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Unique features improve grinder performance

At Rotogran, the granulator tradition met the shredder function on the drawing board, and what emerged is a rotary grinder that combines features of both. Rotogran's second generation rotary grinders ...


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June 1, 2002 by Canadian Plastics



At Rotogran, the granulator tradition met the shredder function on the drawing board, and what emerged is a rotary grinder that combines features of both. Rotogran’s second generation rotary grinders incorporate a few signature touches that will improve the throughput and facilitate maintenance.

Ideas borrowed from granulator designs include: the use of gravity to assist with material infeed, air evacuation of the granulate, and the use of hydraulics to raise the hopper.

“We use gravity feed as well as a hydraulic ram so that the material continues to be in contact with the rotor when the ram is pulled back,” explains Mike Cyr, vice-president, sales. Gravity feed is achieved by the novel use of an angled infeed chute.

“We also learned from granulators: Always use air to evacuate the granulate. It cools the machine and aids throughput because it evacuates material more quickly.”

Using hydraulics to lift the hopper is another trick adopted from granulators, which facilitates access to the cutting chamber.

The Rotofeed RG-4840 grinder has the flexibility to handle anything from scrap film to heavy purgings. The unit shown at right is destined for Enhance Packaging Technologies in Whitby, ON, to grind film. In that application, the grinder will produce 3/8 in. granulate that can be fed directly back into the film extrusion line. In film applications, the grinder can achieve up to 1000 lb./hr. throughput.

One contributor to the versatility of this machine is a second bed knife which can easily be removed when not needed. The second knife is not necessary for film applications, but can increase regrind quality and throughput on more dense materials, such as purgings and thick-walled parts.

The cutters are designed to be maintenance-friendly. Once they’ve rotated through all four cutting faces they can be resharpened.

“The downside to shredders has always been low throughput and the poor quality of regrind. We’ve addressed that by making the cutters smaller and increasing the size of the screen area,” says Cyr. “Now, by incorporating this grinder into your size reduction system, you can use granulators sized appropriately for your parts, and use the grinder to handle flash, purgings and other large scrap.”

Rotogran International Inc. 905-738-0101