Foundry sand testing is a foundry process used to determine if the foundry sand has the correct properties for a certain casting process. The sand is used to make moulds and cores via a pattern. In a sand casting foundry there are broadly two reasons for rejection of the casting — metal and sand — each of which has a large number of internal variables. The defects arising from the sand can be prevented by using sand testing equipment to measure the various properties of the sand.
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The testing process is divided in to three stages: sampling of the bulk material, sample preparation, and testing.[1]
Sampling is usually done at three different points of the process: upon first arrival from the supplier, en transport for processing (usually on a conveyor), and after processing. In each situation it is important to take a representative sample by mixing the sand or by taking multiple samples in different locations. Also, the sample must be stored in an airtight container to keep from spoiling it.
There are more than 25 basic tests, however only the important ones for the given casting process are used. The basic test measure the following parameters: wet tensile strength, mouldability, friability, moisture content, permeability, green compression strength, compactability, loss on ignition, volatiles content, grain size & distribution, dust (dead clay) content, and active clay content. Each of these tests can lead you to obtain specific characteristics of sand which can be crucial quality of casting.[2] Advanced testing tests for other parameter, such as splitting strength, shear strength, and high temperature compression strength.
Green sand is made up of basic sand (shell sand), bentonite or another binder, pitch powder or coal dust, and uninvited dust. Green sand properties cannot be standardized for all foundries and castings as such, yet place to place and job to job the specifications can be set to maintain minimal amount of rejection. A basic set of parameters to test are:
For parameters 1, 2, 4 and 5 standard bulk material sampling methods can be applicable or sampling can be done with help of sand muller, sand sampler and sand splitter to do it in a standardized manner.