Wire Feed Welding Filler Metals and Feeders

120103b

Welder

Wire Feed Welding

Filler Metals and Feeders

GMAW, FCAW, MCAW and SAW

First Period

Table of Contents

Objective One ............................................................................................................................................... 2

GMAW Filler Metal Terms ...................................................................................................................... 2

GMAW Filler Wire Manufacturing .......................................................................................................... 3

GMAW Filler Wire Selection ................................................................................................................... 5

GMAW Electrode Wire Characteristics and Applications ....................................................................... 9

GMAW Filler Metal Packaging .............................................................................................................. 12

Storing and Handling Consumables ........................................................................................................ 13

FCAW Wire Manufacturing ................................................................................................................... 14

FCAW Filler Wire Selection ................................................................................................................... 15

FCAW Filler Metal Packaging ............................................................................................................... 16

FCAW Filler Wire Classifications .......................................................................................................... 17

FCAW Electrode Wire Characteristics and Applications ....................................................................... 19

MCAW Electrode Wire Characteristics and Applications ...................................................................... 22

Objective Two ............................................................................................................................................. 25

Metal Transfer ......................................................................................................................................... 25

Objective Three ........................................................................................................................................... 30

Wire Drive Systems ................................................................................................................................ 30

Welding Gun and Cable Assemblies....................................................................................................... 33

Wire Feed Control and Drive Units ........................................................................................................ 36

Objective Four ............................................................................................................................................ 43

Wire Feeder Operating Variables ........................................................................................................... 43

Self-Test ...................................................................................................................................................... 50

Self-Test Answers ....................................................................................................................................... 54

Wire Feed Welding Filler Metals and

Feeders

Rationale

Why is it important for you to learn this skill?

Filler metals play an important role in reaching the performance goals required of finished welding products. You must choose the appropriate filler metal and the proper feeder system to obtain the desired results.

Outcome

When you have completed this module, you will be able to:

Select wire feed welding consumables.

Objectives

1.

Identify wire feed welding equipment filler metals.

2.

Describe the modes of metal transfer.

3.

Describe wire feed drive systems and gun and cable accessories.

4.

Describe wire feed operating variables.

Introduction

This module will give you the knowledge you need to select wire feed filler metals and wire feeders to suit job requirements. You will also learn the operating variables critical to all wire feed processes.

NOTES

© 2014, Her Majesty the Queen in right of the Province of Alberta

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NOTES

2

Objective One

When you have completed this objective, you will be able to:

Identify wire feed welding equipment filler metals.

GMAW Filler Metal Terms

The following terms describe gas metal arc welding (GMAW) filler metals. You should be familiar with them to communicate with others in the trade.

Term Definition

AWS American Welding Society. cast The diameter of a circle formed by one loop or a maximum of 3 m (10') of electrode wire when cut from a package and laid unrestrained on a flat surface.

CSA Canadian Standards Association. consumable electrode An electrode that is consumed into the molten weld and provides filler metal. composite electrode A generic term for multi-component filler metal electrodes in various physical forms such as stranded wire, hollow tubes and covered wires. filler metal flux

The metal or alloy added to make a welded, brazed or soldered joint.

Material that hinders or prevents the formation of oxides and other undesirable substances in molten metal and on solid metal surfaces and to dissolve or otherwise facilitate the removal of those substances from the weld zone. helix

ISO International Organization for Standardization. mechanical property A metal's ability to withstand or resist an applied force. Some mechanical properties are tensile strength, ductility and fracture toughness. specification

A cork screw effect exhibited by a ring of electrode filler wire when placed on a flat surface without restraint. If both ends of the wire lie flat, there is no helix. If one end is raised, then the distance off the surface is the helix.

Types of standards that use the words shall and will to indicate the mandatory use of certain materials or actions.

Specifications are usually associated with products, for example AWS Specification A5.18 for Carbon Steel Filler

Metals for Gas Shielded Arc Welding . standard welding wire

A document that governs and guides welding activity.

A form of welding filler metal (normally packaged as coils or on spools) that may or may not conduct electrical current depending upon the welding process with which it is used.

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GMAW Filler Wire Manufacturing

Due to the large number of available metals, no single filler metal joins all base metals satisfactorily. Filler wires for the welding of various metals must be manufactured to match the base metal chemistry and mechanical properties such as tensile strength, ductility and impact strength. Manufacturers add various elements to various degrees to give each filler metal its distinct characteristics. Filler metal manufacturers follow stringent specifications to ensure that they consistently meet AWS and CSA standards.

As a standard for the manufacture of welding wires, the AWS has specifications for most classifications of GMAW filler wires. The CSA has largely adopted the AWS classification system. The following characteristics are referenced when setting out specifications for welding wires:

 chemistry and wire sizing,

 testing requirements,

 identification and packaging,

 cast and helix and

 wire finish.

Chemistry and Wire Sizing

Filler wires for GMAW are drawn to form a solid wire that is continuous in length and from the same batch number to ensure uniform chemical composition throughout each roll of wire. The wire size is maintained within a given tolerance to ensure its compatibility with wire feed equipment. Electrode wires for GMAW are available in diameters ranging from 0.5 mm - 3.2 mm (0.020" - 1 /

8

"). The wires are drawn through dies to bring them down to the desired diameter (Figure 1).

NOTES

Figure 1 - Drawing wire to size. (Courtesy ESAB Welding & Cutting Products)

Testing Requirements

Filler metals for GMAW must meet or exceed specified testing requirements. Most AWS specifications and CSA standards include testing requirements for:

 chemical analysis,

 radiographic acceptability,

 tensile strength,

 yield strength,

 ductility and

 impact values.

Most welding jobs or contracts reference that filler metals must be certified to a certain standard or specification. If the filler metal is to be classified to a CSA standard or AWS specification, it must pass several mechanical tests before being classified.

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NOTES

Identification and Packaging

Wires must be identified by classification, wire and spool size, batch number, manufacturer and any other information set out by the standard to which it is made. The

AWS and CSA have specific guidelines outlining the identification information on filler metal packaging. This information can be found on the wire spool. Packaging must be standardized to allow wire spools or drums to fit equipment manufacturers' standardized holding devices. Packaging must also be designed to prevent damage during shipping or storage.

Cast and Helix

Wires are tested to ensure that they feed smoothly to the weld zone, so specifications for continuous solid wire must include the required cast and helix .

Cast

Wire usually takes on a permanent set when wound on a spool. This deformation characteristic is called cast (Figure 2A). The harder and stiffer the wire is, the larger the cast is. This means the wire is straighter, so it deforms less as it travels through the feed rolls. This allows smooth feeding with longer cables and gives the operator greater control. In addition to smooth wire feeding, the cast of the wire ensures that the welding current transfers to the wire as it passes through the contact tube (Figure 2B).

Too small a cast gives the wire too much curl, which causes extreme drag in the liner and contact tip. This may in turn cause wire feeding problems that interfere with the operation of the wire feeder and result in an unstable arc. Smooth wire feeding results when the wire manufacturer stays within specified cast limit requirements.

Figure 2 - Wire cast.

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Helix

Helix is the result of a natural twisting action of the wire during forming. It is the space between two unrestrained loops of wire (Figure 3). If the helix of the wire is excessive, the wire does not exit straight out of the contact tip, which can cause the wire to wander.

The arc becomes unstable as this corkscrew effect causes a change in the direction of wire feed. Helix should not exceed the specifications set out in the standard to which the wire is made (Figure 3).

NOTES

Figure 3 - Wire helix.

Wire Finish

The surface of all filler wires must be clean with a smooth finish free of defects such as depressions, slivers or foreign material that could affect the welding properties or equipment's operation. Some wires are copper-coated to improve the wire's electrical conductivity as it passes through the contact tube. This increased electrical conductivity aids in extending the life of the contact tip. The copper coating also provides a degree of corrosion and oxidation resistance to the wire. Copper-coated wires can flake and cause liner clogging and erratic feeding. This occurs if the copper coating is excessive and the feed rolls are out of alignment or set too tight. Some wires are available uncoated or coated with an inert, waxy finish that promotes smooth feeding with less clogging of the wire feeder and cable liner.

As long as you ensure that the base metal and the electrode are free of moisture and other contaminants, GMAW is capable of depositing low hydrogen content weld metal.

Lubricants are used during the drawing process. If these lubricants remain on the wire, they can cause arc instability, porosity and, in extreme cases, cracking. To check for wire cleanliness, run the wire between your fingers while wearing a white glove. If the glove becomes soiled, place a felt scrubber ahead of the drive rolls. For particularly dirty welding environments, use wire spool covers to help keep the electrode wire clean.

GMAW Filler Wire Selection

Factors that influence the selection of a filler wire are base metal chemistry, the shielding gas you use, type of metal transfer, welding position, service requirements and condition of the base metal. Wires with a higher content of deoxidizing elements are better for use on slightly scaled or rusty materials and with carbon dioxide shielding. Several AWS specifications cover GMAW wires to suit most common construction materials.


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5

NOTES

The mechanical and physical properties of a weld metal may vary from the wire electrode mechanical and physical properties just by altering a welding factor. Some of these factors are:

 electrode size,

 current,

 base metal composition,

 dilution with the base metal,

 base metal thickness,

 joint geometry,

 preheat,

 interpass temperatures,

 surface condition and

 shielding gas.

For example, using argon-O

2

shielding gas for GMAW does not affect chemical composition, but when you use carbon dioxide shielding gas under the same conditions, the weld metal deposit shows a reduction in carbon content, manganese, silicon and other deoxidizers. The loss of these elements reduces the tensile and yield strength of the weld, so you must use the recommended shielding gas for the wire.

Choosing the Correct Wire Size

When choosing a wire size, consider the following factors.

 Melting rate is a function of current density. With all other factors being equal, the smaller the wire diameter is, the higher the melting rate is.

 Penetration is a function of current density. The smaller the wire diameter is, the deeper the penetration is.

 Larger wires deposit wider beads under identical travel speeds and joint configurations.

 Wire size can increase as the base material thickness increases.

 Welding position affects the choice of wire diameter.

 Spot welds often require a large diameter wire to obtain the largest interface or nugget diameter.

GMAW Filler Wire Classifications

The AWS and CSA both have specifications for continuous filler wires with GMAW similar to what is used for SMAW electrodes. Solid wires ( hard wires ) are classified according to their chemical composition as manufactured and to the as-welded mechanical properties of the deposited weld metal.

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AWS Specifications

Table 1 lists the AWS specifications relevant to GMAW filler metals and shielding gases.

Number Title

A5.7

A5.9

A5.10

A5.14

A5.16

A5.18

A5.28

A5.32

Copper and Copper Alloy Bare Welding Rods and Electrodes

Corrosion Resisting Chromium and Chromium-Nickel Steel Bare and Composite Metal-Cored and Stranded Welding Electrodes and Welding Rods

Bare Aluminum and Aluminum Alloy Welding Electrodes and

Rods

Nickel and Nickel Alloy Bare Welding Electrodes and Rods

Titanium and Titanium Alloy Welding Electrodes and Rods

Carbon Steel Filler Metals for Gas Shielded Arc Welding

Low-Alloy Steel Filler Metal for Gas-Shielded Arc Welding

Welding Shielding Gases

Table 1 - AWS specifications for GMAW filler metals.

CSA Standards

The CSA has worked with the AWS to standardize as closely as possible the specifications for filler metals. Standard CSA W48 covers filler metals and allied materials for metal arc welding. Its scope is to provide requirements for the classification and certification of:

 carbon steel SMAW electrodes,

 stainless steel SMAW electrodes,

 low alloy steel SMAW electrodes,

 non-alloy and fine grained steel GMAW wires,

 carbon steel FCAW and MCAW electrodes and

 fluxes and solid/composite steel SAW electrodes.

To align Canadian manufacturing standards closer to those found internationally, the

CSA adopted an ISO standard for the GMAW process in 2006. In doing so, CSA created

CAN/CSA-ISO 14341 . CSA W48-14 (14 indicates the year) which uses this designation and its classification requirements. This new standard classifies and certifies wire electrodes and deposits for GMAW of non-alloy and fine-grained steels. The title of

CAN/CSA-ISO 14341-14 is Welding Consumables - Wire Electrodes and Weld Deposits for Gas Shielded Metal Arc Welding of Non-Alloy and Fine Grain Steels.

NOTES


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NOTES

Low-Carbon Steel Filler Metals for GMAW

The CAN/CSA-ISO 14341 W8-14 and AWS Specification A5.18 cover solid low-carbon steel filler metals for gas shielded arc welding. The AWS Specification A5.28

covers lowalloy filler metals for gas shielded arc welding (welds with 49/10 MPa tensile strength).

In the CAN/CSA-ISO W48-14 classification B-G 49A 5 C G6, the letters and numbers represent the following.

 The letter B designates that the electrode was classified by tensile strength and tested with an average 27 joule impact test.

 The letter G designates a gas shielded metal arc welding process.

 The 49A designates the minimum tensile strength of the deposited weld metal in the as-welded condition in megapascals (MPa) divided by 10.

 The 5 designates a minimum of -50°C temperature for impact tests.

 The C designates CO

2

shielding gas.

 The last combined letter and number ( G6 ) designate variations in the chemical analysis of the filler metal.

The CAN/CSA-ISO 14341 classification system is explained in Figure 4.

8

Figure 4 - CAN/CSA-ISO 14341 W48-14 classification system.

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Figure 5 outlines the AWS Specification A5.18

filler metal classification system.

NOTES

Figure 5 - AWS Specification A5.18 filler metal classification system.

NOTE

The recommended positions for welding are not included in the classification as it is with SMAW electrodes. Other variables such as the wire diameter, shielding gas and mode of metal transfer determine the position.

GMAW Electrode Wire Characteristics and Applications

There are many common GMAW wire electrodes. Each electrode has its own characteristics and applications.

B-G 49A 3 C G2 (ER70S-2)

B-G 49A 3 C G2 filler wire is a multiple deoxidized steel filler metal containing nominal amounts of aluminum (Al), titanium (Ti) and zirconium (Zr). Manganese (Mn) and silicon (Si) are present as deoxidizers. CO

2

, argon-O

2

or argon-CO

2

shielding gases may be used. The amount of Al, Ti and Zr remaining in the weld after welding rimmed and semi-killed steels is generally too low to affect impact properties. A disadvantage of this filler metal is that it produces shiny silicon islands of slag on the surface of the weld bead, which should be removed prior to completing subsequent passes.


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9

NOTES

This wire is generally intended for single-pass applications, but may be used for some multi-pass welds. Sound welds are produced on killed, semi-killed and rimmed steels. It can be used on steels that have a rusty or dirty surface, but with a possible sacrifice in weld quality depending upon the degree of contamination.

B-G 49A 2 C G3 (ER70S-3)

B-G 49A 2 C G3 filler wire is a deoxidized steel filler metal containing nominal amounts of manganese and silicon as deoxidizers. CO

2

, argon-O

2

or argon-CO

2

shielding gases may be used. This filler metal works well in short circuit and spray transfer modes. Some loss of strength may occur when high amperages are used with CO

2

shielding.

This wire can be used for single- or multi-pass pass applications on:

 low carbon steel plate,

 tubing,

 piping,

 structural members,

 steel castings,

 pressure vessels and

 other equipment.

This filler metal can be used on steels that have a rusty or dirty surface, but with a possible sacrifice in weld quality depending upon the degree of contamination. Sound welds are produced on killed, semi-killed and rimmed steels. It can be used for out of position welding with small diameter electrodes using short-circuiting transfer with argon-CO

2

and argon-O

2

shielding gas mixtures.

B-G 49A 3 C G4 (ER70S-4)

B-G 49A 3 C G4 filler metals contain slightly more manganese and silicon than B-G 49A

2 C G3 and produce a weld deposit of higher tensile strength. Short-circuiting or spray transfer using CO

2

, argon-O

2

or argon-CO

2

shielding gases can be used. Silicon slag residue should be removed between passes. B-G 49A 3 C G4 gives good arc stability with an extremely fluid puddle that produces a wider and flatter weld bead than

B-G 49A 3 C G2 or G2 filler wires.

The primary recommended use is for CO

2

shielding gas applications where longer arcs are used or for material conditions that require more deoxidization than that obtained with B-G 49A 2 C G3.Impact properties are not required for this filler metal. It may not be suitable for low temperature service applications.

B-G 49A 3 C G5 (ER70S-5)

B-G 49A 3 C G5 filler metals contain aluminum and manganese and silicon deoxidizers.

They are not intended for short-circuiting metal transfer or for use with oxygen-rich shielding gases. Argon-O

2

or argon-CO

2

shielding gases can be used with spray and globular transfer modes, which produces a very fluid puddle, which generally restricts welding to the flat position.

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This filler metal can be used for welding rimmed, semi-killed or killed steels with CO

2 shielding at high welding currents using globular transfer. It is suitable for steels that have a rusty or dirty surface with a possible sacrifice of weld quality depending upon the degree of contamination. Impact properties are not required for this filler metal. It may not be suitable for low temperature service applications.

B-G 49A 3 C G6 (ER70S-6)

B-G 49A 3 C G6 filler metals have the highest combined amount of manganese and silicon. They produce welds meeting the highest impact requirements when used with

CO

2

shielding. Short-circuiting transfer using CO

2

or argon-CO

2

shielding gases can be used. This is probably the most versatile filler wire because it can be used in the short-circuit or spray transfer modes. It is also the most widely used carbon steel filler metal for GMAW.

This filler metal may be used at high current settings for welding rimmed steels and for smooth weld beads on sheet metal. These filler metals can be used on rusty or dirty steels, but with a possible sacrifice of weld quality depending upon the degree of contamination.

B-G 49A 3 C G6 is also recommended for out of position applications using shortcircuiting metal transfer and for single- and multi-pass welds on:

 low carbon steel plate,

 tubing,

 piping,

 structural members,

 steel castings,

 wheels,

 automotive frames and

 other equipment.

B-G 49A 3 C G7 (ER70S-7)

B-G 49A 3 C G7 filler metals have higher manganese and lower silicon content than B-G

49A 3 C G6. They display good wetting action and improved weld appearance. This in turn may permit faster welding speeds. They are generally recommended for use with argon-O

2

shielding gas, but are usable with argon-CO

2

and CO

2

gases. They may be used on materials with moderate amounts of rust and scale.

These metals are well suited to robotic welding applications in the automotive, heavy equipment and farm implement industries.

B-G 49A Z C G0 (ER70S-G)

B-G 49A Z C G0 filler metals classification is for new multi-pass electrodes which are not covered under any of the presently defined classifications. (The CSA-ISO G0 designator and the AWS G designator indicate general classification). The slag system, arc characteristics, polarity and finished weld appearance are not yet defined. They must meet some requirements of the standards that cover them. The specific chemistry and testing requirements of this classification are agreed upon by the supplier and the purchaser.


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NOTES

11

NOTES

The main purpose for this classification is to allow a filler metal that does not meet any other specified classification to be classified under an existing CSA or AWS specification.

GMAW Filler Metal Packaging

Electrode wires for GMAW are available on spools ranging from 0.454 kg - 27 kg

(1 lb - 60 lb), coils from 11.3 kg - 27 kg (25 lb - 60 lb) and drum sizes up to 454 kg

(1000 lb). Figure 6 shows a 227 kg (500 lb) drum feeding to a remote wire feed unit.

Figure 6 - GMAW wire fed from a drum.

Choice of spool size depends on shop conditions, equipment capabilities and production requirements. The CSA standards and AWS specifications set out requirements for filler metal wire diameters and packaging. Solid wire for GMAW is available in sizes ranging from 0.5 mm - 3.2 mm (0.020" - 1 /

8

") in diameter. Figure 7 shows some of the different size spools and wire diameters.

12

Figure 7 - Filler wire packaging. (Courtesy ESAB Welding & Cutting Products)

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To meet specifications, GMAW wire is wound on the spools to ensure uniform feeding.

Figure 8 shows a spool that has been level wound for easy, uniform wire extraction.

NOTES

Figure 8 - Level winding.

Storing and Handling Consumables

All consumables should remain in their containers until required for service. This includes drive rolls, contact tips, nozzles, insulators, liners, guides and wires. Most wires are packaged in sealed containers with a moisture-absorbing agent. While in use, protect all wires from moisture, dust and foreign substances. Wire spool covers greatly reduce wire contamination from airborne particles in the shop environment.

Protect opened filler metals packages from extreme temperatures and humidity changes.

Discard wires that are coated with rust. If partial rolls of wire are to be stored for an extended period of time, return them to their original plastic wrapper and box. For best results, consume filler metals as soon as possible.

Storing GMAW Consumables

When using GMAW, take extra care to protect these filler metals from moisture, hydrocarbons and extreme temperature changes while in storage. GMAW is an inherently controlled hydrogen process. The hydrogen levels obtained in the weld metal must be consistently within the limits prescribed for these filler metals as indicated in the relevant

CSA standards and AWS specifications.


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13

NOTES

FCAW Wire Manufacturing

Manufacturers for filler wires for FCAW electrodes generally form the wires from a strip of low-carbon steel. They place the flux materials inside as the strip forms into wire

(Figure 9). Wire sizes range from 0.8 mm - 4 mm (0.030" - 5 /

32

").

14

Figure 9 - Schematic of the manufacture of FCAW wires.

(Courtesy ESAB Welding & Cutting Products)

Depending on the system of manufacture, FCAW wires are available with several types of joints or folds that surround the flux (Figure 10).

Figure 10 - Cross-sections of flux-cored wires.

FCAW Wire Characteristics

Flux-cored wires have been developed for welding low-carbon steels, low-alloy steels, stainless steels and hard facing alloys. Each flux-cored wire has its own characteristics, so welders must understand the operating characteristics of each wire type. Some wires are designed for use with an externally applied gas shield; others produce their own shielding from the flux. The type of flux and slag determine the type of wire suitable for a given job.

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Flux-cored wires have the following subdivisions. Rutile cored wires have good operational and positional capabilities with easy slag removal. Mechanical properties are as good as or better than solid wires. Increased low temperature notch toughness may be achieved by adding nickel.

Basic cored wires have a limestone/fluorspar flux core. Arc transfer is globular, which gives reasonable operating performance and produces good mechanical properties.

Positional performance characteristics in larger sizes are not as good as with rutile-cored electrodes. Basic cored wires have very low levels of diffusible hydrogen similar to those of the basic electrodes used for SMAW.

Self-shielded wires have either rutile or basic cores that contain fluorides, carbonates, aluminum and magnesium compounds. These can be designed for single- or multi-pass and out of position welding. The operating characteristics vary depending on the wire used. Self-shielded wires are generally used outdoors or with fume extraction systems due to the large volumes of smoke produced. Diffusible hydrogen content is low due to the fluorides in the flux makeup.

Functions of Flux

The primary functions of the compounds the flux core contains are as follows.

 They provide deoxidizers and scavengers to remove impurities.

 They form a slag cover to protect the weld metal from atmospheric contamination and to control the shape and appearance of the weld bead.

 They act as an arc stabilizer by providing an electrical path, which results in a stable arc, less spatter and a uniform weld bead.

 They add alloying elements to provide the required mechanical, metallurgical and corrosion-resistance properties.

 They provide a shielding gas to displace atmospheric air.

FCAW Filler Wire Selection

The selection of a filler wire is influenced by base metal chemistry, shielding gas, type of metal transfer, welding position, service requirements and condition of the base metal.

The tubular exterior of FCAW wire is usually of mild steel, and the powder core content is varied as appropriate to produce welds of the desired alloy content under specified welding conditions. Several AWS specifications cover FCAW wires to suit the majority of common construction materials.

Choosing the Correct Wire Size

When choosing a wire size, consider the following factors.

 Melting rate is a function of current density. With all other factors being equal, the smaller the wire diameter is, the higher the melting rate is.

 Penetration is also a function of current density. The smaller the wire diameter is, the deeper the penetration is.

 Larger wires deposit wider beads under identical travel speeds and joint configurations.

 Wire size can increase as the base material thickness increases.

 Welding position affects the choice of wire diameter.


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NOTES

15

NOTES

FCAW Filler Metal Packaging

Flux-cored electrode wires are available on spools ranging from 0.454 kg - 27 kg

(1 lb - 60 lb) and coils from 11.3 kg - 27 kg (25 lb - 60 lb). Drum sizes up to 454 kg

(1000 lb) can feed FCAW wire to a remote wire feed unit.

Choice of spool size depends on shop conditions, equipment capabilities and production requirements. The CSA standards and AWS specifications set out requirements for filler metal wire diameters and packaging.

Flux-cored wires are available in sizes from 0.8 mm - 4 mm (0.030" - 5 /

32

") in diameter.

Figure 11 shows some of the different size spools and wire diameters in their packaging.

The containers are often the same size as those containing the wires for GMAW.

Figure 11 - Filler wire packaging. (Courtesy ESAB Welding & Cutting Products)

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FCAW Filler Wire Classifications

The AWS and CSA both have specifications for FCAW filler wires. The position for which the electrodes are suitable are also included in the specification.

AWS Specifications

Table 2 lists the AWS specifications relevant to FCAW filler metals and shielding gases.

Number

A5.9

A5.21

A5.22

A5.32

A5.36

Title

Corrosion Resisting Chromium and Chromium-Nickel Steel Bare and Composite Metal-Cored and Stranded Welding Electrodes and Welding Rods

Bare Electrodes and Rods for Surfacing

Stainless Steel Electrodes for Flux-Cored Arc Welding

Welding Shielding Gases

Carbon and Low-Alloy Steel Electrodes for Flux-Cored Arc

Welding and Metal-Cored Arc Welding

Table 2 - AWS specifications pertaining to FCAW filler metals.

AWS A5.36 specifies flux-cored and metal-cored electrodes. It took effect in May 2012 and merges AWS A5.20 (Specification for Carbon Steel Electrodes for Flux Cored-Arc

Welding) and AWS 5.29 (Specification for Low Alloy Electrodes for Flux Cored-Arc

Welding) into A5.36

. As of January 1, 2016 manufacturers will have to list the new A5.36

classifications on their packaging for flux-cored and metal-cored electrodes.

CSA Standards

The CSA has worked with the AWS to standardize the specifications for FCAW wires.

With the exception of some minor differences with respect to position of welding, the only major difference between the AWS and CSA classification systems is in the units of measure for tensile strength values.

 The AWS system uses imperial measure (psi).

 The CSA system uses the metric system of measure (MPa).

The title of CSA W48-14 is Filler Metals and Allied Materials for Metal Arc Welding.

Filler Wire Classification Systems

Filler wire classifications for FCAW are designated using a system similar to the solid continuous wires for GMAW. Variations between the filler wire classifications are as follows. CSA W48-14 classifies metal-cored wire together with the flux-cored wire specifications. CSA W48-14 for FCAW uses numbers for positions.

 1 indicates the wire can be used in all positions.

 2 indicates use for flat and horizontal positions only.

AWS A5.36

covers carbon steel flux-cored wires and uses a different numbering system to designate positions.

 0 designates flat and horizontal positions.

 1 indicates the wire can be used in all positions.

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NOTES

17

NOTES

The basis for the CSA and AWS classifications of FCAW electrodes are on the:

 shielding gas used,

 suitability for single or multi-pass applications,

 type of current,

 positions of welding and

 as-welded mechanical properties of the weld metal.

Figure 12 shows the CSA Standard W48-14 filler metal classification system for a typical flux-cored wire.

Figure 12 - CSA Standard W48-14 filler metal classification system.

Figure 13 interprets AWS Specification A5.36

filler metal classification system.

18

Figure 13 - AWS Specification A5.36 filler metal classification system.

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FCAW Electrode Wire Characteristics and Applications

Flux-cored wire is commonly used to fabricate steel structures and pressure vessels.

There are many FCAW electrode wires. Each electrode has its own characteristics and applications.

E492T-1 (E70T-1) / E491T-1 (E71T-1)

Flux-cored wire E492T-1 (E70T-1) / E491T-1 (E71T-1) is designed to use with carbon dioxide (CO

2

) shielding for single- and multi- pass welding. This flux-cored wire has rutile-based slag and works well on spray transfer. The design of E492T-1 wire is for flat position welds and for horizontal fillets; E491T-1 is designed for all positions. Wires in this classification require that you remove excess oxides from the weld area and rid it of oil and other contaminants to obtain a weld of radiographic quality.

Welds with this wire have the following characteristics:

 quiet arc,

 high deposition rate,

 low spatter loss and

 flat to slightly convex bead configuration.

These wires are easy to control and produce an easily removed slag. They produce welds that have good impact properties. To increase usability for out of position welding, you may use an argon/carbon dioxide shielding gas mixture on these wires. Increasing the argon content may increase the manganese and silicon content in the weld deposit. This in turn increases yield and tensile strength and may affect impact properties. These fluxcored wires are used for building bridges, pressure vessels, earth-moving equipment and ship-building.

E492T-2 (E70T-2)

Flux-cored wire E492T-2 (E70T-2) was designed primarily for use with single-pass fillet welding in the flat and horizontal positions. These wires are recommended for use with carbon dioxide shielding. If you require multiple pass welding, appreciable dilution with the base metal likely affects the finished chemistry. The weld deposit and the arc characteristics are similar to E49XT-1 wire except that this wire contains higher percentages of manganese and silicon. Flux-cored wires in this category tolerate more mill scale, rust or other materials on the base material. These flux-cored wires are used for building bridges, pressure vessels, earth-moving equipment and ship-building.

E492T-3 (E70T-3)

The design of flux-cored wire E492T-3 (E70T-3) is primarily for high-speed single-pass welding in the flat and horizontal positions on thin materials no more than 5 mm ( 3 /

16

") in thickness. These wires are used without externally applied gas shielding and have a rutile flux. When used with DCEP, it produces a spray type arc metal transfer. Welds from these electrodes are sensitive to cracking when quenched; you should not use them for thicker materials or multi-pass applications. These flux-cored wires are well-suited to fully automatic applications, such as truck and bus frames and automotive body section welds.

NOTES

19


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NOTES

E492T-4 (E70T-4)

The design of flux-cored wire E492T-4 (E70T-4) is for the flat and horizontal positions for single- or multi-pass applications. Use these wires without externally applied gas shielding. The welds have a low sensitivity to cracking due to the low penetration and other properties that the wire and flux develop. These flux-cored wires works well on joints with poor fit up, such as farm machinery, frame and auto body components, rail cars, heavy construction equipment and structural steel.

E492T-5B (E70T-5 or E70T-5M)

The design of flux-cored wire E492T-5B (E70T-5 or E70T-5M) is primarily for fillet welding in the flat and horizontal positions. This electrode requires an externally applied shielding gas and has a lime-fluoride (basic) flux core. It produces a thin slag that may not entirely cover the weld metal. To reduce spatter, you may use E49XT-5 with argon-CO

2

mixes, but consult suppliers before you do so.

These electrodes use globular transfer with a slightly convex bead. The lime-fluoride flux produces reduced oxygen content in the weld puddle and has impact properties and crack resistance superior to rutile-based electrodes. In general, these electrodes are more difficult to weld with than the rutile-based wires. These flux-cored wires are used for heavy construction equipment, mining equipment and heavy structural components.

E492T-6 (E70T-6)

The design for flux-cored wire E492T-6 (E70T-6) is for use without externally applied shielding gas and for flat and horizontal positions. You may use this kind of flux-cored wire for single and multi-pass welds, using spray type metal transfer. This electrode has good low temperature impact values when used with DCEP. Weld bead is flat to convex with an easily removed slag.

These flux-cored wires work well for down hand applications where high deposition rates and good penetration are required. They are well-suited to fully automatic high production welding, such as bridge, ship, barge and offshore drilling rig construction.

E491T-7 (E71T-7)

The design for flux-cored wire E491T-7 (E71T-7) is for use for single- and multi-pass welds in all positions and with DCEN. Weld deposits have low sensitivity to cracking because the weld has low sulphur content. Use without externally applied shielding.

These flux-cored wires work well for structural and general fabrication weldments. You may use them for tack welding.

E492T-8 (E70T-8)

The design for flux-cored wire E492T-8 (E70T-8) is for use on single- and multi-pass welds in the flat and horizontal positions. Use these wires without externally applied shielding gas. Weld metal has low sensitivity to cracking and good notch toughness.

These flux-cored wires work well for structural ship building, bridge construction and offshore rigs.

20

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E49XT-9 (E7XT-9)

The design for flux-cored wire E49XT-9 (E7XT-9) is for single-pass and multi-pass welds. These wires require an externally applied CO

2

shielding gas and have a rutile flux core that uses globular metal transfer. They also have low spatter loss, leave a slightly convex bead and have similar operating characteristics to E492T-1, but have improved notch toughness capabilities. You may use argon-CO

2

or argon-O

2

-CO

2

mixes to improve usability for out of position welds. These electrodes are used general fabrication and heavy equipment applications.

E492T-10 (E70T-10)

Flux-cored wire E492T-10 (E70T-10) is used without externally applied shielding gas. It is designed for high travel speed, single-pass welding and is recommended for use with

DCEN in the flat and horizontal positions. It is suitable for spray type transfer with low spatter loss and fully automatic welding. It can be used for single-pass welds on gauge thickness low-carbon sheet steels.

E491T-11 (E71T-11)

Wire E491T-11 (E71T-11) is used without externally applied shielding gas and can be used in all positions on DCEN using spray type metal transfer. It can also be used for single- and multi-pass welding. Preheat is recommended for base metal thickness greater than 9.6 mm ( 3 /

8

"). Field welds on carbon steels ranging from 2 mm to 19.2 mm (16 gauge to 3/4") can also use this wire.

E49XT-12 (E7XT-12)

Wire E49XT-12 (E7XT-12) is similar to T-1 types, but has improved impact properties.

To maintain these properties, it is important that these wires are used with shielding gas mixtures recommended by the manufacturer. Applications include heavy equipment, offshore drilling rig equipment and ship building.

E491T-13 (E71T-13)

Wire E491T-13 (E71T-13) is self-shielded. Its slag system is capable of welding in all positions. It is not recommended for multi-pass welding. Its main application is root pass welding pipe joints.

E491T-14 (E71T-14)

Wire E491T-14 (E71T-14) is self-shielded. The slag system for this electrode allows high travel speeds and all-position welding. It is not recommended for thicker metals or for multi-pass welds. This wire is capable of welding galvanized or aluminized sheet metals up to 5 mm ( 3 /

16

") thick.

E492T-G (70T-G)

This is a general classification for multiple pass wires that are not included in other classifications. Consult the wire supplier for the characteristics and intended use of these wires as the slag system, shielding gas, arc characteristics and polarity are not defined.

E492T-GS (70T-GS) are classified in the same way as the G classification except that GS filler metals are intended for single pass applications only.


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NOTES

21

NOTES

MCAW Electrode Wire Characteristics and Applications

Metal-cored wires are manufactured the same way as FCAW wires. Manufacturers form them from a strip of low-carbon steel. The metal powder and other additives are placed inside the strip as it is formed into wire.

Metal-cored wire has distinct applications for which it is best suited, such as heavy equipment manufacturing, rail car fabrication and food and petrochemical fabrication. It is also used on automotive exhaust fabrication and wheel and chassis manufacturing.

Metal-core excels in these applications because the filler wire can be alloyed for almost every type of steel (from low carbon to stainless).

You can use metal-cored wire in many of the same applications that use solid wire, especially those requiring single-pass welds that are 3 inches or longer or applications in the flat and horizontal position using spray transfer. Metal-cored wire works well in applications prone to burn-through and piping components where poor fit-up can occur.

The wire can weld through rust and mill scale and produce a weld bead with very little spatter. This helps reduce the time needed for cleaning, grinding or applying anti-spatter prior to welding.

Figure 14 illustrates the difference between metal-cored and solid wire spray transfer.

22

Figure 14 - Metal-cored vs. solid wire.

Because the structure of the metal-cored wire is different than solid wire, it generates different arc and weld profile characteristics. During the welding process, the metal-cored wire carries the current through the outside of the metal sheath, resulting in a broad coneshaped arc with a wide penetration profile. The outside of the wire melts first and the powder in the centre flows as a stream of smaller droplets into the weld puddle; solid wire sprays its full diameter.

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Metal-cored wires are classified under Specification AWS A5.36 and Standard CSA W48 .

Metal-cored wires carry the same basic classification for strength level and chemical composition as solid GMAW wire, but are denoted by a C which defines a composite wire. For example, metal-cored wire with a chemical composition and mechanical properties similar to an E70S-6 solid wire would be classified as E70C-6 composite wire.

NOTE

AWS classifies metal-cored wires similar to solid wires, so they are all position. CSA classifies metal-cored wires similar to flux-cored, so they are all position.

There are three main types of metal-cored wires. Each electrode has its own characteristics and applications.

E491C-3 (E70C-3)

Wire E491C-3 (E70C-3) exhibits characteristics similar to both EXXT-1 and ERXXS-3 wires and can be used in all positions. It requires external gas shielding. Spray transfer is common when using argon/CO

2 required for good weld quality.

shielding gas mixes. Thoroughly cleaned joints are

E491C-6 (E70C-6)

These electrodes are similar to the C-3 classification, but contain higher levels of deoxidizers such as silicon and manganese. They require external gas shielding. They can be used on less thoroughly cleaned joint preparations and in all positions. You should consult the wire manufacturer if you are planning to use an argon-rich shielding gas.

E491C-G (E70C-G)

These wires are intended to encompass electrodes that may provide mechanical properties outside those specified for C-3 and C-6 electrodes. Figure 15 shows a welder using E491C-6-CH with 85% argon/15% CO

2 structure.

shielding on a bridge sub-assembly

NOTES

Figure 15 - MCAW using metal-cored E491C-6-CH filler metal.

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23

NOTES

Table 3 summarizes several flux-cored (T) and metal-cored (C) wires with respect to the recommended number of passes, shielding, current and polarity.

CSA

Classification

Recommended

Passes

Shielding Gas Current Polarity

EXXXT-1 multiple

2

* dc

EXXXT-2 single

2

* dc

EXXXT-3

EXXXT-4 single pass multiple pass

None

None dc dc electrode positive electrode positive

EXXXT-5B multiple

2

* dc

EXXXT-6

EXXXT-7 multiple pass multiple pass

None

None dc dc electrode positive electrode negative

EXXXT-8 multiple pass None dc electrode negative

EXXXT-9 multiple

2

* dc

EXXXT-12 multiple

2

* dc

EXXXT-G multiple †

EXXXT-GS single † † † pass

2

** dc pass

2

** dc

EXXXC-G multiple †

EXXXC-GS single † † †

* Electrodes may also be certified with other shielding gases.

** 85% argon - 15% CO

2 recommended

† As agreed upon between supplier and user.

Table 3 - Welding conditions and shielding gases.

NOTE

Contact the supplier to ensure the products you use are compatible with the job and meet the required chemical and mechanical properties.

The AWS Specification A5.36

for MCAW also covers low alloy fillers:

 E80C-Ni1-H4, which contains 1% nickel,

 E80C-Ni2-H8, which contains 2% nickel and

 E90C-B3-H16, which contains 2 ¼% Cr and 1% Mo.

24

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Objective Two


Describe the modes of metal transfer.

Metal Transfer

The mode of metal transfer is the way that the weld metal transfers across the arc from the end of the electrode to the weld zone. The following factors determine the mode of metal transfer:

 welding current,

 filler wire diameter,

 arc length (voltage),

 type of shielding and

 position of welding.

In GMAW, the following basic modes of metal transfer exist:

 short-circuiting transfer,

 globular transfer,

 spray transfer,

 pulsed spray transfer and

 modified short-circuit transfer.

Short-Circuiting Metal Transfer

Short-circuiting metal transfer (Figure 16) uses small diameter filler wires that are 0.76 mm (0.023") to 1.1 mm (0.045"). This type of metal transfer can be used in all positions.

It is usually associated with lower current settings and a specific voltage range. For example, a 0.9 mm (0.035") wire fed at 120 A with carbon dioxide shielding requires 19 -

20 arc volts to produce an acceptable short-circuiting arc.

NOTES

Figure 16 - Short-circuit transfer, 12 to 22 arc volts.

In the short-circuit mode, the welding filler metal does not transfer across the welding arc. It is only transferred when the filler wire is in direct contact with the base metal, which creates a short-circuit in the arc. Figure 16 illustrates the process.

1.

The filler wire makes direct contact with the work piece at point A (arc off, dead short).

2.

A controlled surge of current causes the filler metal to melt off (pinch effect) and results in metal transfer at point B .

3.

There is a momentary arc length at point C (arc on).

4.

The filler wire feeds towards the weld puddle until another short-circuit occurs and the cycle repeats itself (points D and E ).

The number of short-circuits varies from 20 - 200 times per second.

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25

NOTES

With GMAW short-circuiting transfer, the molten metal is separated from the end of the filler wire by a squeezing force created by a magnetic field that builds up around the end of the electrode. This is known as pinch effect (Figure 17). As this squeezing force becomes stronger, it pinches the molten metal from the end of the electrode. This pinch effect occurs each time the wire contacts the work.

26

Figure 17 - Pinch effect with short-circuiting.

A key advantage of short-circuiting metal transfer is the minimal distortion due to low heat input. It is also ideal for joining light gauge metals and for fit-ups with wide gaps.

Globular Transfer

This form of metal transfer occurs when the weld metal passes through an open arc in the form of large globules. The globules are often larger in diameter than the filler wire and irregular in shape (Figure 18). The current setting is higher than for short-circuiting, but lower than that needed for the spray transfer mode. Due to spatter problems and poor weld metal appearance, globular transfer is generally avoided in GMAW.

Figure 18 - Globular transfer, 22 to 26 arc volts.

Spray Transfer

Spray transfer occurs when using DCEP with a shielding gas containing at least 85% argon and by increasing the welding current above a critical value called the transition current . For example, the minimum spray arc or transition current is 165 amperes when welding on mild steel using a 0.9 mm (0.035") filler metal and a shielding gas mix containing 98% argon and 2% oxygen. If the current is less than 165 amperes, no spray transfer occurs as the transition current has not been attained. Although arc voltage can vary, it is higher for spray transfer than for short circuit transfer. A typical voltage for the example would be approximately 26 arc volts.

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A transition takes place from a globular transfer to a stream of tiny metal droplets crossing the welding arc from the filler wire to the base metal (Figure 19). The size of the droplets is smaller than the diameter of the wire and the rate of detachment is increased to several hundred droplets per second. The droplets are ejected in line with the axis of the electrode, sometimes referred to as an axial spray transfer . The arc is on all the time and has a smooth hissing sound when welding conditions are right.

The transition from globular to spray transfer depends on the liquid metal surface tension and the composition of the shielding gas. If the shielding for welding carbon steel contains less than 85% argon, there is no transition from globular to spray transfer.

Spray arc welding produces high weld metal deposition rates. The spray mode of metal transfer is used for joining materials 2.4 mm ( 3 

32

") and greater in thickness. Mild steel can be welded out of position when a small weld puddle is used, but spray transfer is used most for flat and horizontal positions. This mode produces the least amount of spatter.

NOTES

Figure 19 - Spray transfer, 26 to 35 arc volts.

Pulsed Arc Transfer

The pulsed arc metal transfer mode is a variation of the spray arc transfer mode. The pulsed arc reacts similarly to the spray arc, but uses lower average current values. Pulsed spray arc produces lower heat input, which results in less distortion. This allows the welding of thinner materials in all positions while producing high deposition rates with little or no spatter. MCAW generally uses pulsed arc to weld positions other than flat and horizontal. Shielding gases used for spray arc transfer are also used for pulsed arc transfer. Fume particulate emission is lower.

The power source is like having two machines in one. A low background current, which preheats the wire, is used to maintain the arc. A high pulse of welding current, higher than the transition current needed for a spray transfer, is used to obtain the metal deposit, penetration and metal flow. The current is changed rapidly at regular intervals to allow for cooling on the low pulse and metal deposit on the high pulse. A rate of 60 - 200 pulses per second may occur.


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27

NOTES

Figure 20 shows the characteristics of pulsed arc current.

Figure 20 - Characteristics of pulsed arc current.

The power source is specially designed for the purpose of pulsing the arc. With the pulsed arc process, pinch effect (Figure 21) occurs as the filler wire is heated by the background current and the filler wire begins to melt and form a droplet. When the high current pulse occurs, the metal droplet is pinched off and propelled across the arc into the puddle. The pulse may transfer more than one droplet across the arc.

28

Figure 21 - Pinch effect with pulsed arc.

Machines available for pulsed arc usually have microprocessor control systems. Inverter design power sources lend themselves to this type of metal transfer because they are capable of very fast response times and accurate current control. These power sources are sometimes called synergic (working together) because they automatically adjust all welding parameters to obtain optimum background and pulse current for a set wire feed speed and wire type. Some power sources designed specifically for pulsed arc have pre-set programs for welding on a variety of materials. This allows you to change welding programs with the adjustment of just one control.

Pre-programmed pulse height, width, frequency and background current can be manipulated somewhat by fine tuning adjustments on the control panel of the power source. Some power sources use an external microprocessor-controlled accessory to control the pulse current. You can also do this by plugging a microcomputer loaded with special software directly into the power source or the accessory.

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Modified Short-Circuit transfer

Welding companies developed the new technology of modified short-circuit metal transfer to minimize some of the problems that exist with the traditional short-circuit

GMAW metal transfer. Modified short-circuit transfer is also known as controlled dip transfer . Specific companies call it surface tension transfer (STT), regulated metal deposition (RMD) or cold metal transfer (CMT). Their power sources combine inverter technology with advanced waveform control. Some companies use hardware to control the waveform; others use software.

Unlike conventional constant voltage GMAW power sources, the new modified short-circuit machines have no voltage control knob. The power source controls the current to adjust the heat on the wire, independent of the wire feed speed. Changes in electrode extension do not affect the heat input.

With traditional GMAW, short-circuits and pinches occur at irregular intervals and vary in intensity. This may cause the puddle to agitate and splash onto the sidewalls of the joint which may result in cold lap, lack of fusion or excess spatter. Companies tend to avoid traditional GMAW because it requires a high level of skill to produce code-quality welds.

With traditional GMAW, changing the electrode extension changes the welding current, which may also lead to weld quality issues. Electrode extension is the distance from the end of the contact tube to the end of the wire. When the electrode extension increases, actual arc voltage lowers slightly; lower arc voltage increases weld-bead convexity. Some operators using conventional GMAW when welding pipe ended up with excessive penetration on the root pass, which is a common weld fault. The modified short-circuit process compensates for operator differences by maintaining a constant arc length regardless of electrode extension.

The modified short-circuit metal transfer greatly reduces the amount of heat that is generated in the weld. The metal transfer process is regulated precisely, and the arc inputs only heat into the material for a short period of time. When the wire touches the metal it starts to ball and wet out in the puddle. Current increases to a level sufficient to pinch the wire. As the pinch effect is about to take place, the machine senses that the wire is about to break and it reduces the current. This avoids the explosion, which in turn avoids excess spatter. This low heat input generally produces welds with minimum distortion and less melt through on thin materials.

NOTES


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29

NOTES

Objective Three


Describe wire feed drive systems and gun and cable accessories.

Wire Drive Systems

Wire drive systems may be one of three types:

1.

push,

2.

pull or

3.

push-pull.

Push System

With a push system, a set of drive rolls are located in the wire feed unit that feeds the wire (Figure 22). The drive rolls pull the wire from the spool and push it through a conduit liner to the welding gun. The maximum recommended distance for pushing is

4.5 metres (15 feet). The push system is mainly used with solid or metal-filled wires for the welding of steel structures. The electrode wire may be located at the wire feeder some distance behind the wire feeder (Figure 22) or in large spools or drums located near the wire feed unit.

30

Figure 22 - Push type wire drive system.

(Courtesy ESAB Welding & Cutting Products)

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Pull System

Pull systems have the drive rolls mounted in the gun close to the contact tip. Air pressure, a flexible shaft or an electric motor may drive the rolls. The pull system overcomes the inherent wire hang-up problems normally associated with pushing soft wires through a long flexible liner. The pull system is preferred for small diameter or soft electrode wires such as aluminum or copper and their alloys. Pull type feed systems are generally used for aluminum wire up to 1.6 mm ( 1 /

16

") diameter.

A popular pull system includes a small spool of electrode wire in the gun beside the drive rolls. Known as a spool-on-gun unit, this pull system can use constant current (CC) or constant voltage (CV) power sources. Figure 23 illustrates a pull type system with an onboard spool of filler wire.

NOTES

Figure 23 - Spool-on-gun (pull type). (Courtesy Miller Electric Mfg. Co.)

Push-Pull System

This system combines the two other systems. It is well suited to feeding soft wires. The gun has drive rolls that pull the wire while simultaneously pushing the wire from a wire feeder. This provides positive wire feed speed control and allows greater machine-towork distances. Feed distances for push-pull systems can reach 15 metres (50 feet) or more, depending on the manufacturer. The conduit may use a plastic liner to reduce drag.

A gun similar to that in Figure 24 is used with a specially designed wire feed unit.

Figure 24 - Push-pull gun. (Courtesy ESAB Welding & Cutting Products)

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31

NOTES

Choosing a Wire Feed System

Choosing which wire feed system to use depends on the type of wire you are welding with, the location of welding and the size and shape of the structure being welded on.

 Several shop operations are very successful using boom-mounted wire feed equipment.

 Many shops that weld aluminum on large awkwardly-shaped structures favour the spool-on-gun pull system so that they can operate in confined spaces at significant distances from the power source.

 Other operations weld a significant amount of aluminum at a bench or static location at extreme distances from the power source where the push-pull system may be the best choice.

Maintenance

You must keep the wire conduit and wire feed unit clean to prevent the electrode wire from clogging and subsequently hanging up during welding. Common practice is to clean the liner each time you change a spool of wire. More frequent cleaning may be necessary, depending on wire spool size and shop conditions. Clean the unit by blowing clean air or shielding gas through the liner in reverse of feed direction.

DANGER

Never use oxygen to clean wire conduit liners because oil may be present, and this presents an explosion hazard.

Check the alignment of feed rolls with the wire liner to prevent scraping of the wire, which may lead to feed problems later. Check the alignment of the wire feeder guide tubes and for the accumulation of debris. Manually check how smoothly the wire feeds through the wire feeder and liner whenever you change the wire spool. Taking the time to ensure the equipment is clean and in good operating condition can save time and effort.

32

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Welding Gun and Cable Assemblies

Wire feed welding guns and their components are much more complex than electrode holders for SMAW.

Welding Guns

Welding guns (Figure 25) are air-cooled or water-cooled and have a straight pistol grip or curved neck design for both light-duty and heavy-duty use. The curved neck gun is the most popular because it maximizes operator comfort in the semi-automatic welding mode and helps the wire make solid contact against the inside of the contact tip. This ensures positive, continuous transfer of current to the wire. Various available curve angles give the operator more comfort for all-position welding.

NOTES

Figure 25 - Welding gun. (Courtesy Miller Electric Mfg. Co.)

Wire feed guns are generally rated by their current-carrying capacity. You may use air-cooled guns intermittently up to 600 amps with CO

2

shielding. These guns are usually limited to 50% of their current rating when you use argon or helium for shielding. This is due mainly to the high heat build-up at the gun nozzle associated with the spray transfer mode.

Water-cooled guns are available for current ranges from 200 - 750 amperes (Figure 26).

The choice of cooling is based on current requirements, voltage, type of shielding gas, joint design, operating mode and mode of metal transfer.

Figure 26 - Water-cooled mechanized welding gun.

(Courtesy Miller Electric Mfg. Co.)

Essential components of a typical air-cooled gun are the:

 gun body,

 gas diffuser,

 contact tube,

 nozzle,

 cable assembly and

 conduit and liner.


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33

NOTES

For water-cooled guns, you also require a water or coolant source, connecting hoses and a pump unit. The system must circulate the water continuously during the time of welding.

The cooling water may contain an antifreeze solution and rust inhibitors if conditions warrant its use. For semi-automatic operation, the gun trigger switch controls the welding current and gas and coolant flow. The coolant must flow around the contact tube and nozzle to provide efficient cooling.

Contact Tubes

The contact tube ( contact tip ) is usually made of copper or copper alloys (Figure 27). Its main functions are to transfer electrical current to the electrode and to direct the wire to the weld zone. Contact tubes are wire-size specific, so make sure you use one that matches the wire diameter you are using.

Figure 27 - Contact tube with tube body/gas diffuser.

For some applications, the contact tip is purposely bent to ensure positive wire contact so that smooth electrical transfer occurs. The contact tip should be held securely and centred within the nozzle. The position of the contact tube in relation to the end of the nozzle depends on the mode of metal transfer and the type of welding. In short-circuiting mode, for example, the tube is usually flush or extended just beyond the nozzle. For spray transfer, the tube is usually recessed about 3.2 mm ( 1 /

8

").

Figure 28 shows threaded and elliptical twist-lock style contact tubes. Check the contact tube periodically for wear or clogging, which may result in poor electrical contact and an erratic arc. Contact tubes are considered a consumable item on wire feed guns. Keep a supply on-hand so that you can change contact tubes when required, resulting in minimal interruption to your work.

34

Figure 28 - Contact tubes.

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Nozzles

Nozzles ( gas nozzles ) are normally made of copper alloys with inside diameters ranging from 9.6 mm - 22.4 mm ( 3 /

8

" - 7 /

8

"). The nozzle directs shielding gas onto the weld zone to prevent atmospheric contamination. The nozzle’s design (Figure 29) supplies an even flow of shielding gas when an external shielding gas is required. The size and shape of nozzle should be based on the application. A sleeve of insulating material is usually placed inside the nozzle to prevent electrical contact between the nozzle and the wire. If the nozzle were electrically live and should touch the work, it would tend to arc and hang up on the work. This would in turn interfere with gun movements and cause nozzle damage.

NOTES

Figure 29 - Nozzles.

Cable Assemblies

Use cable assemblies and connectors to join the power source to the gun. They are a flexible means of transmitting welding current, shielding gases and filler metals to the weld zone. The current-carrying part of the cables may be made from copper or aluminum, although copper is most common. The cable is hollow to accommodate the cable liner and a passageway for shielding gas (Figure 30). The size of cables depends on the current rating of the gun, the output capacity and duty cycle rating of the welding machine and the distance between the power source and the work.

Figure 30 - Cable assembly.

The function of the conduit and liner is to guide, support and protect the wire between the drive rolls and the contact tube. The liner may be an integral part of the conduit or supplied separately. A helical (wound up like a spring) mild or stainless steel liner is recommended for hard wires. Use nylon, Teflon or plastic liners for soft wires like aluminum and copper because their smooth inner contours help the wire to feed smoothly. Make sure that the liners are kept clean and in good condition.

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35

NOTES

Take care to prevent crimping or excessive bending of the conduit. When getting ready to weld or when repositioning, do a quick visual check to make sure there are no sharp bends or kinks in the cable. Follow the manufacturer's instructions when choosing liners for size and type of wire used.

Figure 31 shows steel and plastic conduit liners.

Figure 31 - Conduit liners.

Wire Feed Control and Drive Units

Wire feed units ( wire feeders ) consist of the following:

 a spindle to hold a roll of spooled filler wire,

 a control unit,

 a variable speed electric motor,

 a drive roll assembly and

 accessories for maintaining electrode wire alignment.

They may also have electrically operated solenoid valves tied into the control system for shielding gas and water cooling systems. Variable speed controls are generally mounted on the wire feeder front panel (Figure 32).

36

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Figure 32 - Wire feeder.


Many types of wire feeders are available. A popular wire feeder set-up includes provisions for two wire spindles and drive roll systems ( dual head wire feed unit ) to accommodate two different wires for a quick changeover. Types of controls typically found on wire feeders include:

 wire speed control,

 remote voltage control (optional),

 drive roll system control,

 voltage sensing control (if required),

 microprocessor-controlled pre-settings (optional) and

 shielding gas control.

Wire Feed Systems

There are two main types of wire feed systems:

1.

constant-speed wire feeders and

2.

voltage-sensing wire feeders.

Constant Speed Wire Feeders

A constant-speed wire feeder is usually used with a constant-voltage (CV) power source.

This system maintains arc length by automatically adjusting the amperage output as the electrode extension changes.

With constant speed wire feeders, an electronic governor regulates the wire feed speed at a constant rate. This type of control is used mainly with a CV type power source. To select the desired voltage, set the power source output voltage at a suitable point. Change the rate of wire feed to adjust the welding current. If you increase wire feed speed, the welding current automatically increases and the arc length and voltage remain relatively close to the selected setting (Figure 33).

NOTES

Figure 33 - Constant speed feed controls.


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37

NOTES

Voltage-Sensing Wire Feed Feeders

A voltage-sensing wire feeder is normally used with a constant current (CC) power source. The arc voltage change caused by a change in electrode extension is sensed by the motor drive, which in turn adjusts the wire feed speed to maintain the selected arc length.

Most wire feed processes generally use the constant speed type with a CV power source.

The voltage-sensing wire feeder sets its speed according to arc voltage. Arc voltage values are fed to the control system of the wire feeder through a pickup lead attached to the workpiece. As the arc lengthens, the voltage increases and in turn increases the speed of the feeder. As the arc shortens and produces less voltage, the motor slows down to maintain the desired arc length.

This set-up (Figure 34) is more prone to stubbing or burn-back problems because the wire must be fed at the rate at which it melts. The operator selects the desired output current.

Wire feed speed is adjusted at the drive unit, and voltage produced depends on arc length.

Figure 34 - Voltage-sensing controls.

Figure 35 shows a voltage-sensing wire feeder that uses the pick-up lead for sensing arc voltage.

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Figure 35 - Voltage-sensing wire feeder unit.

(Courtesy of Lincoln Electric)


Microprocessor Controls

A microprocessor-controlled wire feeder can be programmed to store welding variable data in memory and execute different wire feeding programs. When used with an inverter power source, this type of feeder can be useful for using repeated variable settings, multiple machine set-ups and pulsed arc applications.

Drive Roll Assemblies

A drive roll assembly connects to the feed motor. Its main function is to move the wire through a cable liner to a gun or welding head. Feed units may use two or four rolls, with the drive rolls connected directly to the motor unit. The positioning of the electrode wire is between the upper drive roll(s) and the lower roll(s). When the drive roll system activates, the motive force of the drive rolls drives the wire by imposing pressure against it.

The upper drive roll has a manual adjustment to set the amount of pressure between itself and the lower drive roll. If the drive roll pressure setting is too low, the wire electrode slips and feeding is erratic. If the pressure is set too high, the wire can pile up inside the wire feed unit if the wire stubs on the work or freezes inside the gun contact tube.

Set the drive roll pressure to ensure that the wire feeds smoothly, yet will slip if a problem occurs in the gun and cable assembly. Figure 36 shows a typical two-roll arrangement with a drive roll pressure adjustment knob on top of the upper drive roll assembly bracket.

NOTES

Figure 36 - Two-roll drive unit.


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39

NOTES

Figure 37 shows a typical four-roll arrangement in which the upper drive rolls have been swung up and away from the lower drive rolls. This feature allows easy threading of the electrode wire through the assembly when changing wire electrode spools and drive rolls or clearing wire hang-ups.

Figure 37 - Four-roll drive unit.

Drive Roll Design

Drive rolls should be a minimum of 19 mm ( 3 /

4

") in diameter. If the drive roll is too small, it tends to put a cast (curvature) on the wire and may distort its cross-sectional shape. Small diameter drive rolls also increase pressure and increase the possibility of damaging the wire electrode. This in turn can damage the liner and the inside wall of the contact tube, which leads to wire hang-ups.

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Figure 38 illustrates three typical wire drive roll profiles.

NOTES

Figure 38 - Drive roll designs.

Each profile is preferred for different tasks.

 The V-groove (Figure 38B) rollers are preferred for solid wire because they provide a three-point contact to grip the wire with minimum of pressure while maintaining the wire's shape.

 The U-groove design (Figure 38C) is preferred for soft wires such as aluminum and copper.

 The flat rolls (Figure 38A) are much more likely to cause shape changes that can lead to feeding problems through the gun and cable assembly.

 The knurled rolls in (Figure 38A) also tend to shave off metal, especially with softer wire alloys. Although in some cases where a spool gun is used, knurled drive rolls may be used on soft wires.

 Serrated or knurled feed rolls are generally used for flux-cored and metal-cored wires when maximum drive force with minimum drive pressure is required to prevent distortion of the wire. These are not recommended for soft wires because they tend to cause flaking, which can eventually clog the liner and contact tube.

You should change drive rolls that are grooved to fit the contour of the wire whenever you use a different size of wire. Many drive rolls have two sets of grooves so they can be used for more than one size of wire. The size range and shape of grooves are generally stamped onto the rolls (Figure 39).

Figure 39 - V groove drive rolls for 0.9mm (0.035") wire.

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41

NOTES

Wire Feeder Panel Controls

The panel controls and switches in Figure 40 are typical of a dual head wire feed unit. A wire speed control sets the wire speed. An optional voltage control sets open circuit and/or arc voltage depending on the power source and wire feeder. Wire speed and voltage controls can be accompanied by analogue dial indicators or digital readouts that provide wire speed and voltage pre-settings and actual values during welding.

Figure 40 - Panel controls.

Also included is a multi-pin connector for the gun trigger switch connection. In the semi-automatic mode, the gun trigger switch activates the wire feed unit. Most wire feeders include a two-way switch.

1.

When raised, the switch jogs (feeds) the wire without having the wire energized.

2.

When lowered, the switch purges the gun with shielding gas without feeding or energizing the wire.

Prior to using any power source or wire feed unit, you should learn the purpose of all controls in your system. Consult your operator's manual for specific information.

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Objective Four


Describe wire feed operating variables.

Wire Feeder Operating Variables

To set up ideal welding conditions for a given job, you must understand the main operating variables in a wire feed system and how they can influence the quality of welding. These variables are:

 voltage,

 amperage,

 polarity,

 electrode extension (stickout),

 slope and

 inductance.

Voltage

Voltage is the force that overcomes resistance to allow amperage flow. Arc length directly relates to arc voltage; any increase in output voltage results in a longer arc as measured from the end of the electrode wire to the puddle surface.

Voltage also controls puddle fluidity. Higher voltage settings result in a wider flatter weld bead with shallower penetration. The CV power sources have a voltage control on the front panel. Voltage on most CC machines is pre-set or may have a range switch or separate cable attachment lugs to step the open circuit voltage up or down.

Amperage

Amperage is the amount of current flow. Amperage controls penetration and burn-off rate of the electrode. At a given travel speed, increasing the amperage produces a narrower, higher bead with less metal flow and deeper penetration. On CV power sources with a constant feed-speed wire drive, the wire speed control has a direct bearing on the output amperage. The machine automatically adjusts the amperage as the wire speed adjusts. A

CV power source does not have an amperage control.

Most CC power sources feature a single current control that sets the welding amperage.

The current setting adjusts in the range required to burn off the electrode wire in question.

The wire speed is set so that the wire feeds at the same rate as it melts into the weld.

NOTE

Always experiment on scrap material before starting the job to ensure your voltage and wire speed settings are compatible with the wire size, position and material.

NOTES

43


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NOTES

Polarity

When welding with direct current, you can connect the electrode to either the positive or the negative poles of the circuit. This means you can change the polarity of the welding circuit. Direct current electrode negative (DCEN) is widely known as straight polarity

(Figure 41). The welding cables connect to the machine so that the electrode is on the negative pole and the workpiece is on the positive pole of the welding circuit.

Figure 41 - DCEN.

Direct current electrode positive (DCEP) is widely known as reverse polarity (Figure 42).

The welding cables connect to the machine so that the electrode is on the positive pole and the workpiece is on the negative pole of the welding circuit.

44

Figure 42 - DCEP.

Direct current (DC) flows in one direction only. The electron theory states that currentcarrying electrons move from negative to positive. This has the effect of causing current to flow through the electrode to the workpiece on straight polarity or through the workpiece to the electrode on reverse polarity.

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Polarity and Heat Distribution in the Arc

In general, when you weld with DC current, the arc energy distribution is between 1

When you use GMAW, 2 



3

– 2

3 of the arc energy is associated with the negative side of the



3

. welding circuit. This heat distribution affects arc reactions.

Use DCEP with GMAW, FCAW and MCAW wires and occasionally with SAW. The arc reactions are as follows.

 2 

3

of the arc energy is in the base metal.

 The electrode burns off somewhat cooler, which allows slower welding speeds.

 Narrow metal flow is general unless the arc is lengthened.

 Penetration is deeper especially with a short arc length.

Use DCEN with FCAW using some self-shielding wires and sometimes with SAW. The arc reactions are as follows.

 2 

3

of the arc energy is in the electrode.

 The electrode burns off hotter, which causes faster welding speeds.

 Wider metal flow is noticed.

 Penetration is shallower.

Alternating current (AC) is not used with most wire feed processes because of inherent difficulties with arc stability.

Electrode Extension

Electrode extension ( stickout or electrical stickout ) is the distance between the electrode contact tip and the end of the unmelted electrode (Figure 43). As electrode extension increases so does the resistance to electrical current flow, which causes the electrode to heat. Because of this, less current is required to melt the wire at a given rate of feed and a faster rate of metal deposition results.

NOTES

Figure 43 - Electrode extension.

Variations in electrode extension have the following effects.

 Increasing electrode extension decreases the welding current.

 Decreasing electrode extension increases current.


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45

NOTES

When electrode extension increases, actual arc voltage lowers. Lower arc voltage increases weld-bead convexity and reduces the likelihood of porosity. When electrode extension is excessive, spatter and an irregular arc action results; short electrode extension gives greater penetration. When electrode extension is too short, spatter builds up on the nozzle and contact tube. Short circuiting metal transfer generally uses electrode extensions of 6 - 10 mm ( 1 transfer modes.

/

4

" - 3 

8

") and 12 - 25 mm ( 1 /

2

" - 1") for globular and spray

Slope

The main purpose of slope is to limit the short circuiting current so that spatter reduces when short circuits between the filler wire and work piece are cleared. When using short circuiting metal transfer, short circuits occur by design, so greater control of short circuiting current is essential to prevent excessive spatter. This is where slope control applies.

Slope ( choke) describes the general contour of a volt-ampere curve (Figure 44). Slope refers to the reduction in output voltage that accompanies increasing amperage. Anything that adds resistance to the welding circuit adds to the slope such as power cables, connections, loose terminals or dirty contacts.

46

Figure 44 - Effect of slope on volt-amp curves.

Figure 44 illustrates the volt-amp output curves that result when the slope control changes.

 Line 1 has no slope control. On short circuit contact with small diameter wires, a very rapid high current surge occurs, causing an explosion of the molten filler wire at the end. This explosive behaviour causes spatter and a ropy-looking bead.

 Line 2 shows that some slope has been added, limiting the amount of current rise available when the filler wire short circuits. This is extremely useful when welding stainless steel. Stainless steel does not conduct heat well and the bead tends to pile up unless more voltage is available to wet the edges of the weld puddle.

 Line 3 shows maximum slope (steep slope) applied. Excessive slope results in insufficient current available to melt the wire off cleanly. This results in the wire freezing to the work piece, bending over ( stubbing ) as it is fed and finally melting off.

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Figure 45 illustrates what happens when stubbing occurs.

NOTES

Figure 45 -Stubbing.

Slope Control Systems

Some machines have a fixed slope setting with no adjustment available. Others have a method of controlling the slope. Two systems are used to control slope. Stepless slope control ( variable slope control ) uses a hand wheel and brush arrangement that enables the operator to adjust to any slope setting (Figure 46).

Figure 46 - Stepless slope control.

Tapped slope control uses mechanical connections to make changes (Figure 47).

Figure 47 - Tapped slope control.


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47

NOTES

Open Circuit Voltage

The changes Figure 46 and Figure 47 show are the result of changes in slope only; no change was made in the open circuit voltage. In Figure 48, only the open circuit voltage has changed, so the output curves remain parallel.

48

Figure 48 - Results of changing open circuit voltage, but not slope.

Inductance

Inductance controls the time rate of response for current rise and fall. A reactor within the power source produces inductance. Inductance is important in short circuiting transfer because it influences arc on time by decreasing the number of short circuits per second.

This decrease does the following:

 increases puddle fluidity,

 improves penetration,

 makes the bead flatter and smoother and

 helps reduce spatter.

Inductance provides what is known as a soft arc. A small amount of inductance added during spray arc transfer eases arc starting; too much inductance creates an erratic start.

Inductance may be pre-set or available with a separate control on the power source, which may be stepped or continuously adjustable.

Figure 49 illustrates short circuit current response using low and increased inductance. In

Figure 49B, current rise is slower than current rise in Figure 49A, which minimizes spatter.

Figure 49 - Inductance.

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Figure 50 illustrates a weld where the left side weld was performed without inductance and the right side was done with inductance added to the circuit. A significant amount of spatter is near the bead where no inductance was used. Inductance is controlled at the direct current side of the power source and does not affect voltage or slope control settings.

NOTES

Figure 50 - Effect of inductance. (Courtesy ESAB Welding & Cutting Products)


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49

NOTES

50

Self-Test

1.

The composition of the base metal is the major factor to consider when selecting: a) a shielding gas. b) filler materials. c) a power source. d) current settings.

2.

Which organizations have written specifications for wire feed filler metals? a) WCB and CSA b) CWB and AWS c) ASME and CWB d) AWS and CSA

3.

When added to ER70S-2, silicon, aluminum and manganese are used as: a) stabilizers. b) deoxidizers. c) lubricators. d) indicators.

4.

Cast refers to the: a) circle formed by one wrap of the wire. b) method of forming the wire. c) natural twisting action of the wire during forming. d) ability of the wire to be pushed through a plastic liner.

5.

Describe the helix of a wire and the effect that it may have on welding.

6.

Interpret the B-G 49A 3 C G2 electrode classification. a) B ___________________________________ b) G ___________________________________ c) 49A __________________________________ d) 3 ___________________________________ e) C ___________________________________ f) G2 ___________________________________

7.

When wires are packaged in sealed containers, it is mainly to protect them from: a) smoke and fumes. b) moisture contamination. c) transportation damage. d) ultraviolet light radiation.

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8.

Improperly cleaned wires most often produce welds with: a) wagon tracks. b) cold lapping. c) slag inclusions. d) porosity.

9.

Filler metals containing additional deoxidizers are intended for use on: a) moderately rusty low-carbon steels. b) alloy steels containing chromium. c) non-ferrous metals. d) stainless steels with more than 18 % chromium.

10.

What are the primary functions of the flux in FCAW wires? a) b) c) d) e)

11.

Explain the E491T-9CH FCAW electrode wire classification.

12.

What does the G stand for in the CSA FCAW electrode classification E492T-G? a) gas shielded b) general classification for electrodes not covered under any other classification c) for use on Class G secondary containment vessels for nuclear service d) general purpose electrode for use on carbon and low-alloy steels

13.

Name two (2) FCAW wires that can be used without external gas shielding. a) b)

14.

In the GMAW short-circuiting transfer mode, metal is transferred: a) when the electrode comes in contact with the weld pool. b) as large globules released from the filler wire. c) as fine droplets moving axially across the open arc. d) when a high current arc pulse ejects metal from the filler wire.

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NOTES

51

NOTES

15.

Very fine droplets of metal transferred across the arc in an axial fashion describes what mode of metal transfer? a) short-circuiting b) globular c) spray d) pulsed spray

16.

Which GMAW mode of metal transfer is best suited for welding thin metals? a) short-circuiting arc transfer b) globular spray arc transfer c) spray arc transfer d) pulsed arc transfer

17.

Which MCAW mode of metal transfer is best suited for welding thin metals? a) short-arc transfer b) globular spray arc transfer c) spray arc transfer d) pulsed arc transfer

18.

Where are the drive rolls located on a pull-type drive system?

19.

A pull type welding gun is designed to be used with: a) hard wires. b) soft wires. c) solid core wires. d) tubular wires.

20.

What type of wire drive system allows greater machine-to-work distances? a) push system b) push-pull system c) 2 drive roll system d) 4 drive roll system

21.

When using GMAW on mild steel, the most popular type of wire feed system is a: a) pull system. b) push system. c) push-pull system. d) spool-on-gun system.

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22.

What is the gun shown in Figure 51 primarily used for?

NOTES

Figure 51 (Courtesy Miller Electric Mfg. Co.)

23.

In addition to maximizing operator comfort, what is the purpose of the curved neck on a welding gun? a) It allows the use of a wider range of wire sizes. b) It helps prevent a burn-back of the electrode to the contact tip. c) It ensures proper electrical transfer to the wire electrode. d) It allows use of all wire electrode types.

24.

The welding cable assembly is constructed to: a) supply current from the machine to the electrode holder. b) supply current, gas and wire to the welding gun. c) complete an electrical circuit between the machine and the work. d) supply current from the wall receptacle to the welding machine.

25.

What types of conduit liner are most often used with soft wires? a) b) c)

26.

What is generally the longest practical feed cable used with small diameter wire and a push feed system?

27.

What is the main purpose of the contact tube? a) It transfers the welding current to the filler wire. b) It prevents pre-ignition of the arc in the nozzle. c) It directs shielding gas to the weld zone. d) It acts as an insulator between the wire and the gun.

28.

What is the purpose of a gas nozzle?


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53

NOTES

54

Self-Test Answers

1.

b) filler metals.

2.

d) AWS and CSA

3.

b) deoxidizers.

4.

a) circle formed by one wrap of the wire.

5.

Helix is the result of a natural twisting action of the wire during forming. If the helix of the wire is excessive, the wire does not exit straight out of the contact tip. This in turn can cause the wire to wander. The arc becomes unstable as this corkscrew effect causes a change in the direction of wire feed.

6.

a) B indicates the electrode is classified by tensile strength and with an average

27-joule impact test. b) G designates using a gas shielded metal arc welding process.

c) 49A refers to minimum tensile strength of the deposited weld metal in the as-welded condition in megapascals (MPa) divided by 10. d) 3 indicates a minimum temperature of -30°C for impact tests. e) C designates CO 2 shielding gas. f) G2 is a specific chemical analysis of this designated filler metal.

7.

b) moisture contamination.

8.

d) porosity

9.

a) moderately rusty low carbon steels.

10.

a) to provide deoxidizers and scavengers to remove impurities b) to form a slag cover to protect the weld metal from atmospheric contamination and to control the shape and appearance of the weld bead c) to act as an arc stabilizer by providing an electrical path which results in a stable arc, less spatter and a uniform weld bead d) to add alloying elements to provide the mechanical, metallurgical and corrosionresistance properties as required e) to provide a shielding gas to displace atmospheric air

11.

a) E indicates electrode. b) 49 indicates tensile strength measured in megapascals divided by 10. c) 1 refers to all-position application. d) T indicates tubular wire. e) 9 indicates the slag system, current, polarity and shielding gas. f) CH refers to controlled hydrogen.

12.

b) general classification for electrodes not covered under any other classification

13.

Any of the following types are correct: EXXXT-3, -4, -6, -10, -11, -13 or -14.

14.

a) when the electrode comes in contact with the weld pool.

15.

c) spray

16.

a) short-circuiting

17.

d) pulsed arc transfer

18.

on the gun unit

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19.

b) soft wires.

20.

b) push-pull system

21.

b) push system.

22.

welding aluminum

23.

c) It ensure proper electrical transfer to the wire electrodes.

24.

b) supply current, gas and wire to the welding gun.

25.

a) nylon b) Teflon

26.

The maximum recommended distance for pushing is 4.5 metres (15 feet).

27.

a) It transfers the welding current to the filler wire.

28.

The nozzle directs shielding gas onto the weld zone to prevent atmospheric contamination.

NOTES


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55

NOTES

56

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NOTES


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NOTES

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Module Number 120103b

Version 6.0