casting procedures & defects pallavi

8/13/2019 Casting Procedures & Defects Pallavi

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CASTING PROCEDURES AND

DEFECTS

Presented by:Dr. Pallavi B. Gopeshetti,CODS, Dvg.


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Investing the pattern-investment materials-hand investing-vacuum investing-high & low heat technique-controlled water- added technique

Burnout of the wax pattern & heating of the ring Accelerated casting method Casting procedure-melting of the alloy-casting crucibles-casting machines -a) air pressure casting machinesb) vacuum pressure casting machinesc) centrifugal casting machines-casting technique Recovery & cleaning the casting Finishing the casting Cementing the casting

Gas torch flameElectrical energy


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CASTING DEFECTS-distortion-surface roughness & surface irregularities-porosities-discoloration-incomplete casting

References Conclusion


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INTRODUCTION


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HISTORY

WILLIAM H TAGGART(1855-1933), Hedemonstrated on fabrication of cast inlay restorationdeveloped in 1905 before the New York OdontologicalSociety in 1907.


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CASTING is defined as the process in which molten material ispoured into a mold and allowed to hardened into the shape of the

mold.

LOST WAX TECHNIQUE is so named because wax pattern of arestoration is invested in a investment material, then the pattern isburned out (lost) to create a space into which molten metal is placed

or cast.


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DIMENSIONAL CHANGES IN

LOST WAX TECHNIQUE

Wax shrinkage + metalshrinkage(1.25-2.5 )=setting expansion+ hygroscopicexpansion

+ thermal expansion


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ACCURACY OF THE LOST

WAX TECHNIQUE

Tolerance limit 0.05% ( 2m)


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STEPS IN METAL CASTING

PROCEDURESSTEP 1: cavity preparation in the toothSTEP 2: Direct wax pattern OR impression of the prepared toothSTEP 3: Preparation of the die from impression & indirect waxpattern on the dieSTEP 4: Preparing the wax pattern for investing, includes spruedesign, crucible former, casting ring & liners


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STEP 5: Investing the patternSTEP 6: Burnout of the wax patternSTEP 7: Casting proceduresSTEP 8: Cleaning the castingSTEP 9: Finishing the castingSTEP 10: Cementing the casting.


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STEP 1

CAVITY PREPARATION


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STEP 2

A) DIRECT WAX PATTERN Type I medium waxIndication.

B) IMPRESSION OF THE PREPARED TOOTH


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STEP 3A) PREPARING A DIE FROM IMPRESSION Most commonly useddental stone IV & V

Disadvantage.

Modifications.DIVESTMENT

Other die materials.

Recent advances

B) INDIRECT WAX PATTERN :type II soft waxDie spacer:


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Methods for removal of wax pattern MOD PATTERN

MO/ DO PATTERN CROWN PREPARATIONS


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STEP 4: PREPARING WAX

PATTERN FOR INVESTING

VARIABLES & PRINCIPLES OF SPRUEDESIGN

SPRUE is defined as

Purpose of the sprue


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SPRUE FORMERType of sprue formers

waxes metals plastics


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SPRUE DESIGNS


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5 PRINCIPLES OF SPRUEDESIGN

SPRUE DIAMETER : Diameter range: 6- 12 gauge( 4.1- 2mm)

Too large??? Too small??? Narrow sprues indicated in.

Large inlay- 14 gauge( 1.6mm) Small inlay- 16 gauge (1.2mm)

Large crowns, molars or metal ceramic crowns- 10 gauge (2.5mm)

Small crowns or premolars or partial coverage restorations- 12 gauge(2.0mm)


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SPRUE LENGTH: Average length

Too long sprue???

Too short sprue???

Large inlays: 4-5mm

Small inlays: 3-4mm Large & small crowns: 4-5mm


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SPRUE POSITION: Bulkiest portion of the pattern because.

Largest non-centric cusps.


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SPRUE ATTACHMENT: Flared attachment/ constricted attachment.

At the largest cross-section of the pattern.

Direct spruing

Indirect spruing


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Reservoir:


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SPRUE DIRECTION:

Away from thin delicate parts of the pattern

45 angulations

Not at 90 angulations


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CRUCIBLE FORMER:


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VENTING:


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CASTING RING:

Average size: 29mm(1 1/8 ) diameter38mm(1 ) in height

Split rings, flexible rubber rings.


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RINGLESS CASTING SYSTEM

Phosphate-bonded investments

Paper & plastic casting rings

Powercast ringless system- whip-mix


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CASTING RING LINERS:

Asbestos liners

Non-asbestos liners

Application wet

- dry

Aluminosilicate ceramic liner

Cellulose liner


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Advantage??


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PHOSPHATE- BONDED INVESTMENTS:-alloys with higher melting range(>1200c) like

metal ceramic restorations,

higher melting gold alloys, base metal( chrome- cobalt),

pure titanium & titanium alloys.

Properties:- Expansion

- Porosity

- Strength

- Temperature


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SILICA- BONDED INVESTMENTS:- Alloys with high melting range like Base metal alloys

Chrome- cobalt alloys

to make cast removable partial dentures

Disadvantage..


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3.25mm6mm

Wax patter

sprue

Crucible

former3.25mm

Investment

material

Casting ring

Ring liner

INVESTING TECHNIQ E


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INVESTING TECHNIQUE

Preparing the pattern- wetting agents

Pattern should not stand for >20-30 mins

Methods for investing-hand

-vacuum

Preweighing of powder & liquid


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Mechanicalmixer-100turns

Paintinvestmenton thepatternFill thecastingring

Forgypsum-bonded....Forphosphate-bondedinvestment

HAND INVESTING:


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VACUUM INVESTING:

VACUUM MIXING:

VACUUM INVESTING:


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VACUUM INVESTING:

Techniquevac-u-spat investor

Advantage ???


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LOW HEAT TECHNIQUE:NORMALSETTINGEXPANSION (0.7 )

HYGROSCOPICEXPANSION (1.5 )

LOW-HEATTECHNIQUE


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HIGH HEAT TECHNIQUE:NORMALSETTINGEXPANSION (0.7 )

THERMALSETTINGEXPANSION(1.25 )

HIGH-HEATTECHNIQUE


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CONTROLLED WATER ADDEDTECHNIQUE: Technique.

Why rubber rings ???

Purpose ???

STEP 6: BURNOUT OF THE WAX


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STEP 6: BURNOUT OF THE WAX

PATTERN Burnout ovens: manual, semiautomatic, fully programmable

Position of the ring in furnace


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Gypsum-bonded investments: Temp.- 650c-700c in 60mins & held at higher

temp. For 15-30mins

-2 stage: keep in 200c preheated furnace for 30 mins,later 480c for hygroscopic & 650c for thermal expansion &held for 45mins.


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Precautions:Avoid rapid heating of furnace Never heat above 700cCaSo4+ 4C CaS+4CO

3CaSo4+CaS 4CaO+4So4Burnout wax when invst. is still wet..


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Phosphate-bonded investment: Temp: ranges from 750c - 1030 c

Method: -slow till 315 c & rapid thereafter

-held in upper temp. for 30mins.


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After Burnout: Heating the ring ???

Immediately cast

Cherry Red color

ACCELERATED CASTING


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ACCELERATED CASTINGMETHOD

Conventional:1 hr bench setting for investment

1-2 hrs wax elimination

Accelerated casting method:15 mins bench setting15 mins wax burnout (815c)

STEP 7: CASTING PROCEDURE


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STEP 7: CASTING PROCEDUREMELTING OF THE ALLOYUSING TORCH FLAME:Types of gases: 1) natural gas( propane) & air

2) natural gas & oxygen

3) air & acetylene/oxygen & acetyleneTypes of tips.

Temp. 870-1000c

Typical flame.


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CONICAL FLAME


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USING ELECTRICAL ENERGYTypes:-electrical resistance

-induction melting

-direct-current arc melting


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ELECTRICAL RESISTANCEPrinciple.Advantage


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INDUCTION MELTING MACHINEPrincipleUsed for base metal, co- ch alloys, titanium alloys


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DIRECT CURRENT ARCMELTING MACHINEPrinciple

Tempexceeds 4000c

Disadvantage


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CASTING CRUCIBLESTypes1) Clay, graphite- crown & bridges, alloys of high noble metals

& noble types

2) Carbon-high noble crown & bridges, higher fusing gold basedmetal ceramic alloys.

3) Quartz, alumina, silica, ceramic - high fusing alloysof any type and the sensitive to carbons.


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CASTING MACHINESAIR PRESSURE CASTING MACHINE:Principle: -pneumatic forces

-CO2 or nitrogen..

- pressure of 10-15 psi

- thin sprue

Used for metal ceramic casts

VACCUM CASTING MACHINE


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Principle: -pneumatic forces

Used for base metal alloys

CENTRIFUGAL CASTING MACHINE


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Types:*motor driven or spring driven*vertical rotating casting machine or horizontal

casting machine.

principle...broken arm principle


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p p

pressure- 30-40 psi (0.21- 0.28 Mpa)

Handle

Balancing weight

Metal

Crucible

Casting ring

Locking arm


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Amount of driving energy depends on:


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i. Density

ii. Porosity

iii. No. of sprues

iv. Length of the spruev. Diameter of the sprue

vi. Size of the pattern

vii. Amount of metalviii.Angulations & funneling of the sprue

ix. Configuration of the pattern & details.


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CASTING TECHNIQUE

STEP 8: RECOVERY & CLEANING


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OF THE CASTING

QuenchingAdvantage

pickling- Gypsum bonded investments:


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50% HCl- disadvantagemethod of pickling

precautionsother pickling solutions

Galvanic cell

Phosphate bonded investments:


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pUltrasonics

Cold hydrofluoric acid

Sand blasting.. AlO(50), 100psi

STEP 9: FINISHING OF THE


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CASTING

Initial stage: rubber, rag or felt wheels impregnated withabrasives like diamond, silicone carbide, emery, AlO, granet, sand,tripoli, rouge etc

Final stage: beilby layervarious oxides of tin & Al, small rag or chamois

buffing wheel, iron oxide rouge

Finally polishing compound removal

STEP 10: CEMENTING THE


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S 0: C G

CASTING

Shrinkage of 1.4- 1.5%

CASTING DEFECTS


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CASTING DEFECTS

CLASSIFICATION:

1. Distortion

2. Surface roughness & irregularities3. Porosity

4. Incomplete or missing details

INVESTMENTALLOYNodules

Ridges or veins

Fins

Surfaceroughness

Internalporosity

Incompletemargin

Gasbubble

DEFECT AFFECTING THE SHAPE


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DEFECT AFFECTING THE SHAPE

DISTORTIONCauses

Prevention

DEFECT AFFECTING SURFACE


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DEFECT AFFECTING SURFACE

SURFACE ROUGHNESSis defined as..SURFACE IRREGULARITIES is defined as

INVESTMENTALLOY

Nodules

Ridges or veins

Surfaceroughness

Fins

Causes & prevention


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& pAIR BUBBLES:

WATER FILMS:INVESTMENTALLOY

Ridges or veins


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RAPID HEATING RATES:fins

UNDERHEATING:

Fins

INVESTMENTALLOY


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PROLONGED HEATING:LIQUID/ POWDER RATIO:


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TEMRATURE OF THE ALLOY:CASTING PRESSURE: air pressure- 0.10-0.14MPa

centrifugal- 3-4 turns


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COMPOSITION OF THE INVESTMENT:ADA No. 2FOREIGN BODIES:


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IMPACT OF THE MOLTEN ALLOY:PATTERN POSITION: 3mm btn patterns

CARBON INCLUSIONS:

POROSITIES


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CLASSIFICATION:I) Solidification defects-localized shrinkage porosity-microporosity

II) Trapped gases-pin hole porosity-gas inclusion porosity

-subsurface porosityIII) Residual air-back pressure porosity


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SOLIDIFICATION DEFECTSLOCALISED SHRINKAGE POROSITY: suck-back porosity


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MICROPOROSITYFine grain alloys

TRAPPED GASES


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PIN- HOLE POROSITY

GAS INCLUSION POROSITY

SUB- SURFACE POROSITY

Internalporosity

Incompletemargin

Gasbubble

RESIDUAL AIR


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ENTRAPPED AIR/ BACK- PRESSUREPOROSITY

DISCOLORATION OF THE ALLOY


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DEFECT AFFECTING SIZE


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F FF G

INCOMPLETE CASTING:causes..a) insufficient venting, b) incomplete wax

elimination

prevention..

LARGE CASTINGSMALL CASTING


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COMPLETE CASTING FAILURE

REFERENCES


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1. Phillip`s Science Of Dental Materials-11thEdition, Kenneth J Anusavice

2. Restorative Dental Materials-11thEdition, Robert

G Craig, John M Powers3. Dental Materials & Their Selection-3rdEdition,

William J O`brien

4. Materials In Dentistry. Principles & Applications-2ndEdition, Jack L Ferracane

5. Essentials Of Dental Materials- S H Soratur

6 Contemporary Fixed Prosthodontics- 3rd


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6. Contemporary Fixed Prosthodontics- 3 Edition, Rosenstiel, Land, Fujimoto

7. Fundamentals Of Fixed Prosthodontics-3rdEdition, Herbert T Shillingburg

8. Textbook Of Operative Dentistry- 2ndEdition,

Vimal K Sikiri9. www.google.com

10. Department of prosthodontics, casting

laboratory. CODS, Davangere.

CONCLUSION
http://www.google.com/http://www.google.com/


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A DENT IN YOUR MERCEDES,

A CRACK IN YOUR MOBILE,A TEAR IN YOUR BRAND NEW LOUIS

PHILLIPPE,

A SCAR ON ABEAUTIFUL FACE,

A FRACTURE IN A TOOTH,

NOT SO DESIRABLE RIGHT???

NOR ARE CASTING DEFECTS


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