The document discusses various properties of moulding sand including porosity, plasticity, adhesiveness, cohesiveness, and refractoriness. It describes different types of moulding sand such as green sand, dry sand, loam sand, and core sand. It also discusses functional requirements of moulding materials including flowability and green strength. The document covers mould hardening techniques and sand testing methods including compression, shear, tensile, and transverse tests.

1. Properties of moulding sand
porosity or permeability
It is the property of sand which permits the steam and other gases to pass through the sand
mould.
depends upon
grain size, grain shape, moisture and clay components of the moulding sand.
If the sand is too fine, the porosity will be low.
Plasticity
It is that property of sand due to which it flows to all portions of the moulding box or flask.
The sand must have sufficient plasticity to produce a good mould.
Adhesiveness
It is that properties of sand due to it adheres or cling to the sides of the moulding box.
Cohesiveness
It is the property of sand due to which the sand grains stick together during ramming.
It is defined as the strength of the moulding sand.
Refractoriness
The property which enables it to resist high temperature of the molten metal without
breaking down or fusing.
Collapsibility
determines the readiness with which the moulding material will break down in knockout and
cleaning operations.

2. Classification of Moulding sand according to their use
Green sand
The sand in its natural or moist state is called green sand.
It is also called tempered sand.
It is a mixture of sand with 20 to 30 percent clay, having total amount of water
from 6 to 10 percent.
The mould prepared with this sand is called green sand mould, which is used for
small size casting of ferrous and non-ferrous metals.
Dry Sand
The green sand moulds when baked or dried before pouring the molten metal
are called dry sand moulds.
The sand of this condition is called dry sand
The dry sand moulds have greater strength, rigidity and thermal stability.
These moulds used for large and heavy casting.
Loam Sand
A mixture of 50 percent sand grains and 50 percent clay is called loam sand.
It is used for loam moulds of large grey iron casting.
Facing Sand
A sand which is used before pouring the molten metal, on the surface is called
facing sand.
It is specially prepared sand from silica sand and clay.

3. Backing or Floor Sand
A sand used to back up the facing sand and not used next to the pattern is
called backing sand.
The sand which have been repeatedly used may be employed for this purpose. It
is also known as black sand due to its colour.
System Sand
A sand employed in mechanical sand preparation and handling system is called
system sand. This sand has high strength, permeability and refractoriness.
Parting Sand
A sand employed on the faces of the pattern before the moulding is called
parting sand
The parting sand consists of dried silica sand, sea sand or burnt sand
Core Sand
The cores are defined as sand bodies used to form the hollow portions or
cavities of desired shape and size in the casting
Thus the sand used for making these cores is called core sand
It is sometimes called oil sand.
It is the silica sand mixed with linseed oil or any other oil as binder.

4. Functional requirements of moulding materials
A foundry moulding mixture passes through four main production stages
preparation and distribution
mould and core production
casting
cleaning and reclamation
The principal properties required at the moulding stage
flowability
green strength
flowability: measure of the ability of the material to be compacted to a uniform
density
balance of these properties depends largely upon the intended
method of compaction (vary from hand ramming with tools to jolt)
green strength: The need for green strength arises when the pattern is withdrawn
and the mould must retain shape independently without
distortion or collapse.

5. Moving to the pouring stage
many moulds are cast in the green state,
but others and for heavy castings - hardened to generate greater
rigidity under the pressure and erosive forces of the liquid metal.
This state was formerly achieved by the high temperature drying of
clay bonded sands or the baking of traditional core sands,
but this has been largely outdated by the chemical hardening of
sands containing reactive binders of the modern organic and silicate
types.
At this stage, dry strength i.e. strength in the hardened or dried
condition is significant
even in greensand practice dry strength is required to avoid friability
mould partially dry out during standing before casting.

6. Moulding practice and the special requirements of coresands
Many castings, including most of those made by machine moulding, are cast in
greensand moulds,
Introduction of high pressure moulding machines enabled even castings in the
tonnage weight range to be produced to acceptable quality standards.
There are strong economic incentives to use this low cost system, but hardened
moulds are preferred in many cases, particularly for heavier castings.
Greensand practice
1. Clay binders involve low material costs and avoid the additional costs of
mould hardening, whether by chemical or thermal means.
2. The rapid turn round of moulding boxes and the smooth moulding and
casting cycle are advantageous in mechanized systems.
3. The sand is readily reconditioned, since there is little dehydration of the
clay bond.
4. Greensands, having lower compression strength, offer less resistance to
contraction than hardened moulds, so that the risk of hot tearing is
reduced.
5. Moulds joint closely, leaving little flash for removal by fettling.
6. The process is environmentally friendly.

7. Hardened mould or dry sand practice
1. Hardened moulds offer maximum resistance to distortion- metallostatic
pressure- mould erosion during prolonged pouring. They are therefore suitable
for castings of the largest dimensions and provide high standards of accuracy.
2. In the production of cast irons in particular, mould rigidity contributes to
internal soundness as well as to dimensional accuracy.
3. The venting problem is reduced in the absence of steam generated from
moisture.
4. impermeable mould surfaces are readily attainable, since sands of lower
permeability can be used, with coatings where required.
5. Surface chilling is greatly reduced, facilitating metal flow in thin sections.
6. Problems of drying-out during delays in casting, leading to surface friability,
are avoided.

8. Mould hardening
Chemical hardening is accomplished either by liquid or gaseous reagents.
Liquid reagents are commonly employed in the cold-set mode and are blended
into the sand at the mixing stage, in some cases at the point of entry to the
mould, so that no separate hardening operation is required.
Gas or vapour hardening is performed after compaction and is mainly applied
to cores and smaller mould parts.
Full mould drying has been largely superseded by the above practices, but
stove are still used in some circumstances.
These are usually operated in the temperature range 200–400°C.
Surface drying can also be carried out, using gas torches or hot air drying
hoods.
Surface hardening can be enhanced by prior treatment with sprays of water or
dilute binder solutions, and inflammable mould coatings can also assist in the
process.

9. Sand testing techniques
Specimens for bulk testing
• Mechanical properties and certain other characteristics are determined on
specimens compacted to a bulk density similar to that encountered in a well
rammed mould.
• Many tests utilize the 2 in X 2 in cylindrical AFS specimen or its 50mm X
50mm DIN equivalent, prepared by subjecting a weighed quantity of sand
– to a selected number of blows from a compatible standard rammer,
– transmit to a close fitting piston in a tubular mould
• The weight of sand is adjusted to produce a close tolerance specimen,
which can be expelled from the tube on a stripping post.
• This specimen may be used for
– permeability testing and for a number of green and dry strength
measurement behaviour during ramming can be used as a criterion of
compactability or flowability.

10. Green and dry strength tests
• The principal strength tests measure stress to failure under a
constant rate of loading.
• In the low green strength range, compression testing can be carried
out on a simple, manually operated, spring loaded machine,
• But most strength testing is carried out on universal machines
• the load is applied by means of a pivotted weight, progressively
brought to bear on the specimen as the motorized pusher arm climbs
the calibrated rack.
• For very high strengths machines such as that illustrated in Figure are
available.
• In this example motorized loading up to 20 kN can be applied to the
selected test specimen
• the force being measured through a strain gauge load cell.
• The unit symbolize computer display and recording of test results.
• Green strength tests are carried out on newly made specimens
• dry or cured strength tests on specimens hardened in a standard
manner

11. Testing machine for higher strength materials
Universal sand strength testing machine

12. Compression tests
• The cylindrical specimen is axially loaded through
flat faced holders
• Standardization of the rate of loading is particularly
important in the green compression test, since
creep of greensand occurs readily under constant
load.

13. Shear tests
• The compressive loading system is modified to
provide offset loading of the specimen
• Under most conditions the results of shear tests
have been shown to be closely related to those of
compression tests, although the latter property
increases proportionately more at high ramming
densities.

14. The tensile test
• A special waisted specimen is loaded in tension through a pair of grips.
The transverse test
• A plain rectangular specimen is supported on knife edges at the ends and
centrally loaded to fracture
• Tensile and transverse tests are commonly applied to high strength sands
• The conditions being especially relevant to the stresses incurred in cores during
handling and casting.
• Both tests, unlike the compression test, provide values well within the working
ranges of normal types of universal sand testing machine.
• Versions of these two tests are also used for the evaluation of shell moulding
mixtures, being carried out on cured specimens approximating to the thickness
of a production shell.
• Studies of correlations between various strength properties are particularly
valuable and can greatly reduce the volume of testing
Transverse test

15. The shatter index
• shatter test is used as an indicator of sand toughness
• The ability to deform rather than fracture under shock loading.
• The standard compression test cylinder is ejected from its mould and allowed
to fall from a fixed height of 1.83m on to a flat steel anvil.
• Fragments retained on a concentric 13.2mm aperture BS410 sieve are weighed,
together with the residual core from the anvil,
• the shatter index is this weight expressed as a percentage of the total weight of
the specimen
• A low value is an indication of poor lift, or friability in pattern withdrawal and
subsequent handling, whilst too high a value is associated with unsatisfactory
moulding qualities resulting from excessive clay or water content.
• Values of 50–85 represent the mouldable range.

16. Surface hardness
• The hardness of a compacted sand surface can be determined using portable
spring loaded indentation testers
• For the measurement of green hardness, a spherical or conical indenter is used
depending on the expected hardness level
• the depth of penetration from the flat reference surface of the instrument
corresponds to an empirical scale of hardness in the overall range 0–100.
• The hardness can be measured on actual mould surfaces to check the degrees
of uniformity and the ramming efficiency.
Deformation
• The deformation behaviour of moulding sands has received less consideration
than the properties reflected in the above tests.
• Deformation can be determined during the green compression test by
measurement of the decrease in length of the cylindrical specimen to the point
of failure, whilst more comprehensive data can be derived from full stress–
strain curves,

17. Permeability
• Permeability is determined by measuring the rate of flow of air through a
compacted specimen under standard conditions.
• The test for green permeability is carried out on the A.F.S. standard
cylindrical specimen, retained in its ramming tube
• The permeability meter, incorporates a graduated bell of 2 litres capacity
containing a volume of air over water.
• A tube from the air enclosure communicates directly with the specimen
tube, placed over an ‘O’-ring seal, so that the air can escape through the
specimen as the bell descend.
• The time for exhaustion of 2 litres of air is determined.
• The permeability number P is defined as the volume of air in cm3/min
passing through a specimen of length 1 cm and cross-sectional area 1 cm2,
under a pressure difference of 1 cm water gauge:
P = Vh/atp
where V = volume of air, cm3
h = height of specimen, cm
a = c.s.a. of specimen, cm2
t = time, min
p = pressure difference, cm water.

19. Using the standard apparatus and technique,
the permeability may be derived directly from the formula
P = 3007.2/t
where the time t is expressed in seconds.
• A standard orifice, of small cross section in comparison with the porosity of
the specimen, is placed between the pressure chamber and the specimen.
• The pressure between orifice and specimen now lies at a value
intermediate between the chamber pressure and atmospheric pressure,
depending on the permeability of the specimen.
• The value is derived directly from this pressure, measured by calibrated
water manometer.
• A similar principle is embodied in the portable quick reading instrument
• The required air pressure is in this case generated by a high speed electric
fan and the pressure drop is indicated on a sensitive gauge calibrated
directly to read the permeability number.
• Either type of permeability meter can be used in conjunction with a flexible
tube and contact pad to provide a direct indication of the level of
permeability at any flat mould surface.
• Permeability determinations on dried or hardened sands require a modified
specimen holder enabling the cylindrical walls of the test piece to be sealed
against the bore surface of an enlarged tube, using molten wax or an
inflatable rubber sleeve

20. Bench life
• Compression tests are made on specimens rammed at successive intervals of five
minutes from mixing.
• The bench life is defined as the time to reach the value of 10 kN/m2, beyond which the
strength of subsequently compacted material will be prejudiced by interruption of the
bonding process already under way in the loose sand.
• Other relevant time intervals can be applied, depending on the sensitivity of the
mixture under test.
Strip time
• Numbers of compression test specimens are moulded in multi-gang boxes immediately
after mixing.
• Tested at intervals to detect the time at which the strength reaches350 kN/m2.
• A full strength–time plot of the type shown, can be developed from this form of test to
characterize the setting behaviour in full, including the maximum potential strength of
the material.
Scratch hardness
• A four point spring loaded penetrator is contained within a concentric
reference surface which is pressed against the hardened sand surface.
• The penetrator is manually rotated though a fixed number of revolutions,
normally two, and the depth of penetration is shown on a dial gauge as an
indication of relative surface density and scratch resistance.

21. Impact penetration
• A sharp spring actuated probe graduated in 1 cm divisions, is repeatedly
triggered by manual pressure against the sand surface,
• And the number of blows required to reach a given depth represents the
relative resistance of the sand body to penetration.
• The test can be carried out on production moulds or on sample 10 cm
cubes, molded and tested whilst in the corebox.
• A valuable feature of this test is its ability to explore the rate and depth of
hardening and to detect any lack of through cure
• plots of numbers of impacts against penetration depth enable the degree of
uniformity to be investigated.
Gas evolution
• The rate and volume of gas evolved from a dried sample of hardened sand
can be determined using a sealed, temperature controlled, silica tube
furnace with provision for a nitrogen atmosphere.
• The weighed sample is propelled into the hot zone of the inert gas-filled
tube, normally at a temperature of 850°C, and the pressure rise is
continuously recorded until a maximum is attained.
• The pressure readings can be converted to volumes, using a calibration
chart derived from the known total evolution from a standard substance.
• Both rate and total volume are significant in relation to potential gas defects
in castings.

22. Impact penetration tester with internal spring
loaded hammer

23. Hot distortion
• The hot distortion test is carried out on a flat strip sand specimen which is fixed
at one end and loaded in cantilever mode at the other
• The underside is heated and the deflection at the loaded end continuously
measured.
• Upward movement due to initial expansion of the lower layers of the strip is
followed by sagging with the progressive thermal softening and eventual
breakdown and collapse of the material.
• Strain–time curves provide a guide to the behaviour of different binders and
curing conditions.
• Typical curves representative of hot box, cold set and silicate bonded sands,
including the influence of iron oxide additives, were produced in a
comprehensive study by Morgan and Fasham

24. Schematic arrangement of hot distortion test

25. High temperature properties
• High temperature tests are particularly relevant to the study of mould and core
materials, since they simulate in some degree conditions met in the casting
process.
• more suited to longer term laboratory assessments than to routine testing
• Gas evolution and hot distortion tests - given their particular value in relation to
the chemically hardened sands.
• hot strength test include the determination of compressive strength to failure at
specified temperatures, -prior soaking periods for the specimen to reach the test
temperature
• measurements of total deformation can also be obtained from the same test
• To assess the retained strength, a property relevant to knockout behaviour, the
specimen is put though the thermal cycle, but cooled to room temperature before
testing to failure
• Collapsibility can be assessed through determination of the time to failure under
constant load
• more suitable than isothermal hot strength tests for organically bonded sands, in
which the bond can be completely decomposed during the soaking period.
• Free expansion in the absence of loading can also be measured using a dilato meter
• this type of measurement can be relevant to certain types of sand defect incastings

26. High temperature and retained strengths of sodium silicate bonded sand

27. Moisture testing
• Moisture content is readily determined by loss in weight on drying at 110°C.
• Various rapid aids are employed, including balances directly calibrated to
read the moisture content of a standard sample after drying;
• samples can be dried by the passage of hot air through a filter cloth tray.
• For shop control the Speedy moisture tester can be employed.
• This makes use of the reaction
CaC2 + 2H2O = Ca(OH)2 + C2H2
• The sample is placed in the cap of a metal flask fitted with a pressure gauge
and an excess of the carbide reagent placed in the flask body.
• The flask is closed, clamped and shaken and the acetylene pressure
provides a direct reading of moisture content on the gauge.
• Electrode probe devices have been used to determine the moisture content
of loosely heap sand, but are not employed for the accurate assessment of
samples.
• an electrical method employing measurements of microwave absorption in
compacted samples is employed with success to control moisture in
mechanized system sands

28. Active clay
• The live bentonite clay present in a sample of reconditioned sand
can be determined by the methylene blue test,
• discriminate between active clay and other particles of similar size
which are included in the normal clay grade determination.
• Methylene blue dye, when added to an acidified slurry of clay and
water, is adsorbed by the clay to a point at which the appearance
of excess dye can be observed by spotting drops of the liquid on to
a filter paper.
• weighed sand sample is agitated and heated in the selected initial
solution, using stirring or ultrasonic means.
• The standard methylene blue solution is then progressively added
from a burette until the spot tests reveal the end point, which is
represented by a halo around the spot.
• The volume of the standard solution required can be directly
related to the active clay content using an appropriate calibration
curve.

29. pH and acid demand
• The pH value of a solution, a reciprocal function of the hydrogen ion
concentration, is the standard representation of the degree of acidity or
alkalinity on a scale from 1 to 14.
• Values from 1–7 represent acid
• 8–14 alkaline condition
• The pH value can influence the behaviour of clay binders
• readily measured using a meter depending on electrochemical potentials.
• In chemically bonded sands employing acid catalysts, account needs to be
taken of the presence of alkalis already present in the base sand before the
addition of the binder.
• Since pH measurements are only influenced by substances in solution, the
purpose of the acid demand test is to assess the full effect of insoluble alkalis
as well.
• The test involves the introduction of a standard volume of hydrochloric acid of
known concentration to a sample of the sand suspended in water.
• The acid reacts with the whole of the alkali content, leaving an excess of HCl.
• This can be quantified by titration with a standard solution of sodium
hydroxide, so enabling the true acid demand value of the original sample to be
determined by difference.

30. Loss on ignition
• Loss on ignition is employed to determine the presence of organic
and other gas forming materials present in the sand mixture or its
individual constituents, including new and reclaimed sands.
• A weighed sample of pre dried material is fired in a silica crucible
held in a muffle furnace at 925°C for 2 hours.
• The percentage loss in weight is determined and arises from the
volatilization, oxidation and decomposition of substances forming
gaseous products.
• These include additions or residues of carbonaceous additives
such as coal dust, chemical binders, cereals, and carbonates in sea
sands.
• Although the test does not discriminate between such sources, it
does in practice provide a check on the consistency of binder
contents and the condition of new and reclaimed sands.
• Actual volatiles can if necessary be separately determined by
similar tests conducted in inert atmospheres.