good morning friends in the previous lectures
we have learnt about the risering system and
the gating system now in this lecture let
us learn about the casting defects now what
is a casting defect a casting defect is an
irregularity in the metal casting process
that is undesired some defect or an irregularity
on the surface of the casting or inside the
casting which is not desirable this is a casting
defect some defects can be ignored or they
can be tolerated or some defects can be repaired
by some welding and so on
whereas some defects because of their severity
the casting has to be rejected so these are
the what say broad classification of the casting
defects so we can say that the casting defects
can be what say minute defects right and ah
ah what say medium scale defects and the large
scale defects that is the one classification
now there is another broad classification
this is the broad classification of the defects
defects due to evolution of the gases means
a gases used to arise from different sources
because of these gases some defects arise
so this is the first classification of the
casting defects next one defects due to pouring
of the melt melting means the molten metal
or the molten alloy now something is wrong
with the melt thats why some other defects
are arising so these are the defects due to
pouring of the melt now the third type is
defects due to metallurgical factors next
one defects caused by the moulding material
moulding material means the moulding sand
or the moulding medium so in this moulding
medium there is some defect thats why we are
getting these defects
next one defects caused due to other factors
next one defects due to the shrinkage so the
casting defects broadly can be classified
into six types and among them the first one
is the defects due to the evolution of the
gases now let us see what are the defects
falling under this category let us study one
by one then we will go on to the other categories
first let us see the defects due to the evolution
of gases under this category we have blowholes
pinhole porosity rat tail dispersed shrinkage
blister and so on
so these are the defects that arise due to
the evolution of gases first let us see the
blowholes now this is the typical appearance
of blowholes you can see smooth and semi round
holes on the surface of the casting so this
is a casting you can see these are all the
what say a smooth and semi round holes on
the surface of the casting so certainly this
cannot be tolerated and ah ultimately the
casting has to be rejected so this is one
of the severe defects that arise among the
castings now why this ah blowholes is arising
causes excessive moisture in the mould we
know that the moulding sand comprises of the
base sand next one it comprises of the clay
next additive and the moisture
when the moisture content is more than required
then what happens excessive steam will be
produced and because of the excessive steam
these blow holes can form so that is the first
reason responsible for the blowholes second
one is the slag in the metal reacts with carbon
in the metal and liberates carbon monoxide
now when we are preparing the molten metal
inside the furnace the slag will be collected
now what is this slag composed of slag is
the main ingredient of the slag is the silicon
oxide or the silicon dioxide
now the slag contains oxygen now it react
this oxygen in the slag reacts with the metal
right ah it reacts with the carbon in the
metal first of all does the metal contains
contain carbon yes cast iron contains carbon
steel contains carbon cast iron contains ah
carbon from two point one percent to four
percent whereas steel it contains carbon less
than two point one percent in all the cast
irons and in all the steels carbon is present
now the oxygen in the slag reacts with the
carbon in the molten metal and forms carbon
monoxide and this carbon monoxide comes outside
and it stays on the surface of the casting
that is how the blowholes will arise
now there is another reason iron oxide on
the mould wall reacts with carbon in the metal
and liberates carbon monoxide now iron oxide
on the mould wall from where this iron oxide
is coming we use the chills for what say directional
solidification or we use the chaplets for
supporting the cores now what are these chills
and chaplets made up of these are the metallic
elements most of the times these are the chills
are made up of what say steel ah components
now again if these are what say a rusted for
a long time what happens there is iron oxide
on the surface of the chills now this iron
oxide comes and reacts with the carbon in
the molten metal then what happens the oxygen
from the iron oxide comes and reacts with
the carbon in the molten metal and forms the
carbon monoxide this carbon monoxide yes it
comes outside and it stays on the surface
of the casting finally we get the blowholes
so these are the main causes of the blowholes
now let us see what are the remedial measures
provide vent holes yes no doubt there are
gases arising gases are the steam but provide
the vent holes when we ah make sufficient
vent holes all the gases that arise will be
escaping through the vent holes next one avoid
excessive compaction of the mould the moulding
sand should not be compacted then what is
required then what happens there is a term
we have learnt about one permeability what
is this permeability permeability is the ability
of the moulding sand to allow hot gases through
it
now thats why if the moulding sand is compacted
very tightly the permeability of the moulding
sand drastically comes down then the steam
and the hot gases cannot pass through the
what say ah neighboring grains of the moulding
sand then what happens the gas will be accumulated
inside the mould thats why we have to avoid
the excessive compaction of the mould next
one avoid excessive moisture in the moulding
sand we should not cross the required proportion
of the ah moisture in the moulding sand
next one extra care has to be taken to segregate
slag from the liquid metal this slag has to
be removed from the liquid metal there will
be a process called centrifuging by centrifuging
the slag can be collected and it can be segregated
then the molten metal is free from the slag
then only the molten metal should be poured
inside the moulding mould cavity next one
we use the chills and chaplets chills are
meant for directional solidification or rapid
cooling of the casting at the required locations
whereas chaplets are meant for supporting
the cores
now we have to check before placing the chills
before placing the chaplets inside the mould
cavity we have to check what is their condition
are they in good condition or are they rusted
if they are rusted they must be cleaned so
if we take that much care then we can minimize
the blowholes now ah we have seen completed
the blowholes now under the defects due to
the evolution of the gases we have the pinhole
porosity that is the second defect now let
us see the pinhole porosity
now this is the typical appearance of pinhole
porosity now this is a casting you can see
here small small what say holes are there
on the surface of the casting and the size
of this holes are as a small as the what say
a pinhead you can see a large number of uniformly
dispersed tiny holes on the surface of the
casting so this is the pinhole porosity whereas
in the blowholes they were what say big holes
on the surface of the casting whereas pinhole
porosity is a small holes as a small as the
head of a pin they will be dispersed everywhere
on the surface of the casting
so this is the typical appearance of pinhole
porosity now why this pinhole porosity is
arising inside a casting hydrogen is absorbed
by the molten metal inside the furnace and
also inside the cavity so this is the main
reason for the ah what say evolution of the
pinhole porosity the main factor that ah influences
the formation of the pinhole porosity is the
hydrogen this hydrogen is absorbed by the
molten metal inside the furnace what is happening
when we are melting the ah metal inside ah
in the open atmosphere the at at hydrogen
is present in the atmosphere
the hydrogen present in the atmosphere readily
comes and reacts with the molten metal now
the molten metal rapidly absorbs the hydrogen
now when we pour it inside the cavity that
time also it can absorb the hydrogen now as
the melt gets solidified as the molten material
gets solidified then what happens whatever
hydrogen it has absorbed it slowly liberates
outside it sends outside then what happens
it ah ah they dissolved hydrogen will be liberated
outside then it comes on the surface of the
casting
now small small holes are created because
of the presence of the hydrogen so this is
the a cause of the pinhole porosity now how
to prevent this what are the remedial measures
to prevent the pinhole porosity before that
ah let us see the solubility of hydrogen in
aluminum now if you see here this is the x
axis indicates the melt what say temperature
whereas y axis indicates the hydrogen solubility
now in the solid state you can see this is
the solubility this much is the solubility
now at the melting point you can see here
the solubility is almost four times than its
solubility in the what say solid state so
in the liquid state its ah what say hydrogen
solubility is drastically increasing now these
are the remedial measures one is the vacuum
melting instead of a melting the metal in
the open atmosphere if we melt it in the vacuum
then no what say atmospheric hydrogen will
come and ah interact with the molten metal
but this vacuum melting is quite expensive
next one vacuum degassing of course it may
not be possible for us to melt the metal in
the vacuum but after melting before pouring
it inside the moulding cavity we can do the
vacuum degassing whatever gases and whatever
hydrogen is absorbed by the molten metal it
will be removed by vacuum so this is another
remedial measure next one avoid very high
pouring temperatures now what happens is there
are two temperatures one is the melting temperature
is the temperature where the metal starts
melting but that is not enough for pouring
right at that temperature if we try to tap
the metal and try to pour ah before we pour
it may solidified right
so if we have to pour then the temperature
of the metal should be more than the melting
temperature this is known as the pouring temperature
and so the pouring temperature for ferrous
components is at least ah hundred degrees
above the melting temperature but if someone
keeps on melting to a very high pouring temperature
then what happens more hydrogen is absorbed
by the metal thats why avoid very high pouring
temperature next one let us see the third
defect under this first category defects due
to the evolution of the gases under that the
third category is the rat tail
what is this rat tail it is in irregular depression
on the surface of the casting similar to a
rat tail impression so this is the surface
of the casting and here we can see something
ah like the tail of a rat what say tail impression
if a rat is ah crawling on some surface then
we can detect some impression of its tail
and here we can see a similar impression on
the surface of the casting this is known as
the rat tail now what are the factors influencing
rat tail one is the moisture in the moulding
sand evaporates and turns into sand yes this
is well known to us
now as the what say a mould cools down the
steam condenses and forms a thin layer of
moisture between the mould surface and the
metal being solidified between mould surface
and the metal being solidified a thin layer
of steam is condensed now as the moulding
sand expands now what happens after sometime
the moulding sand can expand then the layer
of the moisture shears out to accommodate
the expansion of the sand now what happens
the thin layer of the moisture is ah sheared
due to the expansion of the sand now the expanded
sand comes here and because of that it leads
to a rat tail depression on the surface of
the casting
so that is how the rat tail generates the
rat tail impression on the casting generates
now what are the remedial measures measures
should be taken to reduce the mould wall movement
first of all why this is happening because
because of the mould wall movement if there
is no mould wall movement if there is no mould
wall expansion this rat tail would not occur
so we have to take measures to reduce the
mould wall movement and also the mould expansion
for that in the what say ingredients of the
moulding sand design are the in the moulding
sand design we have seen the role of the additives
like wood flour what it does it what say comes
between the neighboring sand grains
once this wood flour comes and occupies between
the neighboring sand grains even if these
two sand grains are what say expanding the
wood flour comes between the two neighboring
sand grains and ah it accommodates the expansion
of the sand grains the what is the net effect
the mould wall moment will be minimized so
additives like wood flour can be added to
the moulding sand to reduce the moulding sand
expansion now ah we have completed a blowholes
pinhole porosity and rat tail
now under the first category let us see the
dispersed shrinkage what is this dispersed
shrinkage so now this is the typical appearance
of the dispersed shrinkage now this is the
casting you can see here there are small shrinkage
cavities dispersed throughout the casting
these are all the small small cavities here
you can see this is one casting this is one
what say a small ah what say ah cavity shrinkage
cavity this is one small shrinkage cavity
these are all dispersed all over the surface
of the casting thats why it is known as the
dispersed shrinkage why this is happening
one is excessive moisture second one very
high pouring temperature
now these are the remedial measures appropriate
moisture and pouring temperature are to be
taken next one let us see the blister you
can see this is the typical appearance of
a blister now you this is the casting and
here we can see a bubble like bumps are there
so you can see here one kind of bubble like
bumps is here and here we can see another
bubble like bump and here also so we can see
these what say a bubble like bumps are known
as the blisters causes why these blisters
are arising
one is the gases trapped in the cavity cause
depressions on the moulding surface now the
gases will generate from different sources
due to different reasons now if these gases
are not escaping outside what will happen
they will be causing some depression to the
moulding what say surface now what will happen
a depression will be created because of the
pressure applied by the gases that are produced
then what will happen in the depression the
moulding what say a molten metal comes and
occupies then what will happen yes we can
see a projection on the surface of the casting
now finally the insufficient strength of the
moulding cavity at some locations because
of that this depression takes place and molten
metal comes and occupies here so this is the
blister now how to prevent this blister remedial
measures ensure sufficient and uniform compaction
of the mould if the compaction of the mould
is not sufficient then this kind of problems
arise and also the compaction should be uniform
now with this we are completing the a first
category that is the defects due to the evolution
of the gases
now let us see the defects due to the pouring
of the melt under this category we have mis-run
cold shut elephant skin inclusion and so on
first let us see the mis-run now this is the
typical appearance of a mis-run defect now
you can see here this is a casting and it
has got the ribs five ribs are there now you
can see this rib is perfectly cast this rib
is perfectly cast this rib is perfectly cast
and this rib is also perfectly cast now if
you see this rib and we can see some kind
of imperfection we can see here and here it
is ah not perfectly cast means ah the molten
metal has not ah occupied exactly in the narrow
surface or on the narrow cross section of
the rib this is the mis-run means molten metal
could not fill the thin section of the mould
cavity here
the cross section of this rib is very narrow
because of that the molten metal could not
occupy successfully this is a mis-run you
can see here this is another example this
is the casting and here the molten metal could
not occupy properly this is a mis- run this
is another example this is the casting and
here the molten metal could not occupy in
this region now this is another example you
can see here this is a turbine blade the turbine
blade actually if had it been successfully
cast it should come like this or it should
come like this it should come like this
but because the cross section of the blade
is very narrow the molten metal could not
occupy that narrow region that is how there
is a discontinuity this is the mis-run now
what are the causes of the mis-run defect
one is the insufficient fluidity the fluidity
is not sufficient thats why the molten metal
is not able to pass into that narrow region
of the casting next one low pouring temperature
if the pouring temperature is low then what
happens the viscosity will be more
once the viscosity is more it cannot penetrate
into narrow sections thats why ah we should
not go for the very low pouring temperature
next one too small ingates the ingates are
too small too narrow that is how the molten
metal is not able to pass through the small
ingates next one low pouring speed so these
are the four causes that influences the mis-run
now let us see the remedial measures first
one increase the pouring temperature this
is the main reason which influences the mis-run
defect increase the pouring temperature always
the pouring temperature must be at least hundred
degrees above the melting temperature then
only ah the fluidity will be sufficient to
flow into the even into the narrow regions
next one increase pouring speed next one make
ingates larger so these are the remedial measures
to prevent the mis run defect now under the
second category we have the cold shut what
is this cold shut now here we can see this
is a casting and here there is an ingate and
here there is an ingate and ah what say two
streams are flowing through these two ingates
one stream is coming like this and another
stream is coming through this ingate these
two streams are coming and they are supposed
to meet here and they are supposed to fuse
together perfectly and become one casting
one component
now what happens these two molten streams
from different ingates are not fused together
properly causing a discontinuity or a weak
spot at the center or it at some other position
they were not able to fuse together though
apparently it look after solidification it
looks to be a single casting inside there
is a in a in unseen discontinuity or a weak
spot here there is a discontinuity these two
streams could not fuse together this is the
cold shut now what are the factors influencing
the cold shut defect
now before that let us see one more example
this is a cold shut defect in a bronze screw
nut this is the bronze screw nut now ah right
so here the one stream is coming like this
and another stream is coming like this but
they are not fused together properly then
what will happen after solidification after
solidification also it looks like a one casting
only but if you try to what say strike it
these two will be separated into two halves
here at the center there was a discontinuity
that is how it got separated into two parts
so this is the cold shut defect
now what are the causes longer distance between
the ingates next one large surface to volume
ratio now longer distance between the ingates
what happens when the distance between the
ingates is very large by the time the mould
the molten metal is entering like this by
the time it reaches the center or by the time
it reaches the other stream it travels very
long distance and ah the moulding what say
medium are the ah mould rapidly absorbs its
heat because of that it its temperature drastically
comes down and by the time it comes to the
center the pouring its temperature will be
very low then what happens the viscosity will
be very high then because of that they are
not able to fuse properly
second reason is large surface area to volume
ratio what is this large surface area to volume
ratio large means this ratio is very large
surface area to volume ratio is very large
means what does it mean surface area is very
large surface area is very large means what
happens more heat is dissipated to the mould
wall because of the large surface area of
the casting then what happen within no time
its temperature will be falling down by the
time the two streams come to the center they
will be reaching very low temperature they
will be obtaining very less temperature and
because of that they are not able to fuse
together
so this is the another reason large surface
area to volume ratio now what are the remedial
measures to prevent the cold shut one is use
more number of ingates next one secondary
is second ah remedial measure increase the
pouring temperature we know that because of
the design of the casting or because of the
large surface area of the casting we know
that the melt loses its ah what say temperature
and heat by the time it travels to the center
that be the case increase the pouring temperature
than the usual practice then this problem
can be minimized
next one we have the elephant skin under the
second category what is this elephant skin
now this is the typical appearance of a elephant
skin defect you can see here this is the casting
and we can see ah somewhere on the surface
of the casting some kind of projection is
there and it looks like elephant skin right
so this is an extreme case of magnesium silicate
contamination in the melt in the melt there
is a what say a mixing of the magnesium silicate
because of that say different streams come
and they are not able to fuse properly right
the melt is contaminated by the magnesium
silicate
next one when separate streams meet the surface
films will not allow complete fusion then
this results in the formation of the elephant
skins like surface so these are the ah what
say causes of the elephant skin now how to
prevent this ensure proper separation of slags
from the melt next one under the second category
we have the inclusion defect what is inclusion
undesirable foreign material present in the
metal right like oxide slag death and so on
so this is the casting and this is the inclusion
slag inclusion right and here we can see ah
these are the foreign particles oxides are
slags and these will be removed at a later
stage and a depression will be caused on the
casting
and again we can see here this is a inclusion
right undesirable foreign material present
in the metal like oxide slag that and so on
what are the main sources of inclusions from
where these inclusions are coming one is the
slag metal oxidation product products next
one refractory materials next one refining
agent residuals and next one mould materials
and erosion products from the moulds and cores
so there are different sources from where
foreign materials will come and they will
be occupying on the surface of the cavity
or surface of the casting one could be slag
metal oxidation product or the refractory
materials or the refining agent residuals
or the moulding materials and they may come
due to erosion
and eroded paints sometimes we use the scrap
in the furnace we take ah what say a what
say a unused and ah what say a scrap materials
and put it inside the furnace for melting
remelting and these scrap materials may have
the eroded paints and they will be collected
and they will be coming along with the melt
and they will be occupying on the surface
of the casting and they have the inclusions
they are the foreign materials next one the
sixth ah factor that is the endogenous inclusions
formed in consequence of the metallurgical
reactions in the metal
next one non dissolved inoculant allowing
addition of the residuals how inclusions are
harmful inside a casting one is deterioration
of the casting surface and its quality the
surface of the casting will be deteriorated
because of the inclusions next one deterioration
of the mechanical properties because of the
presence of the these ah what say inclusions
the mechanical properties will be deteriorated
next one the machinability of the casting
will be deteriorated after the solidification
is over we break the sand and we clean the
stand then we used to machine it for getting
the required geometrical tolerance for getting
the required surface finish it is tough time
because of the presence of the inclusions
the machinability will be deteriorated
next one casting leakage will be there next
one formation of the gas bubbles will be there
so these are all the consequences of the inclusions
in a casting now how to prevent these inclusions
what are the remedial measures one is the
skimming of molten metal before pouring the
inclusion may come through the molten metal
that be the case through the slags that be
the case the slag must be perfectly removed
from the molten metal for that we need to
skim the molten metal before tapping the molten
metal from the furnace
next one choosing a moulding sand with adequate
hot strength now if the moulding sand doesnt
possess required hot strength what happens
when we pour the molten metal the sand will
be damaged now this damaged sand could become
it it gets eroded and it can flow along with
the molten metal finally it becomes a foreign
material and it can cause a an inclusion so
always we have to choose a moulding sand which
has got the adequate hot strength
next one third remedial measure is placing
ceramic foam filters inside the gating system
these ceramic foam filters are ready made
foam filters that are available in a different
shapes different sizes now once we place the
ceramic foam filters inside the what say a
gating system now all the foreign materials
that are about to come inside the moulding
cavity we will be trapped and they will be
stopped near the foam filter now ah this is
a what say very effective method placing the
ceramic foam filters inside the gating system
so we need to learn little more about these
ceramic foam filters now position of the filters
inside the gating system where these are to
be positioned these ceramic foam filters one
is vertical position of the filter close to
the sprue nearer to the sprue nearer to the
choke this can be placed next one horizontal
position of the filter close to this sprue
it can be positioned in a horizontal way also
next one vertical position of the filter in
the distribution of the runner next one horizontal
position of the filter next one slanting position
of the filter in different ways the filters
can be positioned inside the gating system
now here we can see this is this sprue and
this is the choke and this is the sprue well
and here we can see this is the runner and
between the what say a sprue and the runner
and this is the filter vertical position of
the filter close to the sprue this is the
filter so this is one of the ways of placing
the filters now let us see the second way
horizontal position of filter close to the
sprue now this is the sprue and this is the
choke and this is the runner
we are placing the filter in a horizontal
way this way also we can place the filter
next one vertical position of the filter in
the distribution runner now this whole thing
is runner somewhere inside the runner we are
placing this filter so this is another way
of placing the filter next one horizontal
position of the filter somewhere inside the
runner here also the whole thing is runner
and here we are placing the filter this is
another way next one slanting position of
the filter
now this is the runner the position is placed
in a slant position not vertical not horizontal
now we have seen the different positions of
the filters inside the gating system now what
are the ah types of the filters one is the
ceramic strain strainer cores second one extruded
filters third one cloth filters fourth one
foam filters so these are the four types of
the filters available which can be kept inside
the gating system to prevent this inclusion
defects or to prevent the foreign materials
to come inside the moulding cavity
first let us see the ceramic strainer cores
ceramic strainer cores right strainer cores
are flat ceramic bodies they have straight
circular holes with diameter ranging from
four to ten mm their thickness ranges from
six to twelve mm now this is the ceramic strainer
core you can see here and they have straight
circular holes like this circular holes are
there and the molten metal is coming like
this and it passes through the what say a
strainer pour now if any impurity or if any
foreign material is present inside the molten
metal they will be stopped only only the pure
metal will be coming outside
now this is the ah position of the filter
and if we see from side we can see the filter
like this and we can see a different holes
are there several holes and the diameter will
be ranging from four to ten mm and the thickness
will be six to twelve mm so this is the shape
and what say construction of the ceramic strainer
core which is placed inside the gating system
next one what is the mechanism of filtration
in say in a ceramic strainer core filter how
does this ah strainer core filter stop the
what say a foreign material from entering
into the mould cavity
one is the filtration by straining next one
filtration due to cake formation next one
depth filtration due to adhesion now these
are the three ways by which a ceramic strainer
core can filter the foreign materials from
entering into the mould cavity let us see
this how they workout this is the filtration
by straining now this is the filter now the
molten metal is coming like this and it goes
like this now this is a hole on the strainer
core now this is a foreign body now what happens
this foreign particle cannot pass through
this small hole or the strainer core finally
it will be stopped
but the thing is it can stop only a big bigger
particles now what is happening here now small
particles are entering they will be passing
through right so that is the advantage is
it can stop the larger particles from entering
into the passing through the filter it cannot
stop the smaller particles next one filtration
due to cake formation now this is the filter
now what is happening is now the small in
the previous case we have seen the small particles
are ah coming inside now what happens is there
is another mechanism by which it can stop
the foreign materials by due to the cake formation
now all these what say a small small particles
they are collected on one side on the at the
entry of the strainer core like this now once
this cake is formed no more foreign materials
can enter into the filter only the pure metal
can enter pass through the filter so this
is the second mechanism by which a strainer
core can prevent the foreign particles from
entering into the mould cavity now this is
the third mechanism depth filtration due to
adhesion now ah previously we have seen that
it was a able to stop the larger particles
from entering into the filter
now if the small particles are going inside
now what is happening now the small these
the this is the filter now the small particles
are adhering to the filter particles due to
adhesion now this small particles ah can no
more go inside the moulding cavity why because
they are trapped by the strainer core due
to the adhesion so we have among the types
of the filters we have seen the ceramic strainer
cores now let us see the extruded filters
so this is the second type of the filters
how does it look like it looks like this
these are the extruded filters extruded filters
are also filters with straight runners they
are produced by extruding plastic ceramic
material through a die with a rectangular
square holes first one is the right ceramic
strainer cores so these are made up of the
ceramics whereas the extruded filters are
made up of the plastic ceramic material so
that way the material is different but the
construction is similar right they are produced
by extruding plastic ceramic material through
a die with rectangular square holes will be
there and here we can see this is the filter
and ah several what say ah holes are there
and they will be starting ah ah they will
be passing ah it will be there they will be
passing through the other side the holes
now this is the extruded filter with captured
inclusions now what is happening is it allows
small foreign particles to penetrate into
the holes now they will be captured here this
is the hole a rectangular hole inside the
what say this filter now a extruded filter
now it is they are captured here so this is
one of the mechanisms by which the the extruded
filters used to stop the ah inclusions from
entering into the mould cavity next one the
cloth filters this is the third type of the
filters
now these are the cloth filters they look
like this cloth filters are woven from refractory
textiles into shapes roughly similar to metal
gratings so the this is the ah what say typical
appearance of the cloth filters and cloth
filters for the pouring basin now ah usually
they are kept near the pouring basin now when
we place this ah near the pouring basin the
molten metal is poured like this and it passes
through that then it enters into the sprue
the choke and the gating system runner and
so on
now whatever be the what say foreign particles
coming along with the molten metal they will
be screened here at the pouring basin then
only they will go then in this process all
the foreign particles that are coming along
with the molten metal will be captured by
this cloth filter so this is the mechanism
of the cloth filter finally we have the foam
filters so this is widely use these foam filters
so these foam filters are based on a system
of mutually linked cells linked cells in the
shape of pentahedron
now this is the what say a shape of a single
cell of a foam filter it looks like this like
the in the shape of a pentahedron now these
are the of ah what say shapes and sizes of
the foam filters they are available in different
shapes and different sizes and ah these are
also having different holes here we can see
so many holes are there several holes are
there now what is the difference between the
holes of these foam filters and the holes
of the strainer cores and extruded filters
and we have seen ceramic strainer cores and
the extruded filters there also we have seen
holes
what is the difference here they the holes
were starting from the one side and they were
going up to the next side they were straight
holes for there in the case of the strainer
cores and the what say the other type the
extruded filters whereas in the foam filters
what is there the holes are different here
we can see ah the shape of a pentahedron and
again these are the different foam filters
the what is the mechanism of the ah foam filters
capture of the inclusions due to adhesion
in say in a foam filter
now this is the what say magnified view of
the foam filter so now this is the foam filter
what say cell here we can see and the impurities
are coming like this and they are captured
by the ah foam filter due to adhesion and
here we can see the what say inclusions are
captured here due to adhesion and here we
can see these are all the inclusions so these
are all the inclusions all these inclusions
all these foreign materials are what say captured
by the foam filters by adhesion
so these foam filters are highly effective
in most of the castings and here we can see
ah there is another benefit of the foam filters
and here here we can see this is the foam
filter and this is kept inside the gating
system now the molten material is coming like
this and until it has ah what say come to
the what say a foam filter there was turbulence
you can see here there is turbulence now when
it is passing through the foam filter this
turbulence will be minimized and we can see
almost there is no turbulence here very steady
what say a flow is there right transition
from turbulent to laminar flow of the metal
due to a filter
so this is the second advantage that we obtain
from the foam filters friends in this lecture
we have seen defects due to the evolution
of the gases and defects due to the pouring
of the melt and we have seen different defects
and they causes and we have seen ah the remedial
measures and finally in the second category
we have seen the inclusions and how to prevent
the inclusions and we have seen the concept
of the filters we have seen different types
of the filters and ah how does they what say
filter the foreign particles we have seen
in the next lecture we will see the defects
due to the metallurgical factors defects caused
by the moulding materials materials and so
on we will meet in the next lecture
thank you
