The technique will involve the application of a gauge to determine "go, no-go" through a series of tests (trials & errors) correlated for your downstream process application, i.e, what you are trying to accomplish next step.

I have performed similar go, no-go testing of polymer powders in large bins using a depth measuring rod plunged manually down into a large bin. This depth data is then correlated to your downstream process application. If it is 0 labor involvement you desire, of course dependent upon accessibility, balanced with cost, research for a device like a rotating bin indicator, with rotating paddle or suitable modified end fitting - suitable to your material packing density - connected to a power strain-type gauge. The applied power and strain gauge would be adjusted to accomodate the range of resistance you expect to encounter in the large bin down on though to specific depths. With the proper communication links/controls, trial and error testing with this setup can be made to ultimately provide go, no-go gauging of your powder packing.

Don't overlook the value of trying to determine additional "non-intrusive" means of accomplishing the same, such as process and pack-out temperatures, settling times, warehousing temperatures, moisture and humidity conditions, etc. Oftentimes with polymers, "upstream" processing variables can be identified through data collection and monitoring - framed and controlled - thereby reducing the range of variability in packing density. ■

There is no such instrument, to my knowledge, as the flow condition of a bulk material depends on many material dependent factors. One way to determine the state of density would be to press a circular rod attached to a force gauge into the bed to a standard depth. The resistance would be a measure of density, but the tool would either have to be calibrated for samples taken or forget density and use the information as a comparative device that can be reconciled against how previous recorded batches have performed.

Referring to your later comment 'that there is no instrument that will tell how the material will flow as packed in a container' opens a wider subject. Whilst density is an important feature with regard to flow, it is also important to know what stresses are acting on the material in the situation of interest. I suspect that you interested in the way in which the product can be extracted from the container, and here the position becomes more murky because the density and flow condition will vary at different depths in the bed according to how the bulk has packed down with time. Scooping or vacuuming from the surface exposes a further unconfined surface and replicating the conditions of each section will allow its shear strength to be measured, which will provide data about potential gravity flow but is likely to be unhelpful for other uses.

If the concern relates to emptying drums, the application can only be assessed in each individual case based on the economics of the situation and more data would be needed to offer specific advice. ■