PET Flakes

Plastic flakes require cutting forces for a rapid comminution. With our standard cutting mills like the Universal Cutting Mill PULVERISETTE 19, often sieve cassettes up to 0,5 mm trapezoidal perforation can be used. The optional high-performance cyclone separator with sample exhauster would be required with this setup. The air flow would chill grinding parts and sample, also the output would be removed out of the grinding chamber and separated inside the cyclones attached collecting glass.

For finest grinding results, our Variable Speed Rotor Mill PULVERISETTE 14 premium line is capable to achieve < 0,2 mm results when the mill was converted into a cutting mill.

With a start size of ~ 10 mm, we recommend a comminution in two steps. We started our first precutting trial with a 1,0 mm perforated sieve shell set.

A batch of 200 grams of sample was prepared and the complete sample was transferred into the mill within 2:45 minutes. The grinding sound vanished instantly after the last fragment was fed.

Only a small amount of ground sample was left loose inside the grinding chamber. Higher amounts of sample should precut without problems. With 200 grams, the used collecting glass was filled with ~ 500 ml output. We expect about 20 – 22 minutes would be required for a comminution of 1,5 kg. A 5 liters collecting glass should be used on the high-performance cyclone separator side.

Cleaning was performed rapidly by vacuuming with a soft brush.

With result 02, we used the precut sample of result 01 for fine grinding. A higher amount of sample (< 1 mm) was prepared and we ground sample with a proper feed rate for 10 minutes.

Within 10 minutes, we fed 130 grams of sample. The grinding sound was typical and vanished instantly, after the last fragment was fed. Also after this trial, the sample was not clogging the used set of sieve shells significantly. Surely a higher amount of particles about 80 – 160 µm would be present. Not all sample could be packed, because electrostatic charged fine particles could not be brushed out of the cyclones collecting glass properly.

We expect that about 2 hours would be required to comminute the desired 1,5 kg of sample. It is possible to partly automatize the grinding process when a Vibratory Feeder LABORETTE 24 would be used to feed the flakes or precut sample material.

With this result, we ground precut sample of < 1 mm to a fineness of < 0,12 mm. We prepared a proper batch of the precut sample and transferred the sample with a very low feed rate into the mill.

The mill was equipped with a sieve shell holder with 0,12 mm shells. We fed about 22 grams of sample within 5 minutes. With this throughput, the motor load was already moderate; faster feeding should lead to a rapid clogging of sieve shell perforations. After 5 minutes, the temperature of the grinding chamber was already > 45 °C and about ¼ of sieve shell perforations were blocked (mainly in front of the static knives).

We don’t expect that more than 30 grams of sample could be ground. Most likely an intensive cleaning step needs to be performed afterwards. For higher amount as required, we cannot recommend this setup for comminution.