Maintenance of Machinery-Online Learning

 Maintenance 

How do you maintain a machine?

1- Total plant profitability is obviously affected both by on-stream factors and maintenance costs. 

2- One cannot be separated from the other. 

3- Any system, therefore, must account for how cheaply maintenance can be performed from an organizational setup, and also what must be done and how often. 

4- The ability to update maintenance requirements and improved planning based on experience at a group of plants has a large bearing on overall maintenance costs. 

5- Other than breakdown maintenance, all maintenance work is planned. 

6- Some can be done while the plant is operating and the rest during shutdown. 

7- The effectiveness of this planned or preventive maintenance (PM) program to reduce breakdowns and the organizational methods used to accomplish the planned major maintenance work will determine maintenance costs.

8- Preventive maintenance as discussed here covers all planned maintenance work, whether major or minor, regardless of whether the plant is running or shut down. 

9- The selection of what shall be done as part of the PM program and how often it shall be done is one of the most important factors affecting corporate maintenance costs and the realization of an optimum on-stream factor. 

10- It is a generally accepted practice to let each plant manager handle the PM program for his facility. 

11- In some plants, this is being done with individual check sheets or production boards using equipment manufactures recommendations and the limited experience of plant personnel. 

12- However, the demand for plant operation attention often prevents time maintenance performance. 

13- Another defect is that it lacks uniformity and, does not provide compliance reports to home office management. 

14- And, there is often no effective way to compare the PM performance at similar plants or equipment at different locations. 

15- Most important of all, equipment fail uses may occur because proper consideration and judgment is not given to maintenance items whose significance is best understood by qualified specialists.

Preventive maintenance 

Why maintenance is required?

1- The machine tools are of high precision, and are sensitive and expensive. 

2- They must be handled and maintained carefully in order to give good and long service. 

3- The basic function of the maintenance department is the upkeep of the machines and equipment's in good operating condition. 

4- Earlier the maintenance of the equipment used to receive attention only when the equipment suffered some setback or break down as a result of some minor/major fault. 

5- Such breakdowns not only brought a serious production hold-up but also used to upset the production flow of the industry where the other equipment also had to stand idle. 

6- This resulted in a more cautious approach to the maintenance of the equipment and this brought up the more scientific way of tackling the maintenance problem, through preventive maintenance (PM ). 

What is Preventive maintenance

1- Preventive maintenance consists of a few engineering activities which help to maintain the machine tools in good working order. 

2- The basic activities of preventive maintenance are the 

i) Periodic inspection of machines and equipment's to uncover conditions leading to production breakdowns or harmful depreciation. 

ii) Upkeep of machines and equipment's to avoid such conditions or to adjust, repair or replace them while they are still in the initial stages. 

Functions of preventive maintenance department 

1- Periodic inspection Functions of machines and equipment's as per "Check – lists". (Annexure I). 

2- Lubrication of machines and equipment's as per the manufacturer's instruction manuals. 

3- Servicing and overhauling of machine and equipment as per the PM schedule. Activate.

4- Keeping basic records of each machine and equipment. Annexure – II. 

5- D Analysis of inspection reports and systematic review of reports of machines and equipment's. 

Advantages of preventive maintenance system 

1- Less downtime in production. 

2- Improves quantity and quality of product. 

3- Standby equipment is not needed which saves capital investment. 

4- Lower unit cost of manufacture. 

5- Reduces major and repetitive repairs of machines. 

6- P.M. helps in prolonging the life of the machines and reduction in un-expected breakdowns. 

How can we improve maintenance?

1- Periodic inspection 

Periodic inspection of machines and equipment's as per the check - list 

1- Check-list itemizes for the inspector all the points to be checked on-individual machines. 

2- While preparing the check-list of the machine, make sure that no machine part or item that is omitted needs attention. 

3- The inspection of machine tools like lathe and drilling machine includes the following. 

i)• Driving system and feeding system. 

ii) Lubricating and coolant system.

iii) Slides and wedges and gibs. Belts, bearings, clutch, brake and operating controls. 

iv)- Guide ways, lead screws and their mating parts.

v) After inspection of each machine, the inspector has to make out the list of parts which need repairs or spares for replacement. 

2- Frequency of Inspection 

1- The frequency of inspection depends on the age, kind of machine and its operating conditions. 

2- Frequent inspection of machines and equipment may be expensive and frequency with long intervals may result in more breakdowns. 

3- A good balance is needed to bring optimum savings. 

 3- Lubrication of machines and equipment's 

1- The length of time a machine will retain its accuracy and give satisfactory service depends on the lubrication and care it receives. 

2- It is essential that lubrication of machines should be carried out systematically at regular intervals as recommended in the service manual supplied by the machine manufacturer. 

2- The manufacturer's manual contains all the necessary details like grade of oil, grease, oiling and greasing points and also indicates the time intervals of lubrication. 

3- Maintenance Records: (Annexure III) 

1- Keep a detailed record of faults, failures, repairs and replacement's done for machines. 

2- It is useful to analyses the cause of a fault and rectification. 

4- Maintenance Records Analysis 

1- Systematic review and regular analysis of the equipment records will help to 

i) Re-design the weak part which gives repetitive trouble. 

ii) Substitute with better material for high cost items. 

iii) Minimize frequent breakdowns.

iv) Reduce the cost of production.

5- Acceptance test charts

1- Most makers of machine tools do this by means of test charts which indicate the maximum permissible error, together with the actual error of the part when it was tested at the maker's works.

2- Such information and tests are invaluable for checking machines after repairing so as to ensure that 

i) It has not been distorted in transit.

ii) It has been properly fixed in position.

iii) It will yield an accurate product. 

3- The test charts are in three sections. 

i) Levelling.

ii) Geometrical test. 

iii) Performance test.

Levelling 

1- The machine must first be carefully levelled on a rigid floor by means of steel wedges, packing etc. and checked with precision level as specified in the charts. 

 Geometrical test. 

1- Each test is based on the correct erection and levelling of the machine. Geometrical test 

i)- This test is carried out to know the grade of accuracy of the assembled machine while idle and in an unloaded condition and after running the main spindle for at least an hour at its mean speed. 

ii)- The machine should be tested in its fully assembled state. 

iii)- Ensure that the machine is levelled before the test is done. 

Performance test 

1- This test is to ascertain the precision of a machine tool for the finishing operation for which the machine has been designed. 

2- The practical tests should be carried out on pieces, the production of which does not require operations other than those for which the machine has been built. 

3- The degree of working accuracy of the machine, besides depending on the machine itself, is also Influenced by the following factors. 

i) The type of cutting tools. 

ii) The material of the cutting tool and work piece.

iii) The cutting speed feed and depth of cut 

iii) Tool and work-holding units.

iv) The skill of the operator.

Test charts

1- A test chart is prepared for each machine by the manufacturer of the machine.

2- It consists of instruction for testing names of the measuring instruments used, sketches and details of permissible error and actual error. 

3- It provides a convenient basis for conducting tests.

Periodic acceptance test

1- The machine tool is expected to produce accurate work pieces not only when it is new but throughout its working life. 

2- A machine tool must be able to produce work pieces within specified limits.

3- For this reason the wear of the machine must not exceed certain limits. 

4- It must be watched, and parts which are faulty, due to wear or other damage, must be replaced or repaired without delay.

5- The periodic acceptance tests are to be carried out after overhaul and re- conditioning of the machine tool. 

6- Apart from the regular general inspection of the machine tool, immediate steps must be taken when faulty works pieces are produced by a machine when machined dimensions lie outside the specified limits. 

7- In such cases, the accuracy and performance of the machine must be tested without delay. 

8- Faults can be eliminated only if the causes of the errors are known.