Applied Dental Materials 1 Lecture 9 (Casting Failure Analysis)

Front 1

What are the 4 main categories of casting defects

Back 1

distortion

surface roughness/irregularities/discoloration

porosities

incomplete/missing detail

Front 2

What 3 things cause distortion?

Back 2

improper manipulation of wax

improper handling of wax pattern

uneven movement of pattern walls

Front 3

What is defined as relatively finely spaced surface imperfections whose height, width and direction establish the surface pattern

Back 3

surface roughness

Front 4

surface roughness of casting is (lesser/greater) than that of pattern

Back 4

greater

Front 5

surface roughness of casting depends on particle size of ____ and its ability to reproduce surface detail

Back 5

investment

Front 6

True or false, improper manipulation can lead to surface roughness AND surface irregularities

Back 6

True

Front 7

What is defined as isolated imperfections like nodules that do not characterize the total surface area?

Back 7

surface irregularities

Front 8

Surface irregularities can interfere with what step in the crown fitting process?

Back 8

seating

Front 9

What defect results in small nodules?

Back 9

air bubbles

Front 10

What defect results in minute ridges or veins?

Back 10

water films

Front 11

What defect results in fins or spines, or surface roughness?

Back 11

rapid heating rates

Front 12

What defect results in voids or porosity, or a tenacious carbon coating?

Back 12

underheating

Front 13

True or False, liquid:powder ratio does not affect surface roughness or irregularities

Back 13

False

Front 14

(prolonged/shortened) heating as well as (high/low) heating temperature result in surface roughness

Back 14

prolonged, high

Front 15

What is considered 'high' casting pressure? (in MPa)

Back 15

above 0.14 MPa

Front 16

True or False, the composition of the investment material can create surface roughness and irregularities

Back 16

True

Front 17

What is caused by solidification shrinkage of alloy before casting is completely filled?

Back 17

localized shrinkage porosity

Front 18

Where does localized shrinkage porosity usually occur?

Back 18

near the sprue-casting junction in the interior (sometimes exterior)

Front 19

Localized shrinkage porosity is created by a __ __ on the mold wall where molten alloy impinges

Back 19

hot spot

Front 20

The hot spot is the (first/last) to solidify

Back 20

last

Front 21

Hot spots result in what?

Back 21

suck back porosity

Front 22

What is caused by solidification shrinkage of fine grain alloys before microvoids can segregate to the liquid pool

Back 22

Microporosity

Front 23

Microporosity usually appear as small irregular voids within the body of the ___

Back 23

casting

Front 24

Microporosities occur if the casting temperature is too (high/low)

Back 24

low

Front 25

Pinhole and gas inclusion porosities are usually __ in shape

Back 25

spherical

Front 26

Which are larger, pinhole or gas porosities?

Back 26

gas

Front 27

(pinhole/gas) porosities are due to dissolution of gasses in molten metals [like Cu, Ag, Pt, Pd] that re expelled on solidification

Back 27

pinhole

Front 28

(pinhole/gas) porosities are due to entrapment of gas in molten metal

Back 28

gas

Front 29

Castings severely contaminated with gasses like sulfer are usually what color when removed from investment? Will pickling clean these?

Back 29

black

no, not easily

Front 30

What causes subsurface porosities?

Back 30

unknown; but might be caused by the simultaneous nucleation of solid grains and gas bubbles at the first moment that the alloy freezes at the mold walls

Front 31

How can subsurface porosities be diminished?

Back 31

control rate at which molten metal enters mold

Front 32

An entrapped-air porosity is also known as what?

Back 32

back-pressure porosity

Front 33

Entrapped-air porosity can produce large (concavities/convexities) at cavity surface of crown or MOD casting

Back 33

concavity

Front 34

What is caused by the inability of air in the mold to escape through pores in the investment?

Back 34

entrapped-air porosities

Front 35

What is caused by a pressure gradient that displaces air pocket towards the end of the investment via the molten sprue and button?

Back 35

entrapped-air porosities

Front 36

If solidification occurs BEFORE the entrapped air can escape, you get what defect? Is this found on the outside or inside of casting?

Back 36

entrapped-air porosity, outside

Front 37

Incidence of entrapped air porosities is (increased/decreased) in dense modern investment

Back 37

increased

Front 38

Incidence of entrapped air porosities is (increased/decreased) by an increase in mold density produced by vacuum investing

Back 38

increased

Front 39

Incidence of entrapped air porosities is (increased/decreased) by tendency for the mold to clog with residual carbon when the low-heat technique is used

Back 39

increased

Front 40

Factors that (slow/speed up) the venting of gases can cause entrapped-air

Back 40

slow

Front 41

What 4 things eliminate entrapped-air porosities?

Back 41

proper burnout

adequate mold and casting temp

sufficiently high casting pressure

proper liquid/powder ratio

Front 42

Thickness of investment between to of pattern and end of casting is less than or equal to __mm

Back 42

6mm

Front 43

Label all colors with either "increased", "decreased", or "no effect"

Back 43

decreased - green, red, orange, purple
increased - blue
grey - no effect

Front 44

If molten alloy is somehow prevented from filling the mold, this results in what?

Back 44

incomplete casting

Front 45

What two things can prevent alloy from filling mold?

Back 45

insufficient venting of mold

high viscosity of fused metal

Front 46

If the alloy is heated too (high/low), it will be too viscous and not properly fill the mold

Back 46

low

Front 47

If the casting pressure is too (high/low), you get a dull, rounded, and incomplete margins

Back 47

low

Front 48

If you don't completely eliminate all wax residue, this can result in what?

Back 48

incomplete casting

Front 49

When too many combustion products remain in the mold and fill pores in investment material, you have (increased/decreased) venting of air

Back 49

decreased

Front 50

Contact of molten alloy with moisture or wax particles produces and explosion and creates __ pressure, preventing filling of mold

Back 50

back

Front 51

Incomplete elimination of wax results in (dull/shiny), incomplete, rounded margins die to what gas in the residual wax?

Back 51

shiny, carbon monoxide