SAND TESTING
Various kind of tests are done on moulding sand. They are:
1. Moisture content test
2. Clay content test
3. Grain fineness test
4. Permeability test
5. Strength tests
(a) Green and Dry compression
(b) Green tensile
(c) Green and Dry shear
(d) Transverse (bending)
Moisture Content Test
- Amount of water contained in moulding sand controls the properties of moulding sand.
- If moisture content is low strength will not be developed.
- If moisture content is high, permeability reduces. Moisture content can be determined by the following methods.
Using direct reading moisture teller
The reaction is produced by providing calcium carbide
Calcium carbide reacts with the moisture of moulding sand and produces acetylene gas.
The pressure of C2H2 gives a direct reading of the water content of the pressure gauge.
Using infrared heating
The following steps are followed in this process.
(i) Fixed weight of 20 to 50 gms of prepared sand is placed in pan and is heated by infrared heater bulb for 2 – 3 minutes.
(ii) The moisture present evaporates.
(iii) Moulding sand is taken out of the pan and reweighted.
(iv) The percentage of moisture can be calculated from the difference in weights of original moist and final dry sand samples.
(v) The apparatus is shown in Fig.
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| Moisture determining apparatus |
Clay Content Test
Clay is a bonding agent for sand particles. The clay content of a moulding sand can be determined as follows :
- Take a small quantity of moulding sand and dry it throughly
- Take out 50 gms of dry moulding sand and put in a wash bottle.
- Add 475 cc of distilled water and 25 cc of 3% NaOH solution.
- Using a rapid sand stirrer, stirr the mixture for 10 minutes.
- Fill the wash bottle with water upto indicated mark.
- Allow 10 minutes for settling of sand, then takeout water from the bottle.
- Clay comes out with water in dissolved condition.
- Again add water to the sand and stir it, let the sand to settle down and take water out.
- Follow the above step till water over the settled sand is clean.
- So all the clay has been removed out of sand.
- Dry the sand.
- Calculate the clay content by measuring the difference in weights between initial and final sand sample.
Grain Fineness Test
This test determines
(i) Grain size
(ii) distribution
(iii) grain fineness
- The apparatus in shown in Fig.
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| Grain Finesess Tester |
- It has a number of standard sieves mounted one above the other on a power driven shaker.
- The shaker vibrates the sieves and sand poured on top sieve gets screened and collected on different sieves depending upon the various sizes of grains present in moulding sand.
- There are generally eleven number of standard sieves mounted one above other and under the bottom most sieve pan is placed.
- The top sieve is the coarsest and bottom most sieve is the finest, in between sieves are placed in order.
- A sample of dry sand without clay is placed in upper sieve.
- Sand is vibrated for a definite period of time.
- The amount of sand obtained in each sieve is weighted and percentage distribution is calculated.
- For calculating grain finess number, each percentage is multiplied by a factor.
- The resulting products are added and divided by total percentage of sand grain retained.
Permeability Test
Permeability may be defined as the property of moulding sand which allows stream and other gas generated in the mould during the pouring of molten metal to escape out.
It depends on
(i) grain size
(ii) grain shape
(iii) binder type and amount
(iv) degree of ramming
(v) water of content of moulding sand
- First, a specimen of standard size is prepared by Specimen Rammer.
- Permeability of sand specimen is determined by passing given volume of air through the sand.
- Permeability tester consists of
- an inverted bell jar, which floats in water.
- specimen tube to hold the sand specimen.
- manometer to read the air pressure.
The apparatus is shown in Fig.
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| Permeability Tester |
Process of Permeability Testing
(i) 2000 cc of air held in inverted bell jar is forced to pass through sand specimen.
(ii) At some point the airflow stabilizes i.e., amount of air entering the specimen = amount of air escaped through the specimen to atmosphere.
(iii) By this, a stable reading is obtained in manometer.
(iv) Using stopwatch, time required for the total 2000 cc of air to pass through the sand specimen is also recorded.
(v) Now permeability number can be calculated as follows:
Strength Test
- Strength test are done in order to control sand strength properly.
- Strength of a moulding sand can be determined by
- Compression
- Tensile
- Shear and
- Transverse test
- Among all these compression test is most commonly used.
- All the tests can be done on sand specimen tester by using different attachments.
- The strength testing equipment is shown in Fig.
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| Strength Testing Equipment |
Process of Strength Testing
(i) The specimen is held between the grips.
(ii) Hand wheel is rotated, it builds hydraulic (oil) pressure on specimen.
(iii) Dial indicator measures the deformation occurs.
(iv) There are two manometer indicators. One is for low strength sand and other is for high strength core sand.
(v) Each indicator has three scales. First for reading compressive strength, second for tensile (traverse) and third for shear strength.
(vi) The shape of specimen and the grips are shown in Fig
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| Shapes of specimen and grips for strength tensing: G for Grip, S for Specimen |
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