There are many different types of metal joining processes in the industry and each offers a unique set of advantages as well as limitations. Therefore, there is a specific type of process which is suitable for a certain type of job. When it comes to welding, you probably already know about some popular types of welding, such as flux core welding, MIG welding, TIG welding, etc.
Today, we are going to discuss Oxy Acetylene or Oxyfuel welding in detail. This is also one of the popular welding methods that is quite popular for a wide range of applications. One of the biggest benefits of Oxyfuel welding is that it does not require a controlled pressure or any kind of filler material. On top of that, this is a versatile process that has many other applications apart from welding.
If you are not sure how Oxyfuel welding works, or just getting started with the Oxyfuel process, you have come to the right place. On this guide, you will find detailed information about the process, its benefits, types, parameters, and some handy tips for perfect Oxyfuel welding jobs. So, make sure you check our guide until the end so that you don’t miss out on some crucial points.
Oxyfuel Welding & Its Types
Oxyfuel welding is basically a type of process that makes multiple welding and a few other processes possible. In this process, the welder basically joins metals by heating them above their melting points with the help of a high-temperature gas flame. As we mentioned earlier, Oxyfuel welding does not require pressure or a filler material at all.
In any Oxyfuel process, Oxygen is used as the main gas which is mixed with other gasses in proportion to generate a high-temperature flame. Some common additions made to Oxygen for Oxyfuel welding are acetylene and hydrogen. In this process, the high-temperature flame melts the base metal completely. Or, it can also melt a filler material if needed for the job.
Once the base metal is melted, it gets mixed in a common pool of molten metal and filler material if induced. Once cooled, the molten metal fuses together to form a strong and solid continuous layer of the base material. There are 3 major types of Oxyfuel welding that are as follows:
1. Oxy Acetylene
In this process, Oxygen is mixed with Acetylene gas to form a heating medium for the flame. It is also known as gas welding since it is the most popular form of Oxyfuel welding. If mixed in correct proportions, Oxyacetylene flame could reach up to 3200°C temperature, which is well above the melting point of many commonly used metals. One can also adjust the temperature of the flame by controlling the proportion of Oxygen and Acetylene in the mixture.
2. Oxy Hydrogen
The Oxyhydrogen welding process on the other hand uses a mixture of Oxygen and Hydrogen as the heating medium. This welding process is suitable for light and heavy welding operations. One can also use Oxyhydrogen welding for brazing on small to medium-sized objects. As for the temperature, the flame temperature in Oxyhydrogen welding reaches up to 3000°C, which is still very high. It allows the welder to easily weld or solder the material without overheating the weld.
3. Pressure Gas
Pressure gas welding is basically a sub-type of Oxyacetylene welding that can produce a uniform weld over the joint surface without needing a filler material. It can be further categorized into low-pressure gas welding and high-pressure gas welding. In this method, the cross-section of the joint is heated at up to 1200°C to 1300°C, and then pressure is used to form the joint. While the method is well-known for its advantages, such as portability and versatility of applications, its applications are limited since the joints offer lesser strength.
Benefits of Oxyfuel Welding
There are many advantages of Oxyfuel welding that make it an ideal joining process for a wide range of applications. But, there are 3 major benefits of the process that you should know of before you implement it in your workshop.
1. Optimal Heat Control
One of the biggest advantages of oxyfuel welding is that the welder has constant control of the heat available at the tip of the welding gun. And with that, you can also control the temperature of the welding zone and avoid problems like oxidizing of the base material. It also helps to maintain the welding atmosphere and keep the base metal strong and reliable for future applications.
2. Optimal Weld Bead Control
Apart from controlling the heat input, you also get control of the weld bead generated during the Oxyfuel welding process. It includes the size of the bead, its shape, and even the viscosity of the molten metal puddle formed after starting the process. It also helps you to understand the amount of filler material needed for the job and avoid introducing excessive filler which can compromise the integrity of the joint.
3. Wide Range of Applications
Oxyfuel welding can be used for a wide range of applications. It is an ideal process if you are working with thin sheets or tubes of metal such as rods or pipes. It can also be installed in a workshop where repair jobs are carried out. Oxyfuel welding can also be introduced to non-ferrous metals along with ferrous metals, which further increases its application diversity.
Required Accessories And Kits For Oxyfuel Welding
Another great benefit of the Oxyfuel welding process is the fact that the equipment or accessories needed for the job are quite affordable and can be used for various other applications in a standard workshop. So if you get a set of versatile and portable Oxyfuel welding accessories, you will be able to use a lot of tools from the set for other applications like bending, preheating, surface treatment, brazing, etc.
It is also possible to make changes in the Oxyfuel welding process by making small changes in the equipment. It allows you to use the process for Oxyfuel cutting instead of welding without any problem. And since the process is usually preferred for metal alloys like low-alloy steel or nonferrous metals, it gets even easier to manipulate the process.
Which Gasses Are Suitable For Oxyfuel Welding?
There are many different types of gasses that are combined with Oxygen and used for Oxyfuel welding. Since Oxygen is always the primary element of the mixture, it is possible to use a variety of gasses for Oxyfuel welding.
And almost all commercially available welding gasses have but one requirement: the need of Oxygen in the mixture to allow a high-temperature flame. So, you could select a gas for Oxyfuel welding from many different options on the market, given that they offer the following properties:
- The generated flame temperature should be high enough for welding or cutting the metal.
- The rate of propagation of the flame should also be high as it increases the efficiency of the process.
- The total amount of heat energy that could be released after burning the gasses mixture should not be too high as it could cause faster fuel consumption.
- The generated flame should offer minimal chemical reaction with the base material, or the filler if one is used for the job.
For the above reasons, a lot of professional welders and welding workshops practice Oxyfuel welding with a mixture of Oxygen and Acetylene. Acetylene is basically a combination of carbon and hydrogen which is then mixed with Oxygen to form an Oxyacetylene mixture. It offers a high welding temperature range and is suitable for cutting through almost all standard metals.
Some other alternatives available for Acetylene mixture are MAPP gas, Propene, natural gas, propylene, and other similar variants. Most of these gasses exhibit the properties stated above and offer a high flame temperature. But, a major disadvantage of most other alternatives is a lower flame propagation rate.
Different Types Of Oxyacetylene Flames
You will also find variations in the flame generated while performing Oxyacetylene welding. There are basically 3 types of flames that you will observe in Oxyfuel welding. These 3 categories are based on the physical appearance of the flame as well as its effect on the base metal. FOr each of these flames, the mixture, or rather the proportions of the Oxyacetylene mixture have to be different.
1. Carburizing/Reducing Oxyacetylene Flame
To generate carburizing Oxyacetylene flame, the Acetylene percentage needs to be higher than that of the Oxygen in the Oxyacetylene mixture. In terms of appearance, carburizing flames appear bluish-white at the beginning with white and blue color in the middle. The edge of the flame also appears purple like other types of Oxyacetylene flames. And as for the temperature, a carburizing flame usually has around 3100°C or 5700°F temperature. This flame is usually introduced for welding, soldering, or brazing applications.
2. Neutral Oxyacetylene Flame
Coming to the next variant, the neutral Oxyacetylene flame shows shades of blue instead of purple inside the flame. While the beginning of the flame appears to be bluish-white, the edge still appears purple. The middle part of the flame has more of a light blue shade and this section is rather long compared to other flame types. This is the most common type of Oxyacetylene flame created using a balanced mixture of Oxygen and Acetylene. Due to the lower temperature level of 3200°C or 5800°F, it results in slower metal melting and does not create a lot of sparks. It also helps to prevent the oxidation of steel since the welding part does not boil.
3. Oxidizing Oxyacetylene Flame
On the other hand, Oxidizing Oxyactylene flame is generated with the help of an Oxygen-rich mixture of gasses. Here, the proportion of Oxygen is higher than that of Acetylene. As a result, an Oxidizing flame has a very high temperature, ranging up to 6300°F or 3400°C. Such high temperatures are usually not recommended for welding since the excessive heat can cause oxidation at the surface and make the weld bead weaker. It is pretty easy to identify Oxidizing flame since it is rather short in length and appears purplish-white at the beginning.
How To Prepare Base Metal For Oxyfuel Welding?
Now that you know the different types of gasses used for Oxyfuel welding and the types of flames generated with the Oxyacetylene mixture, let us talk about the base metal and what you need to do to ensure perfect welding results. Just like all other welding practices, an impure base metal can severely damage the quality of the weld. Impurities such as dirt, oil, and oxide formation on the surface can lead to improper fusion of the metal and even cause porosity due to the combustion of said impurities.
Therefore, it is crucial to remove all the contaminants from the surface before starting the welding process. Apart from that, you also need to consider the thickness of the base material that you are welding using Oxyfuel welding. The thickness of the base metal should create a gap that can be connected using Oxyfuel welding. But, it should not be so thick that the flame cannot penetrate the base metal completely. Usually, sheet metal with 3/16-inch thickness is welded using Oxyfuel welding to create butt joints.
If the material thickness exceeds the 3/16-inch mark, the welder needs to create a root opening or a groove to ensure complete penetration. Workpieces ranging up to ¼-inch thickness also require filler material to create a strong weld bead. And if you are working on a joint-edge on a ¼-inch thick workpiece, you will have to practice beveled-edge welding having 35 to 45 degrees angle of the bevel. Bevelling on both sides of the joint can effectively reduce the amount of filler material needed for the job, and the total fuel consumption along with that.
Oxyfuel Welding On Multiple Layers
Multi-layer welding is a rather rare occurrence in the Oxyfuel welding process and it is only practiced if higher ductility is needed from the workpiece, or if there are multiple layers on the workpiece that are to be welded together. For that, you will have to pass filler material between each layer until the joint is completely filled. Fortunately, the resulting puddle will be smaller since the area that is covered in each pass is also small.
Using oxyfuel welding for multi-layer welding also has some benefits. It allows the welder to get complete penetration of the material without overheating the joint. And since the puddle size is small, the process is easier to control and one can easily avoid problems like oxidation or slag formation. It also introduces grain refinement in the subsequent passes due to the reheating which further increases the ductility of the workpiece.
Quality Of The Weld
The appearance of the weld surely represents the technique used for the process as well as the mastery of the welder who performed the job. However, it does not always show the strength or quality of the weld. From visual inspection, one can only determine the penetration level of the flame or any existing welding defects. If you are noticing improper penetration, it may be caused by an excessively high welding speed or wrong torch or flame handling.
You may also notice the weld to appear overly large or small compared to the base material size. If it is not visually detectable, you can also use weld gauges to determine the size of the weld and see if the results are good enough or not. As for defects like interior cracking or sub-surface porosity, it is pretty hard to notice from visual inspection. But, there are testing methods available for that too. A lot of welders use X-ray testing for a few jobs of the set and repeat the process parameters once all defects are cleared.
Oxyfuel Welding Pressure Requirement
Some welders also seem to be confused when it comes to the pressure control needed for Oxyfuel welding. To put it simply, you just need to understand that the working pressure needed for Oxyfuel welding increases with an increase in the orifice diameter of the tip. You can also easily check the diameter of the tip you are using by comparing its tip number with the catalog created by its manufacturer. But if you know that you have a tip of a smaller number, it most probably has a smaller diameter as well.
What Is An Oxyfuel Welding Rod?
The welding rod that is fused inside the welding joint is also a crucial factor in the whole Oxyfuel welding process. Apart from streamlining the process, it also plays an important role in the overall quality of the weld as well as the strength of the joint. A good quality welding rod allows quick melting so that the free-flowing metal can easily fuse with the base material. It generates a clean and high-quality weld without compromising the composition of the joint. Generally, welding rods are made up of a selection of standard metals such as Steel, Aluminum, Stainless Steel, etc.
What Is An Oxyfuel Welding Flux?
A recurring problem that a lot of welders face is oxidation at the surface of the workpiece at the time of welding. Most of the time, the oxides of metals have a higher melting point than the base metal itself. It results in a viscous surface on the top even after the base metal is properly melted. To avoid that, welding flux is introduced in the process. It basically reacts with the oxides to form a slag. The resultant slag has a lower melting point which allows it to get carried away from the welding bead.
So while maintaining the quality of the weld, welding flux also keeps the base metal clean and efficiently removes the oxides to avoid welding defects. On top of that, it also acts as a protective field to avoid oxidation of the surface by preventing its contact with the surrounding air. Since there is a lot of variation in the melting points of metal oxides, there are currently no standards for Oxyfuel welding fluxes. So, you will have to try out various options and see which one works out the best in your case.
Oxyfuel Cutting Process
As we mentioned earlier, the Oxyfuel process can be used for welding as well as cutting, thus being a versatile option for professional workshops. Oxyfuel cutting is carried out by first bringing the base metal up to its kindling temperature, and then introducing Oxygen to the surface for rapid oxidation, or burning. For example, iron is brought up to 1600°F temperature and then put in contact with Oxygen to form Iron Oxide that gives us immense amounts of heat.
The resultant heat can easily melt through the oxide as well as the base metal. And with that, more of the base metal will get exposed to the Oxygen and the process will continue. This reaction of Oxygen with Iron is the key aspect of cutting via the Oxyfuel process. Once the base material reaches kindling temperature, the rest of the work is done by the continuous supply of Oxygen. Not only does it induce rapid oxidation, but also sweeps off the molten metal with its high-pressure flow.
1. Oxyfuel Cutting On Steel
If you are cutting plain carbon steel with the carbon content being lower than 0.25%, the workpiece could be cut easily using the Oxyfuel process without any special treatment. On the other hand, the process gets a little complicated if we are talking about high-carbon steel. Unlike the previous alloy, high carbon steel reacts with the cutting torch and results in the hardening of the surface.
So in this case, the surface is hardened by heating it above its critical point which is then quenched by the rest of the workpiece, being comparatively colder. It is possible to increase the efficiency of this process with the help of preheating the workpiece up to 600°F before starting the cutting process.
2. Oxyfuel Cutting On Cast Iron
Cast iron has a lower melting temperature than cast iron oxides. So during the Oxyfuel cutting process, the iron tends to melt faster than the Oxide created at its surface. Therefore, a high-pressure oxygen jet is to be applied on the surface to quickly erode the surface when cutting cast iron using the Oxyfuel cutting process.
Preheating is also carried out in this condition to further improve the efficiency of the process. While preheating, the mixture needs to contain a higher amount of Acytelene to obtain optimal results. Some welders also use mild iron welding flux to maintain the high temperature, increasing the effectiveness of the procedure.
Various Tip Sizes For Oxyfuel Welding
The size and material of the tip are also worth taking a look at before you could start the Oxyfuel process. The oxyfuel process can be carried out using any tip without much difference in the flame temperature or type. However, it may cause inefficient burning of the fuel and some tips may end up melting due to excess temperature, hindering the process. Therefore, there are specific types of tips created for different types of Oxyfuel gas mixtures. So, it is recommended to use the right type of tip designed for the fuel you are using.
It is done to simply allow the tip to match the flame propagation and burning velocity based on the type of gas and the overall size of the orifice. With that, the welder can easily obtain an efficient flame temperature as well as a size suitable for the job. You might be surprised to know how effective and economical it can be to choose the right type of welding tip for the job since it has an effect on the cut quality, fuel usage, travel speed, and many other factors.
Conclusion
Whether you are a professional welder or a beginner in the field of Oxyfuel welding, there is always a lot to know and understand in the field, and it would simply help if you keep in touch with the basics and freshen up on the parameters of Oxyfuel welding as well as a cutting process. For that, we have prepared this helpful guide that follows the Oxyfuel process thoroughly and offers a deep insight into the process and its versatility regarding various applications.
Here, you will find all the necessary information about the process, the fuel used, and all the parameters you need to know about. If you are unsure about any parts covered in this guide, you can reach us via the comment section below.
