Polyvinyl Butyral (PVB)

Desired was a fineness of 80 % < 350 μm. With the present start size of > 20 cm. A manual precutting would be required. We don’t provide such a large mill and used a table top scissors to cut the sample into thin strips with ~ 2,5x10 cm.

We used the high-performance cyclone separator with sample exhauster for the comminution. Basically, this equipment would not be required for a precutting to < 4 mm. This optional equipment will chill samples and grinding parts and removes a ground sample out of the grinding chamber, within the moment it is capable to pass the used sieve cassette.

The 380 grams of < 2,5 cm wide precut sample was slowly fed into the mill which was equipped with a standard rotor with V-cutting edges and a sieve cassette with 4,0 mm square perforations for precutting.

The sample pusher was used every now and then to support feeding. It took 140 seconds (2:20 minutes) until the complete batch was fed and ground. The sound of grinding was typical and comminution was performed without problems.

The sample which passed the 4 mm sieve cassette will be used for fine grinding in our next trial. We also checked a fine grinding step with a 0,5 mm sieve cassette, but the softer PVB sample clogged its perforations rapidly. Only a small amount of sample passed that fine sieve cassette. The new Variable Speed Rotor Mill PULVERISETTE 14 premium line would be required to grind higher amounts (see next result).

Cleaning of the grinding chamber was performed rapidly by vacuuming with a soft brush. The fine sieve cassette with 0,5 mm perforations was cleaned with a wired brush (made of brass).

Our Variable Speed Rotor Mill PULVERISETTE 14 premium line can be converted into a cutting mill. With a knives gap of only 0,1 mm and a speed up to 18.000 rpm, much finer results can be realized, compared to a standard cutting mill (with a gap of ~ 0,2 mm and up to ~ 3000 rpm). For this type of cutting mill, a fine precutting is required.

We used the 4 mm output of result 1 for our grinding trial. A batch of 150 grams of precut sample was used. The mill was equipped with our high-performance cyclone separator and sample exhauster. Sieve shells with 0,5 mm trapezoidal perforations were equipped for this trial.

The batch was slowly transferred into the feeding funnel. The sound of grinding was smooth. It took 4 minutes until the complete sample was fed and ground.

After comminution, only electrostatically charged fine sample dust remained inside the collecting vessel. The majority of trapezoidal perforations were not clogged with sample. We estimate that about 5-10 % of perforations were blocked with residues.

Surely higher amounts of sample could be ground this way. For a desired amount of 500 grams, we don’t expect that a cleaning step needs to be performed. Cleaning was performed rapidly by vacuuming with a soft brush. For the sieve shell holder, compressed air is beneficial for cleaning.