ENG 411 Mid-Term Exainale certain department of the factory u2 The mean time bet

Question

ENG 411 Mid-Term Exainale certain department of the factory u2 The mean time between failures and mean time to repair in a are 500 hours and 10 hours, respectively. The department operates 30 machines ourng w hour shift per day, five days per week, 52 weeks per year. Each time a machine breaks down per hour( to install a preventive maintenance program in this department. In this program preventive maintenance would be performed on the machines during the-none vworing expected to be that the aver normally accomplished during the working shifts will be performed during none-working sh hours so that thore s to production during the regular two shifts. The effect of this program s t age MTBF will be 800 hours, and half of the emergency repair time cost of the maintenance crew will be $2500 per week However, a reduction of maintenance personnel on the working shift will resuit in a savings during the regular shin of $500 per week The average time that the machines spend waiting for the maintenance crew is 3 hours (a) Calculate the availability of machines in the department both before and after the preventive maintenance program is instaliled. N.B. Availability (MTBF MTTRYIMTBF)

Explanation / Answer

a) availability without preventive maintaince

A1=( 500-10)/500= 0.98 = 98%

availability with preventive maintance

A2 =(1000-10)/1000= 0.99 =99%

we will ignore this

as half of the reparing is done in evening

MTTR = 10/2= 5 HRS

NOW AVAILABILITY IS A3 = (1000-5)/1000 = 0.995 = 99.5%

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