Polymer

For our first trial, we used a cutting mill in combination with the active cyclone system. With an airflow of up to 2800 liters per minute, sample be chilled additionally and removed out of the grinding chamber in the moment when it is able to pass the sieve cassettes openings.

We fed the sample constantly for about 30 seconds until the grinding chamber is about filled by ~1/3. Air flow is still present, openings of the sieve cassette are not blocked, but after further 30 seconds, the sample is starting to melt inside the grinding chamber.

No further grinding is possible with this combination of sieve cassette and cyclone separator.

Without previous embrittlement, the sample can be comminuted with the Variable Speed Rotor Mill PULVERISETTE 14, combined with a sieve ring of 0,5 mm and the active sample exhauster system with cyclone separator.

During the feeding, grinding sound of the fed pellets has been “kind of sharp” – probably a sieve ring with reinforced edges might be beneficial for a grinding of higher amounts of sample, also a sieve ring with coarse openings will be made of thicker sheets of steel and will not get damaged that fast.

The ground particles use to be kind of “fluffed up” and lightly stick together. We checked the particle size by static laser scattering, but such results are not very reasonable when surface of single particles should be assessed.

About 30 grams of sample use to be found in the collecting glass of the cyclone separator. The rest of sample is attached to the collecting pans wall by electrostatic charge. After the grinding process, the lid has been opened and the lightly attached sample has been removed with the cyclone separator too. By grinding of further sample, the speed of air inside the collecting vessel with outlet will get higher and take out much more sample, so after a certain amount of sample will be attached, no further sample will remain inside the collecting vessel with outlet. As usual, a small amount of ground sample will also stay attached to the separation part of the cyclone separator by electrostatic charge.

For a grinding of higher amounts of sample, a Vibratory Feeder LABORETTE 24 can be connected to the PULVERISETTE 14. The smaller the trapezoidal perforations, the faster problems will occur (with heating of sample particles which will start sticking between rotor and sieve ring; heating of engines – mainly of the cyclone separator, etc). We cannot estimate after which fed amount of sample a cleaning step will be required or a security switch will turn off a motor because of heating.

We recommend choosing the sieve ring with the largest openings and a tolerable grinding result. For this, also a further trial with 1,0 mm sieve ring will be performed as well (see result 3).

We expect that we fed the sample with an almost maximum speed of ~ 40 g/min. After 80 grams of sample got fed (within 115 seconds), about 44 grams of ground material has been found in the collecting glass of the cyclone and 35 grams of lightly attached sample inside the collecting vessel.

We determined the fineness, using our Laser Particle Sizer ANALYSETTE 22 NanoTec plus plus, but because of fluffed up particles, the measured particle size distribution is not very accurate in behalf of achieved particle surface.

With 40 g / minute, it will take minimum 4-5 hours (+ cleaning / chilling times) until the desired amount of sample (10 kg) will be comminuted.