This document discusses various tests used to evaluate the properties of molding sands used in foundries. It describes 11 key properties tested: specimen preparation, compression, shear, flow ability, hardness, green strength, dry strength, hot strength, collapsibility, plasticity, and lists references for further information. The tests are important for characterizing molding sands to ensure they have sufficient strength and ability to retain the mold shape during the casting process.

1. 1
Contents
Introduction ..................................................................................................................................... 2
Specimen Preparation ................................................................................................................. 3
Compression .................................................................................................................................... 4
Shear ................................................................................................................................................ 5
Flow ability ..................................................................................................................................... 6
Hardness .......................................................................................................................................... 7
Green Strength ................................................................................................................................ 8
Dry Strength .................................................................................................................................... 9
Hot Strength ................................................................................................................................. 10
Collapsibility ................................................................................................................................. 10
Plasticity ........................................................................................................................................ 10
List of Reference ............................................................................................................................ 11

2. 2
Introduction
The testing process is divided in to three stages: sampling of the bulk material,
sample preparation, and testing.
Sampling is usually done at three different points of the process: upon first arrival
from the supplier, en transport for processing (usually on a conveyor), and after
processing. In each situation it is important to take a representative sample by
mixing the sand or by taking multiple samples in different locations. Also, the
sample must be stored in an airtight container to keep from spoiling it.
There are more than 25 basic tests, however only the important ones for the
given casting process are used. The basic tests measure the following
parameters: wet tensile strength, cone jolt, friability, moisture content,
permeability, green compression strength, compact ability, loss on ignition,
volatiles content, grain size & distribution, dust (dead clay) content, and active
clay content. Each of these tests can lead you to obtain specific characteristics of
sand which can be crucial quality of casting. Advanced testing tests for other
parameters, such as splitting strength, shear strength, and high-temperature
compression strength.
A large variety of molding materials is used in foundries for manufacturing molds
and cores. They include molding sand, system sand or backing sand, facing
sand, parting sand, and core sand. The choice of molding materials is based on
their processing properties. The properties that are generally required in molding
materials are :
Specimen Preparation
Compression
Shear
Flow ability
Hardness
Green Strength
Dry Strength
Hot Strength
Plasticity
Collapsibility

3. 3
Specimen Preparation
Since the permeability of sand is dependent to a great extent, on the degree of
ramming, it is necessary that the specimen be prepared under standard
conditions. To get reproducible ramming conditions, a laboratory sand rammer is
used along with a specimen tube. The measured amount of sand is filled in the
specimen tube, and a fixed weight of 6.35 to 7.25 Kg is allowed to fall on the
sand three times from a height of 50.8 ±0.125 mm. The specimen thus produced
should have a height of 50.8± 0.8 mm. To produce this size of specimen usually
sand of 145 to 175 g would be required. After preparing a test sample of sand as
described, 2000 cm of air are passed through the sample and time taken by it to
completely pass through the specimen is noted.

4. 4
Compression
Sand moulds are supposed to take up all the load that is inflicted upon it. The
load may be structural as applied by the mould material. Or it may also be due to
the weight of the casting material when it is poured in to the mould. Although the
moulds are designed with utmost care, taking established material property data
and practices into consideration, it may not always be possible to obtain the
desired characteristics due to the difference in processing the materials. Hence
at the end of a design, it is customary to prepare a test specimen and obtain the
property specific to that design or the batch.
Compression test is carried out on symmetrical specimen which may either be
cylindrical or cubical/rectangular. The size of the specimen is taken as per the
prevailing standard usually accepted in the locality. There are some universally
accepted test standards as laid down by ISO and BIS, too. These standards
clearly specify the test method and specimen shape or dimensions to be used in
the test. They also make the data acquisition and reporting method universal so
that reports from different test labs or places can be compared and conclusions
can be arrived upon with accuracy.

5. 5
Shear
For green shear, test heads are placed in lower position on the pusher arm and
weight of the
Universal Sand Strength Machine as for the compression test. When the heads
are placed in the
upper position the breaking force is increased five time, and the scale designated
“dry shear” is
read. Shear strength tests up to 220 psi (AFS) or 1530 kN/m2 (DIN) can be made
by using these
test heads in the High Dry Strength Accessory .

6. 6
Flow ability
“Flowability” is the property which enables a sand to flow readily into a mould and
fill up the interstices when subjected to ramming. It is influenced by moisture,
permeability, grain shape, fineness and clay content. The indicator is a specially
constructed dial gauge calibrated to read in percentage flowability, and may
be readily attached to the Sand Rammer. The stem rests on top of the plunger
shaft and the movement between the fourth and fifth drop of the weight is
registered as flowability. The further the plunger descends, indicating incomplete
flow the lower the percentage flowability. When the Sand Rammer is used for
ramming test specimens, the indicator is rotated out of position. The flowability
indicator can be supplied to fit either an imperial (AFS) rammer or a metric (DIN)
rammer.

7. 7
Hardness
The mould hardness is measured by a method similar to the Brinell hardness
test. A spring loaded steel ball with a mass of 0.9 Kg is indented into the
standard sand specimen prepared. The depth of indentation can be directly
measured on the scale which shows units 0 to 100. When no penetration occurs,
then it is mould hardness of 100 and when it sinks completely, the reading is zero
indicating a very soft mould.
Besides these, there are other tests to determine such properties as deformation,
green tensile strength, hot strength, expansion, etc

8. 8
Green Strength
The molding sand that contains moisture is termed as green sand. The green sand particles must
have the ability to cling to each other to impart sufficient strength to the mold. The green sand
must have enough strength so that the constructed mold retains its shape.
This is an alternative tester for determining green compression strength. When
fitted with the low capacity balance it is specially suited for testing unbaked oil-
sand core mixtures and uncured resin bonded sands of very low green strength.
The test specimen is rammed in the Split Specimen Tube and stripped directly on
to a special carrying plate .

9. 9
Dry Strength
When the molten metal is poured in the mold, the sand around the mold cavity is
quickly converted into dry sand as the moisture in the sand evaporates due to the
heat of the molten metal. At this stage the moldings and must possess the
sufficient strength to retain the exact shape of the mold cavity and at the same
time it must be able to withstand the metallostatic pressure of the liquid material.
The High Dry Strength Accessory provides the means for determining the dry
compression and dry
shear strengths of moulding and core-sand mixtures by increasing the capacity of
the Universal
Sand Strength Machine by a factor of three. It is of sturdy design and produces
accurate results.

10. 10
Hot Strength
As soon as the moisture is eliminated, the sand would reach at a high
temperature when the metal in the mold is still in liquid state. The strength of the
sand that is required to hold the shape of the cavity is called hot strength.
Collapsibility
The molding sand should also have collapsibility so that during the contraction of
the solidified casting it does not provide any resistance, which may result in
cracks in the castings. Besides these specific properties the molding material
should be cheap, reusable and should have good thermal conductivity .
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.

11. 11
List of Reference
FOUNDRY SAND TESTING EQUIPMENT
CATALOGUE NO. 750
http://engineeringhut.blogspot.com/2010/11/moulding-sand-properties-and-its-
types.html
http://www.mechanicalengineeringblog.com/2950-moulding-sand-silica-sand-
foundry-sand/
http://www.scribd.com/doc/18096886/Moulding-Sand-Properties