Re: Right Methode For Measuring?
Andrew Jenike in his bulletin titled "Storage and Flow of Solids" says it best:
"(The angle of repose) is not a measure of the flowability of solids. In fact it is only useful in the determination of the contour of a pile, and its popularity among engineers and investigators is due not to its usefulness but to the ease with which it is measured."
Some grades of acetominophen have angles of repose that are lower than those of sand. By this definition, acetaminophen is more flowable than sand, but when was the last time you saw an hourglass filled with sand?
There are less elegant tests than shear testing for measuring flow properties of powders, but their utility is questionable. Why don't you find a lab that will give you a student's discount, especially since you will not be asking them to build a silo or using the data to build a structure?
Good luck... Greg... ■
Re: Right Methode For Measuring?
Well as they say necessity is the mother of invention !!! If u don’t have the equipment improvise.
For tapped density you just need a plastic beaker of known volume and something to tap it with. Pour the material in the beaker weigh it from the weight you get the poured density. No start tapping the beaker and the material will settle down add the material on top and continue this process until no more material could be added. Weight it and you will get the tapped density.
Angle of repose is even simpler; take a funnel cut the stem put it on a wide stand pour the material to a suitable height and measure the angle. Repeat it few times and take the average. Easiest thing is to take the pictures and print them very east to measure angle of repose from there.
I must admit Jenkie shear cell is an expensive piece of kit so lets make one for you which doesn’t cost a an arm and an leg. Lets say you want to measure effective angle of wall friction. For this you will need a Table. Pulley, string, small container, suitable size circular ring to act as the cell. It could be metal but Perspex / plastic does just fine, a lid for the cell (make sure it is of suitable size) and of course weights. Fix the pulley on the side of the table put the wall material sheet next to it. Fix the cell to string (jubilee clip works well) pass it over the pulley and hang the container on the other side 5 – 6” from the ground, make sure the sheet is bigger then the cell. Your shear cell is ready to go.
Fill the material in the shear cell place the lid on the top put the weight on it ( 0.5 – 5 Kg is normal range). Now walk around the lab and find a material which has the highest bulk density so u don’t need a large container (sand is good). Now slowly start pouring the sand in the container until it moves. Immediately stop the addition and weight the container. Repeat the procedure with increasing weights. I assume u know the rest of the calcs. For internal angle of friction I think you can find your way by now. This is a crude method but then for your student project; I think the results will be suitable. Good Luck ■
Re: Right Methode For Measuring?
Thank you for your constructive answers,
I have additional questions in relation to Mantoos answer.
I will definitely try to design shear cell according to your suggestions, is the diameter of cell ring cca 100 mm suitable?
I have problem calculating angle of wall friction and angle of internal friction from results of your experiment?
How can I calculate these values from results of experiment.
Ok, I know that I can calculate force that is needed to move the cell and probably the friction, but how can I calculate the angles?
all best
Davor ■
Re: Right Methode For Measuring?
I remember when I was doing physics at school (aged about 14), we had an experiment to measure the coefficient of friction of a steel block on a wooden surface. The method we used was similar to that descrbed by Mantoo.
Doing the experiment we learnt about coefficients of friction, the relationship between the normal load and frictional force.
The methods Mantoo describes use the same theory as solid friction so any basic text book on physics or mechanics will discuss this and lead you to an understanding of the relationships and the friction angle.
However, if you are careful in your measurements you will find that the relationship between normal load and frictional force is maybe not a simple one. This will be your start on the path of understanding of the properties of a bulk solid. ■
Re: Right Methode For Measuring?
4” cell is fine for powders. As far as the calc’s are concerned designer have given u a good hint to very easy basic reading. Hope you can find your way through it or if you read any basic bulk solids handling / silo design book you will get the answers. I don’t think it’s a good idea to spoon-feed students. You have been put on the right path just follow it.
As far as basic physics experiment is concerned indeed the principle Jenike Shear cell is similar 8th grade physics experiment. The expensive bit in the modern shear cells are the constant drive motor / gearbox and the load cell bits (power supply and data logging). ■
Powder Testing
You do not require expensive equipment to secure a measure of the flow properties of loose solids. The first thing to understand is that such a value can not be expressed by a single figure as there are many features that determine how well a product will flow, occording to the cirumstances of the application. Key features of interest, in roughly their order of importance (although this again depends on the type of interest) is: -
- A measure of shear strength
- Wall friction
- Bulk Density
- Porosity
- 'Compressability'
A recent publication by Eddie McGee of Ajax equipment describes a 'spider' diagram technique for showing in a grphical form the various characteristics that are relevant to different circumstances.
Ajax also publishes information on the characterisation of bulk materials that summarises simple and advanced powder tests method and equipment. For more information contact tech@ajax.co.uk
Lyn Bates ■
Right methode for measuring?
Hi all!
I need to measure some of the flowabilitiy indicators of powders (angle of repose, tapped density) for my diploma and I have couple of problems:
1.I don’t have sufficient resources to by some of the modern equipment (shear cell testing) so I need to choose method that is simple (poured and drained angle of repose, tapped density).
Do I need to follow some standard design of equipment that I plan to build and use for measuring purpose or I can design it and adopt it according to powder properties?
2.I know that cohesive powder properties can not be measured with angle of repose method. I plan to make experiments with uncohesive powder (mixture of salt and flour) and than gradually add some fat in that mixture. Fat in the mixture will probably change properties of mixture and mixture will become cohesive at some percentage of added fat. How can I measure at which point the mixture has change from uncohesive to cohesive and how can I measure flowability of the cohesive powder whit some simple method?
Thank you all !
Davor Janjatovic, student PBF Zagreb ■