organic fibers (dry sample)

Grinding sound stopped after ~ 10-15 seconds. Because some of the (mainly wooden) fibers use to be left loose inside the grinding chamber, we run the machine for a total of 25 seconds. Afterwards, only a few fibers are left loose on top of the sieve cassette.

A grinding of higher amounts of sample is still possible.

Cleaning can be performed rapidly by vacuuming with a soft brush.

The ground sample use to show a maximum thickness of ~ 0,5 mm, because fibrous material can pass the sieve cassette longitudinal, still longer pieces can be found.

Eventually the grinding result can be improved somehow, when sample will be fed batchwise without the cyclone separator. Sample will remain longer inside the grinding chamber and particles will have more time to get comminuted.

To testify, we recommend fixing a plastic bag to the connector of the cyclones tube. Be aware of temperature and pollution of grinding tools when operate without cyclone separator.

By grinding the sample with a 0,25 mm sieve cassette, the amount of particles which will be > 1 mm length will be reduced (especially compared with the sample you ground with a 1,0 mm sieve cassette).

Just like result 1, grinding sound stopped rapidly, after 25 seconds, only a few fibers use to lie loose on top of the sieve cassette. A grinding of higher amounts of sample is possible.

On special request, sieve cassettes smaller than 0,25 mm are available. Because the gap between rotor knives and fixed knives uses to be bigger, we can only recommend using smaller sieves with very brittle samples like e.g. coke or coal.

For demonstration, we took the 0,1 mm sieve cassette and tried grinding 30 g of original sample.

Output after 45 seconds of grinding has been 12 g. After a total grinding time of 90 seconds, already 16 g of ground sample has been found in the collecting glass of the cyclone separator. We aborted the grinding process after 2:30 minutes after an output of 21 g has been achieved.

Some of the sieve cassettes openings (~ 20%) use to be blocked with fibrous material which use to stick inside the trapezoidal openings.

For this, we are guessing that a grinding of up to 100 g might be possible before a cleaning step will be required.

Instead of cutting, a Variable Speed Rotor Mill will comminute sample by impact force on the ribs of the rotor and shearing force between rotor and sieve ring. For this, we are guessing that fewer particles will pass the openings of the sieve ring longitudinal.

In combination with the optional cyclone separator, we have been able to grind 50 g of sample (pre cut material with 1 mm sieve cassette and PULVERISETTE 19) within 60 seconds. Majority of ground sample has been found in the collecting glass of the cyclone separator. A bit of sample use to stick lightly to the collecting pan of the Variable Speed Rotor Mill PULVERISETTE 14 and the outside of the sieve ring.

Eventually, for a grinding of higher amounts of sample, it might be necessary to interrupt the grinding process for a cleaning step, if electrostatic charged sample will stick stronger to the sieve ring.

In our last trial, we ground the remaining pre ground sample (< 1 mm with Universal Cutting Mill PULVERISETTE 19 and sample exhauster system with cyclone separator). Instead of a 0,12 mm sieve ring, we used a 0,2 mm sieve ring for grinding.

A lower feeding speed might improve the grinding result. Probably more sample will be blown out of the pan into the collecting glass of the cyclone. Probably less fine particles will be blown into the pre filter element of the cyclone separator as well.

The ~ 103 g of pre ground sample have been fed within 3 minutes. Afterwards, about 102 g of ground sample have been found in the cyclone’s collecting glass. Fineness of ground sample appears to be better, compared with 0,25 mm sieve cassette result of Universal Cutting Mill PULVERISETTE 19.

So if a with PULVERISETTE 19 and 0,25 mm sieve cassette is not satisfying, probably a Variable Speed Rotor Mill PULVERISETTE 14 with 0,2 mm might be an option.