Casting Defects - Sand Mold, Metal Casting
Introducing various metal
casting defects with many pictures by Dandong Foundry in
China. These are the common
sand casting defects
on the surface and inside of cast iron and cast steel parts.
1. Blowhole is a kind of cavities defect, which is also divided into
pinhole and subsurface blowhole. Pinhole is very tiny hole.
Subsurface blowhole only can be seen after machining.
2. Burning-on defect is also called as sand burning, which includes
chemical burn-on, and metal penetration.
Sand Burning Defect
3. Sand inclusion and slag inclusion are also called as scab or
blacking scab. They are inclusion defects. Looks like there are slag
inside of metal castings.
Sand Inclusion Defect
4. Sand hole is a kind of shrinkage cavity defect. They are empty
holes after sand blasting.
sand hole defect
5. Cold lap or also called as cold shut. It is a crack with round
edges. Cold lap is because of low melting temperature or poor gating
Cold Lap Defect
6. Joint flash is also called as casting fin, which is a thin
projection out of surface of metal castings. Joint flash should be
removed during cleaning and grinding process.
Joint Flash Defect
7. Misrun defect is a kind of incomplete casting defect, which
causes the casting uncompleted. The edge of defect is round and
8. Shrinkage defects include dispersed shrinkage, micro-shrinkage
and porosity. For large porosity on the surface, you could see them easliy, but for small dispersed shrinkage, you may see them after machining.
Porosity Shrinkage Defect
9. Shrinkage cavities are also called as shrinkage holes, which is a
type of serious shrinkage defect, you can see them easily on the rough surface of the metal castings.
Shrinkage Cavity Defect
10. Shrinkage depression is also a type of shrinkage defect, which
looks like depressed region on the surface of metal castings.
Shrinkage Depression Defect
11. Elephant skin is a type of surface defect, which cause irregular
or wrinkle shapes surfaces.
Elephant Skin Defect
12. Veins defect is also called as rat tail, which looks like many
small water flow traces on the surface of metal castings.
13. Rough surface, coarse surface is also a kind of surface defect.
Normal rough surfaces can not be judged as defects, but too rough
and uneven in surface will be a defect.
Rough Surface Defect
14. Mismatch in mold defect is because of the shifting molding
flashes. It will cause the dislocation at the parting line.
Mismatch Mold Defect
15. Mechanical damage is because the damage during machining or
Mechanical Damage Defect
16. Slag inclusion is also called as exogenous inclusion, entrapped
Slag Inclusion Defect
17. Raised mold defect. Because of the flotage of liquid metal, the
mould flasks are raised, which caused the top part of casting become
higher or thicker than lower part.
Raised Mold Defect
18. Crack defects normally happen inside of metal castings. This
defect will reduce the physical properties of metal castings.
19. Abnormal nodulizing or under-nodulizing defects. Because of many
reasons, the spheroidization of graphite for ductile iron will be
affected, therefore, caused the bad spheroidization rate. By metalloscope, you can see very few graphite balls, and many worm-like grahite.
Abnormal Nodulizing Defect
20. Uneven hardness defect means the uneven hardness on the same
surfaces. When machining to harder positions, the machining will
become more difficult.
Uneven Hardness Defect
21. Sand drop is also called as sand crush. The sand mold drops part
of sand blocks, so they will cause the similar shaped sand holes or
Sand Drop Defect
22. Deformation will cause the oversized tolerance for flatness and
straightness. This is very common defect for long castings, and flat
castings with thin wall thickness. The reasons are the natural
deformation during cooling process in sand molds, or in air,
sometimes, the overly sand blasting also could cause this problem.
23. After welding repair, even after machining
or grinding, the welding marks will still be visual. As for
unimportant casting surfaces, if the client allow welding repair,
then these marks should be acceptable. But for high pressure-bearing
positions, or the client has clearly forbidden any welding repair,
then these marks will be taken as defects.
Welding Repair Marks
24. Chill iron could effectively reduce the
shrinkage for the key positions, so using chill iron is very common
in iron foundries. However, the edges of chill irons could be
clearly found by visual inspection. Some clients will not require to
grind them if these marks do not affect the appearance. However, the
clients could require the casting manufacturer to grind them just
for better surface looking. Please clearly notice that these marks
should not be judged as the casting defects. Refer to iron-foundry.com.
Chill Iron Marks
25. Chill defects are also called as "casting
chilling defects". The surface of the castings with this defect will
be extremely white, shiny and smooth. The left one of the parts on
the following photo is showing this defect. The defective castings
will be fragile and crispy, so during machining, some edges and tips
will be broken. This defect was caused by the low temperature of
sand molds, and prematurely out of sand molds, so the hot iron
become chilled quickly. The proper annealing heat treatment to them
could solve this defect.
Casting Chilling Defects
26. Massive free carbide. On metallograph, you could see many fish-bone free carbide. This is a serious defect of
cast iron material, normally happen on ductile iron. Because of inverse
chilling defects and poor inoculation, there will be mass free
carbide, which will cause fragile, poor welding property to ductile
iron castings. High temperature annealing heat treatment could
improve its quality.
Massive free carbide
27. Internal sweating, or called as cold short, short iron. There
are iron beans in the castings. This is because of unreasonable
gating design, which caused some liquid iron became beans suddenly,
then these beans were wrapped by other liquid irons. This is a
surface defect, but will cause serous problem if they located in key
Internal sweating, cold short, short iron
28. Stripping defect. There is very thin iron skin on the surface of
castings. Two layers. This is because of unreasonable gating system,
which caused very thin air layers existed. This defect is a surface
defect, so normally it can be grinded off. However, it should be
discarded if it is not just on the surface.
29. Cast iron graphite floatation. This defect is a kind of material problem. It is caused because of low pouring temprature and high content of carbon element. This defect is very harmful, will cause material very fragile. On the broken surface, you can see the obvious black surface caused by this defect.
Cast iron graphite floatation