Casting defects can be classified into general defects common to all casting processes and defects related specifically to sand casting. General defects include misruns where the mold is not fully filled, cold shuts where two metal flows fail to fuse, cold shots where metal splatters during pouring, and shrinkage cavities caused by solidification shrinkage. Sand casting defects include sand blows caused by trapped gases, pin holes of small gas cavities, and penetration where molten metal enters the sand mold. Proper design and production processes seek to eliminate defects and ensure casting quality.
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.
Special Casting Processes
Centrifugal Casting
Semi centrifugal casting
Centrifuging
Die Casting
Gravity Die Casting
Pressure die casting
Hot chamber die-casting:
Submerged plunger die casting
Air blown or goose neck die casting machine
Investment Casting
Defects in Casting
Blow holes Casting Defects
Shrinkage
Crack
Inclusions
Lift and shift
Swell
Fins
Misrun and cold shut
Metal Penetration
Hard spot
Run out
Drop
Warpage
Lost Foam Casting defects are influential and complex, and cross each other.
The quality of raw and auxiliary materials is very important, in that case the procurement of material has to be very careful.
Fine process management and convergence, to strengthen the fine control of the process.
Responsibility is more important than the system, to strengthen discipline and supervision, assign responsibility to every staff.
Improve the theoretical quality of workers and good operating habits.
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The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
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Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
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A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
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Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
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2. Casting defects
• Gas defects
• Shrinkage cavities
• Molding material defects
• Pouring metal defects
• Metallurgical defects
3. Gas Defects
These defects are mainly caused by lower gas
passing tendency of the mould.
• Blow holes and open blows:-
Spherical, flattened or
elongated cavities caused by moisture left in
the core.
On the surface they are called open blows and
inside they are called blow holes
4. • Air Inclusion:-
The atmospheric and other gases absorbed by
molten metal in furnace, laddle or during flow in
mould, if not allowed to escape will weaken it.
• Pin hole Porosity:-
when the molten metal solidify, its solubility with
gases decreases. If hydrogen is present, it will
expell from molten metal and will cause a long
pin hole shape cavity. High pouring temperature
is main reason for that defect.
5. Shrinkage cavity
• These are caused by liquid shrinkage occurring
during the solidification of the casting. To
compensate for this, proper feeding of liquid
metal is required.
6. Moulding material
defects
These defects are caused by characteristics of
molding material
• Cuts & Washes:-
Appears as rough spots and area of excess metal
due to erosion of moulding sand by the
flowing molten metal.
Caused by poor strength of moulding sand or
molten metal flowing at high velocity.
7. • Metal penetration:-
When the molten metal enters the gap between sand
grains resulting in rough casting surface. This
could be due to coarse grain size or no mould
wash is applied to mould cavity.
• Fusion:-
fusion of sand grains with molten metal resulting in
brittle, glassy appearance. Reason may be lower
refractoriness of clay in moulding sand or higher
pouring temperature.
8. • Runout:-
A runout is caused when the molten metal leaks out
of the mould. Caused by faulty mould making or
faulty flask.
• Rat tails and buckles:-
caused by compression failure of the skin of mould
cavity. Due to excessive heat, sand expands
resulting in a small line on casting surface.
Buckles are rat tails that are severe.
Reasons may be poor expansion properties of sand
or high pouring temperature.
9. • Swell:-
Under the metallostatic force mould wall my
move back causing a swell in the dimension.
This may result in increased feeding
requirement.
• Drop:-
The dropping of loose moulding sand or lumps
from the cope surface into the mould cavity.
Caused by improper ramming of the cope
flask.
11. Pouring metal defect
• Misrun & Coldshut:-
Misrun is caused when the metal is unable to fill
the mould cavity completely.
Coldshut is caused when two metal streams
while meeting in the mould cavity do not fuse
together properly.
These are caused due to lower fluidity of molten
metal or section thickness is too small.
12. Metallurgical defects
• Hot tears:-
Since metal has low strength at higher
temperature, any unwanted cooling stress may
cause rupture of the casting.
• Hot spots:-
These are caused by chilling of the casting.
13. Casting Quality - Defects
• Misruns - unfilled region exists
– insufficient fluidity of melt
– low pouring temperature
– slow pouring
– cross-section too thin
• Cold shut - premature freezing at
fusion point. Similar reason as
misrun
14. Casting Quality - Defects
• Cold shots - Splattering during
pouring forming solid globules.
Redesign of pouring procedure or
gating system is needed.
• Shrinkage cavity - depression or
internal void caused by
solidification shrinkage. Solved by
proper riser design.
15. Casting Quality - Defects
• Microporosity -Network of small
voids caused by localised
solidification shrinkage. Caused
by the freezing manner of the
alloy.
• Hot tearing - Occurs at location
with high stress due to inability
to shrink naturally. Resolve by
mold collapsing or removing
from the mold immediately
after freezing.
16. Casting Quality -
Defects (Sand Casting)
• Sand blow - cavity caused by mold gas during pouring.
Low permeability, poor venting or high moisture content.
• Pin holes - small gas cavities.
• Sand wash - erosion of sand mold during pouring.
• Scabs - mold surface locally flakes off and embedded in
the casting during solidification.
17. • Penetration - penetration of molten metal into the
sand. Harder packing of sand is needed.
• Mold shift - shift of the cope relative to the drag.
• Core shift - shift of the core, usually vertical.
• Mold crack - mold strength insufficient, liquid metal
form a fin of the final casting.
Casting Quality -
Defects (Sand Casting)
18. Product Design Considerations
• Geometric simplicity - Avoid unnecessary complexity.
• Corners - Avoid sharp corners, generous fillet radius.
• Section thickness - Uniform section thickness to avoid
shrinkage cavities and hot spots.
• Draft - Facilitate removal of parts from mold. (1 deg. For
sand and 2/3 deg. for permanent)
• Use of cores - minimize the use of core
• Dimensional tolerance and surface finish - proper choice of
casting method.
• Machining allowances - For assembly purposes, typically 1.5
to 6 mm.
21. Casting Quality
• There are numerous opportunities for things
to go wrong in a casting operation, resulting in
quality defects in the product
• The defects can be classified as follows:
– General defects common to all casting processes
– Defects related to sand casting process
22. A casting that has solidified before
completely filling mold cavity
Figure 11.22 Some common defects in castings: (a) misrun
General Defects: Misrun
23. Two portions of metal flow together
but there is a lack of fusion due to
premature freezing
Figure 11.22 Some common defects in castings: (b) cold shut
General Defects: Cold Shut
24. Metal splatters during pouring and solid
globules form and become entrapped
in casting
Figure 11.22 Some common defects in castings: (c) cold shot
General Defects: Cold Shot
25. Depression in surface or internal void
caused by solidification shrinkage that
restricts amount of molten metal
available in last region to freeze
Figure 11.22 Some common defects in castings: (d) shrinkage cavity
General Defects: Shrinkage Cavity
26. Balloon-shaped gas cavity caused by
release of mold gases during pouring
Figure 11.23 Common defects in sand castings: (a) sand blow
Sand Casting Defects: Sand Blow
27. Formation of many small gas cavities at
or slightly below surface of casting
Figure 11.23 Common defects in sand castings: (b) pin holes
Sand Casting Defects: Pin Holes
28. When fluidity of liquid metal is high, it may
penetrate into sand mold or core,
causing casting surface to consist of a
mixture of sand grains and metal
Figure 11.23 Common defects in sand castings: (e) penetration
Sand Casting Defects: Penetration
29. A step in cast product at parting line
caused by sidewise relative
displacement of cope and drag
Figure 11.23 Common defects in sand castings: (f) mold shift
Sand Casting Defects: Mold Shift
30. Foundry Inspection Methods
• Visual inspection to detect obvious defects
such as misruns, cold shuts, and severe
surface flaws
• Dimensional measurements to insure that
tolerances have been met
• Metallurgical, chemical, physical, and other
tests concerned with quality of cast metal