Zweibrücken, Germany based Pallmann, a manufacturer of size reduction machinery, has launched a new grinding system for recycling of vulcanized rubber waste back into fine powder for direct reuse in rubber processing.
Named Karakal, Pallmann explained that its latest machine has the ability to devulcanize the rubber as it pulverizes it, so that it can be used in place of virgin material.
The machine is a type of twin-roll mill that the company said has been designed specifically for recycling waste from production of technical parts, as well as waste arising from retreading truck tyres.
The manufacturer added that it accepts material that has been pre-cut to a particle size of 4mm or less, and which is fed to it continuously by a series of screws positioned along the gap between the rollers.More Waste Management World Articles
Large amounts of rubber waste from old tyres are already re-used, but according to Pallmann this is mostly as a low-grade filler in building and construction, while some is also pyrolyzed into carbon black, oils, fuel gas, and other residues.
In the past, cryogenics have been used for producing powder from rubber waste, but the company said that this creates particles with cubic geometries, which are not best suited for incorporation into new compounds.
More recently, conventional roller mills have been used, but these are said to create particles of around 800 to 1000 micron, which is too big for reprocessing operations, and is also very energy intensive.
The Karakal relies on friction to reduce the size of the rubber particles, which the company said that be accurately controlled.
“What we are getting is size reduction by shear, not by cutting, and this produces powder with rough surfaces,” explained Rolf Gren, senior executive vice president at Pallmann Group.
The machine has two main rollers with a diameter of 400 mm and a length of 1000 mm, each covered with micro-serrations. Roller speed and direction of rotation are controlled via variable-frequency drives.
According to Pallmann, the distance between the rollers can be adjusted to an accuracy of 0.1 mm. The rollers are pre-tensioned by an assembly of springs and a hydraulic cylinder. The temperature at which the process runs is also controllable.
The machine from a distance resembles an ordinary twin-roll mill, but the company noted that a closer inspection reveals the micro-serrations on the surfaces of the rolls.
The company added that the rolls are segmented, and the surfaces sections can be taken off, so that the serrations can be re-sharpened by the user with no need to return them to the manufacturer for sharpening.
Two additional smaller rollers located below each of the two main rollers to clean them can be fitted on request.
Pallmann said that it has applied for several patents on technology incorporated into the equipment.
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