Shielded Metal Arc Equipment, Setup, and Operation

Shielded Metal Arc Equipment,Setup, and Operation

Look at:◦SMAW Process◦Basic Electricity (and I mean basic)◦Welding Polarity◦Open Circuit Voltage (OCV)◦Arc Blow◦Duty Cycle◦ Types of Welding Equipment

Chapter #8 – SMAW Equipment Setup and Operation

S = Shielded

M = Metal

A = Arc

W = Welding


FIGURE 8-1 Shielded metal arc welding.American Welding Society


1. ARC LENGTH

2. ELECTRODE ANGLE

3. SPEED OF TRAVEL

4. AMPERAGE


THE DISTANCE BETWEEN THE TIP OF THE ELECTRODE AND THE BASE METAL BEING WELDED


a) THE ANGLE FROM THE VERTICAL PLANE IN THE DIRECTION OF WELDING: 20 – 30 DEGREES

b) THE ANGLE AS SEEN FROM THE END VIEW : 90 DEGREES


Welding current◦Electricity that jumps across the arc gap

Between electrode end and metal being welded

Electric current ◦ Flow of electrons◦Resistance to electron flow produces heat

Greater resistance: greater heat Air has high resistance


Basic Electricity:

1.Voltage

2.Amperage

3.Watts

4.Resistance


Units to describe electrical current

◦Voltage or volts (V): measurement of electrical pressure

◦Amperage or amps (A): measurement of the total number of electrons flowing

◦Wattage or watts (W): measurement of electrical energy or power in the arc

◦Resistance (R): opposes the flow of electrons


Welding arc temperature◦Dependent on voltage,

arc length, and atmosphere

Heat produced by the arc ◦Determined by amperage

FIGURE 8-5 Energy is lost from the weld in the forms of radiation and convection. © Cengage Learning 2012


Types of currents used for welding

◦Direct-current electrode negative (DCEN) Electrode is negative and work is positive

◦Direct-current electrode positive (DCEP) Electrode is positive and work is negative

◦Alternating current (AC) Electrons change direction every 1/120 of a second Electrode and work alternate from anode to cathode


DCEP = DC Electrode PositiveDCRP = DC Reverse PolarityDC +


Electrode -

Work +

DCEN = DC Electrode NegativeDCSP = DC Straight PolarityDC -


FIGURE 8-9 In an alternating current, electrons flow back and forth. © Cengage Learning 2012

Sketch of a AC arc welding circuit for SMAW


The coating on the SMAW electrode Larger selection of electrodes for DC current


SMAW process◦Requires a constant current arc voltage characteristic◦SMA welding machine

Voltage output decreases as current increases

FIGURE 8-10 Constant voltage (CV) and constant current (CC). © Cengage Learning 2012


CC – Amperage Adjustment only

- See next slide for photo



CV – Voltage Adjustment

- WFS (wire feed speed) Adjustment

- see next slide for photo


Voltage WFS


1. AC Machines

2. Portable Engine Driven Power Source (AC/DC)

3. AC/DC Rectifier

4. Multi-Process Inverter (AC/DC).


1) AC MACHINES


2) Portable Engine Driven Power Source (AC/DC)


3) AC/DC Rectifier


1. AC/DC Rectifier

Half Wave Rectification

Full Wave Rectification


4) Multi-Process Inverter (AC/DC)


Voltage at electrode before striking an arc

Maximum Voltage – 80V

The higher the OCV the easierit is to strike an arc

The higher the OCV the increase inchance of electric shock

Newer technology drops OCV below30V once arc is established

FIGURE 8-11 Electricity can have an initial surge muchlike the surge of water when a garden hose nozzle is firstopened. © Cengage Learning 2012


When welding with DC current the arc flares uncontrollably to the side of the electrode instead of straight down

Caused by a constriction of magnetic flux lines

Possible Solutions Switch to AC Move work lead clamp Short arc length and different electrode angle Change welding direction Lower current setting


Percentage of time a welding machine can be used continuously at a specified amperage◦ Increases as amperage is

reduced◦Decreases as amperage is

raised

FIGURE 8-31 Duty cycle of a typical shielded metal arc welding machine. © Cengage Learning 2012


Characteristics◦Should be of proper amperage rating and in good

repair◦Used at maximum amperage rating or less

FIGURE 8-33 The amperage capacity of an electrode holder is often marked on its side.Thermadyne Industries, Inc.


Characteristics◦Must be correct size for current used◦Must clamp tightly to material◦Must be in good repair

FIGURE 8-35 A work clamp may be attached to the workpiece. © Cengage Learning 2012


Loose connections at the power source Loose connection at the work connector or electrode

holder Splices in the cable Too small of cable for amperage being used Broken strands in cable not properly repaired Enlarge hole in cable lug to fit larger stud size Use of excessively long cables


When some or all of the welding current does not return to the power source through the work lead

Usually results from poor cable connections or work piece connection (cable damage, loose fittings, painted surfaces, etc.)


PADDING TECHNIQUE:

THE PLACING OF BEADS OR WEAVES SIDE BY SIDE SO THAT EACH NEW WELD OVERLAPS THE ONE PRECEDING IT


Practicing Padding in The Shop


PADDING IS USED:

1. SHAFTS

2. SHOVELS

3. GRADER BLADES


Documents

Shielded Metal Arc Equipment, Setup, and Operation