Die Penetrant-English

8/18/2019 Die Penetrant-English

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Discontinuities which can be revealed by penetrantinspection:

•opened - clean, without coating, and electroplating,

•hot and cold cracks, fatigue cracks, hardening cracks, pitting,porosity,

•shallow defects cause of fatigue cracks,

•minimum dimensions of detected defects (cracks): 1μmwide, 10 mm depth and 1 mm in length.

•it is possible to detect material discontinuities of semi-fnished and fnished products, with even the mostcomplicated shapes

Liquid Penetrant esting



Discontinuities which can be revealed by penetrant inspection:

Eamples:

Liquid Penetrant esting

a) cold crack

b) hot crackc) grinding crack

d) shrinking crack

e) stress

corrosion crack

f) porosity

g) bubblesh) foam structure

i) shrinkage

porosity



!i"uid #enetrant $esting

• Workpieces tested by liquid penetrant can not

be highly porous (ceramic, wood) and have

high roughness (metals).

• Materials used for testing (solvent, penetrant

or developer) can not react with tested

workpieces (plastic).



!i"uid #enetrant $esting is based on penetration

the liquids %called penetrant& with low sur'acetension, proper viscosity, wettability and lowdensity$he wettability phenomena

a& ( ) *0+ - good wetting

b& and c & ( ) *0+ - poor wetting



!i"uid #enetrant $esting$he capilary rise phenomenon

%a&() *0+ - capillary rise%b&( *0+ - no capillary

depression or rise.%c&( *0+ - capillary depression



!i"uid #enetrant $estingLipophilic and hydrophilic

postemulsifiable penetrants



$here are stages o' thepenetrant inspection

1./ur'ace preparation

- cleaning, drying, oil and rust free

surface (and other contaminantion)




. #enetration

- after cleaning operation penetrant is appliedinto the surface in the form of thin liquid !lm,

- the !lm should remain on the surfacedepends of the penetration time called as adwell time (recomendation of the penetrant

producer, mosty between " to #$min)%




. 2emoval o' ecess penetrant

• e&cess penetrant must be removed from thesurface, removing method depends of the type of

penetrant%• many penetrants easily removed with water'

others require the use of emulsi!ers (lipophilic orhydrophilic) or solventremover%

• removing of e&cessive penetrant is necessary foreective inspection, but overremoval must beavoided (no discontinuities will be revealed)%




3. Development

• developer starts seepage procees ofthe penetrant,

• time of developing depends of the

developing agent used (mostlybetween " to #$min%)




. 4nspection

• after developing process the surface is visually

e&amined for indications o' penetrant which isvisible like a colored stains%

• visible penetrant inspection is performed in whitelight,

• when the 5uorescent penetrant is used,inspection is performed in a dark room underultraviolet light, (penetrant is shinning)%




Advantages of Penetrant Testing

• elative ease of use.

• !an be used on a wide range of material types.

•"arge areas or large volumes of parts#materials can beinspected rapidly and at low cost.

• $arts with comple% geometries are routinely inspected.

• &ndications are produced directly on surface of the partproviding a visual image of the discontinuity.

• &nitial equipment investment is low.

• 'erosol spray cans can make equipment very portable.



Limitations of Penetrant Testing• nly detects surface breaking defects.

• equires relatively smooth nonporous material.

• $recleaning is critical. !ontaminants can mask defects.• equires multiple operations under controlled

conditions.

• !hemical handling precautions necessary (to%icity, fire,waste).

• Metal smearing from machining, grinding and otheroperations inhibits detection. Materials may need to beetched prior to inspection.

• $ost cleaning is necessary to remove chemicals.



6agnetic $esting %6$&6789E$4 #72$4!E 49/#E$4;9

• *ethod of locating sur'ace and subsur'ace discontinuitiesin 'erromagnetic materials%

• +hen the material or part under test is magneti<ed,magnetic discontinuities that lie in a direction generallytransverse to the direction o' the magnetic feld causea leakage !eld to be formed at and above the surface of thepart%

• he discontinuity, is detected by the use of !nely dividedferromagnetic particles applied over the surface, with someof the particles being gathered and held by the leakage !eld%



!imitation 'or 6agnetic #article $esting:• he method can be used only on 'erromagnetic materials,

• or best results, the magnetic !eld must be in a direction that willintercept the principal plane o' the discontinuity' thissometimes requires two or more se"uential inspections with

dierent magnetiations,• Demagneti<ation following inspection is often necessary,

• #ostcleaning to remove remnants o' the magnetic particlesclinging to the surface may sometimes be required after testing anddemagnetiation,

•.&ceedingly large currents are sometimes needed for very large parts,• /are is necessary to avoid local heating and burning of !nished partsor surfaces at the points of electrical contact

• 0lthough magnetic particle indications are easily seen, e&perienceand skill are sometimes needed to 1udge their signi!cance%

6agnetic $esting %6$&



6agnetic $esting %6$&=E22;6789E$4 67$E247!/*etals which conduct magnetic !eld:

• elements: iron,

nickel,

cobalt,

• alloys: cast iron

carbon steel



Ferromagnetic Materials• ' material is considered ferromagnetic if it can be

magnetized. Materials with a significant &ron, nickel or cobalt

content are generally ferromagnetic.

• *erromagnetic materials are made up of many regions in

which the magnetic fields of atoms are aligned. +heseregions are call magnetic domains.

• Magnetic domains point randomly in demagnetied material,

but can be aligned using electrical current or an external

magnetic field to magnetie the material.

-emagnetied Magnetied

/



*agnetic esting (*)irections of the discontinuities



6agnetic $esting %6$&The !ays of magnetization

circular

l o n g i t u d a l



6agnetic $esting %6$&Magnetizing current

• 0oth direct current "dc) and alternating current "ac) are suitable for

magnetiing parts for magnetic particle inspection.

• +he strength, direction, and distribution of magnetic fields aregreatly affected by the type of current used for magnetiation.

• +he important difference with regard to magnetic particle inspection

is that the fields produced by direct current generally penetrate

the cross section of the part, while the fields produced byalternating current are confined to the metal at or near the

surface of the part, a phenomenon known as the skin effect.

+herefore, alternating current should not be used in searching for

subsurface discontinuities.



6agnetic $esting %6$& #o$es

+wo basic types of yokes that

are commonly used for

magnetiing purposes1 •permanent2magnet,•electromagnetic yokes.

0oth are hand held and

therefore quite mobile.



Dry 6agnetic #articles

*agnetic particles come in a variety of colors% 0color that produces a high level of contrastagainst the background should be used%



>et 6agnetic #articlesWet particles are typically supplied as visible or

fluorescent. 3isible particles are viewed under

normal white light and fluorescent particles are

viewed under black light.



$oe rac? in /67> >eld

@isible, Dry #owder 6ethod



7dvantages o' 6agnetic #article4nspection • /an detect both sur'ace and near sub-sur'acedefects%

• /an inspect parts with irregular shapes easily%

• Precleaning of components is not as critical as it is for

some other inspection methods% *ost contaminantswithin a 2aw will not hinder 2aw detectability%

• ast method of inspection and indications are visibledirectly on the specimen surface%

• /onsidered low cost compared to many other 34

methods%• 5s a very portable inspection method especially

when used with battery powered equipment%



!imitations o' 6agnetic #article4nspection

6/annot inspect non-'errous materials such asaluminum, magnesium or most stainless steels.

65nspection of large parts may require use of equipmentwith special power requirements%

67ome parts may require removal o' coating or platingto achieve desired inspection sensitivity%

6Limited subsurface discontinuity detection capabilities%*a&imum depth sensitivity is approimately 0.AB(under ideal conditions)%

6#ost cleaning, and post demagneti<ation is oftennecessary%

60lignment between magnetic 5u and de'ect isimportant

Die Penetrant-English

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