There are 6 methods used for Foundry Sand Testing.
- Grain fineness test
- Moisture content test
- Clay content test
- Permeability test
- Strength test
- Mould and core hardness test
Let’s discuss each of these foundry sand testing methods one by one.
#1) Grain fineness test
For designation of the grain size of the sand, the Grain fineness number is used.
From this grain fineness number, we can easily make out whether the grains of the sand are small or large.
It is very essential to know the grain size number of the moulding sand, as it affects the porosity or permeability.
If all the grains of foundry sand are of similar size, then it increases the porosity. But if the grains are of different sizes, then it will reduce the porosity and increase the compactness of the mold.
For testing the grain size of the sand, the sieve shaker vibratory unit is used.
The sieve shaker vibratory unit consists of a set of standard sieves which are graded according to the fineness of the meshes.
The sand sample which is to be tested is washed off to remove the clay and then it is dried.
This sample of sand is kept at the top most sieve and then the vibratory unit is shaken for around 15 minutes.
The amount of sand present on each of the standard sieves placed in the vibratory unit is noted down and it is multiplied by a constant.
The products of this multiplication are added to find out the total product.
Now, the fineness number can be calculated by using the following formula.
Fineness number = (Total product) / (Total percentage of sand retained on screen)
#2) Moisture content test
For moisture content test of moulding sand, the infrared heater is used.
This equipment consists of cast iron, infrared bulb and a drying pan having handle.
About 25 gram sample of the foundry sand is taken for the test and it is kept in the vessel inside the infrared heater.
The bulb is switched on for 3-4 minutes and then it is switched off.
The pan is removed and then the sand sample is weighted again.
The difference of the weight of sand before and after heating is found out.
This difference is expressed as a percentage of the total weight of the sand sample.
The percentage of the moisture present in the sand can be calculated from this difference in weights of the moist sand and dry sand.
The percentage of moisture content is calculated by the following formula.
Moisture content = [(W1 – W2) / (W1)] × 100%
W1 = weight of sand before drying, and
W2 = weight of sand after drying.
#3) Clay content test
Clay content testing of foundry sand is very simple.
First of all, the weight of the original sample is measured.
Then that sand sample is washed off to remove the clay and mud particles from it.
After washing this sand sample, the sand sample is weighted again.
Hence, the difference in the weight of original sample and weight of washed sample gives the amount of clay content in the sand.
The percentage clay content can be found by using a similar formula as discussed in the moisture content test.
Clay content = [(W1 – W2) / (W1)] × 100%
W1 = weight of sand before washing, and
W2 = weight of sand after washing.
#4) Permeability test
In order to perform the permeability test of foundry sand, first of all you should know about the permeability number.
What is Permeability number?
The volume of air in cubic centimeters that will pass per minute under the pressure of 1 g/cm2 through the standard sand specimen having cross section area of 1 cm2 and 1 cm depth is defined as a permeability number.
The major parts which are required for the Permeability test of moulding sand are listed below.
- Inverted Bell jar that can float on water
- Specimen tube
- Manometer (for measuring air pressure)
As shown in the above image, the air of 2000 cm3 which is held in the bell jar, is forced to pass through the sand specimen.
So at this stage, the amount of air that is entering the sand specimen is equal to the amount of air that is escaping the specimen.
Take the pressure reading in the manometer.
Note down the time required for all the 2000 cm3 of air to pass through the sand.
From this, you can now calculate the permeability number.
Permeability number, Np = (V × h) / (a × p × t)
V = volume of air in cm3
h = height of specimen (in cm)
p = pressure of air (in g/cm2)
a = cross sectional area of specimen in cm2
t = time taken by air to pass (in minutes)
#5) Strength test
Moulding sand should have enough compressive strength in its moist condition.
Strength testing of moulding sand is carried out by using a machine known as strength tester.
A well rammed sand specimen having height 50.8 mm and diameter 50.8 mm is used for testing the strength of the sand.
As shown in the diagram above, this sand specimen is placed on the universal testing machine (strength tester machine).
On this sand specimen, a continuous increasing load of 20 N/mm2 is applied until the rupture of the specimen takes place.
During this stage, the readings are noted down from the scale mentioned on this machine, and that value determines the strength of the sand.
#6) Mould and core hardness test
The mould which is prepared by ramming the sand, should possess enough hardness which can resist the flow of molten metal and other loads.
The device called hardness tester is used to test the hardness of the mould.
The harness tester is small like a dial of a wrist watch and it has a tip at the bottom.
The tip is penetrated in the mould for testing its hardness.
There is a spring loaded shaft inside the hollow body of the device, which measures the hardness of the mould and shows the reading on the dial attached at the top.
In this way, mould hardness test or core hardness test is carried out.