Lec 1/19? Investing and Casting

Question 1

Sprue former is attached to:

Answer 1

crucible former

Question 2

Direct surround investment material in casting:

Answer 2

ring liner, then casting ring

Question 3

investment material must be:

Answer 3

heat resistant

Question 4

Benefit of plastic prefabricated sprues:

Answer 4

added rigidity, minimizes distortion

Question 5

this can be used for multiple castings:

Answer 5

runner bar

Question 6

sprue allows for:

Answer 6

wax to escape mold, molten metal in

Question 7

is more or less turbulence desired as molten metal flows into sprue?

Answer 7

less

Question 8

What provides a reservoir to compensate for shrinkage during solidification of casting alloy?

Answer 8

Metal in sprue must remain molten slightly longer than the alloy that has filled the mold

Question 9

What is the crucible former usually made of?

Answer 9

rubber

Question 10

Function of crucible former:

Answer 10

base for the casting ring during investment

Question 11

Function of casting ring:

Answer 11

container for the investment while it sets and restricts the setting expansion of the mold

Question 12

Technique designed to allow unrestricted expansion of casting ring:

Answer 12

Ringless casting ring, uses plastic casting ring

Question 13

Investment to use with ringless technique:

Answer 13

higher strength, phosphate-bonded investment, usefull for high melting alloys that melt more

Question 14

Function of ring liner:

Answer 14

allow more expansion, slightly compressible

Question 15

What to do if you require increased setting expansion of the investment material.

Answer 15

Use a 2nd liner

Question 16

How to increase the hygroscopic expansion of the ring liner:

Answer 16

wet it

Question 17

TF? Wax has both high CTE and shrinkage.

Answer 17

T

Question 18

Why remelt, readapt, and resmooth wax margin directly before investing:

Answer 18

wax pattern tends to release ito incorporated strain

Question 19

Sprue size/gauge recommended for molar and metal ceramic patterns:

Answer 19

2.5mm (10-gauge)

Question 20

Sprue size/gauge recommended for premolar castings and most partial-coveage restorations:

Answer 20

20.mm (12 gauge)

Question 21

Where to attach sprue:

Answer 21

bulkiest, non critical part of the pattern, normally the largest non-functional cusp

Question 22

Cusps for sprue, #30:

Answer 22

MB or ML cusps (?)

Question 23

attach sprue w this:

Answer 23

sticky wax (goes in sprue as well)

Question 24

to reinforce joint bw sprue and cusp and allow a smooth flow of molten alloy:

Answer 24

inlay wax

Question 25

Attachment of sprue and crucible former:

Answer 25

wax pattern and sprue should be centered

Question 26

TO avoid shrinkage porosity:

Answer 26

position a reservoir of the sprue at the heat center

Question 27

Min distance to leave bw wax pattern and top of crucuble

Answer 27

6mm

Question 28

lid of crucible is __mm.

Answer 28

3mm

Question 29

is the reservoir typically closer to the crown or further from?

Answer 29

closer to

Question 30

Base of crucible is __mm.

Answer 30

3

Question 31

Types of investment materials:

Answer 31

gypsum, phosphate, or silica bonded

Question 32

investment material to use with metal alloys: ADA Type II, III, and IV:

Answer 32

gypsum bonded

Question 33

investment material to use with metal ceramic framework:

Answer 33

phosphate-bonded

Question 34

investment material to use with high-melting base metal alloys:

Answer 34

silica bonded

Question 35

Beauty cast is what type of investment?

Answer 35

gypsum bonded

Question 36

Spray mounted pattern w:

Answer 36

surfactant, gently blow excess liquid from pattern

Question 37

Trim this before burnout:

Answer 37

top glazed surface

Question 38

What to do if mold was allowed to set more than 12h:

Answer 38

rewet prior to burnout, soak 1-3m

Question 39

Removed this layer after burnout:

Answer 39

dense oxide layer

Question 40

Trim this once the investment has set and before burnout:

Answer 40

the "skin" (glassy part) at the top of the ring, remvoe rubber crucible former, place in oven

Question 41

Preheated oven for burnout is using this technique:r

Answer 41

apid technique

Question 42

Preheat temp for most alloys:

Answer 42

1200'F

Question 43

How long to heat the soak at final temperature for both rapid and standard techniques?

Answer 43

30m

Question 44

standard burnout technique:

Answer 44

cold oven, molds in oven at room temp, heat to desired temp at 25-40'F/ m

Question 45

For a complete casting, the casting force must be:

Answer 45

high enough to overcome the high surface tension of molten alloys, as well as the resistance of the gas within the mold.

Question 46

Casting force we use:

Answer 46

centrifugal force

Question 47

Heat sources for casting:

Answer 47

gas and compressed air torch, electricity

Question 48

steps to use gas and compressed air torch:

Answer 48

light gas, then turn on air flow valve

Question 49

zone within flame of torch:

Answer 49

unburnt gas --> burning gases (reducing atmosphere, hottest zone) --> burnt gas (oxidizing atmospheree)

Question 50

Direction and number of turns for casting anything but metal ceramic:

Answer 50

3, clockwise

Question 51

Direction and number of turns for casting metal ceramic:

Answer 51

4, clockwise

Question 52

Steps after winding arm and placing pin:

Answer 52

place crucible with preheated allop in machine, pull crucible away from cradle

Question 53

Function of the plux we sprinkle on alloy surface:

Answer 53

in fluidity, prevent or reduce oxidation (don't add to metal ceramic alloy)

Question 54

Place casting ring with molten alloy here:

Answer 54

in cradle

Question 55

Use tongs to move:

Answer 55

crucible platform into contact w casting ring

Question 56

How to get the pin to drop and the arm to release:

Answer 56

pull arm forward

Question 57

Do this after red glow is gone from button

Answer 57

submerge casting ring in cold water, break off investment from the casting and clean w stiff brush

Question 58

How to clean casting:

Answer 58

ultrasonically

Question 59

Can cause rough casting:

Answer 59

excess surfactant, improper water/powder ratio, excessive burnout temp

Question 60

Can cause large nodules:

Answer 60

air trapped during investment procedure

Question 61

Can cause nodules on occ surface:

Answer 61

excessive vibration

Question 62

Can cause multiple nodules:

Answer 62

inadequate vacuum during investment, improper brush technique, lack of surfactant

Question 63

Can lead to fins:

Answer 63

inc water/powder ratio, pattern too near edge of investment, premature heating (mold still wet), too-rapid heating, dropped mold

Question 64

Can cause incomplete casting:

Answer 64

wax pattern too thin, cool mold, or inadequate heating, not enough metal, insufficient casting force

Question 65

Can cause suck-back porosity:

Answer 65

improper pattern position too narrow or too long sprue