basics in maintenance

Today we are going to learn the basics of maintenance & the method for the accountability of losses & the method to over come those losses by appropriate maintenance activity. By,

Raghuttam Jorapurkar

Basics in Maintenance


What is Maintenance?

Maintenance is defined as engineering actions which are necessary for retaining or restoring an equipment, machine or system to the specified condition to achieve its maximum useful life.


Types of Maintenance

There are major three types of maintenance

1. Preventive Maintenance

2. Breakdown Maintenance

3. Corrective Maintenance


1. Preventive MaintenanceIt includes two types of Maintenance

1.1 Periodic Maintenance (TBM : Time Based Maintenance)

1.2 Predictive Maintenance (CBM : Condition Based

Maintenance)


1.1 Periodic Maintenance (TBM)

In this type of maintenance, spares / consumable replacement activity of the equipment or machine is carried out as per predefined time period.

Disadvantage : Spare cost become high

Note : TBM is only spare part replacement activity


1.1 Periodic Maintenance (TBM)

A Periodic time based maintenance plan is to be prepared for our

company.


1.2 Predictive Maintenance (CBM)It is the determination of the condition of in-service equipment in order to predict when maintenance should be performed

This maintenance can be easily carried out by electronic equipment like bearing echo meter, multimeter, IR temperature meter etc.

Advantage : Cost effective & utilization of spares can be achieved up to 99%


1.2 Predictive Maintenance (CBM)A Periodic condition based

maintenance plan is to be prepared for our company.


1.2 Predictive Maintenance (CBM) While performing this type of maintenance,

check sheet should be updated for further analysis. Machine / equipment history card is to be updated regularly for analysis & timely action.


2. Breakdown Maintenance

This maintenance is carried out on all items where the time of failure or wearing out are not yet captured in history of the machine or equipment.

The maintenance activity conducted to bring back the machine / equipment in working order which has worn out or failed.


3. Corrective Maintenance

To improve reliability & maintainability, corrective maintenance is must

It can be achieved by implementation of kaizens on :

a. MTBF improvementb. MTTR reduction


Breakdown

If downtime is more than 10 minutes due to equipment problem, it is “breakdown”

Minor Stoppage

If downtime is less than or equal to 10 minutes due to equipment problem, it is

“minor stoppage”


Mean Time To Repair (MTTR)• It is a basic measure of the maintainability

of repairable items. • It represents the average time required to

repair the equipment


Total Breakdown Time

Total Breakdown Incidences M. T. T. R. =

Mean Time To Repair (MTTR)

• It can be measured in minutes, hours or days

• It should be very low & ideally it should be zero

• While calculations of MTTR, there is no consideration of minor stoppages




Question : Calculate MTTR for the month of May 2014 in which there were 2 breakdowns of 65 & 75 min


Mean Time To Repair (MTTR)According to formula of

Total Breakdown Time

Total Breakdown Incidences MTTR =

65 min + 75 min

2MTTR =



140 min

2MTTR =

70 min =

70/60 hours =

1.16 hours =


Mean Time Between Failure (MTBF)

It is nothing but the average time between failures of the

system/equipmentTotal Working Time – Total Breakdown Time

Total Breakdown Incidences MTBF =


• It can be measured in minutes, hours or days

• It should be very high & ideally it should be infinite

• There is no consideration of minor stoppages




Question : Calculate MTBF for the month of May 2014 in which there were 2 breakdowns of 111 & 222 min

(Given : No. of working days were 24)



Working time = Working Days X 24 hours

Working time = 24 days X 24 hours

= 576 hours



Breakdown time= 111 min + 222 min

Breakdown time = 333 min

= 333/60 hours

= 5.55 hours


Mean Time Between Failure (MTBF)Now as per formula of MTBF

Total Working Time – Total Breakdown Time

Total Breakdown Incidences MTBF =

576 – 5.55

2MTBF =

285.22 hoursMTBF =


Uptime

It is a measure of the time a machine has been up without any downtime

It is measured in percentage

Available Time – Breakdown Time

Available Time Uptime = X 100


UptimeSuppose, available time is 24 day & breakdown time is 4 hours, then uptime will be Available Time – Breakdown Time

Available Time Uptime = X 100

(24 X24) – 4

(24 X 24)Uptime = X 100

Uptime = 93.31 %


Any Queries ?

basics in maintenance

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