Module 7 (Maintenance Practices) Sub Module 7.2 (Workshop Practices)

7/26/2019 Module 7 (Maintenance Practices) Sub Module 7.2 (Workshop Practices)

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For Training Purpose OnlyISO

9001:2008

Certified

PIATRAININGCENTRE(PTC) Module7 MAINTENANCE PRACTICES

Category A/B1 Sub Module 7.2- Workshop Practices

PTC/CM/B1.1 Basic/M7/01

Rev. 007.2 Mar 2014

MODULE7

SubModule7.2

WORKSHOPPRACTICES


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For Training Purpose OnlyISO

9001:2008

Certified



PTC/CM/B1.1 Basic/M7/01

Rev. 007.2 Mar 2014


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ISO9001:2008Certified ForTrainingPurposeOnly



PTC/CM/B1.1 Basic/M7/01 Rev. 007.2 i Mar 2014

Contents

MAINTAINING TOOLS ---------------------------------------------------- 1

TOOL CATEGORIES ------------------------------------------------------ 1

CARE OF TOOLS ---------------------------------------------------------- 2

CONTROL OF TOOLS ---------------------------------------------------- 5

USE OF WORKSHOP MATERIALS ----------------------------------- 8

DIMENSIONS -------------------------------------------------------------- 11

TOLERANCES AND ALLOWANCES -------------------------------- 15

STANDARDS OF WORKMANSHIP --------------------------------- 18

CALIBRATION OF TOOLS AND EQUIPMENT ------------------- 19

CALIBRATION STANDARDS ----------------------------------------- 28


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PTC/CM/B1.1 Basic/M7/01 Rev. 007.2 ii Mar 2014

Page Intentionally Left Blank


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PTC/CM/B1.1 Basic/M7/01 Rev. 007.2 4 Mar 2014

essential for the effective maintenance of electrical equipment,and the work of these personnel is assisted if any defect, suchas overheating or excessive sparking, is reported immediately.

Workshop tool kits

Special tool kits are supplied for servicing certain machines,assemblies, etc., and these kits must, of necessity, be availablefor general use. The fact that a kit is used by more than oneperson is not an excuse for neglect or maltreatment by theindividual; such kits must be given the same care and attentionthat a good craftsman gives to his personal kit.

Measuring instruments and appliances

Equipment of this nature are normally kept in the workshop ortool store locker, and is issued on short-term loan as required.These items must be returned immediately after use; under nocircumstances should they be left lying about on workbenchesor stowed in personal toolboxes. In order to maintain theaccuracy measuring instrument need proper handling Measuringinstruments are usually issued with the storage box andother than during the time at which measurements are

taken the instrument should be kept in the case.

Gauges and special tools

These items should be kept in labeled boxes wheneverpracticable; the label should indicate the special purpose forwhich the gauge or tool may only be used.

Drills and reamers

Twist drills, when not in use, should be kept in a graded drill

stand. Reamers should be kept in partitioned boxes or laid ingrooved trays cut to receive each type of reamer.


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transferred to another part of the register or separatedocuments for alternate action

If work is not spanned across shifts then outstandingentries are to be considered very serious and aninvestigation should be carried out to locate thetools as the possibility exists of such tools becomingthe source of FOD (Foreign Object Damage).

When the user should carry out a cursory inspection ofthe tool at book out and should bring to the notice of the

stores personnel of any discrepancy immediately.

Upon completion of the work the user should make aneffort to return the tools to the stores as soon as it isconvenient to enable another user to use the same toolif required and also to minimize the chances ofmisplacing the tools.

When returning the tools to the tool stores the staff

at the issue counter should check for the condition ofthe tool and properly mark the issue register forreceived status and position the tools in the assignedlocation. When documenting of a toolkit is done thenumber of tools issued and received are also mentioned

in the register.

It is the responsibility of the user to report of anydamaged or malfunctioning tool or equipment to therelevant person in charge of tools so that it can berepaired in time.

Unserviceable tools due to damage or malfunctionis to be routed to the relevant sections or externalrepair organization for repair at the first availableinstance to prevent disruption due to unavailability. Fortools that require frequent repairs an investigationshould be done for possible mishandling or misuse.

Tools that require calibration will be tracked andsent for necessary re-calibration prior to calibrationdue date or earlier if continued availability during acritical period is forecasted.


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are designed and never mixed together, unless the twomaterials are designed to be mixed, such as with two part epoxyadhesives and sealants.Many liquids used in workshops and in the hangar have (asmentioned earlier) a fixed life. This date is printed on thecontainer and must be checked before use, because manymaterials are unsafe if used beyond their expiry date.


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The disposal of liquids is a critical operation, and must only becarried out in accordance with company (and, often, national orinternational) regulations.

Liquids must never be disposed of by pouring them into spareor unidentified containers and they must not be allowed to enterthe domestic drains systems.

The working with, and the use of, high pressure gas containersand oxygen systems, was adequately discussed in the SafetyPrecautions topic.


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Fundamental and derived dimensions

After a few dimensions are defined, it should be obvious thatother dimensions can be obtained by combining one or more ofthem. This observation leads to the need to differentiatebetween the original dimensions and the combineddimensions, and thus the terms fundamental and derived

dimensions were born.

Fundamental dimensions

The most elementary dimensions, like length (L), mass (M), andtime (T), are known as fundamental dimensions.Fundamental units

Quantity Standard Unit Symbol

1 Length meter m

2 Mass kilogram kg

3 Time second s

4 Electric Current ampere A

5 Temperature Kelvin K

6Luminous

IntensityCandela Cd

7 Matter mole mol

8 Plane Angle Radian rad

9 Solid Angle Steradian sr

Derived dimensions

Dimensions obtained by combining one or more fundamentaldimensions are called derived dimensions.

Area (L2) and volume (L3) are examples of deriveddimensions obtained by combining the same dimension

(i.e., L).

Velocity (LT-1), acceleration (LT-2), and pressure (ML-1T-2), on the other hand, are examples of deriveddimensions obtained by combining different fundamentaldimensions (i.e., M, L, and T).


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Named units derived from SI base units

Name Symbol QuantityExpression in terms of other

unitsExpression in terms of SI base

units

hertz Hz frequency 1/s s-1

Newton N force, weight mkg/s2 mkgs2

Pascal Pa pressure, stress N/m2 m

1kgs

2joule J energy, work, heat Nm = CV = Ws m2kgs2

watt W power, radiant flux J/s = VA m2kgs3

coulomb C electric charge or electric flux sA sA

volt Vvoltage, electrical potentialdifference, electromotive force

W/A = J/C m2kgs3A1

farad F electric capacitance C/V m2kg1s4A2

ohm electric resistance, impedance,reactance

V/A m2kgs3A2

Siemens S electrical conductance 1/m2kg1s3

A2

Weber Wb magnetic flux J/Am2kgs2

A

1

tesla Tmagnetic field strength, magneticflux density

Vs/m2 =Wb/m2 =N/(Am)

kgs2A1

Henry H inductance Vs/A = Wb/Am2kgs2

A2


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Although dimensions are necessary to describe an object or anevent, they are not sufficient. That is, it could be correctly statedthat both a football field and a matchstick possess thefundamental dimension of length, but if one were interested inknowing their relative sizes, additional information wouldobviously have to be provided about the dimension of length.This additional information is provided in the form of the units

associated with each dimension.

A unit is the standard of measurement applicable to a givendimension. For example, inches, feet, meters, furlongs, andfathoms all are units associated with the dimension of length.Similarly, cubic inches, liters, cubic meters, and gallons areunits associated with the dimension of volume.

Throughout history, different units have been adopted for

quantifying the various dimensions, as illustrated for length andvolume. Therefore, we may often need to convert numbers fromone set of units into another (e.g., feet to meters, yardsto centimeters).


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Tolerance The difference between the upper limit and thelower limit of a dimension. The amount that the size of amachine part is allowed to vary above or below a basicdimension; for example, 3.650 0.003 centimeters indicates atolerance of 0.003 centimeter.

Bilateral Tolerance When variation is allowable in both

directions from the basic size. Here the actual dimensions of theobject may be larger or smaller than the basic size by anallowable margin.

Unilateral Tolerance When the variation is allowed only inone direction from the basic size. Here the actual dimensions ofthe object must comply with either of the following conditionsbut not both.

Actual size can be larger than the basic size but theminimum allowable size should be that of the basic size and notless.

OR

Actual size can be smaller than the basic size but maximumallowable size should be that of the basic size and not more.

Allowance An allowance is a planned deviation between anactual dimension and a nominal or theoretical dimension, orbetween an intermediate-stage dimension and an intended finaldimension. The unifying abstract concept is that a certainamount of difference allows for some known factor ofcompensation or interference. For example, an area of excessmetal may be left because it is needed to complete subsequent

machining.


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Bilateral Tolerance Unilateral Tolerance


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CALIBRATION OF TOOLS AND EQUIPMENT

Instrument calibration is one of the primary processes used tomaintain instrument accuracy. Calibration is the process ofconfiguring an instrument to provide a result for a sample withinan acceptable range. Eliminating or minimizing factors thatcause inaccurate measurements is a fundamental aspect of

instrumentation design. their accuracy.

In any industry, measurements related to product quality are anessential part of quality control systems. In the aviationmaintenance industry such measurements play a moreimportant role, as decisions that have a direct impact on safetymay be based on them.

Measurements affect the product quality directly or indirectly.

Measurements affect the product directly when they takethe form of dimensional measurements that determinesthe quality of the product. E.g. Diameter of a roller whenchecking for wear.

Measurements affect product quality indirectly whenthey take the form of monitoring and controlmeasurements of a process. E.g. Temperaturemaintained during heat treatment of material.

In trying to maintain and improve on product quality and level ofsafety, a fundamental requirement is the use of instruments thatwill provide measurements that are accurate to a high degree ofthe actual property being measured. Before dealing with

calibration it is important to know the characteristics ofmeasuring instruments and what factors affect their accuracy.


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system is merely modulating the value of the voltage from thisexternal power source.

In active instruments, the external power source is usually inelectrical form, but in some cases it can be other forms ofenergy, such as pneumatic or hydraulic.

One very important difference between active and passive

instruments is the level of measurement resolution, which canbe obtained. With the simple pressure gauge shown, theamount of movement made by the pointer for a particularpressure change is closely define by the nature of instrument.

While it is possible to increase measurement resolution bymaking the pointer longer, such that the pointer tip movesthrough a longer arc, the scope for such improvement is clearly

bounded by the practical limit on how long the pointer canconveniently be.

In an active instrument, however, adjustment of the magnitudeof the external energy input allows much greater control overmeasurement resolution. While the scope for improvingmeasurement resolution is much greater but it is not infinitebecause of limitations placed on the magnitude of the externalenergy input, in consideration of heating effects and for safety

reasons.

In terms of cost, passive instruments are normally of a simplerconstruction than are active ones, and are therefore cheaper to

manufacture. Choice between active andpassive instruments for a particular

application thus involves balancing the measurement-resolution requirements carefully against cost.

Fig. 2.1 Passive Pressure Gauge


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Fig. 2.3


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Fig. 2.4

Monitoring/ control instruments

An important distinction between different instruments is madeaccording to whether they are suitable only for monitoringfunctions or whether their output is in a form that can be directlyintroduced as an input into an automatic control system.Instruments, which only give an audio or visual indication of themagnitude of the physical quantity measured, such as a liquid-in-glass thermometer, are only suitable for monitoring purposes.This class normally includes all null-type instruments and mostly

passive transducers.

For an instrument to be suitable for inclusion in an automaticcontrol system, its output must be in a suitable form for directinput into the controller. This usually means that an instrumentwith an electrical output is required, although other forms ofoutput such as optical or pneumatic signals are used in somesystems.


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Fig. 2.5 Dead Weight Pressure Gauge (Null Type)

Analogue/ digital instruments

Instruments which use a needle or a hand moving around a dialto provide information are called analogue instruments whiledigital Instruments provide a numerical display of information Ananalogue instrument gives an output, which varies continuouslyas the quantity being measured changes. The output can havean infinite number of values within the range that the instrumentis designed to measure. The deflection type of pressure gauge

described earlier in this chapter is a good example of ananalogue instrument. As the input value changes, the pointermoves with a smooth continuous motion. Though the pointercan therefore be in an infinite number of positions within itsrange of movement, the number of different positions, which theeye can discriminate between, is strictly limited, thisdiscrimination being dependent upon how large the scale is andhow finely it is divided.

A digital instrument has an output, which varies in discrete stepsand so can only have a finite number of values. The rev countersketched in Figure 2.6 is an example of a digital instrument. Inthis, a cam is attached to the revolving body whose motion isbeing measured, and on each revolution the camp opens andcloses a switch. The switching operations are counted by anelectronic counter. This system can only count wholerevolutions and therefore cannot register any motion, whichis less than a full revolution.


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The distinction between analogue and digital instruments hasbecome particularly important with the rapid growth in theapplication of microcomputers to automatic control systems.

Any digital computer system, of which the microcomputer is butone example, performs its computations in digital form. Aninstrument whose output is in digital form is therefore particularly

advantageous in such applications, as it can be interfaceddirectly to the control computer. Analogue instruments must beinterfaced to the microcomputer by an analogue-to-digital (A/D)converter, which converts the analogue output signal from theinstrument into an equivalent digital quantity, which can be readinto the computer. This conversion has several disadvantages.Firstly, the A/D converter adds a significant cost to the system.Secondly, a finite time is involved in the process of convertingan analogue signal to a digital quantity, and this time can be

critical in the control of fast processes where the accuracyof control depends on the speed of the controllingcomputer. Degrading the speed of operation of the control

computer by imposing a requirement for A/D conversion thusdegrades the accuracy by which the process is controlled.


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Fig. 2.6 Revolution Counter (Digital)

Static instrument characteristics

Instrument Performance Characteristics are of two types:

Static having nonlinear or statistical effectsDynamic described by linear differential equations


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Static calibration

All inputs (desired, interfering and modifying) except one arekept at some constant values. Then the input under study isvaried over some range of constant values. The input-outputrelationship is valid under the stated constant conditions of allthe other inputs.

Measurement method: ideal situation all other inputs areheld constant

Measurement process: physical realization of themeasurement method

Steps in Static Calibration

1. Examine the construction of the instrument and identifyand list all the possible inputs.

2. Decide which of the inputs will be significant in theapplication for which the instrument is to be calibrated.

3. Procure apparatus that will allow you to vary all thesignificant inputs over the ranges considered necessary.Procure standards to measure each input.

4. By holding some inputs constant, varying others, andrecording the output(s), develops the desired staticinput-output relations.

The various static characteristics are defined in the followingparagraphs.

CALIBRATION STANDARDS

History


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5 Calibration procedures shall be documented.

6 Objective evidence that the measurement system iseffective shall be readily available to customers.

7 Calibration shall be performed by equipment traceable tonational standards.

8 A separate calibration record shall be kept for eachmeasuring instrument. These records must demonstratethat all measuring-instruments used are capable ofperforming measurements within the designated limits.The record for instrument shall contain as minimum:

a description of the instrument and a uniqueidentifier;

the calibration date;

the calibration results;

The calibration interval (plus date when next calibration due).Some or all of the following information is also required in thecalibration record, according to the type of instrumentinvolved:

the calibration procedure;

the permissible error limits;

a statement of the cumulative effects ofuncertainties in calibration data;

the environmental conditions required forcalibration;

the source of calibration used to establishtraceability;

details of any repairs or modifications whichmight affect the calibration status;

Any use limitations of the instrument.

9 All equipment shall be labeled to show its calibrationstatus and any usage limitations (if practicable).

10 Any instrument, which has failed or is suspected (orknown) to be out of calibration shall be withdrawn from

use and clabelled conspicuously to prevent accidentaluse.

11 Adjustable devices shall be sealed to prevent tampering.

Documents

Module 7 (Maintenance Practices) Sub Module 7.2 (Workshop Practices)