If you travel Ohio’s State Route 43 in Aurora, look to the west and you will see the expanding campus of Rotek Inc., a world leader in the engineering, manufacture, service and support of large-diameter slewing-ring bearings and seamless rolled rings. The company manufactures ball- and roller-type slewing-ring bearings in single-row and multi-row designs in diameters from 12 inches to 50 feet.
Since Rotek’s founding in 1962, the company has helped pioneer both the development of large-diameter bearings and their introduction as a substitute for king post, hook roller and other older techniques for controlling loads in rotational applications. Over the years, Rotek has introduced large-diameter bearings to a variety of applications, including power cranes and excavators, machine tools, medical equipment, large radar and radio-telescope antennas, and wind turbines.
In addition to its headquarters in Aurora, Rotek has a facility in Florence, Ky., that employs about 135 associates. The company is a subsidiary of Rothe Erde of Dortmund, Germany, a global leader in the production of slewing bearings and of seamless rolled steel and nonferrous metal rings. Rothe Erde is also a well-known manufacturer of turntables and structural elements. The company has been part of the ThyssenKrupp Technologies Group since 1998.
Large rings in “as-rolled” condition await further processing in storage area.
Design Expertise Helps Customers Find Solutions
The company prides itself on its ability to offer a unique combination of experience and technology in designing large-diameter bearings and seamless rolled rings. It has designed and manufactured thousands of slewing rings for an array of applications across many different industries. The firm’s extensive experience, coupled with the use of sophisticated CAD/CAM technology, enables it to accurately predict final product capabilities and performance.Customers and potential customers are encouraged to complete design-assistance worksheets available on the Internet. These worksheets are then analyzed by Rotek’s team of application and design engineers, who then provide a preliminary design evaluation based on application requirements. This evaluation includes a review of bearing design parameters, static and dynamic load capacities, bolt requirements, suggested gear specifications and more.
A matching set of machined rings is destined for the wind-energy market.
Integrated Facilities Provide Manufacturing Control and High Quality
Once the application engineers are finished with a part’s design specifications, production is scheduled. Rotek has two fully integrated manufacturing facilities, including two bearing plants (in Ohio and Kentucky) and a seamless ring-rolling mill. New construction is under way that will soon increase Rotek’s capabilities and capacity, including the addition of another ring-rolling mill (see sidebar). Each facility utilizes advanced CNC and CAD/CAM technology, Total Quality Management (TQM) disciplines and Manufacturing Resource Planning (MRP II) systems.These facilities allow Rotek complete control over quality and scheduling, beginning with the raw materials through ring rolling and continuing with thermal treatments, machining and assembly. With an inventory stock of more than 75 different base materials, most material specifications are easily met. Materials processed by the company include carbon, carbon alloy, stainless steel, aluminum alloy and high-alloy steels.
The company’s main production facility includes a Wagner press and rolling mill, complete heat-treatment capabilities and value-added machining operations. The current rolling mill is capable of producing seamless rolled rings from 16-158 inches in diameter with a weight range of 180-8,000 pounds. The size and weight range of product offerings will increase considerably after the expansion is complete.
Utilizing its in-house thermal-treatment capabilities, the firm has strong flexibility in obtaining optimum processing and application properties for each material type and grade. In addition to standard thermal treatments such as normalizing, annealing, soft annealing, austenitizing and tempering, other program-controlled processes allow precise adherence to specific time-temperature requirements for specialized alloys.
Backing up Rotek’s considerable capabilities is its quality management system, which has been certified by Det Norske Veritas, a leading registrar, as complying with ISO 9001 and ISO 9002. Additionally, every aspect of its business is governed by the principles of TQM and continuous measurement and improvement.
Post-Sale Services
Rotek offers a variety of services designed to help extend the service life of its slewing-ring bearings in the field. These include installation/change-out consultation and supervision, preventative-maintenance programs and in-use slewing-ring bearing analysis. The company also offers refurbishment and replacement programs for slewing-ring bearings that require removal from service. Its large-diameter-bearing refurbishment program includes:- Inspection, analysis and non-destructive testing to determine the feasibility and extent of remanufacturing required
- Redesign of slewing-ring bearing, if required
- Cutting of gears to international standards
- Machining and grinding of gearing, raceways and mounting surfaces
- Refitting of seals, rollers or balls, spacers and cages
- Raceway reconditioning through induction hardening and heat treating
Looking Ahead
The future is promising at Rotek, as attested to by the large investment in expansion that is under way on the company’s Ohio campus. As new facilities and equipment are completed and brought on-stream, Rotek’s captive ring-rolling operation will expand in capacity and capability. A second ring mill will be installed and commissioned in about a year, at which time Rotek will become the leading U.S. producer of large-diameter rings. Although additional North American competition looms closely in Mexico, Rotek is actively and aggressively positioning itself to maintain its status as a leading supplier to the markets it serves.
SIDEBAR: Expansion is Part of Rotek's Future
In May 2008, Rotek broke ground on an $82 million expansion project at its Aurora, Ohio, facility. The expansion – driven in part by brisk markets for wind-energy turbines, tunnel-boring machines, power cranes and excavators, and other types of equipment – will create an estimated 150 new jobs and bring employment at the facility up to 365. Production from new facilities is expected to come on-stream in the first quarter of 2010.The investment includes a second ring mill at the Aurora site to serve its own expanding large-diameter slewing-ring production and help meet growing demand in the U.S. for seamless rolled rings. With the capability of producing ring diameters of up to 280 inches and individual weights of 17 tons, the company expects the new SMS Meer RAW 400/400/6000 ring mill will make it the most modern facility of its kind in the U.S., providing high-quality rolled rings for high-integrity applications. Large-diameter slewing-ring production at the site will be further expanded by the addition of a 116,000-square-foot manufacturing plant housing the latest in production machinery and tooling.
“The planned expansion is an integral part of the company’s growth strategy,” said Leonard F. Osborne, Rotek’s president. “This significant investment represents our continued commitment to provide the highest-quality products and customer service possible.”
“Rotek is developing and manufacturing components for several high-growth industries, including wind energy, where Ohio has become a national leader with a strong competitive advantage,” said Ohio Governor Ted Strickland, who was present at the groundbreaking. “We welcome Rotek’s growth and the 150 new jobs in the city of Aurora. Rotek is an outstanding partner to this city and the state of Ohio.”
ThyssenKrupp Rotek received funds from Ohio’s Department of Development for job creation and training as well as machinery and equipment purchases. Additionally, the city of Aurora offered property-tax abatement and funds for road infrastructure improvements.
Photo sequence shows how a ring is formed: a) saw cuts ingot; b) manipulator moves the mult from the preheat furnace; c) the mult is compressed at its plastic-deformation temperature into a bloom; d) on the same press, the bloom is pierced in two stages – the center slug is removed and a ring is formed; and e) the ring-rolling mill shapes the ring into its radial and thickness specifications.
SIDEBAR: How a Ring is Wrung
The rolling of large-diameter rings begins with the acquisition of the appropriate raw materials. In Rotek’s case, bottom-poured or continuous-cast ingots of carbon, alloyed or stainless steels are received from U.S. and European suppliers. The company also forges aluminum. Ingot is received in large round stock ranging from 12-32 inches in diameter by 12-30 feet in length. The first step in the ring-making process is to cut the raw material into calculated lengths as determined by a ring’s specified weight requirement. The cut blank is called a mult.Once cut at the sawing station, the mult goes to a preheat furnace. Manipulators on rails load the mults, one at a time, to predetermined locations within the rectangular box furnace. Depending on its weight, the mult will spend 4-18 hours in the preheat furnace. The mult, along with others, is placed in a defined position in the furnace so it may be monitored and removed in the proper sequence for subsequent operations.
Upon completion of preheating, a separate rail-mounted manipulator moves the mults, each in their turn as they become ready, from the furnace to the forging press. Rotek uses a 3,000-ton SMS Wagner press in itsupsettingprocess, which compresses the heated piece at its plastic-deformation temperature into what is then called a bloom. This compression introduces wrought properties into the bloom and begins the development of a workpiece preform configuration.
The bloom is then ready to be pierced, which also occurs on the Wagner press. A swing arm brings the pre-piercing punch to the workpiece, which is forced into the hot upset stock and causes material to be displaced radially. The pre-pierce does not go all the way through the bloom. A second piercing stroke removes the center slug from the workpiece. The slug is eventually returned to the supplier as scrap for recycling. By this time, the workpiece has lost too much heat and must be reheated for further plastic deformation.
Upon reheating, the doughnut-shaped bloom is placed over the ID roll of the Wagner ring-rolling mill. All ring sizes are wrought on this same mill. The free-turning ID roll pushes against the OD roll by the application of radial hydraulic pressure, which reduces the ring’s wall thickness to specification. Coordinated with the radial rolls is a pair of tapered axial rolls that contact the top and bottom of the workpiece and form it to the proper height.
Depending on the size of the ring, rolling can take from two to five minutes. Rings that take longer to roll may have to be reheated and completed in two stages. A laser measurement system determines when a ring has met its dimensional specifications. At that point, the ring is removed by forklift or overhead crane and made ready for whatever further thermal treatments, machining or other operations may be necessary. After final quality checks, the ring is ready for shipment.
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