If you want to learn about hard facing, spend one hour with Jerry Dubie. After running more than 24 tons of wire in 1999, he has a few insights to share.

As a millwright at Lafarge Corp.'s Alpena, Mich. cement plant, part of Dubie's responsibilities include maintaining two sets of 40-ton steel rollers that help turn big rocks into little ones. The first set of rollers crushes 3-in.-diam limestone chunks into flakes, which are then mixed with fly ash and iron ore tailings and heated to 2,700Degrees F.

"Because we're one of the largest U.S. cement suppliers, 3.9 million tons of limestone must go through those rollers every year to keep up with production demands," Dubie said. "Needless to say, the rollers wear down quickly, and with a 5-ft width and 15-ft circumference, that's far too much steel to replace. Resurfacing the rollers is our most economical option."

Focused improvement Supervisors of the raw grind operations, Bernie Andrzejewski and Dave Markowski, assembled a focused improvement team to understand and resolve issues, adjust processes, and reduce downtime while enhancing the overall resurfacing process. Dubie and the rest of the focused improvement team were empowered to solve resurfacing problems as part of Lafarge Alpena's Total Productive Manufacturing (TPM) program.

Production at the Alpena plant depends on the availability of raw grind to match kiln capacity. Thus, when the rollers are taken out of production for resurfacing, welding goes on around the clock for about five days to complete the job as quickly as possible. "We can't afford to shut down a kiln for lack of raw material," says Dubie.

The first step involved selecting ITW Welding Automation's Travel Master SB-10D automatic side beam with two independent travel carriages, each with a digital carriage control, automatic 1DA weld control, wire drive assembly, and water-cooled GMAW gun. "By automating the process, we can set up everything in a couple of hours. Also, we could use less experienced welders and get good results with the machine," Dubie said.

Because the rollers get heated to 300Degrees F, Dubie customized the beam by moving all the controls to one side. He also mounted the wire feed and gun assembly high to compensate for the roller size (i.e., the welding is done in the flat position on top of the roller).

The next step for speeding productivity involved finding the right power source. "We originally had different welders, but we weren't real happy with the production out of them and we had to make a lot of modifications," Dubie explained. "Then Bill Kelly of Alpena Supply Co., our local welding distributor, and Miller Electric Manufacturing Co.'s District Manager Doug Priem suggested we try the Dimension 652. We've run the Dimensions for 10 straight days at 100% duty cycle without a hitch."

The 652 delivers 650 amps of DC weld output at 100% duty cycle and offers high arc quality in both the CC and CV modes, according to Miller Electric. Its remote terminal strip and 14 pin amphenol connector can be connected to automated systems. For this application, Lafarge paired the welders with Miller's Coolmate 4 water coolers and GW-60A-style guns.

Lots of wire Each roller's approximate 75-sq-ft of surface area requires as much as 3 tons of wire to reface it. Before welding, the welding team smoothes out any large holes, or break outs, in the worn roller by paralleling two 652s and using their CC mode to air carbon arc gouge with 51/48- or 31/44-in. carbons. Switching back to the CV mode, the welders start the new surface by building a 3-in. layer of metal using a 71/464-in.-diam medium carbon filler wire.

The roller slowly rotates underneath the weld heads, taking about 20 minutes for a single revolution. The Travel Master then indexes over, and the process repeats hundreds of times until reaching the desired build up.

"You've got to watch the crusher roll machine all the time to ensure a hard, uniform surface," Dubie noted. "Sometimes we stop and gouge to eliminate variations in the thickness."

After completing the fill passes, the welding team switches to a transition layer of hard surface wire, then finishes with a very hard surface layer wire. "We used to rebuild the rollers every four months. Then we changed to a special welding wire, and it jumped to nearly eight months. It certainly demonstrates the importance of selecting the right filler metal," Dubie said.

Harsh conditions While one roll press is shut down for resurfacing, another roll press continues to operate. During this time the 652 welders must operate around emissions generated by the removal, transportation, and handling of raw product along with the welding processes.

"The real culprit that damages lesser welding machines is the iron ore tailings," Dubie said. "Remember, welders are just big electromagnets. Before you know it, there's iron ore tailings attracted to the welder. Fortunately, the 652 can take this environment. I just take the covers off and blow them out when I put them away."

To withstand such harsh environments, the 652 features an enclosure to protect the internal circuit boards. It also incorporates Fan On Demand, a cooling system that operates only when needed.

"This system worked so well that we purchased a second system. And we'll need it," Dubie said, "because our roller rebuilding time could be reduced as part of an effort to increase production."

This article was adapted from materials provided by Miller Electric Manufacturing Co., Appleton, Wisc.