Galvanized metal is a modern-day miracle. Metals tend to corrode and oxidize over time, due to the oxygen present in the air, and this can ruin metal items and even make metal structures unstable and dangerous. Galvanization is the adding of a protective layer of zinc over a ferrous metal surface such as steel that keeps it from corroding and does it at a much cheaper rate than, say, stainless steel.
But metals need to be welded together if you want to use them in any industrial process. How do you weld galvanized metal?
Can You Weld Galvanized Metals?
Galvanized metals such as steel can be welded in a similar way to uncoated steel if it is adequately prepared. If you try to weld it without doing away with the galvanizing layer from the area that is to be welded, the weld puddle pops and blows out, making it a safety hazard to anyone around.
Though the heat from the arc can quickly burn off the zinc layer, the weld produced could have issues like porosity, an unsatisfactory bead, lack of fusion, and too much spatter. The weld can burn the zinc off, but porosity is almost inevitable and is mainly only dependent on how thick the zinc coating is.
Preparing to Weld Galvanized Steel
The best way to weld galvanized steel is to get rid of the zinc coating, regardless of which welding process you are going to use. This means that you will have to add two tasks: removal of coating and respraying the weld seam after the weld is complete to regain the corrosion resistance that is lost. In some cases, respraying or painting is done even if the zinc coat was not removed before the process.
Though two processes are added, you can eliminate or at least dramatically reduce the amount of spatter that is produced as well as the amount of cleanup work this way. Porosity, lack of fusion, and cracking should also be removed. Usually, removing the zinc coat before the weld reduces reworking tasks, and so dramatically reduces the overall cost of the weld.
Once the zinc coat is removed, the steel can be welded just like you would weld regular, uncoated carbon steel. An important aspect to keep in mind is that you should leave the workspace before you take off your mask, and give the area a decent amount of time for it to air out.
How Does Welding Galvanized Steel Work?
Once you’ve ground the zinc coating from the area you’re going to weld, place the pieces together on the work surface in the arrangement you want to set them in. If you lay the pieces on the floor, you should make sure you’re not welding on a combustible surface.
Clamp the pieces with a welding clamp to hold them together, and then you can start welding. For galvanized steel, a standard arc welder is probably the best way since arc welding is versatile, and the alternating currents allow you to create a good arc that can melt the flux quickly. Arc welding sometimes creates flux, so you may want to work outside if possible.
Select the welding rod you will use based on the size of the metal. Bigger rods weld larger areas than smaller rods, and there is no difference in rods for regular metals or galvanized metals. Weld your workpieces together.
Preventing Corrosion When Welding Galvanized Steel
Maintaining corrosion resistance after welding is another hurdle to overcome with welding galvanized steel. The zinc coating around the weld burns away and leaves the area uncovered and hence exposed. If corrosion resistance is still needed after the welding is complete, you might have to paint or re-galvanize the material.
Safety Hazards of Welding Galvanized Metals
The difference between welding of galvanized steel and regular steel is that the zinc coating around the galvanized metal has a very low vaporization temperature compared to the steel. Since the welding process involves melting the steel itself, the zinc around it doesn’t stand a chance against the extremely high temperatures of the welding arc and burns off.
When it burns, the zinc vaporizes immediately and adds to the volume of welding smoke and fumes. This vapor then mixes and reacts almost instantly with the oxygen in the air to become zinc oxide. Zinc oxide, on its own, is non-toxic and non-carcinogenic, and though breathing in these fumes could cause some temporary effects, there are no long-term health risks. However, this is not where the safety hazard lies.
Most zinc that is used for galvanization has a natural lead composition of about 0.5%. Lead is not soluble in zinc over 0.9%, so the amount of lead used in zinc also has a concentration of a maximum of 0.9%. Lead vaporizes with the zinc during welding and mixes with oxygen to form lead oxide.
Lead oxide, unlike zinc oxide, is an extremely toxic compound which should not be inhaled, since it can cause not just temporary health effects such as headaches and nausea, but also more severe conditions such as anemia, kidney dysfunction, and even cancer.
Safety measures taken to avoid inhalation of zinc oxide will also prevent you from inhaling lead oxide fumes.
Safety Measures to Take When Welding Galvanized Steel
When welding galvanized steel, you should make sure to avoid the fumes. By getting a good welding mask and a respirator that is designed for welding metal, you can avoid inhaling these fumes in, and a pair of welding gloves and an apron can protect your hands and clothes.
It would help if you also looked into getting helmets and masks that manage to avoid fumes rising into the hood itself since many workers who have to stand in one place for a long time might face this problem. A helmet that covers the front of the neck is much safer in terms of avoiding fumes than an open neck helmet.
Fume extractors can help get the fumes out of the environment you’re working in to make it safer for you to breathe. If possible, you should try to weld outside, and if you are indoors, keep as many windows open as possible.
Make sure to ground the welder to prevent shocks from electrical currents. If you are working outdoors, you would want to ground the object itself as well.
Why Can’t You Galvanize After Welding?
It is a lot easier and a lot less costly to galvanize steel before welding than to do it after. Though in the past, steel products were galvanized after welding because there used to be no practical method of restoring the effectiveness of galvanization after the welding process was complete.
However, now, this is not the case. This is because now the process of galvanizing after welding has to be carried out very carefully, since water can get trapped, and rough finishes do not top coat very easily. Zinc deposits from welding can also cause trouble when galvanizing after you have already welded the steel, and the process can be very time consuming and requires a lot of care.
Galvanize before welding, as it results in smoother surfaces and more uniform appearances.
What happens if you weld galvanized steel directly?
If you weld galvanized steel without first getting rid of the zinc coating through processes like grinding, the welding process would produce emissions of dense, noxious, yellow-green smoke. This smoke can envelop the welder(s) if proper ventilation measures have not been taken, and continuous exposure could even result in galvanizing poisoning. The symptoms for this are headaches and nausea and can be removed by moving to a location with fresh air and drinking milk to help your stomach settle.
What method is best suited to welding galvanized steel?
Flux core welding is the preferred method for metals that have been galvanized. It is a more tolerant process when it comes to the existence of contaminants such as rust, and the flux in the core will bring these contaminants up to the surface and allow them to be burnt off into the air, or get trapped in the slag that is a byproduct of the welding process.
Why do welders drink milk?
When welding metals, there could be an issue of inhaling metal vapor, which can prove to be quite dangerous if the metal is toxic, and can cause ‘metal fume fever’ even if it is not. Although the concept of drinking milk to avoid these side effects altogether is a myth, nausea, and heaviness of the metals inhaled can be settled by drinking milk after or during welding. Some people suggest holding the milk in your mouth; since this will force you to breathe in through your nose and could disturb your respiratory system, it is not recommended.