Granulators: it’s not just a matter of throughput

• In-line application requires more than throughput
• Cooling as decisive factor
• Getecha designs central and large granulators for blow moulding

Throughput alone is not the only decisive factor when it comes to the design of central and large granulators for blow moulding. The plant manufacturer Getecha can adapt its latest rotary cutter series to various requirements and customer preferences.

Central granulators for blow moulding applications

Large hoppers, aggressive intake zones, rugged segmented rotors: especially the central granulators of the RS 3000/ RS 3800 series and the large granulators of the RS 6000 series rotary cutter range are very suitable for blow moulding applications. Depending on the conditions on site, they work as stand-alone units or as in-line systems. The throughput is becoming less the sole criterion. In addition to the dimensions of the plastic parts to be shred, factors such as granulated material temperature, material reclamation and energy efficiency are increasingly relevant.

In-line application requires more than throughput

For example, the central granulators of the RS 3000 and RS 3800 series feature throughputs from 200 to 540 kg/h and 600 to 1,100 kg/h. The further design of the granulator is usually based on these values. However, as soon as it shall be used for the shredding of top and bottom slugs as in-line add-on directly at the blow moulding line, the throughput alone is not the only factor to consider, but but also the size of the hollow objects to be shred (canisters, etc.). As a rule of thumb: The smallest dimension of the largest container to be shred shall be smaller than the radius of the rotary cutter.

Super-tangential infeed and offset blades with protruding edges

In order to avoid building completely oversized granulators, which would provide a much higher throughput than required, the RS 3000 and RS 3800 series are designed to allow them to be equipped with a smaller, optimally matched, grinding unit. This also results in a smaller overall footprint of the granulator. The granulators feature super-tangential infeeds and offset blades with protruding edges which easily grab and pull in large-volume parts. This prevents inefficient “dancing of the containers” on the rotor. The rotor blades can be easily preset from the outside. In addition, the spray flaps in the hopper allow the manual feeding of large containers. Air fans protected against granulate backspray inside the hopper prevent the pneumatic conveyor from pulling up the spray flaps and granulate from escaping from the hopper. Cooling of the granulate by the intake air of the pneumatic conveyor, another important factor, is thereby ensured.

Cooling as decisive factor

The importance of material cooling becomes especially apparent with the rotary cutters of the RS 6000 series with throughputs of 600 to 2,500 kg/h. They are often used to shred large blow moulded parts, such as plastic tanks. The larger the lumps the slower the cooling process of the material.

The temperature of the plastic material to be ground often lies above 150°C. It is then very pasty and sticky. On the one hand, the granulator must achieve enough throughput to prevent material from accumulating in the granulator chamber. On the other hand, the granulated material must be cooled down to at least 80°C for storage in tank or silos. The granulated material must not be hotter than 65°C if it shall be processed further in-line.

Pneumatic conveyors cool and transport the granulated material

To meet such temperature requirements, Getecha can equip the granulators of the RS 6000 series with various measures for cooling the granulated material. The options range from water cooling at the rear of the granulating chamber to supplying cold air to the cutting granulator to an open rotor geometry for optimal air circulation. The pneumatic conveyors do not only handle cooling but do also transport of the granulated material.