Magnetic Particle Current Determination for Toronto.pdf

8/10/2019 Magnetic Particle Current Determination for Toronto.pdf

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Magnetic ParticleCurrent Determinationand Monitoring

SystemsPresented by

Magnaflux



Introduction

The purpose of this discussion is to

provide a general working knowledgeof MAGNETIC PARTICLE

Current Determination TechniquesProcess ControlsProcess Enhancements



Current Determination

No Single Method Can Be Used• All methods need some type of

independent verification– Formulas– Known Defects– Artificial Defects



Magnetic ParticleInspection

• Used for the detection of surfaceand near- to- surfacediscontinuities in ferromagnetic

materials, by applying a magneticfield and a medium, sensitive to

areas of magnetic flux leakage. Themedium will be attracted and heldto the surface whereby the visibleindication can be interpreted.



Broken Magnet Principle

Opposite and attractingpoles are established across

each break.



Types of Magnetic

FieldsCIRCULAR FIELD

45 0 Crack

will show



Magnetic Field TypesLONGITUDINAL FIELD

45 0 Crackwill show



Multi-Directional

• Most Commonly Combination of

Longitudinal and Circular Fields• Other Common Names

– Swinging Vector– Moving Vector– DuaVec (Dual Vector)



What is a Vector

• FOR MPI Purposes:– A vector is a line

representation showingthe intensity anddirection of themagnetic field

• Direct Contact Shotsproduce CircularVectors

• Induced Coils produceLongitudinal Vectors

LONGITUDINAL FIELD

CIRCULAR FIELD



What is a Vector

X

Y





#1 Preparation of Surface:

• Surface roughness tends to decrease

test sensitivity(particle mobility).• Part should be clean, dry, and free of

grease, oil, rust and scale or anycontaminants that may interfere withthe formation of indications.



#2 Apply medium

• Wet Method

– Oil Base– Water Base

• Dry– Color selection



Centrifuge Tube• Run Bath through Pump for agitation

– 10-15 minutes

• Allow filling Hose to run 30 seconds to get freshlyagitated bath in the hose

• Fill Tube and place inside Coil then demag– If possible

• Stand tube away from the machine in an area free ofvibration

• After proper settling time check mixture– Check Level– Check Quality under UV





#3 Magnetization of the

Surface.• Two types of magnetic fields:– Circular– Longitudinal.

• Factors for use:– Orientation of discontinuities.– Size and shape of the part.– Equipment available.

• Balance the Fields – MultidirectionalApplications– Same magnetic intensity– Amperages may be different



Factors Affecting Choice of

Equipment:• Size & Shape of part.

• Location of part to be inspected.• Type and location of the

discontinuity.• Cost.

• Specifications.• Amperage requirements and

availability.• Run Rate





Indicating Medium

Application• Continuous Method must be used in

Multi-directional Applications– Some of the indications are

MECHANICALLY held• Field Intensity Measurement shouldbe done in the same manner asprocess dictates– Continuous vs. Residual



Magnetic Hysteresis

• All ferrous materials have specific magnetic

properties• The data is collected by applying analternating current

• Increase magnetic field strength (H) in smallincrements

• Measuring flux density (B) at each increment• Relationship between magnetic field

strength and flux density can be plotted



B+ (Flux Density)

B- (Flux Density ofopposite Polarity to B+)

H-

Magnetizing force ofopposite Polarity to H+

H+

Magnetizing force

a

o

HysteresisCurve

SaturationPoint

Zero magnetic

field strength Virgin Curve



B+ (Flux Density)


H-


H+

Magnetizing force

ba

c o

HysteresisCurve

Residualmagnetism

Coerciveforce



B+ (Flux Density)


H-


H+

Magnetizing force

b

a

c o f

e

d

CompleteHysteresis

Curve



Amperage Calculations

• Calculations will ballpark needed

levels– Formulas are written for THREE PHASEFWDC and simple geometry

• Should only be used as a guide, useother methods for verification

• Start low and work your way up• Multidirectional amperages should be

done one at a time, then combine thefields



Circular Field Amperage

• Expressed in amperage• General rule, 300 -800 amps per inch

diameter or diagonal width of crosssection.

• Example: Part is 12” long x 2” diameter• 2” Dia.) x 300 - 800 amps = 600 –

1600amps



Circular Field - CentralConductor

• Two x Thickness + Central Conductor Diameterx 300 - 800:– Use the thickness of inner wall

• 2 1/2) + ¾) x 300 – 800 amps = 525–1,400amps

½”



Coil AmperageWhen Part Positioned to Side of Coil

I = AMPERAGE

K = 45,000 CONSTANT VALUE. (Codes may vary)

L = TEST PART LENGTH. (Max. 18” range)

D = TEST PART DIAMETER. (Inches) N = NUMBER OF COIL TURNS (5)



L / D Ratio Calculations

L = 12 inches

D = 4 inches

K = 45,000

N = 5 turns

12” / 4” = 3 x 5 (turns) = 45,000 / 15 = ? Amp.

Answer: 3000 Amps, 1 coil shot



L / D Ratio Calculations18” Max Range

L = 27 inches

D = 3 inches

K = 45,000

N = 5 turns

18” / 3” = 6 x 5 (turns) = 45,000 / 30 = ? Amp.

Answer: 1500 Amps, 2 coil shot



Vectors and Field Indicators

Sensor

B

A



Hall Effect Probes

• Magnetic Fields falls off as a cubic

function of Distance in Air• Near Surface– Will vary from probe type– Will Vary between Manufacturers

• 30-80 Gauss

– Use residual or Continuous– Probes are designed for LongitudinalField



Magnetic Intensities• Hall Effect Probes

– Most are directional sensitive– The sensor is also offset from

edge• NO SET STANDARD

• Common Mistakes

– Used to check fordemagnetization– Probe not perpendicular to

magnetic field



Sensitivity Checks

• Steel Tool Ring

• Magnetic Test Bar

• Paste on shims



Sensitivity Checks – Steel Tool

(Ketos) Ring• More for verification of

Process– Most Parts do not lend them

selves to cross reference of

ring shape, finish, heattreat…

• Ring performance will varybetween types of units

• Best to verify consistencyof performance



Sensitivity Checks –Magnetic Test Bar

• Can be used forMultidirectional

• Has Longitudinal and

Circular Type Indications• Has Surface and

Sub Surface Indications• All the bar says is

SOMETHING is Wrong

– UV, Bath, Process,Inspector, Machine



Sensitivity Checks

Quantitative Quality Indicator• Artificial Flaw Near Surface sensor

• Good Approximation in many cases• Not True Indicator as usually different

material, different finish, separate part

Quantitative Quality



Quantitative Quality

Indicators• Low Retentive Steel Shim• Multi-Directional Indications• Small and Pliable• MISTAKES

– Clean off protective coating– Indication Side Down– Must make intimate contact with part– Still does not duplicate actual flaw, but it is the

best so far

• All the QQI says is SOMETHING is Wrong– UV, Bath, Process, Inspector, Machine, Poor Field

Balance



Multi-Directional Amperages

• QQI’s are the easiest to get you close

• Real flaws in both orientations confirm• Part shapes will warp the field, so

multiple shots may still be required



Pie Field Indicator• Inexpensive, quick checker• Should be used to verify direction ONLY



#4 Inspecting the Part

• Discontinuities will be interpreted as

relevant, non-relevant, or false.• Interpretations will be evaluated as to

accept, repair, or reject.





ASTM E-1444 / 709• UV Meters– 365 nanometers

– Check once per shift– Most UV bulbs do degrade over

time. As well filters get miss seated

and get cracked allowing white lightto escape

• White Light Meters– 760 to 400 nanometers– Less then 2 fc (florescent

applications)– Greater then 100 fc (visible

applications)



#5 Demag

• Normal Industry Standard

– LESS THEN +/-3 Gauss– Earth’s Magnetic Field is Approx 0.5

Gauss

• Sensor for Demag purposes offsetapproximately 5/8” from surface



Field Indicators• Designed for a Specific

Range

– Because of range limitationsshould be used residually only!

• Sensor is Offset from End ofPart

• Consistent Method forverifying DEMAG LEVELS

• Longitudinal Fields Only• Bulky for Tight Spaces



Post Clean as Needed



Application Training Tools• Electrical Discharge Machining (EDM) Notches

– Fill in with NON Fluorescing Epoxy– Should be part Specific– Still not true representation of actual flaw

• But better the QQI if done correctly

• Actual Flaws– Best out there if truly representative– Flaw will grow, and will clog over time

• Need to demag, clean, and monitor

• Pictures– Easy, will not change– Great for Cross Reference– Great for Teaching



Teaching / Education• Pictures• Books, Specifications, Reference Material• Classroom Refreshers

• Hands On, Procedures



Machine AccessoriesFor Process Improvement

• Central Conductors• Small Part Adaptor• Contact Pads (Braided, Lead or Heavy duty)

• Steady Rests• Induced Current Fixtures



Machine OptionsFor Process Improvement

• Auxiliary Output• Recipe (setting) Storage• Separate Coil/Contact Current Control• Automatic Bathing Systems• Rotating Contacts



Items to Avoid

• Tim Taylor Effect– MORE POWER– Lower levels will result in smoother processing

down the line, less back ground, easier demag• Assume Each Machine Model works the

same– Verify on each Machine type

• One Method fits all– Use at least two methods for current

determination• Defects do Saturate (Life Cycle)



Thank You

Questions?

Documents

Magnetic Particle Current Determination for Toronto.pdf