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How to select a gas-shielded welding electrode
PRACTICAL WELDING TODAY® JULY/AUGUST 2003
JULY 24, 2003
BY: Lisa byall, doug krebs
Are you looking for ways to improve quality, raise productivity, and save costs in your current welding operations? If you haven’t examined the various electrode choices, you could be missing an opportunity to take your production welding to the next level.
Many fabricators overlook the efficiencies they can gain by changing a wire or process. In fact, when you ask fabricators why they’re using a particular electrode, some respond with “That’s the way it’s always been done here,” even though another way might yield significant improvement.
Many gas-shielded electrodes—each with different mechanical properties, arc behaviour, and intended applications —are available for almost any welding project. Depending on your requirements for quality, productivity, and cost, you can select from among three different gas-shielded arc welding wires for your application:
- Solid gas metal arc welding (GMAW) wire
- Composite GMAW (metal-cored) wire
- Gas-shielded flux-cored arc welding (FCAW) wire
Solid GMAW Wire
GMAW requires a solid wire electrode or a composite metal-cored electrode. Solid wire electrodes commonly are referred to as GMAW electrodes. The mechanical properties and strength of the weld deposit depend first on the chemistry of the wire and second on the type of shielding gas used (see Figure 1). Shielding gas is necessary to protect the weld from the atmosphere. Fabricators often prefer GMAW because the weld deposit is slagless and requires little or no cleanup, which increases efficiency.
Dirty Steel. Many classifications of GMAW wire exist, each with varying levels of deoxidizers. Highly deoxidized wire can tolerate light to medium levels of surface contaminants. For these applications, look for ER70S-6 wire, which has higher levels of silicon and manganese than an ER70S-3. You also can choose an intermediate electrode, ER70S-4, for applications requiring more deoxidizers than ER70S-3 but less than ER70S-6.
Remember to select GMAW wire from a creditable manufacturer to ensure consistent chemistry, diameter, and feedability from lot to lot or spool to spool. Some imported GMAW wires are labelled as ER70S-6 but actually conform to the European SG2 classification. Many European wires labelled as ER70S-6 do not meet ER70S-6 chemistry required by the American Welding Society (AWS) and therefore might not be suitable for your application.
Travel Speed. On blasted plate, solid GMAW wire performs well. On a plate with heavy mill scale, GMAW wire doesn’t perform as well as metal-cored wire or flux-cored wire. Solid GMAW wires don’t deoxidize mill scale as readily, affecting bead shape and travel speeds adversely.
Out-of-position Welding. Solid GMAW wire can be used for out-of-position welding using a short-arc procedure on thin materials, which yields low deposition rates. As an alternative, pulse-spray welding with these electrodes can increase the deposition rates while still providing out-of-position capabilities.
Mechanical Properties. Generally, the strength of a weld deposit made with a solid GMAW electrode is limited to the strength of the electrode. If you have a high-strength, low-alloy base material, it may be difficult to find a solid steel GMAW wire that will meet the base material requirements. For these applications, a metal-cored or flux-cored electrode might be more appropriate.
Postweld Operations. For certain modes of metal transfer with solid GMAW wire—such as short-arc and globular—some spatter may occur that requires postweld cleanup. Silicon islands can be deposited during GMAW that might need to be removed before painting or coating. However, GMAW with solid wire generally is a clean process that requires minimal postweld operations.
Metal-cored wires are tubular electrodes with metallic constituents in the core. Like solid GMAW wire, metal-cored wire produces a slagless weld that requires little or no cleanup. The performance characteristics also are similar to those of solid GMAW wire. Formerly classified as a flux-cored wire, metal-cored wire now is classified as a composite GMAW electrode.
Dirty Steel. Metal-cored wire can handle mill scale and surface contaminants better than GMAW wire because of its metallic components. These components help the metal-cored electrode deoxidize the scale better than solid wire, which is the reason this type of wire is a better choice if you don’t want to blast material before welding.
Deposition. Due to the tubular nature of metal-cored wire, the current density of a metal-cored wire is higher at a given amperage than a solid wire of the same diameter. This can result in higher deposition rates at a given amperage. In some automated applications, large-diameter metal-cored wire can match or exceed the performance of gas-shielded flux-cored wire. However, large-diameter metal-cored wire might not be suitable for semiautomatic welding because of the high amperages used and heat radiated from the arc.
Travel Speed. Metal-cored wire should be your first choice if travel speed is your primary concern. On a plate with mill scale, metal-cored wire can produce improved wetting and a flatter bead shape as well as increase productivity because of lower spatter levels (less postweld cleanup) and faster travel speed.
Out-of-position Welding. Although it is possible to use metal-cored wire out of position at low amperages in a short-arc mode, metal-cored wire generally isn’t used for out-of-position welding, except for in the vertical-down position. Like with solid GMAW wire, pulse welding can improve out-of-position deposition rates with metal-cored wire.
Mechanical Properties. Metal-cored electrodes are available for high-strength, low-alloy applications. Low-alloy metallic components can be added to the core to achieve the desired mechanical properties. This ability to add components can make it easier to produce the desired mechanical properties with metal-cored electrodes than with solid wires of comparable strength.
Postweld Operations. You may need to do some postweld cleanup to remove the silicon islands deposited from metal-cored electrodes before painting or coating the base metal. However, cleanup time may be reduced overall because metal-cored wire typically produces little spatter.
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