Chapter 20 - Preventative Maintenance Flashcards
Historically, what forms have industrial machine maintenance taken?
- responding to breakdowns as they occur with servicing, adjustments, and minor repairs
- or it may be and elaborate program designed to prevent breakdown or to detect minor problems that, untreated, can lead to breakdown
What styles of maintenance programs are practiced in industry today?
- breakdown maintenance
- preventive (planned/scheduled) maintenance
- predictive maintenance
- proactive maintenance
What are the disadvantages of breakdown maintenance?
- sometimes sudden failures result in injury or fatalities
- replacement parts and overworked maintenance workers may not be readily available
- special tools are sometimes difficult to arrange for or keep on hand
- overtime cost to get equipment up and running can become exorbitant
- large amounts of expensive spare parts or even entire spare machines have to be kept on hand, adding to the cost
- erratic and sporadic minor breakdowns can be disruptive to efficient production
What are the advantages and disadvantages of preventative maintenance?
- advantages
- replacement of worn components usually lessens the frequency and severity of critical breakdowns
- detailed inspection can be used to reveal even the most detailed problems - through inspection and NDT
- problems can be analyzed further to determine their cause and prevent or eliminate them.
- -disadvantages
- time between inspections could be difficult to determine, resulting in over inspection which is time consuming and expensive
- parts may be replaced too soon (over-maintenance)
- occasionally, machinery is damaged or degraded by too frequent disassembly
- some machinery problems are not evident unless the machine is running. These may be overlooked
What are the advantages of predictive maintenance?
- problems can be detected in the very early stages, without interrupting the operation of the machinery
- production shutdown for adjustments, more thorough investigation and repairs can be scheduled for the most opportune time
- labour, tools, and spare parts can be prepared far in advance
- extensive damage can be averted or minimized
- repairs can be reduced
- inspection time can be shortened
- inspection for quality standards and help in the development and testing of new equipment
Describe proactive maintenance programs
- takes action to correct conditions that could lead to machine degradation
- identifies and corrects root causes of failures
- factory personnel monitor equipment constantly to ensure normal operation – “condition based monitoring”
List the other maintenance programs used in industry to increase efficiency
- total productive maintenance
- preventive engineering
- reliability engineering
- productive maintenance
Describe the system of preventative maintenance from primitive to elaborate
- primitive - maintenance has little to no equipment documentation
- elaborate - recorded and reviewed equipment records showing work history and equipment repairs
List the pertinent specifications that should be recorded on the machines record files
- manufacturer’s name
- serial, model, inventory number
- specifications for: horsepower, speed, wattage, amperage, voltage, speed ratio, pressure, flow capacity, etc.
- in addition, blueprints, parts lists, stock numbers, suppliers’ names and information about availability may be included
- operating requirements may include temperature limitations, maximum pressures and flows, allowable wear limits, normal service life or production capacity
What is the significance of the repair history of a machine?
- the dates, times, nature, and extent of repairs to machinery are all useful information, that help in the analysis of problems
- a record of spare parts and materials used to make repairs, hours of work by maintenance personnel, and any special tools or equipment used can all help to determine type and frequency of problems likely to occur
- minor repairs recorded, eventually modifications and design changes can be made to permanently rectify machine weaknesses
How does machine inspection assist the maintenance program?
- used to determine the frequency and amount of repairs needed
What are the general levels of priority for production machines?
- high priority numbers are assigned to equipment that is so critical that it can shut down the whole plant
- next level priority is assigned to machinery relied on to keep whole departments running. Also assigned to those that are critical to product quality
- decreasing priorities are assigned, down to auxiliary equipment and even random clean-up and decoration
What other records may be used in planning a more efficient maintenance program?
- work order requests
- store requests
- purchase requisitions
- maintenance stores inventory
- maintenance personnel requirements
- production records
How is a machines vibration characteristics used to determine machine maintenance needs?
- can be monitored and analyzed to determine their root causes
List the causes of vibration
- unbalanced rotating parts
- misalignment
- bent shafts
- bad bearings, gears, belt and chain drive
- hydraulic forces
- any looseness in the machine
How are the conditions and/or causes of vibration detected?
- screwdriver probe
- stethoscope
- dials
- computer
How is vibration characterized?
- frequency
- displacement
- velocity
- acceleration
- phase
- pulse or shock vibrations
Define the following terms:
- frequency
- number of vibrations that happen in a particular unit of time
- expressed as:
- a number of vibrations per second or per minute
- cycles per minute (cpm)
- cycles per second (cps)
- hertz (Hz)
1 Hz = 1 cps = 60 cpm
(cpm = Hz x 60)
Define the following terms:
- displacement and amplitude
- displacement – the distance of a vibrating object from its original rest position
- amplitude – the distance from one extreme to another (when the displacement is at its maximum)
Define the following terms:
- velocity
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Define the following terms:
- acceleration
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Define the following terms:
- phase
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Define the following terms:
- pulse vibrations
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What is the purpose of a transducer?
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Describe the operating principles of “moving coil” and “piezoelectric” velocity transducers
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Compare accelerometers to velocity transducers
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