5 Process Parameters

8/19/2019 5 Process Parameters

1/22

Application of penetrants:

•Workpieces should be thoroughly anduniformly coated with penetrant by

•owing

•brushing

•swabbing

•

dipping•spraying.

•

Small workpieces requiring completesurface inspection are usually placed in abasket and dipped in the penetrant. Largerworkpieces are usually brushed or sprayed.


2/22

Application of Penetrantcontd…

• lectrostatic spray application is also!ery e"ecti!e and economical. Afterthe workpiece has been coated witha light #lm of penetrant$ it should bepositioned so that it can drain and so

that e%cess penetrant cannot collectin pools. Workpieces should not besubmerged during the entirepenetration dwell time.

• &eating the workpiece is also not

necessary or recommended$because certain disad!antages canoccur$ such as !olatili'ation of thepenetrant$ di(culty in washing$ anda decrease in uorescence.


3/22

Dwell Time

•After the penetrant has been applied tothe workpiece surface$ it should beallowed to remain long enough forcomplete penetration into the aws.

•)well time will !ary$ depending mainlyon the si'e of the defects sought$cleanliness of the workpiece$ andsensiti!ity and !iscosity of the penetrant.

•*n most cases$ howe!er$ a minimum of+, min and a ma%imum of -, min isadequate for both uorescent and

!isiblepenetrant types.


4/22


5/22

Prerinse

•When using method ) 0hydrophilic1$ a coarsewater spray prerinse is needed to assist inpenetrant remo!al and to reducecontamination of the emulsi#er.

•A coarse water spray is recommended$ using

a pressure of 234 to -54 kPa. 6he prerinsewater temperature should be +, to 5, 78.

• 6he prerinse time should be kept to a

minimum 0that is$ -, to 9, s1 because thepurpose is to remo!e e%cess penetrant sothat the emulsi#er does not becomecontaminated quickly.


6/22

Emulsier Application

•*t is !ery important that all surfaces of theworkpiece be coated with the emulsi#er at the

same time.•Small workpieces are dipped indi!idually or inbatches in baskets or on racks$ whiche!er is themost con!enient.

•:or large workpieces$ methods must be de!isedto achie!e the fastest possible co!erage; twomethods often used are spraying or immersing.

•Locali'ed emulsi#cation of large workpieces canbe achie!ed by spraying.

• 6he temperature of the emulsi#er is note%tremely critical$ but a range of 2, to -, 78 03,to 9, 7:1 is referred.


7/22

Emulsication Time

• emulsi#cation time depends mainly on the type ofemulsi#er employed$ its concentration$ and on the

surface condition of the workpieces.•/ecommendations by the manufacturer of theemulsi#er can ser!e as guidelines$ but the optimumtime for a speci#c workpiece must be established by

e%perimentation.• 6he surface #nish$ si'e$ and composition of theworkpiece will determine more precisely the choice ofemulsi#er and emulsi#cation time.

•mulsi#cation time ranges from appro%imately -, sto - min and is directly related to the concentration ofthe emulsi#er.

•*f emulsi#cation time is e%cessi!e$ penetrant will be

remo!ed from the aws$ making detection impossible.


8/22

Rinsing• /inse time should be determined

e%perimentally for speci#c workpieces; it

usually !aries from +, s to 2 min.• :or spray rinsing$ water pressure should be

constant. A pressure of about 234 kPa 05, psi1

is desirable; too much pressure may remo!epenetrants from the aws.

• A coarse water spray is recommended and canbe assisted with air.

• Water temperature should be maintained at arelati!ely constant le!el.


9/22

/insing contd…..

• )rying is best done in a recirculating hotairdrier that is thermostatically controlled. 6he

temperature in the drier is normally between =4and 94 78 0+4, and 2,, 7:1.

• 6he temperature of the workpieces should not

be permitted to e%ceed 3, 78 0+=, 7:1.• Workpieces should not remain in the drier anylonger than necessary; drying is normallyaccomplished within a few minutes. %cessi!e

drying at high temperatures can impair thesensiti!ity of the inspection. >ecause dryingtime will !ary$ the e%act time should bedetermined e%perimentally for each type ofworkpiece.


10/22

)e!eloping ?)epends on the type of de!eloperused.

Dry-developer powder (form A)

• *t is applied after the workpiece has beendried and can be applied in a !ariety of ways.

• 6he most common is dusting or spraying.

• lectrostatic spray application is also !ery e"ecti!e.

• *n some cases$ application by immersing the workpieceinto the dry powder de!eloper is permissible.

• :or simple applications$ especially when only a portion of

the surface of a large part is being inspected$ applying

with a soft brush is often adequate.• %cess de!eloper can be remo!ed from the

workpiece by a gentle air blast 0+5, kPa$ or 2,psi$ ma%imum1 or by shaking or gentle

tapping.


11/22

ater-solu!le developer (form ")

• *t is applied @ust after the #nal wash andimmediately prior to drying by dip$ owon$ or spray techniques.

• o agitation of the de!eloper bath isrequired.

• /emo!al of the de!eloper coating fromthe surface of the workpiece is required

and easily accomplished because the

dried de!eloper coating is water solubleand therefore completely remo!able by awater rinse.


12/22

ater-suspendi!le developer (form #)

• *t is applied @ust after the #nal wash andimmediately before drying.

• )ip$ owon$ and spray are common methods ofapplication.

• 8are must be taken to agitate the de!eloper

thoroughly so that all particles are insuspension; otherwise$ control of theconcentration of the applied coating isimpossible.

• /emo!al of the watersuspendible de!elopercan best be achie!ed by water spray rinsing.

• *f allowed to remain inde#nitely on theworkpiece$ the de!eloper can become di(cultto remo!e.


13/22

$olvent-suspendi!le nona%ueous developer(form D)

• *t is always applied after drying by spraying$

either with aerosol containers or bycon!entional or electrostatic methods.

• Proper spraying produces a thin$ uniform layerthat is !ery sensiti!e in producing eitheruorescent or red !isible indications.

• 6he !olatility of the sol!ent makes it impracticalto use in open tanks. ot only would there be

sol!ent loss$ reducing the e"ecti!eness of thede!eloper$ but there would also be a ha'ardous!apor condition.

• )ipping$ pouring$ and brushing are not suitable

for applying sol!entsuspendible de!eloper.


14/22

Performance check of materials

• 8hecking the performance of materials onthe daily basis.

•


15/22

&erication of Penetrant $ystemPerformance

$ince penetranttesting involvesmultiple processingsteps' teperformance of tematerials and teprocesses sould !eroutinely ceced

using performanceverication tools'wic include:

– TA* Panels

–

#rac $ensitivityPanels


16/22

• 6his is a stainless steel panel$ ,.,9,Bthick and measuring 5 % = inches.

• :i!e crack centers are e!enly spacedin the chrome plating in order of

magnitude; the largest is readily!isible with low sensiti!itypenetrants$ while the smallest isdi(cult to obser!e e!en with highsensiti!ity materials.

•

Ad@acent to the chrome plate sectionis a grit blasted area of CmediumroughnessB to @udge penetrant washcharacteristics.

• 6he /4 Panel comes in two!ersions. >oth !ersions are

manufactured to PrattWhitney PD 6A< +5=,5, speci#cations. – Ene has a chrome strip$ which has been

lightly grit blasted in order to dull thesurface.

– 6he chrome plate strip of the second!ersion is not grit blasted

Tam panels

li l f i l


17/22

+uality #ontrol of Penetrant Test *aterials

Aluminum Test "locs F 6hey pro!ide a good meansof e!aluating general purpose penetrants. 6heyshould be used for comparisons only and not forabsolute e!aluations. 6hese blocks are nonuniform$ and the depth and width of cracks areuncontrolled. 6he si'e of the blocks may !ary butare about -DG by 2 inches of 2,256- aluminum.

About - inches long. 6he blocks are heated andquenched to produce an o!erall crack pattern. 6heycan be reused by reheating$ quenching$ and carefulcleaning.


18/22

$ensitivity Tests F While there ha!e been no simple%uantitative tests de!eloped for measuringpenetrant sensiti!ity. A simple comparative test isusually ade%uate,

A small sample of the penetrant from the testing areais placed on one side of an aluminum test block$ and asmall sample of new penetrant on the other side. >y!isual obser!ation it is determined if the old penetrant

* i T t P id ti l t t f


19/22

*eniscus Test F Pro!ides a practical test fore!aluating the dye concentration in thinliquid #lms.

6he test utili'es a at glass platen and a con!e% lens.

When a drop of solution is placed between the lens andplaten$ a colorless or nonuorescent spot is formedaround the point of contact.

6he resultant contact angle simply indicates the ability

of a liquid to wet a surface. Te diameter of teremaining spot. of colorless penetrant provides ameasure of lm ticness which can be used tocompare the dye concentration of penetrants.

Prolonged e%posure of a #lm to ultra!iolet light oraccidental contamination by acids or alkalis will a"ectthe dye concentration and therefore change the spotdiameter.

# i "l T t 8 i t f l d i


20/22

#eramic "loc Test / 8onsists of an ungla'ed ceramicdisc which has thousands of micro pores and cracks onits surface.

A pencil mark is made on the block and a small amountof a test penetrant is placed on one side and areference penetrant is applied to the other side. Afterthe correct dwell time$ te two penetrants arecompared in a side-!y-side visual e0amination,

A reduction in the number or apparent !rigtness ofpore indications should be obser!ed when comparinga fresh and old batch of penetrant.

ater #ontent Test F 6he AS6< standard )94describes a test where +,,


21/22

&iscosity Test F A !iscometer is used to measure the!iscosity in centistokes to determine if the penetrant is

within the range recommended by the manufacturer. Atypical standard is AS6< )554.

1luorescent Penetrant 1ade Test F 6his testin!ol!es the use of the aluminum test !locs in a

side-!y-side comparison test, 6he uorescent penetrant is placed on both sides of theblock and processed normally. Ene half of the block isthen e%posed to a standard black light for one hour$

while the other side is co!ered with paper. 6he 2uorescent !rilliance of te two sides iso!served and$ if one side in noticeably less brilliant$the penetrant is discarded.

t !ilit T t 6hi t t l t t


22/22

ater asa!ility Test F 6his test evaluates tee3ciency of te emulsier by comparing two di"erentpercentage blends of penetrant and emulsi#er.

A special steel block is placed at a 34I angle and the twoblends are allowed to ow separately down the block.After a #!eminute waiting period$ te !loc is wasedand e0amined for traces of remaining penetrant.

Developers / Dry Developers are simply visually

inspected to see that they are not lumpy or cakedinstead of u"y and light.

et developers are often checked using aydrometer to assure that the density of the powder in

the !ehicle is within the range recommended by themanufacturer.

1iltered Particle *etod of Penetrant 4nspection /When testing a porous surface with #ltered particles. 6he

increased area created !y a crac will lter. te

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5 Process Parameters

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