Holland, MI is home to a regional leader in the recycling and processing of metal, paper and plastic. This company services the area of western Michigan with approximately 400 employees. An important business segment for this recycler is the wholesaling of ferrous metal scrap, as well as waste and secondary nonferrous metals.
To process metal scrap for sale, the company uses a monstrous shredder, known in the industry as a hammermill— the primary purpose of which is to turn large pieces of metal material into small pieces. It's essentially a steel drum containing a horizontal rotor on which freeswinging pivoting hammers are mounted. The rotor is spun at a high speed inside the drum while material is fed into the drum. Material fed into the unit is impacted by the hammers, shredded into small pieces and expelled through screens in the collection drum.
Because it's required to shred large items like cars and structural steel scrap, this hammermill is particularly large and powerful (4000 hp)—and capable of withstanding considerable stress and abuse during operations. Tom Spettel is quite familiar with the machine and its operations. The president of Predictive Maintenance Services, Incorporated (P-M-S-I), he and his company provide engineering and maintenance reliability services for a wide range of industrial rotating machinery—including the large shredders at the Michigan recycling facility. According to Spettel, "this particular mill is about 10 years old with 34 heavy rotating hammers, each weighing 240 to 250 pounds. The metal is fed into the machine while the hammers rotate at 720 RPM."
A need for continuous predictive maintenance
Spettel explains that because the shredder is a bruteforce machine, there always are going to be mechanical issues impacting its uptime. For safety reasons, no one is allowed to be on or near the shredder while it is running. Consequently, past mechanical problems often had gone unnoticed until there was significant collateral damage or a breakdown. "They had me coming up on a periodic basis to take vibration readings with the mill at idle, as well as when an operator thought there were vibration problems," Spettel says. "It was a cumbersome process. Each time the customer thought there might be an issue, I would take measurements and analyze the cause of the increased vibration amplitude."
Because of the critical nature of this machine and concern that he may not always be available on a moment's notice to deal with potential problems, Spettel recommended installing an ITT Goulds Pumps brand ProSmart® condition monitoring system to help keep watch on the machine on a continuous basis. With this system, the focus of a Predictive Maintenance Program (PdM) can change from data collection to analysis and improvement activities. In addition, by continuously monitoring rotating equipment, the system can proactively warn of on-setting machinery problems.
The installation of ProSmart on the shredder was intended to measure the various causes of possible vibration, including rotor imbalance and bearing failure. The shredder does not lend itself to monitoring the unfiltered vibration amplitude with a simple vibration transmitter that provides a 4-20 mA signal. That's because a bearing defect doesn't generate enough vibration energy to cause a change in the overall vibration signal that could be as high as 1.0 in/sec during normal operation. Using the ProSmart system's capability to set independent alarm levels in up to 10 user-defined frequency bands, the machine can be monitored to alarm on a bearing amplitude of 0.10 in/sec and an imbalance at 1.0 in/sec. Spettel notes that it typically is an 8-to-10- hour job to change out a bearing. If, however, the bearing spins on the shaft, the repair time could be more than two days. "There is a lot of consequential damage if you do not detect a problem in time," he says. "ProSmart has a significant advantage over other monitoring systems because of the band alarming capability."
This remote monitoring system also incorporates wireless technology for sending machine health data over the Internet. When machine vibration, temperature or any other process parameter exceeds established limits, ProSmart provides notification within seconds by e-mail or phone. Should there be a potential problem, Spettel receives an e-mail via his cell phone. "If I have a concern about a particular frequency band," he continues, "I fire up my laptop so that I can request a spectrum and perform analysis without ever going on-site."
Imbalance leads to alarm
Recently, ProSmart alerted Spettel while he was in Detroit; about a four-hour drive from the recycling facility. Coincidentally, he was teaching a vibration seminar when increased vibration triggered an alarm condition, and thus was unable to quickly get over to the site. With ProSmart, though, he was able view the data and perform the analysis remotely—during a coffee break, in fact.
The problem was an imbalance. Inspection revealed that two 35-pound caps protecting the bolts that held the hammer shafts in place had broken free and were shredded right along with the rest of the scrap. This threw the machine badly out of balance. As the vibration increased, ProSmart notified Spettel to request shutdown of the machine. Upon inspection, the two caps were found to be missing.
This giant shredder clearly qualifies as a critical machine. For it, and other critical equipment, Spettel maintains that continuous monitoring is the smart thing to do, and at this busy Michigan recycling operation, ProSmart is the way to do it. MT