Hot solution finds hot bearings

The value of predictive maintenance programs (PdM) lies in effectively troubleshooting small problems before they become large ones.

While vibration analysis is often the PdM technology of choice for monitoring large, accessible, relatively high-speed bearings, thermography can be a good alternative, or a good addition to, vibration analysis. Thermography can be performed at a safe distance while the equipment is operating. Also, capturing a thermal image with a handheld imager takes less time than performing vibration analysis.

Thermal imagers capture two-dimensional infrared maps of bearing and housing temperatures, helping technicians to compare current operating temperatures to pre-established benchmarks. This can help detect potential failures, saving companies the time, labour and financial risks of downtime.

That’s exactly why Dave Feniak, electrical maintenance supervisor at Weyerhaeuser Co., in Drayton Valley, Alta., purchased a thermal imaging camera for the sawmill’s fledgling PdM program.

Weyerhaeuser is one of the world’s largest forestry products companies, with operations in 18 countries around the world. Downtime at the company’s sawmills is incredibly expensive, racking up tens of thousands of dollars in losses in a single shift.

The Weyerhaeuser Drayton Valley sawmill has employed outside contractors to perform routine infrared scans as a core part of its preventive maintenance (PM) program since 1992. But the in the ever-present quest for increased productivity, Feniak wanted to add a PdM program to help spot potential problems more effectively.

He arranged the purchase of an infrared (IR) camera and put it to use immediately. The camera, and the new PdM program, soon proved valuable.

“I was looking at bearings in the planer mill and noticed a very hot spot in the far distance,” Feniak recounts. He turned on the camera’s laser pointer option and found that heat was being generated from the sawmill trim-saw motor 150 ft away.

“Taking the camera right over to the motor, we saw the motor windings were at 90 degrees Celsius (194*F),” he continues. “We did amp checks and found a severe imbalance between phases. This was on a Thursday, so we got our spare motor out and installed it the next morning on the maintenance shift, with no downtime. If the motor had failed on shift, the cost would have been approximately $30,000 for the downtime, plus the repairs would have been more expensive.”

Feniak got instant ROI from his thermal imaging camera, a Fluke Ti30, which helped to avert a potential problem that could have cost three times the purchase price of the imager. It not only justified the cost of the camera to the company, says Feniak, but it helped reinforce the value of predictive maintenance as well as preventive maintenance.

“Our sawmill is constantly pushed to be faster and we target increased reliability. Using this tool has already shown us problems in early stages, allowing us to add oil to a gear reducer or replace a fan on a motor before the problem got worse.”

These measures give Weyerhaeuser the time it needs to plan, schedule and make repairs before equipment fails, avoiding major breakdowns and costly downtime.

Studies show that a planned repair job typically takes only half as much time as an unplanned job. In his book, Plant Engineer’s Handbook, Keith Mobley links the following benefits to preventive maintenance:

* Maintenance costs — down by 50%

* Unexpected failures — reduced by 55%

* Repair and overhaul time — down by 60%

* Spare parts inventory — reduced by 30%

* 30% increase in machinery mean time between failures (MTBF)

* 30% increase in uptime.

By adding a PdM inspection program to Weyerhaeuser’s existing PM program, Feniak is getting all those benefits and more. The thermographic camera, he says, has helped him expand his existing PM program, while increasing the frequency and efficiency of inspections with PdM.

“Since 1992, we have had a reputable contractor scan our site every nine months, and our faults continue to decrease each year. Yet using the Ti30, we found several interesting warm spots that we corrected before they became a problem.

“The opportunity for us is that we can scan every item in our plant more frequently, not just the critical points on our contractor’s list every nine months. We can also do in-house PM on more equipment than we currently do with a contractor.”

Thermography in practice

As the Weyerhaeuser example illustrates, using thermography as part of a regular PdM program can be a simple way to avoid costly downtime. It can be integrated into an already-existing inspection routine, or as a core part of a new program.

Mechanical equipment should be inspected when it has warmed up to steady-state conditions and is running a normal load. That way, measurements can be interpreted at normal operating conditions.

Capture a thermal image of the bearing to be checked, and if possible, capture images of bearings in the same area performing the same or a similar function, e.g., the bearing at the other end of a conveyor or paper machine roller or another pillow block on the same shaft.

Problems with bearings are usually found by comparing the surface temperatures of similar bearings working under similar conditions. Overheating conditions appear as hot spots within an infrared image and are usually noticed by comparing similar equipment. In checking motor bearings, this procedure entails comparing end bell to end bell (for motors and bearings of the same type) or stator to end bell temperatures.

Save a thermal image of each piece of key equipment on a computer and track your measurements over time. This will help determine whether a hotspot is unusual or not and help verify when repairs are successful.

Equipment conditions that pose a safety risk should take the highest repair priority. Estimating the cost of possible equipment failure can be easily determined by calculating the cost of the repair versus lost production opportunity and lost labour costs.

By allowing the user to ‘picture’ the heat generated by bearings as they work, thermal imaging reveals the condition of the bearings in relation to each other and to established baseline norms. This means the technology can be a valuable addition to preventive maintenance programs, especially for equipment with bearings in hard-to-access, or potentially dangerous, places.

Colin Plastow, industrial product manager, Fluke Electronics Canada LP, has worked with Fluke since 1987 in various support and product management positions. He may be contacted by e-mail at colin.plastow@fluke.com.g8