Rolling mill mixers.

The rolling mill is furnished with two rolls. The rolls have internal water-cooling. Both
rolls have slightly different peripheral speeds giving a more efficient mixing.

The ratio of the peripheral speeds is usually 1:1.2. Typical roll dimensions are l = 1.5 m,
Φ = 0.5 m. The power rating is around 200 kW with a roll speed of 20 rpm. Typical
mixing cycle takes 30 min. and batch sizes are 60 – 70 kg.

At mixing, the mix is following one of the rolls and the additives are added in between
the two rolls. During mixing the roll gap is slightly opened. After mixing, the rubber strip
is cut in slices and fed in between the rolls, a number of times. This is to ensure thorough
mixing.

An important difference between rolling mills and batch mixers is that the former gives a
“good” (quality) mix while the latter gives a “fast” (productivity) mix. Furthermore,
technological advancement opportunities in the rolling mill mixing procedure are nil
compared to the internal batch mixers. Automatization is also a hurdle in rolling mill
mixers.