Re-Testing Density
Non-cohesive powders will yield similar density results on retesting. With powders that form strong bonds under compaction it is necessary to break these contacts to secure realistic density values. Of course it is difficult to appreciate the stress history of any powder that is to be tested so it is good practice to pre-screen the material if the measurement has sensitive overtones. In most cases it is adequate to give the sample a good shaking and if it behaves in a loose condition it will normally give reasonably reproducable values under similar loading or tapping conditions.
Some care must be taken with hygroscopic products, delicate granules and materials that change with time to ensure that there are no fundamental changes in the nature of the material being tested. ■
Reproducibility Of Tapped Bulk Density
I have designed a Bulk Density Meter a couple of decades ago, conforming to standards set by myself. This model is widely used in the Tea industry and also in a few other industries in India. Subsequently I designed another Bulk Density Meter conforming to ISO & ASTM standards a few of which are in use by different industries.
You can see images and a brief description of both these models in my website <www.chandy-john.com>.
Since I am also based in Bangalore, INDIA, I invite Pradeep Prabhu to contact me (00-91-080-25584986) and fix an appointment to come and see these two models at Peenya in Bangalore and carry out any experiments he may like to do at no cost, or obligation.
Regards,
Chandy John ■
Main Influences
If the powder is at all cohesive you un the risk of agglomerating it. To get repeatable measurements will then require it to be brushed through a fine sieve each time to get these agglomerates to a repeatable size, but be careful of electrostatic effects if it is a dry powder - these will also affect it!
I second the other comments about attracting or losing moisture too - a controlled environment will be required to get repeatable results if the material has any significant propensity to attract or lose moisture with changing RH and this affecting the flowability.
Even if you control all this, you may get a repeatable result after a number of tests but the repeating value is not likely to be the same as the first value because the first value will be controlled by what has happened to the powder before you got it in the apparatus! If you want something meaningful to process analysis, you should repeate the test many times with fresh samples (one fresh sample carefully subdivided if it is the repeatability of the test you are trying to establish - I would suggest subdivision using a spinning riffler).
What is the point of this exercise, may I ask?
Mike. ■
Reproducibility of tapped bulk density.
Firstly,I would like to thank everybody who contributed with their views in my previous thread.Please keep your suggestions coming in.
The second issue which i am really interested in now is whether tapped bulk density is a destructive analytical method or u can subject the analysed(tapped sample) after homogenization to retest.I shall be carrying out experiments to check that but if you had any experience do share it.
Lets be symbiotic.
Regards,
Pradeep Prabhu. ■