Delicate materials such as alginate or even raw liquorice can be ground quickly and effectively thanks to a new impact rotor insert accessory and sieve ring
New features the Pulverisette 14 variable rotor speed mill make it possible to grind difficult materials.
The new impact rotor insert accessory consists of a rotor with eight ribs, an impact blades insert, and a 1mm sieve ring.
Other rotors and trapezoidal sieve rings are also available for other applications.
The sieve ring is protected by using the impact blades insert, which pre-crushes the coarse, medium hard and brittle grinding materials; grinding is then gentler because of the larger distance between sieve ring and rotor.
A few examples from daily lab procedures illustrate the new application possibilities. Previously, the Pulverisette 14's maximum feed size was 8-10 mm.
Now samples up to 2cm can be fed into the instrument: 100g food pellets (<20mm) were pre-crushed down to about 5mm within three minutes in the first run with the impact blades insert (without sieve ring), and during the second run they were finely milled with a 0.5mm trapezoidal sieve ring within eight minutes. In the past, it was not possible to grind, for example, raw liquorice with the Pulverisette 14.
The milled material melted and became sticky after a few grams - even with the widest sieve ring.
Now, there are no problems.
It is possible to grind 70g raw liquorice within one minute down to <15 mm in one single process using the impact blades insert, a 1mm trapezoidal sieve ring and a rotor with 12 ribs.
The inserted sieve ring is free of deposit formations and sticky residue, so that larger amounts can also be ground.
A final example illustrates another interesting use: an alginate sample (<300µm) should be ground so that average particle size is around 30-40µm.
Using the conversion kit for larger quantities, the standard 80µm sieve ring and a rotor with 24 ribs, a maximum of 25g can be ground within 90 minutes. The material should be feed via the Laborette 24 vibratory feeder.
The alginate discoloured even with this extremely slow feeding: temperature development between rotor and sieve ring was still too large.
During the second experiment, comminution was done with the standard sieve ring, the impact blades insert and with a 80µm trapezoidal sieve ring a little larger in diameter: 100g of the almost white alginate sample was now ground within one hour without the sample discolouring.