Page 57 - MetalForming September 2013

ple use the terms interchangeably. PM is time-based (number of cycles, num- ber of hours, number of days, etc.) while PdM is event-based, activity determined through data acquisition (temperature, vibration frequency, die signature analysis, etc.).
Reliability-Centered Maintenance (RCM)—more commonly known as proactive maintenance—not only looks after equipment condition, but also seeks to improve performance. It relies on monitoring and diagnostics to determine equipment health and performance.
RCM practices focus primarily on determining the root causes of main- tenance failures and dealing with those issues before problems occur. Main- tenance may even be performed on healthy equipment if a performance improvement can save or make money. Rigorous use of proactive maintenance can actually make maintenance prof- itable. Consider this example:
We determine that the root cause for air-pressure fluctuation in our car tire analogy related to corrosion at the seal bead and air permeating through the tire. An analysis of multiple com- pressed-air sources reveals that most of the compressed air comprised 21- percent oxygen and 78-percent nitro- gen, along with water vapor and other gases.
Water, present as a vapor or a liquid in a tire, causes more of a pressure change with temperature swings than does dry air. It also promotes corro- sion of the rim, which can lead to seal failures. The oxygen molecules in the compressed air also are smaller than the nitrogen molecules. Oxygen per- meates the polymer chains in the solid rubber, reducing the air volume and pressure in the tire.
Here we can implement a proactive maintenance program, to replace com- pressed air with pure dry nitrogen. This eliminates any water vapor that may cause corrosion and the oxygen that permeates through the rubber poly-
mer chains. The result: stable tire pres- sure over longer time periods, at all operating temperatures. This improves fuel economy, extends tire life and pro- motes safety.
The higher initial cost for pure nitro- gen compared to that for compressed air is easily justified by the long-term
cost savings and safety benefits. This is an excellent example of proactive maintenance, and it’s the reason why nitrogen is used in many automobile tires today.
What types of maintenance do you employing? More importantly, what types should you employ? MF
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