Class: Senior Secondary School 2 (SS2 / SSS2)
Term: Second Term
Week: 5
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Striking the Arc Methods.
Topic: Electrodes
Subject Matter: Meaning of welding electrodes (current carrier and filler metal), function of electrode coating (protection from atmospheric contamination), classification of electrodes.

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define welding electrodes.
State at least three functions of electrode coating.
Classify electrodes according to welding conditions.

Affective Domain:

Appreciate the importance of selecting the correct electrode for different welding tasks.
Show willingness to learn more about various electrode types.

Psychomotor Domain:

Identify different types of welding electrodes by their physical characteristics or markings.
Demonstrate how to select an appropriate electrode for a given welding scenario.

Work collaboratively in groups to identify and discuss different electrode types.
Participate actively in classroom discussions about electrode applications.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
Metal Work for Senior Secondary Schools Textbook
https://www.lincolnelectric.com/en/welding-resources/welding-procedures/electrode-selection-guide
https://www.esabna.com/us/en/education/blog/what-is-a-welding-electrode.cfm

Instructional Materials

The teacher will teach this lesson with the aid of:

Different types of welding electrodes (e.g., E6013, E7018)
Charts showing electrode classifications and functions
A diagram illustrating electrode coating functions

Rationale for the Lesson

Understanding electrodes is important for pupils because electrodes are fundamental to arc welding processes. This lesson helps pupils to properly select and use electrodes, which is essential for producing strong and safe welds in practical metalwork applications.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of welding processes and the components involved in arc welding from previous lessons.

Lesson Content/Board Summary

Electrodes

Meaning of Welding Electrodes

A welding electrode is a coated metal wire that conducts electric current to create an arc and melt metal. It serves as both a current carrier and a filler metal, supplying material to the weld joint to fill gaps and create a strong bond.

Function of Electrode Coating

The coating on a welding electrode performs several vital functions during the welding process:

Protection: It forms a gaseous shield around the arc and molten weld pool, preventing atmospheric gases (like oxygen and nitrogen) from contaminating the weld metal.
Arc Stabilization: It helps to stabilize the electric arc, making the welding process smoother and more consistent.
Slag Formation: It melts to form a protective slag layer over the cooling weld metal, which slows down the cooling rate and prevents rapid oxidation, improving weld quality.
Deoxidizers: It contains chemicals that remove impurities and oxygen from the molten metal, leading to a cleaner weld.
Alloying Elements: It can introduce specific alloying elements into the weld metal to enhance its mechanical properties, such as strength, ductility, or corrosion resistance.

Classification of Electrodes

Welding electrodes are classified based on various factors, including their core wire material, coating composition, and suitability for different welding conditions (e.g., welding position, type of current, and base metal). Common classifications according to welding conditions include:

Rutile Type Electrodes (e.g., E6013):
- Coating: High titanium dioxide (rutile).
- Characteristics: Produce a smooth, stable arc, easy slag removal, and good bead appearance.
- Applications: General-purpose welding of mild steel, suitable for all positions, especially for AC current and DCEN (Direct Current Electrode Negative).
Basic Type Electrodes (e.g., E7018):
- Coating: High lime-fluorspar.
- Characteristics: Produce welds with excellent mechanical properties, good ductility, and very low hydrogen content, reducing cracking risks.
- Applications: Welding heavy sections, high-strength steels, and critical applications. Primarily used with DCEP (Direct Current Electrode Positive) and can be used in all positions.
Cellulosic Type Electrodes (e.g., E6010):
- Coating: High cellulose content.
- Characteristics: Produce a deep penetrating arc, fast-freezing slag, and strong, tough welds.
- Applications: Excellent for welding in vertical-down and overhead positions, particularly for pipe welding. Typically used with DCEP.
Stainless Steel Electrodes:
- Coating/Core: Designed to match various stainless steel grades.
- Applications: Used for welding stainless steel to maintain corrosion resistance and mechanical properties.
Cast Iron Electrodes:
- Coating/Core: Often have nickel or monel core wires.
- Applications: Used for repairing and joining cast iron components, providing compatible weld metal.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson briefly, and then introduces the new topic, “Electrodes,” by asking pupils what they think an electrode is in welding.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils are prepared for the new lesson and connect it to previous knowledge.

Step 2: Meaning of Welding Electrodes

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher explains the meaning of welding electrodes, emphasizing their dual role as current carriers and filler metals, using simple language and practical examples.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification on the definition of electrodes.
Learning Point: Pupils understand what a welding electrode is and its basic function.

Step 3: Function of Electrode Coating

Time: 8 minutes
Teaching Skill: Elucidation/Listing
Teacher’s Activity: The teacher explains the various functions of the electrode coating, such as protection from atmospheric contamination, arc stability, and slag formation, pointing to a chart if available.
Pupils’ Activity: Pupils listen, observe the chart, and list the functions of electrode coating in their notebooks.
Learning Point: Pupils can state and explain the importance of electrode coating.

Step 4: Classification of Electrodes (Part 1)

Time: 8 minutes
Teaching Skill: Categorization/Description
Teacher’s Activity: The teacher begins classifying electrodes, focusing on rutile and basic types, explaining their characteristics, and showing physical examples of these electrodes.
Pupils’ Activity: Pupils observe the actual electrodes, note the characteristics of rutile and basic types, and ask questions.
Learning Point: Pupils identify and understand the differences between rutile and basic electrodes.

Step 5: Classification of Electrodes (Part 2)

Time: 7 minutes
Teaching Skill: Categorization/Description
Teacher’s Activity: The teacher continues the classification, covering cellulosic, stainless steel, and cast iron electrodes, discussing their specific applications and suitable welding conditions.
Pupils’ Activity: Pupils listen, take notes, and identify the specific uses and conditions for these electrode types.
Learning Point: Pupils can differentiate between various electrode types based on their applications and characteristics.

Step 6: Practical Identification and Selection

Time: 5 minutes
Teaching Skill: Demonstration/Application
Teacher’s Activity: The teacher demonstrates how to identify different electrodes by their markings and discusses how to select the appropriate electrode for a simple welding task (e.g., joining mild steel plates).
Pupils’ Activity: Pupils pay close attention to the demonstration and ask questions about electrode identification and selection.
Learning Point: Pupils gain practical insight into identifying and selecting electrodes.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a welding electrode.
State three functions of electrode coating.
Mention two types of electrodes and their primary applications.
Why is it important to select the correct type of electrode for a welding job?

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson on electrodes and assigns homework, which may include researching other types of electrodes or their numbering systems.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their understanding and are given tasks to reinforce learning.

Lesson Keywords

Electrode – A coated metal rod that conducts electricity and acts as filler metal in arc welding.
Coating – The flux material covering the core wire of an electrode.
Arc – The electric discharge between the electrode and the workpiece.
Filler Metal – Material added during welding to form the weld bead.
Slag – A non-metallic byproduct formed on the surface of the weld pool.
Rutile – A type of electrode coating rich in titanium dioxide.
Basic – A type of electrode coating rich in lime-fluorspar.
Cellulosic – A type of electrode coating rich in cellulose.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research the AWS (American Welding Society) electrode classification system. For those who need more support, the teacher can provide simplified diagrams and additional one-on-one explanations of electrode functions and classifications.

Note for teachers using this lesson plan

Teachers should ensure they have actual welding electrodes available for demonstration to aid pupils’ understanding and identification. Emphasize safety precautions related to handling welding equipment and materials, even during theoretical discussions. Encourage pupils to relate the theoretical knowledge to practical applications in metal fabrication.