Sieve analysis
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A sieve analysis is a practice or procedure used for any type of non-organic or organic granular round materials including sands, clays, granite, feldspars, coal, soil, etc. It can also be used for grain and seeds.
A typical sieve analysis involves a series of circular sieves with a wire mesh cloth. They also have a fixed height. The sieves are nested in a series involving eight to nine sieves. This is typically called a column.
Wire mesh cloth are defined by their number of openings per inch. For example a 14 mesh will have 14 openings per inch, a 12 mesh will have 12 opening per inch, and so on. The higher the mesh number the smaller a particle has to be to pass through the column.
A sample is taken and split in a "splitter." The sample is then poured into the top sieve which has the smallest number of openings per inch. The next sieve than has more openings per inch. Traveling down the column the opening per inch on each wire mesh cloth increases. The last "sieve" is a round container much like a baking pan, and is called "the pan."
The column is placed in a mechanical shaker usually called a Ro-Tap shaker. The shaker will shake the column for a fixed amount of time, usually three minutes up to ten minutes. After the shaking is complete each sieve with its material sitting on its cloth is then measured in a unit of weight (usually grams). With the total weight the weight of the sample of each sieve is then divided by the total weight to give a percentage sitting on each sieve.
After the tabulation a particle size distribution is defined by the sieve analysis. Generally, the distribution is presented as a percentage passing a sieve and retained on a sieve.
For example, a 20 - 40 gradation is all the material passing the 20 mesh and retained on the 40 mesh. Other presentation can be singular such as +16, all material retained on the 16 mesh and above or -40, all the material passing the 40 mesh.
The particle size distribution is very important in academic science and in industry because this information is one indicator of the property of the material. The distribution can define how the material behaves related to viscosity, particle packing, rates of reaction, etc.
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[edit] Examples Where Sieve Analysis is Useful
Foundry sand is usually mined and graded through a screening process. In process testing, monitors the material's particle size. The particle size indicates the material's property to pack, as packing is crucial in casting processes.
Coke and Coal or coke or coal is grounding in a coal mill for power plant or kiln firing. The grounded coal needs to be fine enough to ignite to continue the burning process. The material's particle size distribution is defined by how fine it is. An example how fine a material is by defining it as 90% passing the-200 M or 85% passing the -325 M.
Sieve analysis and particle size distribution are also determined in industries such as ceramic manufacturing and glass manufacturing.
[edit] Drawbacks to Sieve Analysis
Sieve analysis in general has been used for decades to monitor material quality based on particle size. For course material relative to a size range, sizes that range from 8 mesh to 200 mesh, a sieve analysis and particle size distribution is accurate and consistent.
However, for material that is finer than 200 mesh, a sieve column for material less than this is useless. This is because the mechanical energy required to make particles pass through an opening increases as the mesh size increases and the particle size decreases. At 200 mesh or finer, the energy to pass material is greater than the capacity of a mechanical shaker. If one were to use a mechanical shaker, the shaking time would need to be increased to infinity to separate the finer grades.
There are other means of determining particle sizes less than 200 mesh. Some devices utilizes a single sieve and has a vacuum under it with a rotating receptacle that causes a wave to form as it passes over the material.
Wet sieve analysis can be utilized but its drawback is that water can fill the opening as much as material can pass through it and could lead to inaccurate results.
Other than light scattering or x-ray devices, a simple procedure hydrometer analysis, which uses Stoke's Law and sedimentation one can measure the changing specific gravity over time and use Stoke's equation to determine size.
Another draw back to sieve analysis is the assumption that all particle will be round or nearly round and will pass through the square openings. For elongated and angular particles a sieve analysis will not yield reliable results. Even Stoke's Law assumes that the particles are spherical.
[edit] Additional Information
When using sieve columns each sieve has a US Standard Sieve No., this number usually corresponds to mesh size, but with the courser sizes like No. 8 to No. 18, the Sieve No. does not equally match with the mesh size. For the finer sieves like 100 M, 200 M, and 325 M the Sieve No. and mesh do match. Therefore, care must be taken to either identify a grade by Sieve No. or by mesh size, but realize one may not substitute for the other.
However, in industrial settings the common notation for gradation is by Sieve No.'s. When one is designing a screening operation based Sieve No. care must be taken to factor in this difference.
[edit] Example of a Sieve Analysis Table
| U.S. Standard Sieve No. | Sieve Opening (mm) |
|---|---|
| 4 | 4.75 |
| 10 | 2.00 |
| 20 | 0.85 |
| 40 | 0.425 |
| 60 | 0.25 |
| 100 | 0.15 |
| 140 | 0.106 |
| 200 | 0.075 |
When the gradation of a soil is known, it can be classified using one of several different systems such as the Unified Soil Classification System. The classification of a soil is indelibly linked to several of the soil's engineering properties.
[edit] See also
Soil Gradation --Deekayfry 22:55, 17 February 2007 (UTC)
