Area and/or Course Introduction to Welding
Lesson Title Introduction to Oxygen/Acetylene (Oxy-Acetylene) Cutting
No. Periods1 (73-minute period)
Teacher Goal(s):
- Students will demonstrate how to safely set up an Oxy-acetylene cutting torch, and ignite the welding torch
- Students will practice cutting metal using the Oxy-acetylene Torch
Rigor/Relevance
Framework
Knowledge / 6
5
4
3
2
1 / C
Assimilation
______/ D
Adaptation
___X____
A
Acquisition
______/ B
Application
______
1 2 3 4 5
Application
Objectives:
The student will be able to (TSWBT). (Oregon Skill Set numbers in parentheses at the end of the objective statement.)
1. Describe the set-up and shut-down process for an Oxy-acetylene cutting torch (AG 10.02.01.04)
2. Demonstrate igniting the acetylene gas and properly adjusting the flame (AG 10.02.01.04)
3. Describe the process for making proper cuts using an Oxy-acetylene torch (CS.EF.02)
4. Demonstrate cutting metal with the Oxy-acetylene torch (EL.HS.RE.08)
5. Evaluate torch cuts against industry standards, using problem solving methods (CS.PS.06)
State Standards met by Objectives:
SubjectStrand Eligible Content
1. AgricultureAG 10.02.01.04Demonstrate the set up and adjustment of tools and equipment
2. CRLSCS.EF.02 Select, apply, and maintain tools and technologies appropriate for the workplace.
3. CRLSCS.HS.02 Listen attentively and summarize key elements of verbal and non-verbal communication.
4. CRLSCS.PS.06 Assess results and take corrective action.
4. EnglishEL.HS.RE.08 Understand, learn, and use new vocabulary that is introduced and taught directlythrough informational text, literary text, and instruction across the subject areas.
Materials, Equipment, Audio-Visual Aids:1. Oxygen/Acetylene welding torch
2. Gloves
3. Welding face shield
4. Striker
5. Various metal / References:
Anticipatory Set/Introduction/Motivation/Interest Approach:
Review Yesterday’s Lesson:
When you are evaluating your MIG welds; what are some things to look for?
(Q) Why does your weld look thin?
(A) My travel was too fast
(Q) Why is there excessive spatter on your metal?
(A) I was too far away
(Q) What are some ways for you to go slower
(A) Use a method such as half-moons or circles to create a motion instead of just pulling the puddle straight
(Q) Why is your bead too tall?
(A) Too slow
Set:
Teacher’s personal story
When I was in high school we had an O/A torch and a plasma cutter, most of use chose to use the plasma cutter. Does anyone know why? A plasma cutter is a piece of equipment used to cut metal, but it requires much less skill than the O/A torch, it makes much cleaner cuts using forced air. It was a very good piece of equipment to use except for what happened when I went back home for the summer and my Dad asked me to cut off a piece of metal for him? Did I have the skill to run the O/A torch?
I was at a disadvantage because I never learned how to properly use the torch, and properly practice it. The O/A torch is important to learn because most people who have small shops or farms are likely to have the oxy-acetylene torch over a plasma cutter.
Transition (Use Objective):
1. Describe the set-up and shut-down process for an Oxy-acetylene cutting torch
2. Demonstrate igniting the acetylene gas and properly adjusting the flame
3. Describe the process for making proper cuts using an Oxy-acetylene torch
4. Demonstrate cutting metal with the Oxy-acetylene torch
5. Evaluate torch cuts against industry standards, using problem solving methods
Strategy – Includes Teacher Activity, Student Activity, Questions/Answers and Objectives / Subject Matter Outline/Problem and Solution (Application Points Lace in Throughout Lesson) (Modeling, Guided Practice, and Content)Objective #1
In a review of safety, the teacher will ask questions about O/A system.
(Q) Why do we double check to make sure the tanks are secured to the cart?
(A) Because we don’t want the tanks falling over
(Q) What can happen if the top is sheared off of the tank?
(A) Rocket
(Q) What is the pressure where acetylene becomes unstable?
(A) 15 p.s.i.
The teacher will then ask the students to help with the set up of the O/A system. Questions are designed to get students thinking about why we turn the O/A system on in a certain manner. This part of the lesson is a review from Introduction to O/A welding
(Q) Why is the oxygen tank valve opened all the way, but the acetylene only opened ¼ of a turn?
(A) So we can more easily turn the acetylene tank off if needed.
(Q) There are two pressure indicators on each tank; what are their purposes?
(A) The one on the right is usually tank pressure and the pressure valve is on the left is for line pressure. / Setting up the O/A System, and shutting it down
Turn the valve on the top of the oxygen tank all the way open. These valves work fine if only partially opened, but the shaft should be sealed when the valve is fully opened. This prevents a leak an accidental loss of oxygen.
Turn the valve on the acetylene tank 1/4 to 1/3 of a turn to open. Gas will flow freely at this setting but the tank will be quick to close in the event of a fire.
Verify that the oxygen valve on the cutting torch is closed.
Fully open the oxygen valve on the torch handle by turning it counterclockwise.
Crack open the cutting torch oxygen valve so that a very slight oxygen flow is started.
Light the torch by making a spark with the spark lighter at the end of the cutting tip while also opening the acetylene valve slightly.
Adjust the two valves (cutting torch oxygen and acetylene) until the strongest flame is obtained. The flame should have a short, bright blue flame at the torch tip and no yellow in the flame.
Adjust the acetylene regulator to approximately 10 psi. Turn the screw in to increase the pressure and out to decrease it.
Adjust the oxygen regulator in the same manner to a pressure in the 40 to 60 psi range.
Adjust the acetylene and oxygen valves as necessary to maintain the correct flame.
Objective #2
(Q) Why do we only open the acetylene valve a little bit RIGHT before we are ready to strike?
(A) So we do not have an explosion with too much acetylene
(Q) Should there be any oxygen in the mix when we are lighting the torch?
(A) No, we do not add oxygen until we have an acetylene flame properly adjusted
(Q) After we have lighted the acetylene; what do we want our flame to look like?
(A) No black smoke, but the tip of the flame is just feathering / Striking the Cutting Torch
Open the acetylene torch valve about one-quarter turn. Light the acetylene with a spark from a "striker". Do not use matches or a butane lighter.
Adjust the flame, using the acetylene torch valve until the flame has just lost its "smoky" quality. If the flame "blows out" or blows away from the tip of the torch, the valve is too far open. If the flame jumps away from the torch tip, you have it too far open. Close the valve a bit and then slowly reopen.
With the proper shade gas welding lens over your eyes (#4-7), slowly open up the oxygen torch valve. A small, pointy flame very close to the torch tip will appear. This is called the �inner cone'. At the same time, a distinct, blue flame will begin to appear at the end of the flame. Continue to slowly open up the oxygen torch valve until the distinct blue flame has just shrunk to the same size as the inner cone. This is the proper welding flame called a neutral flame.
Objective #3
The teacher will demonstrate how to use the Oxy-acetylene torch so the students can visualize the concepts. Each student will also practice the torch operation in front of their peers.
(Q) Has anyone in the class every used oxyacetylene for cutting?
(Q) Why do we wait for the metal to become red hot before we forcefully add oxygen?
(A) So the metal will fall away from the metal easier
(Q) What do you do if the torch starts popping?
(A) Move the tip away from the metal
(Q) When you were watching me cut; how close was the tip?
(A) The blue part of the flame was almost touching the metal / Using the Oxy-acetylene Cutting Torch
Ensure that the piece to be cut is positioned such that no part of the support is under the cut line. Cutting torches can cut several inches of steel easily, so anything in the path could be damaged.
Hold the torch close to the work. The bright blue portion of the flame should just touch the edge of the area to be cut.
Heat the work until the edge starts to glow. There may be small sparks start to come off the metal at this point.
Press down on the cutting lever and open it fully. Move the torch along the line you want to cut. The speed of your movement will depend on the thickness of the metal and the size tip on the torch. The proper speed will be result in a continual stream of sparks as the metal is cut. You should go as fast as you can control the torch and get continual cutting. This will reduce the slag on the cut edge.
Shut off the torch when done. Close the acetylene valve first, then the cutting tip oxygen.
Close the tank valves.
Open the acetylene valve on the torch to purge the gas from the hose. Then press the cutting lever to purge the oxygen hose. Finally, close the oxygen valve on the torch handle.
Objective #4 & #5
The teacher will ask students to practice making cuts.
Students will work in pairs for cutting, and students will evaluate each other’s welds according to industry standards
(Q) How does the cut compare to the industry standard?
(A) more slag
(Q) What causes the build up of excessive slag?
(A) Moving the torch too slow
(Q) What type of flame do we actually cut with?
(A) The same as welding, a neutral flame
(Q) What is happening when we hear the torch pop?
(A) Something is wrong with our operation of the torch or an incorrect mixture of gases is being used.
(Q) If there is a band on the cutting edge; what is the problem?
(A) The height of the tip was too far above the metal / Demonstrating and Evaluating Oxy-acetylene Cutting
Using an oxyacetylene torch, makes a straight and clean cut with the propercombination of travel speed, flame height, pressures, torch angle, and flame intensity
a. Uses proper tip size for the job
b. Opens valve slowly on both tanks
c. Checks tanks for leaks
d. Sets the flow gauge regulators to correct setting for the task
e. Never allows rate of tank withdrawal to exceedapproximately 1/7 of tank capacity perhour (to cause release of solvent and tank debris, damaging system)
f. Adjusts the oxygen and acetylene flow to achieve a precise neutral flame
i. bright blue inner cone
ii. no pale orange or “feather” present (carburizing flame)
iii. no shrill sound or sharper, less bright cone (oxidizing flame)
g. Performs the cutting task smoothly without excessive “popping” (caused by an oxidizingflame) and “blow back”
h. Uses appropriate cutting guides when needed
i. Finished cut is straight, smooth, and clean
i. proper cutting technique (little or no slag at bottom of cut)
ii. proper height of tip above material (no black band on the cut edge)
iii. proper travel speed and oxygen pressure (top of cut edge is not rounded)
iv. neutral flame is maintained (no splatter buildup on tip)
j. Properly shuts down the torch and tanks
Closure/Summary/Conclusion (Tie in Objectives)
What have we learned about using the Oxy-acetylene cutting torch?
1. Describe the set-up and shut-down process for an Oxy-acetylene cutting torch
2. Demonstrate igniting the acetylene gas and properly adjusting the flame
3. Describe the process for making proper cuts using an Oxy-acetylene torch
4. Demonstrate cutting metal with the Oxy-acetylene torch
5. Evaluate torch cuts against industry standards, using problem solving methods
Evaluation: (Authentic forms of Evaluation, Quizzes, or Written Exam)
Visual and verbal checks for understanding will be done by the teacher to ensure the students are understanding the concepts of O/A cutting and striking the torch
Self-evaluation
Assignments: (Student Activities Involved in Lesson/Designed to Meet Objectives)
Daily calendar
Self-evaluation
Set up and shut down procedural check sheet
Lesson Reflection
This lesson was similar to the O/A welding lesson, so I was able to use the set up process of the lesson to check for student comprehension of the process. I allowed students to use their procedural check sheet for answering my questions on setting up the system, to increase the value of the check sheet. I think I would keep that part of the lesson, but I might not do as much peer evaluation because students actually seemed to tell each other they had good cuts, just so they didn’t hurt people’s feelings.