How to Weld Cast Iron Effectively; Steps Involve

As there is a general knowledge that cast iron welding is difficult, welding cast iron effectively is often asked by people who want to overcome the difficulties they encounter.

Before getting into the how-to's, we would answer commonly asked questions about cast iron and its welding.

This is to enable you to learn about cast iron and the reason for specific procedures in this article.

Frequently Asked Questions about Cast Iron Welding:

Is it possible to weld cast iron?

Yes, it is doable to weld cast iron. However, it isn't easy because it is made up of different materials (usually iron, carbon, and steel) at different proportions.

This makes it hard to identify how strong the metal you're working with is and how much heat it can withstand before cracking.

     #  What welding technique is the best to use? Every welding technique has its pros and cons. Therefore, the best welding technique to use in welding cast iron would be dependent on their suitability to the cast iron alloy being welded.

   #  What are the best rods to use for welding? 99% Nickel rods. This rod produces highly machinable welds that work best on casting with low or medium phosphorus contents. They are, however, expensive to purchase.

Pre-Steps to Cast Iron Welding:

Before getting right into the welding process, there are steps to ensure that the iron welded does not suffer a crack and choose the right welding process to use. These steps include:

Identifying the Alloy:

This is the first pre-step to be taken. Not correctly placing the alloy you are about to weld can cause a crack during the welding process. The different alloys of cast iron are:

Grey Cast Iron:

This shows grey and a fracture point due to the graphite in its microstructure.

White Cast Iron:

This is whiter along a fracture due to its cementite.

Ductile, nodular, or malleable iron:

This alloy is also entirely white along the fracture. However, it is much more weldable than White Cast Iron.

Selecting a preheat temperature:

As cast iron is prone to cracking under stress, a proper heat control mechanism should be set in place to avoid breaking. The process of ensuring this includes Preheating — Low heat input — Post-heating Cooling.

Preheating and Post-heating cooling are performed because cast iron undergoes thermal expansion due to its temperamental nature. When warmed, it expands. Besides, a too-quick change from room temperature to welding temperature builds stress on the metal, causing it to crack. In like manner, if the cast iron cools too fast after welding, contraction occurs, this creates brittle and easily fractured welds.

Preheating is done between the temperature of 260- 650 degrees Celsius. Once the welding temperature goes above 780 degrees Celsius, overheating occurs. It is performed by using a blowtorch to heat the material.

When proper heating is not obtainable, one should minimize heat input — select a low-temperature welding process and low melting point welding rods or wires.
Post-heating Cooling is obtained by using a Charcoal BBQ to sit the piece of iron in a bucket of sand or by placing the chip on top of a wood fire oven, allowing it to cool down as the fire dies. This eliminates fast calm, thereby reducing hardening and contraction stress.

Selecting a Rod:

The commonly used rods for welding are 99% Nickel rods, 55% Nickel rods, and Steel rods. Each of these rods has its advantages. 99% of Nickel rods being the most recommended as it is highly machinable.

The 55% of Nickel rods are also machineable and used in repairing thick sections. When doing simple repairs and fillers in the home, Steel rods are recommended. They are user-friendly when arc welding and can tolerate castings that are not entirely clean before welding.

Unfortunately, they are not machineable and produce hard welds, requiring some extra grinding to finish.

Selecting an appropriate welding technique:

The proper welding technique chosen is dependent on the type of alloy to be welded and the welder's level of expertise. According to Industrial Metal Supply Co., the best welding technique beginners should start with is the inert metal gas (MIG).

WELDING TECHNIQUES

Metal inert gas (MIG):

This type of welding is also known as Gas Metal Arc Welding. It is a form of electric arc welding based on creating an electrical circuit running through the objects to be welded together and a welding wire to act as an electrode. Nickel and Steel electrodes are suitable for this welding technique.

Once the welding wire touches the metal object, the circuit gets completed. The wire is pulled back a short distance. This causes an electric arc that heats up to about 10,000 degrees Fahrenheit, thereby melting the wire and partly melting the two metal pieces. This then creates a melt pool where the three metals merge and become one as it solidifies.

As the welding continues down the seam, the wire melts off as more is continuously input from the welding gun's tip. Simultaneously, the gas is diffused from the arc. Then it spreads around the bend to shield the welded area from contaminants such as oxygen and nitrogen.

Oxy-acetylene welding:

Oxy-acetylene welding also uses electrodes, but rather than an arc generated by the current, an oxy-acetylene torch provides the energy for welding. Cast iron electrodes, and copper-zinc electrodes, are both suitable for oxy-acetylene welding of cast iron. The welding rod is to be melted in the molten weld pool and not directly from the flame to minimize temperature gradients, which could cause a crack.

The welder must take proper care to oxidize the cast iron during oxy-acetylene welding. This causes silicon loss and the formation of white iron on the weld.

Stick Welding of Cast Iron:

This technique is known as shielded metal arc welding or MMA. It makes use of a consumable electrode covered with flux. Depending on the amount of machining to be done, application, and color match needed, different electrodes can be used.

An electric arc that is placed between the electrode and welding melts the metals, thereby causing fusion. This arc is to be directed at the weld pool and not the base metal to minimize dilution. To reduce heat stress, one should use the lowest current setting approved by the manufacturer. The pieces should then be preheated to 260°F before welding using copper or cast iron electrodes. Nickel electrodes can, however, be used without having to preheat.

The above methods of welding cast iron all make use of an electrode. Each of them has electrodes that work well with them, and this should always be remembered when selecting a welding method.

Selecting a Welding Equipment:

When looking to find welding equipment, one can choose either a MIG welder or a MIG/Stick/TIG, which can be used for all types of arc welding. The TIG welder offers a weld that can be very precise and require little cleanup/grinding when done.

The TIG, however, runs slower than a MIG, so if you have a very long weld to do, a MIG welder is recommended. A MIG welder might be the answer for production runs, but if you are looking for short-run, highly precise welds, then consider a TIG.

With the information above, one can successfully 

 (a) identify the alloy of cast iron to be welded,

 (b) select an appropriate welding method

 (c) And purchase all of the pieces of equipment and tools needed to repair/fill cast iron.

Safety tools include:

(a) Cap/Welding Helmet: This is to protect the entire face from the electric arc's light and heat.
(b) Sturdy leather gloves and shoes.
(c) Long-sleeved cotton shirts
(d) Overalls, or aprons to protect their skin from sparks.

Conclusion:

Cast iron welding is often time seen as impossible because of its difficulty level and its many easy to make mistakes. However, with proper care, anyone can afford to properly weld it, whether for home repairs or as a job.

Leave a comment below, let us know how your cast iron welding went after reading this article.