By By Carroll McCormick
Our previous issue (April 2013, page 11) offered up eight practical, field-proven tips for keeping your bearings and seals happy. In this issue, we offer Part 2 of that feature, with another eight great tips to keep your bearings turning and...
June 1, 2013
By By Carroll McCormick
Our previous issue (April 2013, page 11) offered up eight practical, field-proven tips for keeping your bearings and seals happy. In this issue, we offer Part 2 of that feature, with another eight great tips to keep your bearings turning and for avoiding unpleasant surprises.
Tip 9 |
Temperature alarm settings: “I am frequently asked what the alarm shutoff temperature should be,” says Jennifer Moritz, training manager, SKF Canada. “A 10° Celsius rise above normal operating temperature indicates that a problem is developing, perhaps the need for lubrication. A 20°C rise is clear evidence of an application that is ready to go south fast. You need to plan a shutdown fast.
“Take a typical industrial motor, with an operating bearing temperature of 90°C. At 100°C, there is a problem. If you re-grease and the temperature drops to 90°C, you have established a new lubrication frequency. If the temperature goes back up, to 110°C, the motor is about to fail. Set the alarm at 10°C to look at it. Set the alarm to shut the equipment down at 20°C above the normal operating temperature.”
Tip 10 |
Breaking in high-speed bearings: Do newly greased bearings need breaking in? Absolutely, says Chris Mackenzie, owner, Advanced Machine Services LLC, Oxford CT. “It can take up to a week to bring the spindle up to speed. It is a question of getting the grease distributed. I will build a spindle and run it at 20% of rated speed, monitor it for temperature and vibration, and gradually increase the speed.
“The temperature is a monitor of the happiness of the grease. A rule of thumb for the temperature is 110° Fahrenheit. When we build a spindle and break it in right, we consider it greased for life. We don’t recommend ever greasing it again.”
Once broken in, the machine can be turned on and immediately run at normal operating speed, although turning a machine on and letting it warm up at lesser speeds is preferable.
Tip 11 |
Is this the correct bearing? Speaking of rebuilds and new bearings, do you assume the new bearings that shops install in your motors are the correct size? While at a pulp and paper mill recently, I saw a great tip in action. Jonathan Walker, an electrician at Domtar’s Windsor, QC, mill, was getting ready to fire up his torch to heat up a bearing for removal.
This is what he said: “We just got this motor back from an outside shop. I always check to make sure the right bearing was installed, and this time, it was the wrong bearing.”
Tip 12 |
Proper seal installation orientation: “There are two possible seal orientations,” Jennifer Moritz explains. “Grease-purgeable, where the primary intent of the seal is to lift under internal pressure and let excess grease out. Under external pressure it sits tighter, keeping contamination out.
“Grease non-purgeable seals sit tighter under internal pressure, keeping grease in. But if contamination exclusion is a big concern, especially with high-pressure washdowns, remember that seals mounted in the non-purgeable direction can lift, letting contamination in. This is a fast route to premature bearing failure,” Moritz advises.
Tip 13 |
Take care of your lubricant: Lubricants are carefully formulated and prepared to exacting standards of cleanliness to extend bearing life. Yet, observes Marcus Wickert, engineering division manager, NTN Canada, “Poor storage or handling practices can frequently allow them to become contaminated prior to use.
“Likewise, poor sealing or movement of a bearing and its mating components — for example, between a shaft and its housing — can create a way for dirt to get in and contaminate the lubricant, which is the core substance that keeps our machinery moving. Keeping lubricants free from contamination is the ultimate priority in achieving bearing performance.”
On this topic, Chris Mackenzie comments, “I’d also say that the leading cause of bearing failure is contamination. A common example of that is if you aren’t very careful to wipe contamination off the fitting and grease gun.”
Tip 14 |
Greasing high-speed bearings: Chris Mackenzie, a mechanical engineer, offers this thumbnail primer on how much grease to put in high-speed bearings, say for a CNC machine tool.
“There is a mentality out there to pack bearings, but in precision and high-speed applications, too much grease in a bearing can fail it. High speeds; e.g., from 10,000 to 50,000 rpm, will generate heat that can burn up the grease and bearing. I will fill as little as 15% of the void space of the bearing.
“Use 15-25% as a typical rule of thumb when you want to run a bearing at its rated speed. It’s the wrong hope that the excess will squeeze out the other end. This is the kiss of death.”
Tip 15 |
Lubrication type: This is a book-worthy topic, but Chris Mackenzie offers these thoughts as a starting point for more research. “In any given application, you are looking at speed, temperature, cleanliness of the environment, sealed or open bearings, exposure to pressure wash, steam cleaning, acids …. Some greases are very resistant to wash out and others will wash out right away. You will see greases with EP (extreme pressure) on them. Not using them in a high-load situation will lead to bearing failure.”
Do you have the need for speed? Mackenzie offers a quick primer on how speed is rated. “In the bearing and grease industry, we look at ‘speedability’. Bearing catalogues give a rated speed for the size of the bearing. A grease rating (dN) is the product of the bore of the bearing in millimetres multiplied by the RPM. If a grease is rated for 200,000 dN, do not use it in a 500,000-dN application.
“It absolutely happens that the wrong grease is used. My general sense is that as plants get leaner, the guys that are into PM and have all those interests are fewer. The expertise may not be there. Ask your lubricant suppliers or distributors. They are pretty knowledgeable,” Mackenzie advises.
Tip 16 |
Consider automatic lubricators: These clever devices may be the ticket to making all of your greasy dreams come true. Installation is as simple as screwing out a grease fitting and installing an automatic lubricator. The delivery schedule is adjustable on the unit. “You can set it to exhaust itself in anywhere from a month to a year. The lubrication schedule depends on load, speed and bearing size,” Chris Mackenzie says.
Manufacturers have various ways of powering them. The lubricators that Mackenzie sells, made by Simatec Smart Technologies, are powered by gas cartridges. These sealed, disposable units can even be installed under water. “They are particularly advantageous in hard-to-reach places, such as high up. Those places tend to get ignored,” he says.
Carroll McCormick is MRO Magazine’s award-winning senior contributing editor. He has been writing for us since 1998.