Oxy-acetylene (or oxy-fuel) welding is one of the oldest welding processes still in use today. First used in 1903, it has gained widespread use over the years. It continues to be popular due to its low cost, the simplicity of equipment required, and the ease of operation.
What Is Oxy-Fuel Welding?
Oxy-fuel welding uses oxygen mixed with a fuel gas (most commonly acetylene). The torch heats the base metal to a molten state to achieve the welded connection. Oxy-fuel welding may be performed with or without a separate filler metal.
How Oxy-Fuel Welding Works
Oxy-fuel welding is a relatively simple welding process that involves several key factors.
The Combustion Process
The flame in oxy-fuel welding is produced by the combustion of oxygen and the fuel gas.
Controlling Heat and Flame
The flame is adjusted first by changing the flow from the gas cylinders by using the regulators and then by using the knobs on the torch itself. This achieves the desired type and size of flame.
Understanding Flame Types
There are three main types of flames used when oxy-acetylene welding - neutral flame, carburizing flame, and oxidizing flame.
Neutral Flame
The neutral flame (also called the balanced flame) has a one-to-one ratio of oxygen to fuel and is the preferred flame for welding. It has a clear and well-defined cone, which indicates that the combustion of the fuel gas mixture is complete.
Carburizing Flame
The carburizing flame is the result of an excess of acetylene. It is identifiable by the presence of a feathery edge extending beyond the inner cone.
Oxidizing Flame
The oxidizing flame is produced by an excess of oxygen in the fuel-gas mixture. It has a small inner cone that remains proportionate to the excess of oxygen in the flame. The oxidizing flame has the potential to oxidize the weld metal and is only suitable for certain special applications.
The illustration below offers a visual of the types of flames described above:
Tools and Materials
One of the primary advantages of oxy-acetylene welding is the low cost of tools and equipment.
Welding Torch
The first thing you need for oxy-fuel welding is the torch. There are many sizes, models, and manufacturers to choose from. Consider the amount and type of work you will be performing before making a purchase.
Oxygen and Fuel Tanks
Next, you’ll need the designated fuel gas and oxygen tanks.
Regulators and Hoses
Once you’ve secured the tanks, connect the gas cylinders to the welding torch by attaching the regulators to the bottle. Note that most fuel gas cylinder valves have a left-handed thread pattern. This prevents accidentally reversing oxygen and fuel gas connections. Use the hoses to connect the regulators to the torch.
Safety Gear
Prior to lighting the torch to begin welding, don safety gear. At a minimum, this includes:
-
Safety goggles, glasses, or a full face shield with a rating of shade 3 to 5
-
Welding gloves
-
A welding jacket or coat
-
Full-length denim pants
-
Safety-toe shoes
If the welding will take place in a confined space and may produce fumes, you may also need respiratory protection.
Getting Ready to Weld
Now the tools and equipment are in place, you are ready to set up for the welding operations.
Choosing and Preparing Materials
Clean the metal you will be welding to keep it free from all surface contaminants. The cleaner the material, the lower the likelihood of trapping contaminants in the weld puddle, which could lead to defects in the weld upon solidification of the weld puddle.
Select the appropriate matching filler metal — you can always ask local welding distributors for assistance!
Setting Up Your Gear
There are a couple of remaining steps you need to perform before beginning the welding process.
Securing the Workspace
Secure the work area by removing all flammables from where you will be welding. This includes any wood, cardboard, paints, oils, gas, and anything else that could easily catch on fire.
Close doors or set up windscreens, if necessary, to protect the torch flame and molten weld puddle from contamination.
Ensure adequate ventilation for the removal of hazardous fumes generated by the welding process.
Inspecting the Equipment
Before lighting the torch, perform one last check of the welding equipment. Make sure gas cylinders are upright and secured, hoses are connected tightly, and there are no leaks. Check the gas cylinder pressures one last time and adjust as necessary.
Step-by-Step Guide to Oxy-Acetylene Welding
Although it’s a relatively simple process, oxy-fuel welding involves several steps to achieve a consistent quality weld, free from defects.
Preparing the Pieces
One of the most important steps in any welding process is the preparation. Clean the workpiece thoroughly, removing any dirt, rust, debris, oils, grease, paints, and excessive mill scale that could result in weld defects.
Lighting and Adjusting the Torch
Light the torch by opening the fuel gas valve approximately one-quarter turn. Open the oxygen valve only slightly. Light the torch with a sparking tool, NEVER A CIGARETTE LIGHTER. Always point the torch in a safe direction, being mindful of the presence of other people and flammable objects and materials.
Establish a neutral flame. There’s no strict rule for flame size, it just requires some trial and error based on experience. In general, thicker materials need a larger flame to properly heat both the base metal and filler metal to a molten state.
Heating the Metal
Heat the filler metal until you’ve established a molten weld puddle. It may be necessary to manipulate the torch, moving it in a small, circular motion to heat enough of the base metal to initiate a molten weld puddle.
Adding Filler Metal
Now you’ve established the puddle, add filler metal by dipping the filler wire into the molten puddle and melting the desired amount of material with the torch flame. Deposit enough material to fill the joint and achieve the desired weld size. Repeat this process along the length of the weld joint. If the filler metal seems to favor one side of the weld over the other, adjust the torch angle until you’ve created a uniform U-shaped puddle. Adjust the size of the flame and travel speed as necessary.
Cooling and Cleaning Up
When you’ve achieved a weld of the desired size and shape, allow the workpiece to cool at a normal rate until ambient. Do NOT quench or cool by any other means, as this could mean the completed workpiece becomes brittle or even cracks under the stress.
Visually inspect the weld, looking for indications of incomplete fusion, undercut, underfilled welds, porosity, or other defects that may lead to failure in service. Perform repairs as necessary by repeating the above steps.
It may be necessary to clean the weld with a wire brush or sanding disc to achieve the desired finish.
Welding Tips and Techniques
Oxy-acetylene welding is a manual welding process where the quality of the weld is more dependent on the skill of the welder than on any other variable.
Holding and Moving the Torch
A smooth, steady hand is a major factor in making quality welds. It is important to align yourself comfortably with the weld joint to the fullest extent possible. Consider performing a “dry run”, moving the unlit torch over the length of the weld joint to make sure you can complete the desired weld pass without having to stop and reposition more than is necessary.
Creating Clean Welds
As with any welding process, preparation is an important step for creating a clean, consistent-quality weld. Make sure the base metal is clean and free of dirt, rust, grease, oils, paints, or other debris that could lead to impurities becoming trapped in the molten weld puddle.
Working with Different Metals
Each metal has defining physical and mechanical properties. Before welding on different metals, it is important to understand how a metal will react to heat, whether a preheat is necessary, and which filler metals are compatible with the base metal.
Steel
One of the most commonly welded metals, and perhaps one of the easier metals to weld with the oxy-acetylene process, steel is known for its high strength and relatively low cost.
Aluminum
The practiced hand can create aesthetically pleasing welds on aluminum with the oxy-fuel welding process. Aluminum is known for being lightweight and rigid, is often used in trailers, frames, awnings, and even fuel tanks, all of which are possible to weld using oxy-fuel.
Copper
Another metal suitable for the oxy-fuel welding process is copper. Popular among artists and sculptors for its high degree of malleability as well as for the golden-brown luster achieved when it is polished, you can weld copper for a relatively low cost with the oxy-fuel welding process.
Avoiding Common Mistakes
As with any welding process, it takes time and practice to learn to produce quality welds with a high degree of consistency using oxy-acetylene welding. Some of the most common mistakes when using oxy-acetylene welding include the following.
Welding Too Hot
Sometimes, less is more. Too much heat will create a puddle that is too large and therefore difficult to control. If the welds are flat and inconsistent, consider reducing the size of the flame and welding with a slightly reduced travel speed.
Trying to Weld Poorly Fit-Up Weld Joints
Inconsistencies in the weld joint may be difficult to correct during welding operations. The more consistent the joint, the easier it will be to create a uniform weld.
Failing to Clean Adequately
Impurities from the base metal that enter the weld joint may be drawn into the molten weld puddle. This may make the weld joint more erratic and difficult to control and increase the likelihood of weld defects. Make sure to clean the base metal, removing all surface impurities, especially in the weld joint.
Different Fuel Options for Oxy-Fuel Welding
One of the advantages of oxy-fuel welding is it is possible to weld with several different gases mixed with oxygen to produce the heat required.
Oxy-Acetylene
Acetylene is the most common gas for oxy-fuel welding. Acetylene burns at a high temperature, making it ideal for welding thick sections of material.
Oxy-Propane and Oxy-Natural Gas
A widely used alternative to acetylene, propane is less expensive and more readily available and similarly produces a high heat.
There are a couple of limiting factors to be aware of before deciding to weld with propane:
-
You may need a special torch hose specifically rated for propane. (Propane corrodes regular oxy-acetylene torch hose, creating an aneurysm that could fail while welding, posing a potential fire hazard.)
-
You need different torch tips.
-
Some torches may require a different mixer within the torch assembly itself. Only a qualified professional should change these.
(Some models may mix in the torch tip; others mix internally and CANNOT be easily switched back and forth.)
Consult the torch manufacturer’s recommendations or call your local welding distributor for advice before welding.
Comparing Fuels
Let’s take a look at some of the pros and cons of each of these commonly used welding fuel gases to see which may be the best option for your specific needs.
Acetylene
Acetylene welds at high temperatures, which makes it highly efficient in heating metals to the required welding temperature.
Acetylene is, however, highly flammable, unstable under high pressures, and only available at specialized welding gas distributors.
Note: You MUST store acetylene cylinders fully upright due to the presence of acetone in the cylinder, which serves as a stabilizing agent.
Propane
Propane is a lower-cost alternative to acetylene. It is widely available and produces the high heat required for welding.
Propane may require more oxygen than acetylene, which may offset some of the cost savings. Propane may also require specially designed tips and hoses.
Other Gases
Butane is used as a welding gas with oxygen due to its portability and safe, easy handling.
Since butane produces less heat than either acetylene or propane, it is not well suited to welding thicker, heavier sections of material.
Staying Safe While Welding
In all welding processes, safety should be of paramount concern. Welding with the oxy-fuel process poses its own set of potential hazards, which you need to understand and address before starting welding operations.
Personal Protective Equipment (PPE)
At a minimum, welders should use the following PPE:
-
Welding gloves made from leather or a comparable material, capable of protecting hands and wrists from high heat and sparks from welding and grinding operations
-
Glasses, welding goggles, or a full face shield with a shade 3 to 5 rating
-
Long-sleeve welding shirt or jacket
-
Denim or canvas-type cloth pants
-
Steel-toe work boots
Avoid clothing with synthetic fibers that could melt and cause severe burns to the skin.
Handling Gas Tanks Safely
Gas cylinders are heavy, so handle them with care. Consider using an appliance dolly with a chain or ratchet strap when moving gas cylinders. Always make sure the safety cap is on securely to protect the valve from damage during handling. If the valve is damaged or sheared off due to improper handling, the sudden release of pressure may create a projectile out of the cylinder, capable of significant damage and serious bodily injury.
Preventing Fires and Fumes
Flashback arrestors are an important part of oxy-fuel welding equipment. Flashback arrestors keep gases from flowing backward into the regulator or torch. This is especially important for protecting the welder in the event of a fire. Most newer torches and regulators come with flashback arrestors built into the torch and regulator, but it is a good idea to check the manufacturer’s recommendations to see what additional safety equipment you may need.
Check hoses and connections for damage and leaks that could turn into a serious safety hazard if they were to be ignited by sparks generated during welding, cutting, or grinding operations.
Fixing Problems with Your Welds
Oxy-fuel welding takes time and practice to master. Below are a few things to keep in mind when trying to improve quality and consistency in oxy-fuel welding.
Why Your Welds Look Bad
Excessive heat is a common reason for inconsistent welds with a poor profile. Too much heat will result in a puddle that is too large and therefore difficult to control. Consider reducing the size of the flame to make the puddle more manageable by adding filler metal at a normal rate and maintaining a reasonable travel speed.
Flame Issues
The type of flame is also important in oxy-fuel welding. A neutral flame (see the image above) is almost always preferred for welding operations. Too much oxygen will lead to oxidation in the base metal. An excess of acetylene may introduce carbon into the weld, which may result in brittleness.
Equipment Problems
Regulators that are not in proper working condition may lead to incorrect or inconsistent flow rates in either the fuel gas or oxygen supplied to the weld puddle.
Damaged torch hoses, leaking fittings, and other faulty equipment may likewise lead to an inadequate supply of gas at the weld, which may result in welds that are too hot, too cold, or unstable, adversely impacting weld quality.
A clogged, dirty torch tip may also cause an inconsistent weld, by restricting gas flow and creating a dirty and inconsistent flame. Clean the torch tip regularly or replace it altogether.
Keeping Your Equipment in Shape
Regular equipment maintenance is an important aspect of a quality-focused welding program. Keeping welding equipment in proper working order will eliminate costly repairs and interruptions to workflow.
Cleaning and Maintenance
Clean torch tips regularly to ensure a flame capable of producing consistent-quality welds.
Wrap torch hoses neatly over a suitable hanger to keep them off the ground, away from dirt, debris, and other contaminants. Avoid storing torch hoses in direct sunlight to prevent them from drying, which makes them prone to cracking and leaks.
Storing Gas Safely
Store gas cylinders in the upright position, keeping oxygen and fuel cylinders a safe distance apart (a minimum of 20 feet).
Safety caps should remain on the gas cylinder until it is time to connect the regulator for use. Even then, you should secure the cylinders with either a chain or ratchet strap to a wall, rack, or movable torch cart. Special safety caps designed for use with the regulator provide an additional layer of safety. These caps are relatively inexpensive and available for purchase at any local welding distributor.
Do NOT, at any time, use petroleum-based products on threads on the regulator or safety caps near the cylinder valve. The presence of products like WD-40 or other similar substances poses a fire hazard during welding and cutting operations.
Regular Inspections
Visually inspect torch hoses, regulators, and the torch itself for obvious signs of wear and damage. Fix or replace as necessary.
Perform a leak check on hoses and all connections in the system. You can do this by spraying a soap solution onto the connection and checking for bubbles. Repair as necessary. It’s a good idea to keep a torch hose repair kit handy in case you encounter a leaky or broken hose.
Why Use Oxy-Fuel Welding?
There are many reasons why oxy-fuel welding remains advantageous for many applications.
It’s Affordable
The equipment required to perform oxy-fuel welding is inexpensive, especially in comparison to equipment for forms of welding that rely on electric or engine-driven power sources. All you need is a torch, torch hoses, regulators, and a set of bottles.
Easy to Transport
Oxy-fuel welding is highly portable. You can easily transport all the equipment to a worksite.
Suitable for Many Jobs
Oxy-fuel welding is a versatile welding process, suitable for several different metals, in nearly all positions, on a wide variety of different joint configurations, and for various applications. Oxy-fuel welding can create copper art sculptures, aluminum awnings, lead pipes, or steel brackets, to name just a few of the many possible applications.
Simple to Learn
The principles of oxy-fuel welding are fairly simple, meaning the technique takes little time to learn. With practice, you’ll be able to make consistent-quality, aesthetically pleasing welds on many different weldments.
Challenges of Oxy-Fuel Welding
Oxy-fuel welding is not without its challenges. There are some potential limiting factors that you should carefully evaluate prior to deciding whether to use oxy-fuel welding.
Not Suitable for All Materials
Oxy-fuel welding is unsuitable for some materials. Some high-strength steels or certain alloys may be challenging to weld with the oxy-fuel welding process. Thicker, heavier sections of material may also be more difficult to weld with the oxy-fuel process than with other arc welding methods, due to the high heat inputs required to achieve the necessary weld penetration depth.
Heat Damage Risks
Oxy-fuel welding requires the use of a flame at high temperatures but is also restricted to slower travel speeds. This means a high heat input, which may result in warping and distortion in the workpiece.
Slower Welding Speeds
Oxy-fuel welding is a much slower welding process than most arc welding processes, which makes it a poor choice where high productivity is a requirement.
Less Precision
Unlike arc welding processes (which have a quantifiable amp or voltage setting on a power source), there is no objective measure to tell the welder when the flame is right. Much of oxy-fuel welding is done by touch and feel — it is more intuitive than technical. This lack of precision may make it a poor choice when precise welding parameters and heat inputs are necessary.
Safety Risks
Flammable gases and high-pressure cylinders are fire and explosion hazards. It is important to handle cylinders with care, properly maintain equipment, and keep all flammable materials out of the work area to reduce risks to the fullest extent possible.
Environmental Concerns
Oxy-fuel welding is challenging in windy and drafty environments, where excessive air movement may disrupt the flame and negatively impact weld quality and consistency.
FAQs
What metals are suitable for oxy-acetylene welding?
-
Carbon steel — Some of the higher carbon content steels may require preheating before welding.
-
Cast iron — Commonly welded and sometimes brazed with oxy-acetylene.
-
Copper and aluminum — Suitable for oxy-acetylene welding.
-
Brass and bronze — It is theoretically possible to weld these metals with oxy-acetylene welding, but it is better to use brazing due to their low melting points.
How do you set the flame appropriately for oxy-fuel welding?
There is no set rule around the ideal flame size for oxy-fuel welding. Time and practice will help the welder determine the proper size flame for the material.
Thicker material may require a higher flame, but too much heat may lead to excessive heat input. This may make the weld puddle hard to control and even lead to burn-through and a flattened-out weld profile.
Too small of a flame may lead to low travel speeds and possible fusion defects. If it takes an excessive amount of time to generate a weld puddle and melt the filler metal into the weld puddle, slightly increase the flame size until you have achieved a consistent weld.
What safety precautions should you take when working with gas cylinders?
You should always store gas cylinders in their full upright position and secure them with a safety chain. Safety caps should be screwed on until the cylinder is in use. It’s a good practice to use safety caps designed to fit over the valve with the regulator attached. These are available from any local or regional welding distributor.
At NO time should you leave a cylinder unsecured with no safety cap on. If a cylinder were to fall in a way that resulted in damage to the valve, it could become a projectile and cause serious injury or property damage.
Featured photo courtesy of mkarasch0 // Pixabay
Leave a comment 0 comments, be the first!