Introduction to Basic Manufacturing Processes and ... - always yours

Mold and Core Making 215
increased production resulting from sound castings. Generally the following tests are performed
to judge the molding and casting characteristics of foundry sands:
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. Specific surface of sand grains
7. Water absorption capacity of sand
8. Refractoriness of sand
9. Strength Test
10. Permeability Test
11. Flowability Test
12. Shatter index Test
13. Mould hardness Test.
Some of the important sand tests are discussed as under.
12.6.1 Moisture Content Test
The moisture content of the molding sand mixture may determined by drying a weighed
amount of 20 to 50 grams of molding sand to a constant temperature up to 100°C in a 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 thus 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. The percentage of moisture content in the molding
sand can also be determined in fact more speedily by an instrument known as a speedy
moisture teller. This instrument is based 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. This instrument is provided with a pressure gauge
calibrated to read directly the percentage of moisture present in the molding sand. Some
moisture testing instruments are based on principle that the electrical conductivity of sand
varies with moisture content in it.
12.6.2 Clay Content Test
The amount of clay is determined by carrying out the clay content test in which clay in
molding sand of 50 grams is defined as particles which when suspended in water, fail to settle
at the rate of one inch per min. Clay consists of particles less than 20 micron, per 0.0008 inch
in dia.
12.6.3 Grain Fineness Test
For carry out grain fineness test a sample of dry silica sand weighing 50 gms free from clay
is placed on a top most sieve bearing U.S. series equivalent number 6. A set of eleven sieves
having U.S. Bureau of standard meshes 6, 12, 20, 30, 40, 50, 70, 100, 140, 200 and 270 are
mounted on a mechanical shaker (Fig. 12.1). The series are placed in order of fineness from