Fall 2011 Edition

The Impact of Nozzles on Cost, Quality and Productivity

Like other gas-shielded metal arc (GMAW) gun consumables, nozzles are often an overlooked component in the welding operation. However, knowing how to select the best one for a given welding application can have a measurable impact on the quality, productivity and overall cost of the welding operation. That’s because the nozzle is responsible for directing the shielding gas to the weld pool and protecting it from contamination. Without that proper gas flow, the final weldment is prone to a range of problems, including excessive spatter and porosity that can ultimately lead to downtime for rework. Plus, having the wrong nozzle for an application often causes problems with overheating that may lead to premature consumable failure.
 
For that reason, it is important to select the right shape and style of nozzle, as well as the right material for each application. Too, knowing how to store and handle nozzles properly can go a long way in helping keep the welding operation up and running. Consider these tips:
 

What Shape, Style and Material Are Best?

The goal when selecting a nozzle is to find one that provides the best joint access for the application and allows for the proper gas flow to the weld puddle. Keep in mind that nozzles with smaller inside diameters may be more prone
to collect spatter, so it is best to use as large of a nozzle as possible to ensure greater gas flow. 
 
There are several shapes of nozzles available, including straight, bottleneck and short or long taper nozzles. Straight nozzles typically have larger inside diameters (e.g., 3/4 inch), but don’t offer as good of joint access.  Bottleneck nozzles can improve this situation, particularly on automated welding applications. A common inside diameter for a bottleneck nozzle is 1/2 inch. Semi-automatic applications often use short and long taper nozzles, although the former are also
common in automated welding. Note that long taper nozzles typically have a smaller inside diameter and may collect spatter more readily. When possible, using a short taper nozzle can help prevent such a problem.
 
Each shape of nozzle is typically available in heavy-duty or standard styles, and in slip-on or thread-on varieties. Heavy-duty nozzles have thicker walls as well as thicker insulators, and are designed for use in applications ranging from 400 to 600 amps. Due to their heavier construction, these nozzles resist heat better than standard varieties. Standard nozzles tend to have a thinner wall and are better for 100- to 300-amp applications. Slip-on nozzles, as their name implies, simply slip on to the front end of the GMAW gun. These nozzles are quite prevalent in the industry, compared to thread-on nozzles that need to be twisted to install, and they offer the advantage of being able to change over more quickly. A note of caution: when installing slip-on nozzles, be certain that they are securely connected to the retaining head. Doing so helps prevent shielding gas leaks that could lead to poor weld quality.
 
Nozzles are typically available in brass or copper, although chrome-plated nozzles are also available. Brass nozzles tend to resist spatter well and are good for lower-amperage applications (100 to 300 amps), whereas copper nozzles are better for high-amperage applications (above 300 amps) or for those with longer arc-on time.
 
For high-amperage water-cooled applications, there are also nozzles available that circulate coolant around the nozzles, but these tend to be much more expensive.
 

From the Nozzle to Contact Tip

The relationship between the nozzle and contact tip can have a significant impact on weld quality and should be selected carefully for all applications. Generally, welding operators maintain a recessed or extended contact-tip-to-nozzle relationship. A recessed contact tip offers the best gas coverage, but it also minimizes the electrode extension. As a result, this contact-tip-to-nozzle relationship offers less accessibility to the joint. Conversely, an extended contact-tip-to-nozzle relationship allows the welding operator greater access into confined areas or joints. In this scenario, however, the shielding gas coverage may not be as good as compared to a recessed contact tip. Typically, an extended contact tip is used in automated applications, but it can also be used in the semi-automatic process. In these applications, there is an increased chance of the welding operator touching the contact tip to the work piece because of the extension, which can damage the consumable and also cause poor weld quality.

When determining the best contact-tip-to-nozzle relationship for a given application, the welding operator will need to weigh these advantages and disadvantages to decide whether a recessed or extended contact tip provides the best welding performance for the job.

Tips for Making Your Nozzle Last Longer and Perform Better

As with any front-end consumable, handling, storing and maintaining the nozzle properly helps ensure good welding performance and greater longevity. Selecting high quality nozzles can help, too.

Look for nozzles that are engineered to have a smooth surface finish and edges, as these resist spatter build-up compared to nozzles that have an uneven surface or burrs on the edges. Nozzles that have a bit of mass to them are also more desirable than lighter or thinner ones since they tend to resist heat better. Also, consider purchasing nozzles that feature a brass insert, which helps maintain the inner diameter of the nozzle and prevents the nozzle from rocking and wearing prematurely. The addition of a high-temperature fiberglass insulator can also help extend nozzle life. Finally, look for heavy-duty crimping on the nozzle — the crimping holds the layers together and is an indication that the nozzle has been built for longevity.

When storing nozzles, keep them in their original packaging, usually a small plastic bag. Removing them from that packaging and placing them in a bin can lead to scratches or dents that allow spatter to adhere and will ultimately shorten the life of the nozzle. Use gloves when handling nozzles or replacing nozzles to prevent dirt, oil or other contaminants from adhering to them and inadvertently entering the weld puddle.

Periodically inspect the nozzle for spatter build-up and clean it using the tool recommended by the manufacturer as needed and/or consider using an anti-spatter compound to protect against spatter. To apply the anti-spatter, dip approximately the front inch and a half of the nozzle into the anti-spatter compound.  Avoid submerging the nozzle in the compound, as it can saturate the fiberglass insulator inside and cause it to fail prematurely.

Finally, never use the nozzle to chip away spatter. It can dent or misshape the nozzle, requiring it to be replaced.

As with any front-end consumable, nozzles play an important role in maintaining good weld quality and can have a measurable impact on productivity and costs, too. Take the time to select the right ones for each application and maintain them properly. Doing so can minimize downtime and keep the welding operation running more smoothly in the long run.