Powder staying in hopper

[Sorex]

Hello,

We are experiencing problems with a powder not getting out of it’s hopper. This powder has been replaced recently by a powder (the same material) of a new supplier. The powder is sucked out of the hopper whenever the next hopper in the process is empty. Approximately 2,5 meters from the hopper an air suction valve is present in the line.
The hopper is also equipped with a vibrator, which was necessary for the powder type we used to have.

The effect we see is that the powder piles up before the opening of the hopper. The vibrator only makes this worse. The flow properties of the powder are fine.

Can it be that the cohesive strength of the new material is higher resulting in an opening size that is too small? Or isn’t it that simple….

Is it common for the air suction valve to be located after the hopper? In my opinion it would be more effective if it was in line in front of the hopper, creating an air flow right below the opening.
Thnx 4 ur input in advance!

Grtz, Sorex

 

[rmw]

Do some research on your material with respect to its angle of repose. It appears to me that the hopper design with respect to the slope of the sides is different than what the angle of repose of your material requires.

rmw

 

[IRstuff]

What else has changed? Humidity? Size and shape of material particles?

TTFN

 

[Sorex]

Thnx for ur input.

RMW, should the angle of the hopper be larger or smaller than the angle of repose. I can think of reasons for both options. Or should it just not be in say 10% of that angle.

TTFN, The size and the shape of the particles has changed. The problem is that the old type of powder isn't used anymore, so we can't compare the two. All other process conditions are still the same.

Sorex

 

[m777182]

Your hopper is not designed for mass flow: as you pointed out the possible sources of your trouble yourself, "The flow properties of the powder are fine..".This statement is false. You probably measured the angle of repose but it does not correlate the flowability.
Further,"Can it be that the cohesive strength of the new material is higher....?" The answer is Yes. And the friction of new material with the wall material is different too.
"The vibrator only makes this worse..." . True, because vibrations make material more dense.
All these facts call for redesign of your hopper(PE lining, maybe aeration, insertions..).
m777182

 

[Sorex]

thnx,

I didn't measure the angle of repose yet. During testing we see the powder flow perfectly when it gets out of the hopper. I suspect the cohesive strength and the angle of repose cause our problems. The powder sticks to itself like for instance snow.

The powder sticks a little bit to the stainless steel wall of the hopper, but not more than the old powder used to do.

I'd like to change the angle of the hopper and replace the vibrator by a knocker (after strengthening the system).

What should the angle of the hopper be compared to the angle of repose of the material? Smaller, bigger, the same?

 

[m777182]

It won't be this easy: a knocker will consolidate your material similar to a vibrator action. A strong knocker will break the wall of your hopper-don't walk arround it, a broken M14 screw acts like a small tromblone!)
you should measure the so called flow function of your powder and that has not much to do with the angle of repose.With the flow function in your hand you can start geometry calculation of your hopper. Try to get some information on "

http://www.zeppelin-nt.com"

in Germany or
"

http://www.jenike.com/"in

USA or in UK at"Freeman Technology [news@freemantech.co.uk]".You will save your time and your energy.
m777182

 

[corrosionman]

Sorex every job has its own peculiarities - - yours sounds typical of silo problems. Sometimes a solution is to line the cone with a low friction sheet, or even to paint with a low friction coating. Has your silo got a rough surface at present ?
Often than not these methods don't make any difference.
We once solved the product from "bridging" by installing an air jet but it depends onthe material. We also heard of an air canon that blasted at regular intervals.
Good luck CM

 

[MJCronin]

Sorex,

It sounds like you have the classic problem of bulk material handing, old equipment - new process ingredients.

See if there is a way that you can change the properties of the powder delivered via a change in spec with your supplier. Has there been a sample tested for moisture content ?

If you want a quick solution to your problem, I would investigate the addition of a small air cannon to your silo (

http://www.powderandbulk.com/conveying/activators.htm)

and try some of the negineering forums devoted specifically to these issues (

http://www.bulk-online.com/Forum/)...

Good luck

Please complete this thread and tell us about your solution


-MJC

 

[kenvlach]

I agree with the suggestion to test for moisture content -- do one sample as-received & another after exposure to ambient air for a few days.
Don't know if applicable to your material, but some powders can be purchased with an anti-caking additive. Useful if problem due to absorbing moisture from air.