International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 7 - Mar 2014
Reducing the Rejection Rate by Removing the
Impurities from Sand
Nikhil Poulose#1 , Elias George*2,
#
M.Tech-Mechanical (production and industrial engineering)SSET,
MG University, Thrissur, KERALA, Assistant professor SSET*2
Abstract— The actual reason behind impurities in sand can be
found out by analysing the quality of sand used for moulding
and also the various moulding variables.These factors are then
cross checked with the standards priscribed in the British Cast
Iron Research Assosiation hand books.In the industry there are
two processes conventional moulding process and green sand
process.In the conventional moulding process major defects are
found.The major defects are shrinkage,blow hole,sand
inclusion,sand fusion.these are the major defects found in the
conventional moulding.
Keywords— Foundary,sand materials, testing of sand, moulding
I. INTRODUCTION
The topic ‘impurities in sand’ is being made the subject of this
particular study. This is one of the cause of defects that occur
in sand casting. The surface finish of a casting is dependent on
the moulding process. The mould materials as well as the
moulding variables a,part from other factors not related to
mould. The various factors are Poor treatment of sand ,Use of
different
type
of
sand
particles
used
in
moulding ,Accumulation of spend dead clay in the moulding
sand ,Use of badly compacted mould or cores due to Sand
moisture not throughly mixed or not possesing sufficient
flowability in clay bounded sand moulding, Exceeding bench
life of sand moulds or sand cores, Inadequate compaction of
moulds or cores in normal moulding.Pouring temperature of
the molten metal to be poured into the mould.These are some
of the reasons for surface defects over castings. In this
particular session the problem of sand fusion is being discused
in detail. The various possible factors for sand fusion and the
ways to aviod these factors are also discussed. This paricular
study was conducted in AUTOKAST LTD, Cherthala, Kerala
and the standards adopted are from the British Cast Iron
ResearchAssosiation (BCIRA) broad sheet. This is an
internationally accepted standard for foundries
II. RAW MATERIALS USED FOR SAND MOULDING
1. Clays
Illite(found in natural sand)
Kaolinie(china clay)
Montmonillonites(brentonite and fullers earth)
Sodium bentonite
Calcium bentonite(these are naturally occuring)
Sodium bentonite gives medium strength and high dry
strength.
ISSN: 2231-5381
Calciunm bentonite gives medium green strength and low dry
strength.
Calcium bentonite with sodium salts like sodium carbonate or
soda ash gives the property similar to sodium bentonite. If the
dead clay and spend coal dust content exceeds 2.0% then sand
must be fed into it with appropriate additions of clay and other
additives.
Dead clay contents cannot be foundout practically, but its
active content an be obtained by means of the methlene blue
test. Control of dead and spend coal dust helps maintain
molding sand quality.
Dead clay
This is the clay at and near the mould face affected by the heat
and losses its property to recombine with water and thus
losses bonding property.
2. Moulding sands
a)synthetic (silica sand plus the clay added)
b)natural (sand containing its own clay)
c)semi synthetic (a mixture of natural and synthetic)
Amount of clay allowable is 5 to 7 % for most foundry. The
use of exess clay in an indication that the milling time is
insufficient or that the mill is operating inefficiently.
III. TESTING METHODS
Moisture
Mosture helps the foudry by the ease of casting,good quality
of mould and thereby good casting
Methods of testing
Standard
50gms of the smple to be tsted is taken and heated to 105 to
110 degree celsius for about one to two ours to obtain a
constnt weight. Then moisture is given as Moisture %=(50gm[constant weight of sand after drying])*2
RAPID
Rapid testing of moisture is done on a electric hot air drier or
IR lamp. Here 25 gm sample is kept in the equipment for
about two to five minutes to obtain the moisture content by its
percentage.
PERMIABILITY
It exibits the ventig quality of te mould and core. This
property is influenced by size, shape and distribution of grains
ofsand. The type and quality of bounding material. The
density to which the ramming is done and the moisture
content.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 7 - Mar 2014
Method of testing : Standard
A specimen of dimension 2”  2” is taken and the time taken
by 2l of air passing through it is found. Then permiability is
calculated as
p=
,
p-permiability
V-volume of air passed(2 l)
h-height of the specimen
P-pressure of air passed
a-cross section area of the
specimen
t-time taken in minutes.
Rapid
Permiability is tested rapidly using an equipment called
permmeter.
 Approach to solve problem
The problem of impurities of sand over the casting surface can
be due the following reasons:
poor quality of the sand.
poor quality of the sand mix.
The solution to this problem of impurities in sand can be
found only by identifing the actual causes mentioned, of the
problem. This can be done by testing the various factors
coming across during moulding and casting.The factors to be
analysed for causing the problem of impurities in sand over
the surface of casting are
 Quality of sand.
The various quality checks for silica sand were performed.
They are listed below
a) Total clay content
Test
A 50 gms sample of dried silica sand was taken and
washed thoroughly using NaOH solution and water.
The washed silica sand sample was dried and
weighed again. The loss in weight is accounted as the
total clay content. This process was repeated for
three different samples.
Result
The total clay content analysis gave the following
result
 Sample no: total clay in percentage
1 4.5
2 4.0
3
4.3
b) Sand grading Sieve analysis Test
A 50 gms sample of clay washed silica sand was
taken and dried in the oven at 120c for about one
and a half hour. This dried sand is then taken and put
into the sieve analysis apparatus and sieved. The
sand retained in each sieve is then found out by
weighing the sand in each sieve. The sieve analysis
report for three samples taken is given

Testing of sieve analysis 1:
Sample no: 1
supplier : self (AUTOKAST)
1. Moisture content : 2%
2. Clay content
: 4.5%
3. A F S Fineness No: 37
TOTAL DISTRIBUTION IN SIEVE NO: 40, 50, 70 – 87%
TOTAL DISTRIBUTION IN SIEVE NO: 50, 70, and 100 69.6%
REMARKS: To obtain AFS no: above 40 discard the sand in
the sieves 12, 20, 30,140 and 200. The resulting sand is best
for high pressure moulding

Testing of sieve analysis 2:
Sample no: 2 supplier: self (AUTOKAST)
1. Moisture content : 3%
2. Clay content
: 4.0%
3. A F S Fineness No: 37
TOTAL DISTRIBUTION IN SIEVE NO: 40, 50, and 70 –
88.6%
TOTAL DISTRIBUTION IN SIEVE NO: 50, 70, 100-58.6%
REMARKS: To obtain AFS no: above 40 discard the sand in
the sieves 12, 20, 30,140 and 200. The resulting sand is best
for high pressure moulding

Testing of sieve analysis 3
Sample no: 3
supplier : self (AUTOKAST)
1) 1. Moisture content : 2.6%
2) 2. Clay content
: 4.3%
3) 3. A F S Fineness No: 36
TOTAL DISTRIBUTION IN SIEVE NO: 40, 50, and 70 –
85%
Therefore the average clay content of the samples taken was
TOTAL DISTRIBUTION IN SIEVE NO: 50, 70, 100obtained as 4.26%
53.6%
Inference
The silica sand used for moulding should be clay free.
REMARKS: To obtain AFS no: above 40 discard the sand
Here the average clay content is below 5%. The silica
in the sieves 12, 20, 30,140 and 200. The resulting sand is
sand should be properly washed and dried before
best for high pressure moulding .
using it. This will allow us to use over 95% of high
quality sand.
 Testing of dry shear strength
First we have to take silica sand of 500 kg and clean it by
water to remove the clay contents and then we have to heat it
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 7 - Mar 2014
in a oven to dry the sand and add 22.5 kg sodium silicate to
the sand and mix it very well. And add carbon dioxide gas in
to the sand the sand will be put into a cylinder block and then
pass the gas into it.And then we got a cylinder block mould.
And then we have put into the machine that find out the dry
shear strength.
Sample number Dry shear strength
1 5.24 kg/ cm2
2 4.5 kg/cm2
3 5.78 kg/cm2
4 5.34 kg/cm2
5 4.8 kg/cm2
6.3 Testing of dry compression strength
The mixing of sodium silicate into the sand that we have to
put 500 kg sand and put into the cylinder block and pass the
air into it.And then we got cylinder type mould and then put
into the dry compression strength testing machine. And then
we get the tested results.
Sample number dry compression strength
1
17.01 kg/cm2
2
18.05 kg/cm2
3
16.12 kg/cm2
4
19.96 kg/cm2
5
16.32 kg/cm2
The various tests were conducted on the sand and it was found
out that ,there is a wide variation between properties of sand
as per company standards and properties in the tested
samples.by the testing it was found that very little importance
is given to the quality of the sand used in making the mould.
CONCLUSION
This particular study was done at AUTOKAST LTD,
Cherthala, Kerala. The main objective of this study was to
find the problems related to defects of castings, especially
about impurities of sandand also to find suitable remedy for
this problem.Due to the impurities present in the sand, by that
major defects were found.by that the fettling department had
to perform shot blasting for longer duration to improve
surface finish. But this was a waste of both money and time.
The various tests are conducted on the sand and it was found
out that ,there is a wide variation in properties between the
samples of sand test it was found that very little importance is
given to the quality of sand used in making the mould.At the
end of this study methods to prevent the problem of sand
impurities are discussed. This was done by analysing the
various moulding materials and moulding variables of the
company and comparing them to the standards set by British
Cast Iron Research association.
REFERENCES
 Result and Discussion
The problem identified in the industry was ‘the impurities
present in the sand causes major defects in the casting’. Due
this the casting has to undergo prolonged shot blasting to
remove sand over it to improve its surface finish. Shot
blasting is done for about 45 minutes to one hour to get rid of
the sand fused on the surface of castings. Whereas for good
quality casting shot blasting is done only for about five
minutes. This prolonged shot blasting causes heavy economic
and time loss. This also lead to the situation where the wall
thickness of the casting get redused.
1. American foundry men’s society Foundry Sand Handbook
The impurities that present in the sand causes major defects in
the castings,by that we have taken tests for sand.In the testing
we found that clay amount is more present in the sand by that
so many defects that we have found from this.And the testing
of moisture.In the testing sand moisture content is more
present in the sand.The company have a standard value for the
moisture.but the tested results we got more amount of
moisture content presented in the sand.
6. Foundry sand hand book – APS 6 the edition 1952
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2. http://www.AUTOKAST LTD.com
3. http://www.indianfoundry.com
4. Quality manual of AUTOKAST LTD.
5. Foundry moulding sands in india-Jatinder mohan, R Krishnan, P K Gupta,
National metallurgical laboratory
7. Foundry technology – P R Beeles, Bultenworthslondon 1972
8. American foundry men's society Foundry Sand handbook
9. Annual report of AUTOKAST LTD
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