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Coil Processing
Monday | 24 October, 2011 | 12:58 pm

Specialized slitting

By Nick Wright

October 2011 - When selecting a coil slitting line provider, requirements for high tolerances naturally create higher stakes. The choice is easy when that company not only has extensive experience accommodating custom specifications but also when it turns out to be a repeat for the client.

With more than 30 years of experience installing high-performance coil processing lines, Chicago Slitter, Itasca, Ill., delivered Chattanooga, Tenn.-based JIT Steel Service its second slitting line in late 2009 after installing a customized line in 1996 for JIT Steel’s parent company, Mapes & Sprowl, Elk Grove Village, Ill.

“There’s a comfort factor of working with a vendor you’ve had a lot of success with, so we went through a quoting process,” says Jim Stolpa, division vice president with JIT Steel. The company is a full-service processing and distribution facility for flat-rolled steel. “Not only was Chicago Slitter very competitive, they had a proven track record that they could make the line.”

JIT Steel serves a niche market that requires high-tensile strength, high-hardness flat-rolled steel, which only a customized, tight-tolerance line could process, according to Stolpa. “Our customers are extremely picky on burr and flatness. Most of our customers expect a burr of about 0.0005 inch and flatness on the edge around the order of 1⁄16 inch, max,” he says. “So it’s got to be perfect slitting.”

Indeed, the specifications are tight. Jim Russell, vice president of sales and marketing at Chicago Slitter, says the custom slitting line is capable of cutting light-gauge steel from 0.005 inch to 0.045 inch thick at 48 inches wide and handling coil weight up to 40,000 pounds. “But most of the production, the so-called bell curve, is for the real light gauge,” he says, referring to the steel coils in the middle range—between 0.006 inch and 0.01 inch.

Multifunction slitter
The slitting line is a double-loop line that runs up to 1,500 feet per minute for which JIT Steel constructed a 25,000-square-foot addition in 2009. JIT Steel’s facility sits across from downtown Chattanooga on the banks of the Tennessee River where barges dock and deliver the light-gauge steel coils, says Stolpa. “We get steel in from New Orleans that came [from] overseas or down the Ohio from the Midwest,” he adds, noting it’s a cost-effective way to have steel delivered.

From there, coils are stored in a 50,000-square-foot building before they’re routed into the slitting area with a 25-ton crane onto a four-arm turnstile that loads the slitter. “The average-size coils we get in for this are only about 7 or 8 tons, tops because they’re really light gauge,” Stolpa says, noting the gauge allows for more linear feet in a coil.

After the coil gets loaded onto the unwind mandrel, it’s fed carefully through guides and tables into the 37-foot line. “It’s a challenge because it’s so thin, and if you’re threading the line, it doesn’t really want to push very well as your slitter head is feeding the strip,” Stolpa says. “We almost say it’s like pushing rope.”

The multifaceted line ensures feeding this light-gauge material is quick and efficient. Beginning with the uncoiler and all the way to the recoiler, the equipment handles feed-up well. The uncoiler unwinds the coil and then draws it through the slitter head, where it’s cut into individual strips. Once it’s slit, “it gets fed across the looping pit into the tension rolls. From there, it’s fed into the recoiler drum, where the leading end of the coil gets clamped,” after which the coil is rewound with all of the slit strips on the recoiler mandrel, Russell says.

The slitter knives do not make a clear cut through the material, Russell says. Rather, the knives cut about 30 percent of the material, depending on hardness and tensile strength, “leaving more of a score” from which the strip breaks away evenly and, if done correctly, eliminates the need for deburring and further finishing. “If the tooling is right and the machine is calibrated properly, the slit edge should be—I’ll call it—perfect.”

“A scrap baller collects the two edges of scrap coil,” which gets recycled back to the mill or the customer. After the processing, the finished, narrow-slit coil strips get packaged on a skid and placed in a warehouse before shipment.

Harnessing hydraulics
One of the features of Chicago Slitter’s line is its slitting head power tooling lockup, which at the push of a button keeps all the tooling—in this case, blades and spacers—locked into place on the tool arbor. This eliminates the need for hydraulic jet nuts and ensures constant locking force on the tooling. “You pack out your arbor all the way out to the power tool lockup, to the area where the clamp closes it. And [Chicago Slitter] has a bar that goes all the way across the arbor,” Stolpa says. “It’s hydraulically wedged, and the bar clamps all the tooling together.”

The line’s power generates hydraulic pressure and compresses the tooling bar, which is stronger and easier to use as opposed to a manual locking nut with a grease fitting. “I would say that the grease fitting loses pressure over time,” Stolpa says. With the hydraulic locking nut, “it’s going to be consistent and you can put a lot more pressure on that hydraulic bar than you can a grease fitting.”

Chicago Slitter developed the technology for the hydraulic tooling bar about 30 years ago, according to Russell. “It’s standard on all of our equipment and it really makes it easy and fast to lock the tooling up,” he says.

Ground-level service
Before the line and facility were constructed, a 35-foot-deep pit needed to be dug for the line’s foundation and looping pit. At about 8 feet, the subcontractor, John Rademacher, working alongside the building contractor, hit water, Stolpa says. “We’re really close to the river, so we had to shore up some of our foundation. It would be a challenge for someone who wasn’t prepared for it, but Chicago Slitter and their foundation guys were all prepared for it,” he says. “The making of these pits was critical.”

Russell says it’s not uncommon to encounter water, and specialists working with the companies can bolster foundations. “Water is pretty common no matter where you’re at, especially when you’re going down 30 to 40 feet. Even here in Chicago, we hit water after a certain amount of depth. Sometimes you hit it at 5 feet, sometimes at 20 feet.”

JIT Steel sources Chicago Steel for training, maintenance and other needs. The slitting line’s computer connects to the Internet, so Chicago Slitter can dial in remotely to assess, diagnose and suggest solutions before determining it necessary to come on-site. In less than an hour, Chicago Slitter’s technicians can determine a problem remotely via the Internet and have the line back up and running before sending someone out, Russell adds. “We can even make changes in there, [including] upgrades [or] software upgrades if we need to,” he says. “If an operator wants to change something in one of the screens of the [human machine interface], we can do that in here and just download it. It’s really been a nice feature of supporting the line.”

Stolpa notes training is provided on more advanced aspects of the line every few months or as needed. “They’ll teach your folks how to take care of the line.” MM

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