Troubleshooting motors and hydraulic cylinders
Thermal image of cylinders on the rock crusher after the problem was resolved.
Everybody knows that motors get quite a workout in the day-to-day operation of a typical industrial plant. But imagine the beating those motors take when they run 16 hours a day, transporting and crushing rock? That's the story we recently heard from a roofing products plant electrician in Arkansas.
CertainTeed Corporation, a subsidiary of Saint-Gobain - one of the top 100 industrial companies in the world - is a leading North American manufacturer of innovative and sustainable building products. Its products include roofing, vinyl and fiber cement siding, trim, fence, railing, decking, insulation, gypsum, and ceilings products. Headquartered in Valley Forge, Pennsylvania, CertainTeed has approximately 6,000 employees and 65 facilities throughout the United States and Canada.
Its Glenwood, Arkansas plant produces roofing granules for composite shingles. The company mines slate from an open-cut mine in Glenwood, and then crushes it into various sized granules as requested by the shingle manufacturers. The mining and crushing operations run 16 hours a day and include nearly 100 motors running 14 conveyors, 11 elevators, and 4 crushers, plus vibrating feeders, and automated screens that separate the various sizes of crushed rock.
For plant electrician Larry Vallee, that's a lot of equipment to keep moving, so preventive maintenance is important. But still problems occur that need immediate attention. "Most of the problems I run into are overloaded motors," says Vallee. The overloads can be caused by a glitch in the process, resulting in too much rock going onto the conveyor or into the elevator, or just the normal wear and tear on the motor. When a motor goes down it stops the whole operation, and that costs money.
"Three-phase 480V motors last a long time, but eventually they do fail," says Vallee. "In this environment, when a motor is overheated you can't just go reset it; you have to watch it to make sure it overheated because of too much product rather than because it's about to fail."
When Vallee is called in to troubleshoot a tripped motor he first asks the operator what the situation was when it failed. If it was the result of too much rock, he first clears the rock, resets the motor, and waits five to ten minutes to see if it trips again. If it does he looks further.
At that point Vallee brings out his Fluke 1587 insulation multimeter and checks the insulation and the voltage. If it shows the correct voltage and a significantly lower insulation resistance than the previous test on that motor, then it's a pretty sure bet the motor is about to fail. "If you can tell that a motor is about to fail, it's a lot better to go ahead and replace it before it fails rather than to wait until it actually does," says Vallee.
Where there's heat there could be problems
In addition to the 1587, Vallee uses a Fluke Ti9 Infrared Camera to identify air duct leaks and to detect heat in a variety of electrical and mechanical components. He uses the Ti9 to perform an annual check of all of the motors and the common electrical components, such as fuses, wires, insulators, connectors, and splices, for abnormal heating. The Ti9 also comes in handy for checking heating on motor disconnect switchgear and pistons in hydraulic cylinders.
In fact, the Ti9 helped Vallee unravel quite a challenge regarding hydraulic cylinders. He was called in to figure out why a crusher wasn't crushing the rock consistently. The crusher had six hydraulic cylinders - all piped in parallel - to hold it down and keep it pressurized.
"One of the cylinders wasn't holding pressure, so it was bypassing," says Vallee. "We couldn't hold pressure on the crusher, so it wasn't crushing the rock right. We couldn't see why it wasn't holding pressure, so I got out my Ti9 and looked at all the cylinders. The temperature on one cylinder was higher on both sides of the piston. The other cylinders were cool on the unpressurized side."
With further investigation, it turned out that the rings on the piston inside the cylinder were bypassing, so all the oil was flowing past the piston rather than building pressure inside. Since the cylinders are all piped in parallel, none of them were pressurizing. Vallee and the maintenance staff replaced the cylinder and the problem was fixed.
In addition to the 1587 and the Ti9, Vallee relies on the Fluke 1AC II A1 VoltAlert Electrical Tester, T5-600 Voltage, Continuity and Current Tester, and the 1625 Advanced GEO Earth Ground Tester. "I've used Fluke tools for more than 20 years because they are the most reliable," says Vallee. "I've tried some different brands and nothing compares to a Fluke."