"We put in a lot of effort to propose a design that maximized the benefits of the installation, as opposed to taking something that we had already designed and trying to make it fit," says Jock Buta, executive vice president of Butech Bliss. "Many of the design principles we used aren’t typical for hot crop shear designs, but we’ve been refining designs throughout more than 150 shears, and they’ve evolved to a high degree of functionality."
The new equipment will replace ArcelorMittal Bremen’s existing crop shear in a 90-inch hot strip mill. It will process high-strength steel up to 3 inches thick by 87 inches wide.
Replacement is necessary for several reasons. "Their old shear is showing signs of failure," Buta says. "It has some major cracks, and they’ve had to do quite a bit to patch it up. With worldwide steel trends, the tendency is to go thicker, which, with respect to the shear, requires higher forces to cut as well as dimensional changes because it has to be able to open up wide enough to handle an even thicker transfer bar."
Kai Küstner, project manager for ArcelorMittal Bremen, points out if the hot mill line at ArcelorMittal’s Bremen facility shuts down for any reason, the entire plant shuts down. As a result, Butech Bliss’ challenge was to reuse the entire existing foundation and the existing motors from the previous crop shear to minimize the impact of the outage during installation.
The existing design, which is about 40 years old, is a four-crank design. "Almost everyone who quoted proposed this type of design," says Buta. "We did a different design."
"We wanted a crank-type crop shear," says Küstner. "We want-ed to be able to cut 76-millimeter-thick transfer bars with a width of about 2.2 meters for high-strength steel grades. We chose Butech because of the unique design of the crop shear that they presented to us. It was clear to us that this was the best design."
The design "has a lot of advantages," according to Buta. "It’s a two-crankshaft design that uses cam-roll guiding. However, it’s a much larger scale than you would typically ever see, so we have to design these giant cam rolls. The cam rolls give you smoother action and can be preloaded so that you have very tight clearances and can hold positions without enormous forces to overcome the friction of typical sliding way designs."
The shear not only is using high forces to cut material but also has to keep up with high speed. "This is a flying shear or a shear that has to cut while the material is moving," Buta says. "The top line speed is 400 feet per minute, and it doesn’t stop while it’s passing through the shear. You have to accelerate the knife holders so they are going the same speed as the transfer bar and make the cut without slowing the transfer bar down."
Continuously processing tough materials at high speeds inevitably will cause fatigue on components.
"Our analysis of the existing design showed why failures occurred," Buta says. "Long term, you get fatigue failure. It’s one thing to see the stresses on certain parts of the machine and then design the parts to be high-strength steel, heavy enough and thick enough to withstand those, but you also need to consider longer-term fatigue where you may not be stressing something past its point of failure, but if you repeatedly take it to a certain degree of stress, it will fail."
To mitigate the heavy stresses the crop shear will face every day, Butech Bliss used specialized materials for the crankshafts. "The two crankshafts were forged at Ellwood City Forge, Ellwood City, Pa.," Buta says. "It was a challenge to take the forgings from the design stage to the actual finished forging and maintaining their strength throughout the critical areas. Ellwood used some specialized heat treating and some trial and error to make it work."
When construction is finished, the crop shear will weigh about a million pounds. As a result, "we have to design large fixtures just to handle the equipment," Buta says. "In some cases, we have to design lifting beams or spanner beams that go through two crane hooks because one single crane will not be enough."
"For the re-assembly and installation, the trickiest thing will be to get the old crop shear out and lift it out all in one piece," Küstner says. "Then we need to assemble the new crop shear, which has many heavy parts. It is a completely new type of crop shear for us. We are very excited to see how it will work."
Because the shear is such a crucial component of the hot-mill line, the ability to perform maintenance service quickly is key. Buta says it is imperative for the team at ArcelorMittal Bremen to have access to parts, should they fail. All the parts are custom-designed, and the company bought large spare components, like the crankshaft and other vital drive components, because it doesn’t have time to wait for the long delivery of new ones.
"Mills do have crashes, accidents happen when something too thick comes through the mill, or if the material has cooled too much, the force required to cut it will be that much harder," Buta says. "If while the bar is moving through, it runs into something or slows down, you may be stopping a giant, many-ton piece of metal in its tracks, which can put tremendous forces on the components of the shear. As a result, you try to design for some of the worst-case scenarios where you need to be able to go in and replace the components as quickly as possible.
"The highest-wear item in the shear would be the shear knives. Those will need to be replaced regularly, so part of the design was a quick knife-change feature to allow these big, heavy knives, the old ones, to be pulled out from the shear automatically, new ones put in and locked back into place to hold the tight tolerances that are required in a relatively quick period of time. In all of our shears, the largest-wear items are the knives, so the quick-change knife feature is a design aspect that we’ve highly refined."
Employees at Butech Bliss and ArcelorMittal Bremen are excited about the project, and it’s given Butech a boost in business.
"The whole project is exciting because it is a new type of crop shear," Küstner says. "Butech is not really known in Europe for these type of projects. It was a surprise for both Butech and the other vendors that Butech received this offer. For us, we were sure that the best technical solution came from Butech. We chose our contractor very carefully, focusing on technology, delivery time and guarantees."
"During the 2008-2009 downturn, cancellations, placement on hold and a dropoff in new orders forced us to do quite a number of layoffs," Buta says. "This project was key in allowing us to bring some of the engineering and manufacturing workers back." He estimates for this project alone the company will buy more than $6 million of parts and services, especially out of northeastern Ohio.
"It’s also allowed us to be considered for some other large-gauge crop shears," Buta notes. "It’s exciting. It’s energized the whole company, and it was a nice morale boost after coming out of the doldrums of the major recession." MM