Stephan de Bruin is a game and vegetable farmer, but he’s also a fitter and turner with a passion for steel and engines. By just listening to a running engine, he is often able to tell where the problem lies and how to fix it. He says farmers often struggle with welding – not because they don’t know how, but simply because they’re using the wrong equipment or failed to prepare the steel properly.
It’s very important to give the steel a proper sanding to remove any rust, oil and paint before you start with any welding. It’s especially important to sand down the stained steel where it’s been cut with a cutting torch. The blue burn marks are actually a layer of oxidation and no welding will bind to it properly.
With cast iron you need to sand down the spot where you’d like to weld with a grinder first. It’s especially when people are mending exhaust and inlet manifolds that they’re prone to weld on top of the rusted steel. It won’t last.
Once everything has been sanded down properly and you have a shiny layer of steel to weld on, heat the entire area you’d like to weld with a gas flame until the steel has gone a cherry red colour from the heat. Allow a minute or two for the heat to spread before you start welding.
Without this method, the manifold will break at exactly the spot you’ve welded it as soon as it heats up.
Choose the right rods
The correct selection of welding rods will determine how easy or difficult a welding job is going to be. Rods that are too thick will easily burn holes in the steel. Weld steel thinner than 1,2 mm with 2 mm rod and steel from 1,2 mm to 5 mm thick with a 2,5 mm rod. For thicker steel and large channel irons you can use 3,5 mm rods.
Use low hydrogen electrodes for much tougher steel and not for mild steel. Any vibration will cause the steel next to the welding spot to crack. Use it, for example, to reattach the head of a bolt or to weld tougher metals, like Benox and Rocktuff.
What about holes?
It’s not the end of the world if you burn a hole in the steel, but it takes some patience to repair it properly. Remove all the solder from the damaged spot and ensure that the edges are clean. Use a 2 mm electrode and start welding small dots around the opening. The 2 mm rod works at a lower temperature which will prevent you from burning an even bigger hole.
Don’t try to weld in a solid line around the gap. It could cause the steel to heat up and create an even bigger opening. It’s important that you remember to remove the solder once you’ve done the first set of dots. Continue in this fashion until the hole is covered.