Cast Iron Welding Procedure [Step-By-Step Guide] - Cruxweld

Cast iron is a brittle, cheap, and thorn in the flesh to fix but used everywhere from workshop to kitchen. It is a calamity to locate a crack in cast iron components for such machine owners. There can be a huge financial loss in replacing the broken part or hiring trained cast iron welding specialists to fuse the crack. You take it as an opportunity to learn how to weld cast iron, a new skill.

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Taking the challenge to welding cast iron flawlessly as a wrong move can destroy your broken part even worse. Stick to the guidelines religiously so that your cast iron welding has no cracks and achieve the internal strength sufficient to withstand the purpose of the component. Your mission to accomplish, how to weld cast iron parts can save your money and time.

The inhouse-weld of cast iron needs thorough research in four key steps to know how to weld cast iron.

• Identification of the alloy
• Thorough cleaning of the part
• Selection of preheat temperature
• Selection of welding technique

1. Identify the type of cast iron

A family of iron-carbon alloys with 2-4% carbon makes them a hard cast iron metal. It is less malleable, less ductile, and doesn’t stretch or deform when heated.  Instead, they crack and making the process of welding enormously difficult.

There are many types, and we show the weldability of cast iron.

Gray cast iron – Weldable with difficulty

White cast iron – Unweldable, almost

Malleable cast iron – Welding changes the properties making it useless

Ductile cast iron – Rarely weldable, slow, and extensive process.

It is always better to determine the type of cast iron from the user manual, manufacturer’s advice. Examine the crack as it changes its character with the passage of time. The weldable cast iron from the kitty is a gray type. This is the only cast iron which can be attempted for the fusion. You may seek help from an experienced cast iron welder for the ideal weld.

2. Cleaning the cast weld surfaces

As in most welding, the cleaner the surface, the better is the welding. Clean the surfaces from paint, grease, oil, and foreign material. Better to apply heat carefully and slowly to the weld area for a shorter time to remove the entrapped gases.

We have designed a simple test to judge the readiness of cast iron. We deposit a weld pass on the metal, in case of impurities, the weld zone will be porous. We will grind this welding pass and repeat the test until the porosity vanishes.

In peening the surface of the component is deformed deliberately by hammering, thus expanding the surface layer laterally. The stable subsurface thus allows expanding the surface layer, which is a beneficial, compressive residual stress layer. A ball-peen hammer to prevent cracking can do it. It is not a mandatory phenomenon that can be a useful tool when a crack is irregular. Preheating and slow cooling of the component is the crux for the cast iron welding procedure.

3. Preheating or cold weld

Welding cast iron has two schools of thought, one is hot, and the other is cold welding. Masses agree to preheat as a better choice while few goes with minimal heat or cold weld. We need to adopt one because unlike other metals the cast iron is brittle and has a minimal ability to deform when bending, contraction, and expansion.

Every metal has a property to deform on heating due to thermal expansion. Suppose one part of metal heats or cools faster than the other, then crack, and stress happens in the cast iron weld. Preheating minimizes this effect of heating near the weld zone, keeping the temperature near similar to the weld zone. It makes the whole component alter uniformly. It is better not to put excessive heat into the component, as cast iron has a character to change once the temperature is over degrees Fahrenheit.

The cold manner of welding cast iron without preheating may be helpful as it reduces the overall temperature. This process is not producing any visible cracks and stronger weld. The looks may be great, but internal strength remains poor in cold welding. 

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We have observed that the trained cast iron welders who are repairing or manufacturing the part, prefer the preheating method only. We need a finished cast iron weld not just visibly crackles but internally strong as well.

4. Choosing welding techniques and consumables

You have determined that gray cast iron is to weld, now it is time to choose the iron welding procedures. The best way to weld cast iron is with each and every welding process, provided you choose the accurate filler material and process. We base the choice of welding process on personal preference, but few factors remain to consider before the conclusion.

If we have come across a machined surface to weld then the preference may be TIG weld as the spatter from a stick and MIG welding cast iron may damage the clean surface. Tig welding remains to spatter free and a choice.

Once you try to curtail the extreme heat and quick cooling of the electric welding process, then oxy-acetylene is the option. It easily maintains the temperature of components and other wonderful options to weld cast iron.

Stick welding is the alternative method for welding cast iron where the electrode with flux is used. The machining is required after we complete this process. The selection of proper filler metal is the foundation of the cast iron welding.

Brazing can be another process of joining the cast iron, but it is not a welding process. You can adapt it when there is trouble in welding for some reason. Dirty or rusty surfaces may not join, so it is essential to cleanse the surfaces. Cast iron welding rod acts as filler material which sticks the surfaces and joins the parts once cooled.

Choosing the Proper Electrode & Wire Consumables

The range of filler wire and electrode that can weld cast iron are tiny. The available in the market are not designed specifically for cast iron only. They can cool quickly, cause stress cracks, and do not join properly. The following are a few available options in the market.

Nickel content-rich: This one is the best available electrode in the market, as it is soft and machinable. Looks are similar to cast iron and it does not cool quickly too. The disadvantage with this electrode is that it is very expensive and not suitable to weld thick sections.

Mix Nickel 55%, Iron 45%: The looks the same as cast iron when it is welded but quite affordable. The weld it produces is machinable but much harder than the nickel weld. The shrinkage is smaller than most iron rods to make the electrode with the least possible cracking.

Iron: The welding with this rod gives a distinct color than cast iron. The shrinking property is evident and makes it a challenge to use in weld cast iron. It hardens during welding but not machinable. It is an economical option and can be ground back.

Stainless steel: Cast iron on joining with stainless steel does not alter the property and harden as with iron consumables. It does not expand and contract significantly during the heating and cooling of the fusion process and poses a challenge to use it. It yields a machinable process after welding.

Bronze brazing: We have a choice to braze with oxy-acetylene or use it with Tig welder. We can provide a strong patch in a crack or between 2 components looking to join. The brazing here will Jon the two surfaces without changing the basic properties of cast iron.

Finish with slow cooling

Cooling is the most crucial part of the cast iron welding process. Slower the cooling, better the results. No dousing of the welded part by anything like chilly water or compressed air in any situation.

Let the cooling may take a few days even for better crack free results. The slow cooling can be achieved by putting the welded parts into sand or a warm oven. Uniform cooling is mandatory, which can not be achieved by cooling on a bench. It is a challenge to achieve a weld quality without extending the cooling time. We can apply periodic heat to cool the part uniformly.

Crack results from the tensile stress of thermal contraction. Once this stress reaches a critical junction, the crack in the weld happens. We may apply compressive stress to decrease the tensile stress which occurs on the cooling of the welding. Peening is the process which can be a significant help to prevent crack.

In Closing

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