How To Improve Safety When Welding Cast Iron?

Welding cast iron is one of the most difficult to achieve. Although you can accomplish various in-house welding tasks, it is highly recommendable to engage the experience of a welding professional. According to experts, this will help you avoid the problems that occur during welding. Unlike wrought iron and steel, cast iron is very brittle and less ductile. It can easily crack during heating or cooling. Various other factors influence the outcome you get from welding cast iron. For industries, it is critical to creating safe welding conditions for strong, durable cast iron welds and joints. Here is a brief look at how to improve safety when welding cast iron.

1. Choose the right alloy

Cast iron belongs to a large family of iron-carbon alloys. As such, there are various kinds of cast iron welding alloys available on the market. Because of the high carbon content, cast iron is very hard. However, the same property makes them less malleable and ductile. Some cast iron is very brittle that it is practically impossible to weld them effectively. Others are much easier to work with. Cast iron does not expand or deform during heating. This can result in the quick buildup of tensile stress during the heating-cooling cycles. When the material reaches critical tension, it cracks. To avoid this, expert welders recommend adding different alloys.

 Grey cast iron is the most popular form available on the market. It depicts a crystalline microstructure that comes from graphite flake precipitates that form naturally during manufacturing. Grey cast iron is more ductile and malleable, making it easy to weld. The only downside is that graphite flakes can enter the weld pool, causing embrittlement of weld material. Another common choice is white cast iron. Rather than precipitating graphite flakes, white cast iron holds the carbon inside, making it very hard and brittle.

2. Clean the welding area and base metal

It is essential to prepare the casting and ensure all materials are clean before welding. Regardless of the alloy you choose, no surface materials such as grease, paint, oil or foreign residue should be present in the casting. A clean surface significantly improves wetting and bonding. It also removes any compounds that might compromise the structure of the weld.

It is recommendable to apply heat carefully and gently to the weld area. This will aid the escape of entrapped air and gas from the base metals and weld zone. To determine if your cast iron surface is ready, you can deposit a weld pass on the surface. If there are impurities on the surface, the weld pass will be porous. Grind off the pass, clean the surface and reapply until there are no more impurities.

3. Heat control

According to experts, heat control is a very crucial part of cast iron welding safety. All forms of cast iron are vulnerable to cracking under critical stress. A quintessential cast iron weld involves three steps that require heat control. These are:

Pre-heating

Most metals expand when you apply heat to them. This thermal expansion varies from metal to metal. When a metal warms and expands at the same rate in all places, it causes no stress. However, when you apply heat on a localized section surrounded by colder metals, pressure builds up, and the metal may crack if the tension reaches a critical point. This is very popular when welding cast iron.

The primary goal of pre-heating is to control thermal expansion. Since cast irons have relatively poor ductility, pre-heating reduces thermal gradient across the casting surfaces, thereby minimizing tensile stress between the casting body and heat-affected zone (HZ). The pre-heat temperature will depend on your welding temperature. If you are welding at high temperatures, you will need higher pre-heat temperatures as well.

Low heat application

Welding cast iron requires low heat application. The goal behind low controlled heat is to regulate thermal expansion. It also ensures the tensile stress builds up slowly. Small heat application also prevents cracking. Use low-temperature welding process and low melting point welding rods.

Slow cooling

The cooling rate is another critical factor in the safety and effectiveness of a cast iron weld. Rapid cooling will result in brittle welds that easily crack. There are two main methods you can use to slow down the cooling rate. The first is to cover the weld using an insulating material. The second method involves applying periodic heat to the weld. This disrupts the natural cooling rate.

4. Choose a suitable welding technique

Various welding techniques work for cast iron. When choosing a welding process, pay close attention to the weldability of the cast iron and alloy you are welding. Some of the best welding techniques you can use include:

Stick welding (shielded metal arc welding SMMA) - uses flux-covered consumable electrodes to weld.

Oxy-acetylene welding - uses electrodes and energy from an oxy-acetylene torch to weld.

Braze welding - uses a filler rod to join cast iron parts.

Conclusion 

Ensuring safety when welding cast iron is something you can achieve with minimal effort. It is vital to work with high-quality weld materials and supplies. If you are welding critical parts, you can benefit from contracting welding experts. This kind of welding requires precision and experience. You should also choose the right welding technique.