PREDICTIVE MAINTENANCE

Maintenance philosophies

•  Breakdown or run to failure maintenance 
• Preventive or time-based maintenance 
• Predictive or condition-based maintenance 
• Proactive or prevention maintenance.

 

Reactive Maintenance

• Reactive maintenance also is referred to as breakdown, repair, fix-when-fail, or run-to-failure (RTF) maintenance.
• When this is the sole type of maintenance practiced, a high percentage of unplanned maintenance activities, high replacement part inventories, and inefficient use of maintenance effort typify this strategy
• Examples of components where RTF is applicable are non-critical electric motors less than 7.5 HP, comfort cooling, restroom exhaust fans, water heaters, and items where the consequences of failure are negligible.

 Break Down Maintenance

• Membiarkan mesin beroperasi sampai terjadi kerusakan,tindakan dilakukan setelah adanya kegagalan 
• Biasa disebut dengan Run To Failure Maintenance
  

Keuntungan 

• Murah
• Mesin tidak dirawat dengan berlebihan

Kerugian

• Tidak ada persiapan terhadap terjadinya kerusakan mesin (down time) karena terjadinya mendadak
• Kerusakan akan menyabar ke komponen yang lain dan bisa terjadi kerusakan fatal sehingga biaya perbaikan akan semakin mahal 
• Kerugian produksi besar

Preventive Maintenance

• Dikenal juga dengan Calender based Maintenance jenis perawatan ini menggunakan  teori yang menyebutkan bahwa umur mesin terbatas dan memungkinkan terjadinya kegagalan seiring dengan meningkatnya umur mesin
• Jadwal perawatan dilaksanakan sebelum mesin membutuhkan

 Preventive Maintenance (PM)

• PM consists of regularly scheduled inspection, adjustments, cleaning, lubrication, parts replacement, calibration, and repair of components and equipment. PM is also referred to as time-driven or interval-based maintenance. It is performed without regard to equipment condition.
• PM schedules periodic inspection and maintenance at pre-defined intervals (time, operating hours, or cycles) in an attempt to reduce equipment failures for susceptible equipment.
• Depending on the intervals set, PM can result in a significant increase in inspections and routine maintenance; however, it should also reduce the frequency and seriousness of unplanned machine failures for components with defined, age-related wear patterns.

 

  From approximately 1960 until the late 1980s, Preventive Maintenance (PM) was the most advanced technique used by progressive facilities maintenance organizations. PM is based on two principle:

1. a strong correlation exists between equipment age and failure rate, and 
2. individual component and equipment probability of failure can be determined statistically, and therefore, parts can be replaced or rebuilt prior to failure.

PM assumes that failure probabilities can be determined statistically for individual machines and components and parts or adjustments can be replaced or performed in time to preclude failure. rate increases whit time in service. This has proven to be ineffective

• Figure 1–2 shows the failure distribution of a group of thirty identical 6309 deep groove ball bearings installed on bearing life test machines and run to failure.
• The wide variation in bearing life is obvious and precludes the use of any effective time-based maintenance strategy2
• The X axis is the individual bearing being tested while the Y-axis is the number of revolutions achieved prior to fatigue failure of the individual bearing.
• Traditional PM is keyed to failure rates and times between failures. It assumes that these variables can be determined statistically, and therefore one can replace a part due for failure before it fails 
• PM schedules periodic inspection and maintenance at pre-defined intervals (time, operating hours, or cycles) in an attempt to reduce equipment failures for susceptible equipment. Depending on the intervals set, PM can result in a significant increase in inspections and routine maintenance; however, it should also reduce the frequency and seriousness of unplanned machine failures for components with defined, age-related wear patterns.
• For some items, while failure is related to age, it is not equally likely to occur throughout the life of the item. In fact, the majority of equipment is not subject to wear-out (sharply increasing conditional probability of failure at a specific operating age). Therefore, timed maintenance can often result in unnecessary maintenance. In summary, PM can be costly and ineffective when it is the sole type of maintenance practiced.
• Failure rate or its reciprocal, Mean-Time-Between-Failures (MTBF), is often used as a guide to establishing the interval at which the maintenance tasks should be performed. The major weakness in using these measurements to establish task periodicity is that failure rate data determines only the average failure rate  

 

• Type A - Constant or gradually increasing failure probability, followed by a pronounced wear-out region. An age limit may be desirable. (Typical of reciprocating engines.)
• Type B - Infant mortality, followed by a constant or slowly increasing failure probability. (Typical of electronic equipment.)
• Type C - Low failure probability when the item is new or just overhauled, followed by a quick increase to a relatively constant level.
• Type D - Relatively constant probability of failure at all ages.
• Type E - Bathtub curve; i.e., infant mortality followed by a constant or gradually increasing failure probability and then a pronounced wear-out region. An age limit may be desirable, provided a large number of units survive to the age where wear-out begins.
• Type F - Gradually increasing failure probability, but no identifiable wear-out age. Age limit usually not applicable. (Typical of turbine engines.)
• Types A and E are typical of single-piece and simple items such as tires, compressor blades, brake pads, and structural members. Most complex items have conditional probability curves of types B, C, D, and F.

 
Predictive Maintenance