MAKING SMARTER STEEL: THE ONE-CRANE SOLUTION REVISITING NUCOR S JEWETT MELT SHOP

Transcription

1 MAKING SMARTER STEEL: THE ONE-CRANE SOLUTION REVISITING NUCOR S JEWETT MELT SHOP

2 Eight years in, Nucor s new-design melt shop in Jewett, TX shaves $10.2 million from capital expense and operating costs and approaches zero unplanned crane-related downtime.

3 Executive Summary The One-Crane Solution at Nucor Jewett has resulted in: saving Nucor significant money in initial equipment cost substantial maintenance savings over traditional DC controls a safer working environment for maintenance crews in the Control Rooms on the cranes reduced time that crews are on the cranes, exposed to the Melt Shop environment more time to work on other equipment to keep reliability of the entire facility higher improved cost-competitiveness of its operation, on multiple levels, including saving over $10.2 million in building, equipment and maintenance costs We re very happy with the reliability we re seeing after eight years, as the cranes have not caused any significant downtime. We attribute that to two factors: the design and quality of the cranes themselves, and the preventive maintenance practices we ve established around a single-crane solution, he said. But one of the very best aspects of this whole project has been the cooperation between Konecranes and Nucor in designing the reliability into these cranes. - Tommy Massey, Maintenance Manager We received some criticism from the industry when we first embarked on this project, but we had confidence in Konecranes and their capability. I also had confidence in our team here in Jewett that we had looked around every corner, and that this was the right thing for Nucor. We felt confident that we had done everything that we could, and that Konecranes was going to meet their side of the bargain. We couldn t be more pleased about how it has worked out. - John Farris, Mill Manager The greatest contribution to safety is that the cranes are reliable. - Tommy Massey, Maintenance Manager Making Smarter Steel 3

4 When Nucor began designing a new melt shop for its Jewett, TX mini-mill in 2002, the centerpiece of the design was what came to be known as the one-crane solution. Nucor conceptualized the $100 million mini-mill expansion with a single crane for each critical function: one charge crane, one ladle crane, one caster-maintenance crane, and one billet-handling crane. With no backup cranes anywhere in this scenario, industry-watchers were skeptical, both of the single-crane approach and the unconventional cranes they selected. It was the first time a U. S. steelmaker had purchased hot-metal cranes of this capacity featuring AC variablefrequency controls, which offer substantial maintenance savings and reduced downtime over traditional DC controls. Nucor s primary motivation for the new melt shop was to improve the cost-competitiveness of its operation. Since the mill s products are merchant-grade bars, angles and light structurals, cost-per-ton is a primary factor in improving market share. 4 Making Smarter Steel The steel making business is capital intensive. We were confident we could complete the project on budget and on time. The challenge was how much value could we pack into $100 million. The team s mission was to build a melting and casting facility that would provide a competitive advantage in safety, quality and operational performance for years to come. To accomplish this, our team challenged tradition and searched for different ideas from around the world and in other industries. One key area begging for something different was overhead cranes. We could not get comfortable with the traditional notion of a backup crane and instead decided to find a crane manufacturer capable of building a single crane with built-in redundancy. Konecranes was selected as the partner to innovate our severe duty crane application, said John Farris, Jewett s maintenance manager at the time, and now mill manager. In short, we did not see the additional backup cranes adding value to our operation. In fact, the one-crane solution saved Nucor significant money in initial equipment cost by eliminating backups for the charge, ladle and billet cranes. Nucor s team looked at every design element that could impact cost, from the cost of the buildings and cranes to long-term maintenance and reliability issues. Manpower was a factor too more cranes require more maintenance workers and operators. The concept of purchasing a single crane for each function was revolutionary, particularly in an operation whose goal was zero unplanned downtime for its cranes. Ten years later, with eight years of actual data on crane uptime performance and maintenance cost savings available for review, the results of Nucor s commitment to a new crane paradigm are there on the page for all to see.

5 An AC approach to steel mill cranes As Nucor s material handling partner in this venture, Konecranes worked with the steel producer to design four AC-powered cranes with extensive redundant features that gave Nucor the equivalent of two cranes in one when it came to reliability. The AC variable-frequency controls also eliminated some of the worst maintenance headaches of DC powered cranes. According to Tommy Massey, who succeeded John Farris as maintenance manager at the Jewett mill, the controversial AC versus DC choice has also been amply vindicated over the past eight years. After moving into Farris s position, Massey implemented new parameters for tracking all of the costs and downtime attributed to the cranes, with up to 40 data points in some areas. Eight years after installation in 2004, it is this data that can be referenced to evaluate the choices Nucor made in 2002 when the purchase orders were written. Purchasing high capacity cranes with AC inverter rather than DC controls has significantly reduced both our maintenance and downtime costs, because AC motors don t require the same frequency of preventive maintenance, says Massey. DC motors with brushes and commutators as part of their electrically engineered structures require frequent checking, and brush wear causes degradation of the motors due to a buildup of carbon dust. Purchasing high capacity cranes with AC inverter rather than DC controls has significantly reduced both our maintenance and downtime costs, because AC motors don t require the same frequency of preventive maintenance. - Tommy Massey, Maintenance Manager Making Smarter Steel 5

6 According to Damon Burrow, Nucor s melt shop electrical lead, the AC motors are more economical. Many long-timers in the industry believe DC is the only way to go because of the amount of torque and life you get out of them, he said. I can tell you just from our experience, we have far fewer problems from AC motors, and they are much less expensive to replace than a DC motor. Even if you have a DC motor rebuilt, you can buy a brand new AC motor replacement for less money. Savings through limiting building size But maintenance savings through the AC versus DC choice was only the tip of the iceberg when it came to Nucor s cost-reforming strategies for the Jewett melt shop. Another major factor was overall 6 Making Smarter Steel building cost. Nucor has estimated that the one-crane solution reduced their building cost by 30 percent. The new melt shop replaced an outdated facility at the same site with only 850,000 tons of capacity. Nucor s new facility elevated capacity to 1.2 million tons a year nearly 50 percent more. Replacing three 45-ton electric arc furnaces was a single 90-ton EAF that shaved melt time from 70 minutes to 35 minutes at 3,000 degrees. Yet the new EAF bay with its 225- foot runway was very compact by most standards. It would have required at least another 100 feet of runway and two additional bays in both the charge and ladle areas to accommodate a redundant crane, and the added square footage would have required more capacity for the emission control system. When the new melt shop opened, the cost savings for eliminating those four bays was estimated at $4 million USD. If the facility were built today, the savings would be even more.

7 Savings on crane equipment In addition to a larger building footprint and emission system, a traditional two-crane solution would have required purchasing backups for the charge, ladle and billet cranes, at a potential additional cost of another $4.4 million USD in 2002, plus $300,000 in installation costs. (In a two-crane solution, the second ladle crane would replace the caster-maintenance crane.) Instead, Nucor and lifting partner Konecranes met this challenge by essentially combining the mechanical and electrical resources of two cranes into one structural package for maximum reliability. On each of the four cranes, the bridge and trolley are equipped with four to eight drive motors. Even with half the drives out of operation the trolley or bridge can still operate, although at reduced speeds and with longer acceleration times. Similarly, the main hoists on the ladle, charge and billet cranes are equipped with two hoist motors and differential gearboxes that permit them to remain fully functional at reduced speeds in the event of failure of one of the main hoist motors or inverters. This capability was critical to address Nucor s challenge of zero unplanned mill downtime attributed to the cranes. Looking at the initial cost of two cranes versus one you pay more by having redundancy on the crane but not the same cost as buying two individual cranes to do the same task, said Damon Burrow. In our situation we do not have a dedicated crane crew we have one maintenance team that works on all of the equipment at the plant. Time spent doing preventive maintenance on two cranes takes away time from our other equipment. Having only one crane for each job gives us more time to work on other equipment to keep reliability of the entire facility higher, Burrow continued. Making Smarter Steel 7

8 Also contributing to uptime was the design of the AC control house. On the Nucor charge, ladle and billet cranes, each control function has two inverters. In pursuit of reliability, Nucor has a spare inverter pre-wired in the control house for each motion on the crane. A simple switching process is all that is needed to bring a spare inverter on line. Inverters will accept two sets of parameters, so Konecranes put one inverter between each two primary controls that can run either A or B motion. Downtime cost savings Maintenance Manager Tommy Massey says the downtime cost savings realized through this feature is a major plus. To replace one of those drives might take us 30 hours, and a repair could take hours. With a spare installed, in a matter of 30 minutes we can switch the drive and then schedule a repair of the problem drive. It s given us a significant savings over repair or replace time. With melt-shop downtime currently estimated at around $15,000 per hour, cost savings through inverter redundancy in the scenario Massey outlined could range from $90,000 to $225,000, depending on how much time the repair ultimately requires. Downtime savings for a 30- hour replacement would add up to a staggering $450,000. In eight years, the mill attributes no significant downtime to the cranes. Safety considerations According to Massey, the control e- house has also influenced downtime cost by providing a safe working environment for maintenance crews engaged in service or diagnosis on the cranes. Work gets done faster with fewer trips up on the crane. The e-house was designed with double door enclosures for two reasons: first, to keep dust away from the electrical equipment which improves reliability, and second, it is air conditioned at 80 degrees maintained, Massey says. If we have an electrical fault, a lot of the trouble-shooting or work goes on in the air-conditioned space instead of out in the environment of the melt shop, where temperatures can reach degrees ambient outside the e-house on the crane, he continued. 8 Making Smarter Steel

9 He noted that the redundant features, notably gearboxes and drives, allow workers to keep cranes operating without having to address issues while the shop is under pressure for production. Also, the design of the control systems with the interlocked safety features that are built in to the operating system have had a significant impact on reducing the amount of operational errors that can damage the crane. With the reliability of the cranes being so high, our crews are not on the cranes nearly as much as we would be on an unreliable crane, says Massey. The greatest contri bution to safety is that the cranes are reliable. According to Damon Burrow, the cranes also benefit from a groundbased diagnostics feature. A maintenance worker can check many conditions without actually getting on the crane, which has rotating equipment and pinch points to think about, he said. If you can limit the times workers need to get on the crane, you reduce their exposure. The job becomes safer and more effective fewer hazards need to be mitigated to get the same sort of information you d normally have to go on crane to retrieve, he continued. But according to Massey, they haven t used it much. It s great when there is something going on and we can take a quick look from the ground first. But honestly, the cranes have been so reliable that it just hasn t been a major factor, he said. Trimming costs along with spares With an eye to managing costs, the Nucor and Konecranes team also worked to design the cranes with a high commonality of spares. Nucor didn t need to purchase as many individual items because a spare bridge wheel or hoist motor would work in several places. Initially it was estimated that the number of

10 spares Nucor needed to carry was reduced by 90 percent. When asked whether that had translated into real savings, Massey was affirmative, although the spares inventory is not among the costs monitored in his tracking project. The spares we did purchase were chosen to make sure we didn t have extended downtime waiting to order something, Massey said. Here s where the savings comes in if we have one hoist motor spare in the warehouse it s good in one of five spots. Had we not had similar hoist motors on the cranes, in the worst-case scenario if we had a different hoist motor in each location we would have needed five spares. The cost savings is in the inventory value we have to keep to maintain reliability. Waiting for spares to be delivered is not an option, he stated. Factoring maintenance cost reduction for a single crane solution Getting back to Nucor s cost-tracking project, the system tracks expenses individually for each of the four cranes by year, breaking this down into three categories: Labor that the team spends on the cranes, Material checked out of the MRO inventory, and Purchases of non-inventory parts and services required for cranes. (See Sidebar B, Table 2.) Knowing what the actual expenditure was for one redundant crane, Massey and Burrow estimated that maintenance for the two-crane solution that they did not purchase could be arrived at by multiplying actual cost by a factor somewhere between 1.25 to 1.5. Because the redundant crane would be used less than full time, parts would not wear as quickly. Also, because more repairs and PMs must be done on the single crane that is used constantly, maintenance cost is higher that it would be on one of a pair of traditional cranes. Still, the $1,785,710 USD Massey and Burrow estimate that they saved (using 1.4 as the factor) by not having duplicate cranes is a significant chunk of their overall cost savings. Also, due to Nucor s personnel structure, savings on operator salaries and benefits did not figure as part of the total, as they might have at another operation. Maintenance planning also becomes more important in a single crane scenario. In a traditional dual crane system you will have a crane that is always available as your backup one crane that is in operation the majority of time. You can easily work on the second crane if something is wrong, says Burrow. With a single crane system you have to plan out when you will do work and repairs much more in depth. I look at it as operating from a preventive style instead of a fix it when it breaks because we have a backup style. You will have more upkeep on the individual crane, but you will also have fewer workers doing preventives on two cranes. Burrow said that a good example of this philosophy is Nucor s billet crane, which has the least amount of time available for maintenance and repairs, as it services both rolling mills and the melt shop with a capacity of 1.2 million tons. It actually handles 2.4 million tons a year, as it moves everything twice, says Burrow. With new customer orders, we expect throughput on this crane will soon total three million tons per year.

11 According to Burrow, the billet crane has stacked eight million tons of steel since it was installed and then moved it again for shipment, making it the hardest-working crane in the facility. The Nucor billet crane has an unusual rotating trolley that enables it to stack billets side by side until they have a square stack. Then the trolley can rotate 90 degrees to build the next stack which prevents domino-like falls in the 1,200-foot-long billet bay. The next step for Nucor s cranes In the eight years since Nucor purchased their four melt shop cranes, lifting technology has continued to advance. Nucor is now upgrading their charge crane to incorporate DynAReg, one of Konecranes newest technologies that recaptures the braking energy of the hoist and recycles it into the electrical grid. We don t expect significant savings from the electrical capture, says Massey. Where it will really help is improving the design for maintainability. On the current drive system there are resistors outside the e-house, exposed to the environment, dust, dirt and heat. With the new DynAReg system there is no need for those high-maintenance resistors, he said. Final thoughts from the Nucor team Looking back over the past eight years Tommy Massey and Damon Burrow have calculated that Nucor s Jewett melt shop has saved over $10.2 million USD in building, equipment and maintenance costs with its crane program, while successfully moving eight million tons of steel. A sideby-side comparison of the cranes they purchased alongside a more traditional two-crane solution, also quoted by Konecranes in 2002, shows where the savings can be found. (See Sidebar B, Table 1.) For those considering following in Nucor s footsteps, Damon Burrow had some parting thoughts about crane design and how it can contribute to operational flexibility and reliability. We ended up with so many more benefits we didn t expect, like having extra equipment up on the crane and being able to select a different motor or drive and then go back to operating, he said. We can also use those as troubleshooting tools if we are having problems or want to do maintenance. We can use all these options to get the crane back in operation faster. Before having redundant systems, we had to completely change a piece of equipment to find out if what we thought was the issue was really it, he said. Of course, the gold standard remains no unplanned mill downtime attributed to the cranes, and Nucor has come very close to achieving it. Burrow, who serves as Chairman of the AIST crane committee, had this to say: You re going to have to get your maintenance team and production team on the same page as far as operating time and work time, he emphasized. I would definitely say that the one-crane solution at our facility has changed the way we do things now it s just a part of how we operate, he said. A lot of concerns voiced when we first went with the one-crane solution (that it wouldn t work, and that no one had even attempted it before!) have fallen by the wayside. We ve proven over the last eight years that it can be done and done reliably. Nucor s Maintenance Manager Tommy Massey agreed. We re very happy with the reliability we re seeing after eight years, as the cranes have not caused any significant downtime. We attribute that to two factors: the design and quality of the cranes themselves, and the preventive maintenance practices we ve established around a single-crane solution, he said. But one of the very best aspects of this whole project has been the cooperation between Konecranes and Nucor in designing the reliability into these cranes. Making Smarter Steel 11

12 According to Nucor s Mill Manager John Farris, the financial impact of the one-crane solution on the Jewett mill s bottom line supports the feeling they had in 2004 that Nucor had partnered with the innovator in overhead crane heavy lifting applications. I would say that $10.2 million is a very conservative number, says Farris. Looking at a traditional approach, the cranes themselves would have been $4.5 to $5 million each that we did not have to buy. That s $10 million in savings right there. An increase in the building All of the things we wanted to build in, Konecranes was successful in giving us. Our operating cost reflects that. With the technology that is available now, and with what s been proven here, I can t imagine anyone designing a new melt shop with double cranes today. The only thing that would motivate a business to do that would be if specific material handling demands dictated that having two cranes was the only way to do the work. - John Farris, Mill Manager According to Farris, the single-crane paradigm allowed the shop to be smaller, and improved efficiency from the environmental control standpoint. We had a very compact material flow throughout the plant, so material handling of the scrap and liquid metal is very efficient the entire operation doesn t have to traverse very far. That is key to the efficiency of this melt shop. size would be another $5 million, and the bag house would add another million. I can see the savings in today s dollars from the onecrane solution being $15 to $16 million, and I am confident that is still a conservative estimate. Farris also pointed out that much of the number-crunching that substantiated the $10.2 million in savings Nucor has documented from the one-crane solution came from expenses they incurred early on, and do not resemble current costs for construction and lifting equipment. 12 Making Smarter Steel

13 Crane by Crane: Examining the Details (Sidebar A) All four of Nucor s melt shop cranes are top-running, double girder designs from Konecranes featuring AC inverter controls. Nucor s radio-controlled charge crane is rated CMAA Class F at 200 tons, with two auxiliary hoists rated at 75 and 25 tons. The crane is also rated at CMAA Class B at 300 tons for handling major equipment during maintenance outages. Its process begins when the charge crane picks up an 80-ton bucket loaded with around 100 tons of scrap steel, and conveys it to the electric arc furnace, ferrying loads each day. The 5,000 cubic foot capacity bucket required for one charge operation weighs 198 tons when full. The crane s 75-ton auxiliary hoist is used to open the charge bucket, and the 25-ton auxiliary allows the operator to change furnace electrodes and access areas that cannot be reached by the 75-ton hoist. The 25-ton hoist is equipped for magnet use, further enhancing its maintenance value. Total travel distance for the charge crane is only 100 feet, with a vertical lift of 90 feet. The 200-ton ladle crane is a virtual twin to the charge crane, but without the 25-ton auxiliary hoist, and with the addition of an operator s cab. Both cranes are designed for continuous duty in extremely harsh environments, with splashing molten metal, sparks, flame and fumes, in ambient temperatures from 140 degrees to 165 degrees. Carefully located heat shields protect key areas of the cranes, which are engulfed in flame at each furnace charge, and exposed to searing heat during ladle handling in the caster aisle. This crane picks up the ladle of molten steel from a ladle car and moves it to an alloying station and then to the caster, which converts the steel into billets. After depositing the ladle, the crane returns for another load. The ladle crane travels just 130 feet from alloying station to caster, with a vertical lift of 90 feet. The caster maintenance crane, CMAA service class D, is rated at 100 tons with a 35-ton auxiliary hoist. It is used to clean the slag out of empty ladles and prepare them for their next use. Full ladles are handled by the ladle crane; when they are empty, the caster crane takes over. This crane is also equipped for magnet use on its auxiliary hoist. The caster maintenance crane has horizontal travel of more than 400 feet, and vertical lift of 90 feet. Nucor s innovative billet crane, rated CMAA class E, is a two-magnet crane with a 75-ton main hoist and a 12.5-ton auxiliary. It has a unique trolley, which allows turning the hoisting machinery through 270 degrees of rotation to position the magnets in any orientation required for billet handling. It handles up to (19) 6.25-in square billets at a time. Because it was designed to fit into an older building with limited headroom, this crane had to be designed with much of the trolley recessed between the girders. The billet crane travels 1,200 feet with a vertical lift of only 50 feet.

14 Overview of Cost Savings Totaling $10.2 Million USD (Sidebar B, Table 1) Nucor has been able to verify the cost savings of the one-crane solution at least partially because Konecranes initially offered pricing on a traditional, two-crane solution that was not selected. Looking back at those equipment cost numbers, circa 2002, and extrapolating what costs would have been to operate and maintain seven traditional cranes compared to four redundant cranes, Nucor s Tommy Massey and Damon Burrow developed a comparison of the two solutions. 14 Making Smarter Steel

15 Maintenance Cost Comparison for the One-Crane Solution Sidebar B, Table 2) When Nucor s Jewett melt shop became operational in 2004, crane maintenance costs were divided into three categories for tracking and analysis. (See below.) This allows managers to see what part of the crane incurs cost, making it easier to make decisions about where maintenance dollars should go. Nucor s system monitors 40 different data capture areas on the charge crane. Making Smarter Steel 15

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