gives breif insight about foundry casting quality control

1. CASTING QUALITY CONTROLCASTING QUALITY CONTROL
VINAY . SVINAY . S

2. AGENDAAGENDA
 INTRODUCTION TO CASTING QUALITYINTRODUCTION TO CASTING QUALITY
CONTROL.CONTROL.
 CASTING DEFECTS, FACTORS RESPOCASTING DEFECTS, FACTORS RESPO
NSIBLE , REMEDIES.NSIBLE , REMEDIES.
 CLEANING OF CASTINGSCLEANING OF CASTINGS
 INSPECTION METHODS AND TESTINGINSPECTION METHODS AND TESTING
METHODS TO EVALUATE A CASTMETHODS TO EVALUATE A CAST..
 Q / AQ / A

3. Sand Casting Steps

4. IntroductionIntroduction
 Reduces total output, increases the cost of production.Reduces total output, increases the cost of production.
 Casting defects may be defined –Casting defects may be defined – those characteristics thatthose characteristics that
create a deficiency or imperfection to quality specificationscreate a deficiency or imperfection to quality specifications
imposed by design and service requirements.imposed by design and service requirements.
 Even in modern foundries the rejection rate – as high uptoEven in modern foundries the rejection rate – as high upto
20% of the number of casting produced.20% of the number of casting produced.
 Hence all efforts must be taken to bring down theHence all efforts must be taken to bring down the
percentage of rejection.percentage of rejection.
 For this to happen one should have sound knowledge ofFor this to happen one should have sound knowledge of
principles of casting, casting design, potential defects,principles of casting, casting design, potential defects,
causes, remedies for same, inspectional methods, testingcauses, remedies for same, inspectional methods, testing
methods.methods.

5. Types of Defects
ƒ Based on Location: ƒ Based on Cause:
 External  Raw materials
 Internal  Product design
 Tooling design
ƒ Based on Type:
 Process parameters
 Geometric
 Process control
 Integrity
ƒ Based on Stage:
ƒ Based on Size/Severity:
 Casting
 Small/Minor
 Rough machining
 Large/Major
 Finish machining
ƒ Based on Process:  Service
 Moulding-related ƒ Based on Reparability:
 Filling-related  Repairable
 Solidification-related.  Irreparable

6. CLASSIFICATION OF CASTING DEFECTSCLASSIFICATION OF CASTING DEFECTS
Casting Defects
Based on nature
of defects
Based on contributing
factors
Surface defects
Internal defects
Incorrect chemical compo.
Unsatisfactory mech.
properties
Defects caused by pattern
Making & molding
Defects caused due to
improper
Gating & rise ring
Defects caused by
molten metal

7.  Surface defectsSurface defects : may be visible on surface: may be visible on surface
incorrect shape & size, laps, flashes, poor surfaceincorrect shape & size, laps, flashes, poor surface
finish.finish.
 Internal defectsInternal defects : these are present in interior of: these are present in interior of
cast. Can be revealed through NDT techniques.cast. Can be revealed through NDT techniques.
 Incorrect chemical compositionIncorrect chemical composition – formation of– formation of
undesirable microstructure.undesirable microstructure.
 Unsatisfactory mechanical properties –Unsatisfactory mechanical properties – lowlow
quality, poor percent of usage.quality, poor percent of usage.
BASED ON NATURE OF DEFECTSBASED ON NATURE OF DEFECTS

8. BASED ON CONTRIBUTING FACTORSBASED ON CONTRIBUTING FACTORS
 Defects caused by pattern making and mouldsDefects caused by pattern making and moulds::
results in incorrect dimensions, poor surface finish,results in incorrect dimensions, poor surface finish,
flash, mismatch.flash, mismatch.
 Defects – improper gating & riseringDefects – improper gating & risering
results in cold shut, misrun, inclusions, pulls,results in cold shut, misrun, inclusions, pulls,
shrinkage cavities.shrinkage cavities.
 Defects caused – molten metalDefects caused – molten metal
results in cold shut, metal penetration, porosity.results in cold shut, metal penetration, porosity.

9. CAUSES FOR DEFECTSCAUSES FOR DEFECTS
 Unsuitable and unsatisfactory raw materials.Unsuitable and unsatisfactory raw materials.
 Application of unsatisfactory casting principles.Application of unsatisfactory casting principles.
 Use of improper tools, equipment, appliances orUse of improper tools, equipment, appliances or
patterns.patterns.
 Unprofessional management.Unprofessional management.
 Unsatisfactory setting up of procedures, poor workUnsatisfactory setting up of procedures, poor work
discipline, lack of training.discipline, lack of training.

10. CASTING DEFECTS ,FACTORSCASTING DEFECTS ,FACTORS
RESPONSIBLE FOR THEM AND REMEDIESRESPONSIBLE FOR THEM AND REMEDIES
 CORE SHIFTCORE SHIFT
 WRAPED CASTINGWRAPED CASTING
 SWELLSWELL
 FINFIN
 BLOW HOLESBLOW HOLES
 PIN HOLESPIN HOLES
 GAS HOLESGAS HOLES
 SHRINKAGE CAVITYSHRINKAGE CAVITY
 HOT TEARHOT TEAR
 INCLUSIONSINCLUSIONS
 MISRUN AND COLD SHUTMISRUN AND COLD SHUT
 EXPANSION SCABSEXPANSION SCABS

11. CORE SHIFTCORE SHIFT
 Results in mismatch of the section.Results in mismatch of the section.
 Usually easy to identify.Usually easy to identify.
 Can be repaired provided with in tolerableCan be repaired provided with in tolerable
limits.limits.
 Misalignment of flasks is a common cause.Misalignment of flasks is a common cause.
 Can be prevented by ensuring proper alignmentCan be prevented by ensuring proper alignment
of pattern, die parts, molding boxes.of pattern, die parts, molding boxes.

12. CORE SHIFTCORE SHIFT

13. WARPED CASTINGWARPED CASTING
 Warpage - Undesirable deformation in a casting.Warpage - Undesirable deformation in a casting.
 Large cross sections or intersections areLarge cross sections or intersections are
particularly prone to warping.particularly prone to warping.
 Can be reduced by proper casting design,Can be reduced by proper casting design,
judicious use of ribs.judicious use of ribs.
 Cannot be eliminated but allowances can beCannot be eliminated but allowances can be
given along with machining allowance, togiven along with machining allowance, to
remove by machining.remove by machining.

14. SWELLSWELL
 Swell- enlargement of the mould cavity by metalSwell- enlargement of the mould cavity by metal
pressures, results – localized or overallpressures, results – localized or overall
enlargement of castingsenlargement of castings
 Caused due to insufficient ramming of the sand.Caused due to insufficient ramming of the sand.
 Also due to rapid pouring of molten metal.Also due to rapid pouring of molten metal.
 Also due to insufficient weighting of mouldAlso due to insufficient weighting of mould
 Remedies – avoid rapid pouring, provideRemedies – avoid rapid pouring, provide
sufficient ram on sands , proper weighting ofsufficient ram on sands , proper weighting of
moulds.moulds.

15. FINFIN
 A thin projection of metal – not a part of cast.A thin projection of metal – not a part of cast.
 Usually occur at the parting of mould or coreUsually occur at the parting of mould or core
sections.sections.
 Causes - Incorrect assembly of cores andCauses - Incorrect assembly of cores and
moulds, improper clamping, improper sealing.moulds, improper clamping, improper sealing.
 Remedy is proper clamping of cores and mould.Remedy is proper clamping of cores and mould.

16. FINS OR FLASH

17. BLOW HOLESBLOW HOLES
 They are entrapped gases.They are entrapped gases.
 This is result of gases from mould, molten metalThis is result of gases from mould, molten metal
and steam sand.and steam sand.
 Remedy is to provide sufficient permeability,Remedy is to provide sufficient permeability,
making vent holes, use minimum quantity ofmaking vent holes, use minimum quantity of
water.water.
 Also use of dry sand moulds, use of no bakeAlso use of dry sand moulds, use of no bake
sands.sands.

18. BLOW HOLE

19. SHRINKAGE CAVITYSHRINKAGE CAVITY
 It is a void or depression in the casting causedIt is a void or depression in the casting caused
mainly by uncontrolled solidification.mainly by uncontrolled solidification.
 Remedy is apply principles of casting, provideRemedy is apply principles of casting, provide
adequate risers, feeders, which supply theadequate risers, feeders, which supply the
molten metal to compensate the shrinkage.molten metal to compensate the shrinkage.

20. Shrinkage cavity

21. HOT TEARHOT TEAR
 If the mould surface is rigid, it restrains solidifyingIf the mould surface is rigid, it restrains solidifying
casting from contraction and resulting incasting from contraction and resulting in
development of cracks or tear, also called pulls.development of cracks or tear, also called pulls.
 Remedy is avoid excessive ramming.Remedy is avoid excessive ramming.
 Controlled ramming should be done.Controlled ramming should be done.

22. Hot Tears
ME 6222: Manufacturing Processes and Systems 7
Prof. J.S. Colton

23. METAL PENETRATIONMETAL PENETRATION
 When molten metal penetrates in the spacesWhen molten metal penetrates in the spaces
between sand grains.between sand grains.
 Result - sand will be tightly held to the casting.Result - sand will be tightly held to the casting.
 Remedy – good optimum mould hardness.Remedy – good optimum mould hardness.

24. MISRUN & COLDSHUTMISRUN & COLDSHUT
 Misrun occurs particular section of casting isMisrun occurs particular section of casting is
solidified before filling .solidified before filling .
 when two streams of molten metal which arewhen two streams of molten metal which are
too cold to meet and do not fuse then results intoo cold to meet and do not fuse then results in
coldshut.coldshut.
 Prevented by proper casting design.Prevented by proper casting design.

25. Casting Defects
ME 6222: Manufacturing Processes and Systems 6
Prof. J.S. Colton

26. EXPANSION SCABSEXPANSION SCABS
 This is due to expansion property of sand.This is due to expansion property of sand.
 Due to high temperature sand will expand.Due to high temperature sand will expand.
 Low thermal stability of sand used.Low thermal stability of sand used.
 This expansion is prevented by mould condition,This expansion is prevented by mould condition,
results in cracks, poor surface finish.results in cracks, poor surface finish.
 Remedy is to reduce use clay content.Remedy is to reduce use clay content.
 Use of additives which reduce thermalUse of additives which reduce thermal
expansion of sand.expansion of sand.

27. Casting Defects
ME 6222: Manufacturing Processes and Systems 6
Prof. J.S. Colton

28. CLEANING OF CASTINGSCLEANING OF CASTINGS
 This operation is also referred a fettling.This operation is also referred a fettling.
Operations may beOperations may be
 Knocking out of dry sand cores.Knocking out of dry sand cores.
 Removal of gates and risers.Removal of gates and risers.
 Extraction of fins and unwanted projections.Extraction of fins and unwanted projections.
 Cleaning and smoothening of surface.Cleaning and smoothening of surface.
 Repairing the casting, to fill up defects.Repairing the casting, to fill up defects.

29. Knocking out of dry sand coresKnocking out of dry sand cores
 Dry sand cores can be removed by rapping orDry sand cores can be removed by rapping or
knocking with an iron bar.knocking with an iron bar.
 For quicker removal hydraulic and pneumaticFor quicker removal hydraulic and pneumatic
equipments can be used.equipments can be used.
 These devices also helps in cleaning andThese devices also helps in cleaning and
smoothening.smoothening.

30. Removal of gates and risers.Removal of gates and risers.
 Choice of removal methods – depend upon sizeChoice of removal methods – depend upon size
and shape, type of cast.and shape, type of cast.
 Using hammer to knock off, this is particularlyUsing hammer to knock off, this is particularly
suitable for brittle materials.suitable for brittle materials.
 Sawing- may be band saw, circular saw, powerSawing- may be band saw, circular saw, power
hacksaw.hacksaw.
 Using flame generated by oxyacetylene gas.Using flame generated by oxyacetylene gas.
 Employing abrasive cutting machines.Employing abrasive cutting machines.

31. Extraction of fins and unwantedExtraction of fins and unwanted
projectionsprojections
 This operation is also called snagging.This operation is also called snagging.
 Methods include – using grindersMethods include – using grinders
 Chipping with hand tool.Chipping with hand tool.
 Flame cutting.Flame cutting.
 Using electric arc equipment.Using electric arc equipment.
 Filing.Filing.

32. Cleaning and smoothening of castingCleaning and smoothening of casting
 Manual methodManual method ––
 Done using wire brushDone using wire brush
 Extremely tedious and time consuming.Extremely tedious and time consuming.
 As a result mechanical methods are employedAs a result mechanical methods are employed

33. Cleaning and smoothening of castingCleaning and smoothening of casting
 Mechanical methods include –Mechanical methods include –
o TumblingTumbling
o Compressed air impact cleaningCompressed air impact cleaning
o Mechanical impact cleaning or shot blastingMechanical impact cleaning or shot blasting
o Hydro blasting.Hydro blasting.

34. TumblingTumbling
 Components are place sin barrel along with steelComponents are place sin barrel along with steel
rodsrods
 Barrel is then rotated its central axis – peeningBarrel is then rotated its central axis – peening
action takes place – casting are cleaned.action takes place – casting are cleaned.
 Care should be taken – not to charge very tightlyCare should be taken – not to charge very tightly
to prevent any relative motions.to prevent any relative motions.
 Hard castings - are not fragile enough areHard castings - are not fragile enough are
suitable for tumbling.suitable for tumbling.

36. Compressed air impact cleaningCompressed air impact cleaning
 Stream of suitable abrasive particles along withStream of suitable abrasive particles along with
compressed air is directed – at high velocities.compressed air is directed – at high velocities.
 This is done in tightly closed chambers.This is done in tightly closed chambers.
 Due to impact surface gets cleaned.Due to impact surface gets cleaned.

37. Mechanical impact cleaning or shot blastingMechanical impact cleaning or shot blasting
 Abrasive particles are thrown by centrifugalAbrasive particles are thrown by centrifugal
force.force.
 Has vane rotating at speed of 1800 to 2500 rpm.Has vane rotating at speed of 1800 to 2500 rpm.
 Abrasive particles are fed at angular positionsAbrasive particles are fed at angular positions
near the centre.near the centre.
 Centrifugal force causes particles to moveCentrifugal force causes particles to move
outwards the periphery until it reaches the outeroutwards the periphery until it reaches the outer
tips and is thrown at workpiece.tips and is thrown at workpiece.
 Due to impact surface is cleaned.Due to impact surface is cleaned.

39. Hydro blastingHydro blasting
 High velocity stream – 15% sand and 85% water isHigh velocity stream – 15% sand and 85% water is
directed against the surface through nozzle.directed against the surface through nozzle.
 Thus by nozzle pressure increases – up to 600 m /Thus by nozzle pressure increases – up to 600 m /
min.min.
 Smallest casting that can be cleaned, weighs at leastSmallest casting that can be cleaned, weighs at least
120 kgs.120 kgs.
 Provisions are made to recover sand.Provisions are made to recover sand.

40. INSPECTION OF CASTINGINSPECTION OF CASTING
 PROCESS INSPECTIONPROCESS INSPECTION
 VISUAL INSPECTIONVISUAL INSPECTION
 DIMENSIONAL INSPECTIONDIMENSIONAL INSPECTION

41. PROCESS INSPECTIONPROCESS INSPECTION
 Inspection done while parts are being processed.Inspection done while parts are being processed.
 This is helpful to detect defects at the start andThis is helpful to detect defects at the start and
allow the corrections.allow the corrections.
 This is an preventive act.This is an preventive act.

42. VISUAL INSPECTIONVISUAL INSPECTION
 Simplest and most fastest inspectional methods.Simplest and most fastest inspectional methods.
 Most commonly employed.Most commonly employed.
 Usually good to check surface defects.Usually good to check surface defects.
 Fails to identify internal defects.Fails to identify internal defects.

43. DIMENSIONAL INSPECTIIONDIMENSIONAL INSPECTIION
 Before casting are to be machined dimensionalBefore casting are to be machined dimensional
inspection is done.inspection is done.
 Castings are placed on surface plate or surfaceCastings are placed on surface plate or surface
table with angle - measuring instruments.table with angle - measuring instruments.
 Various measuring instruments are employed forVarious measuring instruments are employed for
a first set of castings, so as to standardizea first set of castings, so as to standardize
subsequent castings.subsequent castings.

44. TESTING METHODSTESTING METHODS
 PRESSURE TESTINGPRESSURE TESTING
 DESTRUCTIVE TESTINGDESTRUCTIVE TESTING
 NON DESTRUCTIVE TESTINGNON DESTRUCTIVE TESTING

45. PRESSURE TESTINGPRESSURE TESTING
 Casting that is used for containing or conveyingCasting that is used for containing or conveying
liquids, gases, such type are subjected toliquids, gases, such type are subjected to
pressure testing.pressure testing.
 It is tested for any leaks through their walls.It is tested for any leaks through their walls.
 Leaks may be detected by submerging theLeaks may be detected by submerging the
complete casting under water for gas pressures.complete casting under water for gas pressures.
 Or by visual inspection by liquid pressures.Or by visual inspection by liquid pressures.

46. DESTRUCTIVE TESTINGDESTRUCTIVE TESTING
 This test is done causing harm to the casting i.e.This test is done causing harm to the casting i.e.
by destroying it.by destroying it.
 Various tests include fatigue tests, compressionVarious tests include fatigue tests, compression
tests, creep tests etc.tests, creep tests etc.

47. NON DESTRUCTIVE TESTINGNON DESTRUCTIVE TESTING
 Here parts to be tested are inspected for internalHere parts to be tested are inspected for internal
defects and surface defects without destroying thedefects and surface defects without destroying the
component.component.
 Various methods available are:Various methods available are:
 Liquid penetrate test LPILiquid penetrate test LPI
 Magnetic particle inspection MPIMagnetic particle inspection MPI
 X – Ray radiography XRRX – Ray radiography XRR
 Ultrasonic testing UTUltrasonic testing UT
 Eddy current test ECTEddy current test ECT
 Gamma ray radiography GRRGamma ray radiography GRR

48. Liquid penetrant testLiquid penetrant test
 Surface preparationSurface preparation
 Penetrant applicationPenetrant application
 Penetrant dwellPenetrant dwell
 Excess Penetrant removalExcess Penetrant removal
 Developer applicationDeveloper application
 Indication developmentIndication development
 InspectionInspection
 Clean surface.Clean surface.

49. Magnetic Particle Inspection - MPIMagnetic Particle Inspection - MPI
 Most satisfactory method Used to find surfaceMost satisfactory method Used to find surface
and sub surface defects.and sub surface defects.
 It is quick, cheap, very sensitiveIt is quick, cheap, very sensitive
 Can only be applied to ferrous metals like steel,Can only be applied to ferrous metals like steel,
cast iron etccast iron etc

50. Principle - MPIPrinciple - MPI
 When a metal placed in magnetic field, magneticWhen a metal placed in magnetic field, magnetic
flux are intersected by the defect – magneticflux are intersected by the defect – magnetic
poles are induced on either side of discontinuity.poles are induced on either side of discontinuity.
 Abrupt change in path of flux – local leakageAbrupt change in path of flux – local leakage
 This can detected when magnetic particles areThis can detected when magnetic particles are
attracted towards defective region.attracted towards defective region.
 Magnetic particles piles up in defective region.Magnetic particles piles up in defective region.

51. ProcedureProcedure
 Preparation of specimenPreparation of specimen
 Surface should be cleaned thoroughly, free fromSurface should be cleaned thoroughly, free from
rust, grease, oil, paint etc.rust, grease, oil, paint etc.
 Cleaning of surface can be done using wire steelCleaning of surface can be done using wire steel
brushes, shot blasting technique or by usingbrushes, shot blasting technique or by using
solvents.solvents.

52. MagnetizationMagnetization
 To induce magnetic lines – two methods –To induce magnetic lines – two methods –
permanent magnet – electromagnet.permanent magnet – electromagnet.
 Electromagnet is proffered as it has capability toElectromagnet is proffered as it has capability to
produce stronger magnetic field.produce stronger magnetic field.
 Magnetization – two types – longitudinal or forMagnetization – two types – longitudinal or for
parallel defects – circular or for perpendicularparallel defects – circular or for perpendicular
defects.defects.
 For a defect to be detected flux lined shouldFor a defect to be detected flux lined should
pass perpendicular line.pass perpendicular line.

53. Application of magnetic particlesApplication of magnetic particles
 Magnetic particles are applied uniformly so thatMagnetic particles are applied uniformly so that
they move on the surface freely.they move on the surface freely.
 The particles must be as fine as possible.The particles must be as fine as possible.
 Generally pulverized iron oxide, carbonyl ironGenerally pulverized iron oxide, carbonyl iron
powder are used.powder are used.
 Powder can be ofPowder can be of
 Powder suspended in liquid petroleumPowder suspended in liquid petroleum
 Dry powderDry powder
 Fluorescent powder – can be viewed in UV light.Fluorescent powder – can be viewed in UV light.

54. Inspection of defectInspection of defect
 Generally carried out in good light.Generally carried out in good light.
 If no defects then regular pattern, if presence ofIf no defects then regular pattern, if presence of
defects then flux lines distorted.defects then flux lines distorted.
 Magnetic particles spreads out at the point ofMagnetic particles spreads out at the point of
defects indicating presence of defect.defects indicating presence of defect.

55. X – ray radiographyX – ray radiography
 X – Rays are produced when high energy electronsX – Rays are produced when high energy electrons
collide with the nucleus of an atom .collide with the nucleus of an atom .
 The x – ray equipment ---which producesThe x – ray equipment ---which produces
incandescent light, placed near a highly chargedincandescent light, placed near a highly charged
cathode, causing the electrons to flow from thecathode, causing the electrons to flow from the
cathode which is attributed by the anode or target.cathode which is attributed by the anode or target.
 The intensity of x – rays produced is directlyThe intensity of x – rays produced is directly
proportional to the number of electrons produced atproportional to the number of electrons produced at
the filament.the filament.
 The pattern of the x – ray so produced depends onThe pattern of the x – ray so produced depends on
the shape of the target.the shape of the target.

56. X – ray radiographyX – ray radiography
 A radiographic film is placed next to the part to be tested andA radiographic film is placed next to the part to be tested and
x rays are directed against the part.x rays are directed against the part.
 The x – rays will pass through the part to be testedThe x – rays will pass through the part to be tested
proportional to the density and thickness of the part.proportional to the density and thickness of the part.
 The absorption of x – rays is directly proportional to theThe absorption of x – rays is directly proportional to the
density of and thickness of the part. If the part has nodensity of and thickness of the part. If the part has no
defects, the x- rays will pass uniformly through the part.defects, the x- rays will pass uniformly through the part.
 However if there are any defects such as porosity which leadsHowever if there are any defects such as porosity which leads
to lesser density, the penetration of x – rays will be moveto lesser density, the penetration of x – rays will be move
through them which shows as darker areas on the film.through them which shows as darker areas on the film.
 X – Rays technique is effective in locating cracks, slayX – Rays technique is effective in locating cracks, slay
inclusions, porosity, blow holes, pin holes etc.inclusions, porosity, blow holes, pin holes etc.
 X- Rays can be used for inspection of casting in all type ofX- Rays can be used for inspection of casting in all type of
metals, like steel, aluminum, magnesium etc.metals, like steel, aluminum, magnesium etc.

58. Ultrasonic TestingUltrasonic Testing
 Ultrasonic Testing (UT) uses high frequency soundUltrasonic Testing (UT) uses high frequency sound
energy to conduct examinations and make measurements.energy to conduct examinations and make measurements.
 Ultrasonic testing is based on piezoelectric effect whichUltrasonic testing is based on piezoelectric effect which
converts electrical energy to mechanical energy thusconverts electrical energy to mechanical energy thus
generating ultrasonic wavesgenerating ultrasonic waves
 Ultrasonic waves are generated when a high frequencyUltrasonic waves are generated when a high frequency
alternating current of about a million times per second isalternating current of about a million times per second is
impressed across the forces of piezoelectric materials likeimpressed across the forces of piezoelectric materials like
quartz crystal.quartz crystal.
 The crystal expands in full half of the cycle and contractsThe crystal expands in full half of the cycle and contracts
when the electric field is increased, thus producingwhen the electric field is increased, thus producing
mechanical vibrations.mechanical vibrations.

59. UT arrangementUT arrangement

61. Ultrasonic TestingUltrasonic Testing
 When there is a discontinuity (such as a crack) in the waveWhen there is a discontinuity (such as a crack) in the wave
path, part of the energy will be reflected back from the flawpath, part of the energy will be reflected back from the flaw
surfacesurface
 The reflected wave signal is transformed into an electricalThe reflected wave signal is transformed into an electrical
signal by the transducer and is displayed on a screensignal by the transducer and is displayed on a screen
 In the applet below, the reflected signal strength isIn the applet below, the reflected signal strength is
displayed versus the time from signal generation to when andisplayed versus the time from signal generation to when an
echo was received. Signal travel time can be directly relatedecho was received. Signal travel time can be directly related
to the distance that the signal traveledto the distance that the signal traveled
 From the signal, information about the reflector location,From the signal, information about the reflector location,
size, orientation and other features can sometimes besize, orientation and other features can sometimes be