Foundry sand testing
Encyclopedia
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.
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. Advanced testing tests for other parameter, such as splitting strength, shear strength, and high temperature compression strength.
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.
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...
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
Core (manufacturing)
A core is a device used in casting and molding processes to produce internal cavities and reentrant angles. The core is normally a disposable item that is destroyed to get it out of the piece. They are most commonly used in sand casting, but are also used in injection molding.An intriguing example...
via a pattern
Pattern (casting)
In casting, a pattern is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.Patterns used in sand casting may be made of wood, metal, plastics or other materials...
. 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.
Process
The testing process is divided in to three stages: sampling of the bulk material, sample preparation, and testing.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. Advanced testing tests for other parameter, such as splitting strength, shear strength, and high temperature compression strength.
Sand control
Green sand is made up of basic sand (shell sand), bentoniteBentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
or another binder, pitch powder or coal dust
Coal dust
Coal dust is a fine powdered form of coal, which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal.-Explosions:...
, 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:
- Fineness number (grain size/AFS Number) of the base sand
- Moisture content in the mixture (ranges from 2-7% depending on the casting method)
- Permeability (ability of compacted mould to pass air through it)
- Total clay content (dust content)
- Active clay content (presence of active bentonite/clay which can readily bond)
- Compressive strength
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.