Straight answers to the questions people ask when choosing, cleaning and replacing MIG torch gas nozzles.
Is a bigger nozzle bore always better?
Not always. A larger bore gives the shielding gas more room and is usually the better choice for higher currents, but it can make it harder to reach the joint. A sensible rule is to choose the largest bore that still lets you get at the work.
A nozzle that is more constricted around the contact tip tends to collect spatter faster, and spatter build-up restricts the gas flow and can lead to porosity. If you move to a larger contact tip or a different wire size, check that the nozzle still suits it, and follow the torch maker's guidance on nozzle choice.
How do I know when spatter in the nozzle is a problem, and how do I clean it?
Spatter that builds up in the nozzle, and on the contact tip and diffuser, can restrict the shielding gas or make it turbulent, which causes porosity. If you see rough, pitted welds, a hissing or uneven gas flow, or a visible crust inside the nozzle, it is time to clean.
Let the torch cool, remove the nozzle and clear the spatter with the proper tool, such as welder's pliers or a reamer. Replace the nozzle if it is too damaged to clean. While it is off, check that the diffuser's gas ports are clear.
How much shielding gas flow should I use with my nozzle?
There is no single figure. The right flow depends on the nozzle bore, the welding current, the gas and any draughts, so start from the welding wire maker's or gas supplier's guidance and the machine manual.
More is not better. If the flow is set too high it can cause turbulence in the gas column, which draws air in and causes porosity as well as wasting gas. If you get porosity, check for leaks, spatter in the nozzle and draughts before simply raising the flow.
What is the difference between cylindrical, conical and bottleneck nozzles?
A straight (cylindrical) nozzle has a constant bore and is generally used where a wide, steady gas shield is wanted, including at higher currents, but it can limit access to the joint. A tapered (conical) nozzle narrows towards the end, which gives a better view of the weld and easier access, and is a common all-round choice for manual welding.
A bottleneck nozzle steps down at the end to reach deeper or more restricted joints. Because its front end is more constricted around the tip, it may collect spatter faster and need cleaning more often. Choose the shape for the joint access you need, and make sure the nozzle is the one designed for your torch.
Why do draughts matter, and can a nozzle fix them?
Moving air can blow the shielding gas away from the weld pool, which allows porosity. A bigger nozzle will not cure a strong draught, and simply increasing the gas flow can make things worse through turbulence.
The better fix is to screen the work area, keep fans from blowing across the weld and position the work out of the airflow. A nozzle held close to the work also gives better protection than one held too far away. For outdoor work, a windbreak is usually the first thing to try.
How do I check the nozzle is not leaking gas or blocked behind the nozzle?
Gas can escape from loose connections, damaged hoses or a poorly seated nozzle, and can be blocked at the diffuser if its ports clog with spatter. Check the connections, the hose and the torch for leaks, and make sure the nozzle is fully fitted.
With the nozzle off, look at the gas ports on the diffuser and clear them if they are blocked. If the gas flow seems low at the regulator or at the torch, or you get porosity with no obvious cause, work through these checks before changing your settings.