Are you looking for ways to weld cast iron? Brazing cast iron is one of the best solutions. It’s an easy-to-learn and cost-effective technique that can save you time and money.
In this article, we’ll explain exactly what brazing does, how it works, and what rod is best for braze welding. We’ll also answer questions like “Can cast iron be brazed?” and “Can you braze cast iron with MAPP gas?”.
Brazing cast iron is an excellent alternative to welding because it doesn’t require a lot of heat or special tools or skills. This makes it a great choice for DIYers or people starting in the repair industry.
Plus, it’s much easier to clean up afterward than other options such as torch welding.
So, if you’re looking for ways to repair cast iron without spending too much time or money, let’s get started learning about how to braze cast iron!
Contents
Introduction to braze welding
Braze welding is a useful process that blends various metals to create a strong, cohesive bond. It is often used to weld white cast iron and malleable cast iron parts together.
The process involves using a molten filler material, usually a steel or nickel shot, and a high heat source such as a torch to preheat or slow cooling medium.
The melted filler then bonds and seals the two pieces of metal together.
The strength of the welded cast iron can be tested by performing a fracture test. This is done by applying stress to the braze welded parts to evaluate any potential weaknesses in the welding joint. Once identified, these weaknesses can be corrected and the braze weld repaired to ensure that the resulting component is of high quality and will stand up to regular use!
Braze welding is suitable for grey, austenitic, and malleable cast irons. However joint strength equivalent to fusion welds is only possible with grey cast iron.
Types of cast iron for braze welding
Braze welding is an important process for joining two pieces of metal without melting either of them. It involves using heat, filler metal, and flux to create a bond between the two metals.
When it comes to braze welding cast iron, several different types can be used. These include:
White Cast Iron
White cast iron does not deposit carbon as graphite; instead, it retains carbon in the form of iron carbide. This type of cast iron is very hard and brittle, making it difficult to weld. As a result, it must be preheated before any welding can take place.
Malleable Cast Iron
Due to its malleable nature and ductile iron chemical composition, it is better equipped to endure the extremely high temperatures involved in welding. In addition, malleable cast iron is also easier to weld due to its lower melting point.
Filler Metals
Filler metals are used to create a stronger bond between two pieces of metal when braze welding. Commonly used cast iron filler metals for braze welding include steel and nickel shot, although other alloys may also be used depending on the application.
Grey Cast Iron
Grey cast iron is often used when braze welding because it has a low melting point and good strength properties.
However, gray iron still presents a challenge for aspiring welders because graphite flakes can get into the weld pool and weaken the weld metal.
When braze welding with any type of cast iron, it’s important to remember that the filler material must be heated until it is fully molten before being applied and allowed to cool completely before inspecting the joint.
Filler metals for brazing steel & cast iron
Brazing steel and cast iron require different filler metals. For steel, a mild steel filler metal is best; for cast iron, brass or bronze are considered preferable.
To ensure proper bonding between the two metals, it is important to select the correct filler metal that melting temperature and flows at the same temperature as the joint pieces.
Malleable cast iron is an ideal material for welding with brass or bronze: its low melting point allows for fast, efficient heating and cooling of the weld area. Gray cast iron is a harder material suitable for welding with nickel shot.
When using low-temperature welding methods such as oxy-fusion welding, it is important to select the right alloy that will provide optimal joint strength. The advantage of fusion welding is the filler metal and the base metal melt, mix, and solidify.
It is also recommended to perform a fracture test on the completed weld metal to verify the strength of the joint. The test should be repeated after heat treatment has been done to ensure proper restoration of the part’s integrity.
Preparing for the brazing process
Preparation is key to a successful brazing process. The components to be brazed must be adequately prepared and the equipment should be ready and functioning properly. The edges of the two pieces should also be clean and free of any foreign material.
Cleaning components
To ensure a uniform application, base metal as well as the weld zone should be cleaned before the brazing process. The typical cleaning methods used for steel as well as nickel shot include grinding, sandblasting, or wire brushing.
Filler material selection
The most commonly used filler materials for white cast irons, malleable cast irons, steel, and nickel shot are bronze, silver, or copper-based alloys.
Copper-based alloys are preferred for gray cast iron because they provide good fluidity and strength in low temperatures.
Additionally, copper-based alloys have excellent corrosion resistance properties which make them suitable for use in highly corrosive environments.
Heat preparation
The molten filler material must reach its melting point to form a strong bond between the two pieces being brazed.
This is done by preheating the components using oxy welding or other heat sources such as blow torches with slightly oxidizing flame or furnaces before the actual braze welding takes place.
After the weld is complete, it is important to perform a fracture test to determine its strength and integrity before using it in any application.
Cast irons can be soldered without melting the base metal because the soldering rod already contains a flux.
The fluidity of molten filler metal
When it comes to braze welding for white and gray cast irons, the most important factor is the flow rate of the molten filler metal.
This determines whether or not the weld is successful. The molten filler material should be able to flow freely and penetrate the edges of both pieces that are being welded together.
To ensure a successful weld cast iron, there are several steps you will need to take:
- Make sure you select the right filler metal for your project. Steel or nickel shot is typically used for braze welding gray cast irons, while oxyacetylene welding can also be used.
- Heat both pieces at the same time before adding any filler metal to limit any potential thermal shock.
- Use adequate amounts of filler metal and make sure it completely penetrates both pieces that are being joined together.
- Once the weld has been completed, do a fracture test to ensure that there is enough strength and integrity within your weld repair or joint.
Following these steps will help ensure that your braze metal job is done properly, resulting in greater heat conduction and less likelihood of fracturing or cracking with heat treatment.
Troubleshooting & repair techniques
If you’re braze welding on white cast iron or malleable cast iron, there are a few troubleshooting and repair techniques you should be aware of.
Filler metals
When welding on white cast iron or malleable cast iron, it is important to use the correct filler metals that give off low levels of hydrogen when heated. This will prevent micro-fissures, or tiny fractures in the weld metal, which can degrade the joint strength.
Gray cast iron castings
When welding on grey cast iron, it is important to first ensure that it is dry before applying the molten metal. If the material isn’t dry, the weld could come apart due to porosity or cracking.
Steel & nickel shot
If welding on nickel or steel shot surfaces, make sure that the surfaces are free of unwelded pieces of metal before continuing with your oxyacetylene welding process.
Otherwise, they may cause weak spots in your welds.
Fracture test
Finally, if you need to perform any weld repair work on larger jobs such as boilers and pressure vessels, always perform a fracture test afterward to ensure there were no structural weaknesses caused by the repairs. Since welding stresses are challenging to remove from the heat-affected zone, fractures are prone to spread over time.
Conclusion
Brazing cast irons can be a tricky process, but with the right tools, a good understanding of the technique, and practice, you can be successful. Brazing cast iron with MAPP gas is possible but not optimal as the temperature is not sufficient for a strong, lasting repair.
Using flux and a proper brazing rod, however, can yield quality results. Keep in mind, safety should be your top priority when working with a flame and brazing rod.
Make sure you follow all safety guidelines and wear the proper safety equipment to ensure the best results.
FAQ
You may have plenty of questions about brazing cast iron and that’s understandable. Here are the answers to some of the most frequently asked questions:
Can cast iron be brazed?
Yes, cast iron can be brazed. It is a great way to join two pieces of metal together without the need to weld them. Welding of cast iron is carried out using a higher current than that for shielded metal arc welding.
Brazing cast iron should not lose any of its base metal properties during the brazing heating process. However, you must use the right equipment and follow safety guidelines otherwise you might end up with a poor-quality joint that won’t last long.
What rod is best for brazing cast iron?
A brass-based rod is the best choice for brazing cast iron. These rods contain less phosphorus than other rods, which helps reduce the risk of cracking during cooling.
The brass also prevents any oxidation caused by heat treatment as it melts easily and forms a strong bond between two surfaces.
Can you braze cast iron with MAPP gas?
Yes, MAPP gas can be used for brazing cast iron but it is not recommended as it produces more heat than other gasses, making it more likely for the joint to crack during cooling down.
It is better to use an acetylene-oxygen fuel torch for this job, which will provide a smoother application of heat and will make it easier to form an airtight seal between two pieces of metal.