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October 2012
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Roller Leveler on Steroids

Engineers at Herr-Voss Stamco have designed a roller leveler with Enhanced Leveling Technology, which they claim produces stay-flat steel comparable to a stretcher leveler, but at a much lower capital cost.

By Tim Triplett, Editor-in-Chief

High-tech cutting machines such as lasers, plasmas and water-jets have become commonplace in job shops all over the country, producing parts with amazing accuracy at lightning speeds. That is, of course, if the material they start with is flat. Most steel is anything but, unfortunately.

A piece of plate may look as flat as a tabletop, but still have “coil memory” from being rolled, cooled and coiled at the mill. Internally, a host of differential strains still compete with one another. They hold each other in place until the material is cut, then the released stresses cause the metal to deform. Steel that bends and twists during the cutting process can ruin cut parts and do serious damage to a CNC-controlled cutting head as it travels over the surface of the sheet.

As customers’ cries grow louder for steel sheet that arrives flat and stays flat after cutting, processors have a decision to make: invest in new leveling technology or risk getting left behind. Until recently, that decision boiled down to two options: install a temper mill or a stretcher leveler. Herr-Voss Stamco, Callery, Pa., now offers a third choice, its ELT or Enhanced Leveling Technology.

Taylor Steel, Stoney Creek, Ontario, was the first to install the new Herr-Voss ELT system in November 2011. The decision to invest in the untested technology was driven by growing customer demands for stress-free steel, says Randy Smith, Taylor vice president of operations. “We felt ELT was a technology that would provide us with the stay-flat product we needed.”

Taylor Steel is a major distributor and value-added processor of carbon flat-roll with five plants in Stoney Creek and one plant in Lordstown, Ohio. It serves the automotive, construction and appliance markets, among others.

Taylor was able to retrofit one cut-to-length line for enhanced leveling at its Stoney Creek Plant No. 1 in a process that was fairly simple, Smith says. The ELT unit was installed at the end of the line, requiring only the addition of some conveyors and relocation of the stacker. Today, steel coils pass through a standard roller leveler at the front of the line, then through a shear that cuts them to length, just as before.

Then the blanks are conveyed individually through the ELT before being stacked for packaging and shipment. Each “enhanced” sheet is free of the trapped internal stresses that might cause it to bend or twist after cutting, Smith says.

Taylor spent considerable time working out the bugs and testing samples for flatness before passing product on to customers. After nearly a year of experience with the machine, Smith and his crew have found the ELT works best on light-gauge carbon steel up to 3/8ths inch thick. The addition of the ELT did not affect the speed of the line, which has an annual processing capacity of 50,000 to 60,000 tons.

Smith is particularly impressed with Herr-Voss Stamco’s intuitive approach to the controls. The system is easy to operate and has built-in logic that records job histories so it can automatically duplicate settings for repeat customers. “The ELT has allowed us to compete with people that are supplying stretcher leveled product,” he adds.

How the technology works
The ELT is the product of three years of R&D and makes Herr-Voss Stamco a player in the market for equipment that produces stay-flat steel. For years, the ultimate leveling technology was the temper mill, which flattens the material by compressing it between two work rolls under enormous pressure. Temper mills are still widely used today, with about 25 in operation in North America. They are very costly, however, and only practical for fairly large companies.

Thus makers of stretch leveling technology saw a market opportunity. Stretcher levelers relieve the internal stresses in the steel sheet by gripping and stretching the material past its yield point. Stretcher leveling has been around for over 50 years, but companies such as Red Bud Industries and Leveltek have introduced refinements that allow heavier-gauge materials to be leveled, as well as steel in coil form. Stretcher levelers are roughly half the cost of temper mills.

“Stretcher leveling is a great process, but it does have its limitations,” says Wes Dias, ELT product manager at Herr-Voss Stamco. For one, it must stop and start as it stretches each section of coil. This stop-start process reduces the throughput of the processing line. For another, it has a larger footprint and requires more space than the ELT.

Herr-Voss Stamco considered developing its own stretcher leveler, but after careful study decided “there has to be a more elegant solution,” Dias recalls. As one of the market’s leading providers of corrective roller levelers, the company opted to build on its core strength and design a roller leveler with enhanced leveling features. “We decided to look at bending the material in the same manner as a roller leveler, but to do it in a very severe and precise fashion, with monitors measuring all the work going into the metal,” Dias says.

Like most temper and stretcher level lines, cut-to-length lines using the ELT also incorporate a conventional leveler. The coil first passes through the standard corrective roller leveler to remove most of the defects, such as crossbow, center buckle or edge wave. Then it is cut into blanks and each blank passes through the ELT for final enhanced leveling before moving on to the stacker.

The enhancing process is dependent on feedback from the rolls. Sensors inside the system are very sensitive. That’s why it was designed to level discrete plate rather than coil, so its measurements of the bending process are not distorted by energy needed to convey the coil through the system, Dias explains. “We needed to be able to measure, monitor and calculate how much work is being put into the material in this ELT process. To accomplish that, you need to be able to isolate that specific work. So it has to be corrective leveled first and then enhanced.”

More than just a different spin on roller leveling, the sophisticated controls of the ELT make it truly innovative, Dias maintains. “We monitor the torque on each and every roll as the material hits it. By measuring how much power is being consumed by the drive, in excess of what it takes to turn over the motor, the gearbox, the spindles and the work rolls, we can identify how much energy was put into a piece of material.

Through a calculation based on the material thickness, yield and width, the patent-pending Advanced Enhancing Meter provides immediate feedback to the operator, showing him the bandwidth in which he needs to keep the material to be sure it has been 100 percent enhanced.”

Except for the sophisticated controls, the ELT looks much like a conventional leveler. The configuration of the work rolls is basically the same. One fundamental difference is the heavy-duty construction of the entire machine. “We have created such a rigid assembly that there is virtually no deflection. The machine does not breathe or grow as the material passes through it, despite the remarkable separating forces trying to push the machine apart. This works the entire width and length of the material incrementally as it passes through with much greater bending force than corrective leveling,” Dias says.

The ELT can be operated in a conventional leveling mode as well as the enhanced leveling mode. It is designed to handle carbon steel, stainless steel and aluminum sheet from 1/8th- to ½-inch thick.

So far, the ELT is in operation in three locations: Herr-Voss Stamco’s headquarters, Taylor Steel and Samuel, Son & Co. Ltd., Mississauga, Ont. Two other ELTs are under assembly. Their price tag is around $2 million.

“At about half the cost of a stretcher leveler, the Herr-Voss Stamco ELT will make high-tech leveling accessible to service centers and processors of all sizes,” says Kip Mostowy, Herr-Voss Stamco president and CEO. “In our opinion, we can actually provide a catalyst to the growth of the market by adding a lower-cost option to obtain a superior material, just like the stretcher levelers did to temper mills.”

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