Area and/or Course Introduction to Welding
Lesson Title Introduction to Oxygen/Acetylene (O/A) Welding
No. Periods 1 (73-minute period)
Teacher Goal(s):
1. Students will demonstrate how to safely set up an (O/A) system, and ignite the welding torch
2. Students will practice creating O/A welds
Rigor/RelevanceFramework
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. Identify the set up process for an Oxygen/Acetylene welding torch (AG 10.02.01.04)
2. Demonstrate properly striking the welding torch (AG 10.02.01.04)
3. Select applications in a real-world setting where O/A welding would be used (CS.EF.02)
4. Create O/A welds using safety, correct techniques, and form (EL.HS.RE.08)
5. Demonstrate properly shutting down the O/A welding torch (CS.HS.02)
State Standards met by Objectives:
Subject Strand Eligible Content
1. Agriculture AG 10.02.01.04 Demonstrate the set up and adjustment of tools and equipment
2. CRLS CS.EF.02 Select, apply, and maintain tools and technologies appropriate for the workplace.
3. CRLS CS.HS.02 Listen attentively and summarize key elements of verbal and non-verbal communication.
4. English EL.HS.RE.08 Understand, learn, and use new vocabulary that is introduced and taught directly through informational text, literary text, and instruction across the subject areas.
5. Power Science PST 04.04.07.c. Construct and/or repair metal structures and and Technology equipment using welding fabrication procedures, including those associated with SMAW, GMAW, GTAW, fuel-oxygen and plasma arc torch methods.
6. Power Science PST 04.04.07.b. Distinguish welding processes, positions, and
and Technology materials preparation.
Materials, Equipment, Audio-Visual Aids:1. Oxygen/Acetylene welding torch
2. Gloves
3. Welding face shield
4. Striker
5. Various metal / References:
http://www.artmetal.com/brambush/forum/ bramyak3/messages/9.html
http://www.stanford.edu/group/prl/ documents/html/OAweld.htm
Anticipatory Set/Introduction/Motivation/Interest Approach:
Review Yesterday’s Lesson:
Yesterday we talked about using the arc welder to create welds. What do you guys think are some differences between arc welding (SMAW) and O/A welding?
- Electricity
- Pulling the puddle opposed to pushing the metal
- Speed
What are some of the similarities?
- Angles
- Safety
Set:
The teacher will begin the Introduction to O/A Welding lesson with a personal story about an issue which arose during the O/A process.
As most of you know, the only piece of equipment which I have had students get hurt on is the Oxygen/Acetylene welding torch. This particular issue arose because the student was not paying attention to safety or his surroundings. At the beginning of the class I had announced not to use one of the welding torches because the acetylene hose was leaking. I was working with some students in the arc booth, and another student calmly said, “Mr. Sherman, Billy is on fire.” As I turned around I noticed that Billy was not only on fire, but he had no idea it was happening.
(Q) Who can guess what I did? (A) Remained calm
(Q)Exactly right I remained calm and turned off which gas first? (A) Acetylene
The most important fact to remember about that story is to remain calm, but also to try and diffuse a situation. I trust all of you guys will pay attention to daily safety instructions and remember what to do during an emergency. Right?
Transition (Use Objective):
1. Identify the set up process for an Oxygen/Acetylene welding torch
2. Demonstrate properly striking the welding torch
3. Select applications in a real-world setting where O/A welding would be used
4. Create O/A welds using safety, correct techniques, and form
5. Demonstrate properly shutting down the O/A welding torch
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.
(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
First check over the condition of the equipment. Are the cylinders chained to the cart (or to a wall)? Are the torch valves closed? Are the hoses in good condition?
Check that the adjusting screws on each regulator are loose. Loose means turned out counterclockwise. This releases the pressure on the diaphragm.
Open up the acetylene cylinder valve slowly so that it is one-half to one full turn open (one full twist of the wrist). The needle on the high pressure gauge should now indicate the amount of acetylene pressure in the cylinder. If no pressure is indicated - stop at this point.
Screw in the adjusting screw on the acetylene regulator (clockwise) until the needle on the low pressure gauge indicates the desired working pressure. The working pressure depends on the torch tip size.
Now bleed out the acetylene hose and check the actual working pressure at the same time. To do this, open up the acetylene valve on the torch. Let the gas flow out of the torch for a few seconds. While the torch valve is still open, look at the low pressure gauge and readjust to the desired working pressure. Close the torch valve.
Open up the oxygen cylinder valve stem just a crack. Once the needle on the high pressure gauge has stopped, open up the valve all the way. This back-seats the valve. Oxygen cylinders must have the valve opened up all the way because of the high pressure in the cylinder. There is a back-seating valve on the oxygen cylinder. This prevents the high pressure gas from leaking out through the threaded stem.
Screw in the adjusting screw on the oxygen regulator (clockwise) until the needle on the low pressure gauge indicates the desired working pressure. Note that this gauge is usually calibrated in 5-pound increments, differing from the acetylene regulator low pressure gauge.
Now check the actual working pressure of the oxygen in the same way as was done for the acetylene. If you screw it in too far and obtain too much pressure, be sure to open the torch valve before readjusting the pressure.
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 Welding 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
Before the students begin actually welding with the O/A system, the teacher will discuss with the students some of the practical applications of using oxyacetylene welding.
(Q) Has anyone in the class every used oxyacetylene for welding?
(Q) What are some applications where O/A welding could be used?
(A) Welding pipes, brazing, at-home uses, etc.
(Q) What are some of the advantages of oxyacetylene welding over many other types?
(A) Easy to learn, equipment is mostly portable, can be used to cut as well with the proper tip
(Q) What could some of the disadvantages be?
(A) Rougher in appearance due to the heated zones / What are the Applications of O/A Welding?
However, it is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork. Oxyfuel equipment is versatile, lending itself not only to some sorts of iron or steel welding but also to brazing, braze-welding, metal heating (for bending and forming), and also oxyfuel cutting.
In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded.
Advantages of Oxy-Acetylene Welding :
· The equipment is cheaper than most other types of welding rigs (e.g. TIG welding)
· The equipment is more portable than most other types of welding rigs (e.g. TIG welding)
· OA equipment can also be used to "flame-cut" large pieces of material.
Disadvantages of Oxy-Acetylene Welding :
· OA weld lines are much rougher in appearance than other kinds of welds, and require more finishing if neatness is required.
· OA welds have large heat affected zones (areas around the weld line that have had their mechanical properties adversely affected by the welding process)
Objective #4
The teacher will demonstrate how to make O/A welds using the welding torch, and then after asking and answering questions the students will be able to start practicing safe and effective methods of creating oxyacetylene welds.
(Q) When we are oxyacetylene welding, are we pushing or pulling the metal?
(A) pushing
(Q) Why do we only move the puddle in one direction?
(A) The gases coming out of the welding torch will help to move the puddle across the metal and heat the metal before our puddle gets there
(Q) How do you know when you have a puddle?
(A) The metal will get red, and then all of the sudden the puddle will appear.
The teacher will ask students to put their face shields on watch for the puddle to form, asking the students to say “now” when the puddle forms
(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. / Creating O/A Welds
1) Put on a dark face shield to protect your eyes from the light of the flame. Make sure you have on long sleeves and all natural fibers. You can wear a leather welding jacket and/or gloves if it makes you feel more comfortable.
2) Apply the flame to the parts to begin heating. Use the region of the flame near the tip of the bluish inner region.
3) The metal will begin to glow. Continue heating both parts being welded until a small pool of welded metal appears near the edge of each of the parts. You must get molten pools on BOTH parts simultaneously to create the weld. The may require adding more heat to one side than the other, and takes some practice.
4) After the molten pools have formed on both sides of the weld, use the flame to gently stir the two pools together to form the weld. This also takes a little practice.
5) After the two pools have joined, slowly move the flame along the weld line, lengthening the pool using metal from both parts. A gentle, circular, swirling motion will help mix the molten metal from both sides as the puddle is lengthened. This process is highly dependent on the materials and part geometries being welded. Practice, practice, practice to get better control. Welding sample parts is a good idea.
6) Continue this process until the entire weld line is complete.
7) Once you're done, turn off the flame. Close the oxygen pin valve first, and then the acetylene valve. Note: Welded parts can remain hot for a LONG time.
Backfiring
Improper operation of the torch may cause the flame to go out with a loud snap or pop. This is called backfire. It is caused by one of a few things. The first thing to do is turn the gas in the torch off, check all the connections and try relighting the torch. Backfiring can be caused by touching the tip against your work piece, overheating the tip, operating the torch at other than recommended gas pressures, by a loose tip or head or by dirt on the seat.