Smart Methods: Part 2
by Christer Idhammar
Note: This column is a continuation of the December P&P maintenance column by Christer Idhammar. In the December column, Mr. Idhammar reviewed smart corrective maintenance methods that are valuable for both new and experienced maintenance personnel. This month’s article focuses on smart preventive and inspection methods.
Most maintenance problems are the result of neglecting the very basics of essential component care and inspections, including improper lubrication, poor operating practices, faulty alignment and balancing, and lack of thorough, frequent inspections. Although predictive maintenance methods such as vibration analysis, wear particle analysis, thermo vision using infrared technology, and other advanced methods are great tools, I would like to focus on very basic preventive and inspection methods that can easily be taught to operators and craftspeople.
If you start teaching your craftspeople and operators the smart methods mentioned here, I can assure you that, in turn, you will inject new interest and enthusiasm in your basic inspection programs. People will also change the way they think about preventive maintenance inspections. Effective maintenance requires more than just a checklist for components. It requires guidelines and training in what to check for during the inspection.
MISALIGNED COUPLINGS. In most cases, a vibration analysis will pick up a misaligned coupling, and this is the first method that comes to mind when such a problem is suspected. However, vibration analysis requires an expert, as well as expensive equipment.
Another way of diagnosing a misaligned coupling is to shut down the equipment and physically inspect alignment with dial indicators or laser alignment. This can take a long time, since you often have to check many good alignments before you find the bad ones.
The strobe light method is a third way of diagnosing a misaligned coupling. With this method, you punch a fine line across the coupling halves, or shaft and coupling, when the coupling is new. Using a strobe light, the coupling can be stopped during normal operation. If the punched line starts parting, it indicates wear of parts such as rubber bushings or gears. During the next opportunity to shut down the equipment, you would then, of course, only check the couplings that are showing signs of wear.
Strobe checks often require modification of guards so that the check can be done safely while equipment is operating. If guards are modified, it is easy to teach anyone in your organization how to do a strobe check. The disadvantage of this method is that the line can be difficult to see because of contamination and coupling design.
An even faster and simpler way to make a valid snapshot check for misaligned couplings is to use a handheld infrared temperature meter. With this device, very fast and reliable comparative measurements of coupling temperatures are possible. A misaligned coupling will always have a higher temperature than other couplings operating in the same environment. When using this method, it is recommended that you use an infrared meter with a laser sight. It is also important that you know the spread of the measurement field. This lets you know how close to the coupling you have to be when you do your measurement. This example highlights three good rules—simplify, simplify, simplify!
THERMOCAPS. In the old days, mills tightened bolts for buzz bars during shutdowns in order to prevent poor conductivity that often resulted in over- heating of electric connections. About 30 years ago, it became more common to use infrared scanning during operation to identify poor connections, and this is still the most common method.
Today, you can apply so-called thermo caps on bolts, nuts, and cable connections. These caps will visually tell you when the temperature increases, and inspection can be done by anyone if safety is maintained.
HEAT EXCHANGERS. Many heaters and coolers will operate until they can no longer heat up or cool a media because they are contaminated, limiting the flow of media. Also, insulated tubes can limit the transfer of heat.
Many small heat exchangers, such as coolers for hydraulic fluids, are water-cooled. A sensor in the outgoing hydraulic fluid controls the water flow in these exchangers. This sensor reads the temperature and tells the cooling water valve to open or close in order to adjust the outgoing hydraulic fluid temperature.
A simple inspection of the degree of cooler contamination is to check the water valve position. You should also keep a record of water valve position, because guess what will happen around July if it is fully open in the month of May?