Risers and Casting Defects in Metal Casting Process

RISERS
Mainly used for
Reducing the shrinkage problem in the casting.
Promotes direction solidification
Comparison b/w open & blind riser
Open Riser
Having open top
Feeding force is gravity
force and atm. Pressure
Connected at the top/on
the side at the parting
line
Cylindrical in shape
Comparatively larger
Blind Riser
Closed at the top
Only gravity force
responsible for feeding
Can be placed at any
position in the mold
A rounded cavity
Smaller in size
Continue…..
Due to rapid cooling rate
insulating & exothermic
compounds is
recommended
Height depends on height
of molding box
Easy to mold
Slow cooling rate due to
surrounding molding sand
Height depend on feeding
requirement
Difficult to mold
Casting Defects
Deviation of  casting from its requirements
Flaws- due to improper appearance
Classification of Defects
Visually expectable
Exists under surface
Discovered by testing
1.
DEFECTS CAUSED BY PATTERN &
MOLDING BOX
1)
MISMATCH/MOLD
SHIFT
Mismatch of top &
bottom part of the
casting
2) Variation in wall thickness of casting-
    
due to oversize dimensions
3) Fins, Fash and strain-
 
occurs at parting line.
 
mold movement makes casting thicker
4)crush-
  
displacement of sand during mold closing
 
 
2.  
DUE TO IMPROPER SAND
CASTING
1)
BLOWHOLES-
smooth round holes
visible at surface – open
holes
May occur in cluster
/one large smooth
depression
Causes of blow holes
Excess moisture in sand
Improper baked and inadequately vented core.
Presence of gas producing ingredients
Extra hard ramming of sand
2) 
DROP
mixing of sand into the
molten metal
Causes-
i.
Low green strength
ii.
Low mold hardness
iii.
Insufficient
reinforcement
 
3)
 SCAB-
penetration of molten
metal in sand
Causes-
i.
Too fine sand
ii.
High moisture content
sand
iii.
Local heating
iv.
Uneven ramming
4) 
PIN HOLES/POROSITY-
No of small holes present on
casting surface
Causes
-
High moisture in sand
Metal-mold reaction
5) 
HOT TEARS-
internal/ external cracks with ragged edges
Causes-
i.
High sulphur content
ii.
Low pouring temperature
iii.
very hard ramming
iv.
high dry & hot strength
v.
Too much shrinkage
6) 
 MISRUN-
Incomplete filling of casting
before solidification
Causes-
i.
Too cold metal
ii.
Too thin casting
iii.
Too small gates
7) COLD SHUTS-
Inability of fusing metal coming from 2 gates
8) SLAG HOLES
9) SHRINKAGE DEFECTS
DEFECTS DUE TO MOLTEN METAL
1)
SAND CUTS & WASHES-
Flow of molten metal over mold
/core
Causes-
i.
Soft ramming
ii.
Insufficient draft
iii.
Improper gating system
WARPAGE
HARD SPOTS
SWELLS
INCLUSIONS
FUSION
MELTING FURNACES
used to melt the metal
Remelting created by combustion of fuel,
electric arc, electric resistance
Blast furnace for melting
Electric arc furnace for remelting
SELECTION CRITERION
 cost
Type of metal to be melted
Quality required
Flexibility
Melting efficiency
Degree of control
Furnace for melting
Grey cast iron
Cupola
Air (reveberatory)
Rotary
Electric arc
Steel
Open hearth
Electric
converter
Non-ferrous metals
Crucible
Pot
Air
Rotary
Induction
Electric arc
CUPOLA FURNACE
Melt scrap metal
Economical for gray, nodular, malleable cast Fe
Fuel used
 high grade low sulphur coke
Anthracite coal
Or  C- briquettes
CONSTRUCTION
Cylindrical shell of
6-
10
 mm thick
plate
Tuyeres
dimensions-
50
mm* 
150
mm
Upto 
75cm dia
cupola 3-4 tuyeres
used
CONSTRUCTION
Normal air pressure
12”-16” water gauge for small cupola
16”-35” for large
Capacity- 1-15 tons/heat
Height – 2.5 m - 4 m & 6 m
Inside dia- 75 cm – 2.5m
CUPOLA OPERATION
PREPARATION  OF CUPOLA
Cleaning repairing operation
Patching-(
2 parts ganister/silica & 1 part fireclay)
Cupola block-
Si -  52% -62%
Al-  31%-43%
Titania-  1.5%-2.5%
Fluxing oxides- 3%- 6%
LIGHTNING THE FIRE
Started 
3
 hrs before working
Can be lighten by-
Electric spark ignitor
Gas torch
CHARGING OF CUPOLA-
Adding layers of flux ,iron & coke
Commonly used flux-
CaCO
3
Na2CO3
CaF2
CaC2
Avoid large amount of flux
Amount – 2% - 4% by weight of metal
Fuel used
Low S coke, anthracite coal & carbon briquettes
Metal fuel ratio-   4:1-12:1
Metal charge consists
Pig Fe -30%
Scrap iron -30%
Returns -40%
MELTING
soaking period- 30 min
SLAGGING AND METAL TAPPING
collect slag
Collect metal into the ladle
DROPPING DOWN THE BOTTOM
Shut down the cupola
ZONES OF CUPOLA
WELL
Collect
 
molten metal
SUPERHEATING COMBUSTION/ OXIDIZING ZONE
15-30cm above tuyere level
C, Mn, Si react with O
2
Amount of heat generated-
 14452 BTU/ pound
Temperature 1550 -1850 degree C
REDUCING ZONE/ PROTECTIVE ZONE
Temperature- 1200 degree C
                C + CO
2 
 
2CO  - heat(2910BTU)
MELTING ZONE
90cm above coke bed
Temperature- 1600 degree C
3Fe +2CO 
 Fe
3
C +  CO
2
PREHEATING ZONE
Melting zone – bottom of charging door
Temperature about 1100 degree C
STACK ZONE
Exhaust
Stack gases contains
Nitrogen-76%, 12% CO
2
, CO
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Risers are crucial in reducing shrinkage problems during casting by promoting directional solidification. Open versus blind risers have distinct characteristics affecting feeding and positioning within the mold. Rapid cooling rate and use of insulating compounds impact the efficiency of casting, while defects caused by pattern and sand casting mismatches can result in variations in thickness, fins, and crush defects. Identifying and classifying defects in casting is essential for quality control in the metal casting process.

  • Metal Casting
  • Risers
  • Casting Defects
  • Defect Classification
  • Casting Process

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  1. RISERS http://upload.wikimedia.org/wikipedia/commons/thumb/b/bb/Casting_riser_types.svg/400px-Casting_riser_types.svg.png

  2. Mainly used for Reducing the shrinkage problem in the casting. Promotes direction solidification

  3. Comparison b/w open & blind riser Open Riser Having open top Feeding force is gravity force and atm. Pressure Connected at the top/on the side at the parting line Cylindrical in shape Comparatively larger Blind Riser Closed at the top Only gravity force responsible for feeding Can be placed at any position in the mold A rounded cavity Smaller in size

  4. Continue.. Due to rapid cooling rate insulating & exothermic compounds is recommended Height depends on height of molding box Easy to mold Slow cooling rate due to surrounding molding sand Height depend on feeding requirement Difficult to mold

  5. Casting Defects Deviation of casting from its requirements Flaws- due to improper appearance

  6. Classification of Defects Visually expectable Exists under surface Discovered by testing

  7. 1. DEFECTS CAUSED BY PATTERN & MOLDING BOX MISMATCH/MOLD SHIFT Mismatch of top & bottom part of the casting 1)

  8. 2) Variation in wall thickness of casting- due to oversize dimensions 3) Fins, Fash and strain- occurs at parting line. mold movement makes casting thicker 4)crush- displacement of sand during mold closing

  9. 2. DUE TO IMPROPER SAND CASTING 1) BLOWHOLES- smooth round holes visible at surface open holes May occur in cluster /one large smooth depression

  10. Causes of blow holes Excess moisture in sand Improper baked and inadequately vented core. Presence of gas producing ingredients Extra hard ramming of sand

  11. 2) DROP mixing of sand into the molten metal Causes- i. Low green strength ii. Low mold hardness iii. Insufficient reinforcement

  12. 3) SCAB- penetration of molten metal in sand Causes- i. Too fine sand ii. High moisture content sand iii. Local heating iv. Uneven ramming

  13. 4) PIN HOLES/POROSITY- No of small holes present on casting surface Causes- High moisture in sand Metal-mold reaction

  14. 5) HOT TEARS- internal/ external cracks with ragged edges

  15. Causes- i. ii. Low pouring temperature iii. very hard ramming iv. high dry & hot strength v. Too much shrinkage High sulphur content

  16. 6) MISRUN- Incomplete filling of casting before solidification Causes- i. Too cold metal ii. Too thin casting iii. Too small gates

  17. 7) COLD SHUTS- Inability of fusing metal coming from 2 gates

  18. 8) SLAG HOLES 9) SHRINKAGE DEFECTS

  19. DEFECTS DUE TO MOLTEN METAL 1) SAND CUTS & WASHES- Flow of molten metal over mold /core Causes- i. Soft ramming ii. Insufficient draft iii. Improper gating system

  20. WARPAGE HARD SPOTS SWELLS INCLUSIONS FUSION

  21. MELTING FURNACES used to melt the metal Remelting created by combustion of fuel, electric arc, electric resistance Blast furnace for melting Electric arc furnace for remelting

  22. SELECTION CRITERION cost Type of metal to be melted Quality required Flexibility Melting efficiency Degree of control

  23. Furnace for melting Grey cast iron Cupola Air (reveberatory) Rotary Electric arc Steel Open hearth Electric converter

  24. Non-ferrous metals Crucible Pot Air Rotary Induction Electric arc

  25. CUPOLA FURNACE Melt scrap metal Economical for gray, nodular, malleable cast Fe Fuel used high grade low sulphur coke Anthracite coal Or C- briquettes

  26. CONSTRUCTION Cylindrical shell of 6-10 mm thick plate Tuyeres dimensions- 50mm* 150mm Upto 75cm dia cupola 3-4 tuyeres used A tuyere

  27. CONSTRUCTION Normal air pressure 12 -16 water gauge for small cupola 16 -35 for large Capacity- 1-15 tons/heat Height 2.5 m - 4 m & 6 m Inside dia- 75 cm 2.5m

  28. CUPOLA OPERATION PREPARATION OF CUPOLA Cleaning repairing operation Patching-(2 parts ganister/silica & 1 part fireclay) Cupola block- Si - 52% -62% Al- 31%-43% Titania- 1.5%-2.5% Fluxing oxides- 3%- 6%

  29. LIGHTNING THE FIRE Started 3 hrs before working Can be lighten by- Electric spark ignitor Gas torch

  30. CHARGING OF CUPOLA- Adding layers of flux ,iron & coke Commonly used flux- CaCO3 Na2CO3 CaF2 CaC2 Avoid large amount of flux Amount 2% - 4% by weight of metal Fuel used Low S coke, anthracite coal & carbon briquettes

  31. Metal fuel ratio- 4:1-12:1 Metal charge consists Pig Fe -30% Scrap iron -30% Returns -40%

  32. MELTING soaking period- 30 min SLAGGING AND METAL TAPPING collect slag Collect metal into the ladle DROPPING DOWN THE BOTTOM Shut down the cupola

  33. ZONES OF CUPOLA

  34. WELL Collect molten metal SUPERHEATING COMBUSTION/ OXIDIZING ZONE 15-30cm above tuyere level C, Mn, Si react with O2 Amount of heat generated- 14452 BTU/ pound Temperature 1550 -1850 degree C

  35. REDUCING ZONE/ PROTECTIVE ZONE Temperature- 1200 degree C C + CO2 2CO - heat(2910BTU) MELTING ZONE 90cm above coke bed Temperature- 1600 degree C 3Fe +2CO Fe3C + CO2

  36. PREHEATING ZONE Melting zone bottom of charging door Temperature about 1100 degree C STACK ZONE Exhaust Stack gases contains Nitrogen-76%, 12% CO2, CO

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