Breakdown maintenance
Breakdown maintenance is basically the “run it till it breaks” type of maintenance mode. No actions or efforts are taken to maintain the equipment till its design life is reached. Advantages are, Low cost, Less staff. Disadvantages are: Increased cost due to unplanned downtime of equipment. Increased labor cost, especially if overtime is needed. Cost involved in repair or replacement of equipment. Possible secondary equipment or process, damage from equipment failure, inefficient use of staff.
Preventive maintenance
It is a daily maintenance procedure (cleaning, inspection, oiling and re-tightening), designed to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis by measuring deterioration. Just like human life is extended by preventive medicine, the equipment service life can be prolonged by doing preventive maintenance. It is further divided into Periodic maintenance and Predictive maintenance.
a) Periodic maintenance ( Time based maintenance – TBM) : Time based maintenance consists of periodically (at pre-determined intervals) inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems.
b) Predictive maintenance: This is a method in which the service life of important part is predicted based on inspection or diagnosis, (for Ex., by testing the condition of the lubricating oil in a vehicle for its actual condition and lubrication properties in a good testing centre instead of changing every 5000kM), This type of maintenance allows us to use the parts/equipment to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. Basically, predictive maintenance differs from preventive maintenance by basing maintenance need on the actual condition of the machine rather than on some preset schedule. It is possible to schedule maintenance activities to minimize or delete overtime cost. Also, inventory and order parts can be minimized as required, well ahead of time to support the downstream maintenance needs. It helps to optimize the operation of the equipment, saving energy cost and increasing plant reliability.
Corrective maintenance : It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability
Maintenance prevention : It indicates the design of a new equipment. Weakness of current machines are sufficiently studied (on site information leading to failure prevention, easier maintenance and prevents of defects, safety and ease of manufacturing) and are incorporated before commissioning a new equipment.
Preventive maintenance schedule
Preventive maintenance is the maintenance which has to be carried out to the equipment, in a preplanned way before serious breakdown takes place. If a record is maintained for certain measurable parameters like body and bearing temperature, insulation resistance, earth resistance etc., it is possible from the scrutiny of this record to predict the occurrence of future trouble and necessary steps can be taken to prevent the occurrence of serious breakdown.
The interval of doing various maintenance operations, depend upon the type of equipment, ambient condition and other factors. It is difficult to laydown hard and fast rules covering all conditions but for average normal industrial duty under-mentioned time schedule will serve as guide. This can be modified to suit other conditions at site.
Daily maintenance : 1) Examine visually earth connections and motor leads. 2) Check motor windings for overheating. 3) Examine control equipment. 4) Check condition of bearings. 6) Add oil, if necessary, 7) Check end play.
Weekly maintenance : 1) Check belt tension. In the case of sleeve bearing machines the air gap between-rotor and stator should be checked. 2) Blow out dirt from the windings of protected type motors situated in dusty locations. 3) Examine starting equipment for burnt contacts where motor is started and stopped frequently. 4) Examine oil in the case of oil ring lubricated bearings for contamination by dust, grit etc. (this can be roughly judged from the colour of the oil). 5) Check the intensity of vibrations during operation of the motor. 6) Clean filters where provided.
Monthly maintenance : 1) Overhaul controllers. 2) Inspect and clean oil circuit breakers. 3) Renew oil in high speed bearings in damp and dusty locations. 4) Wipe brush holders and check bedding of brushes of slip-ring motors. 5) Check that the connections of temperature detectors and space heaters, where provided, are proper and these are in working order.
Haly-Yearly Maintenance : 1) Clean windings of motors subjected to corrosive or other elements, also bake and varnish them, if necessary. 2) In the case of slip-ring motors, check slip-rings for grooving or unusual wear. 3) Check grease in ball and roller bearings and make it up where necessary taking care to avoid overfilling. 4) Drain all oil bearings, wash with petrol to which a few drops of oil have been added, flush with lubricating oil and refill with clean oil.
Annual Maintenance
- Check all high speed bearings and renew, if necessary.
- Blow out all motor windings thoroughly with clean dry air. Make sure that the pressure is not so high as to damage the insulation.
- Clean and varnish dirty and oily windings.
- Overhaul motors which have been subjected to severe operating conditions.
- Renew switch and fuse contacts if damaged.
- Check oil for its dielectric strength.
- Renew oil in starters subjected to damp or corrosive elements.
- Check insulation resistance to earth and between phases of motor windings, control gear and wiring.
- Check resistance of earth connections.
- Check air gaps.
- Check condition of all fasteners.