Final Casting distortions and causes matching Flashcards Preview

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Flashcards in Final Casting distortions and causes matching Deck (21)
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1
Q

air bubbles

A
  • small nodules on surface, normally ground off
  • from air entrapment on surface of the wax pattern during investing
  • vacuum investing and a wetting agent that air dries can alleviate this problem
2
Q

water films

A
  • investment becomes separated from surface of pattern

* water films cause veins or ridges***

3
Q

veins and ridge caused by?

A

due to water films and too high of W/P ratio used for investment

4
Q

too rapid heating

A

causes cracks, fins result in the final casting (fins=cracks=fast heating)

5
Q

high W/P ratio of investment

A

higher the W/P ratio the high rougher the casting

6
Q

prolonged heating or heating investment at too high a temp causes?

A
  • disintegration of investment which releasessulfur gases and roughens the sides of mold
  • sulfur containing gold alloy demonstrates a black surface, brittle, and doesn’t pickle
7
Q

overheating a alloy causes

A

surface roughened casting

*bc an overheated alloy attacks the surface of the investment when it impacts the mold

8
Q

foreign bodies cause?

A

well-defined deficiencies in the surface of the casting

9
Q

localized shrinkage porosity? eliminated how?

A

incomplete feeding of molten metal during solidification

*eliminated by flaring the point of sprue attachement pattern and redicing the casting temperature by 85 degrees

10
Q

suck-back porosity is a type of?

A

localized shrinkage porosity

11
Q

microporosity

A

occurs if solidification rate is too high (especially in fine grained alloys) because the mold or casting temps were too low
**small irregular voids within bulk of casting

12
Q

pinhole porosity

what dissolves oxygen and hydrogen?

A

due to gases being dissolved in the metal during melting; avoided by adjusting flame and only using reducing zone of flame

  • Ag and Cu dissolve oxygen
  • Pt and Pd dissolve oxygen and hydrogen
13
Q

gas inclusions?

A

appear as large spherical voids which are caused by gas entrapment during melting

14
Q

back pressure porosity

A

“pocket” on the cavity side of the casting

*eliminated by using proper mold and casting temps, proper W/P ratio, position wax 1/4” from rim of cast

15
Q

incomplete casting due to incomplete wax elimination

A

pores of investment filled with residual combustion products preventing air from being vented from mold space
*ROUND, SHINY MARGINS

16
Q

incomplete casting due to low W/P ratio

A

the investment is too dense to allow air space to escape

*rounded but DULL margins (incomplete waxing causes shiny margins)

17
Q

blackened surface on a gold alloy caused by?

A

burning out a gypsum investent in a 730 degree C oven

18
Q

fins on casting caused by?

A

placing a room temperature, gypsum investment mold directly into a 650 degree C oven (heats too fast)

19
Q

sharply defined irregulat pores cuased by?

A

careless handling when removing the crucible former and sprue former from the investment mold

20
Q

incomplete csting with round. shiney margins caused by?

A

incomplete wax elimination

***using minimum burn out times with a low heat, hygroscopic technique

21
Q

nodules (spheres) of alloy on the casting surface

A

investing without vacuum