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Sand testing of sand casting (4)

7) Shatter Index Test :

In this test, the AFS standard sand specimen is usually rammed by 10 blows and then it is allowed to fall a half inch mesh sieve from a height of 6 feet. The weight of sand retained on the sieve weighing. It then notified as a percentage of the total weight of the specimen is measured on the index shatter.

8) Mold Hardness Test:

The test is performed by mold hardness tester. The work on the tester based on the principle of Brinell hardness testing machine. In AFS hardness tester is a standard half-inch diameter steel ball hemispherical spring loaded with a load of 980 gm. The ball has to do to break into the sand mold or core sand surface. The spot is the point ball into the mold surface shown on dial in thousands of inches. The dial is calibrated to read the mold surface hardness directly ie offering no resistance to the steel ball hardness value would be zero and more rigid model and fully capable to prevent the ball from penetrating steel would hardness value of 100. The gauge can dial the hardness tester to provide direct readings.

9) Compactability flowability :

Compactability test is widely accepted as both a simple and directly related to the transport of sand in shape, especially when associated with compaction squeeze. A fixed amount of loose sand compacted under standard conditions and shows the percentage reduction in the amount of compactability.

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Sand testing of sand casting (3)

5) Strength test:

This is tempered sand strength expressed by its ability to hold model in shape. Sand molds are subject to compressive, tensile, shearing and transverse stress. The compressive strength test green and dry compressive strength of the test most commonly used in the foundry.

- Compression Tests A specimen of sand rammed produced Tempered shape is 2 inches in diameter and 2 inches tall. The sample is then rammed subject to load increase gradually until the sample breaks. The point where the sample taken breaks the compression strength.

- Shear Tests compressive loading system is modified to offset the specimen load to provide. Under most conditions the shear test results shown to be closely associated with the compression tests, although the latter property increases proportionately more high density ramming.

- The tensile test specimen is loaded in tension special waisted by a pair of grips. The test sample is rectangular plain transverse support by the end of knife edges and centrally loaded broken. And transverse tensile tests commonly applied to sand high strength, the conditions to be particularly associated with the stress incurred during handling cores and solutions.

6) Permeability Test:

Permeability is determined by measuring the air flow rate through compacted specimens under standard conditions. Roller sand sample is prepared using rammer and death. This sample (typically 2 inch dia and 2 inches tall) used for testing the permeability or porosity of the sand molding and core. The test is performed in permeability meters flat consists of a tank, water tank, nozzle, lever, adjusting the nose piece for fixing sand specimens and a manometer. The permeability is measured directly. Permeability number P is air volume (in cm 3) passing through sand specimen of 1 cm2 area and 1 cm cross-sectional height, a pressure difference of 1 gm / cm2 in one minute.

P = VH / ATP

Where,
P = permeability
v = volume of air passing through the specimen in c.c.
h = height of specimen in cm
p = pressure of air in gm/cm2
a = cross-sectional area of the specimen in cm2
t = time in minutes.

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Sand testing of sand casting (2)

2) Test Material Clay:

The amount of clay is determined by the test subject of clay a clay in the sand molding of 50 grams defined as particles when suspended in water, fail to resolve at the rate of one inch per min to complete. Clay consists of particles smaller than 20 microns, against 0.0008 inch dia.

3) Test Finer Grain:

The AFS Grain Fineness number (AFS-NBA) is one means of measuring the fine grain of sand system. NBA is a measure of the average particle size (or grain) in a sample of sand. The finer grain of sand molding measured using a test called sieve analysis. The test is carried out in shaker power driven a number of sieves equipped with one over the other. 1. A representative sample of the sand is dried and weighed, then passed through a series of progressively finer sieves (screens) and they are agitated and tapped a 15-minute test cycle. The series is put in order from top to bottom fineness. 2. The sand keep each sieve (grain too large to pass through) is then weighed and recorded. 3. The weight of each sieve to keep out three calculations to get the AFS-NBA.

4) Test refractoriness:

Refractoriness is considered the molding sand by heating the specimen AFS standard sand to the high temperature ranges depending on the type of sand. The heated sand test pieces are cooled to room temperature and examined under a microscope where surface characteristics or by scratching it with a steel needle. If silica sand grains remains sharply defined and easily give way to the needle. Sintering is not yet set in. In the actual experiment the boat porcelain sand specimen submitted in electric furnaces. Is usual practice to start the test from l000 ° C and temperature in steps of 100 ° C raise to 1300 ° C and in steps of 50 ° over 1300 ° C till sintering the grain silica sand held . At each level of temperature, it is kept for at least three minutes and then taken out of the oven for examination under the microscope to evaluate the surface characteristics or by scratching it with a steel needle.

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Sand testing of sand casting (1)

Molding sand and sand core depending on shape, size composition and distribution of grains of sand, clay size, moisture and additives. The increase in demand for good surface finish and higher accuracy in castings requires certainty in the quality of the mold and core sand. Sand often test allows the use of cheaper local sand. It also ensures reliable mixing sand and allow use of the natural properties of molding sand. Will deliver sand test no change from the standard quality, and adjust the mixture to detect sand immediately to the particular needs so that it can minimize the casting defects.

In general the following tests are performed to judge the molding and casting foundry sands characteristics:

1. Moisture content Test
2. Clay content Test
3. Chemical composition of sand
4. Grain shape and surface texture of sand.
5. Grain size distribution of sand
6. Refractoriness of sand
7. Strength Test
8. Permeability Test
9. Flowability Test
10. Shatter index Test
11. Mould hardness Test.

1) Test Moisture Content: can the moisture content of the mixture, molding sand is determined by drying the size weighing 20 to 50 grams of sand molding with constant temperature up to 100 ° C in an oven for about an hour . It is then cooled to room temperature and then reweighing the molding sand. The moisture content in molding sand thus evaporated. The loss in weight of molding sand due to loss of moisture, gives the amount of moisture that can be expressed as a percentage of the original sand sample. Can the percentage of moisture content in molding sand also decide more quickly indeed an instrument called quick teller moisture. The instrument is based on the principle that when water and calcium carbide react, they form acetylene gas can be measured and this will in accordance with the moisture content. The instrument is available with a calibrated pressure gauge to read exactly the percentage of humidity present in the molding sand.

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