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Mobile Hardness Testing

Application Guide for Hardness Testers

GEInspection Technologies


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1. Mobile Hardness Testing is on the Advance1.1 What is hardness?

1.2 Why hardness testing?

1.3 On-site mobile hardness testing

2. UCI Method (MIC 10, MIC 20)2.1 The method

2.2 Selecting the suitable UCI probe

3. Rebound Method (DynaPOCKET, DynaMIC, MIC 20)3.1 The method

3.2 Selection of the suitable impact device

4. Optical Through-Indenter-Viewing Method (TIV)4.1 The method

4.2 Selection of the suitable probe

5. Hardness Testers Instruments5.1 DynaPOCKET

5.2 DynaMIC

5.3 MIC 10

5.4 MIC 20

5.5 TIV

6. Different Methods in the Field6.1 Selecting the test method

6.2 Significance of indentation size

6.3 Relation between penetration depth and minimum thickness for coatings

6.4 Hardness testing on welds (HAZ)

6.5 Test piece mass requirements

6.6 Wall thickness requirements

6.7 Surface quality

6.8 Handling, alignment, and fixing

6.9 Calibration

6.10 Verifying instrument performance

7. Selecting the Most Suitable Test Method7.1 The UCI method (MIC 20 / MIC 10)

7.2 Rebound method (MIC 20 / DynaMIC / DynaPOCKET)

7.3 Optical method Through-Indenter-Viewing (TIV)

7.4 Fundamental questions to the user

Figure 1: Hardness testing using the MIC 20 in

combination with the test support MIC 227 and a UCI

probe in the heat-affected zone (HAZ) of a weld.

Mobile Hardness Testing Application Guide

Content


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Figure 10: Schematic course of the voltage signal

generated by the impact body traveling through the

coil. The signal shows the voltage before and after the

impact. (VDI Report No. 208, 1978).

Figure 9: Cross-section of an impact device.

Coil

Impact body

Magnet

Tungstencarbid ball

1 The Method

n with hardness testers operatingording to the Leebs or rebound method,size of the test indentation generatedepended on the hardness of material.wever, it is in this case indirectly measuredthe loss of energy of a so-called impact

y. Figure 8 illustrates the physicalciple of rebound hardness testing.

ass, in this case the impact body withngsten carbide ball attached to its tip,

red against the test surface at aned speed by spring force. The impact

ates a plastic deformation of theace due to which the impact bodys part of its original velocity, viz. i.e.softer the material, the greater thein velocity. The velocity before andr the impact is measured in a-contact mode. This is done by a

all permanent magnet within theact body (Fig. 9) generating an

uction voltage during its passageough a coil, this voltage beingportional to the velocity (refer to10).

. Rebound Method (DynaPOCKET, DynaMIC andMIC 20) Standardized According ASTM A 956 and

IN 50156

With respect to this relatively younghardness testing method, the questionnevertheless arises as to the extent towhich the Leebs scale is accepted orapplied by the user. Up until now, it hasonly been used in a few cases forspecifications and test certificates. Themeasured speed ratio has mostly beenconverted into one of the conventionalhardness scales (HV, HB, HS, HRB, HR C,or N/mm2). It was only this conversionpossibility which increased acceptanceof rebound hardness testers in the field.

If one wishes to convert a measuredhardness value into another scale(i.e. possibly into the result of a completelydifferent hardness test method), there isno mathematical formula for this purpose.So-called conversion tables are thereforeempirically determined by carrying out acorresponding number of experiments.To do this, the hardness of a certainmaterial is measured using the differenttest methods, and the relationshipbetween the individual scales isdetermined (Fig. 11). A correct and reliableconversion requires the application of aconversion table produced from theresults of a sufficiently large number ofhardness measurements using bothscales and carried out on thecorresponding material of interest.

The main cause for the necessity to havedifferent material groups is the influenceof elastic properties (Youngs modulus) onthe hardness test using the reboundmethod. Two materials having the samereal hardness indicate, under certainconditions, different Leebs hardnessvalues owing to different values of Youngsmodulus. That is the reason why nouniversal conversion relationship existsfrom the rebound hardness HL into theconventional hardness scales. In order todo justice to these facts, several materialgroups, beneath which the correspondingconversion tables are hidden, can beselected in modern rebound hardnesstesters (refer to Table 2).

3.2 Selection of theSuitable Impact Device

The rebound hardness tester variantsinclude the instruments MIC 20 TFT andDynaMIC/DynaMIC DL with three impactdevice versions, and the compactDynaPOCKET. The operation of theseinstruments is based on Leebs method.

To apply this principle, an impact deviceuses a spring to propel an impact bodythrough a guide tube towards the testpiece. As it travels towards the test piece,a magnet contained within the impactbody generates a signal in a coil encirclingthe guide tube. After the impact, itrebounds from the surface inducing asecond signal into the coil. The instrumentcalculates the hardness value using theratio of the voltages and analyzes theirphases to automatically compensate forchanges in orientation.

Table 2: Stored material groups in the hardness testers

DynaPOCKET, DynaMIC, and MIC 20.

Material GroupLow-Alloy/Unalloyed Steel and Cast Steel

Tool Steel

Corrosion-Resistant Steel

Gray Cast IronNodular Graphite Iron

Aluminum Cast Alloys

Brass / CuZn

Bronze / CuAl, CuSn

Wrought Copper Alloys

Table 3: Impact devices for rebound hardness testing, benefits, and typical applications.

Impact DevicesM od el I nde nt er I mp ac t E ner gy T yp ic al A pp lic at io n

Dyna D 3 mm TungstenCarbide Ball

12 Nmm General-Purpose Testing o f HomogeneousMaterials

Dyna E 3 mm Diamand 12 Nmm > 50 HRC, e .g . Forged and Hardened Stee l M il l Ro llsDyna G 5 mm Tungsten

Carbid Ball90 Nmm < 650 HB, e.g. Large Castings and Forgings, Require

Lower Surface Requirements (As Opposed to Dyna D)Dyna-POCKET

3 mm TungstenCarbid Ball

12 Nmm Compact Rebound Hardness Tester

The GE I nspection Technologies hardnetesters MIC 20, DynaMIC, andDynaPOCKET are the only reboundhardness testers to have this patentedsignal processing feature enabling anautomatic direction correction.

The question as to which instrument awhich impact device is suitable for thecorresponding application depends onrequired impact energy and on the typesize of the indenter. Apart fromDynaPOCKET, with integrated impactdevice D, there is a choice between thrimpact devices: Dyna D, Dyna E, and Dynfor MIC 20 and DynaMIC (refer to table

e 8: The basic principle of rebound hardness

ng:

= diameter of indentation

= mass

= potential energy

= height before/after the impact

= kinetic ennergy

= speed before/after the impact

Equation 2: Hardness according to Leeb

HL = VR VI 1000

R = rebound

I = impact

Figure 11: Conversion of Leebs hardness HL into

Rockwell C (HRC) as a t ypical example of conversion

curves as they are stored in rebound hardness testers.

These curves are experimentally determined by

measuring different test objects having varying

hardness values in HL and HRC.

The Leebs hardness value HL, namedafter the inventor of the rebound methodD. Leeb, is calculated from the ratio of theimpact and rebound velocities. Leeb

defined the hardness value as follows:


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A special software is used in a first step todetermine the edges of the indentation.The intersection points with the edges ofthe Vickers diamond (roof angle 136)displayed on the screen are finally takenas a basis to determine the lengths of thetwo diagonals. The average of the twodiagonals is then used for calculating thehardness value according to the Vickersdefinition. The automatic evaluation is notonly fast compared to the use of aconventional measuring micro-scope butsubjective effects due to the user are alsoexcluded which become noticeable,especially in manual evaluation of theVickers indentation.

Figure 13 shows the result of a hardnesstest using the Through-Indenter-Viewingmethod. The optical verification of theshape of the indentation is the onlymethod to allow reliable conclusions to bedrawn with regard to the quality of themeasurement. One look on the display isenough to recognize whether themeasurement has been influenced by thesurface quality, the materialsmicro-structure or by other effects.

In addition to the automatic evaluation,the instrument also makes it possible toevaluate the Vickers indentation manually.The edges of the indentation are adjustedby hand in an enlargement of the picture onthe display. The length of the diagonals isautomatically updated, and thecorresponding hardness value is displayed.

The display of the Vickers diamondpresents the additional possibility ofdirectly checking the condition of theindenter. Any defects on the indenter, suchas edge breaks, are identified at once,therefore avoiding any incorrectmeasurements from the very start.

. Optical Through-Indenter-Viewing Method (TIV)

Figure 16: Hardness testing on different materials

using the Through-Indenter Viewing method.

Sheet

steel

Steel

As soon as the test load is reached, thediagonal lengths of the i ndentation aredetermined and converted into a hardnessvalue according to the Vickers definition.This evaluation can be done bothmanually and automatically. The TIVhardness tester contains stored tablesaccording to DIN 50150 and ASTM E 140that can be selected to convert themeasured hardness value into other scales.

The picture of the indentation or Vickersdiamond on the display does not onlyallow an immediate verification andassessment of the quality of the measuredvalue but also enables direct checking ofthe indenters (Vickers diamond) condition.

TIV can be used to open up new fields ofapplication for mobile hardness testing inwhich conventional instruments could notproduce any reliable results up to date,owing to the optical hardness testingmethod.

Through-Indenter-Viewing enablesahardness test: independent o measurement direction,

on dierent materials without anycalibration (independent of thematerial),

on thin and light components,

on elastic materials.

TIV is the first portable hardness testerthat does not determine the indentationsize of the Vickers diamond andconsequently the hardness of the materialindirectly but directly: Through-Indenter-Viewing means that one can simultaneouslysee the indentation of the Vi ckers diamondgrow on the test objects surface whilethe test load is being applied. This is ensuredby a special optical lens combinationincluding a CCD camera to digitize theindentation picture. As soon as the testload is attained, the picture of the indentationor of the diamond is stored in theinstrument and automatically evaluated.

The results of a test series can begraphically represented as a curve, oreven in tabular form, including statisticaldata (see Figures 14 and 15). All thenecessary data such as average, singlevalue, or statistical data are displayed orupdated during the measurement.

The essential benefits of the Through-Indenter-Viewing method are achieved bythe static application of the test load and tothe direct as well as automatic determi-nation of the diagonal lengths of theindentation made by the Vickers diamond:a) The TIV enables mobile and on-site

measurement of hardness on differentmaterials without having to carry outany additional adjustments andcalibration procedures (see Figure 16) .

b) Due to the static test load application,TIV also enables measurements on boththin and small parts, such as coils, sheetmetal, etc.

c) The live picture of the indentation onthe display enables immediate analysisof measurement quality.

d) The TIV is provided with an automaticevaluation of the Vickers indentation, i.e.the diagonal lengths are directly andautomatically determined.

e) The display of the diamond edges onthe screen enable condition checks tobe made on the indenter.

The TIV opens up a large variety of new

application fields which were previouslynot accessible to mobile hardness testers.

Hardness tests are not only i ndependentof test positions and directions but nowalso of the test objects material and massor geometry.

4.2 Selection of theSuitable Probe

Two different handheld probes, having testloads of 10 N / 1 kgf and 50 N / 5 kgfrespectively, are available for the opticalTIV hardness tester. Table 4 shows thecorresponding ranges of measurement forthe two probes. The measuring range ofthe two TIV probes is essentially limited bythe optical system used. The size of theCCD sensor only allows a certainmaximum size of indentation so that a

minimum value of the measuring range ispredefined by the optics in this case.

In the case of larger hardness values, i.with smaller test indentations, theresolution of the CCD camera limits therange of measurement. Although reliaband reproducible measurements havebeen carried out on ceramic materialswithin the hardness range of 1500 HVusing the TIV105 probe; an upper limitvalue of 1000 HV is nevertheless generspecified because a clear effect of the objects surface quality and of the test loapplication on the measurement resultto be expected at higher hardness valu

1 The Method

s a portable test instrument for opticaldness testing according to Vickerser test load (Fig. 12). An optical systemuding a CCD camera enables viewingough the diamond (Through-Indenter-

wing). For the first time this new method

kes it possible to directly watch thecess of the Vickers diamond penetratingtest material on the display.

Figure 13: Measurement of hardness using the TIV. The

indentation of the Vickers diamond is displayed on the

screen and automatically evaluated.

Figure 15: Display of the measurements results in

tabular form, including statistical data such as e.g

range, standard deviation, and minimum or maxim

Figure 14: Graphic display of the measurement results

as a curve.

Table 4: Probes for TIV hardness testing, benefits, and typical applications.

TIV Hardness Testing ProbesProbe Test Load Hardness Range Typical ApplicationT IV 101 10 N/1Kgf Approx.

30 500 HVOptical Hardness Testing on Thin Components MadeAluminum, Copper, or Brass. Hardness Testing on ThiLayers

T IV 105 50 N/5 Kgf Approx.100 1000 HV

Hardened Surfaces, Mechanical Parts, Semi-FinishedProducts

e 12: The TIV hardness tester in field use.

TIV technique can be used to carry outardness test without any additionalbration on different materials thanks tooptical method of measurement.eover, the static test l oad application

o makes it possible to carry outasurements on both thin and smallects, as well as on coatings.


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1 DynaPOCKET

hod: Rebound hardness testing

cal applications:

olid, coarse-grained test objects

orgings having an inhomogeneous surace structure

ast materials

essories:

est attachments or curved suraces

ardness reerence blocks

2 DynaMIC

hod: Rebound hardness testing

cal applications:

mechanical parts or motor units made o steel and aluminiumast alloys

olid components with surace as rolled

rge serial products during production

essories:

mpact devices D, G, and E

est attachments or curved suraces

ardness reerence blocks

tware UltraHARD

. Hardness Testers Instruments 5.3 MIC 10Method: UCI hardness testing

Typical applications:

fne-grained material

hardened materials

thin layers

hardness progress: on curve on welds, etc.

Accessories:

supports

guides (probe attachment)

hardness reerence plates

sotware UltraHARD

5.4 MIC 20

Method: UCI and rebound hardness testing


all UCI applications

all rebound applications

Accessories:

all UCI probes

all rebound impact devices

supports



sotware UltraDAT

5.5 TIV

Method: Optical hardness testing


hardness testing on dierent materials without calibration

hardness testing on thin components (e.g. sheet metal, coils)

hardened suraces

Accessories:

supports



sotware UltraDAT

Figure 21: TIV.

Figure 20: MIC 20.

Figure 19: MIC 10.

Figure 18: DynaMIC.

Figure 17 : DynaPOCKET.


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1 Selecting the Testethod

UCI method is recommended foring fine-grained material havingost any shape and size. It is especiallyd where material properties are to beermined within narrow tolerances, e.g.determination of the strain-hardeningcess on drop forgings.

TIV method is almost independent ofmaterial and geometry. It , therefore,be used everywhere, whereventional portable hardness testing

ed so far: different materials withoutbration, thin lightweight parts, sheetal and coils, etc.

. Different Methods in the Field

Rebound hardness testing is mainlycarried out on large, coarse-grainedmaterials, forgings, and all types of castmaterials because the spherical tungstencarbide tip of the impact device producesa larger indentation than the Vi ckersdiamond and therefore reveals thecharacteristics of the cast structure better.

On the other hand, the relatively small testindentations of UCI probes enablehardness testing on welds, and especiallyin the critical area of the heat-affectedzone, viz. HAZ.

A large number of UCI probes andrebound impact devices having differenttest loads or indenter diameters enable anapplication-oriented selection of a suitable

method and of a suitable probe/impactdevice. The following applies to the use ofimpact devices available for DynaMIC andMIC 20: in addition to the Dyna D, which issuitable for most fields of application, theDyna G provided with an impact energywhich is nine times higher and with alarger spherical tungsten carbide tip asindenter - can be used, especially onrelatively in homogeneous surfaces, e.g.on cast materials or forgings.

For hard materials (650 HV/56 HRC),causing the spherical tungsten carbide tipto wear faster, we recommend the impactdevice DynaE provided with a diamond tipas indenter.

6.2 Significance ofIndentation Size

In general, the larger the area ofindentation the more consistent the testresults. The variations in microstructureof inhomogeneous materials or incoarse-grained materials are averagedout so that consistent hardness valuescan be achieved. A l arger indentationarea also sets less demands on thesurface finish and requires less surfacepreparation.

In comparison, the resulting indentation

areas yielded by the various impactdevices are much larger than thosecreated by any UCI or TIV probe. Therebound tester is recommended whentesting large castings and forgings. Testingsmall areas of homogenous materialsthat are surface-hardened requires theshallower indentations produced by UCI orTIV probes. Table 6 is provided to comparethe indentation size of rebound impactdevices, UCI and TIV probes at three levelsof hardness.

6.3 Relation BetweenPenetration Depth and

Minimum Thickness forCoatings

For Vickers hardness testing, the thicknessor depth of hardened layer or coating, e.g.chromium on steel rolls, must be substantialenough to support the indentation. As arule, the thickness should be a minimumof ten times the indentation depth.

You can easily calculate the penetrationdepth of the Vickers diamond if you knowthe force of the probe and approximatelythe hardness by using equation 3. Thisformula is based on the geometry of theVickers diamond. Therefore, it only appliesto a Vickers hardness test. Remember:10 N 1 kgf. (Refers also to Fig. 22)

CI, Rebound and TIV Hardness Testing - Typical Applicationsplication UCI Hardness Testing

MIC 1 0, MIC 20Rebound Hardness

Testing DynaPOCKET,DynaMIC, MIC 20

TIV

d Parts + ++ ++rse-Grained Materials ++ o

el and Aluminum Cast Alloys o ++ oZ with Welds ++ - +es: Wall Thickness > 20 mm ++ ++ ++es: Wall Thickness < 20 mm ++ ++et Metal, Coils o ++omogeneous Surfaces + n Layers ++ +d-to-Get-at-Positions ++ +

Especially Well-Suited / + Well-Suited / o Sometimes Suitable / - Not Recommended

e 5: Applications for UCI, Rebound and TIV hardness testing.

e 6: Hardness indentation size for Rebound, UCI and TIV

proximate Indentation SizeDyna G5 mm

90 Nmm

Dyna D3 mm

12 Nmm

HV 10MIC 2010

HV 5MIC 205TIV 105

HV 1MIC 201TIV 101

HV 0,3MIC 2103

roximateentationa (in )

64 HRC 350 152 107 48 2555 HRC 898 449 175 124 56 2830 HRC 1030 541 249 175 79 41

roximateentationpth (in )

800 HV 16 22 16 7 4600 HV 63 28 25 20 9 5300 HV 83 35 35 35 11 6

Equation 3: Penetration depth of a Vickers diamond.

6.4 Hardness Testing onWelds (HAZ)

With the small test indentations made byMicrodur-UCI probes, it i s possible forexample to determine the hardness of awelded component, above all in the criticalarea of the weld, viz. the heat-affected

zone (HAZ). The result of the hardness testgives information about the properwelding of a material. For example, if thereis an excessive martensite content in theheat-affected zone (HAZ), a very hard zonewill be formed there often causing cracks.

Naturally, only hardness testing methodscan be used which reliably cover thecritical area of the weld, viz. the HAZ, withindentations which are not too large. Only

low test loads (HV5 or HV10) produce aVickers indentation which is still situatethe critical area of the HAZ. HV30, HB, atest indentations from the reboundhardness test, as well as measuremenusing the Poldi hammer go beyond thiszone (Fig. 23). Only an average value ovthe whole weld area is determined inthese cases. This leads to lower hardnevalues due to the fact that the adjacenareas are also detected with lowerhardness. Today, Poldi hammers can stbe encountered in weld testing. It isevident that a low hardness value resufrom this test i ndentation, which, for thoperator means, that further heattreatment of the HAZ is no longernecessary. Whether this is a wise decismust be left to the opinion of the reade

Figure 23: Hardness testing in the heat-affected zone

(HAZ).

d = 0,062 .VF/HV

HV = Vickers hardness in HVF = Test Load in Nd = Penetration depth in mm

Minimum thickness s = 10 .d

Figure 22: Penetration depth of t he Vickers diamond vs. the hardness of material (for different test loads).


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6.7 Surface Quality

All hardness testing methods requiresmooth surfaces free of oxide scale, paint,lubricants, oil, plastic coating due tocorrosion protection, or metal coating forbetter conductivity. The indentation depthshould be large in comparison to thesurface roughness.

Figure 25 shows the hardnessmeasurement results compared to thesurface preparation. The rougher thesurface the bigger the range of the readings.At very rough surfaces even the avaragevalue gives no reliable information aboutthe hardness of the test piece.

If surface preparation is necessary, care mustbe taken not to alter the surface hardnessby overheating or strain-hardening.

More practical results can be achieved byusing a battery-driven, high-speed(>12000 rpm) handheld grinder, e.g. theMIC 1060. It takes just 10 seconds.

6.6 Wall ThicknessRequirements

The wall thickness of tubes, pipelines, orvalves is critical for mobile hardnesstesting, especially for the rebound method.For example, a thin wall will start tooscillate like the skin of a drum when itshit by the impact body in a rebound test.

In addition to the mass (Section 6.5), itsmainly the wall thickness which also playsan important part when choosing the testmethods. It can influence the hardnessvalue even when the test object is solidand weighs a few tons (see table 8).

Despite the small mass of the impactdevice Dyna D and the low impact energy,there is a large force of about 900 N (90kgf) produced at the time of impact(compared to that, the maximum force of aUCI probe is 98 N / 10 kgf). That is sufficientto produce vibrations with a wall thicknessof under 20 mm.

This can cause incorrect hardness valuesand large amounts of scatter (Fig. 24). In suchcases, the UCI method should be preferredto the rebound method.

Figure 24 shows the hardness valuesmeasured by a standard Vickers test witha 10 kgf (98 N) force in relation to thosemeasured by a Dyna D impact device.

For a wall thickness beyond 20 mm, bothtests show the same results. Below 20 mm,the Vickers value measured using therebound test method is lower than thetrue value resulting in a deviation fromthe horizontal line.

6.8 Handling, Alignment,and Fixing

Move the MIC probe at a slow and steadyspeed. The probe should be rectangularwith respect to the surface. Maximumangular deviation from the straight axisshould be less than 5 degrees. Avoidturning, dont drill. There should be nolateral forces on the diamond.

The rebound impact device must be withinone or two degrees of being perpendicularto the surface.

Test attachments in the form of supportrings for the impact devices and probeshoes for the UCI probe ensure properalignment.

The standard support rings provided witheach Dyna D and Dyna E are used to testconvex or concave radii greater than 30mm. The larger diameter of the Dyna Gstandard support ring requires the radiusto be greater than 50 mm. Support ringsfor the Dyna D and Dyna E impact devicesare available to cover the range ofr = 10-30 mm f or testing the IDs or ODsof cylindrical and spherical shaped parts.Customized support rings are available onrequest.

Mass Requirements for Test PieceDyna D & E Dyna G UCI-Probes TIV

No Holder / Support Required > 5 Kg > 15 Kg > 0.3 Kg

No RestrictionsHolder / Support Required 2 - 5 Kg 5 - 15 Kg 0.1 - 0.3 KgHolder / Support & CouplingPaste Required

0.05 - 2 Kg 0.5 - 5 Kg 0.01 - 0.1 Kg

Table 7: Mass requirements for the test piece.

Figure 24: Standard Vickers values (HV10) compared

with rebound Vickers values (HVR) for different wall

thicknesses of tubes.

Table 8: Recommended minimum wall thickness.

By coupling to a support plate, small test pieces can

be made rigid and stable to enable measurement of

small wall thicknesses.

Recommended Min Wall ThicknessHardness TestingMethod

Wall Thickness

Rebound 20 mm (0.79)UCI 2 - 3 mm (0.08 - 0.12)TIV 10 x Penetration Depth

of Diamond

For standard length UCI probes, the MIC and MIC 271 probe shoes are offered aaccessories. The MIC-271 probe shoe isrecommended for testing cylindrical pawith radii from 3 to 75 mm. The flat proshoe is designed to test flat surfaces but is useful in testing radii greater than 75 m

Position the TIV probe perpendicular totest piece. Probe attachments for flat acurved surfaces are available. Apply th

load at a slow and steady speed. On thscreen the growing indentation can bobserved. The indentation is evaluatedautomatically when the load is applied

5 Test Piece Massquirements

sideration must be given to the masshe test piece. Although the masseria for Leebs method are higher thanse for the UCI method, the results ofh methods can be influenced by thess and thickness of the test piece.

bs method creates a large force ofrt duration during the impact. Thin andtweight materials yield causing

oneous values. A solution for testingall components having a simplemetry is a machined support thattches the contour of the back surfacehe part. The support reinforces thet to make it rigid and stable. Extremelymaterials may also require the use ofght film of grease or paste to coupletest object to the support.

UCI method is based on measuring auency shift. Test objects weighing less

n about 0.3 kg can go into-oscillation causing erroneous oratic readings. The support plate andpling technique described above are

o an effective method to avoidllations with small components. If theof a support plate is not feasible,ct a probe with a lower test load to

uce the effects of self-oscillation.

le 7 is provided as a guideline forermining holder or support

uirements. The effectiveness of theder or support is determined by howcisely it matches the contour of thepiece.

re are in principle no limitationsarding the test piece mass for the TIV,ong as the probe can be positionedperly and the load can be appliedhout any movements of the test piece.

Figure 25: Range of measured hardness values versus

surface preparation. HVR indicates converted Vickers

hardness values measured by rebound hardness testing.


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average value is adjusted to the actualhardness. This enables to achieve precisecalibration and a calibration offset valuefor that specific material that can be usedto recalibrate the instrument.

UCI probes compatible with the MIC10 andMIC20 series are calibrated on steelreference blocks having a modulus ofelasticity or Youngs modulus of 210,000MPa. Because unalloyed or low-alloy

steels have a similar Youngs modulus,accurate results are obtained with thestandard calibration. In many cases, thedifference in Youngs modulus of medium-alloy and high-alloy steels is so insignificantthat the error created falls within theallowable tolerances of the part.

However, the Youngs modulus fornon-ferrous materials require special

9 Calibration

modulus of elasticity (or Youngsdulus) is a material property that canuence instrument calibration. Properbration is required to ensure theuracy of the test results.

alibrate the DynaMIC or the MIC 20 foround hardness testing, the operatorst first select one of nine material

ups (refer to Table 9). Selecting theropriate material provides a roughbration, and the type of impact devicenected to the instrument determinesavailable conversions. A more precisebration is possible for a specificterial if samples of known hardness ared to calibrate the instrument. Toform the calibration, several readingstaken on the sample and the displayed

calibrations. Several readings are taken ona test piece sample of known hardness toperform the calibration. The displayedaverage value is then adjusted to theactual hardness. This calibrates theinstrument and also establishes acalibration offset value for that specificmaterial that can be used to recalibratethe instrument.

Calibration offset values are referenced

from a factory-set value for steel. Pleasenote that they can be either a positive ornegative value. Table 10 contains a list ofapproximate calibration values that can bereferenced for some common materials.

Because of the principle of the TIV basedon the Vickers test, there is no calibrationnecessary when measuring on differentmaterials. For details see chapter 4.

Table 11: Measuring tolerances for the different test methods.

Measuring Tolerances for the Different Test MethodsPrinciple Measuring TolerancesRebound 5 HL Deviation of Average from the Value of the Hardness Reference Block with

3 to 5 Readings.UCI 3,6 % Deviation of Average from the Value of the Hardness Reference Block with

3 to 5 Readings Using the Test Support MIC 222-A.Larger Deviations are Possible with Freehand Measurements.

TIV 3,6 % Deviation of Average from the Value of the Hardness Reference Block with3 to 5 Readings.

ailable ConversionsMaterial Group HV HB HRB HRC HS N/mmSteel - Unalloyed,Low-alloy or Cast

D, E, G D, E, G D, E, G D, E, G D, E, G

Tool Steel D, E D, EStainless Steel D D D DGray Cast Iron D, GNodular Graphite Iron D, GCast Aluminum D DBrass D DBronze DCopper D

e 9: Material groups and available conversions.

e 10: Approximate UCI calibration offset values.

proximate UCI Calibration Offset Valuesterial Calibration Offset Valueminium 8800omium + 0250per 5800t iron 4800nium 6500-Series Stainless Steel 1500-Series Stainless Steel 0900

6.10 Verifying InstrumentPerformance

The performance of a hardness tester isperiodically verified using standardizedreference blocks.

The perfect functioning of the reboundhardness testers (DynaPOCKET, DynaMIC,and MIC 20) is based on 5 single

measurements on a certified Leebshardness reference block. The average ofthese 5 measurements should be within5 HL of the reference blocks certifiedvalue. The MICD62 hardness referenceblock has a nominal value of about765 HL. If these values are convertedinto a HRC value, the result is a hardnessvalue of 55 HRC with a tolerance of0.5 HRC.

The accuracy of the UCI and TIV hardnesstesters (MIC 10, MIC 20 and TIV) is basedon measurements using Vickers hardnessreference blocks. The average of 5readings should be within 3.6% of thecertified value of the reference block whenusing a rigid/stable support or holder suchas the MIC222 test support. When testingfreehand, a minimum of 10 readingsshould be averaged with the tolerancebeing 5%. The above tolerances for the

dfferent test principles are summarized intable 11.


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7.4 Fundamental Questions to the User

1. What do you want to measure?

2. What is the material?

3. Are there any other requirements?

Depending on the test task, either the UCI method, the rebound method, or the opticaTIV method is used for the hardness test.

A suitable method cannot always be clearly defined right away. An experienced enginis therefore the best person to give the right answer about the test object itself directlyon site.

What Do You Want to Measure?DynaPOCKET DynaMIC MIC 10 MIC 20 TIV

Coatings Hardened Surfaces Weld (HAZ) Different Materials (*withCalibration)

* * * *

Castings/Forgings Partly PartlyTubes Partly Partly PartlySheet Metal, Coils Partly Partly

What is the Material?DynaPOCKET DynaMIC MIC 10 MIC 20 TIV

Steel (alloy, stainless, Other metals (Al, Cu,...) Cast steel Partly PartlyCast Aluminum Partly Partly PartlyCeramics Partly Partly Glass Plastics Partly Partly Partly Partly

Are There Any Other Requirements?DynaPOCKET DynaMIC MIC 10 MIC 20 TIV

Data Memory/PC Interfacing Only DL Only DL Statistical Evaluation Scale Conversions Non-Directional(*Except Motor Probe)

* *

Wall Thickness


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Regional Contact InformationGE Inspection Technologies50 Industrial Park RoadLewistown, PA 17044USA+1 717 242 0327

GE Inspection TechnologiesRobert Bosch Strasse 350354 HuerthGermany+49 2233 6010

GE Inspection Technologies5F, Hongcao Building421 Hongcao RoadShanghai 200233China+86 800 820 1876 (China toll free)

+86 21 3414 4620 (ext. 6029)

2008 General Electric Company. All Rights Reserved. We reserve the right t o technical modifications without prior notice. GEIT-21001EN (01/08)

GE Inspection Technologies: productivity through inspection solutionsGE Inspection Technologies provides technology-driven inspection solutions that deliver productivity, quality and safety. We

design, manufacture and service ultrasonic, remote visual, radiographic and eddy current equipment and systems. We offer

specialized solutions that will help you improve productivity in your applications in the aerospace, power generation, oil & gas,

automotive or metals Industries.

www.ge.com/inspectiontechnologies

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