Rubber Powder

The rubber was already pretty fine. Especially such elastic samples are hard to comminute further. If a further cutting of sample would be possible, it would be with our Variable Speed Rotor Mill PULVERISETTE 14 premium line, converted into a cutting mill. Often, softer samples require a previous embrittlement. The best way would be a chilling in liquid nitrogen (LN2). We start a first test without embrittlement.

We used a sieve shell holder with 0,2 mm trapezoidal perforated sieve shells. The mill was converted into a cutting mill and equipped with high-performance cyclone separator and our sample exhauster. The mill was set to its maximum speed of 18000 rpm and was started.

For our trial, we prepared a batch of 155 grams of sample and manually fed the sample into the feeding funnel with a spoon. The sample was ground within 5,5 minutes. The grinding sound was smoother and also the motor load remained moderate with the present feed rate. After comminution, the trapezoidal perforations were clogged minimally. Surely much higher amounts of sample could be fed this way, too.

Compared to the start size, the sample which passed our 0,2 mm trapezoidal perforated sieve shells was lightly finer. Surely some fragments passed longitudinal; also the width could be somehow wider because of the definition of trapezoidal perforations.

Inside the grinding chamber, only loose fragments remained. Cleaning was performed rapidly by vacuuming with a soft brush. Residues on the sieve shell holder were removed with compressed air. Also, a wired brush is recommended to free clogged sieve shells. For an intensive cleaning, the holder can be disassembled with its 8 top screws.

For higher amounts, it could be beneficial to automatize the feeding process with a Vibratory Feeder LABORETTE 24 to assure a constant, low feed rate of sample into the mill.

With our second trial, we used the 0,12 mm sieve shell set. The trial was performed analogue result 1. With this trial, we fed the sample with a much lower feed rate. With 45 grams within 5 minutes, the motor load remained extremely low. A higher feed rate should be possible.

After grinding, also with this result, only a minimal clogging of sieve shell perforations was observed (< 5 %). Higher amounts of sample could be ground. The output appears to be lightly finer than sample one output.

Finally, we used the 0,08 mm sieve shell set to grind the sample. The sample was slowly transferred into the feeding funnel, but the motor load started rising with every fragment we fed. After one minute and only 3 grams of sample, the motor load indicated that a stop will be required. We found that sample started building up in front of the static knives. About 10-20 % of sieve shell perforations were clogged with sample material, too.

We don’t recommend using such small sieve shells for this type of sample.