Perform routine oxyacetylene welding. This learner resource supports the unit of competency MEM05004 Perform routine oxyacetylene welding

Transcription

1 Perform routine oxyacetylene welding This learner resource supports the unit of competency MEM05004 Perform routine oxyacetylene welding

2 These materials were developed by Manufacturing Skills Australia. Manufacturing Skills Australia With the exception of any material protected by a trade mark and where otherwise noted, all material presented in this document is provided under a Creative Commons Attribution-No Derivative Works 3.0 Australia licence. Disclaimer This work is the result of consultations with Australian industry participants. It is a collaborative view and does not necessarily represent the view of Manufacturing Skills Australia or any specific body. For the sake of brevity it may omit factors which could be pertinent in particular cases. While care has been taken in the preparation of this material, Manufacturing Skills Australia and the original developer do not warrant that any licensing or registration requirements specified here are either complete or upto-date for your State or Territory. Manufacturing Skills Australia and the original developer do not accept any liability for any damage or loss (including indirect and consequential loss) incurred by any person as a result of relying on the information contained in this material. Manufacturing Skills Australia, does not accept any liability to any person for the information or advice (or the use of such information or advice) which is provided in this material or incorporated into it by reference. The information is provided on the basis that all persons accessing this material undertake responsibility for assessing the relevance and accuracy of its content. No liability is accepted for any information or services which may appear in any other format. No responsibility is taken for any information or services which may appear on any linked websites. Published by: Manufacturing Skills Australia Release Date: October 2010 For further information about this resource or any other work being undertaken by Manufacturing Skills Australia (MSA), please visit: Manufacturing Skills Australia Level 3, 104 Mount Street North Sydney NSW 2060 T: F: E: info@mskills.org.au W: NOTE: This resource is not considered to be a definitive manual and must be contextualised and amended to suit end user requirements. Manufacturing Skills Australia Page ii

3 Table of Contents For the trainer... vi Using this manual... vi Assessment... vi For the learner... vii Assessment... vii Recognition of prior learning... vii 1.0 Introduction Uses of the oxy-fuel flame Characteristics of the fuel-gas flame Fuel gases Flame rate of burning Experiment # Acetylene Heat and temperature Filler metals Ferrous metals Mild steel Cast iron Oxyacetylene welding Mild steel welds Factors affecting the weld torch tip size Torch angle Welding rod size Characteristics of the weld Flux Task preparation Experiment # Manufacturing Skills Australia Page iii

4 8.2 Practice # Experiment # Practice # Experiment # Practice # Outside corner joint Practice # Butt joint Practice # Practice # Practice # Lap joint Practice # Tee joint Practice # Your checklist Advantages Limitations Safety Summary Candidate Welding Report Manufacturing Skills Australia Page iv

5 Overview This resource covers preparing materials and performing routine oxyacetylene welding. This resource applies in a maintenance or manufacturing environment where the welding is not required to meet an Australian standard or equivalent. Fillet and butt welds would typically be performed on low carbon/mild steels. All work and work practices must be undertaken to regulatory and legislative requirements. It is applicable in both a learning and assessment pathway and an assessment only pathway. This unit is performed in the context that all materials and equipment needed to carry out this function have been provided, including learning materials, learning programs and learning resources. Elements To achieve competency in this unit you must demonstrate your ability to: 1. Identify weld requirements 2. Prepare materials for welding 3. Prepare equipment for welding 4. Perform routine welding using oxyacetylene. Prerequisite units of competency Nil Manufacturing Skills Australia Page v

6 How to use this resource For the trainer This learner s resource contains information in response to the unit of competency. It is designed to stand alone as a resource to help achieve competency. Using this manual This unit may be assessed on the job, off the job or a combination of both on and off the job. Where assessment occurs off the job, that is the candidate is not in productive work, then an appropriate simulation must be used where the range of conditions reflects realistic workplace situations. The competencies covered by this unit would be demonstrated by an individual working alone or as part of a team. The assessment environment should not disadvantage the candidate. Assessment To satisfactorily assess the learner against the unit of competency you need to gather sufficient evidence about the person s competence. This may require gathering additional evidence (for instance from the learner s workplace) to that provided by the projects. You should refer to the Assessment Guidelines contained in the MEM05 Metal and Engineering Training Package as the final authority for assessment against units of competency in this Training Package. Manufacturing Skills Australia Page vi

7 For the learner This learner s resource contains information in response to the unit of competency and reference material. It is designed to stand alone as a resource to help achieve competency. Assessment Assessment against units of competency relies on your trainer/assessor gathering enough evidence to demonstrate that you can meet the requirements of the unit. To verify that you are competent in this unit of competency, an assessment will be carried out using a combination of practical activities and testing of underpinning knowledge identified in the unit. These results will be recorded by the trainer to contribute to evidence of competency. Alternatively, if you are undertaking this unit in the workplace, you may be assessed by being questioned and observed performing a range of related tasks on the job. You may also wish to speak to your trainer about supplying evidence of competency you have gained elsewhere (e.g. work pieces you have already produced) which may contribute to your assessment. Recognition of prior learning If you believe you can already meet the assessment criteria for a particular unit of competency, or have completed similar training, you may be eligible for recognition of prior learning (RPL). Eligibility for RPL will reduce the learning time or remove the need for you to complete this unit. Contact your trainer to discuss this further. Manufacturing Skills Australia Page vii

8 Perform routine oxyacetylene welding 1.0 Introduction The general grouping of processes known as oxy-fuel consists of a number of separate processes, all of which burn a fuel gas with oxygen. The oxy-fuel flame was used for fusion welding as early as the first half of the 1800s when scientists developed the oxy-hydrogen torch. Before that time, air-fuel torches were used, but because the flame was not hot enough they had limited success. The early use of pure oxygen with hydrogen or acetylene as the fuel gas often resulted in flashbacks and explosions. The use of water traps helped prevent most flashbacks from becoming explosions. But until the early development of the torch mixing chamber, welding was a very dangerous occupation. The mixing chamber gave a more uniform flame that was less likely to flashback. During the early 1900s, the oxyacetylene flame became more popular as the primary means of welding. Since 1900, when the first shielded metal arc welding (stick) electrodes were introduced by Strohmeyer in Britain, the use of the oxyacetylene flame for welding has declined. During oxyacetylene welding prime, plates 25 mm thick or more were gas welded to build everything from large, seagoing ships to massive machines used during the Industrial Revolution. Today, because of improvements in other processes, the oxyacetylene flame is seldom used on metal thicker than 2 mm. The advances in shielded metal arc welding, gas tungsten arc welding, plasma arc cutting, and gas metal arc welding have overshadowed oxy-fuel welding. These processes are faster and cleaner and cause less distortion than oxy-fuel welding. At present, oxy-fuel welding is used mainly for farm repairs, for maintenance and in smaller shops. Manufacturing Skills Australia Page 1

9 2.0 Uses of the oxy-fuel flame The usefulness of the oxy-fuel flame as a primary means of cutting ferrous metals has increased. In 1887 the flame was used to melt through thin metal. Around 1900 the oxygen lance was introduced. The oxygen lance allowed high-pressure oxygen to be directed onto metal heated by a torch, resulting in much improved cuts. The later development of a cutting torch with pre-heating flames surrounding a central oxygen hole in the tip brought oxy-fuel cutting into its own. The cutting torch, used by hand or as part of a machine, is used to rapidly cut out steel parts (Figure 1). Today, a large number of manufactured items are touched in some way by the oxyfuel flame. The parts may have been cut out, heated, hardened or joined with an oxy-fuel flame. The expansion of the role of the oxy-fuel flame in industry has led to the introduction of new fuel gases and gas mixtures. Each of the new gases has certain advantages and disadvantages. The decision of which gas to use must be based on cost, availability, welder skills and skill changes, required equipment changes, safety, handling, performance and other concerns. The information supplied for a special gas often points out its strengths and may use comparisons to prove its advantages. Figure 1: Cutting torch Manufacturing Skills Australia Page 2

10 2.1 Characteristics of the fuel-gas flame The data available for fuel-gas flame characteristics are not gathered in a consistent manner. Temperature and heat, for example, are very basic physical facts about the flame of a specific gas. But even these facts can be misleading. The flame condition, such as neutral, oxidising, carbonising (carburising), and/or the purity of the gases being used will affect the temperature of the flame. The method by which the temperature is measured also affects its value. The highest potential temperature values are determined by chemical analysis and by the calculation of the theoretical energy released. However, no combustion is perfect, so this temperature is never attained. An infrared analysis or optical pyrometer of the flame gives the highest temperature in the flame. But this temperature is concentrated in a thin layer around the inner cone and is so small that it is not of practical use. The optical pyrometer and the infrared analysis both give an accurate temperature reading, but where the temperature is measured makes a difference. Differences in heat values may also be misleading, depending upon how they are obtained. The temperatures, heat and other flame characteristics noted in this chapter are as close as possible to those that occur during use. They are not necessarily the highest or lowest possible values and therefore should not be considered absolute. But they can, however, be compared with each other for the purpose of selecting a fuel gas. Manufacturing Skills Australia Page 3