Many of us are familiar with the various bearing numbers comprising deep-groove and angular contact ball bearings such as 6312, 7208, etc. However, we can have trouble determining what the bearing number is unless it is clearly written on the bearing. Maybe this tip will help.

The bore size of these bearings is usually metric but this will not normally create a problem, even for the inch-entrenched mechanic. The bore size is equal to the last two numbers of the bearing size multiplied by 5. The answer is in millimeters. Look at a 6312 bearing: the last two numbers are 12. Twelve times 5 equals 60 millimeters. Lay your metric scale across a 6312 bearing bore and you will see it is 60 mm. This is also much easier to read than 2.362 inches.

If you reverse this problem and measure the bore of a bearing using a metric scale, you would measure a 60 mm bore and you can easily see that the bore is closer to 60 than to 55 or 65 (6211 and 6213 bearings). Divide by 5 and you know the bore size is a number 12 bore.

Another way to determine the last two numbers is to double the mm size and move the decimal place one mark to the left. For this same 60 mm bore, doubling 60 becomes 120 and moving the decimal place to the left changes 120 to 12, so again this is a xx12 bearing, the ‘xx’ being the first two numbers.

This system normally works well for bearings with bore sizes 20 mm and higher. (Twenty mm divided by 5 is equal to ‘04’. Therefore, a 6204 ball bearing has a 20 mm bore.) Remember, you are calculating the last two numbers of the bearing size.

Since the bore sizes change by 5 mm in the smaller sizes and 10 mm in the larger ranges, getting the mm size is relatively easy, helping to quickly determine the bearing number and shaft size.

You now know the bore number but the type (angular contact, deep groove, etc.) along with the weight class (light, medium, or heavy) will still need to be determined.

Reader tip provided by Lin Langford
Vibration Analyst
Flanders Electric, Inc
Longview Texas

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Many of the laser alignment systems use a 2 plane receiver. It is important to check the angle of the laser as it is passing through these 2 planes, not just that it is “centered”. First, you should always center the vertical and horizontal adjustment of the laser. There will usually be an “X-Y” screen that shows where the laser is in relation to both planes. If you center the laser in both planes, it will lessen the chance of getting a “laser out of range” or “laser not centered” type of message while collecting data.

Reader tip provided by Gary Benner
Analyst
Georgia-Pacific
Camas, Washington

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When seeking cross fire tube leaks on a GE gas turbine the best way we found was to us an infrared temperature gun and pinpoint the change in temperature around the flanges. This works for all leaks where a person can’t enter the compartment to feel for leaks.

We also use the infrared temperature gun to monitor any change in temperature inside the compartment of all our gas turbines. If there is a big temperature swing upward from our trends than we know we have a leak.

Reader tip provided by Sam Patronella
PPM
Dupont
Orange Texas

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Enterprise Asset Management Summit
March 18-20, 2008
FREE Bonus Workshops: March 17
Orleans Hotel - Las Vegas

If you use the SAP Plant Maintenance module as an Enterprise Asset Management resource you will learn how to make it work even better at EAM-2008. This is the only independent reliability focused event with a dedicated SAP PM Strategy Sessions & Learning Zone.

This new feature includes a full day reliability focused SAP Plant Maintenance workshop and 7 SAP PM User case studies and a live SAP PM Learning Lab led by some of the world’s best SAP Plant Maintenance Experts who have helped hundreds of clients develop technically-based maintenance plans in SAP-Plant Maintenance.

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Early bird conference and hotel rates apply - so sign up today! EAM-2007 sold out.

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As you service DC motors, remember that the slick brown surface on the brush face of the armature is a good thing. Don’t remove that surface unless it is rough and burned. The brown patina is a stable conductive surface that your brushes can run on with minimal wear for a long time.

Reader tip provided by Wayne Stewart
Energy Systems Technician
Schreiber Foods
Carthage, Missouri

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Equipment Repair History

One of the most effective tools for improving equipment reliability is equipment repair history analysis. Without meaningful work order completion comments and failure codes it is difficult to analyze equipment failure trends or common component failures. Make sure you have a work order for all maintenance and thoroughly document actual repair information.

Tip provided by AssetPoint
http://www.assetpoint.com

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