Preventive Maintenance

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Preventive Maintenance
Buddhika Lewangama
Marriott School November 2006

Agenda
• • • • • • • • • • Definition of Preventive Maintenance (PM) Reasons for the increased need of PM Advantages of a PM system Risks of running a PM system When to use a PM system The law of PM Guide to a successful PM system Execution process Conclusion Readings

What is Preventive Maintenance?
• Preventive maintenance is a schedule of planned maintenance actions aimed at the prevention of breakdowns and failures. The primary goal of preventive maintenance is to prevent the failure of equipment before it actually occurs. It is designed to preserve and enhance equipment reliability by replacing worn components before they actually fail.

Reasons for the need of a PM system
• Increased Automation • Business loss due to production delays • Production of a higher quality product • Just-in-time manufacturing • Need for a more organized, planned environment

Advantages of a PM system
• Reduced production downtime, resulting in fewer machine breakdowns.

• Better conservation of assets and increased life expectancy of assets, thereby eliminating premature replacement of machinery and equipment.
• Timely, routine repairs circumvent fewer large-scale repairs.

Continued • Reduced cost of repairs by reducing secondary failures. When parts fail in service, they usually damage other parts.

• Better quality products
• Identification of equipment with excessive maintenance costs • Improved safety and quality conditions.

Brainstorming Exercise
• Are there any risks of running a PM system?

• If there are risks when would it be a good time to use PM?

Potential errors or damage of a PM system
• Damage to an adjacent equipment during a PM task. • Reintroducing infant mortality by installing new parts or materials. • Damage due to an error in reinstalling equipment into its original location.

A real life example of a PM error
A review of the data from fossil-fueled power plants that examined the frequency and duration of forced outages after a planned or forced maintenance outage reinforces our point. The data collected from those plants showed that of 3146 maintenance outages, 1772 of them occurred in less than one week after a maintenance outage. Clearly, this is pretty strong evidence that suggests that in 56% of the cases, unplanned maintenance outages were caused by errors committed during a recent maintenance outage.

When Does Preventive Maintenance Make Sense
• This is a logical choice that considers two conditions
– #1. The component in question has an increasing failure rate. – #2. The overall cost of the preventive maintenance action must be less than the overall cost of a corrective action. If both of these conditions are met PM would make sense

The Law of PM
• Higher the value of the plant assets and equipment per square foot of plant, the greater will be the return on a PM program.
E.g. - downtime in an automobile plant assembly line at one time cost $10,000 per minute. Relating this to lost production time an automobile manufacturer reported that the establishment of a PM program in their 16 assembly plants reduced downtime from 300 hours per year to 25 hours per year. With results such as this no wellmanaged plant can afford not to develop a PM program.

How to determine the optimum age of replacement?

How to determine the optimum age of replacement?
• A more technical approach.

Where: • R(t) = reliability at time t. • CP = cost of planned replacement. • CU = cost of unplanned replacement • CPUT(t) = The optimum replacement time

The key for a successful PM system
• Scheduling – Should be automated to the maximum extent possible • Execution – Should be done before the actual break down occurs.

Execution
• The Bath Tub Model – Three stages of new parts
1. 2. 3. Infant morality stage A fairly long run stage Wear out stage



Traditional View according to Bath Tub Model – Replace components just before they entered wear out stage

Execution
• Traditional view says –
Wear out stage = Increased rate of failure. • Point to Ponder – Since, wear out stage represents increased rate of failure, wouldn’t it be plausible to execute the PM program at this stage?

Execution
• United Airlines Research Reliability Centered Maintenance based on research done by United Airlines and the rest of the aircraft industry showed that very few non-structural components exhibit bathtub curve characteristics. Their research showed that only about 11% of all components exhibit wear-out characteristics, but 72% of components do exhibit infant mortality characteristics. These same characteristics have been shown to apply in Department of Defense systems as well as power plant systems.

What really should PM focus on?
• Cleaning • Lubrication • And correcting deficiencies Found through testing and inspection

Predetermined parts replacement should be minimal and done only where statistical evidence clearly indicates wear-out characteristics

In the absence of data
• Age exploration programs • Statistical analysis
Cost shouldn’t be a primary factor in deciding against data collection for a PM

Motivating Preventive Maintenance Workers
• Training programs – most effective

• Establish inspection and preventive maintenance as a recognized, important part of the overall maintenance program.
• Assign competent, responsible people to the preventive maintenance program.

Continued • Follow-up to assure quality performance and to show everyone that management does care. • Provide training in precision maintenance practices and training in the right techniques and procedures for preventive maintenance on specific equipment. • Set high standards. • Publicize reduced costs with improved up-time and revenues, which are the result of effective preventive maintenance

Summary
• • • • PM is not difficult to achieve. It is an essential part for cost reduction There is an element of risk involved in PM Careful planning and execution will reduce the risk of PM • The biggest benefits of a PM program occur through painting, lubrication, cleaning and adjusting, and minor component replacement to extend the life of equipment and facilities.

Readings
• • • • • John M Gross, “Fundementals of Preventive Maintenance”, American Management Association, Pg 228 Richard D Palmer, “Maintenance Planning and Scheduling Handbook”, ch1pg.30 “Is Preventive Maintenance Necessary?”, 28 Nov.2006 < http://www.reliability.com/articles/article37.htm> “The Reliability Hotwire, the eMagazine for the Reliability Professional”, Issue 21, Nov. 2002 http://www.weibull.com/hotwire/issue21/hottopics21.htm “Preventive Maintenance”, Reliasoft Coporation, 28 Nov 2006http://www.weibull.com/SystemRelWeb/preventive_maintenance.htm

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