Bad Vibrations

As a major manufacturer and distributor of uncoated free-sheet papers, containerboard and corrugated containers, newsprint and market pulp, Boise Paper Solutions provides products that aid their customers in making their own products. That is why having to go offline for unscheduled lime kiln shut-downs at a cost of about $87,000 a year in lost production, makeup time and maintenance costs is disastrous.

LORD Corp.’s balancing technology allows for a nickel to be balanced on the edge of a fan bearing while in operation.

Ron Blood, predictive maintenance and reliability supervisor for Boise’s plant in Wallula, Washington, became aware of a continual build-up problem with calcium carbonate on one of their large induction (ID) fans for a lime kiln. According to Blood, particulate had a tendency to stick to the fan rotor and this continuous, nonuniform build-up would throw the fan out of balance. The vibration resulted in an average of 2.5 unscheduled shutdowns per year—at a cost of $33,000 to $35,000 each in lost production, makeup lime and maintenance costs.

“When the fan started to vibrate, my coffee would actually shake in my cup as it sat on my desktop,” said Blood. “Shutting down is a serious process that typically takes three hours to allow the kiln to cool off, and another three hours to conduct the cleaning process. By the time we would get the kiln back in service, at least ten hours of production was lost.”

In addition to lost time and production, frequent episodes of high vibration also were causing accelerated wear on the fan bearing, and the staff was often taken away from regular duties to troubleshoot vibration problems.

Searching for an answer
When faced with finding a solution to this situation, Blood remembered reading an article about a technology that might help solve his problem. After a quick Internet search, Blood located LORD Corp., a provider of management of vibration, motion and noise. Andy Winzenz, sales manager for Lord Corp., visited the plant and helped confirm the diagnosis.

“Boise’s manufacturing process is dependent on the performance of the fans and their ability to maintain process air flow,” said Winzenz. “As such, when the fan was thrown out of balance because of build-up, the result was untimely and expensive shut-downs.”

Although LORD Corp. has a variety of products for the manufacturing industry, Winzenz recommended its balancing system because of its ability to make rapid balance corrections and withstand the harsh environment surrounding the lime kiln ID fan.
LORD’s balancing system is set up to monitor fan-bearing vibration levels and the vibration phase angle and then automatically correct for unbalanced conditions while the fan is running at operating speed, eliminating costly downtime to clean and balance the fan manually. Once levels reach a preset high trip point, the system switches on, commanding balance mass inside the shaft-mounted system to adjust as needed to counteract the imbalance and reduce the vibration.

The balancing ring of the balancing system mounts to the fan shaft. The ring houses liquid counterweight masses that can be repositioned to offset the imbalance detected in the fan rotor. Utilizing vibration sensors, the system monitors the fan bearing vibration. Vibration signals are received and processed by an “adaptive influence coefficient” control system, which then determines the balance adjustments required. The controller relocates the counterweight masses to the desired position to minimize the vibration levels. This process continues until the controller senses that balance has been restored. Typical balance cycle times range from 30 to 120 seconds, depending on operating speed.

LORD Corp. developed and patented the actuator coil assembly used in their balancing system. The actuator coil is traditionally mounted to support brackets located on the bearing pedestal. The noncontact power supply used in the actuator coil eliminates the need for maintenance, sending power across an air gap between the stationary actuator coil and the rotating balancer ring.

Implementing the solution
Installation—during a regular scheduled shutdown—involved moving the motor out of the way, pulling the coupling and bearing off the fan shaft, installation of the balance ring, reassembly of the bearing and coupling, and putting the motor back in and aligning it. Some minor trimming of the stiffening ribs on the fan housing had to be done to make clearance for the balance ring. Other work, such as installing power to the controller and then mounting it in a dustproof, waterproof box near the fan, was completed in advance of the shutdown.

Since installation, the team has endured only one unscheduled shut-down, which was caused by massive particulate build-up and throw-off. Blood said that after the installation, the fan ran so smoothly that the team forgot that build-up was still happening.

“We received a wake-up call several months after installation when a large chunk of build-up flew off the fan,” said Blood. “The resulting vibration was more than the balancer could compensate for, so we had to shut down and sandblast."

Fortunately, because the technology stores balance history and events, data can be analyzed—greatly aiding Boise’s process of calculating the build-up rate of the particulate to better plan for any necessary cleaning and sandblasting.

The proof is in the numbers 

According to Blood, this process improvement has added up to big savings. Boise is running the lime kiln with fewer production interruptions, as well as extending the life of their equipment and causing minimal wear and tear on the fan bearings. Boise still shuts down the lime kiln three or four times per year for routine maintenance.

Blood’s coffee sits calmly in his cup each morning now. He demonstrates the smoothness of the fan operation by balancing a nickel on edge on a fan in operation. Even more important, the production supervisors have few worries about the fan and can perform their daily functions without the hassle of an unscheduled shut-down.

Finally, the vibration figures speak for themselves. Before installation of the balancer, the fan registered 0.3- to 0.8-in. per second within 30 to 60 days of sandblasting. Today, however, Boise reports vibration levels of 0.04- to 0.06-in. per second within the same time frame.

“LORD Corp.’s balancing systems technology paid for itself in six months, not taking into account the expense of wear and tear on the bearings,” said Blood. “Although the installation and learning curve had some glitches, the technology has more than met our expectations. A fan that was once a chronic problem and a constant worry is now one of the smoothest running pieces of rotating equipment in the mill.”

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