Particle size analysis of powders using test sieves is, and has been, the standard for many years. The sieving procedure was formalized in 1925 with the establishment of ASTM E-11. The ASTM standards cover the manufacture of test sieves and the procedure for conducting a manual sieve test.
Beyond ASTM E-11, very little has taken place in the test sieve procedure area to keep pace with technology.
In fact, the ancient method of hand-sieving is still being practiced today. Even mechanical techniques for sieve shakers to a major degree attempt to duplicate the results of ASTM manual procedures. Currently changes are taking place to make mechanical shakers quieter, smaller, and more widely adjustable.
Most of the technological development in the area of particle size analysis has been in the sub micron area (which is difficult with current test sieves methods) with the application of newer technologies such as laser equipment. Also some advances have been made in sieve cleaning by using ultrasonics. This method is a major improvement over the time-consuming brush and poke cleaning that is widely used. In the production of sieves, computer technology is being applied to the selection, manufacture and certification of test sieves/screens.
Since the increasing emphasis on quality control programs such as ISO 9000, certification of test sieve performance has become a growing requirement. New, efficient and effective calibration procedures have been developed for in-plant use that give a solid reference for the more stringent quality control procedures now being introduced. (Refer to How To Calibrate A Working Test Sieve.)
Except for high end automatic systems, little effort has been placed on bringing technology to the actual process of conducting sieve test analysis. As practiced for many decades the sieve test procedure is as follows:
- Weigh a sample and record the starting weight.
- Place the sample in the top sieve of a stack of sieves.
- Shake the stack for a specified length of time at a preset speed.
- When shaking is complete, take each sieve, one at a time, and tap and brush the sample out of the sieve.
- Weigh this segment of the sample.
- Record the sample weight from each sieve.
- Calculate the percent of sample retained in each sieve.
Another way to do the sieve test is to first weigh and note the weight of each sieve. Then do the shaker test and afterwards weigh each sieve again. Deduct the empty sieve weight from the sieve weight with a sample. Record the weights and calculate the percent of sample remaining in each sieve.
Both these procedures are cumbersome, time-consuming and subject to many errors, i.e., not entirely removing all the sample for weighing, transposition errors, calculation errors and missing records.
Figure 1. Sample calculation.
Elasped time from end of shaking was 5:10 (min:sec). There was 5.78% sample loss.
As quality control standards are increasingly applied, sieve test tolerances are tightened resulting in the need for the increased reliability of sieve test results. A simple error in weighing or recording of data can cost thousands of dollars in lost production time or returned goods. The laboratory and production environment of today is high speed, high tech and automated.
With these factors in mind, the CSC Sieve Analyzer was developed to take as many of these variables out of the testing and report processes as possible. At the same time, it was developed with value and economy targets that make it practical for small operations as well as large, high speed processors . With the CSC Sieve Analyzer, the test procedure is shortened to the following:
- Load the sample into the top sieve of a sieve stack (no need to preweigh).
- Run the shaker.
- Place each sieve from the stack on the CSC Sieve Analyzer. (See Figure 1)
At this point the CSC Sieve Analyzer produces the results of all calculations needed to report the amount retained and passed by each sieve and prints a hard copy report. It also has provisions to transfer this test data to a computer.
Figure 2. Sample Printout.
Elasped time from end of shaking was 2:21 (min:sec). No sample loss.
To further enhance the conduct of sieve analyses under a demanding quality control program, the CSC Sieve Analyzer provides for the comparison of each sieve's performance to a certification standard.
This procedure reduces operator error to nearly zero and just as important in many operations, cuts the time for conducting a sieve analysis test to just 20 to 30 seconds after the shaking is completed.
Test sieving for particle size analysis of powders is an age old method that will probably be in existence for the next 100 years. The CSC Sieve Analyzer adds to that history by taking sieve test procedures and moving them into the high speed, high tech, automated world of today.
Click here for more information on the CSC Sieve Analyzer and other sieving equipment.