Photo courtesy of Hobart Brothers Inc.

Weld bead created with metal-cored electrode.

Photo courtesy of Hobart Brothers Inc.

Solid metal electrodes produce a finger-like penetration profile.

Fabricators who are considering the switch from solid-metal electrodes to metal-cored electrodes should base their decision on an understanding of the real advantage of metal-cored electrodes: their ability to solve problems.

Metal-cored electrodes are said to deliver higher deposition rates with less melt-through and spatter and higher travel speeds, and those claims can be true — for the right application, says Tracy Price, a welding engineer at Broshco Fabricated Products, a division of Jay Industries Inc. (www.jayindinc.com). Price's company recently decided to change from solid-metal to metal-cored electrodes on one segment of its production line for automotive seating. That portion of the company's production line includes robotic welding, GMAW and a change to 0.035-in. metal-cored electrodes from 0.045-in. solid-metal electrodes. Price said Broshco found that it could double travel speeds using metal-cored electrodes.

However, it is the application that determines the benefits that can be derived from the use of metal-cored electrodes, and putting them to work requires an understanding of their advantages and disadvantages, says Dave Barton, senior welding engineer in the Applications Engineering Group of The Lincoln Electric Co. (www.lincolnelectric.com). "Most people that start with the premise that I can put down more metal with the same current usually fail sooner or later," Barton says, adding that the decision to change to metalcored electrodes from solid-metal should not be based solely on the premise that more metal will be laid down at the same current.

Better penetration
One of the hallmarks of metal-cored electrodes is that they provide improved penetration of the weld into the base metals. These electrodes help to minimize rework caused by missed joints, blow holes and lack of sidewall fusion, and minimizing rework saves money.

One customer of Motoman Inc. (www.motoman.com) saw more consistent penetration and fewer silicon islands on welds after switching to metal-cored electrodes, says Chris Anderson, welding segment technology leader at Motoman Inc. Reducing the number of silicon islands on welds helped that Motoman customer to cure a problem with painting the part, Anderson said. The customer uses powdered paints that do not adhere to silicon, so eliminating the silicon islands reduced paint flaking and rust in the finished product.

A fabricator based in Kansas was having a similar problem with paint flaking off of finished parts, and that problem also was traced to silicon deposits. Those silicon deposits were located on the toe-line of the weld and were caused by the solid-metal electrode the fabricator was using on high-strength steel, according to Roger Pihl, business development manager at Hobart Brothers Inc. (www.hobartbrothers.com). The problem was resolved by using a metal-cored electrode with a specially formulated core, Pihl said. Metal-cored electrodes offer more flexibility in alloy composition than is possible with solid-metal electrodes manufactured by steel mills because manufacturers can formulate special chemistries for the cores that address specific welding conditions.

The core
Manufacturers of metal-cored electrodes can produce the special formulas for cores that are needed to weld high strength steels, and they say they can make those special formulations in less time, at lower cost and in shorter production runs than a producer of solid electrodes.

The internal components of metal-cored electrodes begin with iron. Other powdered metals, metal alloys and chemicals, such as potassium and sodium, are added, and help to determine the properties of the formulation and the weld it produces. A metal core could be developed to stabilize or to enhance a welding arc or to reduce oxidation in the weld. For example: A 90C-B3 electrode from Select-Arc has a core containing 2.25 percent chromium and 1 percent molybdenum. That electrode is recommended for welding the Cr-Mo and carbon steels used for pressure vessels and for high temperature and high-pressure pipe. Select-Arc says the electrode's advantages include faster travel speeds, better fusion into base metal and greater tolerance for mill scale than solid electrodes.

Mill scale and surface contaminants
Metal-cored electrodes also save money by reducing the amount of work in pre-weld operations, manufacturers say. These electrodes are able to produce an improved bead appearance, less surface porosity and spatter when welding through mill scale, rust and other surface contaminants. However, solid metal electrodes that include deoxidizers also can be used to weld over light and medium mill scale.

Improper base metal preparation can lead to weld porosity when the GMAW process is used. The GMAW process typically does not use flux, which helps to clean the base metal, so the deoxidizers that are included in metalcored electrodes often are the necessary components that reduce porosity with this process.

Less spatter
Metal-core electrodes tend to produce less spatter than solid-metal electrodes because the voltage on the welding machine is set higher when using them. That is because the sheath for metal-cored electrodes burns faster than the materials in the core. To compensate for this, welders run a longer apparent arc length to prevent the wire from shorting and producing spatter. With less spatter, less post-weld cleaning is necessary for the weld.

The downside
In general, the benefits associated with metal-cored electrodes do not apply to applications that use base metals that are 1/8 in. or less because of the longer apparent arc length used in welding with these electrodes.

Also, metal-cored electrodes are not recommended for galvanized materials and with short-circuit welding, but technology is being developed that eliminates those restrictions.

"We have seen some nice things with combinations of pulsed waveforms and metal-cored chemistries that can yield better travel speeds on thin materials and better bead wetting," says Barton of Lincoln Electric. "And we have also done some things with some special rapid arc waveforms that can be combined with metal-cored products that can do some nice things at higher travel speeds. We have also done some things with some galvanized materials, pulsed waveforms and metal-cored electrodes. So there is some newer work being done to improve productivity with coated materials, pulsed waveforms and metal-cored electrodes as a packaged solution," he says.

Metal-cored electrodes have a more complex composition and chemistry, and more chance for variability because more manufacturing processes are used.

Fabricators who are welding alloys that are sensitive to hydrogen in high restraint conditions must be careful in their specification of metal-cored electrodes because these electrodes can range from H4 to H8 in diffusible hydrogen.

It is often necessary to replace drive rollers on wire feeders when using metal-cored electrodes because of changes in wire diameter. For example, a fabricator may have to use a Vgroove knurled roller, rather than a simple V-groove roller, to handle a metal-cored electrode.

Cored electrodes and hardfacing Cored wires — metal-cored and flux-cored — are used almost exclusively when hardfacing with GMAW because of the hardness the electrodes produce and because of their alloy content, says Bob Miller, weld engineer, Postle Industries Inc. (www.postle.com). Getting those characteristics with solid-metal electrodes is not possible, he says.

The following people contributed to this article: Dale Stager, president of Select-Arc Inc. Mike Tecklenburg, national sales director of Select-Arc Inc. Grant Harvey, vice president of sales and marketing, Hobart Brothers, Global Transfer Division, U.S.