fu

sition. Good arc welding depends

the motion of the electrode along thmeta l .

S e t t i n g t h e C u r r e n t

The amount of current used dur

tion depends primarily upon the d

trode. As a r ule, higher currents

electrodes ar e better for welding in the vertical or overhead position. M

trodes usually specify a current ran

size of electrode; this information

the face of the electrode container.

Since most recommended curr

approximat e, final curr ent sett in

need to be made during the weld

example, when the recommended

electr ode is 90-100 amperes, t he u s

th e contr ols midway between t he

amper es. After star ting th e weld, m

ments by either increasing or decre

When the current is too high,

faster and the molten puddle will b

and irregular. High current also le

base metal along both sides of the

undercutt ing, and a n example is sview C.

With current tha t is too low, the

to melt the base metal and the mol

small. The result is poor fusion an

deposit that piles up, as shown in

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Figure 7-12.— C om par i s on cha r t o f w e l d s .

Figure 7-13.— U nder cu t s and ove r l aps i n w e l d i ng .

L e n g t h o f Ar c

Figur e 7-14.— S e t t i ng t he l eng t h

to stick frequently to the base met

uneven deposits with irregular rip

mended length of the arc is equal to tbare end of the electrode, as s hown i

The length of the arc depends

electrode and the type of welding bein

for smaller diameter electrodes, a sh

sary than for larger electrodes Remem

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T rav e l Sp eed

Figure 7 -15 .—W o r k a n g l e .

F igure 7 -16 .—T r a v e l a n g l e .

E l ec t ro d e A n g le

The angle at which you hold the electrode greatly

affects the shape of the weld bead which is very impor-

ta nt in fillet a nd d eep groove welding. The electrode

angle consists of two positions: work angle and travel

angle. Work angle is the angle from the horizontal

measur ed at right a ngles to the direction of welding (fig,

7-15). Travel angle is the angle in the direction of

welding an d ma y vary from 5 to 30 degrees, depending

Travel speed is th e rat e at which

along a weld seam. The maximum

depends on the skill of the operator

weld, the type of electrode, and the t ra t ion.

Normally, when the travel spe

molten pool cools t oo quickly, lockin

causing the weld bead t o be narrow w

as shown in figur e 7-12, view D. O

the travel speed is too slow, the me

excessively and the weld is high and

figure 7-12, view E. In most cases, t

the highest speed that produces a s

appearance of a normal weld, as sh

view A.

B r e a k i n g t h e A r c

The most commonly used meth

is to hold the electrode stat ionar y unt

and then slowly withdraw the elec

reduces the possibilities of crater cr

Rees t a b l i sh i n g t h e A rc

When it becomes necessary t o re

in a long weld that requires the us

electrode), the crater must first be c

ing the ar c. Str ike the tip of th e ne

forwar d (cold) end of the crat er a n

Move the arc backward over the cra

forward again and continue the we

fills the crater and prevents porosity

P e e n i n g

Peening is a procedure that inv

mering a weld as it cools. This proce

built-up stresses and preventing surf

join t a rea ; howe ver , pe en in g sh ould

because excess hammering can wcrease stresses in the weld. This con

embrittlement and early failure. So

ered by specific codes that prohib

should check the weld specification

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Figur e 7-17.—But t j o in t s i n the f l a t pos i t ion .

F L A T - P O S I T I O N W E L D I N G

Ear lier r eexplained tha t welding can be done in

any position, but it is much simpler when done in the

flat position. In th is position, the work is less t iring,

welding speed is faster, the molten puddle is not as likely

to run and better penetration can be achieved When-

can be made on just about any type

you can rotate the section you are

appropriate position. Techniques that

ing butt joints in the flat position, w

use of backing strips, are described b

B U T T J O I N T S WI T H O U

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Figur e 7-18.— B ut t w e l d s w i t h m u l t i pa s s beads .

Figur e 7-19.— W eave m o t i ons u s ed i n m anua l s h i e l ded a r cwelding.

Tack welds should be used to keep the plates aligned for

welding. The electrode motion is the same as that used

in ma king a bead weld.

In welding 1/4-inch plat e or h eavier, you should

prepare the edges of the plates by beveling or by J-, U-,

or V-grooving, whichever is t he most app licable. You

should use single or double bevels or grooves when the

Figure 7-20.—U nder cu t t i ng i n bu

In ma king multipass welds, as s

the second, third, and fourth layers

mad e with a wea ving motion of theach layer of metal before laying ad

may u se one of th e weaving motio

7-19, depending upon the type of

electrode.

In the weaving motion, oscillat

trode uniformly from side to side, wit

at the end of each oscillation. Inclin

15 degrees in the direction of weldi

ing. When th e weaving motion is

undercutting could occur at the joint

7-20. Excessive welding speed also

ting an d poor fusion a t t he edges of

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Figur e 7-21.—U s e o f back i ng s t r i p s i n w e l d i ng bu t t j o i n t s .

For plates u p to 3/8 inch t hick, the backing strips sh ould

be approximately 1 inch wide and 3/16 inch thick. For

plates more th an 1/2inch t hick, th e backing strips shouldbe 1 1/2 inches wide and 1/4 inch thick Tack-weld the

backing strip to the base of the joint, as shown in figure

7-21. The backing str ip acts as a cushion for the r oot

pass. Complete the joint by welding additional layers of

metal. After you complete the joint, the backing strip

Figure 7-22.—H or i zon t a1 g r oo

Figure 7-23.—Hor izonta l f i l l e

HOR IZONTAL-P OSITION WELD

You will discover th at it is impo

pieces in the flat position. Often the w

in the horizontal position The horiz

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Figure 7-24.—Hor izonta l welding angles .

Figur e 7-25.—Tack-weld to hold the t ee jo in t e l ement s in p l ace .

An inexperienced welder usually finds the horizon-

tal position of arc welding difficult, at least until he has

developed a fair degree of skill in applying the proper

technique. The primary difficulty is that in this position

you have no “shoulder” of previously deposited weld

metal to hold the molten metal.

E l e c t r o d e M ov e m e n t

In horizontal welding, position the electrode so that

it points upward at a 5- to 10-degree angle in conjunction

ith 20 d t l l (fi 7 24) U

Figure 7-26.—Posit ion of e lectrode and fuon a t e e j o in t .

As you move in and out of the

each time you retu rn. This keeps the

bead has less tendency to sag.

J o i n t Ty p e

Horizont al-position welding c

types of joint s. The m ost comm on

used on are tee joints, lap joints, an

T E E J O I N T S .— When you m

horizontal position, the two plates a

each other in the form of an invertevertical plate ma y be ta ck-welded

horizonta l plate, as sh own in figur e

A fillet weld is used in making

short arc is necessary to provide go

an d along the legs of the weld (fig

the electrode at an angle of 45 degr

surfaces (fig. 7-26, view B) with an

mately 15 degrees in the direction

When practical, weld light plat

in one pass with little or no weavi

Welding of heavier plates may re

passes in which the second pass or

semicircular weaving motion, as sh

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Figure 7-27.—Weave mot ion for mul t ipas s f i l l e t weld .

Figure 7-28.—O r de r o f m ak i ng s t r i ng beads f o r a t e e j o in t i nheavy p l a t e .

Figure 7-29 —Intermi t t ent f i l l e t welds

Figure 7-30.—T ack w e l d i ng a

Figure 7-31.—Pos i t ion of e l ec t rode

strength to that of a joint t hat has a f

entire length of one side. Intermitte

the advantage of reduced warpage an

L AP J O I N T S .— When you ma

overlapping plat es a re tack-welded

and a fillet weld is deposited along t

The procedure for making this fi

to th at used for mak ing fillet weld

should hold the electrode so it form

30 degrees from the vertical and is i

in the direction of welding. The posit

in relation to the plates is shown i

weaving motion is the same as that

except th at the pa use at the edge of t

enough to ensur e good fusion with

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Figure 7-32.—L a p j o i n t s o n p l a t e s o f d i f fe r e n t t h i c k n e s s .

Figu re 7 -33 .—H o r i z on t a l b u t t j o in t .

F igu re 7 -34 .—M u l t i p l e p a s s e s .

(fig. 7-32). Be careful not to overhe

thinner plate edge.

B U T T J O I N T S .— Most butt jo

horizontal welding, have the beveled

the top. The plate that is not beveleand the flat edge of this plate provi

molten metal so that it does not run o

7-33). Often both edges are beveled t

included a ngle. When th is type of j

skill is required because you do not

shelf to hold the molten puddle.

The number of passes required f

on the diam eter of the electrode and tmetal. When multiple passes are re

place the first bead d eep in th e roo

electr ode holder sh ould be inclined

downward. Clean and remove all sla

each following bead. The second bea

with the electrode holder held about

For the third pass, hold the electrod

degrees downwar d from t he h orizo

weaving motion and ensure that eac

the base metal.

VERTICAL-P OSITION WELDIN

A “vertical weld” is defined as a

to a vertical surface or one that is inc

less (fig. 7-35). Erecting structures,

pontoons, tanks, and pipelines, requposition. Welding on a vertical surf

difficult than welding in the flat or

due to the force of gravity. Gravity

metal down. To counteract this forc

fast-freeze or fill-freeze electrodes.

Vertical welding is done in eit

downward position. The terms used

welding are vertical up or vertical dowelding is suited for welding light g

the penetrat ion is shallow and dimini

of burning through the metal. Furt

down welding is faster which is very

duction work.

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Figure 7-36.—B ead w e l d i ng i n t he ve r t i c a l pos it i on .

To produce good welds, you must maintain the

proper angle between the electrode and the base metal.

In welding upwa rd, you sh ould hold the electrode at 90

degrees to the vertical, as shown in figure 7-36, view A.

When weaving is necessary, oscillate the electrode, as

shown in figure 7-36, view B.

I t i l d ldi i li th t d f

J o i n t Ty p e

Vertical welding is used on most

types of joints you will most often use

lap joints, and butt joints.

When m aking fillet welds in eit

i h i l i i h ld h l

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Figure 7-37.—Fi l l e t welds in the ver t i ca l pos i t ion .

Move the electrode in a triangular weaving motion, as

shown in figure 7-37, view A. A slight pause in the

weave, at the points indicated, improves the sidewall

penetration and provides good fusion at the root of the

When more tha n one pass is nece

weld, you may use either of the weav

in figure 7-37, views C and D. A slig

of the weave will ensure fusion witho

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Figure 7-38.—B ut t j o i n t w e l d i ng i n t h e ve r t i c a l pos i t ion .

slightly at the surface of plate G. Try not to undercut

either of the plates or to allow the molten metal to

overlap a t t he edges of the weave.

Lap joints on heavier plate may require more than

one bead. If it does, clean t he initial bea d th oroughly and

place all subsequent beads as shown in figure 7-37, view

F. The precautions to ensure good fusion and uniform

weld deposits that was previously outlined for tee joints

also apply to lap joints.

BUTT J OINTS.— Prepare the plates used in verti-

cal welding identically to those prepared for welding in

the flat position. To obtain good fusion an d pen etra tion

with no undercutting, you should hold a short arc and

the motion of the arc should be carefully controlled.

with no undercutt ing. Welds made

backup strip should be done in the sa

E -7018 E le ct r od e We ld ing T e c hn iq

The previously described verti

niques generally cover all types of elyou should modify the procedure sl

E-7018 electrodes.

When vertical down welding, yo

electr ode lightly using a very short

using a long arc since the weld depe

slag for shielding. Small weaves and

preferred to wide weave passes. Use

with ac tha n with dc. Point the electro

join t and t ip it forwa rd only a few de

tion of travel.

On vertical up welding, a triang

produces the best results. Do not use

or remove the electrode from the mo

the electrode straight into the joint a

in order to allow the arc force to help Adjust t he a mper age in th e lower l

mended range.

O V E R H E A D - P O S I T I O N W E L D I

Overhead welding is the most d

welding. Not only do you have to con

of gravity but the ma jority of th e tim

assume an awkward stance. Neverthe

it is possible to make welds equal to

other positions.

C u r r e n t S e t t i n g s a n d E l e c t r o d e M

To retain complete control of the

a very short ar c and reduce the am

mended. As in the vertical position o

causes the molten metal to drop or s

When too long an arc is held, the tran

th e electr ode to the base m eta l bec

difficult, an d t he chan ces of large g

metal dropping from the electrode in

i l h d l h h

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Figur e 7 -39.—P o s i t i o n o f e le c t r o d e a n d w e a v e m o t i o n i n t h eo v e r h e a d p o s i t i o n .

cable over your knee. With experien

will become second nature.

WARNING

Because of the possibility ometal, use a protective garment

fitting collar th at buttons or zip

Roll down your sleeves and w

appropriate shoes.

Type of Welds

Techniques used in making bea

and fillet welds in the overhead po

in the following paragraphs.

BE AD WELD S.— For bead we

of the electrode is 90 degrees to the

view A). The travel angle should be

the direction of welding (fig. 7-39,

Weave beads can be made by

shown in figur e 7-39, view C. A ra

necessary at the end of each sem

control the molten metal deposit. Av

ing because this can cause overh

deposit and the formation of a la

pool.

B UTT J OINTS .— Prepare the

butt welding in the same manner as position. The best r esults a re obta

strips are used; however, you must

will not always be able to use a back

bevel the plates with a featheredg

backing strip, the weld will repea

unless extreme care is taken by the

For overhead butt welding, bead

over weave welds. Clean each bearough areas before placing the next

position and the order of depositio

when welding on 1/4- or 1/2-inch

figure 7-40, views B and C. Make th

electrode held at 90 degrees to the

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Figur e 7-41.—F i l le t w e l d i ng i n t he ove r h ead pos i t ion .

Hold the electrode at approximately 30 degrees to the the arc and allow the metal to soli

t th l t d t th t d

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T a b l e 7 - 3 — C a u s e s a n d C u r e s o f C o m m o n W e l d i n g P r o b l e m s

h i i h

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slight circular motion make the second, third, and fourth

passes. This motion of the electrode permits greater

control and better distribution of the weld metal.

Remove all slag and oxides from the surface of each pass

by chipping or wire bru shing before a pplying a dditiona l

beads to the joint.

W E L D I N G D I F F I C U L T I E S

Many of the welding difficulties in metal-arc weld-

ing are the same as in oxygas welding. A few such

problems include undercut, cracked welds, poor fusion,

and incomplete penetration.

Table 7-3 provides an illustration of the most com-mon welding problems encountered during the arc-

welding process and methods to correct them.

Every welder has the responsibility of making each

weld the best one possible. You can produce quality

welds by adhering to the rules that follow.

1. Use only high-quality welding machines,

electrodes, and welding accessories.

2. Know the base mat erial tha t you are working

on .

3. Select the p roper welding process t ha t gives the

highest quality welds for the base material used.

4. Select the proper welding procedure that meets

the service requirement of the finished weldment.

5. Select the correct electrode for the job in

question.

6. When preheating is specified or required make

sure you meet the temperature requirements. In any

case, do not weld on mat erial th at is below 32°F with out

first preheating.

7. Clean the base metal of all slag, paint, grease,

oil, moisture, or any other foreign materials.

8. Remove weld slag and th orough ly clean ea ch

bead before making the next bead or pass.

9. Do not weld over cracks or porous ta ck welds.

Remove defective tack welds before welding

the root gap to maintain the stren

some cases, it is advantageous to m

to avoid extremely large fillet weld

13. Inspect your work afte

immediately remove and replace an

14. Observe th e size requiremenmake sure that you meet or slightly

size.

15. Make sure that the f inishe

weld is smooth and that overlaps

been repaired.

P I P E WE L D I N

Welding is the simplest and e

sections of pipe. The need for comp

and special threading equipment is

pipe has reduced flow restriction

chanical connections and the overa

are less. The most popular method

the shielded metal-arc process; how

arc methods have made big inroadsadvances in welding technology.

Pipe welding ha s become r eco

sion in itself. Even though many of

parable to other types of welding, p

skills that are unique only to pipe

the h azardous mat erials that most p

welders are required to pass specif

can be certified

In the following paragraphs, pip

pipe welding procedures, definition

mation are discussed.

P I P E W E L D I N G P O S I T I O N S

You may recall from chapter 3

there are four positions used in pipe

They are known as the horizontal r

the horizontal fixed position (5G),

(6G), an d th e vertical position (2G

term s refer to the position of the pipe

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Figur e 7 -42 .—B u t t j o i n t s a n d s o c k e t f i t t i n g j o in t s .

Butt joints are commonly used between pipes and

between pipes and welded fittings. They are also used

for butt welding of flanges and welding stubs. In making

a butt joint, place two pieces of pipe end to end, align

them, an d then weld them. (See fig. 7-42.)

When t he wa ll thickness of the pipe is 3/4 inch or

less, you can use either the single V or single U type of

butt joint; however, when the wall thickness is more tha n

3/4 inch, only the single U type should be used.

Fillet welds are used for welding slip-on and

threaded flanges to pipe. Depending on the flange and

type of service, fillet welds may be required on bothsides of the flange or in combination with a bevel weld

(fig. 7-43). Fillet welds are also used in welding screw

or socket couplings to pipe, using a single fillet weld

(fig. 7-42). Sometimes flanges require alignment. Fig-

7 44 h f fl d i i

Figure 7 -43 .— F l a n g e c o n n

Figure 7 -44 .— F l a n g e a l i g

J O I N T P R E P AR A T IO N A N D F I T

You must carefully prepare pip

if you want good results. Clean

surfaces of all loose scale, slag, rust,

foreign matt er. Ensur e tha t th e joint

an d u niform . Remove th e slag frohowever, it is not necessary to remov

When you prepa re joint s for w

tha t bevels mu st be cut accur ately.

by machining, grinding, or using a g

fieldwork th e welding operat or u su

yet not exceeding 3/16 inch that

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Fi gu r e 7 -45 .—Ang l e i r on j i g .

Align the piping before welding and maintain it in

alignment during the welding operation. The maximum

alignment tolerance is 20 percent of the pipe thickness.

To ensure proper initial alignment, you should useclamps or jigs as holding devices. Apiece of angle iron

makes a good jig for a small-diameter pipe (fig. 7-45),

while a section of channel or I-beam is more suitable for

larger diameter pipe.

TACK WELDING

When welding material solidly, you may use tack

welds to hold it in place temporarily. Tack welding isone of the most important steps in pipe welding or any

other type of welding. The number of tack welds re-

quired depends upon the diameter of the pipe. For

1/2-inch pipe, you need two tacks; place them directly

opposite each other. As a rule, four tacks are adequate

for standard size of pipe. The size of a tack weld is

determined by the wall thickness of the pipe. Be sure

that a tack weld is not more than twice the pipe thicknessin length or two thirds of the pipe thickness in depth.

Tack welds should be the sam e quality as t he final weld.

Ensu re th at t he ta ck welds have good fusion a nd a re

thoroughly cleaned before proceeding with the weld.

S P A C E R S

In a ddition to tack welds, spacers sometimes ar e

required to maintain proper joint alignment. Spacers areaccura tely machined pieces of metal t hat conform to the

dimensions of the joint design used. Spacers are some-

times referred t o as chill rings or backing rings, and t hey

serve a number of purposes. They provide a means for

maintaining the specified root opening, provide a con-

yet not exceeding 3/16 inch, that

fusion and penetration without und

inclusions.

Make certain th e welding curr en

recommended by the manufactur

machines and electrodes.

W E A T H E R C O N D I T I O N S

Do not as sign a welder t o a jo

following conditions listed below un

the work area are properly protected

c When the atmospheric tempe

0°F

l When the surfaces are wet

l When rain or snow is falli

condensing on the weld surfa

l Dur ing periods of high wind

At temperatures between 0°F

weld area within 3 inches of the joi

temper atu re warm to the ha nd befor

WEARFACING

The Seabee welder can greatly

construction equipment by the use o

dures. Wearfacing is the process of

special composition metal onto the

type of metal for the purpose of r

selection of a wearfacing alloy for on the ability of the alloy to withst

sion. Impact refers to a blow or s

surface that results in fracture or gr

Abrasion is the grinding action tha

surface slides, rolls, or rubs again

high-compressive loads, t his a ction

ing.

Alloys that are abrasion resistastanding impact. Conversely, those

pact well are poor in resisting abras

are many alloys whose wearfacing

tween the two extremes. These allo

tection against abrasion and withsta

T E C H N I Q U E S

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F i g u r e 7 -4 6 .—W e a r f a c i n g t e c h n i q u e s .

P R E H E A T I N G

Depending on t he t ype of metal, sometimes it is

necessary t o preheat t he base m etal t o lessen distortion,

to prevent spa lling or cracking, and t o avoid ther mal

shock The prehea ting temperat ure depends on the car-

bon a nd a lloy conten t of the base m etal. In general, as

carbon content increases so does the preheating tem-

perature. Improper heating can adversely affect a metal

by reducing its resistance to wear, by making it ha rd an dbrittle, or by making it m ore prone to oxidation a nd

scaling.

To preheat properly, you must know the composi-

tion of the base meta l. A magnet can be used to deter-

mine if you are working with carbon steel or austenitic

manganese steel. Carbon steel is magnetic, but be care-

ful because work-hardened a ustenitic man ganese steel

is also magnetic. Make sure that you check for magnet-

ism in a nonworked part of the austenitic manganese

steel. There are other ways to tell the difference between

meta ls , such as cast iron an d cast s teel. Cast iron chips

or cracks, while cast steel shaves. Also, some metals

give off telltale spar ks when str uck by a chisel.

In preheat ing, you should raise th e surface tempera-

ture of the workpiece to the desired point and then soak

it un til th e hea t r eaches its core. After wear facing, cool

the work places slowly.

T E C H N I Q U E S

Where possible, position the wo

ha nd welding. This a llows you t o fin

and at less cost.

The building up and wearfacing

generally recommended because ccrack. However, some cast-iron parts

str aight abr asion can be wear faced

must preheat these parts to tempera

1200°F and then allow them to cool

facing. Peening deposits on cast iro

stresses after welding.

Welding materials for building u

from those used in wearfacing the s

wearfacing a badly worn part, you m

to 3/16 to 3/8 of an inch of its finishe

material must be compatible with b

and the wearfacing overlay as we

enough t o meet th e s tru ctural requir

must have the properties that enable

flowing, mushing under high-comp

plastic deformation under heavy imp

properties, the buildup mat erials c

wearfacing overlay. When the overl

supported, it will span.

Many t imes high-alloy wearfac

deposited on the parts before they ar

The ma ximum a llowable wear is usu

two layers deep (1/4 inch) before w

deposit the wearfacing alloy in laye

thick. Thick layers creates more problay at all. Usually you only need tw

layer produces an admixture with t

second forms a wear-resistant surfac

In wearfacing built-up carbon-st

high interpass temperatures and us

rather than a stringer bead. (See fig. 7-

ness of a single pass bead t o 3/16 i

technique for each layer and avoid sDeposits made with

check on the surface.

high-alloy

Checking

naturally or if it is unlikely to occu

where h eat builds up You can bri

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Figu re 7 -48 .—W e a r f a c i n g b u l l d o z e r e n d b i t s .

F igu re 7 -49.—W e a r f a c i n g s h o v e l t e e t h .

F igu re 7 -50 .—W a ff le o r c r o s s h a t c h i n g .

(locked-in) stresses. With out checking, th e combinat ion

of residual st resses a nd ser vice str esses ma y exceed

tensile s trength a nd cause deep cracks or spal l ing (fig.

7-47). Be sur e to indu ce checking if it does not occur

where h eat builds up. You can bri

sponging the deposit with a wet clot

with a fine m ist of wat er. Also you c

ing by occasionally striking it with a

cooling. When a check-free dep osit

softer alloy and adjust preheating a

quirements.

Bu l l d o ze r B l ad es

Bulldozer blades are wear-faced

bits in th e flat position a nd welding

outer corners and a long the edges. Be

high-carbon blades before wearfac

bits, weld new corners and then wea

Shovel t ee th

Wear-face shovel teeth when

before being placed into service. The

used in wearfacing can have a mar

service life of the t eeth. Wear -face sho

mainly in rock with beads running t

tooth (fig. 7-49). This allows the rock

metal beads. Teeth that are primaril

dirt, clay, or sand should be wear-

running across the width of each toot

the direction of the mat erial tha t f lo

(See fig. 7-49.) This allows the materia

between the beads and provide more

base m etal. Another effective pat ter

crosshatch (fig. 7-50). The wear facing

and sides of each tooth, 2 inches from

beads behind a solid deposit reduce w

Table 7-4.—Table of Recommended Electrode Sizes , Current Sett ings, and Cutt ing Speeds for Carbon-Arc Cutt ingo f S t e e l P l a t e

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More information on wearfacing applications may The carbon-arc method of cutti

be obta ined from t he N CF Weld in g Mat erial s Han d-

book, NAVFAC P-433.

CARBON-ARC CUT TING

Metals can be cut cleanly with a carbon electrode

arc because no foreign metals are introduced at the arc.

The cutting curren t sh ould be 25 to 50 amps above the

welding current for the same thickness of metal.

The carbon electrode point should be ground so that

it is very sharp. During th e actual cuttin g, move thecarbon electr ode in a vertical elliptical m ovement to

undercut t he meta l; this aids in the r emoval of the m olten

metal. As in oxygen cutting, a crescent motion is pre-

ferred. Figure 7-52 shows the relative positions of the

electrode and the work in the cutting of cast iron.

cast iron because the arc temperatur

melt t he oxides form ed. It is espe

undercut the cast-iron kerf to pro

Position the electrode so the moltenfrom t he gouge or cutt ing area s. T

cutting speeds, plate thicknesses, a

for carbon-arc cutting.

Because of the high currents re

form of carbon electrode is better. To

effect on the electrode, you should no

tha n 6 inches beyond the holder w

carbon burns away too fast, shorteextends out of th e electr ode holder to

Operating a carbon electrode at extre

tur es causes its su rface to oxidize and

ing in a rapid reduction in the electr

Carbon-arc cutting does not req

ators. Standard arc-welding generat

of arc-welding station equipment a

Straight polarity direct current (DCS

Because of the high temperatur

of the a rc, choose a sh ade of helmet

tha n t he normal sh ade you would us

sam e thickness of meta l. A number

i d d f b ld

welding. The electrode holder operat

varying between 60 and 100 psig

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Figure 7 -53 .—A ir c a r b o n - a r c c u t t i n g .

metal . Figure 7-53 shows the process. The equipment

consists of a special holder, as shown in figure 7-54, tha t

uses carbon or graphite electrodes and compressed air

fed through jets built into the electrode holder. A push

button or a hand valve on the electrode holder controls

the air jet.

The air jet blows the m olten m etal away a nd usu ally

leaves a surface that needs no further preparation for

varying between 60 and 100 psig.

During u se, bare carbon or graph

come smaller due to oxidation caused

Copper coating these electrodes r

buildup and prolong their use.

The operating procedures for air

and gouging are basically the same. T

as follows:

l

l

l

l

l

Adjust the machine to the co

electrode diameter.

Start the air compressor and a

to the corr ect a ir pressu re. Upressure possible-just enough

away the molten metal.

Insert the electrode in the h

carbon electrode 6 inches be

Ensure that the electrode p

shaped.

Strike the arc; then open the

air-jet disc can swivel, and th

disc automatically aligns the

electrode. The electrode is adju

holder.

Control the arc and the speed

to the shape and the condition

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Figure 7-56.—S t e e l e le c t r o d e b e i n g u s e

Figure 7 -55 .—V-groove gouged in 2 - inch- th ick ca rbon s tee l .

M E T A L E L E C T R O D E A R C C U T T

.Always cut away from the operator as moltenmetal sprays some distance from the cutting ac-

tion. You ma y use th is process to cut or gouge

metal in the flat, horizontal, vertical, or overhead

positions.

AIR CARBON-ARC GOUGING

Air carbon-ar c gouging is u seful in ma ny var ious

metalworking applications, such as metal shaping and

other welding pr epara tions. For gouging, hold the elec-

trode holder so the electrode slopes back from the direc-

tion of travel. The air blast is directed along the electrode

toward the arc. The depth and contour of the groove are

contr olled by the electr ode angle and tr avel speed. The

width of the groove is governed by the diameter of the

electrode.

When cut ting or gouging a sha llow groove on th e

surface of a piece of metal you should position the

Metal can be removed with the st a

but for good gouging or cutting result

special meta l electrodes th at have been

type of work, Manufacturers have dev

with special coatings that intensify t

rapid cutting. The covering disintegrat

than the metallic center. This creates

produces a jet action that blows the m

(fig. 7-56). The main disadvantage of

is that the additional metal produced

These electrodes are designed for

steel, copper, aluminum, bronze, nicke

ganese, steel, or alloy steels.

Atypical gouge-cutting operation i

7-57. Notice that the angle between

plate is small (5 degrees or less). Thi

remove the extra metal produced by t

The recommended current setting

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Figure 7 -57 .— G o u g e - c u t t i n g o p e r a t i o n u s i n g a s o l i d c o r e a r c -c u t t i n g e l e c t r o d e .

WELDING QUALITY CONTROL

In the fabrication or repair of equipment, tests are

used to determine th e quality and soundness of the

welds. Many different tests have been designed for

specific faults. The type of test used depends upon the

requirements of the welds a nd t he a vailability of testing

equipment. In this section, nondestructive and destruc-tive testing are briefly discussed.

N O N D E S T R U C T I V E T E S T I N G

Nondestructive testing is a method of testing that

does not destroy or impair the usefulness of a welded

item. These tests disclose all of the common internal and

surface defects that can occur when improper welding

procedures are used. A large choice of testing devices is

available and most of them are easier to use than the

destructive methods, especially when working on large

and expensive items.

Vi s u a l In s p ec t i o n

Visual inspection is usually done automatically by

the welder as he completes his welds. This is strictly asubjective type of inspection and usually there are no

definite or rigid limits of acceptability. The welder may

use templates for weld bead contour checks. Visual

inspections are basically a comparison of finished welds

with a n a ccepted st an dar d This test is effective only

Figure 7 -58 .— C i r c u l a r m a g n e t i z a t i o n

Figure 7-59.—L o n g i t u d i n a l m a g n e t i z a t

It is used in metals or alloys in whi

magnetism. While the test piece is m

containing finely ground iron powder

as the magnetic field is not disturbed

will form a regular pat tern on the piece. When the magnetic field is int

or some other defect in the metal,

suspended ground metal also is inte

cles of metal cluster around the defe

to locate

force are in a circular direction, as shown in figur e 7-58. that induces longitudinal m agneti

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g

When the current flow is through a coil around the test

piece, as shown in figure 7-59, the magnetic lines of

force are longitudinal through the test piece.

When a defect is to show up as a disturbance in the

patt ern of the iron par ticles, the direction of the ma gneticfield must be at r ight an gles to th e major axis of the

defect. A magnetic field having the necessary direction

is established when the current flow is parallel to the

major axis of the defect. Since th e orienta tion of th e

defect is unknown, different current directions must be

used during the test. As shown in figure 7-58, circular

magnetism is induced in th e test piece so you can inspect

the piece for lengthwise cracks, while longitudinal mag-netism, as shown in figure 7-59, is induced so you can

inspect the piece for transverse cracks. In general, mag-

netic par ticle inspection is sa tisfactory for detecting

surface cracks and su bsurface cracks that are n ot m ore

tha n 1/4 inch below the sur face.

The type of magnetic particle inspection unit com-

monly used in the Navy is a portable low-voltage unit

having a maximum magnetizing output of 1,000 am-peres, either alternating or direct current. It is ready to

operate when plugged into the voltage supply specified

by the manufacturer. The unit consists of a magnetizing

current source, controls, metering, three 10-foot lengths

of flexible cable, and a prod kit. The prod kit includes

an insulated prod grip fitted with an ON- OFF relay or

current control switch, a pair of heavy copper contact

prods, and two 5-foot lengths of flexible cable. Cablefittings a re designed so that either en d of the cable can

be connected to the unit, to the prods, or to any other

cable. The three outlets on the front of the unit make

changing from alter nat ing to direct curr ent or vice versa

very easy. The outlets are labeled as follows: left is ac,

the center is C O M M O N , an d the r ight is dc. One cable

will always be plugged into the COMMON outlet ,

while the other cable is plugged into either the ac or dc

outlet, depending upon what type of curr ent the t est

requires. For most work, alternating current magnetiza-

tion effectively locates fat igue cracks a nd similar de-

fects extending through to the surface. When you

require a more sensitive inspection to detect defects

g g

workpiece that is surrounded b

(fig. 7-59)0

Although you can use either o

the prod method is probably the ea

instances, it effectively serves to dWith the prods, however, only a s

piece can be magnetized at any on

ized ar ea is limited to th e distance

points a nd a few inches on each sid

To check the entire su rface, you m u

area by changing the location of the

Each area of the test piece must b

once with the current passing throdirection and then with the current

meta l in a direction at r ight an gles

first test. One of the advantages o

that the current can be easily pass

in any desired direction. Thus, w

suspect, magnetic fields of differe

induced during the test.

The prod method is accomplisunit for a curr ent output suitable for

testing of any particular kind of

setting required depends on the di

conta ct points. With the pr od kit tha

un it, the spa ce between pr od con

inches. A current setting between 3

is satisfactory when the material t

3/4 inch. When th e ma teria l thickn

use 400 to 600 amperes. When the

are closer together, the same magne

obtained with less current. With pr

same spacing, more current will in

strength.

After adjusting the unit, place t

Hold them infirm conta ct with t he m

current. Then apply magnetic partiwith th e duster bulb an d look for an

With th e cur ren t st ill on, remove

from the test area with a blower bu

inspection. Do not move the pr ods u

has been tu rn ed off. To do so could

false indications frequently occur you must be able to altern ating current . Set th e curr ent reg

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false indications frequently occur, you must be able to

interpret the particle indications accurately.

The factors that help you interpret the test results

include the amount of magnetizing current applied, the

shape of the indication, th e shar pness of the outline, the

width of the pattern, and the height or buildup of the

particles. Although these characteristics do not deter-

mine the seriousness of the fault, they do serve to

identify the kind of defect.

The indication of a crack is a sharp, well-defined

pattern of magnetic particles having a definite buildup.

This indication is produced by a relatively low-magnet-

izing current. Seams are revealed by a straight, sharp,

fine in dicat ion. Th e buildup of par ticles is r elatively

weak, and the magnetizing current must be higher than

that required to detect cracks. Small porosity and

rounded indentations or similar defects are difficult to

detect for inexperienced inspectors. A high-magnetizing

current continuously applied is usually required. The

particle patterns for these defects are fuzzy in outline

and have a medium buildup.

The specifications governing the job determine

whether or not an indicated defect is to be chipped or

ground out and repaired by welding. Surface cracks are

always removed and repaired. Indications of subsurface

defects detected by magnetic particle inspection are

evaluated by the inspector. When the indication is posi-

tive, the standard policy is to grind or chip down to solid

metal an d mak e the r epair. Unless the inspector can

differentiate accurately between true and false indica-

tions, the use of magnetic particle inspection should be

restricted to the detection of surface defects, for which

this application is almost foolproof.

After the indicated defects have been repaired, you

should reinspect th e areas to ensure that the r epair is

sound. The final step in magnetic particle inspection, is

to demagnetize the workpiece. This is especially impor-tant when the workpiece is made of high-carbon steel.

Demagnetization is essential when you use direct cur-

rent to induce the magnetic field; however, it is not as

necessary when alternating current was used in the test.

In fact, the usual demagnetization procedure involves

altern ating current . Set th e curr ent reg

current identical to that u sed for th e in

on the unit. Gradually decrease the

ammeter indicates zero. On large p

necessary to demagnetize a small porti

a time.

A check for the presence of a magn

made by using a small compass. A

needle from the normal position, whe

held near t he workpiece, is an indicatio

field is present. Also you can use an in

field indicator to check for the presen

field. This instrument usually comes w

particle inspection unit e

L iq u i d P e n e t r a n t I n s p e c t io n

Liquid penetra nt m ethods are used

for surface defects that are similar to

magnetic particle inspection. Unlike

inspection, which can reveal subsurfapenetrant inspection reveals only thos

open to the surface.

Four groups of liquid penetrants

use. Group I is a dye penetrant that i

able. Group II is a wat er washa ble dye

III and Group IV are fluorescent pen

follow the instructions given for each

since there are some differences in thsafety precautions required for the va

Before using a liquid penetrant t

remove all slag, rust, paint, and m

surface. Except where a specific finish

not necessary to grind the weld surfa

weld surface meets applicable specific

weld contour blends into the base met

cutting. When a specific finish is requliquid penetrant inspection before th

This enables you to detect defects th

the final dimensions, but you must m

penetra nt inspection a fter th e specifie

given.

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Figure 7-60.—L i qu i d pene t r an t i n s pec t i on .

mat erials and to make sure that the sur face is ent irely

dry before using the liquid penetrant.

Maintain the temperature of the inspection piece

an d the liquid penetra nt in t he ra nge of 50°F to 100°F.

Do not attempt to use the liquid penetrant when this

temperature range cannot be maintained. Do not use an

open flame to increase the temperature because some of the liquid penetrant materials are flammable.

After thoroughly cleaning and drying the surface,

coat t he surface with th e liquid penetra nt. Spray or brush

on the penetrant or dip the entire piece into the penetrant.

To allow time for t he penetr ant to soak into all th e cracks,

crevices, or other defects that are open to the surface,

keep the surface of the piece wet with the penetrant for

a min imum of 15 or 30 minu tes, depending upon th e

penetrant being used.

After keeping the surface wet with the penetra nt for

the required length of time, remove an y excess penetra nt

from the surface with a clean, dry cloth, or absorbent

paper towel. Then dampen a clean, lint-free material

with penetrant remover and wipe the remaining excess

penetrant from the test surface. Next, allow the test

surface to dry by normal evaporation or wipe it dry with

a clean, lint-free absorbent material. In drying the sur-

face, avoid contaminating it with oil, lint, dust, or other

materials that would interfere with the inspection.

The following actions ta ke pla

penetrants. First , the penetrant th

surface of the material will seep i

open to the su rface, as sh own in f

The penetra nt is norma lly red in colo

ing oil, it seeps into any crack or cr

the surface. Next, the excess penetr

the surface of the metal with the pe

a lint-free absorbent mat erial. Only

of the metal surface is removed

leaving the penetrant that has seepe

Finally, the white developer is a

of the metal, as shown in figure

developer is an absorbing material

the penetrant from the defect. Ther

trant indications in the white deve

defective areas. The a mount of re

from the defective areas indicates

times t he type of defect. When you

the l ighting in the test area must

enable you to see any indications o

surface.

The indications you see duringinspection must be carefully interp

In almost every inspection, some

tions are present. Most of these a

failure to remove all the excess

surface At least 10 percent of all

Remove all penetrant inspection materials as soon

as possible after the final inspection has been made. Use

water or solvents, as appropriate. Since some of the

Eddy current testing operates on

whenever a coil carrying a high-fre

current is placed next to a m etal, an e

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wate o so ve ts, as app op ate. S ce so e o t e

liquid penetrant materials are flammable, do not use

them near open flames, and do not apply them to any

surface that is at a t emperatur e higher th an 100°F. In

addition to being flammable, many solvents are poison-

ous in the vapor form and highly imitat ing to the skin inthe liquid form.

Ra diogr a ph i c I nspe c t i on

Radiographic inspection is a method of inspecting

weldments by the use of rays that penetrate through the

welds. X rays or gamma rays are the two types of waves

used for this process. The rays pass through the weld

and onto a sensitized film tha t is in direct conta ct with

th e back of the weld. When t he film is developed, gas

pockets, slag inclusions, cracks, or poor penetration will

be visible on the film.

Because of the danger of these rays, only qualified

personnel are authorized to perform these tests. As

Seabees, you will rarely come in contact with these

procedures.

U l t r a son i c I nspe c t i on

Ultrasonic inspection of testing uses high-fre-

quency vibrations or waves to locate and measure de-

fects in welds. It can be used in both ferrous and

nonferrous materials. This is an extremely sensitive

system a nd can locate very fine surface and su bsurface

cracks as well as other types of defects. All types of

join t s can be t es t ed .

This process uses high-frequency impulses to check

th e soundness of the weld. In a good weld, th e signal

travels through the weld to the other side and is then

reflected back a nd sh own on a calibrated screen. Irregu-

larities, such as gas pockets or slag inclusions, cause the

signal t o reflect back sooner an d will be displayed on

the screen as a change in depth. When you use this

system, most all types of materials can be checked for

defects. Another advantage of this system is that only

one side of the weld needs to be exposed for testing.

E d d C T i

p ,

produced in t he m etal by induction. T

is called an eddy current.

The test piece is exposed to elec

by being placed in or nea r h igh-fre

coils. The differences in the weld ca

impedance of the coil, and this is indi

instruments. When there are defects,

change in impedance, and the size of

by the am ount of this chan ge.

D E S T R U C T I V E T E S T I N G

In destructive testing, sample por

structures are required. These sampl

loads unt il they actua lly fail. The fai

studied and compared to known stan

the quality of the weld. The most

destructive testing are known as free

nick-break, im pact, fillet welded jo

tensile testing. The primary disadvan

testing is that an actual section of a

destroyed to evaluate the weld. This

usually used in the certification proc

Some of the testing requires ela

tha t is not available for use in the fie

ma y be perform ed in th e field withou

ment are the free-bend test, the guided

nick-break test.

Fr e e - Be nd T e s t

The FREE-BEND TEST is design

ductility of the weld deposit and the

adjacent t o the weld. Also it is used

percentage of elongation of the wel

you sh ould recall, is tha t pr operty of

it to be drawn out or hammered thin.

The first step in preparing a we

the free-bend test is to machine the

ment crown flush with the surface of t

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Figure 7-61.—F r e e - b e n d t e s t

Requirements for a satisfactory

elongat ion of 15 percent an d no cra ck

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Figure 7-63.—G ui ded - bend t e s t s pec i m ens .

test piece by using a hydrau lic press or similar ma chine.

When th e proper precau tions are ta ken, a blacksmith’s

forging press or ha mmer can be used to complete the

bending operation. If a crack more than 1/16 inch devel-

ops during the test, stop the bending because the weld

has failed; otherwise, bend the specimen flat. After

completing the test, measure the distance between the

scribed lines and call tha t m easur ement (y). The percent-

age of elongat ion is t hen determ ined by the form ula:

elongat ion of 15 percent an d no cra ck

inch on the face of the weld.

G uide d- Be nd T e s t

You use the GUIDED-BEND T

the quality of weld metal a t t he face a

join t . Th is t es t is ma de in a sp ecia lly

example of one type of jig is shown i

The test specimen is placed acro

the die. A plunger, operated from a

pressure, forces the specimen into the

requirements of this test, you must b

180 degrees—the capacity of the jig.

appear on the surface greater than 1/

bend tests are made in this jig with th

in t ension (outs ide), as shown in figu

bend tests are made with the root of t

(outside), as shown in figure 7-63.

Figure 7-64 shows a ma chine use

guided-bend test . It is u sed in m any w

which t he t est piece bends by the p

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Figure 7-65.— N i ck - b r eak t e s t o f a bu t t w e l d .

testing laboratories for the daily testing of specimens.

Simple in construction and easy to use, it works by

hydrau lic pressure and can a pply a direct load up to

40,000 pounds, and even more on small specimens.

When you make the test, position the specimen in the

machine as previously indicated and start pumping the

actuator. Keep your eye on the large gauge and watch

the load increase. You will know the actual load under

han d tha t is carr ied along by the ga

remains at the point of maximum

returns to zero.

Nick-Break Tes t

The NICK-BREAK TEST is u

the internal quality of the weld m

various inter na l defects (if presen

sions, gas pockets, lack of fusi

burned metal. To accomplish th

checking a butt weld, you must fi

specimens from a sample weld (fi

cut at each edge through th e cen

depth of cut sh ould be about 1/4 i

Next, place the saw-nicked sp

supports, as shown in figure 7-65

mer, break the specimen by strikin

you made the saw cuts. The weld

break should be completely fused,

sions, and contain no gas pockets g

across th eir greatest dimension.

more th an six pores or gas pocke

exposed broken surface of the wel

I m p a c t T e st

You use the IMPACT TEST

of a weld to absorb energy un

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Figure 7-67.—P er f o r m i ng i m pac t t e s t .

fractur ing. This is a dyna mic test in which a t est speci-

men is broken by a single blow, and the en ergy used in

breaking the piece is measured in foot-pounds. This test

compares the toughness of the weld metal with the base

meta l. It is useful in finding if an y of the mecha nical

properties of the base metal were destroyed by the

welding process.

The two kinds of specimens u sed for im pact test ing

are known as Charpy and Izod (fig. 7-66). Both test

pieces are br oken in an impact test ing machine. The only

difference is in the manner that they are anchored. The

Charpy piece is supported horizontally between two

anvils and t he pendulum strikes opposite the n otch,

as shown in figure 7-67, view A. The Izod piece is

supported as a vertical cantilever beam and is struck on

the free end projecting over the holding vise (fig. 7-67,view B).

Fi l le t -Welded J oint Tes t

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Figur e 7-69.—Ruptur ing f i l l e t weld t es t p l a t e .

(fig. 7-69) un til a br eak occur s in t he joint . This force

may be applied by hydraulics or hammer blows.

In addition to checking the fractured weld for

soundness, now is a good time to etch the weld to check

for cracks.

E tc h in g T e st

The ETCHING TEST is used to determine the

soundness of a weld and also make visible the boundary

between the base metal and the weld metal.

To accomplish t he t est, you m ust cut a t est piece

from the welded joint so it shows a complete transverse

section of the weld. You can make the cut by either

sawing or flame cutting. File the face of the cut and then

polish it with grade 00 abrasive cloth. Now place the test

piece in the etching solution.

The et ching solutions generally used are hydrochlo-

ric acid, ammonium persulfate, iodine and potassium

iodide, or nitric acid. Each solution highlights differentdefects an d a rea s of the weld. The h ydrochloric acid

dissolves slag inclusions and enlarges gas pockets,

while nitric acid is used to show the refined zone as well

as the metal zone.

Figure 7-70.—S t anda r d t en s i l e

The essential features of a ten

are the parts that pull the test spec

that measure the resistance of the te

instrument, known as an extensomis also used to measur e the str ain in

equipment comes with a device th

the stress-strain curve for a perman

The ten sile test is classified a

because the test specimen must b

unt il it fails. Becau se of the design

weld samples must be machined to

This explains why the test is mademen, rather than on the part i tself. It

test specimen represents the part

specimen be given the sam e heat t r

but it a lso must be heat-treated at t

There are many standard types

mens, and figure 7-70 shows one st

men commonly used. The standa

accurately machined specimen. Ov

critical item, but th e diameter a nd g

0.505-inch-diameter (0.2 square inc

of th e reduced portion provides a

nipulate arithmetically. The 2-inch

distance between strain-measuring

portion of the specimen where yo

someter. In addition, you can use

determine percent elongation.

The tensile test a mounts t o

steadily increasing load (or pull) on

measur ing the resistan ce of the spec

Even if recording equipmen t is not

yield point, elastic limit, modulus of elasticity, and other

properties of the material.l Keep welding cables dry and fr

Keep the cables in good condition

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S A F E T Y R E G U L A T I O N S

You, as the welder, must have a thorough KNOWL-

EDGE of the safety precautions relat ing to the job. That

is not all; you should also consider it your responsibility

to observe all of the applicable safety precautions. When

welding, carelessness can cause serious injury to your-

self as well as others.

Bear in mind the safety precautions for operating

welding equipmen t can vary considera bly becau se of

th e different types of equipmen t in volved; th erefore,

only general precautions on operating metal arc-weld-

ing equipment are presented here. For specific instruc-

tions on the operation and maintenance of your

individual equipment, consult the equipment manufac-

tur er’s instru ction ma nua l. In regar ds to genera l precau-

tions, know your equipment and how to operate it . Use

only approved welding equipment, and ensure that it is

maintained properly.

l Before you start welding, ensure that the welding

machine frame is grounded, that neither terminal of the

welding generator is bonded to the frame, and that all

electrical connections are secure. The ground connec-

tion must be att ached firmly to the work, not merely laid

loosely upon it.

appropriate steps to protect them fro

is necessary to run cables some dist

chine, lay them overhead, if at all p

quate support devices.

Q When you are using portabl

sure th at t he primar y power cable is

welding cables so they do not beco

portable equipment mounted on wh

curely blocked to prevent accidenta

welding operations.

l When stopping work for any

of time, be sure t o de-energize the eq

equipment is not in use, you should

nect it from its source of power.

. Keep the work area neat an

possible, make it a practice to dispos

stubs in a metal container.

Chapter 3 contains information o

ing, eye protection, and safe practice

personal safety of the operator and

may be working nearby so that infor

repeated here. If necessary, go bac

section entitled “Safety” in chapter 3

to the next chapter.

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