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Press-Shop Maintenance

By: Peter Ulintz

Sunday, September 01, 2013
 

There are four types of maintenance that can be performed on stamping dies and pressroom equipment: reactive, preventive, predictive and proactive. It is important to understand the differences between them, to avoid using the terms interchangeably (or incorrectly) and to be able to assess the effectiveness of your maintenance operations.

Reactive Maintenance is nothing more than reacting to failed tooling or equipment by restoring its intended function. It is analogous to a tire on a car being very low on air. The owner observes the low-air condition and adds compressed air to the tire to restore its designed pressure level.

Many metalformers rely solely on this reactive maintenance—acceptable in limited circumstances, but generally a costly way to operate. Breakdowns are unpredictable, and labor and material resources may not readily be available. You may have to pay premium rates for overtime and to expedite product to the customer. Downstream processes may be delayed, and tooling and equipment life will suffer.

An operation that solely relies on reactive maintenance generally expends more labor and material resources than if they had a preventive-maintenance program in place.

Preventive Maintenance (PM) comprises formal procedures and tasks that help prevent unplanned breakdowns and ensure that equipment and tooling operate properly. To establish PM tasks and intervals, metalformers consult owner’s manuals, industry standards and guidebooks, and also must consider environmental conditions, equipment criticality, impact on safety and past experience.

Examples of PM tasks include changing lubricant, replacing consumable parts, and cleaning, adjusting, inspecting and testing equipment. In the automobile-tire analogy, PM might include checking and adjusting air pressure at each oil change.

A good PM program keeps equipment running in good condition and helps to extend the period between breakdowns. It also helps managers plan and budget for replacement parts, and schedule the necessary work at predictable and convenient times.

While PM is not the optimum maintenance program, it does provide several advantages over a purely reactive program. Performing preventive maintenance extends the useful life of tooling and equipment. Tooling and equipment generally will run more efficiently when maintained properly. This translates into cost savings. Preventative maintenance alone will not prevent catastrophic failures, but it will decrease the number and frequency of failures.

Adverse consequences of PM:

• Over-maintenance, where unnecessary or ineffective maintenance is performed, such as adding air to a tire at every oil change when the tire does not require additional air.

• Under-maintenance, where failure conditions are not identified or corrected in a timely manner, leading to the consequences described for reactive maintenance.

Predictive Maintenance (PdM) improves on PM by using actual equipment-performance data for scheduling maintenance tasks. PdM tasks data will indicate deteriorating conditions or rate-of-decay. With this strategy, periodic or continuous monitoring detects the onset of wear or degradation. The information helps engineers predict potential problems and determine the best time for maintenance.

Today, most automobile tires include manufacturer-installed pressure sensors to sense when tire pressure falls below a critical level, or when the pressure differential between the tires exceeds a prescribed limit. The sensors send this data to a computer control, which illuminates a low-tire pressure indicator. In this way, the vehicle operator or mechanic can adjust tire pressure based on data rather than on a preset time interval, avoiding over- and under-maintenance.

PdM and PM represent very different strategies, even though many people use the terms interchangeably. PM is time-based (number of cycles, number 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 maintenance failures and dealing with those issues before problems occur. Maintenance 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 profitable. 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 compressed-air sources reveals that most of the compressed air comprised 21-percent oxygen and 78-percent nitrogen, 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 corrosion of the rim, which can lead to seal failures. The oxygen molecules in the compressed air also are smaller than the nitrogen molecules. Oxygen permeates 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 compressed air with pure dry nitrogen. This eliminates any water vapor that may cause corrosion and the oxygen that permeates through the rubber polymer chains. The result: stable tire pressure over longer time periods, at all operating temperatures. This improves fuel economy, extends tire life and promotes safety.

The higher initial cost for pure nitrogen 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

 

Related Enterprise Zones: Tool & Die


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