14. CHAPTER - 14 Marhcine Guarding

8/19/2019 14. CHAPTER - 14 Marhcine Guarding

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CHAPTER - 14

Machine Guarding

1. Requirements of Machine Guarding1.1 Basic Need & Importance1.2 Statutory Requirement

2. Indian Standards3. rincip!es of Machine Guarding "

3.1 #e$nitions3.2 %!imination of a'ard3.3 Groups of #angerous arts "

3.3.1 (ccording to Motions3.3.2 (ccording to .(.

ep)urn3.* Requisite +haracteristics

,#esign rincip!es- of Guards*. %rgonomics of Machine Guarding "

*.1 Meaning of %rgonomics

*.2 (ims of %rgonomics*.3 uman actors in #esign of

Machine and /or0 *.* Safe o) Methods ,rocedures- "

*.*.1 Some Methods*.*.2 ManMachine +hart

. 4ypes and Se!ection of Guards ".1 4ypes of Guards and Se!ection.2 Bui!tin Safety #e5ices

.3 Incidenta! Safety #e5ices and Methods.* Guarding of #i6erent Machines

7. Materia!s for Guard +onstruction8. Maintenance and Repairs of Guards

1 REQUIREMENTS OFMACHINE GUARDING

Machine guarding is required as abasic need as well as statutoryrequirement.

11 !a"ic Need and I#$%r&ance'

Basic need of machine guarding is toprotect against contact with thedangerous and moving parts of amachine, work in process and failure dueto mechanical, electrical, chemical orhuman causes. The guards removeworkers’ fear and thereby increase theirmorale and the production. They allow

the operation at higher speeds andcompensate the expenditure on guarding.

here danger exists from machinery,safe working practice alone is insu!cientand cannot be relied on from safety pointof view. "uards are essential as anengineering and built#in control to preventaccident when other precautions fail.

$ee Table %o. &.', &.(, &.)*, &.)+ and&.) of -hapter#& for accidents due tomachinery. bsence or defect of guard isthe main cause of accidents due tomoving machines or their dangerous

parts. Types of such dangerous parts aremany. $ee /art . for their details.

0t is obvious that when cutting edgesof sharp tools, rotating and pro1ectingparts, point of operation or contact pointof die and punch, nip 2contact3 points of

pulley 4 belts or gears, rollers, calendarrolls, traversing tools or bed etc. areunguarded and workers are exposed tosuch openly moving i.e. unguarded parts,their risk of accident is highest. 5ongsleeves 2shirt3, sadis9 chain, i.e. mu6er,shawl etc can trap or entangle intounguarded rotating parts and serious orfatal accidents are possible. Many suchaccidents have happened also. Therefore,basic need of machine guarding must 7rstbe understood.

Mainly machine guarding is of twotypes8 2+3 "uarding for $%in&" %( %$era&i%n i.e. guarding for cutting edges,tool points, press or shear points, nip orrunning contact points, feed points etc.,and 2)3 "uarding for Power Transmission Machinery i.e. gears9

pu!!ey)e!ts9 coup!ings9 c!utches9 )ra0es9cams9 shafts9 ro!!s9 rods that transmit energy and motion from the source of

po:er ,prime mo5er- to the point of

operation.

1

THEME


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1) S&a&u&%r* Re+uire#en&'

Besides its basic need, machineguarding is a statutory requirement sincea century. ith the growth of industrialisation, need of machineguarding was noticed and incorporated by

the enactment of the 9actories ct in:ngland in +(;; and in 0ndia in +((+.

The 05< -onvention 2%o. ++=3 and>ecommendation 2%o. ++(3 of +=',regarding ;Guarding of Machinery


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gear or other e!cient device to movedriving belts to and from fast and loosepulleys and to prevent the belt fromcreeping back on to the fast pulley, shallbe used and maintained. Eriving belts notin use should not rest or ride uponshafting in motion 2for which belt hangers

are necessary3. ule

&; prescribes machine guarding details inrespect of textile machinery, cottonginning machinery, wood#workingmachinery, rubber mills, centrifugalmachines, power press and shears,slitters and guillotine machines.

/art &.; of this -hapter describesguarding of some such machines.

) INDIAN STANDARDS

Many 0ndian $tandards are available. few are given below in Table +;.+8

Ta3/e 141 ' 0$ on Machine "uarding

N%

Su3ec& IS N%

+ 5ist of 0$ on $afety,

Mechanical :ngineering,9oundry 0ndustry,utomobile 0ndustry andgricultural :quipment0ndustry

##

) Erilling, $afety code ;*(+

-ompressors safety ++;'+

; -onveyor safety ''(?,?+&&

& /rinting machinery safety +)'+=

' Gn7red pressure vessel )()&

? Belting for powertransmission2part 0 for 9lat belt, /art 00for Aee#belt3

)+))

( -are and practice of abrasive wheels

+==+

= Eegrees of protectionprovided by enclosure forrotating electricalmachinery

;'=+

+* ood working machines

2/art + to );3

(=';

++ Mechanical "uarding of Machinery

=;?;

+) Mechanical /ress ?;'(,?;'=,+*';;

+ Machine # shaft heights )*+

+; Machine # metal formingterminology

''&)

+& Machine # working levelheight

?))=

+' Machine tools # safetyrequirements

++*+'

These standards are useful fromdesign to maintenance purposes.

5 PRINCIP6ES OF MACHINEGUARDING

51 De,ni&i%n"'

1 P%in& %( %$era&i%n8 That area on amachine where material is positioned

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for processing by the machine andwhere work is actually beingperformed on the material.

) 7er% Mechanica/ S&a&e 87MS9" Themechanical state of a machine inwhich every power source that canproduce a machine member

movement has been shutClocked oF. This means de#energised, de#pressurised and neutralised conditionof the machine or equipment whichprovides maximum protection againstunexpected mechanical movement.

5 P%er %2' The state in which power2electric, pneumatic, hydraulic,atomic etc.3 cannot ow to themachine is considered a power#oF stage.

4 P%er-/%ced %2 8 The state in whichthe device that turns power oF islocked in the oF position with thepadlock of every individual who isworking on the machine.

: Guarding8 ny means of eFectivelypreventing personnel from coming incontact with the moving parts of machinery or equipment which couldcause physical harm to the personnel.0n case of a power#press, a cover onpoint of operation 2die and punch3 is

called @guard’ while those on otherdanger Hones are called @enclosure’ or@safeguard’.

Sa(e&* 3* Guarding is mostimportant as other methods are notalways possible. Eepending upon thedangerous part, its siHe, position,speed etc., a guard should beselected. "enerally the parts to beguarded fall within three categories 8+. The prime mover.). Transmission parts from the prime

mover to the machine and thetransmission parts in the machineitself. 0t is desirable to minimisethem and enclose completely.

. Sa(e&* 3* P%"i&i%n %r 6%ca&i%n8 0t isa guarding as a result of the physicalinaccessibility of a particular haHardunder normal operating conditions oruse. ords I$afe by locationJ or I$afeby positionJ are used to denote safetyby distance.

The words ?"a(e 3* $%"i&i%n@are used by $ection#)+ of the9actories ct. 0t means the situation2out of reach3 or position in such away that normally it is not possible totouch the dangerous parts. Kowever

intentional contact should beprevented. Moving feed opening canbe made safe by position if gravity orremote feeding device is applied. But,then, it is a type of indirect guarding. distance of ).' m or (’#'J isconsidered safe by position.

1Ing%ing 8in-running9 Ni$"8 haHardarea created by two or moremechanical components rotating inopposite directions in the same planeand in close con1unction or interaction

e.g. calendar rolls, inrunning rolls of textile or paper machines.

11Sa(e&* 3* C%n"&ruc&i%n 8 0tindicates parts so constructed as tocause no haHard, viH. shaft, slidingand link mechanism so located or withslow speed that their contact is notdangerous. !ui/&-in-"a(e&*- is thesimilar word for designing andconstructing new machinery in such away to make the dangerous parts safe

by deep housing or position etc.

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5) E/i#ina&i%n %( HaBard '

KaHards from machinery aregenerally of following types 8

-rushing, shearing, cutting orsevering, entanglement, drawing#in ortrapping, impact, stabbing or puncture,

friction or abrasion, e1ection of materialfrom the machine, contact with movingpart, hot surface or sharp edge, free fallof any material, tool or equipment andhigh pressure uid e1ection.

The 3a"ic "&e$" to preventaccidents are 8

+. :liminate the haHard from themachine, method, material, structureetc.

). -ontrol the haHard by enclosing orguarding it at its source.. Train personnel to know that haHard

and to follow the safe 1ob method toavoid it and

;. Gse personnel protective equipmentnecessary. Thus machine guarding is one of the

basic step to eliminate haHard. ctuallythe machine should be so designed andconstructed that all safety points areincorporated by built#in safety principle

and need of extra guards should beminimum. #achine "a(e&* chec/i"&given by the %$-, G$ is worthmentioning. 0t suggests8

+. Eesign the machine so that it isimpossible for an operator to get atthe point of operation or any otherhaHard point while the machine isworking.

). Eesign the machine so that cornersand edges are rounded.

. 5ocate machine controls so that theoperator will not be in the vicinity of the point of operation while actuatingthe controls.

;. /lace the control so that the operatorwill not have to reach too far or movehis body oF balance in order tooperate the machine.

&. Build power transmission and drivemechanisms as integral parts of themachine.

'. Build overload devices into themachine.

?. Eesign the machine for single#pointlubrication.

(. Eesign mechanical, instead of manualholding devices.

=. Eesign a mechanical device for

feeding and e1ecting parts so as toeliminate the use of hands for suchoperations.

+*. Minimise motor drift#time.++. /rovide fail#safe interlocks so that the

machine cannot be started when it isbeing loaded or unloaded or beingworked on.

+). /rovide a grounding system for allelectrical equipment.

+. /rovide standard access platform andladders for inspection andmaintenance of equipment.

+;. Eesign component parts of equipment for easy and safe removaland replacement to facilitatemaintenance.

+&. >educe sources of excessive noise,vibration, heat etc.

$uch 3ui/&-in-care in constructionprinciples of a machine or equipmentshould also ensure that it will cause no

harm to the environment, no discomfortto the operator, no operationalcontingencies, no contact withoverheated or chilled surfaces, noelectrical accident and no access to thedanger Hone.

$ee also /art &.) for built#in safetydevices.

55 Gr%u$" %( Danger%u"Par&"'

551 Acc%rding &% M%&i%n" '

Eangerous parts to be guardedaccording to their motions are generallyclassi7ed as follows 8

Gr%u$-1 R%&ar* M%&i%n" 8 2+3>otating parts alone viH. shafts, coupling,spindles, pro1ections on moving parts, y#wheel, saw, gear, knife, cutting tool etc.2)3 0n#running nips subdivided as 2a3Between parts rotating in opposite

direction # gears, rolls etc. 2b3 Between

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rotating and tangential moving parts #conveyors, belt drives, rack and pinionetc. 2c3 Between rotating and 7xed parts #grinding wheel, paper machine felt or roll,drums, cylinders, worms, spirals etc.

Gr%u$-) Reci$r%ca&ing S/idingM%&i%n" 8 2+3 >eciprocating sliding

motions and 7xed parts 2a3 pproach type# danger of crushing viH. slides 2rams3 onpower presses and forging hammers,pistons, cross rod of a steam engine andriveting machines 2b3 /assing types #danger of shearing, viH. planningmachine, shaper, spot welder clamping7xtures, guillotine and the shear, powerpress etc. 2)3 $ingle sliding motion #abrasive or sharp nature of ob1ects suchas saws or crocodile clips on belts.

Gr%u$-5 R%&a&ingS/idingM%&i%n 8 cam gear having sliding andturning movement etc. falls within thisgroup.

Gr%u$-4 O"ci//a&ing M%&i%n" 8 Trapping points between two movingparts or between a moving part and a7xed ob1ect viH. a pendulum, crankshaft,closing platens etc.

55) Acc%rding &% HA He$3urn

)& groups of in&rin"ica//*danger%u" $ar&" %( #achiner* asclassi7ed by K.. Kepburn are as follows 8

8a9 Sing/e Re.%/.ing Uni&" - Ri" %(en&ang/e#en&

+. >evolving open arm pulleys andother discontinuous rotating parts# 9an blades, spur gear wheels etc.

). >evolving worms or spirals incasing # Meat mincers, rubberextruders, spiral conveyors.

. /ro1ections on revolving parts #Ley heads, set screws, cotter pins,complying belts etc.

;. >evolving shafts, spindles,mandrels and bars # drills,reamers, boring bar, stock bar,milling etc.

839 Sing/e Re.%/.ing Uni&" - Ri" %( cu&&ing %r a3rading

&. >evolving high speed cages incasings # Kydro#extractors,centrifuge.

'. >evolving or oscillating mixerarms in casings # Eough mixture,rubber solution mixture.

?. >evolving drums and cylinders #

uncased # >umbles, shakingbarrels, rag digesters etc.

(. >evolving cutting tools # -ircularsaws, milling cutters, shears,routers, chain mortisers.

=. brasive wheels # "rinding wheelsetc.

8c9 In-running Par&" - Ri" %( ni$$ingand &earing

+*. 0n running nips of the belt andpulley type # /ulley # belt, chainand sprocket gear, conveyor beltetc.

++. >evolving beaters, spikedcylinders and drums # $cutchers,cotton opener, laundry washers.

+). 0n running nips between pairs of revolving parts # "ear wheels,friction wheels, calendar bowls,mangle rolls etc.

+. %ips between gears and rack

strips.

8d9 Reci$r%ca&ing T%%/" %r Par&" -Ri" %( cu&&ing %r cru"hing

+;. Moving balance weights and deadweights # Kydraulic accumulators,balance weight on slottingmachine etc.

+&. >eciprocating knives and saws #"uillotines for metal, rubber andpaper cutting, trimmers,

perforators etc.+'. %ips between reciprocating and

7xed parts other than tools anddies # $liding table and 7xture,shaping machine and 7xture.

+?. -losing nips between platenmotions # 5etter press platenprinting machine, power presses.

+(. >eciprocating tools and dies #/ower presses, drop stamps, relief stamps, bending press, revolution

press.

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+=. %ips between revolving controlhandles and 7xed part # Traversegear handles of lathes, millingmachine etc.

)*. %ips between revolving wheels orcylinders in pans or on tables #$and mixtures, edge runners,

crushing mill, mortar mill etc.)+. %ips between 7xed parts and

unidirectional moving parts #Buckets or hoppers or conveyorsagainst tipping#bars etc.

)). %ips between connecting rods orlinks and rotating wheels, cranksor disc # 9lat bed printing machine,

1acquard loom, automatic looms.). /awl and notched wheel devices

for intermittent feed motions #/laner tool feed motion, powerpress dial feed table etc.

8e9 Running Edge" - Ri" %( cu&&ing

);. -utting edges of endless bandcutting machines # Band saws,band knives.

)&. /ro1ecting belt fasteners and fastrunning belts # Bolt and nutfasteners, wire pin fasteners,centrifuge belt etc.

54 Re+ui"i&e Charac&eri"&ic"8De"ign $rinci$/e"9 %(

Guard"'

Twelve characteristics, designprinciples, speci7cations, basicrequirements or good guarding practicefor machine guarding are8

+. ith its primary purpose of protection,

it should also facilitate the work i.e. itshould be convenient, reliable and nothampering the work or rate of production.

). 0t should fully satisfy the legalprovisions and 0$ prescribed i.e. itshould conform the standards, be acomplete guard and not incomplete orgiving any access to the part to beprotected. 0t should be as close aspossible.

. 0t should be suitable and eFective tothe 1ob and the machine. 0t should notweaken the machine.

;. 0t should allow for oiling, inspection,ad1ustment and repair. 0f it requiresopening for this purpose, it should beeasily and quickly replaceable.

&. 0t should withstand wear, shock,vibration and long use with minimummaintenance. 0f it requires frequentopening and closing, this factorbecomes more important.

'. 0t should be of proper material andconstruction. 0t should be well 7tted.9ire and corrosion resistant material ispreferable.

?. 0t should be free from self#haHard suchas sharp or rough edges, nails,splinters, more opening, noise,vibration etc.

(. 0f visual watch of operation isnecessary, it should be transparentand yet durable.

=. 0f dusting is possible as in case of machining of wood, rubber, brass, castiron etc., apart from the guard, dustsuction device should also be 7tted asa special guarding.

+*. 0t should be fail#safe i.e. if it fails orbreaks it should stop the machine or at

least it should give warning 2alarm3 tostop the machine.

++. 0t should be interlocking type i.e. themachine will not start till it is notclosed and will stop soon if it isopened.

+). 0t should ful7l special requirementdepending upon its purpose viH.distance guard should providesu!cient protective distance, tripguard must immediately trip themachine etc.

0t may be di!cult to ful7l all theserequirements but it is desirable thatsafety engineers must design guards bykeeping above points in mind. 0f it is notpossible to provide guard withoutinterfering with production, safety shouldbe preceded over production. $imilarlywhen complete protection is not possibleincomplete 2maximum possible3protection should be preferred to no

protection.

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4 ERGONOMICS OFMACHINE GUARDING

41 Meaning %( Erg%n%#ic" '

s explained by .T. $ingleton in 05<

:ncyclopaedia, literal meaning of @ergonomics’ is the study, measurementand organisation of work. 0t is concernedwith making purposeful human activitiesmore eFective. The focus of study is theperson interacting with the engineeringenvironment. The designer shouldconsider complexity arising from humannature and his limitations. To considerhuman factors, it studies anatomy,anthropometry, biomechanics andpsychology as useful sciences. To

consider design aspect of work, systems,workspace, environment, interface andwork situation, it studies technology. Thusan ergonomist is expected to take anover#all view and identify the key designaspects for particular people engaged inparticular tasks.

s explained by L. Logi, a >egionaldvisor to 05


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design engineers, work study engineers,architects, illuminating engineers andothers. 0n G$ the terms Hu#anEngineering and Hu#an Fac&%r"Engineering are used to cover thesame 7eld. Biomechanics and:ngineering /sychology are other

expressions used.$ee /art +* of -hapter#); for further

details.

4) Ai#" %( Erg%n%#ic" '

0ts aims are 8

+. To facilitate whatever a person wishesto do and to ensure that he does itcomfortably and e!ciently. :!ciency

includes eFective work withoutdetrimental health eFects andminimisation of risk to the operatorand others.

). The work, working conditions, plantand infrastructure should be sodesigned that they are best 7tting tothe workers. /urpose is not to 7t aworker to any awkward, unsafe,unhealthy or uncomfortable work. Butthe purpose is to design or providework and working conditions

comfortable to the workers.. To minimise the possibility of human

error or mistake. To ensure industrialactivities with minimal use of energyand materials and without wasteresulting from mistakes.

;. To develop knowledge and techniquesby the combined use of manyexpertise and systems approach.

&. To solve human problems of workperformance by considering humanfactors in design of machines and workand safe 1ob methods which areexplained in the following part.

45 Hu#an Fac&%r" in De"ign%( Machine and 0%r'

Technology has changed the people’sways of working but the people are notchanged much. Many times the people donot adapt physically and mentally, atendency of modern work methods. Thisgenerates negative reactions which also

indicate human factors to be consideredby the ergonomists while designing workand machines. $ome such factors are 8

+. 0ncreased stress.). Gninterested work.. :rrors and accidents.

;. ork related diseases.&. wkward body position causing

di!culty.'. >epetitive tasks producing boredom

and tiredness.?. -onfusing signals causing human

errors in hurry.(. Bent or awkward posture while

handling heavy materials and causingback pain.

=. /erceptual limitation.+*. $hort term memory.++. 0ncompatibility in man#machine

relationship.+). >isk or chance taking.+. /osition or location not suitable to a

worker such as unsuitable work height,seat, layout of control and displays.

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$uch methods and their relatedaspects are described in detail in -hapter#+= D ). -onstant improvement in 1obmethods is important. 0t requires 7vesteps8

+. Break down the 1ob.

). uestion every detail of the 1ob.. Eevelop a new 1ob method.;. pply the method. The procedure

includes 82+3 :liminating certain 1ob details

by using alternative methods.2)3 -ombining some details to

reduce haHards andunnecessary transportation,handling, delay etc.

23 >earranging certain detailsinto better sequence to reducehaHards, handling, delay etc.

2;3 $implifying certain details soas to make the work safer andeasier.

&. Take review or feedback and makechange if necessary.

44) Man-Machine Char& '

Machines being costly, it is desirableto run them e!ciently and economically.

The man#machine chart 2"antt -hart3 is auseful device in this direction to identifyand eliminate losses of capacity. Eurationof elements of operation of man andmachine are recorded in their sequence,placed side by side and compared. Thetime of operations, transports and waitsoccurring in the operator’s cycle and thetime of start up, shut down, machiningtime and idle time in the machine cycleare ruled oF by proportionate symbolcolumns. The length of symbol columnsrepresenting a wait period of man andmachine are coloured in red to distinguishit from their productive periods. /er piecemachine operating time, machine idletime, man#hours and man delay hours areconcluded.

pplication of the chart for groupwork is estimated by 7rst assuming thetheoretical crew necessary to run themachine at the required output and thentrying to organise the same number of

practical people to do the 1ob. generalrule @To decide 7rst what has to be done

and then how to 7t people to do the workand not vice versa’ is followed. Thestandard time found by workmeasurement are divided by a correctionfactor +.)& to consider levelling andcompensating rest allowance. The chartsare prepared for the purpose of analysing

the present method of performance of theoperation and improving on it. The stepsof 1ob improvement method 1ustdescribed in previous part are utilised forsuch improvement.

: TPES AND SE6ECTIONOF GUARDS

ays and means for machine safetycan be classi7ed as under 8

Machine

$afety

$afety by construction

$afety by position

Built#in safety

$afety by machine controls

$afety by precautions andmaintenance$afety by "uarding prime mover,transmission parts and points ofoperation

9ixed guards or fencing

+ Total enclosure) ith limited access ith ad1ustable access; Eistance or barrier guard

0nterlock guards

+ Mechanical interlocking) :lectrical interlocking Trip guard; -ontrol guard

utomatic guards

+ Mechanical type#sweep,knock or push away guard

) /hoto#electric cell type

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$afety devices

+ Two#hand control)


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9ollowing formula was suggested bythe -hief 0nspector of 9actories, GL in his>eport of +=?& #

N O P '

here N O guard opening or gap in mm

andQ O distance from danger in mm

Fied &%&a/ enc/%"ure" are used tocover prime mover and transmissionparts such as headstock gearing, belts,pulleys etc.

Fied /i#i&ed acce"" guard"provide minimum opening in the guard toinsert and remove the 1ob 2material3. 0tdisallows 7nger to trap. 0f the material is

1ammed, it requires special tool andopening and re7tting of the guard. Theyare used on power presses.

Fied adu"&a3/e acce"" guard"provide opening through or around guardto accommodate materials of diFerentsiHes. "uards on band saws, 1igsaws,milling cutter etc. can be raised orlowered as per the thickness to cut. $uchguard known as ?cr%n guard@ oncircular saw or drill tool ad1ustsautomatically as the 1ob or tool moves. 0ts

disadvantage is that it gives littleprotection when thin material isprocessed.

Fencing di"&ance %r 3arrierguard" make it physically di!cult forpeople to gain access. Ni$ guard to in#running rolls and 7xed railing or fencing toengines, motors, planning or shapingmachine are of this type.

In&er/%c guard" make certain thatthe machine cannot be started until theguard screen is in close position and

conversely the guard cannot be removeduntil the working parts have beenstopped. Mechanica/ e/ec&rica/h*drau/ic %r $neu#a&ic systems areused to actuate the guard. Mechanicalinterlocking of a power press, cardmachine and electrical 2limit or microswitches3 interlocking of headstockcovers of many textile machinery aresuch examples. Many times theinterlocking is by#passed or made

ineFective which is not good. This is itsdisadvantage. -orrect working condition

of limit switch is most important. 5imit ormicro switches are used but they are notfully safe.

Tri$ guard" are actuated by anyoneapproaching beyond the safe position andoperate a stop or reverse control viH. triprod along the conveyor belt, hand trip on

a rubber mill, electronic eye, lift door,platen printing guard, calendars or doughbrakes etc.

C%n&r%/ guard" activate themachine when the guard is closed andopening the guard stops it. Thus theguard acts as on#oF switch. $uch guard isuseful for the machine which can bebrought to rest very rapidly. e.g. powerpress.

Au&%#a&ic guard" will ensure thatthe operator is prevented from cominginto contact with dangerous parts whenthe machine is set in motion accidentally.

This guard is itself actuated by themovement of the dangerous part. 0t canonly be used where su!cient time isavailable to remove the body part fromthe danger Hone viH. sweep, knock orpush away guard on a power press orplaten printing machine. Because of itsstroke haHard it is hardly used. Ph%&%-e/ec&ric guard 8de.ice9 operates to

stop the dangerous part when the lightcurtain is interrupted. This type of guardis used on shearing or cutting machine.

Sa(e&* 3* Machine C%n&r%/"' Theseshould be diFerentiated from incidentalsafety devices which are external andwork like guard for protection. But themachine itself has many controls as itsinherent or attached elements. ll levels,buttons, brakes, pedals, switches,handles, wheels, auto controls etc., aremachine controls to run the machine

safely and e!ciently. $uch controls shouldbe clearly identi7ed, marked and suitablyplaced for ease of operation. Theirpurpose and direction of movement shallbe marked. :ach stop button shouldaccompany start button and they shouldbe sunk to prevent accidental pressing.

5evers should be capable of beinglocked in position. 5evers, handles, orwheels should operate to give naturallyanticipated direction 2e.g. clockwise close

and anticlockwise open, up forward, downreverse etc.3, controls should be at rest

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when power is applied and they shouldnot restart the machine after resetting."uard or control should be of fail#safetype i.e. the machine will stop if thecontrol fails. hen there are morecontrols nearly placed or on one boardclear instruction of their use must be

marked to prevent their false operation.5ocks or keys on some controls arerequired to prevent their undesiredoperation by mistake.

Sa(e&* 3* Precau&i%n" andMain&enance' bove paras highlight theneed of utmost precautions in safeoperation and maintenance of all safetyguards, devices and controls. man hasmade them and a man can make themineFective or misuse. Therefore allprecautionary operating measures arenecessary in addition to the machineguarding. The machine operators shouldbe made aware of haHards in their works,location and operation of machinecontrols, regular checking of guards,warning and training not to make theguards ineFective, repairs, ad1ustmentetc., by specially trained person, need of wearing tight#7tting clothing andprotective equipment necessary andusing right tools and equipment.

Cri&eria (%r Guard Se/ec&i%n '$election of a guard depends on followingfactors 8

+. 0ts physical dimensions, weight etc.). Method of drive and power

requirements.. 5imitations of speed, pressure,

temperature etc.;. Materials being processed or handled.&. ccess requirements especially for

setting, ad1ustments and maintenance.

'. :nvironmental factors such as noise,vibration, dust, fumes and

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circumstances, after machine installationcan render the guarding less eFective.

Therefore necessary correction in safetydevice should be made if such change isrequired.

:5 Inciden&a/ Sa(e&*

De.ice" and Me&h%d" '

$ome incidental safety devices2indirect guards3 equally useful asmachine guarding are as below 8

T% Hand c%n&r%/ 8 Two pushbuttons are required to be operatedsimultaneously thus keeping theoperator’s hands engaged and away fromthe dangerous parts. $uch device doesnot protect another approaching person,

is prone to faults and cause di!culties onelectrically, hydraulically or pneumaticallypowered machines. Therefore such devicealone is not advisable. 0t is used ongarment presses etc. here twooperators have to work simultaneously,four push buttons are required to keeptheir hands away from dangerous parts.

O$&ica/ Sen"%r 8 This uses photo#electric cell and a light.


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s) 9ixed guard on

9ency rolls $creen under garnet

& "illBoxes

+ "uard on feed end

) %ip guards on rolls

2Eistances aresuggested3

' $liverC>ibbon,lappers

"uard on calendardrums and lap spool

? $peed9rames

0nterlock doors onhead stock gearing

( $pinningMules

"uard on carriagewheels

= $lashersCEryers

+ %ip guards on in#running rolls

) -ontrol levers within+.? mt from the oor

$topC$tart pushbuttonsconvenientlylocated

+* 5ooms + $huttle guard

) Beam weight fallpreventer

++ Aalve onLiers

+ 5ocking device onvalve

Tanks Dcontainers

) $hut oF valves tostop overowCsplash

+) $hearingMachines

"uard on revolvingblades 2opening lessthan + cm3

+ Bleaching range

%ip guard on rolls

+; MerceriHing range

+ $top button at eachend of the machine

) "uard on framebetween chain D

clip opener %ip guard on

mangle rolls Dwashers

+& -entri#fugalextractors

+ 0nterlock guard onbasket

) Brake to stop basket

+' Mangles,ashersetc.

%ip guards onin#running rolls

+? $anforiHi + %ip guards on

ng and/almerMachines

in#running rolls) $ide guards on

in#running rolls Trip rod, cable or

wire near cylinders.Keight not morethan +.? mt from

working platform+( >ope

washers+ $plash guards) Trip rod near

washers+= ashers

,tumblersorshakers

+ 0nterlock door oncylinder

) Kolding open devicefor cylinder doors

)* /rintingmachine

+ %ip guard on rolls) 9ixed guards on

rollers, gears Dwheel)+ -alendar

s%ip guard on rolls

)) >otarystaplecutter

"uard on cuttingHone

) /latingmachine

"uard on spacebetween knife andcard bar

); Kandbalingmachine

Kandle stop guardat right angle to theframe

)& 9latworkironer

Trip barCguard on7rst pressure 2feed3rolls to stop themachine

%ote 8 $ee -hapter )+ also.

Ginning 0%%d%ring and Ru33er#c '

The machine guarding uCr &;, $ch. ),

and ; is summarised below in Table+;.8

Ta3/e 145 ' "uarding of "inning, woodworking and rubber machines.

Machine Danger%u" Par&"

T*$e" %( Guard"

I C%&&%n Ginning 8Sch )9 '

5ine

shaft torun the

5ine shaft all or fencing

with lockingdoors

15


16/20

gins

II 0%%d%ring Machiner* 8Sch 59 '

+ -ircular$aws

The saw riving knife of prescribeddimensions andsetting.d1ustable top

guards, twometal platesguard, pushsticks

) Band$aws

Top andbottompulleysand theblade

9ixed guards

/lanningmachine

-uttingslot, freed

roller

Bridge guard,e!cient guard

; Aertical$pindleMouldingmachine

-utter,the woodbeingmoulded

$uitable guard, 1ig or holder

& -hainmortisingmCc

-hain andcutters

$uitable guard

III Ru33er Mi//" 8Sch 49 '

+ >ubbermill

0nrunningrolls

Keight morethan ='.& cm,a distanceguard, feedhopper, tripguard 2rod3within +.? mheight

) -alendarmCc

0nrunningrolls

Trip guardwithin +.? mheight, tightwire cableconnected withit

%ote 8 $ee -hapter ) for speci7cindustries.

Cen&ri(uga/ Machine" 8Ru/e :4 Sch :9'

A$$/ica3i/i&* ' This schedule applies tocentrifugal extractors, separators anddryers but does not apply to similarmachines of sugar manufacturingindustry.Re+uire#en&" '

+. ll parts of the machine shall be of good design, construction andadequate strength, properlymaintained and examined thoroughlyby a competent person at regularintervals.

). 5id on cage housing, revolving drum or

basket shall be strong and interlocked.. :Fective braking arrangement is

required to stop the drumCbasket afterthe power is cut oF.

;.


17/20

factory, name of the occupier,identi7cation number or mark to identifythe press or safety device, date of the7rst use, date of each examination andparticulars of defects found and stepstaken to remove them.Di"c/%"ure %( De(ec&" J Mea"ure" '

By any test or examination, when anydefect is disclosed by a competentperson, the defective press or safetydevice shall not be used till it isremedied.

The competent person shall informthe occupier and the 0nspector 2within +;days3 in writing, the defect to be recti7ed.

The defect shall be remedied and itsrecord shall be kept stating the measuresand the date of remedy.In"$ec&i%n J Te"& %( Sa(e&* De.ice 'fter setting, resetting or ad1ustment of any tool, every safety device of the pressshall be inspected and tested by theauthorised 2appointed3 person and thenonly the press shall be used.

Eefect disclosed in a safety device asabove, shall be noti7ed to the managerforthwith.Iden&i,ca&i%n ' :very power press andevery safety device on it shall bedistinctively and plainly marked.

Training J In"&ruc&i%n &% O$era&%r" ' The operators shall be trained andinstructed in the safe method of workbefore starting work on any power press.

Shear" S/i&&er" and Gui//%&ineMachine" 8Ru/e :4 Sch ule &?, prescribes thefollowing machines as @dangerous’ and noyoung person 2below the age of +(3 shallwork on it #

+. Koists, lifts, lifting machines, chains,ropes, lifting tackles and revolving

machinery 2$ections # )(, )=, *3.). /ower presses other than hydraulicpresses.. Milling machines.;. "uillotine machines.&. -ircular $aws.'. /laten printing machines.


18/20

; MATERIA6S FOR GUARDCONSTRUCTION

"enerally metal is preferred formachine guard construction. Bar, pipeand rod are used for structural frame.9iller material may be solid, perforated orexpanded sheet metal or wire mesh.here transparency is necessary plasticor glass material can be used. $afetyglass and plastics are also used to protectagainst ying particles and chips.

ood guards have limited applicationdue to their poor strength and durability,ammability and high maintenance cost.

luminium guards are preferredwhere rusting or damage to tools ormachinery are considerable.

/lastic guards are used whereinspection of the moving parts isnecessary. $afety glass and plastic usedwhere chips or other ying particles arelikely to mar the surface should beprotected by replaceable cover glasses.

hatever material may be selectedfor guard, it must be sound and durableto withstand impacts, vibrations andother forces.

oor guard becomes necessary inaddition to the enclosure guard to preventvehicles from straying into the haHardarea such as guards on aisles or roadside.

Ma&eria/" &% reduce n%i"e 8

"uards are provided near the point of operation and near the transmission of power i.e. near the source of noise."uards are sub1ected to vibrations also.

Therefore they can make noise. Thereforethe guards should be designed as a

barrier against noise in addition to abarrier against in1ury. common way toabsorb sound is to cover the guard framewith sound absorbing material. gaskettype material can be used around theedges to avoid metal to metal contactand noise generation due to it. The guardshould be secured with shockproof 7ttings. $uch type of material and proper7tting will reduce the conducted noise.

This will be an extra bene7t of the guard.

%on#metallic 2e.g. plastic3 machineparts 2e.g. gears3 and guards can alsoreduce the noise.

ell maintenance and lubrication canalso reduce the noise.

< MAINTENANCE AND

REPAIRS OF GUARDS

$ection )+ of the 9actories ct statesthat the guards shall be c%n"&an&/*#ain&ained and e$& in $%"i&i%n. $uchmaintenance is obviously necessarybecause a machine running withoutguards or with open or broken guardspose danger. >egular inspection of guardscan detect the guard removed, damagedor requiring repairs. guard removed for

repair should be 7tted at the earliestpossible and meanwhile temporary guardshould be installed or the machine bestopped. "ood maintenance increases thelife of guards and vice versa. Thesupervisor should pay constant attentionfor this.

guard should be so designed or7tted that it is not to be opened foroilingCgreasing or nearby maintenancework. The parts needing regular serviceshould be located outside the guard. 0f oilCgrease 7ttings are inside the guard, anextension through the guard should beprovided.

utomatic controls for lubrication,ad1ustment or service can be provided bya sophisticated equipment. 0nterlock typeguard ensures that the machine cannotbe operated unless all guards are inposition. $uch planning helpsmaintenance without disturbing guards.

hen a guard cannot be made to

exclude lint, fume, dusting etc., extraventilation should be provided. 5argeguards should have self#closing doors forcleaning. $pace should be provided insurrounding for repair and maintenance.$ome people use red colour for guards toshow dangerous part while some preferthe same colour that of the machine toconsider it as an integral part of themachine.

Guarding during #ain&enance 8Euring maintenance of a machine,

18


19/20

normally a guard is removed andobservation for fault, alignment, repairingor oilingCgreasing is carried out inunguarded condition. $uch condition maykill or in1ure an untrained or unknowingperson. Hero mechanical state 2SM$3 i.e.

all energy sources must be neutralised ormade least eFective before anymaintenance or set#up is to be started.

$ee foregoing /art +.), para @ork onor near machinery in motion’ for statutoryrequirement uCs )) of the 9actories ct.

Eerci"e

1 E$/ain S&a&e Men&i%n %rDi"cu"" '

+. The basic need and importance of machine guarding.

). The (%//%ing &er#" '-2+3 /rime mover 2)3 Machinery 23/ower 2;3 $elf acting machines 2&3>evolving machinery 2'3 SM$ 2?3/oint of operation 2(3 $afety by

position 2=3 Built in care 2+*3 Tripguard 2++3 9eed tools 2+)3 Twohands control 2+3 -rown guard

. The contents of a @Machine $afetychecklist’ as given by %$-, G$.

;. The groups of dangerous partsaccording to motions ccordingto K. . Kepburn.

&. -haracteristics of a machine guard.'. /rinciples of ergonomics for

machine guarding.?. Kuman factors in design of machine

and work.(. -lassi7cation of machine guards.=. Types of 7xed guards Types of

0nterlock guards.+*. EiFerent types of 0ncidental safety

devices.++. Machine guarding for -entrifugal

machines /ower presses.+). Machine guarding for shears and

slitters.+. Methods of Maintenance and

>epairs of guards.+;. "eneral principles of good guarding

practice.+&. The eFects and acceptability of

machine guards.+'. Main mechanical haHards in

engineering operations.+?. The restrictions of employment of

workers on speci7ed machines andconditions under which therestrictions are relaxed.

+(. Methods of eliminating, potentialhaHards from the 1ob.

+=. hat type of guard would yousuggest for 2+3 Eisintegratingmachine 2)3 >ubber mill rollers 23


20/20

+'. Materials for guard construction orMaterials to reduce noise.

+?. "uarding during maintenance.+(. uality of guards.+=. Eesign principles of machine

guards.)*. $afety points while operating a

grinding machine -entrifugemachine.

)+. Machine guarding for rubber millindustry.

)). dvantages of built in guards.). $afety points for working on a

grinding machine.);. Types of point of operation guards.)&. 9ormula for maximum safe opening

in a point of operation guard.

5 E$/ain &he Di2eren& 3e&een8gi.e ea#$/e"9

+. Machinery D Transmissionmachinery.

). /ower D /rime mover.. "uarding D 9encing.;. Built in guard D $afety devices.&. $afety by construction D $afety by

position.

'. 0nterlock guards and utomaticguards.

?. Mechanical interlocking and:lectrical interlocking.

(. $afety by Machine controls and0ncidental $afety devices.

=. Built in safety devices and

0ncidental safety devices.+*. -ontrol guard and 0nterlock guard.++. /ush buttons and push away guard.+). -ircular saw and $litting cutter.+. Kome made guards and "uards

made by manufacturer.

4 C%##en& %n &he F%//%inge$/aining he&her i& i" &rue %rn%& -

+. I$afe by fencingJ and Isafe bypositionJ is one and the same.

). 9it work to workers and not workersto the work.

. ccidents take place due to badmaintenance of machines.

;. Belt hangers are required onoverhead shafts.

Re(erence and Rec%##ended Reading '

+. The 9actories ct +=;( and the "u1arat9actories >ules +='.

). 0ndian $tandards on Machine "uarding.. 05< :ncyclopaedia of

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14. CHAPTER - 14 Marhcine Guarding

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