You must have noticed how normal operation today depends on solid metal structures, from the steel found in automobiles and airplanes to beams in bridges and buildings. These mighty metallic structures are heavy and solid. However, has it ever crossed your mind how metals are joined together to form such marvelous structures?
While screws can hold metal pieces together, that’s not enough for these large structures. To support all the weight they have to and remain strong and sturdy, different metals need to be fused to combine the strengths of both materials. This is where welding comes into play. Welding joins different metals together by heating them at the junction up till the point they melt and fuse together. There are numerous types of welding, of which Oxy-Acetylene welding is one of the most famed welding processes.
What Is Oxy-Acetylene?
Oxy-Acetylene is a volatile mixture of pure oxygen gas and acetylene gas. The two gases are not chemically combined but rather a mixture which is prepared only for a specific purpose – superheating.
The mixture can be explosive, depending upon what percentage of oxygen is involved. However, if the proportions are harnessed and modulated properly, the combustion of these two gases can produce heat and light.
What Is Oxy-Acetylene Welding?
Oxy-Acetylene or Oxygen Acetylene welding is a type of welding that relies on the combustion of oxygen and acetylene gases, hence often referred to as gas welding. It is one of the most versatile types of welding. Oxy-Acetylene welding requires a specific skill set and thorough practice, coupled with which it can be used to weld virtually any metal!
When oxygen and acetylene are mixed in right proportions within a blowpipe or hand-held torch, they can produce a very hot flame, with a temperature as high as 3,200 degrees. This temperature is hot enough to melt all types of commercial metals. As you change the ratio of the two gases used, the action of the flame is adjusted.
Oxy-Acetylene welding works on a simple concept, that is, bring two pieces of metals together such that their edges are touching. Then, heat these touching edges with a flame till they melt and fuse.
Oxy-Acetylene Welding Equipment
The Oxy-Acetylene welding equipment consists of oxygen and acetylene gas cylinders, pressure regulators, hoses, Flame Arrestors, welding torches, and economizers. Once you have a clear understanding of the equipment, you will know exactly how Oxy-Acetylene welding works.
The primary components of Oxy-Acetylene welding equipment are separate gas cylinders for oxygen and acetylene. The gas cylinders should be sealed to perfection, with no leaks at all. In case there is a leak around the spindle, it will be revealed by a hissing sound or a smell. The gland nut around the cylinder valve should be tightened clockwise using a spanner to ensure that no gas is leaking, thereby reducing the risk of accidents.
The color of the oxygen gas cylinder is black with a right-hand thread, and the color of an acetylene gas cylinder is maroon with a left-hand thread.
Pressure regulators can be considered to be precision instruments. The pressure regulator controls the pressure and the flow of gases. It should never be exposed to knocks or sudden surges in pressure that are a result of the rapid opening of the gas cylinder valve. For this very reason, you should always open the gas cylinder valve smoothly and slowly with the help of the Spindle Key. In parallel, you should check the bullnose present on the pressure regulator. If there is any damage to it, the gas will start to leak. Pressure regulators should be changed immediately in case of damage. Moreover, a pressure regulator should only be used with the gas it has been designed for.
The hoses should be well-fitted and attached to the cylinder with permanent clips. They should not be exposed to heat, oil, grease, sparks, slag, traffic, or sharp edges of metal. There should be no leakage in the hoses as these are the pipes through which the gas is transported to the torch. Every hose has a check valve that offers automatic safeguarding by incorporating a non-return valve.
There are specially-designed devices called Flashback Arrestors that are fitted between the regulators and hoses as a safety measure. What these Flashback Arrestors do is that they prevent the flames that have been generated by a flashback from reaching the gas cylinders.
After the pressure of the gases has been regulated and controlled, they are fed to the welding torch through the respective hoses. Each gas is controlled by the valve present on the torch. It is the welding or cutting torch where the two gases, oxygen, and acetylene finally mix. They are ignited and burned at the nozzle of the torch.
It is a device that saves acetylene and oxygen from being wasted when the welding or cutting torch is not in use. When the welding torch is resting, the flame is extinguished automatically. To re-light the torch, all you have to do is remove the welding torch from the lever rod and pass it over the pilot light. The torch will be re-ignited instantly.
Gas welding poses a significant risk of accidents. Therefore, you need to be extremely careful when starting your welding process.
Start by opening the valves of oxygen and acetylene gas cylinders gradually, with the help of cylinder keys. Opening the valves suddenly can not only damage the regulators but might also lead to an accident. The cylinder valve spindles should be opened on a single turn only. Next, open the control valve for fuel gas present on the blowpipe and adjust the regulator until the correct working pressure is achieved. This will ensure that any air present in the hoses is purged before the welding process is started.
The gas should be lit using a suitable spark-lighter only, and that too, held at the right angles to the nozzle. You should never use liquid igniters as they can be extremely dangerous.
The supply of acetylene gas to the blowpipe should be adjusted up to the point the flame stops to smoke. Once the flame ceases to smoke, increase the oxygen supply slowly by means of the control valve. The final flame should have a sharply defined, white-colored inner cone with as little trace of acetylene haze as possible. This is when you’ll know that your blowpipe is correctly adjusted and is ready to be used to Oxy-Acetylene weld.
Types of Flames in Oxy-Acetylene Welding
As mentioned above, the flame has to be adjusted to appear a certain way before you can proceed with the Oxy-Acetylene weld. Different types of flames are used to weld different types of metals.
Carburizing flame contains an excess of acetylene gas. This type of flame is suitable for applications where a low-heat flame is required. It is used for welding nickel, Monel metal, high-carbon steel, and a number of non-ferrous metals. This flame is not used to weld regular steel.
Neutral flame contains equal proportions of oxygen and acetylene gases. This type of flame is used in most welding operations since the chemical effect of this flame on heated metal is the least.
As you can tell by the name, an oxidizing flame has a high content of oxygen (the oxygen and acetylene ratio being 1.5:1). This type of flame is used when welding copper and alloys of copper, such as bronze and brass. It cannot be used to weld steel as it will oxidize it.
Once you have lighted up the blowpipe and achieved a neutral flame, you are all set to start Oxy-Acetylene welding. There are different types of techniques that you can practice, which have been listed below:
The leftward technique of Oxy-Acetylene welding is employed to weld steel plates that are up to 5mm thick. It can also be used to weld non-ferrous metals.
In this technique, the blowpipe is held in the right hand, which forms a weld that runs from right to left. The filler rod is held in place such that it is in front of the nozzle. For this technique, it is necessary that the flame is in a neutral condition. The flame should be close enough to the steel base metal but should not be touching it.
The nozzle is moved in slightly side-to-side or circular motions to ensure consistent heating and achieve an even fusion. Before you start with the leftward technique, play the neutral flame at the edge of the joint until a molten weld pool is formed. As the welding procedure proceeds, simply dip the filler rod into this molten pool.
The filler rod should not be melted by direct flame but by dipping into the molten weld pool only. You should make sure that you do not keep the filler rod dipped into the pool continuously as it would act as a hindrance to thorough heating and keep the heat from the flame to reach the lower parts of the weld, and this might result in an imperfect fusion.
For metal plates that are more than 4mm in thickness, the rightward technique is recommended.
In the rightward technique, the blowpipe is held from the left hand, and the weld moves from the left to the right. The filler rod is preceded by the flame in the direction of the travel. The filler rod is moved forward in a circular motion, with the blowpipe moving steadily along the seam of the weld. The rightward technique is faster as compared to the leftward technique. It also consumes lesser gas and filler rod; hence it is cost-effective. The V-angle is smaller, and there is less distortion.
All-Position Rightward Weld
The all-position rightward weld is a modification of the rightward technique. It is a suitable technique for mild steel pipes and plates in a vertical and overhead position. This technique comes with numerous advantages. It allows the welder to get an even build-up and a very uniform penetration bead. The welder is also given complete freedom to move and a clear view of the fusion zone and weld pool.
This type of Oxy-Acetylene welding can be used on unbevelled steel plates that are 3mm in thickness when two welders are working on each side. The welding starts at the bottom of the plate and proceeds up vertically.
Bronze welding, as the name implies, is used when there is a need to make joints in copper or make repairs to cast iron. It makes use of rods made of bronze alloy. The most commonly used rods include fluxobronze, which is a silicone bronze rod that has been flux-coated, manganese bronze rod, and plain nickel bronze rods with suitable flux. In this technique, it is important that the edges of the metal to be welded are not melted but heated until they become red. The joint that is formed as a result of this type of Oxy-Acetylene welding is absolutely clean and has excellent mechanical properties.
Depositing Hard-Facing Rods
Rods that contain tungsten carbide are deposited using this technique. It involves laying down a layer of hard deposit on the surface or cast iron or steel. This layer of hard deposit is resistant to wear. This technique has widespread applications in building up wear-resistant surfaces on dyes, well-boring drills, punches, knives, picks, valve seals, and excavating and crushing machinery.
To deposit a wear-resistant rod onto a metal’s surface, a flame with an excess of acetylene gas (carburized flame) is used. The base metal, in this case, is pre-heated until the point it begins to sweat. At this point, the rod is melted onto this sweating surface in small deposits. This way, the entire surface is gradually built up.
Hazards of Oxy-Acetylene Welding
Any guide on how to Oxy-Acetylene weld will be incomplete without highlighting the hazards of Oxy-Acetylene welding. We have listed down the most common hazards of this type of welding below:
- Fire explosions
- Careless use of welding or cutting torch
- Gas leaks
Gas welding is one of the riskiest of all types of welding. The following safety precautions must be ensured during the entire welding process.
- Make sure that you’re always wearing protective clothing (flame-retardant overalls) and protective eye goggles
- The acetylene gas cylinder valve should have a spindle key
- The gas cylinders should be stored in an upright position
- Check for leaks with a soapy solution and not with a naked flame
- Do not carry out any makeshift repairs on your welding equipment
- Prevent the contact of your oxygen equipment with oil or grease at all times
- Clean enclosed vessels thoroughly before welding them
- If you’re working in an enclosed vessel, make sure you aren’t alone and that the gas cylinder is always outside
- Fire-fighting equipment should be available on the ground
- Adequate ventilation has to be ensured
- Turn the gas supply off immediately if you detect a leak in the hose
How do you weld Oxy-Acetylene?
Oxy-Acetylene welding involves joining two metals with the help of a flame produced by the combustion of oxygen and acetylene. The gases are transported from the gas cylinders to the welding or cutting torch through hoses, and the flame is emitted through the nozzle at the end of the torch. The temperature of the flame is hot enough to melt the edges of the metal, and hence, fuse two metal pieces together.
What metals can be welded with Oxy-Acetylene?
If Oxy-Acetylene welding is done the right way, it can be used to weld all commercial metals. The metals that are welded with Oxy-Acetylene include low-alloy steel, low-carbon steel, wrought iron, and cast iron.
What should oxygen and acetylene be set at?
Although it depends on the application, generally, oxygen should be set at 40 psi, and acetylene should be set at 10 psi.
Can aluminum be welded with Oxy-Acetylene?
Yes, aluminum can be welded with Oxy-Acetylene. Welding aluminum with Oxy-Acetylene welding is one of the most common applications of this type of welding.