Six very useful tips for sieving analysis
High quality testing sieves are the first choice in particle size analysis work for numerous reasons. For example, simple, efficient and low cost etc. All those reasons made the standard sieve analysis become the most widely use quality control procedure in any powder process control industry. To conduct the correct standard sieving analysis procedure, Glenammer engineers provide six tips below to help ensure the results are as accurate as possible.
Tip No.1 Monitor your laboratory conditions first
Before conducting the experiment, one factor that needs to be considered is the reaction of the material to ambient conditions. Please note that extremely dry conditions can cause fine powders to adhere to sieve components and each other with strong electrostatic charges. The most accurate test sieve available would be of minimal use if the relative humidity in the test lab was 99%.
Tip No.2 Control the size of the sample
For a lot of experiments, the tendency is to use an excessively large sample to get more accurate test results. However, for sieving analysis, the accuracy of the result will be reduced if the sample is too large because that will not permit each of the particles an opportunity to present themselves on the test sieve surface. Generally, a 25-100g sample is recommended. There is a procedure to help with establishing the appropriate sample size, using a sample splitter to reduce sample to different weights (25g, 50g, 100g,200g), test samples with the various weight range. If the test with 50gram sample shows approximately the same percentage passing the fine sieve as 25gram sample, whereas 100 gram shows a much lower percentage, this would indicate that the 50gram sample is the appropriate sample size.
Tip No.3 Consider using “relief screens”
To avoid overloading any sieves and causing damage, care should be taken in selecting the proper sieve aperture sizes. Large concentrations of material to pass through the sieve will result in a large portion of material retained on the test sieve. "Relief sieves" are larger aperture sieves placed above the one you want to retain the sample in. They are used to help remove the burden and avoid damaging fine mesh. Otherwise, particles slightly larger may become wedged in or forced through the sieve opening by the mass of material resting above them. Glenammer test sieves are reinforced with a backing mesh for aperture size 90 microns (No.170) and under to avoid damaging the sieves.
Tip No.4 Adjust your oven temperature
Wet washing sieve test is a different method of analysis where liquid drains through a stack of sieves. After that, the residue needs to be dried - either over a hot plate or in an oven. If the oven temperate is too high, sieve cloth might become loose and the solder joint can be damaged too. Therefore, maintaining the temperature below 149°C (300°F) is recommended.
Tip No.5 Attention on the test results
The starting sample weight should be recorded and compared with the finished total sample weight that is retained on the sieves after the experiment. If the weight of the finished sample deviates by more than 2% from the initial weight, the analysis and sample should be discarded. Technically, sample losses can result in error and inaccuracy of the analysis.
Tip No.6 Sieve care and cleaning
Test sieves should be kept clean and dry at all times. Like any other analytical laboratory equipment, they require regular care and should be ultrasonically cleaned to maintain their performance standard. A quick clean between tests can be conducted too. Use a nylon bristle pan brush with the bristles cut to a length of approximately 25.4mm (1"), the preferred method is to use the brush in a gentle circular motion. Brushing should be avoided on sieves finer than 150 microns (No.100), because brushing can loosen wire mesh. With proper care, Glenammer test sieves can perform accurately for many years, they can last 3 times longer than other brands.
Advantech Mfg. (2001) Test Sieving: Principles and Procedures. Available at: http://www.espanol-advantechmfg.com/pdf/principles_procedures_manual_with_tables-2.pdf (Accessed: 23 February 2017).