Tumeric powder

As mentioned on our main page of the report, a dry grinding of a sample to < 40 µm completely is not possible. When a certain level of fineness is reached (d50 < 30 µm), all samples will start sticking to available surfaces. For a finer result, a grinding in suspension will be required eliminate surface active forces.

We dispersed a small amount of the sample in water and used our Laser Particle Sizer ANALYSETTE 22 NeXT (static light scattering) to check the particle size distribution. We found a start size with d50 <70 µm and about 28 % of sample material < 40 µm (sphere equivalent diameter).

With the largest particles about 250 µm, a Impact rotor with 24 ribs can be used for grinding. For a complete kilogram of sample which should be ground, and for the present fineness of sample, we strongly recommend to combine the mill with a high-performance cyclone separator (with sample exhauster with dust category M). With the air flow of the sample exhauster, ground sample material will be removed out of the grinding chamber, also grinding parts and sample will be chilled additionally.

One bag (500 g) of sample was used for our trial. The mill was equipped with a sieve ring with 0,12mm trapezoidal perforations and the sample was slowly transferred into the mill which was running at maximum speed. The grinding sound was typical and did not change during the feeding process.

It took 6 minutes until the 500 g batch of sample was transferred into the mill. Afterwards, the grinding chamber was opened and the grinding chamber was inspected. Plenty of fine ground sample remained (by surface active forces) inside the grinding chamber and was not removed with the air stream. Also sample dust used to build up directly behind the trapezoidal perforations of the sieve ring. After this 500 g batch, about 10 % of the perforations seemed to be clogged. The residues inside the grinding chamber were merged with the cyclones sample. For this, we brushed the residues of the collecting vessel into the channel of the cyclone while the sample exhauster was running.

The ground sample was packed and we checked the particle size distribution of the ground sample material. The d50 sunk to < 31,4 µm About 60 % of the sample (sphere equivalent diameter).

The cleaning effort after our grinding trial was higher. All grinding parts were slightly colored with sample. The grinding parts were disassembled and washed with warm, soapy water. It took about 10 minutes until all parts were cleaned and dried.

Most likely, also the desired 1 kg batch could be ground within 12 minutes. A cleaning step does not seem to be required for one kilogram. We don’t recommend to comminute more than 1 kg of sample per batch.