Defects in Casting

Question 1

Metallic Projections

Answer 1

1) Fins & Flash
- Material squeezes out between 2 halves
2) Swells
- enlargement of mold cavity localized by pressure

Solution: increase strength of mold

Question 2

Defective Surface Causes

Answer 2

• Wall Erosion
• Pouring too fast
• overheating

Question 3

Defective Surface Solutions

Answer 3

• Slow down pour
• Reduce temp of liquid
• Add additives to sand

Question 4

Porosity Causes

Answer 4

• Thick regions of cast solidify slower

- Thin regions block thick regions if solidified faster

Question 5

Porosity solution

Answer 5

Design cast to have runners go to thick parts of the mold

• Shorten sprue/add well
• Purge metal with inert gas

Question 6

3 types of Cavities

Answer 6

• Porosity (Trapped Gases)
• Blowholes
• Pin Holes

Question 7

3 types of Discontinuities

Answer 7

• Cracks
• Cold/Hot tears
• Cold Shuts

Causes: (stress concentration)
Solution: (avoid sharp corners)

Question 8

Cold Shuts Solutions

Answer 8

• Increase pouring temps

- Increase pour velocity

Question 9

Incomplete casting (2 Types)

Answer 9

Metal doesn’t fill the cavity completely

• Mis-runs
• Runouts

Question 10

Mis runs

Answer 10

Causes:

• Premature solidification
• insufficient volume of metal

Solution:
-increase pouring temp to increase fluidity

Question 11

Run outs

Answer 11

Causes:
-Loss of metal after pouring

Solution:
-Modify parting line or gating system

Question 12

Incorrect Dimensions

Answer 12

Causes:

• Shrinkage
• Uneven contraction
• Uneven flow

Solutions:
-Break up flat surfaces with staggered ribs

Question 13

Inclusions

Answer 13

Causes:

• oxidation reaction
• Foreign material trapped in metal

Solutions:

• Decrease x-sec area to trap ‘dross’
• filters