FOUNDATION AND APPRENTICESHIP LEVELS 1 … Module P3 Theory CoMPeTenCy P3-1 (line C-C1) 12...

BC WELDER TRAINING PROGRAMFOUNDATION AND APPRENTICESHIP

LEVELS 1 AND 2

P3 (Line C): Oxy-Fuel Gas Welding (OFW)Theory Competencies

Acknowledgements & Copyright Permission

The Industry Training Authority of British Columbia would like to acknowledge the Welding Articulation Committee and Open School BC, as well as the following individuals and organizations for their contributions in updating the Welder Training modules:

Version 1 Contributors (2010)

Welding Articulation Committee (WAC) Members and Consultants—“The Working Group”Jim Carson (Welding Articulation Committee Chair), University of the Fraser Valley (writer and senior reviewer)

Peter Haigh (Welding Curriculum Review Committee Chair), Northwest Community College (writer and senior reviewer)

Sheldon Frank, University of the Fraser Valley (writer and reviewer)

Greg Burkett, Okanagan College (writer and reviewer)

Randy Zimmerman (writer and reviewer)

John H.P. Little (reviewer)

Resource Training Organization (RTO)

BC Council on Admissions and Transfer (BCCAT)

The Queen’s PrinterIn 2010, the Queen’s Printer, through its Open School BC unit, provided project management and design expertise in updating the Welder Training Level C print materials.

Open School BCSolvig Norman, Senior Project ManagerEleanor Liddy, Director/AdvisorDennis Evans, Production Technician (print layout, graphics & photographs)Christine Ramkeesoon, Graphics Media CoordinatorKeith Learmonth, EditorMargaret Kernaghan, Graphic Artist

Publishing ServicesSherry Brown, Director of Publishing Services

Intellectual Property ProgramIlona Ugro, Copyright Officer, Ministry of Citizens’ Services, Province of British Columbia

Copyright Permission

The following suppliers have kindly provided copyright permission for selected product images:

Acklands-Grainger Inc.The Crosby GroupJ. Walter Company Ltd.Lincoln Electric CompanyNDT Systems, Inc.Praxair, Inc.Thermadyne Canada (Victor Equipment)The Miller Electric Mfg. Co.ESAB Welding & Cutting Products

Photo of welder walks the high steel at a construction site, Kenneth V. Pilon, copyright 2010. Used under license from Shutterstock.com

A special thank you to Lou Bonin and Jim Stratford at Camosun College (Welding department) for assisting us with additional photographs. An additional thank you to Richard Smith from England, for allowing us to use photographs of hydrogen bubbles.

Version 2 Contributors (2017)

The Welding Level C Modules were updated in 2017 to reflect the 2016 (Harmonized) Program Outline with Levels 1 and 2 referenced throughout the covers, titles, headers, tabs and tab pages.

Welding Articulation Committee

Mark Flynn (Welding Articulation Committee Chair), British Columbia Institute for Technology

Al Sumal, Kwantlen Polytechnic University

Jim Carson, University of the Fraser Valley

Colin Makeiv, Selkirk College

Open School BCJennifer Riddel, Manager of Instructional ServicesSolvig Norman, Project ManagerSharon Barker, Production Technician

ForewordThe Industry Training Authority (ITA) is pleased to release this minor update of learning resources to support the delivery of the 2016 BC Welder Program Foundation and Apprenticeship Levels 1 and 2. It was made possible by the dedicated efforts of the Welding Articulation Committee of BC (WAC).

The WAC is a working group of welding instructors from institutions across the province and is one of the key stakeholder groups that support and strengthen industry training in BC. It was the driving force behind the update of the welding learning modules supplying the specialized expertise required to incorporate technological, procedural and industry-driven changes. The WAC plays an important role in the province’s post-secondary public institutions as discipline specialists that share information and engage in discussions of curriculum matters, particularly those affecting student mobility.

We are grateful to WAC for their contributions to the ongoing development of BC Welder Training Program Learning Resources (materials whose ownership and copyright are maintained by the Province of British Columbia through ITA).

Industry Training AuthorityMarch 2017

DisclaimerThe materials in these modules are for use by students and instructional staff and have been compiled from sources believed to be reliable and to represent best current opinions on these subjects. These manuals are intended to serve as a starting point for good practices and may not specify all minimum legal standards. No warranty, guarantee or representation is made by the British Columbia Welding Articulation Committee, the British Columbia Industry Training Authority or the Queen’s Printer of British Columbia as to the accuracy or sufficiency of the information contained in these publications. These manuals are intended to provide basic guidelines for welding trade practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this module and that other or additional measures may not be required.

BC WELDER TRAINING PROGRAM 5

P3 (Line C): Oxy-Fuel Gas WeldingTheory Competencies

Table of Contents

Theory Competency P3-1 (Line C-C1): Fusion-welding, braze-welding and brazing processes and their applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

P3-1 Learning Task 1: Fusion-welding process and its applications . . . . . . . . . . . . . 11

P3-1 Learning Task 2: Braze-welding process and its applications . . . . . . . . . . . . . 17

P3-1 Learning Task 3: Brazing process and its applications . . . . . . . . . . . . . . . . . 23

Theory Competency P3-2 (Line C-C1 & C2): Braze welding on low-carbon steel and braze welding and fusion welding on cast iron . . . . . . . . . . . . . . . . . . . . . . . . . . 29

P3-2 Learning Task 1: Procedures for braze welding on low-carbon steel. . . . . . . . . . 33

P3-2 Learning Task 2: Procedures for braze welding and fusion welding on grey cast iron . 39

Theory Competency P3-3 (Line C-C7–optional): Silver-alloy brazing on similar and dissimilar metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

P3-3 Learning Task 1: Main factors of silver-alloy brazing . . . . . . . . . . . . . . . . . 51

Theory Competency P3-4: (Line C-C3) Filler metals, fluxes and torch tips for fusion welding, braze welding and brazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

P3-4 Learning Task 1: Filler metals for fusion welding, braze welding and brazing . . . . . 61

P3-4 Learning Task 2: Fluxes for fusion welding, braze welding and brazing . . . . . . . . 71

P3-4 Learning Task 3: Oxy-fuel gas torches and torch tips for fusion welding, braze welding and brazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Theory Competency P3-5 (Line C-C4): Main process factors and joint design for fusion welding with the oxyacetylene-welding process . . . . . . . . . . . . . . . . . . . . . . 87

P3-5 Learning Task 1: Main factors in oxyacetylene fusion welding . . . . . . . . . . . . 91

P3-5 Learning Task 2: Weld faults in the oxyacetylene-welding processes . . . . . . . . 101

P3-5 Learning Task 3: Basic joint designs and welding positions for fillet welds. . . . . . 107

P3-5 Learning Task 4: Basic joint designs and welding positions for butt joints . . . . . . 117

P3-5 Learning Task 5: Review the safe operation of oxyacetylene-welding equipment . . 125

Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Theory CompeTenCy p3-1 (Line C-C1):Fusion-welding, braze-welding and brazing processes and their applications

p3

-1 (F &

L1)


Module P3 Theory CoMPeTenCy P3-1 (line C-C1)

OutcomesThis Theory Competency introduces you to three methods of joining metals: fusion welding, braze welding and brazing. These processes are done using standard oxyacetylene equipment. Arc-welding processes are far more widely used than these processes. But what you will learn about these welding and brazing processes and their applications—together with the skills that you will develop in performing oxy-fuel welding—will transfer to many of the arc-welding processes. Braze welding and brazing are useful for specific applications such as the joining of dissimilar, or unlike, kinds of metals and small-diameter tubing.

When you have completed the Learning Tasks in this Theory Competency, you will be able to define/describe:

• principles of fusion welding• terms used in fusion welding• function of the filler rod in fusion welding• applications of fusion welding• principles of braze welding• principles of brazing• capillary action• applications of brazing and braze welding• braze weld and braze bond

EvaluationWhen you have completed all the Theory Competencies in Module P3, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P3-1:

• oxyacetylene fusion-welding process and its applications• oxyacetylene braze-welding process and its applications• oxyacetylene brazing process and its applications

Resources

All the resources you will require are contained in this Theory Competency.

10 FOUNDATION AND APPRENTICESHIP LEVELS 1 AND 2

Notes



P3-1 Learning Task 1:Fusion-welding process and its applicationsFusion welding is a process used for joining similar metals by melting and joining. There are many fusion welding processes. These differ in their heat source and other factors. Fusion welding that uses oxyacetylene is called “oxyacetylene fusion welding.” It is identified by the process abbreviation “OAW.” Fusion welding that uses oxygen with gases other than acetylene is called “oxy-fuel gas welding.” It is identified by the process abbreviation “OFW.” OFW also includes acetylene, but OAW is limited to acetylene.

Principles of fusion weldingIn the fusion-welding process, the facing edges of two pieces of metal are melted and the molten metal flows together and then solidifies into a single piece of metal.

In oxyacetylene fusion welding, a concentrated flame is applied to the base metal with a welding torch. As the edges melt, they create a weld puddle or pool made up of metal from both edges of the base metal and from the filler rod (if used). Fusion takes place when there is complete blending of the base metal and filler metal in this weld pool. This is called the “weld metal.” As the weld metal cools, it forms a strong bond between the two pieces of metal (Figure 1). The area of fusion between the metals is called the “weld bead.”

Weld pool

Base metal

Filler metal rod

Weld bead

Torch tip

Figure 1—Oxyacetylene fusion welding

Notes



In a fusion-welded joint, the weld bead should be slightly convex (Figure 2). The weld should penetrate to the bottom of the joint. Most often in the fit-up of weld joints, a root opening (gap or space) is left between the two pieces of metal in order to ensure full penetration.

Root penetration Root opening

Fusion Convex bead

Figure 2—Cross-section of a fusion-welded single-vee butt joint

Filler metalA welding rod (filler metal) is almost always used in fusion welding. Filler metal is not always necessary in some joint designs, especially the closed corner and flange joints, because these joints often have enough extra base metal to make a strong bond. For most joints, though, filler metal is necessary. Filler metal provides the extra metal required for reinforcement that will ensure that the welded joint has the required strength and the correct bead shape and depth.

For fusion welding, the base metal and the filler metal rod usually have the same composition. Filler metal rods are made with a wide range of metal alloys to meet most welding needs. They range in size from 1.6 mm to 5 mm (1⁄16 in. to 3⁄16 in.) in diameter.

Applications of fusion weldingOAW and OFW have been largely replaced by various arc-welding processes. Over 90% of all production welding is now being done by electrical welding processes. For many welding jobs, OAW and OFW are too slow and are not cost-effective. Metals like aluminum, stainless steel and most thicker metals are more easily welded with arc welding equipment.

Maintenance and repair workOFW is still used in some types of repair work because it is a low-cost, portable means of welding. It is also very versatile, since it can be used to repair most ferrous metals as well as aluminum, magnesium, nickel alloys, titanium, copper, brass, cast iron, stainless steel and almost any other metal. For specialized maintenance and repair work, the OAW and OFW processes will likely remain widely used for some time to come.

Notes



FabricationOFW is still used for light-gauge metal fabrication in some applications. OFW is sometimes used on small-diameter pipe of less than 19 mm (3⁄4 in.). OFW is a good, low-cost method of learning the manual skills necessary for many other welding processes. After you have learned to OFW weld, you should be able to master other welding techniques.

Now complete Self-Test 1 and check your answers.

Answers



Self-Test 1Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes.

1. The area of fusion where two pieces of metal have been joined is called the

a. slag

b. kerf

c. weld bead

d. filler deposit

2. The weld bead in a properly welded joint

a. is blackened but grey around the edges

b. is slightly convex

c. is slightly pitted

d. has recessed ridges

3. When are filler-metal rods used in fusion welding?

a. on aluminum only

b. for most weld joint designs

c. for corner and flange joints

d. on magnesium only

4. What is the main purpose of filler metal in fusion welding?

a. to cool the weld pool

b. to create a bond

c. to add metal

d. to slow the progress of the weld

5. In fusion welding, the filler metal and the base metal

a. must be preheated

b. usually have the same composition

c. must be prebrazed

d. are usually flame-hardened

Answers



6. Which of the following is a disadvantage of oxy-fuel gas welding?

a. It is too slow.

b. It generates too much heat.

c. It is not portable.

d. It cannot be used on low-carbon steel.

7. Why is a root opening often left between the two pieces of base metal?

a. to get the correct weld profile

b. to allow for adequate cooling

c. to get full penetration in the weld joint

d. to increase the bead size

8. Which of the following is one advantage of oxy-fuel gas welding?

a. It is fast.

b. It can be used to weld any thickness of metal.

c. It can be used to weld almost any metal.

d. It produces little distortion.

Now go to the Answer Key and check your answers .

Notes



Notes



P3-1 Learning Task 2:Braze-welding process and its applicationsBraze welding (Figure 3) is carried out in much the same way as fusion welding. The filler metal is non-ferrous and always has a melting temperature below that of the base metal. In braze welding, the base metal is not melted, so the filler metal and the base metal do not actually fuse together. Instead, the filler rod melts instantly as it touches the preheated base metal. The filler spreads, producing a thin, even coating over the surface of the joint. This process (called “tinning”) creates the bond between the base metal and subsequent deposits of filler metal.

Tinning is a most crucial step in braze welding. Heating the base metal to the correct temperature and tinning properly will produce a strong bond in the joint.

Weld pool

Base metal

Brazing filler metal rod

Weld bead

Torch tip

Figure 3—Braze welding

Although there is no fusion in braze-welded joints, with a microscope you can see a very narrow line where the atoms of the base metal and the filler metal have mixed to form a surface bond. The braze-welding process is identified by the abbreviation “TB” (torch brazing).

The design of braze-welded joints is similar to that of fusion-welded joints, in that a space is usually left between the two pieces to allow for full penetration. The finished braze weld bead should be slightly convex.

Filler rods are always required for braze welding, since the base metal is not melted.

Notes



Braze welding can produce a weld almost as strong as fusion welding, but braze-welded joints cannot be subjected to temperatures higher than 260 °C (500 °F). Beyond this temperature the weld deposit loses its strength. The process should not be used for welds that will be subjected to heavy vibration. Like high temperature, vibration will cause the filler metal to lose its strength.

Filler metalBraze-welding filler metals (brazing rods) melt at temperatures above 450 °C (840 °F), usually around 870 °C (1600 °F). This is still well below the melting point of metals such as low-carbon steel, cast iron and stainless steel. This temperature range, between the melting point of the filler metal and the melting point of the base metal, is where braze welding occurs.

Braze-welding filler-metal rods are made of a brass alloy (copper and zinc) or a bronze alloy (copper and tin).

Flux is needed in order to clean the metal surface and to prevent surface oxidation so that the braze metal can flow easily and form the desired bond with the base metal. Flux can be a powder into which you dip the rod, or it can be a coating on the filler rod.

ApplicationsIn many cases it is easier and faster to braze weld than to fusion weld because the base metal does not have to be melted. Braze welding has a wide variety of applications, especially in factory maintenance and repair work. A common application is the building up of surfaces on damaged or worn parts.

Light-gauge metalsThis is a common application for braze welding. On light-gauge metals, the base metal does not have to be melted, so the temperature is lower, which means less distortion. This process is especially useful on galvanized steel, because the lower temperature does not adversely affect the heat-sensitive zinc coating.

Dissimilar metalsBraze welding can bond almost any type of metal to another type of metal. Steel tubing, for example, can be braze welded to cast iron, copper can be joined to steel, and brass can be joined to cast iron. This versatility makes braze welding very valuable for maintenance and repair.

Notes



Grey cast ironBraze welding is often better for cast iron than fusion welding. Because the base metal does not have to be melted, braze welding is faster and, in some ways, easier. There is less need for preheating, and it might not be needed at all. For instance, a cracked cast-iron pump housing can be repaired with braze welding.

Non-ferrous metalsBraze welding can also be used on many non-ferrous metals. It is widely used for welding copper, brass and aluminum.


Answers




1. The process abbreviation for braze welding with oxy-fuel gas is

a. BW

b. WB

c. TB

d. OAW

2. How does braze welding differ from fusion welding?

a. The joint design is larger.

b. The base metal is not melted.

c. No filler metal is used.

d. No flux is needed.

3. Braze-welding filler metals melt at temperatures

a. above 200 °C (390 °F)

b. above 350 °C (660 °F)

c. below 450 °C (840 °F)

d. above 450 °C (840 °F)

4. Joint designs for braze welding are the same as those for fusion welding.

a. true

b. false

5. The purpose of flux in braze welding is to

a. clean the base metal and prevent surface oxidation

b. make it possible to weld at a lower temperature

c. erode the base metal surface

d. anneal the base metal

6. When using the oxy-fuel gas process, why is braze welding useful on light-gauge metals compared to fusion welding?

a. It is fast.

b. The bonding is better.

c. It is portable.

d. It produces less distortion.

Answers



7. Braze welding is not effective for bonding

a. joints that have been galvanized

b. joints that will be subjected to heavy vibration

c. copper, aluminum and brass

d. cast iron and low-carbon steels

8. Braze welding should not be used

a. on joints between dissimilar metals

b. when the ambient temperature is below 5 °C (40 °F)

c. on joints that are subjected to temperatures above 260 °C (500 °F)

d. on joints that are subjected to temperatures below 15 °C (60 °F)

9. When is a filler rod used with braze welding?

a. always

b. most of the time

c. some of the time

d. never

10. Braze-welding filler-metal rods are usually made of

a. brass or bronze alloy

b. braze alloy

c. aluminum

d. nickel alloy


Notes



Notes



P3-1 Learning Task 3:Brazing process and its applicationsBrazing is another process for joining metals using oxy-fuel gas as a heat source. It is another torch-brazing process and, like braze welding, it is identified by the process abbreviation “TB.”

Principles of brazingIn some ways, brazing is similar to braze welding. In both processes, the base metal is heated but not melted, and both use brazing filler metals. However, joints prepared for brazing must be very tight-fitting. Once the filler metal melts, it is instantly drawn into the tiny space between the joint members by a force called “capillary action” (Figure 4). This action is the same as the one that pulls water up in a small tube when one end of the tube is placed into a container of water.

Brazing filler-metal rod

Exaggerated gap

Concentrate heat here

Filler metal flow

Figure 4—Capillary action

Joint fit-up is very important for successful brazing. The clearance is usually 0.025 mm to 0.13 mm (0.001 in. to 0.005 in.), or about the thickness of a sheet of paper. If the space between members is much greater, over 0.25 mm (0.010 in.), capillary action has no effect and the filler metal will not flow into all areas of the joint.

The bond that brazing produces is similar to that of braze welding, in that surface adhesion between the filler metal and base metal creates the bond. In brazing, however, once this adhesion occurs, the joint is complete. In braze welding, more filler metal is deposited to fill in the weld joint.

Filler metalBrazing filler metals (brazing rods or wires) are made of non-ferrous metals such as silver alloys or brass. They are available in a wide range of sizes, shapes, temperature ranges and composition to match the requirements of the job and the base metal.

Notes



All brazing filler metals have melting temperatures above 450 °C (840 °F). The melting point of the base metals they are used on is higher. The temperature 450 °C (840 °F) is the division between filler metals classified as brazing and those classified as soldering. Filler metals with melting temperatures below 450 °C (840 °F) are called “solder” and, generally, they are softer and weaker than brazing filler metals.

ApplicationsBrazing is widely used in production and maintenance work. It has the same versatility as braze welding in that it can be used on a wide variety of ferrous and non-ferrous metals. It is especially effective on complex shapes because of the way the filler metal is “drawn in” to the joint by capillary action. Welded joints made by this process are strong and corrosion resistant.

Like braze welding, brazing can be used to join both ferrous and non-ferrous metals and to join dissimilar metals. If the correct filler rod is used, almost any metal can be brazed. As in braze welding, the base metal is not melted, so brazing is especially effective on light-gauge metals that would be distorted by the high temperatures used in fusion welding.

Because silver conducts electricity very well, silver alloy brazing is used to fabricate and repair electrical connections. For the same reason, it is also used in the fabrication and repair of refrigeration and air-conditioning equipment.


Notes



Answers




1. In brazing, what is the force that draws filler metal into the joint?

a. capillary action

b. colloid gravity

c. conductivity

d. action

2. Brazing done at temperatures below 450 °C (840 °F) is called

a. fusing

b. silver-alloy brazing

c. soldering

d. furnace brazing

3. What is the most important difference between braze welding and brazing?

a. temperature

b. joint design

c. filler metal

d. the bond

4. What best describes the type of bond in brazing?

a. fusion

b. surface adhesion

c. capillary bond

d. incomplete fusion

5. Brazing sometimes requires considerable buildup of filler material.

a. true

b. false

Answers



6. Brazing filler metals are always made of what material?

a. non-ferrous metal

b. iron

c. stainless steel

d. ferrous metal

7. Silver-alloy brazing is commonly used

a. on sheet metal

b. on electrical connections

c. to build up the base metal

d. all of the above


Notes



Theory CompeTenCy p3-2 (Line C-C1 & C2):Braze welding on low-carbon steel and braze welding and fusion welding on cast iron

p3

-2 (F &

L1)


Module P3 Theory CoMPeTenCy P3-2 (line C-C1 & C2)

OutcomesBraze welding is used to join or repair cast iron, copper, brass and other metals. It is considered to be a low-temperature process because the base metal is not melted, so it is also very useful for joining dissimilar metals.

Braze welding is done in much the same way as fusion welding, except that the base metal is not melted. Like oxyacetylene fusion welding, braze welding takes practice. The skills you develop in braze welding will also be useful to you when you electric arc weld.

When you have completed the Learning Tasks in this Theory Competency, you should be able to describe:

• correct procedure for braze welding• procedures for braze welding and fusion welding grey cast iron• importance of heat treatments to the successful welding of grey cast iron• correct techniques for precleaning grey cast iron• advantages of braze welding over fusion welding and vice versa

EvaluationWhen you have completed all the theory competencies in module P3, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P3-2:

• correct procedure for braze welding• correct procedures for braze welding and fusion welding grey cast iron• heat treatments for welding of grey cast iron• correct techniques for precleaning grey cast iron• advantages of braze welding over fusion welding and vice versa

Resources

All required resources are contained within this Theory Competency.

Notes



P3-2 Learning Task 1:Procedures for braze welding on low-carbon steelWhen you have mastered oxyacetylene fusion welding, you should have little trouble with braze welding. Although most of the techniques you learned with fusion welding apply to braze welding, there are some significant differences you must learn about.

Precleaning and edge preparationIn braze welding, the surfaces of the base metal must be absolutely clean. You must remove all oil, grease, paint, seals, oxides or other surface contamination. Because the braze-welding bond involves surface adhesion, the base metal must be clean so that the brazing filler metal can flow smoothly and evenly over the joint. If the joint is dirty, the filler metals tend to form small balls on the surface of the joint and you will not get a good bond.

The success of the braze welding procedure depends on having a clean surface. You must thoroughly clean the edges of the weld joint as well as an area along the joint for the weld bead.

The condition of the base metal will determine which cleaning method is appropriate. A stiff wire brush or emery cloth is often used if the metal is not too dirty. If the metal is especially dirty, you can use a hand file or grinder to get down to clean, bare metal. If the pieces have oil, grease or paint on them, you can use a solvent or a welding torch flame to clean them. Sweep the torch flame (preferably an oxidizing flame) over the workpiece to burn off surface dirt and impurities.

The joint design for braze welding is the same as for fusion welding metal with the same thickness, except for variations in included angle on single vee butt joints. Lap, tee and butt joints on thin material, 3.2 mm (1⁄8 in.) or less, require no edge preparation. Butt joints on plate thicker than 3.2 mm (1⁄8 in.) must be prepared as a single-vee butt joint. Bevel the plate edges to 45°, which will provide an included angle of 90°. Leave a root opening of 1.6 mm to 3.2 mm (1⁄16 in. to 1⁄8 in.) between the butted ends (Figure 5). The sharp edges or ridges on the top and bottom surfaces must be rounded by grinding or filing. Rounding the edges allows the filler metal to flow freely beyond the edge of the weld joint.

90º

1.6–3.2 mm (1⁄16–1⁄8 in.)

Rounded edges

Rounded edges

Figure 5—Single-vee butt joint

Notes



Flame settingFor braze welding, use a slightly oxidizing flame. The excess oxygen creates a slightly hotter flame temperature and helps to remove surface oxides on the base metal. The result is a stronger bond. Remember that to obtain an oxidizing flame, you first adjust to a neutral flame and then gradually add more oxygen.

Filler rods and fluxThe most common braze-welding filler rod for low-carbon steel is a copper-zinc alloy (RBCuZn). Filler rods with this basic composition are commonly called “bronze rods.” These are available as a flux-coated rod or as a bare rod. A bare rod must be dipped in flux. The correct procedure is to heat the end of the bare filler rod and dip it into a powdered flux. The heat causes the flux to stick to the rod. As the rod is used up you will have to add more flux.

If you are using a bare filler metal rod to braze weld low-carbon steel, choose a general-purpose flux. While you are learning to use flux, be generous with it. It is better to use too much than too little. Too little produces a poor bond, but too much only produces a difficult cleanup job.

Overheating a copper-zinc filler rod will release harmful zinc fumes. These fumes are clearly visible as white smoke. Avoid inhaling these fumes.

You should take special precautions when braze welding. Good ventilation is needed because toxic fumes from the flux, the filler metal and the base metal might be present.

Not only is flux harmful to your respiratory system, it also poses a hazard to your skin and eyes. Take care to avoid direct contact with flux. If any should contact your skin, immediately wash the area with soap and water.

For more detailed information on hazardous materials and related safety precautions, see Module P1, Theory Competency 2, Learning Task 4 (P1-2 LT4).

TinningTinning is essential to successful braze welding because it creates the bond between the filler metal and the base metal. You will only get a good bond by heating the base metal to the correct temperature and tinning properly.

First preheat the base metal to a cherry red colour, the same temperature used to preheat steel for flame cutting. Be careful—you want to melt the filler rod but not the base metal. If the melted filler metal spreads over the surface as a thin, even coat, the temperature of the base metal is correct.

Notes



If the filler metal bubbles, separates into small islands or forms a large amount of white powder, the base metal is too hot. If the filler metal balls up and does not flow over the base metal at all, the base metal is not hot enough.

On sheet steel and other thin metals, you should use a welding tip that is one size smaller than the size used for fusion welding. This will help you avoid melting the base metal. On thicker metal, the danger of melting is not as great. You can use a tip that is one size larger than that used for fusion welding metal of the same thickness.This is because the larger tip produces a greater volume of heat and preheats the base metal more quickly and evenly.

Number of weld passesThe thickness of the base metal also determines how many weld passes you need to produce a good-looking weld. On light-gauge material, you can tin the weld joint and apply the weld in a single pass. On heavier metal and vee butt joints, you need two or more passes. You should tin the entire weld joint on the first pass before making the other passes. Figure 6 shows a single-vee butt joint that needed two passes to complete. Note that the first pass is slightly concave and the final pass has a convex bead shape.

First pass Final pass

Figure 6—Braze-weld bead profiles

Determining the quality of a braze weldA braze weld should have complete weld penetration with a root bead reinforcement of no more than 3.2 mm (1⁄8 in.). There should also be ample weld reinforcement on the cap, but it should not rise higher than 3.2 mm (1⁄8 in.) above the base metal. The weld bead should extend 3.2 mm (1⁄8 in.) beyond the top edge of the weld joint. It should have uniform ripples and be consistent in width and height.


Answers




1. Which flame is recommended for braze welding low-carbon steel?

a. carburizing flame

b. slightly oxidizing flame

c. neutral flame

d. inner cone flame

2. In braze welding, if the filler metal bubbles, separates into small islands, or forms a large amount of white powder, then the metal is too

a. oxidized

b. hot

c. cold

d. dirty

3. When a braze-welding filler rod is applied to a correctly preheated metal, it will spread into a thin film over the surface. Which term describes this action?

a. leading

b. galvanizing

c. tinning

d. soldering

4. The major alloying elements in braze-welding filler rods are

a. copper with iron and chrome

b. zinc with tin and lead

c. aluminum with zinc and tin

d. copper with zinc

5. Braze welding is not a fusion process, because the base metal is never

a. carburized

b. ionized

c. melted

d. oxidized

Answers



6. An oxidizing flame is one that has

a. more acetylene than oxygen

b. equal parts of oxygen and acetylene

c. no acetylene at all

d. more oxygen than acetylene

7. With a bare braze-welding filler rod, you get the flux to adhere to the filler rod when you

a. use glue on the rod and dip it into a powdered flux

b. preheat the rod and dip it into a powdered flux

c. use paste flux on the rod

d. pour the flux on the rod

8. It is better to use too little flux than too much.

a. true

b. false

9. The base metal is at the correct temperature for adding the braze-welding filler rod when

a. the base metal is a dull blue colour

b. the base metal is a cherry red colour

c. the base metal is just starting to melt

d. the filler rod bubbles

10. The final weld pass should have a shape that is

a. slightly concave

b. slightly convex

c. even with the base metal surface

d. slightly below the surface


Notes



Notes



P3-2 Learning Task 2:Procedures for braze welding and fusion welding on grey cast ironGrey cast iron can be fusion welded or braze welded. Both of these processes are used in the maintenance and repair of grey cast iron. They are seldom used in fabricating.

Braze welding on grey cast ironBraze welding grey cast iron is often preferred over fusion welding because it is faster and produces a relatively strong bond. Braze welding takes place at lower temperatures than fusion welding, so there is less expansion and contraction. This means that fewer residual stresses develop that could cause the casting to crack.

Many of the procedures for braze welding grey cast iron are similar to those used for low-carbon steel. The joint design and edge preparation are much the same, although the included angle on vee butt joints is usually 90° rather than 60°. You must use a slightly oxidizing flame and your filler metal will be the same copper-zinc rods. You will also use the same flux as you did on low-carbon steel. Most importantly, the basic weld technique is the same. However, there are a few very important differences involving the precleaning and preheating.

PrecleaningPrecleaning is important for braze welding any metal, but cast iron presents some unique cleaning problems. You should remove all grease, oil, paint, oxides and other foreign matter by using solvents and by grinding. It is especially important to remove the surface layer of the casting. This layer is full of impurities that interfere with the adhesive action of the filler metal. For this you can use a grinder or a file.

Unfortunately, this grinding produces excess graphite flakes on the joint surface. These interfere with adhesion of the filler metal. The weld joints should be seared (quickly burned) with the oxyacetylene torch using an oxidizing flame. This burns away the excess graphite so the tinning action can more effectively spread the filler metal and bond it to the base metal.

PreheatingBraze welding takes place at lower temperatures than fusion welding, so not as much preheating is needed. Some preheat is advisable, especially on larger castings. If the casting is not preheated, the cooler areas of the casting will draw the heat away from the weld joint area, making it difficult to get the weld joint to a high enough temperature for tinning to take place. The welding torch usually provides sufficient preheat, and it is necessary to preheat only the joint area. The preheat temperature is about 427 °C (800 °F).

Notes



Fusion welding on grey cast ironUsing oxyacetylene fusion to weld grey cast iron has some advantages over braze welding, especially in two specific applications:

1. When you want the colour of the weld metal to match the colour of the base metal, you must use fusion welding. Braze-welding filler rods are a copper-zinc alloy, which produces a weld deposit that is yellow/gold in colour. This would not match the grey cast iron base metal.

2. Fusion welding is required for joints that will be subjected to dynamic loads or temperatures higher than 260 °C (500 °F). Braze weld filler metal does not stand up to the stresses of dynamic loads and it loses strength if it is heated.

A weld joint in grey cast iron that has been properly oxyacetylene fusion welded has the same properties as the base metal. This means that the weld joint has the same strength and hardness as the base metal and can handle the same stresses as the grey cast iron. This also means that the joint can be machined.

Special factors in welding grey cast ironDue to the higher temperatures that are involved, oxyacetylene fusion welding of grey cast iron presents some unique problems not found in braze welding.

Grey cast iron is the most common form of cast iron. It is an alloy of iron, carbon and silicon, made by pouring molten metal into moulds that are cooled very slowly. This process produces a metal with a high carbon content. Carbon is present in a free form called “graphite.” The presence of the graphite flakes makes the cast iron brittle. This brittleness, in turn, makes the metal prone to cracking when the temperature changes rapidly.

In order to control the rate of heating and cooling, you need to apply extensive preheat and post-heat treatments. The complete casting must be slowly preheated before welding. After welding, the cooling rate must be controlled by post-heating. If the weld area cools too rapidly, white cast iron will be produced. White cast iron is extremely brittle, cracks easily and is not machinable. Small castings can be easily heated with the welding torch. Slightly larger castings might require heating with a heating tip or a furnace. Very large castings might require heating with a number of heating tips (a tiger torch or rosebud). Whichever method you use, heat the entire casting to about 590 °C (1100 °F).

Post-heating is just as important to prevent cracking after the weld has been completed. It not only improves the grain structure, it also relieves internal stresses. Post-heating consists of heating the entire casting to about 800 °C (1500 °F) as soon as the welding operation has been completed. This heating can be done with the welding torch, a heating tip or a furnace.

Notes



The casting must be cooled slowly to prevent the brittle white cast iron from forming. One method of controlling the cooling rate is to gently play the torch over the casting from a distance. This will help make sure that cooling takes place slowly and evenly. There are industrial heating ovens designed to slowly cool large castings. Small castings are sometimes covered with a fireproof blanket, hot sand or lime to reduce the cooling rate.

The high carbon content is also responsible for the formation of oxides when the metal is heated. These oxides are extremely resistant to melting, and their presence in the weld pool will result in poor fusion. The oxides remain solid at the temperature that melts the base metal (parent metal), and they will interfere with the fusion process. Using flux increases the fluidity of the molten metal, dissolves oxides and floats off impurities to the surface of the weld pool.

Cast iron flux is normally in a powdered form. The hot filler-metal rod is dipped into the flux. It is important to apply the right amount of flux. Too little flux will lead to poor fusion because there is not enough to remove the buildup of oxides. When gas bubbles or white spots appear in or at the edges of the weld pool, you should add flux and play the flame around the specks until the impurities float to the top. Skim any impurities from the weld with the filler rod. You can then remove the impurities that stick to the hot filler rod by tapping the rod against your work table. Experience and the directions on the label will guide you in learning how much flux to apply.

Cast iron filler rodFor oxyacetylene fusion welding of cast iron, you will need a special cast iron filler-metal rod with the same composition as the base metal. Cast iron filler rods are designated by the letters “RCI”:

• R = Gas welding rod• CI = Cast iron

There are several grades of cast iron filler-metal rods, each with slightly different properties. Common grey cast iron castings require welding rods that are high in silicon, while high-strength iron castings require a cast iron filler rod with alloying elements such as molybdenum and nickel. Cast iron filler rods are available in round, square or hexagonal sizes of 5 mm, 6.4 mm, 10 mm and 13 mm (3⁄16 in., 1⁄4 in., 3⁄8 in. and 1⁄2 in.).

Welding techniqueSome aspects of oxyacetylene fusion welding of cast iron are the same as for welding low-carbon steel. You use a welding torch tip the same size as the one you would use for welding low-carbon steel of the same thickness. You also use a neutral flame and you must remove all scale, dirt, grease and oxides from the surface of the weld joint. The only difference in weld joint design is the larger included angle, which can be up to 90° on the vee butt joints (Figure 7).

Notes



90º

1.6–3.2 mm (1⁄16–1⁄8 in.)

Rounded edges

Rounded edges

Figure 7—Joint preparation for cast iron

The same basic technique used to weld single-vee butt welds on low-carbon steel is used for fusion welding cast iron, but you must take care in forming the weld bead. Molten cast iron is very fluid, and the molten weld pool has a tendency to flow without fusing to the base metal. Take care to work gas pockets and impurities to the surface of the molten weld pool.

On a completed weld, the weld bead cap should have a slightly convex shape with no signs of undercutting. It should have complete (but not excessive) penetration. The surface of the weld bead should not have pits or porosity. To properly test a cast iron weld, break it along its length and then examine it for porosity, cracks, hard spots or impurities.


Notes



Answers




1. Which of the following is a disadvantage of braze welding grey cast iron?

a. It is expensive.

b. The high temperatures produce oxides.

c. The colour of the weld deposit metal does not match the base metal.

d. It requires a lot of preheat and post-heat treatments.

2. Braze welding on grey cast iron is mostly used for

a. repair work

b. fabrication

c. pipeline welding

d. shipbuilding

3. Why should you sear the edges of a grey cast iron weld joint?

a. to remove excess graphite flakes from the surface

b. to preheat the joint

c. to melt the flux

d. to promote oxide formation at the surface

4. Which is an advantage of fusion welding over braze welding for grey cast iron?

a. Fusion welding is less expensive.

b. Preheat and post-heat are not required.

c. Fewer oxides are formed.

d. Fusion-welded joints can withstand higher temperatures.

5. Braze-welded joints generally have fewer residual stresses and are less prone to cracking than fusion welded joints

a. true

b. false

Answers



6. Grey cast iron is an alloy of iron,

a. carbon and magnesium

b. copper and lead

c. carbon and silicon

d. copper and silicon

7. Grey cast iron than low-carbon steel.

a. is more ductile

b. is more brittle

c. is more malleable

d. has higher tensile strength

8. Which element adds to the difficulty of welding grey cast iron?

a. carbon

b. molybdenum

c. zinc

d. copper

9. Why is a flux necessary when fusion welding grey cast iron?

a. to tin the joint completely

b. to dissolve oxides and float off impurities

c. to lower the temperature of the filler metal

d. to promote capillary attraction

10. The preheat and post-heat treatments for welding grey cast iron are necessary to

a. prevent oxide formation

b. prevent overlap

c. prevent formation of gas pockets

d. prevent cracking

11. In order to reduce the effects of expansion and contraction when welding grey cast iron, you must

a. tin the joint completely

b. use the correct flux

c. use filler metals with low melting temperatures

d. use heat treatments

Answers



12. What is the free carbon in grey cast iron called?

a. graphite

b. austenite

c. pearlite

d. ferrite

13. The design of single-vee butt joints on grey cast iron is similar to single-vee butt joints on low-carbon steel, except that the

a. reinforcement is usually greater

b. reinforcement is usually smaller

c. included angle is usually larger

d. included angle is usually smaller

14. Which of the following filler-metal rods is used to fusion weld grey cast iron?

a. ECI

b. RCI

c. EBCuZn

d. RBCuZn

15. Which of the following rods is used to braze weld grey cast iron?

a. ECI

b. RCI

c. EBCuZn

d. RBCuZn

16. For oxyacetylene fusion welding of grey cast iron, you should use

a. a slightly oxidizing flame

b. a reducing flame

c. an acetone flame

d. a neutral flame

17. For braze welding grey cast iron, you should use

a. a slightly oxidizing flame

b. a reducing flame

c. an acetone flame

d. a neutral flame


Theory CompeTenCy p3-3 (Line C-C7–opTionaL):Silver-alloy brazing on similar and dissimilar metals

p3

-3 (F &

L1)


Module P3 Theory CoMPeTenCy P3-3 (line C-C7–oPTional)

OutcomesSilver-alloy brazing is a very useful welding process. Many ferrous and non-ferrous metals can be brazed with a silver alloy, producing leak-proof bonds of exceptional strength. It is a low-temperature process because the base metal is not melted, so it is also very useful for joining dissimilar metals.


• fluxes and filler rods used for silver-alloy brazing• joint design and preparation for brazing• silver-alloy brazing techniques

EvaluationWhen you have completed all the Theory Competencies in module P3, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P3-3:

• fluxes and filler rods used for silver-alloy brazing• joint design and preparation for brazing• silver-alloy brazing techniques

Resources


Notes



P3-3 Learning Task 1:Main factors of silver-alloy brazingSilver-alloy-brazed joints are often desirable in refrigeration or hydraulic applications where the weld joint must withstand severe conditions. Soldering will not produce weld joints that are strong enough. Silver-alloy brazing filler rods have a melting temperature above 425 °C (800 °F), while solder alloys have a melting point below 425 °C (800 °F). In order to produce good, sound welded joints using silver-alloy brazing, you must become familiar with some important factors involved in this process.

Joint preparation and designIt is very important that the metal to be silver-alloy brazed is absolutely clean. Remove any oil, grease, paint, rust or scale. If the weld joint is not perfectly clean, the brazing filler metal will not be drawn into the weld joint. Molten filler metal will not flow evenly over an unclean area. It will form small balls on the surface of the base metal.

Some metals, such as stainless steel and copper, have a natural layer of oxides that must be removed. These oxides form a very thin layer that will interfere with forming a good bond. Clean the base metal with stainless steel wool, emery cloth, a grinder or a file.

Silver-alloy brazing can be done on any of the weld joints that can be fusion welded. The clearance between the two pieces being joined is critical. For capillary action to occur, the gap should be 0.025 mm to 0.13 mm (0.001 in. to 0.005 in.). This paper-thin gap is small enough to allow the filler metal to fill the gap, but not so large that the molten filler metal flows out excessively through the back of the joint.

To fit up a lap, tee, butt or corner joint, simply fit one piece on or against the other. You do not have to leave a gap between the pieces. Even though the base metal pieces are resting against each other, there is enough space (due to the roughness of the metal’s edge) for the filler metal to flow between the pieces being joined.

Flux selectionFlux is necessary to chemically clean the metal. Silver-alloy brazing flux is usually manufactured in a paste form and should be brushed onto both edges of the weld joint before brazing. You should choose a flux formulated for the base metal being used. There are many types of general-purpose silver-alloy fluxes available for commonly brazed base metals.

Notes



Filler alloys (rods)Silver-alloy brazing filler metals come in a variety of sizes, shapes and compositions to suit many applications. The size, shape and composition you should use depends on the type of weld joint you are welding.

Even though a silver-brazing alloy might contain mainly copper and zinc (and only a small percentage of silver), it is still called a silver-brazing alloy. A copper-phosphorus filler metal (BCuP-5) that contains 15% silver is commonly used on copper-to-copper weld joints, usually pipe. This filler metal has the advantage of producing a very strong bond at a low cost due to its low silver content. This filler metal is commonly identified by its trade name, Sil-Fos. When you use Sil-Fos on a copper-to-copper weld joint, a paste flux is not necessary because the filler rod provides its own flux.

For other silver-alloy brazing jobs, use a silver alloy that is strong enough for the particular application. The higher the silver content of the alloy, the stronger the weld joint will be, but the alloy will also be more expensive.

There are many silver-brazing alloys manufactured under a variety of trade names. If you are unsure which filler metal to use in a particular situation, contact a welding supply company or check the manufacturer’s specifications.

The flame for silver-alloy brazingUse a reducing (carburizing) flame for oxyacetylene silver-alloy brazing. A lower-temperature, softer flame is necessary. A reducing flame of 3X is usually recommended. In a 3X reducing flame, the acetylene feather is three times the length of the inner cone (Figure 8).

Acetylene feather ConeTorch tip

Heat envelopeX3X

Figure 8—3X reducing flame

The size of the welding torch tip depends on the thickness of the base metal. Since overheating is a very common problem in silver-alloy brazing, be careful not to use a torch tip size that is too large. Check the manufacturer’s torch tip specification chart carefully to make sure you choose the correct size.

Notes



Silver-alloy brazing procedureOnce you have set up (fit) the weld joint and applied the flux, the joint is ready to be brazed. Do not melt the filler metal with the torch. Heat the base metal by applying heat to the entire joint. Do not concentrate the heat on one spot and be careful not to overheat the workpiece. The base metal needs to be only hot enough to melt the filler metal. You do not want to melt or burn the base metal.

The flux is a useful guide in telling when the base metal is hot enough to apply the filler metal. When the flux has a clear, glassy appearance, the base metal has just about reached the correct brazing temperature. At this point, begin to apply the silver-alloy filler metal. If the workpiece is too hot, cadmium fumes are released from the filler rod in a cloud of white smoke. Avoid breathing these fumes and lower the temperature of your workpiece.

For more detailed information on hazardous materials and related safety precautions, see Module P1-2 LT4.

When the workpiece is at the correct temperature, the filler metal will flow instantly into the weld joint when the filler metal makes contact with the base metal.

After the joint is complete and cooled, immerse the weldment in water to clean off most of the flux. If some remains on the weldment, use a wire brush to clean it completely.


Answers




1. Silver-alloy brazing can be used to weld

a. aluminum only

b. low-carbon steel only

c. only non-ferrous metals

d. many ferrous and non-ferrous metals

2. Silver-alloy brazing can be used to join dissimilar metals.

a. true

b. false

3. What force causes the silver-alloy brazing filler metal to flow into the weld joint?

a. gravity

b. capillary action

c. heat difference

d. osmosis

4. What is the purpose of flux in silver-alloy brazing?

a. to chemically clean the weld joint

b. to bring the base metals to the correct temperature

c. to help meet the filler rod

d. to eliminate the need for precleaning

5. On what type of base metal is Sil-Fos filler metal commonly used?

a. stainless steel

b. aluminum

c. low-carbon steel

d. copper

Answers



6. During silver-alloy brazing, ventilation is very important because some silver-alloy fillers have a high content of

a. cadmium

b. carbon

c. calcium

d. tungsten

7. What type of oxyacetylene flame should you use for silver-alloy brazing?

a. neutral

b. slightly oxidizing

c. slightly reducing

d. 3X reducing

8. When silver-alloy brazing, you should melt the filler metal with the torch.

a. true

b. false

9. When the weld joint has reached brazing temperature, the flux has what kind of appearance?

a. clear, glassy

b. cloudy

c. black

d. completely invisible


Notes



Theory CompeTenCy p3-4 (Line C-C3):Filler metals, fluxes and torch tips for fusion welding, braze welding and brazing

p3

-4 (F &

L1)



OutcomesIn this Theory Competency you will learn about the different classifications of filler metals and fluxes for fusion welding, braze welding and brazing. You must choose the correct filler metal and flux for each job. If the filler metal or flux is incorrect, the welds will not be of acceptable quality. You must also learn to choose the correct torch tip for the thickness of metal that you are welding.

When you have completed the Learning Tasks in this Theory Competency, you should be able to identify and describe:

• the AWS classification system for low-carbon steel fusion-welding filler metals• the AWS classification system for braze-welding and brazing filler metals• different welding and brazing fluxes• the correct procedure for using fluxes• torch tips used for welding and brazing• how to choose the right torch tip for welding and brazing

EvaluationWhen you have completed all of the theory competencies in Module P3, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P3-4:

• filler metals• welding and brazing fluxes• torches and torch tips for fusion welding, braze welding and brazing

Resources

All the resources you will require are contained in this Theory Competency.

Notes



P3-4 Learning Task 1:Filler metals for fusion welding, braze welding and brazingFiller-metal rods for fusion weldingAlthough some fusion welding is done by fusing only the edges of the metal, most joint designs need more filler metal. The filler-metal rod (or welding rod) provides the extra metal necessary to form the weld bead.

There are many types of filler-metal rods manufactured to meet the standards set by industry for oxyacetylene welding. Each type contains a special grouping of alloy metals and is classified by composition. The American Welding Society (AWS) has developed specifications for the following types of filler-metal rods:

• iron and steel• cast iron• stainless steel• copper and copper alloy• nickel alloy

A fusion-welded joint should always have the same strength as the base metal. To make sure that it does, you must use filler metal that is made of the same metal as the base metal. On low-carbon steel, for example, you should use a low-carbon steel filler-metal rod; on aluminum alloys, an aluminum-alloy filler-metal rod; on nickel alloys, a nickel-alloy filler-metal rod; and on copper products, a copper-alloy filler-metal rod.

All filler-metal rods used for oxy-fuel gas fusion welding are identified by the letter “R,” which stands for “welding rod.” The “R” is followed by the letter “G” to indicate that this filler rod is used for fuel-gas welding. The numbers that follow the RG designation indicate the tensile strength of the weld produced by that particular rod. The “RG” is how you tell this filler-metal rod apart from filler-metal rods and electrodes used for other kinds of welding: electric arc welding, whose identification begins with “E,” and braze-welding and brazing filler metals, which begin with “B.”

Low-carbon steel filler-metal rodsBy far the most widely used filler-metal rods are the low-carbon steel rods. These rods are made up mainly of iron with small additions of carbon and other elements such as manganese, silicon or chromium. The AWS classifies low-carbon steel filler rods into three categories: RG 45, RG 60 and RG 65. The AWS only uses imperial measurements, therefore the tensile strength is in thousands of pounds per square inch (psi). For example: RG 60 is identified as a low-carbon steel oxy-fuel gas filler-metal rod with a tensile strength of

Notes



60 000 psi. The CSA does not certify filler metals for oxy-fuel gas welding. Therefore, there are no CSA classifications for low-carbon steel filler rods.

RG 45Of the three filler rods, the RG 45 has the lowest tensile strength and is the most economical. It is used to weld low-carbon steel and has a wide application in maintenance work.

RG 60This filler rod is used to weld carbon steels with comparable tensile strength. Of the three filler rods, the RG 60 is the most commonly used. It has many general-purpose applications.

RG 65This filler rod has the highest tensile strength. It is used for welding the high-carbon, low-alloy steels that have high tensile strengths. It can be used on pipe, plate or sheet.

Filler-metal rod sizeSize is another factor to consider in choosing an oxy-fuel gas filler-metal rod. Most filler rods are round and 914 mm (36 in.) long, but the actual rod size is designated by the rod diameter.

Figure 9 lists the most common filler rod sizes and their uses on particular thicknesses of base metal. As you can see, the size of the rod should match the thickness of the metal.

Base Metal Thickness Rod Size

1.6 mm (1⁄16 in.) 1.6 mm (1⁄16 in.)

2.4 mm (3⁄32 in.) 1.6–2.4 mm (1⁄16–3⁄32 in.)

3.2 mm (1⁄8 in.) 2.4–3.2 mm (3⁄32–1⁄8 in.)

4.8 mm (3⁄16 in.) 4.0–4.8 mm (5⁄32–3⁄16 in.)

6.4 mm (1⁄4 in.) 4.8–6.4 mm (3⁄16–1⁄4 in.)

Figure 9—Filler rod size

If you try to use a filler rod size that is too small for the base metal thickness, the weld pool (puddle) becomes too hot and the weld deposit would be brittle and prone to cracking. If the filler rod size is too large, the excess filler metal will cool the weld pool so that penetration and complete fusion become very difficult.

Different manufacturers sell filler rods with similar characteristics, but each manufacturer has its own filler rod classification number and name. Do not be confused by different trade names. Check the manufacturer’s specification chart for welding rods. This chart will tell you which rods meet AWS specifications for composition and strength.

Notes



Oxy-fuel gas steel filler rod is normally purchased by weight, usually in 2.2 or 4.5 kg (5 or 10 lb.) containers. The filler rod has a very light coating of oil or is copper-coated to protect it from humidity and oxidation (rusting). The containers are marked with the filler rod trade name and classification number (e.g., All-STATE® RG 60), the manufacturer’s name, the rod diameter and length and the lot number. A WHMIS label including a warning is printed on each container as a reminder to weld only in well-ventilated areas. The following is an example of that warning:

Welding produces fumes and gases hazardous to your health. Avoid breathing these fumes and gases.

Braze-welding and brazing alloysA brazing filler-metal rod is required for all braze-welding and brazing operations. These filler rods are made of non-ferrous metals in a wide variety of alloy compositions to suit the temperature range, the strength and the colour of all brazeable metals. Because the CSA does not certify filler metals for braze welding or brazing, there are no CSA classifications of brazing alloys, so the AWS classification is used. There are eight AWS classifications of brazing alloys. While low-carbon steel rods are classified according to strength, the brazing alloys are classified according to chemical composition:

• silver• aluminum-silicon• precious metals• copper and copper-zinc• copper-phosphorous• magnesium• nickel• cobalt

Most of these basic classifications contain many different types of filler rods. These rods contain varying percentages of other elements to give them properties that closely match the properties of various base metals.

All brazing filler-metal rods are identified by the letter “B,” which stands for “brazing.” The “B” is followed by abbreviations identifying the one or two elements that form the bulk of the filler rod. For example: RBCuZn identifies a fuel gas brazing filler rod made up of copper and zinc.

This chemical designation can be followed by a number or a letter (or in some cases both) to give more information about the special characteristics of that particular filler metal.

Most brazing filler metals are designed for special purposes. Only a few, such as the silver-based and copper-based alloys, are good general-purpose brazing metals. These are widely used (especially on steel) because they produce the high-strength bonds usually necessary on steel structures.

Notes



Silver (BAg)This is a large group, with many types that contain silver alloyed with varying amounts of copper, cadmium, zinc and nickel. These alloys are used on all ferrous and non-ferrous metals except aluminum and magnesium.

Aluminum-silicon (BAlSi)This group contains seven types that are used only for brazing aluminum.

Precious metals (BAu)This group contains five types. They are made of gold and copper. The gold percentage can be as high as 62%. These alloys are expensive and are used mainly in electronics and jewellery.

Copper and copper-zinc (BCu and RBCuZn) brassThere are six types of filler metal in this category (Figure 10). The filler rods designated RB are used for braze welding and brazing. These alloys can be used on ferrous and non-ferrous metals.

Nominal Chemical Composition (Percentage)

AWS Classification

Cu Zn Sn Fe Mn Ni P PB Al Si Others (max .)

BCu-1 99.9 min.

.08 .02 .01 .10

BCu-1a 99.0 min.

.30

BCu-2 86.5 min.

.50

RBCuZn-A 59.0 39.8 .63 .05 .01 .50

RBCuZn-C 58.0 39.4 .95 .72 .26 .05 .01 .10 .50

RBCuZn-D 48.0 41.0 10.0 .25 .05 .01 .15 .50

Key: B = brazing, RB = welding or brazing rod

Figure 10—Copper and copper-zinc filler metals

Copper-phosphorous (BCuP)The seven types of filler metal in this group are used mainly to join copper and copper alloys, but they can also be used on other non-ferrous metals. They contain some silver and sometimes are used as a less-expensive alternative to silver-brazing alloys.

Magnesium (BMg)The two types in this group are used only for joining magnesium. These two types differ only in their melting temperatures.

Notes



Nickel (BNi)Each of the nine types in this group contains a large percentage of nickel and a variety of other elements. These alloys are used in applications where extreme heat or corrosion is a factor. Typical applications include jet and rocket engines, chemical plants and nuclear reactors.

Cobalt (BCo)There is only one type of cobalt filler metal, and it is used only on cobalt alloys.

The AWS specifications do not cover all the available filler metals. There are many filler metals that are unclassified. These are special-purpose alloy filler metals to be used on specific metals, such as gold, platinum or palladium.

Choosing a brazing filler-metal rodBrazing filler-metal rods are often designated by commercial names or AWS classification symbols. You will have to check a manufacturer’s brazing rod specification chart (Figure 11). Choosing a brazing filler rod from a chart such as this can be difficult. In a shop situation you will likely be told which rod to use.

Silver Brazing Alloy SpecificationsAirco Alloys AWS-ASTN

Class

%

Silver

%

Copper

%

Zinc

%

Cadmium

%

Others

Solidus

°F

Liquidus

°F

Brazing Temp .

Range °F

Aircosil 50 BAg-1a 50 15.5 16.5 18 — 1160 1175 1175–1400

Aircosil 3 BAg-3 50 15.5 15.5 16 Ni 3 1195 1270 1270–1500

Aircosil 45 BAg-1 45 15 16 24 — 1125 1145 1145–1400

Aircosil 35 BAg-2 35 26 21 18 — 1125 1295 1295–1550

Aircosil 15 BCuP-5 15 80 — — P 5 1185 1500 1300–1500

Aircosil A — 9 53 38 — — 1510 1600 1600–1750

Aircosil B — 20 45 35 — — 1430 1500 1500–1700

Aircosil C — 20 45 30 5 — 1140 1500 1500–1700

Aircosil D — 30 38 32 — — 1370 1410 1410–1650

Aircosil E BAg-4 40 30 28 — Ni 2 1240 1435 1435–1650

Aircosil F — 40 36 24 — — 1330 1445 1445–1650

Aircosil G BAg-5 45 30 25 — — 1250 1370 1370–1550

Aircosil H BAg-6 50 34 16 — — 1270 1425 1425–1600

Aircosil J BAg-7 56 22 17 — Sn 5 1145 1205 1205–1400

Aircosil K — 60 25 15 — — 1260 1325 1325–1550

Aircosil L — 54 40 5 — Ni 1 1325 1575 1575–1750

Aircosil M BAg-8 72 28 — — — 1435 1435 1435–1600

Aircosil N — 80 15 4 — — 1360 1490 1490–1650

Aircosil P BAg-Mn 85 — — — Mn 15 1760 1778 1780–2100

Aircosil Q — 50 28 22 — — 1250 1340 1340–1550

Aircosil R — 40 30 25 — Ni 5 1240 1560 1560–1750

Aircosil S BCuP-3 5 88.75 — — P 6.25 1190 1480 1300–1550

Aircosil S — 25 52.5 22.5 — — 1500 1575 1575–1750

Aircosil 60 — 60 30 — — Sn 10 1095 1325 1325–1550

Aircosil AE-100 — 92.5 7.3 — — Li 0.2 1435 1635 1635–1850

Aircosil 105 — 45 30 12 Mn 13 1298 1298 1298–1500

Figure 11—A typical manufacturer’s AWS brazing rod specification chart (in ºF)

Notes



Braze-welding filler-metal rodsBraze-welding filler-metal rods can be used for both brazing and braze welding. Their identifiers begin with the letters “RB,” followed by the chemical composition of the metal and the type (e.g., RBCuZn-A).

Most alloys used in braze welding are an alloy of copper and zinc (brass), with roughly 60% copper (Cu) and 40% zinc (Zn), or bronze alloys containing copper and tin. Small portions of other metals such as nickel, manganese and silicon are added to increase the strength, hardness and flowability of the filler. The tensile strength of these alloys ranges between 275 mPa and 414 mPa (40 000 psi and 60 000 psi).

The three types of copper-zinc filler rods most commonly used are RBCuZn-A, RBCuZn-C and RBCuZn-D. These alloys usually have a composition of around 60% copper and 40% zinc, and they are often called “Muntz metal.” The letters A, C and D indicate the exact proportions of copper, zinc and the other minor elements. The different proportions affect the melting temperature and flow characteristics of the alloy. These filler rods most often come with a flux coating.


Notes



Answers




1. When you fusion weld low-carbon steel, the diameter of your filler-metal rod should generally be equal to

a. the thickness of the base metal

b. the torch tip orifice diameter

c. the length of the torch flame

d. half the thickness of the base metal

2. In fusion welding, filler metal is added to the molten pool to

a. prevent formation of oxides

b. reduce distortion in the workpiece

c. provide additional reinforcement

d. reduce the possibility of contamination

3. The normal length of an oxy-fuel gas filler-metal rod is

a. 610 mm (24 in.)

b. 660 mm (26 in.)

c. 814 mm (32 in.)

d. 914 mm (36 in.)

4. Oxy-fuel gas steel filler rod is copper-coated to prevent

a. distortion of the base metal

b. rusting

c. toxic fumes from being released

d. excess bead buildup

5. A filler-metal rod used to fusion weld low-carbon steel should have the same

a. diameter as the base metal thickness

b. tensile strength as the base metal

c. composition as the base metal

d. all of the above

Answers



6. The filler metals most commonly used for braze welding usually contain

a. copper and iron

b. zinc and tin

c. copper and aluminum

d. copper and zinc

7. Fusion welding always requires a filler rod.

a. true

b. false

8. Which low-carbon steel filler rod has the highest tensile strength?

a. RG 45

b. RG 60

c. RG 65

d. RG 80

9. Low-carbon steel filler rods are classified according to

a. metal content

b. minimum tensile strength

c. chemical composition

d. bonding ability

10. In an RG 45 low-carbon steel rod, the 45 indicates

a. the length in centimetres

b. the diameter in millimetres

c. the minimum tensile strength of the weld deposit

d. a melting temperature of 450 °C (840 ºF)

11. What size filler-metal rod should be used on low-carbon steel that is 3.2 mm (1⁄8 in.) thick?

a. 1.6 mm (1⁄16 in.)

b. 2.4 mm (3⁄32 in.)

c. 3.2 mm (1⁄8 in.)

d. 4.8 mm (3⁄16 in.)

Answers



12. When is a brazing filler-metal rod required?

a. only when brazing low-carbon steel

b. when brazing aluminum or brass

c. when brazing any metal

d. only when brazing at high temperatures

13. How are brazing filler-metal alloys classified?

a. by weight

b. by size

c. by melting temperature

d. by chemical composition

14. Which of the following is considered to be a good general-purpose brazing alloy?

a. silver

b. aluminum-silicon

c. magnesium

d. cobalt


Notes



P3-4 Learning Task 2:Fluxes for fusion welding, braze welding and brazingFlux is a chemical compound that is applied to weld joint surfaces before welding or brazing to help the bonding process. A flux is required for all braze-welding and brazing procedures. Fusion welding of cast iron, stainless steel and some non-ferrous metals also requires a flux. Flux is not usually needed for fusion welding of low-carbon steel.

Purpose of fluxFlux is always necessary for braze-welding and brazing processes to create a good bond. Flux serves three purposes:

1. It chemically cleans the surface of the base metal, removing oxides that might not have been removed during precleaning. Since braze-welding and brazing bonds require a surface adhesion, it is extremely important that the base metal surface be clean and free of oxides.

2. It prevents the formation of oxides during the braze-welding and brazing processes. The heating of the base metal accelerates the formation of oxides. The flux coats the weld joint and acts as a protective coating over the base metal.

3. It allows the filler metal to flow easily on the base metal.

Flux for fusion weldingFor oxyacetylene fusion welding of low-carbon steel, flux is not necessary. The high temperature required produces enough heat to melt any iron oxides already present or that have formed during the welding process. These oxides float to the surface of the weld pool and do not interfere with the fusion process.

When fusion welding cast iron, stainless steel, aluminum or magnesium, you will need a flux. The oxides of these metals have a higher melting temperature than the parent metal. This is the same phenomenon that makes the metals difficult to cut with an oxy-fuel gas cutting torch. The oxides remain solid at the temperature that melts the parent metal and interfere with the fusion process. The flux serves to increases the fluidity of the molten metal, dissolve oxides and float off impurities to the surface of the weld pool.

There is no one universal flux for fusion welding all metals. When choosing a flux for fusion welding, be sure to read the manufacturer’s label carefully to see if the flux is suitable for the metal you are welding. Follow the directions carefully.

Notes



Flux for braze welding and brazingFlux is essential for all braze-welding and brazing processes. The main functions are to clean the surface of the metal, to remove the oxides, to promote wetting and to help the capillary action. Flux also indicates the temperature of the base metal as it is heated. The action of a general-purpose flux changes during the heating process (Figure 12). By watching these changes, you can effectively gauge the temperature of the base metal and decide when to add the filler metal.

870 ºC (1600 ºF)

815 ºC (1500 ºF)

760 ºC (1400 ºF)

705 ºC (1300 ºF)

650 ºC (1200 ºF)

595 ºC (1100 ºF)

540 ºC (1000 ºF)

480 ºC (900 ºF)

425 ºC (800 ºF)

370 ºC (700 ºF)

315 ºC (600 ºF)

260 ºC (500 ºF)

205 ºC (400 ºF)

150 ºC (300 ºF)

100 ºC (212 ºF)

40 ºC (100 ºF)

-20 ºC (0 ºF)Room temperature

Water boils out of flux paste

Flux works and bubbles

Flux begins to melt

Flux clear and quiet

Brazing temperature

Flux protects to here

Figure 12—Temperature indications of a brazing flux

Flux contains potentially toxic substances such as borax, chloride and fluoride. These substances are corrosive and poisonous if ingested. The greatest danger is the fumes they produce when heated. It is essential that you provide for good ventilation when working with flux.

Types of brazing fluxBrazing flux generally falls into one of three categories:

• high temperature• special purpose or low temperature• general purpose

High-temperature brazing fluxThis flux is most commonly used for higher temperature applications, above 800 °C (1500 °F). Because they are well suited to high temperatures, they are used extensively in braze welding, where flux must withstand higher

Notes



temperatures for longer periods than is usual with brazing. They can be used on copper or brass. They are especially effective on stainless steel, cast iron and other metals that produce oxides that melt only at high temperatures.

Special-purpose or low-temperature fluxThis flux has a low melting temperature. It is used mainly on aluminum, aluminum alloys and magnesium.

General-purpose fluxThis flux can be used on all copper and copper-based alloys, except those containing aluminum. They are also effective for a broad range of metals, including low-carbon steel, cast iron, stainless steel, nickel alloys and the precious metals (gold and silver).

Choosing the correct brazing fluxChoosing a brazing flux can be difficult. It is important to consider the following:

• Choose the flux formulated for the base metal.• Choose a flux that will melt at the expected brazing temperature.• Choose the flux for the application method you are using.

Choosing the correct temperature range is especially critical. At about 528 °C (1100 °F), an all-purpose flux will melt and form a clean coating over the joint. If you use the correct flux, the base metal does not melt at this temperature, and you can add the filler rod to form the bond. If you choose a flux with a melting temperature that is too high, the base metal will melt before the flux. If the flux melting temperature is too low, the flux will lose its protective qualities at the filler metal’s melting temperature. The correct melting temperature for a flux is between the melting temperature of the base metal and the melting temperature of the filler metal.

Always make sure you carefully read the manufacturer’s information on the flux containers. Another source of information you should check when choosing a flux is the AWS brazing-flux specifications.

Using fluxFluxes are available as a powder, paste or liquid. They also come as a coating on braze-welding and brazing filler rods (Figure 13). The flux can be applied directly to the weld joint by brushing, rubbing or spraying. In some applications the filler rod is dipped into the flux. The flux is normally applied just before welding so that it does not have time to dry.

Notes



Figure 13—Flux comes in several forms

Many braze-welding and brazing filler rods are precoated. This gives you the advantage of not having to interrupt your welding to put flux on the rod.

When using bare filler rods, you must dip or roll the heated rod in flux. The flux adheres to the rod and is deposited in the joint as the filler rod melts.

You must apply flux properly. If you use too much flux, it can become trapped in the molten metal and cause porosity.

Removing fluxFlux residue must be cleaned from the base metal immediately, because most flux is corrosive and could weaken the joint. Flux residue can be cleaned with hot water or steam. You might have to use a wire brush to remove all traces of the flux.

Flux can release harmful fumes when heated. Always make sure there is proper ventilation when you are using welding or brazing flux.


Notes



Answers




1. A flux is not required when fusion welding

a. low-carbon steel

b. aluminum

c. magnesium

d. stainless steel

2. When choosing a flux for fusion welding, you must consider the

a. thickness of the base metal

b. type of filler rod

c. temperature of the torch flame

d. type of metal to be welded

3. What type of brazing flux is generally used for braze welding?

a. high temperature

b. special purpose

c. general purpose

d. universal

4. When choosing the correct brazing flux, you must consider

a. the composition of the filler-metal rod

b. the melting temperature of the flux

c. the metal being joined

d. all of the above

5. Flux helps bonding by

a. lowering the melting temperature of the filler-metal rod

b. raising the brazing temperature

c. dissolving oxides and floating off impurities

d. lowering the melting temperature of the oxides

Answers



6. You must use high-temperature flux when you are braze welding

a. cast iron

b. aluminum

c. magnesium

d. silver

7. When you use flux, you must make sure

a. the base metal has been precleaned

b. there are no oxides on the metal surface

c. a fire extinguisher is within reach

d. there is good ventilation


Notes



Notes



P3-4 Learning Task 3:Oxy-fuel gas torches and torch tips for fusion welding, braze welding and brazingOxy-fuel gas welding torchesThe oxy-fuel gas welding torch is often called a “blow pipe.” The torch comes in various sizes and styles. It is used for fusion welding, braze welding and brazing. Jewellers and model makers use small, light-duty oxy-fuel gas torches for precision work. Heavy-duty industrial torches are used to heat large sections and to weld metals thicker than 50 mm (2 in.). Oxy-fuel gas Welders most commonly use a medium-duty torch to weld metals from 0.8 mm to 16 mm (1⁄32 in. to 5⁄8 in.) thick.

How oxy-fuel gas welding torches workThere are two major types of oxy-fuel gas torch: the equal-pressure or balanced-pressure torch, and the injector torch. In both, oxygen and the fuel gas are delivered from their respective hoses to separate tubes within the torch handle. The gas flow is controlled by the torch handle oxygen and fuel gas valves, usually located at the inlet points on the torch handle (Figure 14).

Torch handle fuel gas valveTorch handle

Torch handle oxygen valveWelding tip

Figure 14—Oxy-fuel gas welding torch

The torch types differ in how the gases are mixed. On the balanced- or equal-pressure torch (Figure 15), the gases are delivered at about equal pressures to the mixing chamber, where they are thoroughly mixed and then emitted through the tip orifice.

Tip orifice

Torch handle

Mixing chamber

Union nut

Welding tip attachment

Acetylene

Mixed gases

Oxygen

Figure 15—Cutaway view of the equal-pressure torch

Notes



In injector-type torches (Figure 16), the oxygen gas flows at a higher pressure than the fuel gas. The oxygen flows through a venturi into the mixing chamber. As the oxygen passes through the venturi, the venturi effect allows the higher oxygen pressure to draw in the fuel gas through small openings so that the fuel gas is injected into the oxygen stream.

High-pressure oxygen

Low-pressure fuel gas

Injector

Mixing chamber

Figure 16—Cutaway view of the injector type torch

The injector torch is used mainly with fuel gases that have very low delivery pressures. One drawback to the injector torch is the need for different mixers for different fuel gases. Before using an injector torch, you must check the torch carefully to make sure that the correct mixer attachment is installed.

Equal-pressure torches are much more versatile. You only need to select the correct tip for the fuel gas, since the mixing chamber is always correct.

The oxy-fuel gas welding tipModern welding torches have separate, detachable welding tips that attach into the end of the torch handle. These tips are made of copper alloy, which is easily bent or dented, and they must be handled carefully and stored away from oil, grease and paint.

Choosing the correct oxy-fuel gas welding tipThe correct choice of welding tip size for the job you are doing depends mainly on three factors: type of metal, thickness of the metal and type of welding process.

The weld tip size is measured by the diameter of the tip’s flame orifice. A large tip has a large flame orifice and is able to deliver greater volumes of heat.

Note that all welding tips, regardless of size, produce the same flame temperature at the tip. The difference is in the volume of heat delivered.

The numbering system for oxy-fuel gas welding tip sizes is similar to that of oxy-fuel gas cutting tips. The system is not standardized, so you should follow the manufacturer’s recommendations.

Figure 17 shows how metal thickness determines the welding tip size used, and how tip size affects working pressure settings on an oxy-fuel gas welding torch. These listings vary with the type of welding tip, the type of torch and the manufacturer.

Notes



Welding Pressures

Metal Thickness Tip Size Number Oxygen Acetylene

.8 mm (1⁄32 in.) 0–17–14 kPa (1–2 psi)

7–14 kPa (1–2) psi

1.6 mm (1⁄16 in.) 1–214–21 kPa (2–3 psi)

14–21 kPa (2–3) psi

2.4 mm (3⁄32 in.) 1–314–28 kPa (2–4 psi)

14–28 kPa (2–4) psi

3.2 mm (1⁄8 in.) 3–421–34 kPa (3–5 psi)

21–34 kPa (3–5) psi

4.8 mm (3⁄16 in.) 4–528–41 kPa (4–6 psi)

28–41 kPa (4–6) psi

6.4 mm (1⁄4 in.) 5–634–41 kPa (5–6 psi)

34–41 kPa (5–6) psi

9.5 mm (3⁄8 in.) 6–841–55 kPa (6–8 psi)

41–55 kPa (6–8) psi

Figure 17—Typical OAW tip chart for steel plate

The welding tip size number matches the number stamped into the tip (Figure 18).

Figure 18—Tip size stamped into tip

The type of welding process also affects the size of the welding tip you will require. Braze welding and brazing require less heat than fusion welding, and usually a smaller tip size is used for metals of comparable thicknesses.

The type of material also affects your choice of the welding tip size. When you are welding aluminum, copper and other non-ferrous metals, the heat dissipates so quickly that you will need a larger tip size than you would for welding steel of the same thickness.

It is important that you use the correct tip size. If you use a tip that is too large, the metal will heat very quickly and it can burn through. This can be

Notes



disastrous during low-temperature braze welding or brazing, where you don’t want the base metal melting at all.

If you fusion weld using a tip that is too small, it will take a long time for the base metal to melt. In braze welding and brazing, a tip that is too small will cause the base metal to take too long to get to the correct temperature to melt the filler rod. If it seems to be taking too long to reach the desired temperature, do not increase the gas pressure. Change to a larger size tip instead. Trying to increase the gas pressure will generally produce a very noisy, turbulent flame that disturbs the weld pool and creates poor welds.

Choosing the correct welding tip for all circumstances takes experience. Always check the manufacturer’s welding tip specification chart to find out the correct tip size for the thickness of base metal you are welding.

It is important to connect only welding tips and attachments that are specifically designed to mate with the torch handle. After choosing the correct tip size, insert the tip attachment into the torch handle. Examine the threads, seals and seats before attaching the tip to the torch. If there is a damaged seal or seat, the resulting leak can cause a fire or explosion.

Tighten the union nut by hand only. Never use a wrench.

Welding tip maintenanceThe welding tip will need to be cleaned from time to time. It can become clogged with small particles from the welding process, and this can greatly affect the performance of the torch.

The cleaning process is similar to cleaning an oxy-fuel gas cutting tip. Use a flat-tip file to smooth off and remove any carbon or metal particles from the end of the tip (Figure 19).

Figure 19—Use a flat file to remove deposits from the tip end

Notes



Use a cleaning needle that is smaller than the diameter of the tip orifice and clean the inside of the tip orfice. Use a straight up-and-down motion only, taking care not to twist or bend the cleaning needle (Figure 20).

Figure 20—Clean tip orifice with cleaning needle


Answers




1. Which of the following is a factor in determining the size of the oxy-fuel gas welding tip you should use?

a. gas pressures

b. colour of the base metal

c. thickness of the base metal

d. position of the base metal

2. Identify the parts of the equal-pressure welding torch shown in Figure 21.

a. union nut

b. tip orifice

c. mixing chamber

d. tip

1

2

43

Figure 21

3. The larger the orifice of the welding tip, the

a. greater the flame temperature

b. more volume of heat that is delivered

c. less fuel gas that is used

d. thinner the material that can be welded

Answers



4. In a welding torch, the oxygen and fuel gas first meet

a. at the union nut

b. at the tip orifice

c. in the torch valve

d. in the mixing chamber

5. A manufacturer’s welding tip size chart lists the metal thickness, the tip size numbers and the

a. cylinder pressures

b. working pressures

c. type of filler rod

d. welding speed

6. An increase in base metal thickness usually requires

a. an increase in rate of travel

b. an increase in tip size

c. a decrease in tip size

d. a lower torch angle

7. From which material are welding tips made?

a. magnesium

b. aluminum

c. brass

d. copper alloy

8. When you weld copper, the tip size will likely be the size used to weld steel of the same thickness.

a. the same as

b. larger than

c. smaller than

d. much hotter than

9. When attaching a welding tip to the torch handle, you should

a. tighten with a cylinder wrench

b. oil the threads first

c. hand-tighten only

d. open the oxygen valve slightly

Answers



10. All welding tips, regardless of size, produce the same flame temperature.

a. true

b. false

11. To remove slag or carbon deposits on a welding tip, you should use a

a. grinder

b. wire brush

c. tip scraper and a cleaning needle

d. piece of sandpaper

12. Which of the following is true of an injector-type torch?

a. The oxygen and fuel gas are delivered at equal pressures.

b. The oxygen is delivered at a higher pressure than the fuel gas.

c. The same mixing chamber unit can be used with all fuel gas tips.

d. The mixing chamber is an integral part of the tip.


Theory CompeTenCy p3-5 (Line C-C4):Main process factors and joint design for fusion welding with the oxyacetylene-welding process

p3

-5 (F &

L1)



OutcomesIn this Theory Competency you will continue to build on your basic knowledge of oxyacetylene welding and the use of the equipment. You will learn about the main factors that affect the quality of welds, the weld defects you will come across and how to avoid and prevent those defects. You will learn about basic weld joints and welding positions.


• the main factors of fusion welding and their importance• common weld faults, their causes and ways to avoid them• correct weld profiles and reinforcement• the four weld positions• the five basic joint designs• how to fit and weld lap, tee and corner joints• how to fit and weld square and single-vee butt joints• how to examine welds for defects• the safe setup, ignition and shutdown of oxyacetylene welding equipment

EvaluationWhen you have completed all the theory competencies in module P3, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P3-5:

• main factors of fusion welding• weld faults and their causes• weld profiles• weld positions• joint designs• fit-up of joints• setup, ignition and shutdown of oxyacetylene equipment

Resources


Notes



P3-5 Learning Task 1:Main factors in oxyacetylene fusion weldingWhen fusion welding low-carbon steel plate, sheet or pipe, you have to consider many factors in order to produce a good weld. These include:

• correct welding torch tip sizes• correct flame setting• correct flame-to-work distance• types of welding technique• Welder comfort and position

Correct welding torch tip sizesDifferent torch tip sizes are manufactured to correspond to the heat requirements of various thicknesses of base metal. Since the numbering systems from the various tip manufacturers are not standardized, you must always follow the manufacturer’s tip specification chart. If you use a tip that is too small, not enough volume of heat is present to melt the base metal. On the other hand, a tip that is too large produces too large a volume of heat, which can affect your work. The welding tip must also be clean. A clogged tip orifice interferes with the gas flow, causing a distorted flame.

Be sure to set the working pressure of the oxygen and the acetylene at the pressures given in the tip specification chart. If you set the pressures too high, the turbulent flow of the gases will disturb the weld pool. This affects fusion and produces poor appearance. The correct pressures for the welding tip used will produce a flame that is quiet and a weld pool that is calm.

Correct flame settingThe correct flame setting for oxyacetylene fusion welding of low-carbon steel is a neutral flame (Figure 22), the same as for oxy-fuel gas cutting. It is important to avoid using an oxidizing flame. An oxidizing flame causes oxides to form in the weld metal. Oxides will make the weld metal very brittle. You should use a very slightly carburizing flame to prevent an oxidizing flame from being formed if the gas pressures fluctuate. You should learn to recognize the sharp hissing sound and appearance of an oxidizing flame.

Notes



A. Neutral �ame

B. Oxidizing �ame–excessive oxygen

C. Carburizing �ame–excessive acetylene

Blue envelope

Rounded white inner cone

Light blue featherBlue envelope

Light blue envelope

Sharp white inner cone

Rounded white inner cone

Figure 22—Three types of oxyacetylene flames

Flame-to-work distanceThe tip of the inner cone of the flame should be about 1.6 mm to 3.2 mm (1⁄16 in. to 1⁄8 in.) above the base metal (Figure 23). This is the hottest part of the oxyacetylene flame. You want the metal to reach its molten state as quickly as possible and to maintain the weld pool during the welding process.

Direction of travel

1.6–3.2 mm

30–45º

Figure 23—Optimal flame-to-work distance

Types of welding techniqueThere are two basic techniques used in oxyacetylene welding: forehand welding and backhand welding.

In the forehand technique, the direction of travel is the direction the tip is pointing (Figure 24). In effect, the torch is “pushing” the weld pool and the welding flame is preheating the weld joint just ahead of the torch. The filler-metal rod is held in front of the weld pool and is fed in as required.

Notes



In the backhand technique, the torch tip is tilted so that it points away from the direction of travel (Figure 24). In effect, the torch is “dragging” the weld pool and the tip points back toward the weld pool. The filler-metal rod is held in front of the weld pool and follows the movement of the torch.

Forehand Backhand

Direction of travel

30–45º30–45º

Direction of travel

45–75º

90º–120º 45º–90º

Figure 24—Welding techniques

Forehand welding is the most popular technique. It is used in all positions for welding light-gauge sheet up to 3 mm (1⁄8 in.) thick. Typically this technique requires a wider filler metal rod to torch included angle (Figure 25). This gives good control and good weld appearance.

Thick material greater than 3 mm (1⁄8 in.)—narrow angle

Thin material 3 mm (1⁄8 in.) or less—wide angle

90–120º

45–90º

Forehand travel direction Backhand travel direction

Torch tip

Torch tip

Filler metal rod

Filler metal rod

Figure 25—Torch tip to filler metal rod angle

The backhand technique is best for welding material that is more than 3 mm (1⁄8 in.) thick. Typically this technique requires a narrower filler metal rod to torch included angle (Figure 25). This helps to get good penetration at the weld root. The welding tip should be at least one size larger than what would be used on the same material with the forehand method. This is necessary because there is some heat loss. The forehand and backhand techniques have their own applications and you will need to learn both.

Torch angleThe welding torch angle includes two angles: the work angle and the travel angle (Figure 26). Both angles are taken from the surface of the base metal at the weld pool. The work angle is taken across the weld joint (or more

Notes



precisely, in a transverse plane from the weld axis). The travel angle is taken along the length of the weld joint (or, in a longitudinal plane from the weld axis). A torch travel angle of 45° to 75° is typical for backhand welding. A torch travel angle of 30° to 45° is typical for forehand welding. Through experience you will learn to vary the angles of the torch and the filler-metal rod to suit the job you are doing.

45–75º 90º

90º

30º

Backhand travel direction

Forehand travel direction

Work angleTravel angle

Front view End view

Front view End view

Figure 26—Torch travel angle and work angle

The travel angle of the torch varies with the thickness of the base metal. The thicker the metal, the closer to the perpendicular (90°) you must hold the torch. This torch angle provides the heat needed for full penetration of thicker metals.

Speed of travel and movementSpeed of travel (rate of travel) is a very important factor in producing good fusion welds. The speed of travel depends on the base metal thickness, the welding joint design and the volume of heat produced by the welding torch.

If your speed of travel is too fast, the weld bead becomes too narrow and the bead ripples become pointed. The heat has not penetrated and lack of fusion is the result (Figure 27).

Figure 27—Weld bead formed when speed of travel was too fast

Notes



If your speed of travel is too slow, it will result in too much penetration and a scaly appearance on the weld bead (Figure 28).

Figure 28—Weld bead formed when speed of travel was too slow

If you allow too much heat to build up, the molten weld pool will collapse through to the bottom of the plate and leave holes (Figure 29). The underside of the weld might have molten metal that has solidified, forming icicle-like structures.

Figure 29—Weld bead formed with too much heat

If you complete your weld properly, it will have uniform bead ripples, even bead width and a shiny surface appearance (Figure 30).

Figure 30—Weld bead formed correctly

The movement of the torch is also extremely important. As soon as there is a small weld pool (pool of molten weld metal), start to move the torch forward with a side-to-side or circular motion. At the same time, insert the end of the filler rod into the weld pool, dipping the rod into and out of the weld pool. The filler rod should be withdrawn just enough to remove it from the weld pool, but not entirely from the flame, since it should not be allowed to oxidize or cool.

Coordinating the motion of the filler rod and the motion of the welding torch is an important factor in producing a quality weld. You will become better at this with continued practice.

Notes



Welder comfort and positionWhen welding, you should always position yourself so you can clearly see the weld pool, and you should (whenever possible) be in a firm, steady position. Bracing your body against something stationary can help you to hold steady. Place the elbow of your filler-rod arm on something solid or rest your hip against the edge of your workbench to improve your ability to hold steady. Using both your elbow and your hip is the best. Do not brace your torch hand.

If you weld standing upright with no part of your body touching a steady point, you will find that you will have difficulty steadying yourself. Your filler-rod hand or some part of your body must have a physical reference.

Find a way to hold the torch comfortably so that you have good control over the movement of the tip. Support or arrange the gas hoses so there is no interference with torch movement. The important thing is to be comfortable and have good control over the torch. If you are right-handed, welding with the forehand technique, the direction of travel is normally from right to left. If you are left-handed, the direction of travel would normally be from left to right.


Notes



Answers




1. What determines the size of welding tip you should use?

a. the base metal thickness

b. the working pressure

c. the number of oxides

d. your speed of travel

2. What is the correct flame setting for oxyacetylene fusion welding of low-carbon steel?

a. oxidizing

b. carburizing

c. neutral

d. acidic

3. When oxyacetylene welding, what is the flame-to-work distance?

a. 3.2 mm (1⁄8 in.)

b. 6.4 mm (1⁄4 in.)

c. 9.5 mm (3⁄8 in.)

d. 12.7 mm (1⁄2 in.)

4. Where is the hottest part of the oxyacetylene flame?

a. close to the tip flame orifice

b. just outside the outer flame envelope

c. in the middle of the outer flame envelope

d. at the tip of the flame’s inner cone

5. Figure 31 illustrates which welding technique?

a. forehand

b. uphill

c. backhand

d. downhill

Forehand Backhand

Direction of travel

30–45º30–45º

Direction of travel

45–75º

90º–120º 45º–90º

Figure 31

Answers



6. Which welding technique is best for material thicker than 3.2 mm (1⁄8 in.)?

a. forehand

b. uphill

c. backhand

d. downhand

7. What determines the correct torch travel angle?

a. type of filler rod used

b. thickness of the base metal

c. working pressures

d. speed of travel

8. What determines the correct speed of travel when oxyacetylene welding?

a. type of flux used

b. air temperature

c. size of the filler rod

d. volume of heat required

9. Figure 32 illustrates a weld bead that was formed

Figure 32

a. from a slow speed of travel

b. from a fast speed of travel

c. from too much heat

d. correctly

10. In Figure 33, the formation of the weld bead indicates that the

Figure 33

a. speed of travel was too slow

b. speed of travel was too fast

c. torch travel angle was too high

d. torch travel angle was low

Answers



11. Figure 34 illustrates a weld bead that results from

Figure 34

a. too much heat input

b. too little heat input

c. speed of travel too fast

d. good welding technique

12. Figure 35 illustrates a weld bead that results from

Figure 35

a. a weld deposit formed correctly

b. speed of travel too fast

c. speed of travel too slow

d. torch travel angle too low


Notes



P3-5 Learning Task 2:Weld faults in the oxyacetylene-welding processesWeld defectsThere are several common weld defects you should become aware of and learn to avoid. The faults presented here are the ones you are most likely to experience when oxyacetylene welding. These defects are called “structural discontinuities.” They include:

• incomplete penetration• incomplete fusion• undercut

Incomplete penetrationIncomplete penetration occurs when the weld pool and the base metal have not fused at the bottom, or root, of the weld joint (Figure 36).

Complete penetration

Incomplete penetration

Complete penetration

Incomplete penetration

A B

Figure 36—Penetration

This is one of the most serious welding defects. In welding joints such as a butt joint (Figure 36A), the joint can be turned over and inspected for complete penetration. However, in other joints such as lap (Figure 36B) and tee joints, incomplete penetration is impossible to detect.

Incomplete penetration is usually the result of inadequate welding heat. It occurs most often if the welding tip is too small, the speed of travel is too fast or the flame is held too far away from the base metal. Poor weld joint design or fit can also contribute to incomplete penetration.

Notes



Incomplete fusionIncomplete fusion is a very serious problem that is also hard to detect. This fault differs from incomplete penetration in that the weld joint might be full, but the weld deposit has not fully joined with the base metal. In other words, fusion has not taken place. The filler metal has been deposited, but the weld deposit has not fused with the base metal.

Incomplete fusion can occur anywhere in a weld. Incomplete fusion at the edge or toe of the weld is called “overlap” or “cold lap.” Overlap (Figure 37) is most often a sign of poor fusion throughout the weld deposit.

Overlap(Cold lap)

Figure 37—Overlap or cold lap faults

There are several causes of incomplete fusion. The most common is failure to preheat the base metal to the filler rod’s melting point before melting the filler rod into the weld joint. On some metals not using the proper flux can also cause poor fusion and overlap.

UndercutUndercut is a cutting away of the plate surfaces at the edge of the weld (Figure 38). A sharp recess forms in the plate where the next layer or bead must fuse with the base metal. The plate is thinner at this point, so the joint is weaker. Joint failure is especially likely when the undercut occurs at the toe of the weld.

Figure 38—Undercut

Undercut is usually caused by too much heat, improper torch work angle or too slow a travel speed.

Notes



Reinforcement on groove weldsIn addition to these serious structural faults, there are weld faults that affect the dimension of the finished weld. If the dimension of the finished weld does not meet specification, it is called a “dimensional defect.”

Metal deposited above the surface of the plate is called “reinforcement.” In a groove weld, there should be sufficient weld deposit to build up the weld profile above the surface of the base metal (Figure 39). This reinforcement, however, should not be higher than 3.2 mm (1⁄8 in.).

Adequate reinforcement

Insu�cient reinforcement

Figure 39—Reinforcement

Correct weld profile for fillet weldsFillet welds (Figure 40) are used on lap, tee and corner joints. A fillet weld is roughly triangular in shape. The most preferred fillet weld is flat to slightly convex in order to provide the necessary strength to the welded joint. Concave weld profiles can be specified for certain welds, but generally, they should be avoided.

Size

Flat

45º

Size

Concave

Size

Size

Convex

C

Figure 40—Fillet weld profiles


Answers




1. Figure 41 illustrates which weld fault?

a. undercut

b. overlap

c. incomplete penetration

d. insufficient reinforcement

2. When the filler metal has not fully fused with the base metal, it is called

a. incomplete fusion

b. incomplete penetration

c. undercut

d. reinforcement

3. Incomplete penetration can be caused by many factors. One of these is

a. using a tip that is too large

b. using too slow a travel speed

c. poor weld joint design or fit

d. the flame-to-work distance is too close



b. undercut

c. incomplete penetration

d. insufficient reinforcement

5. Which of the following is the most common cause of incomplete fusion?

a. inadequate preheat of the base metal

b. overheating the base metal

c. incorrect filler rod

d. using too much flux

Figure 41

Figure 42

Answers





b. insufficient reinforcement

c. undercut

d. incomplete penetration



b. undercut

c. insufficient reinforcement

d. no weld fault present

8. Generally, which of the following is the preferred shape of a fillet weld?

a. flat or slightly concave

b. flat or slightly convex

c. flat or slightly overlapped

d. convex or slightly overlapped


Figure 43

Figure 44

Notes



Notes



P3-5 Learning Task 3:Basic joint designs and welding positions for fillet weldsFive basic jointsThere are five basic joint designs used in welding (Figure 45). In the module P3 Practical Competencies, you will develop your skill in welding all of these except the edge joint. Of these joint designs, the corner, lap and tee are the type you will weld with a fillet weld. The edge joint is used mainly on light-gauge sheet metal and normally does not require additional filler metal. You will learn about the lap, tee and corner joints at this time and will study the butt joint separately in Learning Task 4.

Lap joint

Butt joint Edge joint

Tee joint Corner joint

Figure 45—Five basic joints

Corner jointThe corner joint joins two pieces of metal at right angles (90°) to each other (Figure 46).

Tack weldsSlight gap

90º

Figure 46—Corner joint

Notes



When forming a corner joint, position the two pieces to form an angle close to 90°. Make sure that the edges of the weld joint meet from end to end and do not overlap.

Incomplete penetration is a relatively common defect in corner joints. It can result from a fit that is too tight. Therefore, it is necessary to leave a slight gap between the plates in order to ensure complete penetration. Incomplete penetration can also be caused by a speed of travel that is too fast. In this case, the weld pool becomes too small to melt through to the bottom edges of the plates. A welding flame that does not supply enough volume of heat to penetrate to the bottom edges of the plates can also cause incomplete penetration.

Lap jointA lap joint is used to join two pieces of metal that overlap. It is a useful way of joining two plates where a “tight” joint is necessary, but great strength is not required. This joint is not practical for many applications. Some base metal is wasted in the overlap (Figure 47), the plates are offset (which might not be desirable) and the joint itself is not as strong as a butt joint.

Tack welds19 mm (¾")

t Tack welds

Figure 47—Lap joint

A good lap joint weld is slightly convex in shape (Figure 48A). If not enough filler metal is added, a concave profile will result (Figure 48B).

A. Good weld bead contour B. Bad weld bead contour

Figure 48—Cross-section of lap joint weld bead contours

Notes



Other faults that are common with lap joint welds are incomplete fusion (cold lap) and incomplete penetration (Figure 49). Incomplete fusion most often comes in the form of cold lap, which results from insufficient heat input to the lower plate. Incomplete penetration occurs at the root of the weld bead so that a gap is left between the bottom of the bead and the inside corner of the weld joint.

Cold lap

Gap under bead

Cold lap Incomplete penetration

Figure 49—Weld defects on lap joints

Tee jointFor a tee joint, the plates are set up so that the edge of one plate is butted to the face of another to form a 90° angle (Figure 50). Once welded, it forms a strong joint that becomes stronger if welded on both sides. Tee joints are especially prone to distortion. You can minimize this distortion by tack welding the joint at both ends and on both sides.

Tack welds90º

Figure 50—Tee joint

A cross-section of the weld profile should show the bead to be flat or slightly convex, with penetration through to the inside corner of the weld joint (Figure 51). The legs of the tee joint weld bead should be equal in length, which means the completed weld should be evenly distributed between the vertical and horizontal members of the joint.

Notes



Figure 51—Tee joint weld bead contour

A fault that is common to tee joints is undercut on the vertical plate (Figure 52A). This is usually caused by using an extreme weaving motion of the torch. Another common problem is a weak, concave weld bead (Figure 52B), which occurs when not enough filler metal is added to the weld pool.

Undercut

Concave

A B

Figure 52—Common faults on tee joints

The tee joint is a difficult weld to master. When you have become proficient, the weld bead will be flat or slightly convex and have good fusion, consistent width, a clean appearance, equal legs and no undercut.

Four basic welding positionsThere are four basic welding positions:

• flat• horizontal• vertical• overhead

These positions are common to all welding processes. You will see these names in qualification tests, specifications and instruction manuals.

Flat position (downhand)In the flat position, the workpiece is positioned so that the weld joint is parallel to the floor (Figure 53). The torch usually points downward and the weld metal is deposited on top of the base metal.

Notes



For corner joints with equal-sized plates, the two joint members can simply be placed on the work bench and welded. Lap joints and tee joints must be supported in an angled position in order to get a true flat position.

Figure 53—Flat position

Horizontal positionIn the horizontal position, the workpiece is also positioned so that the weld joint is parallel to the floor so the surface of the plates are vertical (Figure 54). For butt joints, the two plates are supported in the vertical position. The other four joints are positioned so that one edge surface of the weld joint is parallel to the floor and the weld is on top of the plate. With horizontal welds, the main difficulty is that gravity causes the weld pool to flow toward the lower side of the weld joint.

Figure 54—Horizontal position

Notes



Vertical positionIn the vertical position, the plate to be welded is positioned vertically and the weld itself is vertical. The direction of travel can be uphill (vertical-up) or downhill (vertical-down), but the majority of vertical welding is done uphill (from bottom to top) (Figure 55).

Figure 55—Vertical position

Gravity causes the molten metal to pull away from the edges of the weld, so the weld pool must be carefully controlled.

Overhead positionThe overhead position is the same as the flat position rotated 180°. This is considered to be the “true” overhead position. The overhead position is also the same as the horizontal position rotated 180° (Figure 56). The workpiece is positioned so that the torch and filler rod point upward. Overhead welding is considered the most difficult to master. The force of gravity causes the weld pool to drip. When these drips solidify, they are called “grapes” or “icicles.”

Notes



Figure 56—Overhead position

Abbreviations for weld position and weld typeIn the welding trade, abbreviations are used to indicate the type of weld and the welding position.

Letter abbreviations are used to indicate weld type, as follows:

• F: fillet weld• G: groove weld

Each weld position is designated with a number, as follows:

• 1: flat position (pipe rolled)• 2: horizontal position• 3: vertical position• 4: overhead position• 5: pipe—axis of pipe fixed at the horizontal• 6: pipe—axis of pipe fixed at a 45° incline

The position number and the letter abbreviation are used together. For example:

• 1G is a groove weld in the flat position.• 3F is a fillet weld in the vertical position.• 4G is a groove weld in the overhead position.• 5G is a groove weld in a pipe with the axis of the pipe fixed at the

horizontal.

A common joint design in electric arc welding is a single-bevel butt joint with a specified root opening and a backing bar. This is called a “GF weld,” meaning that it is a combined fillet and groove weld. The welding sequence requires a fillet weld to join the backing bar to the square edge of the joint. The fillet weld and the bevelled edge then form a vee-groove joint. If this joint were done in the vertical position on plate, it would be called a “3GF position.”


Answers




1. There are five basic joint designs used in welding. The lap, corner, tee and butt are four of them. Name the fifth joint design.

a. plug

b. vee

c. bevel

d. edge

2. Tee joints are particularly prone to

a. overlap

b. distortion

c. undercut

d. both a and b

e. both b and c

3. Which type of weld joint is shown in Figure 57?

a. plug

b. tee

c. butt

d. lap

4. Edge joints are generally used on

a. sheet metal

b. pipe

c. heavy-gauge metal

d. castings

5. Which weld defect is shown in Figure 58?

a. undercut

b. concave weld bead

c. cold lap

d. distortion

Figure 57

Figure 58

Answers



6. What is the main purpose of tack welding a joint?

a. preheat the workpiece

b. hold the plate in position

c. prevent undercut

d. start the weld

7. The easiest position for welding is the

a. flat position

b. horizontal position

c. vertical position

d. overhead position

8. Which weld position is shown in Figure 59?

a. flat

b. horizontal

c. vertical

d. overhead


a. flat

b. horizontal

c. vertical

d. overhead


a. flat

b. horizontal

c. vertical

d. overhead

Figure 59

Figure 60

Figure 61

Answers




a. flat

b. horizontal

c. vertical

d. overhead

12. A weld designated as a 1F is a

a. fillet weld in the flat position

b. groove weld in the flat position

c. fillet weld in the horizontal position

d. groove weld in the vertical position

13. A 4F weld is a

a. fillet weld in the flat position

b. groove weld in the vertical position

c. fillet weld in the overhead position

d. fillet weld in the horizontal position

14. On a corner joint, incomplete penetration can be caused by

a. using too much flux

b. using a tip that is too large

c. a travel speed that is too fast

d. a travel speed that is too slow

15. What is the main cause of cold lap in lap joints?

a. too much heat input on the upper plate

b. too little heat input on the lower plate

c. too small of an overlap

d. too large of an overlap


Figure 62

Notes



P3-5 Learning Task 4:Basic joint designs and welding positions for butt jointsButt jointsThe butt joint is formed by placing two pieces of metal beside each other on the same plane (Figure 63). The butt joint is widely used because it is strong and can be a relatively easy joint to weld.

Figure 63—Butt joint

Depending on the thickness of the metal to be welded, a butt joint can be square or can require some edge preparation (Figure 64).

Figure 64—Two butt joint designs

Square butt jointThe square butt joint requires no edge preparation. For the oxyacetylene welding process, the square butt joint is suitable only for thin material, 3.2 mm (1⁄8 in.) thick or less. When fitting a square butt joint, you must leave a small gap between the members about the thickness of the plate. If the filler rod is the same thickness as the base metal, it becomes a handy scale with which to measure the gap (Figure 65).

Figure 65—A square butt joint spaced with a filler rod

Notes



Single-vee butt jointThe single-vee butt joint is normally used on thicker material, up to 19 mm (3⁄4 in.). The single-vee butt joint has several significant dimensions, including the root opening (root gap), the root face (land), the included angle and the bevel angle (Figure 66). These joints can be prepared with an oxy-fuel gas cutting torch or with a grinder.

Groove or included angle

Root opening

Root opening

Root radius

Thro

at

Root face

Root face

Included angle

Bevel angle

Thickness (T)

Thickness (T)

Figure 66—Single-vee butt joint

Often, you will need to make more than one pass to fill a weld joint between thick plate or pipe. The first pass, called a “root pass,” is the most important. If there is incomplete fusion, penetration or reinforcement, the weld will be flawed. In a two-pass weld, the second pass, called a “cap” pass, fills up the weld joint and provides reinforcement at the top (cap) of the weld deposit. In a weld that has more than two passes, the joint is filled up with “fill” passes and a final cap pass. The joint should be filled until it forms a slightly convex bead (Figure 67).

Cap and fill pass

Root passRoot opening

Cap pass

Fill passes

Root pass

Root face

Root opening

Figure 67—Butt joint in multiple passes

Notes



Getting complete penetration is difficult when welding butt joints. In order for the weld to have full strength, the heat must penetrate completely through to the bottom of the joint. As with the corner joint, you need to make sure that there is a “keyhole” at the leading edge of the weld (Figure 68). The keyhole indicates that the weld pool is melted through to the bottom edge of the base metal.

Weld pool

Keyhole

Figure 68—Keyhole at the leading edge of the weld

Avoiding weld defectsOn a finished joint, the top of the weld bead (cap) should be slightly convex. This convexity on butt joints is called “reinforcement,” and it should be built up 1.6 mm to 3.2 mm (1⁄16 in. to 1⁄8 in.) above the surface of the base metal. The bead width for square groove butt joints on 3.2-mm (1⁄8-in.) sheet metal should be between 10 mm and 13 mm (3⁄8 in. and 1⁄2 in.) (Figure 69).

3.2 mm (1⁄8") sheet

10 mm (3⁄8") 1.6 mm (1⁄16") above surface

Figure 69—Reinforcement and bead width

Cold lap and undercut are defects that you need to avoid in welding butt joints (Figure 70). Cold lap is usually caused by not maintaining a consistent molten weld pool (puddle) to accept the filler rod. If the torch travel speed is too fast, you will not be able to maintain a molten weld pool and the filler metal cannot fuse with the base metal. The filler metal just lies on top of the base metal.

Undercut occurs when the torch work angle and movement draw the base metal from the edge of the molten weld pool. This leaves a depression on

Notes



one or both sides of the weld deposit that is lower than the surface of the base metal. This must be filled with filler metal as the weld progresses or the base metal will be seriously weakened at the edge of the weld deposit.

Cold lap

Undercut

Figure 70—Weld defects on square butt joints

Welding positions for butt jointsButt joints can be welded in all four positions (Figure 71).

Flat Overhead

HorizontalVertical

Figure 71—Welding positions for butt joints

Notes



As stated in Learning Task 3, welding positions are abbreviated to number designations and types of welds are abbreviated to letter designations. Butt joints are joined with a groove weld, and so are abbreviated to “G.” The abbreviations for groove welds in the various positions are:

• flat position: 1G• horizontal position: 2G• vertical position: 3G• overhead position: 4G


Answers




1. The square butt joint is used on metals up to thick.

a. 3.2 mm (1⁄8 in.)

b. 6.4 mm (1⁄4 in.)

c. 19 mm (3⁄4 in.)

d. 25 mm (1 in.)

2. The single-vee butt joint is normally used on metals up to thick.

a. 3 mm (1⁄8 in.)

b. 6 mm (1⁄4 in.)

c. 19 mm (3⁄4 in.)

d. 25 mm (1 in.)

3. Which type of butt joint requires edge preparation?

a. edge

b. square

c. single-vee

d. flange-vee

4. Match the letters in Figure 72 with the features of a butt joint listed below.

a. bevel angle

b. root gap

c. included angle

d. root face (land)

2

1

4

3

Figure 72

Answers




a. cold lap

b. undercut

c. distortion

d. porosity


a. cold lap

b. undercut

c. distortion

d. porosity

7. To ensure complete penetration on a butt joint, what must you maintain at the leading edge of the root bead weld pool?

a. a concave weld

b. a 90° torch angle

c. a consistent dipping motion with the torch

d. a “keyhole”

8. What does “3G” indicate?

a. a plug weld in the vertical position

b. a groove weld in the horizontal position

c. a fillet weld in the horizontal position

d. a groove weld in the vertical position


Figure 73

Figure 74

Notes



Notes



P3-5 Learning Task 5:Review the safe operation of oxyacetylene-welding equipmentBefore you begin practising oxyactylene welding, you need to review the safe operation of the oxyacetylene equipment you will be using. Review the general safety considerations when:

• wearing protective clothing• avoiding torch line fires• wearing eye protection• avoiding toxic fumes• practising fire protection• avoiding oil and grease hazards• ensuring ventilation

Review: module P1, Theory Competency 2 (P1-2): Use Safe Work Practices.

Read: module P2, Theory Competency 1, Learning Task 4 (P2-1 LT4): Safety Requirements for Oxy-Fuel Gas Cutting.

Review the correct and safe procedures for handling and storing oxygen and acetylene cylinders, as well as pressure regulators.

Read: module P2, Theory Competency 2, Learning Task 2 (P2-2 LT2): Oxygen and Fuel Gas Cylinders.

Read: module P2, Theory Competency 2, Learning Task 4 (P2-2 LT3): Oxy-Fuel Gas Cylinder Pressure Regulators and Their Functions.

Review: module P2-4 Practical Competency 1, the safe procedures necessary to assemble, ignite, adjust and shut down an oxyacetylene outfit.

Read: module P2, Theory Competency 3 (P2-3): Correct Procedures to Operate and Maintain Oxy-Fuel Gas Cutting Equipment.


Answers




1. Which of the following types of eye protection must you wear when oxyacetylene gas welding?

a. full face shield

b. welding goggles

c. flash goggles

d. safety glasses

2. What is the proper type of footwear you should use when oxyacetylene gas welding?

a. special asbestos shoes

b. CSA-approved high-top leather safety boots

c. CSA-approved running shoes

d. insulated rubber boots

3. Backfires are the result of

a. welding gases igniting inside the torch tip

b. welding gases failing to ignite

c. welding gases mixing in the torch tip

d. using the wrong fuel gas

4. Where might a Welder come across zinc?

a. in lead-based paint

b. in degreasing solvents

c. in chromium alloys

d. as a coating on sheet steel

5. Why are oil and grease a special hazard when working with oxy-fuel gas equipment?

6. What should you do when you notice a leaking acetylene cylinder?

a. keep using it and notify your supervisor

b. try to repair it and notify your supervisor

c. lay it on its side and notify your supervisor

d. move it into an open area and notify your supervisor

Answers



7. When opening an oxygen cylinder valve, you should remember to

a. never open more than 1⁄2 turn

b. open the valve very quickly

c. tap the valve first with a cylinder wrench

d. open the valve fully

8. What effect do temperature increases have on oxy-fuel gas cylinders?

a. The cylinder pressure increases.

b. The cylinder pressure decreases.

c. Too much condensation occurs.

d. The gas is prevented from forming.

9. Why should acetylene cylinders NEVER be completely emptied?

a. The cylinder could explode.

b. The cylinder safety device would rupture.

c. The cylinder would have to be discarded.

d. To prevent acetone from being withdrawn.

10. Oxygen and fuel gas cylinders should be stored in separate locations that are

a. well ventilated

b. kept very warm

c. refrigerated

d. damp and humid

11. When storing oxygen and fuel gas cylinders outdoors, what precaution is necessary?

a. They should be lightly oiled.

b. They should be laid on their side.

c. They should be protected from the weather, especially the sun.

d. The cylinder valves should be left open.

12. Acetylene cylinders must be used in the upright position to prevent

a. acetone being withdrawn

b. the cylinder from rolling

c. damage to the pressure regulators

d. pressure fluctuations

Answers



13. When moving cylinders from a storage area to the work area, you must make sure that the

a. safety lines are properly attached

b. cylinder valves are open

c. cylinder safety caps are in place

d. regulator is attached

14. What type of threads do oxygen containers have?

a. left-hand threads

b. right-hand threads

c. pipe threads

d. metric threads

15. What type of threads do acetylene cylinders have?

a. right-hand threads

b. left-hand threads

c. straight threads

d. horizontal threads

16. To increase the working pressure on acetylene pressure regulators, you

a. turn the adjusting screw counter-clockwise

b. turn the adjusting screw clockwise

c. release the RFCVs

d. open the cylinder valve

17. Before opening cylinder valves, the adjusting screw on the pressure regulator should be

a. lightly tapped

b. removed

c. backed out until tension is relieved

d. screwed all the way in

Answers



18. Which of the following happens when a pressure regulator “creeps”?

a. The torch flame goes out.

b. The cylinder pressure increases.

c. The working pressure increases.

d. The pressure regulator could explode.

19. When shutting down a welding station, the first step is to close the

a. oxygen cylinder valve

b. pressure regulators on both sides

c. acetylene cylinder valve

d. pressure regulator on the oxygen side

20. Cracking the cylinder valves momentarily before connecting the pressure regulators helps to

a. bleed off accumulated moisture

b. blow away any foreign matter

c. release excess pressure

d. make installation of the pressure regulators easier

21. When lighting an oxyacetylene torch, you should use

a. another torch

b. wooden matches

c. a spark lighter

d. a butane lighter

22. Why should you open cylinder valves slowly?

a. to prevent torchline explosions

b. to save oxygen and acetylene

c. to prevent damage to the pressure regulator

d. to prevent arc blow

Answers



23. To extinguish an oxyacetylene flame, you should first

a. close the torch handle acetylene valve

b. close the torch handle oxygen valve

c. loosen the acetylene pressure regulator adjusting screw

d. loosen the oxygen pressure regulator adjusting screw

24. Why should the acetylene cylinder valve NOT be fully opened?

a. to conserve acetylene

b. to prevent the pressure regulator from being damaged

c. so that the valve can be closed quickly in an emergency

d. so that the lines can be purged

25. To ignite an oxyacetylene torch, you should first open the

a. oxygen preheat valve

b. acetylene preheat valve

c. torch handle acetylene valve

d. torch handle oxygen valve


answer Key

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Notes

Module P3 answer Key


Theory Competency P3-1Self-Test 11. c . weld bead

2. b . is slightly convex

3. b . for most weld joint designs

4. c . to add metal

5. b . usually have the same composition

6. a . It is too slow.

7. c . to get full penetration in the weld joint

8. c . It can be used to weld almost any metal.

Self-Test 21. c . TB

2. b . The base metal is not melted.

3. d . above 450 °C (840 °F)

4. a . true

5. a . clean the base metal and prevent surface oxidation

6. d . It produces less distortion.

7. b . joints that will be subjected to heavy vibration

8. c . on joints that are subjected to temperatures above 260 °C (500 °F)

9. a . always

10. a . brass or bronze alloy

Notes



Self-Test 31. a . capillary action

2. c . soldering

3. b . joint design

4. b . surface adhesive

5. b . false

6. a . non-ferrous metal

7. b . on electrical connections

Theory Competency P3-2Self-Test 11. b . slightly oxidizing flame

2. b . hot

3. c . tinning

4. d . copper with zinc

5. c . melted

6. d . more oxygen than acetylene

7. b . preheat the rod and dip it into a powdered flux

8. b . false

9. b . the base metal is a cherry red colour

10. b . slightly convex

Notes



Self-Test 21. c . The colour of the weld deposit metal does not match the base metal.

2. a . repair work

3. a . to remove excess graphite flakes from the surface

4. d . Fusion-welded joints can withstand higher temperatures.

5. a . true

6. c . carbon and silicon

7. b . is more brittle

8. a . carbon

9. b . to dissolve oxides and float off impurities

10. d . prevent cracking

11. d . use heat treatments

12. a . graphite

13. c . included angle is usually larger

14. b . RCI

15. d . RBCuZn

16. d . a neutral flame

17. a . a slightly oxidizing flame

Notes



Theory Competency P3-3Self-Test 11. d . many ferrous and non-ferrous metals

2. a . true

3. b . capillary action

4. a . to chemically clean the weld joint

5. d . copper

6. a . cadmium

7. d . 3X reducing

8. b . false

9. a . clear, glassy

Theory Competency P3-4Self-Test 11. a . the thickness of the base metal

2. c . provide additional reinforcement

3. d . 914 mm (36 in.)

4. b . rusting

5. d . all of the above

6. d . copper and zinc

7. b . false

8. c . RG 65

9. b . minimum tensile strength

10. c . the minimum tensile strength of the weld deposit

11. c . 3.2 mm (1⁄8 in.)

12. c . when brazing any metal

13. d . by chemical composition

14. a . silver

Notes



Self-Test 21. a . low-carbon steel

2. d . type of metal to be welded

3. a . high temperature

4. d . all of the above

5. c . dissolving oxides and floating off impurities

6. a . cast iron

7. d . there is good ventilation

Self-Test 31. c . thickness of the base metal

2. a . 3, b . 1, c . 2, d . 4

3. b . more volume of heat that is delivered

4. d . in the mixing chamber

5. b . working pressures

6. b . an increase in tip size

7. d . copper alloy

8. b . larger than

9. c . hand-tighten only

10. a . true

11. c . tip scraper and a cleaning needle

12. b . The oxygen is delivered at a higher pressure than the fuel gas.

Notes



Theory Competency P3-5Self-Test 11. a . the base metal thickness

2. c . neutral

3. a . 3.2 mm (1⁄8 in.)

4. d . at the tip of the flame’s inner cone

5. a . forehand

6. c . backhand

7. b . thickness of the base metal

8. d . volume of heat required

9. c . from too much heat

10. a . speed of travel was too slow

11. c . speed of travel too fast

12. a . a weld deposit formed correctly

Self-Test 21. b . overlap

2. a . incomplete fusion

3. c . poor weld joint design or fit

4. c . incomplete penetration

5. a . inadequate preheat of the base metal

6. c . undercut

7. c . insufficient reinforcement

8. b . flat or slightly convex

Notes



Self-Test 31. d . edge

2. e . both b and c

3. d . lap

4. a . sheet metal

5. c . cold lap

6. b . hold the plate in position

7. a . flat position

8. a . flat

9. b . horizontal

10. d . overhead

11. c . vertical

12. a . fillet weld in the flat position

13. c . fillet weld in the overhead position

14. c . a travel speed that is too fast

15. b . too little heat input on the lower plate

Self-Test 41. a . 3.2 mm (1⁄8 in.)

2. c . 19 mm (3⁄4 in.)

3. c . single-vee

4. a . 1, b . 4, c . 2, d . 3

5. b . undercut

6. a . cold lap

7. d . a “keyhole”

8. d . a groove weld in the vertical position

Notes



Self-Test 51. b . welding goggles

2. b . CSA-approved high-top leather safety boots

3. a . welding gases igniting inside the torch tip

4. d . as a coating on sheet metal

5. Oil and grease form an explosive combination with pure oxygen.

6. d . move it into an open area and notify your supervisor

7. d . open the valve fully

8. a . The cylinder pressure increases.

9. d . To prevent acetone from being withdrawn.

10. a . well ventilated

11. c . They should be protected from the weather, especially the sun.

12. a . acetone being withdrawn

13. c . cylinder safety caps are in place

14. b . right-hand threads

15. b . left-hand threads

16. b . turn the adjusting screw clockwise

17. c . backed out until tension is relieved

18. c . The working pressure increases.

19. c . acetylene cylinder valve

20. b . blow away any foreign matter

21. c . a spark lighter

22. c . to prevent damage to the pressure regulator

23. a . close the torch handle acetylene valve

24. c . so that the valve can be closed quickly in an emergency

25. c . torch handle acetylene valve

FOUNDATION AND APPRENTICESHIP LEVELS 1 … Module P3 Theory CoMPeTenCy P3-1 (line C-C1) 12...

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Transcript of FOUNDATION AND APPRENTICESHIP LEVELS 1 … Module P3 Theory CoMPeTenCy P3-1 (line C-C1) 12...