Bulk Density of Powder

Check out the American Society of Testing and Materials. ASTM They will have testing procedures.

We use the same method in our factory.

We make the test every 30 minutes or so. We don't expect the density to change much over 30 minutes so there's no need to make a test for every pouch.

Don't worry about it.

regards,

Vulcan

Interesting - I would like to know more as I deal in handling powders and write training manuals. There is the question of straight bulk density and "tamped" bulk density. Do you guys use a vibrator of some sort to ensure constant fluidity?

Yes,

There is freely settled density

and tapped density method.

Thank you.

In the coal carbonization (coking) industry the bulk density of the coal mixtures used are typically monitored by ASTM coal bulk density tests. These tests are generally used only to provide a means for system operators to guarantee that BD has not changed significantly during the operations due to changes in moisture content or size distribution withun the mixture (both of which will cause changes in BD). This then allows the operators to make system adjustments. It is known that the height from which the coal is dropped during the test will significantly alter the reading of BD.

To allow more continuous monitoring for such systems, nuclear systems were developed during the 1950's and are still in use. Such units might be of worth for your case.

My 2 cents worth.

Hello sandeep,

Obviously it will help to find the exact method and frequency to test by. But if you have a machine fed by a single mix machine, and you have to make several mixtures throughout the day, a test at the start and middle, and end of the run should work. This is providing the single mix lasts no longer than about 30 to 45 minutes and than the mixture can in no way get wet or get dry by say evaporation through the machine packing it?

If you have a continuous mix machine that supplies the powder then you should be more rigorous and be certain you check and have proof you checked when you are supposed to.

The checking can be by a light sensor for instance and that way the machinery does not need to stop. There was a chocolate factory near where I live and they used to use the light method for checking for mix consistency.

Hope this helps.

bb

There are several methods, many having already been described. However, the most critical factor is consistency and following a strict procedure.

I have seen people taking BD in a aluminum beaker of known volume and tapping the side of the beaker to get the material to settle. Over time, the beaker became dented so that the volume of product being weighed became lessened. While the APPARENT density remained the same, the ACTUAL density was slowly climbing.

Sounds like someone got carried away with the "tapping" when does Tapping become "bashing". I was once told of a compressed air factory that had trained mice to stamp down the air in the cylinders.

Probably you´re getting underweight pouches even if filling to 100%. Then my friend either you make a longer pouch or somehow increase the bulk density of the mix. It´s not a problem of how you measure density but rather one of having the right pouch size for a given target fill weight. I´ve seen several tricks applied when the problem is a light powder not giving the target weight even if pouch is overfilled, which in any case is not desirable because you´ll get seal contamination. If the material is fryable you can reduce particle size by attrition such as in a screw feeder thereby increasing density. You can fit your bagger with a vibrating device below the horizontal knive, or fit a piston operated tap tied to the filling cycling. Bottom line is powders are tricky monsters and each situation calls for specific solutions.

Probably you´re getting underweight pouches even if filling to 100%. Then my friend either you make a longer pouch or somehow increase the bulk density of the mix.

A properly designed and configured filling machine will always try to fill to the specified net weight.

If the density of the powder is low, you will use more powder (by volume) to get the desired weight. That's usually a loss for the manufacturer.

If the density is high, you will use less powder (again by volume) to get the desired weight. That's a gain for the manufacturer but if a sharp customer notices that he seems to have less powder than usual in his purchase, he could file a complaint.

For these reasons, it's important to maintain a constant density of powder prior to filling. Increasing the pouch dimensions is an expensive and time consuming exercise.

regards,

Vulcan

You´re right of course. But the problem is that if you decrease the fill volume to account for a heavier powder density the pouch will appear underfilled even at the target fill weight. Customer first reaction will be to think that the bag is underfilled, never mind that you fill by weight. Conversely a lighter powder will overfill the bag in trying the get the target fill weight. So you´d better had taken this into account when defining the bag lenght. Once you´ve set the bag lenght and got the printed film for your product your´re stuck until the next batch of film is ordered.

if you decrease the fill volume to account for a heavier powder density the pouch will appear underfilled even at the target fill weight

That's what I said or meant.

So you´d better had taken this into account when defining the bag lenght

Correct.

Once you´ve set the bag lenght and got the printed film for your product your´re stuck until the next batch of film is ordered

As I also said, changing bag/pouch length is not a task to be taken lightly. We usually change our pouch designs (images/text on the pouch) on a yearly basis though the pouch dimensions are usually the same.

So we live with the pouch dimensions and try to control our density. If the density deviates from the norms, we stop production and solve the problem. We don't change the pouch dimensions just so the powder will fit in it.

regards,

Vulcan