Last Updated: April 1, 2021 by Louis Sham
One of the meticulous tasks is to weld cast iron, as it demands expensive equipment and high heat. Along with that, to have the knowledge of How to Weld Cast Iron is also crucial. To have a proper understanding of each step will eventually help you carry out this task effortlessly.
Welding a cast iron involves a series of steps like identifying the various kinds of alloy, selecting the electrode to clean the cast, and most importantly making sure of the temperature. No matter how tough they seem, once you get the grip on it, you are good to go.
These guidelines are directed toward a detailed version of how to weld cast iron, stay connected for a systematic summary of how to weld cast iron in the end.
How to Weld Cast Iron – Step by Step 2021
In order to have a durable cast iron weld, one requires the in-depth knowledge of each step involved in the process. Following seven steps in order would enable you to produce an extremely long-lasting cast iron weld.
1. Suitable Alloy For Your Welding Type
Each cast iron is composed of carbon-rich content as it comes from an iron-carbon family. Due to this, it attains an overall tough shape. Comparatively, the cast iron is a lot less malleable than even iron or steel as per its ductile nature.
Above reasons justify the natural expansion and contraction of the metal while the welding takes place and is heated or cooled during the process. As a result, tensile stress is created.
Tensile stress causes the welding of cast iron a bit difficult due to the heat and stress. Heating leads to cracks in them rather than the expected deformation or stretching. Nevertheless, it can still be controlled by choosing suitable alloys as per the situation.
2. Choice of Electrode
Depending upon the requirement of the single-pass or multiple pass welds, you can choose Tech-Rod 99 or Tech-Rod 55 respectively. However, generally, if you are planning to machine the welded parts, then the nickel-type electrode should be the first hand.
Moreover, to avoid rusting of the cast iron after welding, the Lincoln Ferro weld electrode is preferable. In Tech-Rod 99, root passes can be adjusted while Tech-Rod 55 demands fill passes for successful welding.
3. Preparing Clean Cast Iron
Working in a messy environment will not only increase your workload but will affect the quality of your production too. Therefore, it is necessary to initiate the task with a completely clean area.
Starting with the removal of unnecessary materials from the cast iron surface. Cast iron should be free of grease, oil, dust, paint, and any disruptive material. Also, the focus should be to reach a smooth texture of the cast iron.
Impurities, especially in a metal can adulterate your preparation by increasing its porosity. This troubling phenomenon can be minimized by continuously grinding off the pass. Which in turn makes your base metal’s weld area stronger by reducing any gas trapped in it.
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4. Pre-Heating Cast Iron Before Welding
Cast irons are thermo-sensitive. A slight change in temperature can affect its construction. Therefore, you must maintain the desired temperature throughout the preparation.
Overheating your metal weld or shifting between extreme temperature differences such as from very high temperature to very low temperature or vice versa can crack or fracture your cast iron creating too much stress.
While welding, tensile stress is induced that can increase the thermal gradient between the casting body and the heat-affected area. High temperature pre-heating is performed with high power welding machines to reduce this undesirable effect.
With the help of a blowtorch or even a car engine, welders can easily pre-heat the material. Optimum temperature for pre-heating the cast iron is between 260–650 degrees Celsius. Avoid reaching temperatures over 780 degrees that cause overheating.
Variety of methods are available for preheating. It is advisable to start pre-heating at low temperatures using welding rods or wires with low melting. Welders can also choose to insulate the material when required.
Additionally, after the pre-heating step, the post-heating procedure can be followed to avoid cracks and achieve the desired welded cast iron. Both these processes hold equal importance in welding cast iron.
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5. Appropriate Welding Technique
Depending on the alloy welded and the size of the metal, you can decide which welding technique is suitable for you. So far, we have discussed four key steps that can guide you better in deciding which welding technique will work best for you for a particular task.
6. Closing Undesired Cracks
As per the characteristics of cast iron, even with the best welding process, it results in the formation of tiny cracks in them. Mainly due to the iron cast being water-tight, a problem arises in that case.
The problem of leaking must be avoided with the help of some sealing compound. Otherwise, there is a chance of the iron cast catching rust very soon after the welding process is over.
7. Ultimate Finishing Touch – Defining Point
Just as the initiating step is important during the welding process, the final step of finishing the weld is very crucial too. After the welding process, when cooling occurs the cast iron develops tensile stress and contracts.
During the thermal contraction process, there is a high probability of the iron cast metal to form cracks. Especially when the stress extends to a critical point. However, application of compressive stress may help oppose tensile stress that causes cracks.
Welders adopt a technique known as peening which involves welding a soft weld when it is on the verge of being deformed. It consists of a ball-peen hammer that the welder uses to execute adequate strikes on the soft weld.
Although this technique can only be carried out when the metal being welded is malleable. Nevertheless, this particular technique is successful in reducing the chances of any cracks in the weld as it targets to protect the heat-affected zone.
Lastly, what you need to know about how to weld cast iron are its cooling requirements. Having a proper grip on the cooling controls involves gradual cooling through the help of appropriate insulating materials.
To naturally and gradually cool the cast iron, time-to-time heat can be provided to the weld. It will guarantee a smooth finish of the cast iron weld.
8 Steps Involved In Welding Cast Iron
Step 1: Consider heating or cooling the cast iron at different points of welding. The range between 150 – 500 degrees Fahrenheit (65 to 260 Celsius) must be avoided. At this temperature, the cast iron is very unstable and challenging to work on.
Step 2: From the range of 500 to 1,200 °F (260 to 649 °C), preheat the cast iron pieces that are needed to be welded with appropriate temperatures.
Step3: The iron weld must be cool but not so cold. Even if it reaches a higher level of cold, it can be returned to the desired temperature with the help of machinery.
Step 4: At times of urgency, the repair patch may require to be touched with bare hands. Therefore, they should be cool. Hotter or colder patches are not suitable for the weld, as they will take longer to reach the ideal temperature.
Different iron casts require different temperatures. Consequently, it is better to consult the engineering specifications document to find the suitable temperature for your desired iron compound.
Step 5: Keep the cast iron intact through avoiding and mending any cracks and rips in the cast iron caused.
Step 6: To keep the nearby metal from overheating, there must be a space of about 1 inch (2.5cm) long between short welding patches.
Step 7: Techniques like studding can repair and finish even the major cracks caused. By using the drill machine and making holes in the cast iron, the welder attaches the patch with the screw. The weld is then placed in its part and repaired.
Step 8: It is completely normal to still have a few small cracks in the iron cast weld after all the process. By using sealing compounds, it is possible to make the joints and sections watertight.
To know how to weld cast iron is very complex, yet necessary to perform the task successfully. Preparation and careful heating and cooling is the key. It is common to weld the cast iron but to produce a strong iron cast weld that will last a lifetime is no easy task.
By following all the mentioned steps above, one can fulfil the best iron cast weld criteria. Never opt for short cuts as they would just ruin your cast iron project and end up in cracks or low efficient material that will not last long.