When your GMAW gun's ablazin'
Overheating signs, causes, and solutions
Overheating is a symptom of what could turn into catastrophic gun failure. Striking the right balance between gun size and capacity can increase the efficiency of a welding operation and decrease problems, like overheating, that could damage the equipment.
A lot goes into choosing a gas metal arc welding (GMAW) gun. After all, welding is simply the result of one large electrical circuit, and the gun reflects that. The general rule is to select the lightest, most flexible gun for your application. Duty cycle, amperage requirement, and work site location all should factor into your decision process.
Striking the right balance between gun size and capacity can increase the efficiency of a welding operation and decrease the occurrence of problems, like overheating, that could damage the equipment.
No matter the cause, several signs precede catastrophic gun failure. Knowing these signs and taking steps to prevent them can minimize unnecessary downtime, reduce gun and consumable replacement costs, and prevent weld quality issues.
How GMAW Guns Are Rated
GMAW gun manufacturers test and rate their products to prevent overheating, based on criteria established by NEMA (National Electrical Manufacturers Association) in the U.S. and by CE (Conformité Européenne or European Conformity) in Europe. Assigned ratings reflect the temperatures above which the handle or cable becomes uncomfortably warm, not the point at which the GMAW gun risks damage or failure.
The testing process (IEC 60974-7 Section 8) measures the rise in temperature compared to ambient temperatures for the handle and cable. A maximum allowable temperature differential may exist in order for the gun to pass the test. In addition, specific duty cycles are tested for each gun, such as a 100 percent duty cycle with a 100 percent CO2 shielding gas or a 60 percent duty cycle with a mixed shielding gas (e.g., argon and CO2). The ratings systems do not specify the way a gun must be marketed, however, so there can be discrepancies among manufacturers’ rating systems.
For example, a 300-amp gun from Manufacturer A may weld at 100 percent duty cycle, whereas a 300-amp gun by Manufacturer B may weld at only a 20 percent duty cycle. Duty cycle is defined as the amount of arc-on time within a 10-minute period, so a 20 percent duty cycle would constitute two minutes of arc-on time in a 10-minute time frame. Most manufacturers list the amperage-to-duty-cycle ratios in their product literature, so always research a gun’s ratings before purchasing.
Gun Amperage Background
Many variables are involved with selecting the GMAW gun with the right amperage. The type of material to be welded, the transfer process, and the material thickness all come into play. A gun with amperage that is too high for the application will weigh more, be less flexible, and cost more.
Also, in most cases it is not necessary to use a gun rated to the highest amperage you expect to use. For example, a 400-amp application doesn’t necessarily require a 400-amp GMAW gun. In fact, a gun rated at 300 amps can weld at 400 amps and higher. Moreover, a 300-amp gun may be a good choice since welders do not weld 100 percent of the time and the gun will be easier to maneuver. The biggest difference between low- and high-amperage guns is the amount of copper in the gun cable; the higher the amperage, the more copper and the more heat a gun can contain.
If the application requires more capacity than can be achieved with an air-cooled gun, it may be necessary to change to an equal or potentially lower-
amperage water-cooled gun. These models accommodate applications with longer arc-on time and consistently higher temperatures. Keep in mind, however, that water-cooled guns typically cost more and require additional maintenance and equipment.
What Is Overheating?
During welding, electricity flows through conductors in the GMAW gun, which are typically composed of metallic materials. Overheating results from increased electrical resistance within the GMAW gun and cable. In other words, resistance is the opposition to electrical flow. Resistance is controlled by the following:
- The length of the electrical circuit or conductor
- The cross-sectional area of the conductor
- The conductor material
- The temperature of the conductor
As a general rule, a longer conductor increases resistance, while one with a larger area or diameter decreases it. Also, some materials are naturally better conductors and reduce resistance. For example, copper has a low resistivity to electrical flow, whereas stainless steel has a high resistivity. The higher the physical temperature of the conductor, the more resistance within the material.
Overheating: Signs, Causes, and Solutions
If a gun is overheated or is about to overheat, the most obvious sign is that it becomes very hot to the touch. Other signs are dirty consumables, as well as any gun, liner, or cable discoloration. The latter typically suggests loose connections are the source of the scorching or discoloration.
Whenever symptoms of overheating appear, look for changes with the welding parameters. Knowing the target welding parameters, such as voltage and amperage, and how far out of range they have fallen can often speak to any problems occurring in the welding circuit.
An application that exceeds the amperage and duty cycle of the gun for long periods of time is typically the main cause of a gun overheating. Change in contact-tip-to-work distance (CTWD) is also a common contributor. If you keep the wire feed speed the same but increase the distance from the workpiece, more heat will be created as well as electrical resistance within the welding cable.
This resistance is the result of the electricity flow from the power source being impeded through the cable and cable connections. Essentially, the energy backs up and is lost as heat that can ultimately cause gun overheating and damage. Try to maintain a steady voltage and current to maintain low electrical resistance.
If you are performing the same weld in the same cell but the voltage increases without a change to the CTWD, this signals the presence of electrical resistance within the gun possibly caused by loose connections. Moving from the back of the gun and the cable toward the front-end consumables and the neck, check that all connections are tight and free of debris or spatter and that all threaded connections are secure (see Figure 1).
In addition, a loose ground connection or improper ground clamp can increase resistance in the electrical circuit. To ensure a solid ground connection and firm grip, clean the clamp and the surface where the clamp will be used. Remove any grime or dirt that would prevent direct metal-to-metal contact.
Another potential source of trouble is poor seating of the power pin in the wire feeder, leading again to resistance in the circuit. The power pin connection should be tight and secure. Most feeders have a feature for locking the power pin into position to ensure a clean, firm connection.
Regularly inspect the power cable for any cuts or damage, which can cause the arc to search for the ground through the cut, posing a danger to you and surrounding personnel (see Figure 2). It can also lead to gun overheating
After a gun has been serviced or repaired, it’s possible that some threaded connections may be loose, which can cause heat to build up. To help prevent this problem, be sure to check and tighten all connections after service has been performed. Follow the manufacturer’s specifications for any repairs.
The causes and signs of overheating vary by application. How long a gun has been in use over its temperature range affects how much damage there is to the gun and if it will fail as a result. The goal is always to be proactive to minimize expensive and time-consuming downtime. Watch for indications of overheating and address them immediately. Doing so not only prevents GMAW gun damage or failure, but it also prevents subsequent issues such as poor weld quality and lost throughput.