It’s been called black magic by some; a dark art by others. Despite these cryptic monikers, leveling is an essential step in metal processing, requiring specialized machines and skilled operators.
Traditional leveling, which uses rollers to elongate and flatten a strip of metal, is still the most common method for shape correction in the steel and aluminum industries. However, the introduction of higher strength materials has led to a number of recent innovations in leveling technology and refinement of leveling processes.
“The role of the roller leveler really hasn’t changed a lot, but the material that they’re being asked to work with, in terms of strength, actually has changed quite dramatically in the last couple decades,” says Dean Linders, vice president of marketing and sales at Red Bud Industries, Red Bud, Ill. “What we’re finding is your conventional roller levelers physically are not able to elongate this new material enough in order to fix these shape problems.”
All leveling works on the premise of elongation, according to Linders. The type of machine used to accomplish this depends on the type of material being processed, as well as the type of shape defect you’re trying to correct.
Four main types of levelers exist in the modern metals industry. They are: roller levelers, tension levelers, stretcher levelers and temper mill levelers.
Roller levelers elongate material by bending it over a series of rolls, stretching the inner or outer edges, and correcting various length defects. This is called roll bending and is the primary function of roller levelers.
As materials get thinner and stronger, however, conventional roller levels become less effective and other types of leveling are necessary.
When you double the yield strength of steel, you have to elongate that material twice as much, according to Linders. Even if the material is the same thickness, the stronger material requires more elongation.
“At some point you can’t elongate the material enough to get it to go past the yield point by simply bending it across a set of rolls,” Linders says. “On some of this really high-strength material, we’re finding that we have to put a lot of tension on the strip.”
Tension leveling involves adding high tension to a metal strip before sending it through a series of rolls. By increasing the tension, traditional levelers become significantly more effective and capable of processing additional types of material.
“Through the pure tension and then bending the material across a roll, we can get significant elongation to the point where we can run a lot of this thin, high-strength material in particular and meet the requirements of what a lot of these companies are asking for now.” Linders says.
Al Waigand, vice president of sales and marketing at Salem, Ohio-based Butech Bliss, adds that while traditional roller levelers are effective in eliminating shape defects, they alone are unable to remove all of the trapped internal stresses. For this, two other types of leveling are most effective.
Stretcher leveling is done when a metal strip is gripped and stretched beyond its yield point, providing superior flatness and equalizing the trapped internal stresses. Temper rolling is a process that involves squeezing the material between two rolls with millions of pounds of force, thus reducing the thickness of the strip and elongating it slightly. The material is then fed through conventional roller levelers to flatten the strip and remove any remaining shape defects. Both of these options typically work in conjunction with a cut-to-length line.
Many of the recent advancements and trends in leveling technology are byproducts of the new materials being developed by metals manufacturers.
“I think some of the technology is changing just because of the ultra-high-strength steels that are now in the market,” said Lisa Liposchak, marketing manager at Butech Bliss. “That’s a factor in recent years. We’ve had to make adjustments to some of our technology to accommodate those new steels.”
Waigand says the result has been a move away from conventional roller levelers when processing steel with high yield strength. The aforementioned temper mills, stretch levelers and tension levelers have become more widespread, prompting equipment manufacturers to refine these technologies.
One of the innovative technologies Butech has developed is its Butrax shape leveling technology, which works in conjunction with a tension leveler to limit the amount of material loss associated with traditional tension leveling. And for companies still using roller levelers, Butech’s Synergy leveling system allows operators to change between light-gauge and heavy-gauge materials because two separate work roll diameters are built into the same machine.
Linders of Red Bud notes the development of cassette levelers, which have interchangeable rolls, as an offshoot of this two-in-one design. Whereas before, service centers might have chosen to have two different roller levelers, factors such as cost and warehouse space are promoting the installation of new machines capable of handling different types of material.
“That’s led to what we call cassette levelers,” Linders says. “These machines are designed to actually have the rolls come out very rapidly, sometimes in as little as five minutes. This lends itself to running different types of products, because you can easily clean them but also you can have more than one roll size.”
As for tension leveling, Reb Bud has developed a system which Linders says has a much smaller footprint and is a more economical than traditional tension leveling. “This type of system uses recoiler tension, in conjunction with either a modified roller leveler or an ‘S’ wrap intensifier,” he explains, adding that this type of system is much more effective at processing higher strength materials than conventional levelers. “It can be used for material up to 0.250 inches thick, but it is most effective from 0.150 inches and lighter gauges.”
With thick material, it becomes harder and harder to exceed the tension necessary for elongation, according to Linders. For these metals, stretch levelers and temper mills are the machines of choice.
“We’ve got machines that will stretch 1-inch thick coil,” Linders explains. “You couldn’t do that through the tension leveling process because you couldn’t develop the kind of forces we do in a coil-to-coil system with tension leveling that we can do with stretching.”
The major difference between stretcher leveling and temper leveling, according to Waigand, are the cost and the productivity of the machines. In addition to being more expensive, temper mill cut-to-length lines are designed to run continuously.
“A lot of the people in the service center industry are migrating toward having multiple service centers in different regions of the country,” Waigand explains. “When they do that, they don’t need the high production that you get off of a temper mill cut-to-length line… There haven’t been too many new temper mill cut-to-length lines starting up in recent history, but there have been quite a significant number of more stretch level cut-to-length lines.
Automation is another factor in the evolution of leveling technology. Steven Baker, industry sales leader at the Bradbury Group, Moundridge, Kan., says the goal of automation in leveling has been to make it easier for less-skilled operators to run a machine efficiently.
“Leveling was quite commonly referred to as black magic,” he says. “It takes a long time for an operator to be able to recognize the strip shape coming at him and set the leveler to a certain position to correct that. Customers are now looking for a way to increase production without adding personnel or experience.”
According to Linders, most new levelers now use computers and sensors to monitor the shape of the strip and relay that information to the levelers, which then automatically adjust to address the specific shape defect.
“Leveling is kind of an acquired skill, but some people are just naturally better than others,” he says. “Automation has really opened up a tremendous opportunity for every operator to be your best operator, because the machine’s doing a lot, if not most, of that work for them.”
To that end, Bradbury has developed a laser-based flatness system. The Flat Trak CL Series monitoring system incorporates a laser measurement system to acquire an accurate shape profile of the material, analyzes the shape of the surface of the material to determine the location of loose material and offers suggestion to correct it. Flat Trak can also automatically monitor the surface shape of a coil, and if a problem develops, the software will automatically make adjustments to the leveler for correction.
According to Baker, the system allows even inexperienced operators to run a machine confidently, freeing up your most experienced operators for other tasks and ensuring a consistent product for your customers.
“We’re not just a company that’s looking for ways to measure the strip, and we’re not just a company looking to level it; we’re doing both functions at the same time,” he says. “With this kind of automation, you can have a relatively new employee or an employee who has no experience in the steel business run the line very effectively.”
A similar piece of technology called a yield finder automatically detects the strength of the material entering the leveler. “One of the difficulties operators have is finding the yield strength of the material,” Baker says. “We’ve added a feature to our levelers that takes a sample of the material so that we can find the actual yield strength ourselves.”
Leveling is a mature technology, which means most new innovation will, for the most part, happen at a slower pace. Regardless of where the future leads, once thing is certain: the customer will decide.
“It’s really kind of hard to tell where the technology is going because companies like ours are driven by customer requirements,” Linders says. “We react to what the market requires and the new issues that develop because of these new requirements.”