Preventive Maintenance and Breakdown Analysis
Overview
Preventive Maintenance (PM) and Breakdown Analysis are core topics in ITI Fitter Semester 4. PM involves scheduled, planned servicing of machines to prevent unexpected failures, reduce downtime, and extend equipment life. Breakdown Analysis identifies root causes of machine failures to prevent recurrence. Together, these practices ensure safe, efficient, and cost-effective operation of industrial machinery, forming the backbone of any maintenance engineering programme tested in NCVT ITI Fitter trade examinations.
Typed Notes
Types of Maintenance
Maintenance is broadly classified into four types. (1) Preventive Maintenance (PM): Planned, time-based or condition-based servicing before failure. (2) Breakdown/Corrective Maintenance: Repair after failure; unplanned and costly. (3) Predictive Maintenance: Uses sensors and monitoring (vibration, temperature) to predict failure. (4) Scheduled/Planned Maintenance: Maintenance done during planned shutdowns. In NCVT ITI Fitter exams, PM is the most tested type. Key rule: PM reduces overall maintenance cost by 15–25% compared to pure breakdown maintenance.
Preventive Maintenance Schedule and Checklist
A PM schedule lists tasks at defined intervals. Daily checks include oil level, coolant level, belt tension, and cleaning. Weekly checks cover lubrication of slideways, checking fastener tightness, and filter cleaning. Monthly checks include bearing inspection, alignment check, and electrical connection tightness. Annual tasks involve complete overhaul, replacement of seals and gaskets, and re-calibration. A PM checklist is a written document signed by the maintenance fitter after each task. Colour-coded tags (Green = OK, Yellow = Monitor, Red = Stop) are used on machines to indicate condition status.
Lubrication in Preventive Maintenance
Lubrication is the most important PM activity for a Fitter. Correct lubricant selection depends on load, speed, temperature, and environment. Grease (NLGI Grade 2 most common) is used for slow-speed bearings; oil (SAE 40 or SAE 68 hydraulic oil) is used for high-speed parts and hydraulic systems. Over-lubrication causes overheating; under-lubrication causes wear and seizure. Lubrication points are marked on machine diagrams. A grease gun, oil can, and centralized lubrication system are common tools. Lubrication interval for a lathe headstock bearing is typically every 500 operating hours.
Breakdown Analysis — Root Cause and Tools
Breakdown analysis finds WHY a machine failed so the same failure does not repeat. Steps: (1) Record breakdown details — time, machine, symptom. (2) Identify the failure mode (bearing seizure, belt snap, gear wear). (3) Use 5-Why Analysis: ask 'Why?' five times to reach the root cause. (4) Use Fishbone (Ishikawa) Diagram to categorize causes under Man, Machine, Material, Method, Environment (4M+1E). (5) Implement corrective action and update PM schedule. MTBF = Total operating time ÷ Number of failures. Higher MTBF means better reliability. MTTR = Total repair time ÷ Number of repairs. Lower MTTR means faster recovery.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Types and Objectives of Maintenance
- Preventive vs Breakdown vs Predictive Maintenance
- Objectives: reduce downtime, extend machine life, ensure safety
- Condition-based vs time-based maintenance
- Cost comparison: PM vs breakdown maintenance
A lathe machine in a workshop is serviced every 500 hours (time-based PM) regardless of whether it shows any fault — this prevents unexpected spindle bearing failure during production.
02Preventive Maintenance Schedule and Checklist
- Daily, weekly, monthly, and annual PM tasks
- PM checklist format and sign-off procedure
- Colour-coded machine status tags (Green/Yellow/Red)
- Inspection of belts, fasteners, filters, and alignments
A daily checklist for a drilling machine includes: check spindle oil level (must be between MIN and MAX marks), clean swarf from table, check V-belt tension (deflection should not exceed 10–15 mm under thumb pressure).
03Lubrication Management
- Selection of lubricant: grease vs oil, viscosity grades
- Lubrication intervals and lubrication points on machines
- Tools: grease gun, oil can, centralized lubrication system
- Effects of over-lubrication and under-lubrication
A ball bearing in a conveyor motor is packed with NLGI Grade 2 grease and re-greased every 2000 hours; using the wrong SAE 10 oil instead caused the bearing to run dry and seize within 3 days.
04Breakdown Analysis and Root Cause Methods
- 5-Why Analysis technique
- Fishbone (Ishikawa) Diagram — 4M+1E categories
- Recording breakdown: time, symptom, failure mode
- Corrective action and updating PM schedule
A hydraulic press stopped working. 5-Why: Pump not delivering pressure → Why? Oil level low → Why? Oil seal leaking → Why? Wrong seal material used during last repair → Why? Spare parts store issued NBR seal instead of Viton — root cause: wrong material specification in store records.
05Key Performance Indicators in Maintenance
- MTBF — Mean Time Between Failures formula and meaning
- MTTR — Mean Time To Repair formula and meaning
- Machine availability percentage calculation
- Breakdown frequency and its impact on production
A milling machine ran for 2000 hours and had 4 failures: MTBF = 2000 ÷ 4 = 500 hours. Total repair time was 20 hours: MTTR = 20 ÷ 4 = 5 hours. Machine Availability = (2000 − 20) ÷ 2000 × 100 = 99%.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Preventive Maintenance (PM) is scheduled maintenance carried out at fixed intervals (daily, weekly, monthly, annually) to prevent machine breakdown before it occurs.
- 02Breakdown Maintenance (corrective maintenance) is unplanned repair done after a machine has already failed — costlier and more dangerous than PM.
- 03MTBF (Mean Time Between Failures) and MTTR (Mean Time To Repair) are key performance indicators used in breakdown analysis.
- 04Lubrication schedule, inspection checklist, and replacement of wear parts (belts, seals, bearings) are the three pillars of a PM programme.
- 055-Why Analysis and Fishbone (Ishikawa) Diagram are standard root-cause analysis tools used in breakdown analysis.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is Preventive Maintenance? State its four main objectives.
Differentiate between Preventive Maintenance and Breakdown Maintenance with two points each.
Explain the 5-Why Analysis method with a practical example from a workshop.
Define MTBF and MTTR. A machine operated for 3000 hours and had 6 failures with total repair time of 30 hours. Calculate MTBF and MTTR.
What is a lubrication schedule? State the effects of over-lubrication and under-lubrication on machine components.
Preventive Maintenance is planned servicing at fixed intervals to avoid breakdowns; it includes lubrication, inspection, and part replacement. Breakdown Analysis uses tools like 5-Why and Fishbone Diagram to find root causes of failures. Key metrics are MTBF and MTTR. A good PM programme reduces costs, improves safety, and extends machine life — all critical knowledge for NCVT ITI Fitter Semester 4 examinations.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.What does MTBF stand for in maintenance engineering?
Q2.Which colour tag on a machine indicates that it must be STOPPED immediately and not operated?
Q3.The Fishbone (Ishikawa) Diagram used in breakdown analysis categorizes causes under which of the following?
Q4.A machine operated for 4000 hours and failed 8 times. What is its MTBF?
Mark karo — dashboard par progress dikhega.