Sand testing

MOISTURE CONTENT :

The moisture content of the molding sand mixture will determine by difference in weight of moist sand and dry sand.

1. Evaporation method :

Sample of moulding sand weighing about 20 to 50 grams are allowed to heat at a constant temperature upto 100°C in an oven for about one hour.
It is then cooled to a room temperature and then reweighing the molding sand.
The moisture content in molding sand is evaporated.
The loss in weight of molding sand due to loss of moisture gives the amount of moisture which can be expressed as a percentage of the original sand sample.

2. Moisture teller method:

This method was quite faster than the evaporation method. Sample of moulding sand placed in teller pan having 600 mesh screens at bottom.
Hot air allows blowing over the moulding sand about 3 – 6 minute now the moisture present in the moulding sand is removed.

Once the moisture is removed weighing the sample and find the deviation in weight of sample before.

3. Moisture teller chemical reaction method:

Worked on the principle that when water and calcium carbide react, they form acetylene gas which can be measured and this will be directly proportional to the moisture content.
Sample of moulding sand is placed in teller pan along with calcium carbide (CaC2). This reaction will produce C2H2

CaC2 + 2H2O C2H2 + Ca (OH)2

The amount of C2H2 produced is directly proportional to the moisture content in the moulding sand.

Clay Content Test :

The sample of molding sand weighing about 50 grams is mixed with water and 1% NaOH and allows stirring for 4-7 minute then waiting for 10-15 minute for sedimentation.
Now the sand was settling down. The dirty water is present at the top portion of the pan.
The above process is repeated until to achieve clean water at the top portion of the pan. The water is drained off.

Refractoriness Test :

It is judged by heating the A.F.S standard sand specimen to very high temperatures ranges depending upon the type of sand.
The heated sand test pieces are cooled to room temperature and examined under a microscope for surface characteristics.
If the silica sand grains remain sharply defined and easily give way to the needle.
In the actual experiment the sand specimen in a porcelain boat is placed into an electric furnace.
It is usual practice to start the test from l000°C and raise the temperature in steps of 100°C to 1300°C and in steps of 50° above 1300°C till sintering of the silica sand grains takes place.
At each temperature level it is kept for atleast 3 minutes and then taken out from the oven for examination under a microscope for evaluating surface characteristics.

Grainfitness Test :

GFN is a measure of the average size of the particles in a sand sample. The grain fineness of molding sand is measured using a test called sieve analysis.
The test is carried out in power-driven shaker consisting of number of sieves fitted one over the other.
A representative sample of the sand is dried and weighed then passed through a series of progressively finer sieves while they are agitated and tapped for 15 minute test cycle.
The sand retained on each sieve is then weighed and recorded.

Strength Test :

This is the strength of tempered sand expressed by its ability to hold a mold in shape. Sand molds are subjected to compressive, tensile, shearing, and bending stresses.
The green compressive strength test and dry compressive strength is the most used test.

Compression tests

A rammed specimen of tempered molding sand is produced that is 2 inches in diameter and 2 inches in height.
The rammed sample is then subjected to a load which is gradually increased until the sample breaks.
The point where the sample breaks is taken as the compression strength.

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.

Tensile test

Bending test

A plain rectangular specimen is supported on knife edges at the ends and centrally loaded to fracture.

Permeability Test

Permeability of the moulding sand is determined by measuring the rate of flow of air through a compacted specimen under standard conditions.
It is measured in terms of permeability number.
A sample of moulding sand is placed in a tube. Time taken for 2000 CM3 of air at a pressure of 10 g/cm2 to pass through the specimen is noted.
Permeability meter consisting of the balanced tank, water tank, nozzle, adjusting lever, nose piece for fixing sand specimen and a manometer. The permeability is directly measured.
Permeability number P is volume of air (in cm3) passing through a sand specimen of 1 cm2 cross-sectional area and 1 cm height, at a pressure difference of 1 gm/cm2 in one minute.

Mold Hardness Test

The working of the tester is based on the principle of Brinell hardness testing machine. In an A.F.S. standard hardness tester a half inch diameter steel hemi-spherical ball is loaded with a spring load of 980 gm.
This ball is made to penetrate into the mold sand or core sand surface. The penetration of the ball point into the mold surface is indicated on a dial in thousands of an inch.
The dial is calibrated to read the hardness directly i.e. a mold surface which offers no resistance to the steel ball would have zero hardness value and a mold which is more rigid and is capable of completely preventing the steel ball from penetrating would have a hardness value of 100.

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