Balancers can monitor fan vibration levels in real time and automatically correct for unbalanced conditions

Dec. 9, 2003
Induced draft fans at U.S. Steel Fairfield Works, Fairfield, Ala., are responsible for pulling the air, gases and materials off the basic oxygen furnace. The furnace heats the steel to approximately 2,800 F, and the fans are critical to successful steelmaking.

Imbalance and high vibration were caused by excess build-up of particulate on the fan rotor, which resulted in chunks of buildup falling off the rotor. The fans had to be cleaned and manually balanced at least every three months.

It typically took between three and five balance attempts to successfully perform a manual balance. This often resulted in a violation of the time recommended between starts on the motor, creating high potential for motor failure. Further, when a fan was stopped due to high vibration, it would result in a shutdown of the steel making process.

"We knew we needed a solution," says Jim Mays, maintenance manager, U.S. Steel Fairfield Works. "And since the early 1990s, we had carefully observed Lord's RealTime balancing technology. Once the technology was validated, we knew it was time to implement the solution for our facility."

Does it in real time

Able to correct an imbalance in machinery while in operation, the system continuously monitors fan vibration levels and phase angle, and automatically corrects for unbalanced conditions. This is done while the fan is running at operating speed, eliminating costly downtime associated with manual balancing.

The balancing ring of the system mounts directly to the fan's shaft. The ring is divided into four chambers that contain a unique high-specific-gravity balancing fluid. When the balancer's controller detects an imbalance, the fluid in the chamber on the heavy side heats up, changing from a liquid to a gas. The gas transfers through a shuttle tube to the chamber on the light side where it condenses and returns to a liquid. This process continues until the controller senses that balance has been restored.

The technology was developed and patented for the rotary transformer used in the automatic fan balancer system. A non-contact power supply eliminates the need for maintenance, sending power and data across an air gap between a stationary primary coil and a rotating secondary coil.

Needs custom installation

Implementing such a solution is not as easy as ordering a part. When you are dealing with a 121-inch-diameter, 13-ton, double-wide, double-inlet fannot to mention a finely-tuned manufacturing process that typically runs like clockworkinstallation of any solution must be carefully orchestrated. As such, Mays worked with the supplier to design a housing solution for the online balancer, as well as scheduled installation during a three-day furnace shutdown. Balancing systems were added to the remaining two fans during the course of the next year.

"Our applications and site engineers spent a lot of time coordinating all of the installation details with Mays and his staff at Fairfield," say Andy Winzenz, product manager, Lord Corp. ( "We typically install our systems during longer one- to two-week maintenance outages, so we had to make sure there were no surprises when we arrived on-site. Subsequent installations have taken place in as little as 24 hours."

Results are worth it

"It goes without saying that efficiency is crucial and downtime is deadly in the steelmaking industry," says Mays. "Fortunately though, we were able to transfer the knowledge gained at our Gary Works, Ind. facility to fix a similar problem at Fairfield. This implementation at Fairfield has already improved uptime, which lowers our overall costs."

Since installation of the three balancers, Mays says they average one scheduled maintenance shutdown and one interim cleaning per year. The typical shutdown lasts between eight and 12 hours, so the savings are significant. But beyond saved revenue and time from reduced shutdowns, Mays says the online balancing technology continuously maintains the balance level of the fans below 0.8 mils, as compared to the previous 1.0 mils low level field balance.

Motor and bearing life has been increased, resulting in fewer motor rebuilds at approximately $200,000 each. Mays says "The whole steelmaking process has become more predictable and productive with the online balancer."

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