Working Process of Tap Density Meter

Tap density measurement is one of the classic tests in powder measurements.

What is tap density?

Bulk density is the mass of an aggregate of particles divided by the volume they occupy.

Because bulk density is not an intrinsic value of any material, since it changes depending on how the material is handled, it is often expressed as free flowing density and tapped density.

A powder when tapped or vibrated, causes the particles to rearrange among each other. The way they rearrange is a function of the particles cohesivity. This feature affects the flowability of the powder. These test values are expressed in ratios of the tapped density to the untapped density like the Hausner Ratio and the Carr’s Compressibility Index.

It is a useful compressibility test tool used in R&D and Quality Control of new formulations in the pharma industry. Since resin is molded or extruded by weight, companies calculate their cost of production by the weight of the material used. So, knowledge of bulk density values is required to obtain a certain weight of finished product in the case of plastic resins.

What do the Tap test tools measure?

Good quality Tap density testers help to calculate the Hausner Ratio and Carr’s Compressibility Index by measuring the initial and final volumes (after tapping) as well as the tapping or packing kinetic in repeatable and standardized procedures.

Loose packing is stabilized by inter particulate friction. Tapping reduces this friction and allows the particles to rotate and slide into packing which is denser. Tapping introduces a small amount of kinetic energy which makes the particles jump up and settle to lower levels with reduced potential energy and better packing.

What to look for in a good tap density apparatus?

Any powder rheometer is also designed to allow for the above tap test tools. What one must look for in a good tap density apparatus:

1. It should be having a user friendly software
2. Selectable reports that comply with GLP should be available.
3. It should indicate any errors in measurement;
4. It should give calculated results of Hausner’s Ratio and Carr’s Index – tapped density and bulk density and compressibility ratios.
5. It should be PC and mobile compatible for downloading data.
6. Should meet specification of USP, IP, ASTM etc.

How does it work?

The powdered sample, which is weighed, is poured into a graduated glass cylinder and the volume is measured. The tap density meter is set for the number of taps which are mechanically carried out by raising the cylinder and allowing it to fall a certain distance under its own weight, with readings continually taken till there is no change between successive readings.